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Acute myeloid leukemia (AML) with an FLT3 internal tandem duplication (FLT3-ITD) mutation is an aggressive hematologic malignancy associated with frequent relapse and poor overall survival. The tyrosine kinase inhibitor gilteritinib is approved for the treatment of relapse/refractory AML with FLT3 mutations, yet its mechanism of action is not completely understood. Here, we sought to identify additional therapeutic targets that can be exploited to enhance gilteritinib's antileukemic effect. Based on unbiased transcriptomic analyses, we identified the glutamine transporter SNAT1 (SLC38A1) as a novel target of gilteritinib that leads to impaired glutamine uptake and utilization within leukemic cells. Using metabolomics and metabolic flux analyses, we found that gilteritinib decreased glutamine metabolism through the TCA cycle and cellular levels of the oncometabolite 2-hydroxyglutarate. In addition, gilteritinib treatment was associated with decreased ATP production and glutathione synthesis and increased reactive oxygen species, resulting in cellular senescence. Finally, we found that the glutaminase inhibitor CB-839 enhanced antileukemic effect of gilteritinib in ex vivo studies using human primary FLT3-ITD–positive AML cells harboring mutations in the enzyme isocitrate dehydrogenase, which catalyzes the oxidative decarboxylation of isocitrate, producing α-ketoglutarate. Collectively, this work has identified a previously unrecognized, gilteritinib-sensitive metabolic pathway downstream of SLC38A1 that causes decreased glutaminolysis and disruption of redox homeostasis. These findings provide a rationale for the development and therapeutic exploration of targeted combinatorial treatment strategies for this subset of relapse/refractory AML.

Purpose: CPC634 is a novel nanoparticle entrapping docetaxel, developed to enhance the intratumoral chemotherapy exposure. This randomized cross-over study compared the intratumoral and plasma pharmacokinetics of CPC634 with conventional docetaxel. Patients and Methods: Adult patients with solid tumors were randomized to receive CPC634 (75 mg/m2) in cycle 1, and conventional docetaxel (75 mg/m2) in cycle 2 or vice versa. The study was powered to identify a 25% increase of intratumoral total docetaxel exposure after CPC634 infusion compared with conventional docetaxel. Four patients were allocated per tumor sampling time point, that is, 24, 48, 72, and 96 hours, 7 and 14 days after infusion during both cycles. Total docetaxel and released docetaxel from the nanoparticle were determined in tumor tissue derived from a metastatic lesion and in plasma. Pharmacokinetic data were analyzed using linear mixed modeling. Results: In total, 24 evaluable patients were included. In the tumor, CPC634 exhibited a 461% higher total docetaxel (P < 0.001) and a comparable released docetaxel concentration (P = 0.43). Plasma AUCinf was 27% higher (P = 0.001) and Cmax was 91% lower (P < 0.001) for CPC634 released docetaxel. The median observed neutrophil count nadir after conventional docetaxel treatment was lower (0.50 × 109/L) compared with CPC634 (4.30 × 109/L; P < 0.001). Conclusions: Here, we demonstrated that CPC634 enhanced the intratumoral total docetaxel exposure compared with conventional docetaxel. The lower incidence of neutropenia during CPC634 treatment is presumably related to lower plasma Cmax of released docetaxel. The unique pharmacokinetic profile of CPC634 nanoparticles has the potential to improve docetaxel treatment. A phase II efficacy trial of CPC634 is currently ongoing.

Fixed dosing of oral targeted therapies is inadequate in the era of precision medicine. Personalized dosing, based on pharmacokinetic (PK) exposure, known as therapeutic drug monitoring (TDM), is rational and supported by increasing evidence. The purpose of this perspective is to discuss whether randomized studies are needed to confirm the clinical value of precision dosing in oncology. PK-based dose adjustments are routinely made for many drugs and are recommended by health authorities, for example, for patients with renal impairment or for drug–drug interaction management strategies. Personalized dosing simply extrapolates this paradigm from selected patient populations to each individual patient with suboptimal exposure, irrespective of the underlying cause. If it has been demonstrated that exposure is related to a relevant clinical outcome, such as efficacy or toxicity, and that exposure can be optimized by PK-guided dosing, it could be logically assumed that PK-guided dosing would result in better treatment outcomes without the need for randomized confirmatory trials. We propose a path forward to demonstrate the clinical relevance of individualized dosing of molecularly-targeted anticancer drugs.

PURPOSE To provide recommendations for appropriate dosing of systemic antineoplastic agents in obese adults with cancer. METHODS A systematic review of the literature collected evidence regarding dosing of chemotherapy, immunotherapy, and targeted therapies in obese adults with cancer. PubMed and the Cochrane Library were searched for randomized controlled trials, meta-analyses, or cohort studies published from November 1, 2010, through March 27, 2020. ASCO convened an Expert Panel to review the evidence and formulate recommendations. RESULTS Sixty studies, primarily retrospective, were included in the review. Overall, the evidence supported previous findings that obese adult patients tolerate full, body-size–based dosing of chemotherapy as well as nonobese patients. Fewer studies have addressed the dosing of targeted therapies and immunotherapies in relation to safety and efficacy in obese patients. RECOMMENDATIONS The Panel continues to recommend that full, weight-based cytotoxic chemotherapy doses be used to treat obese adults with cancer. New to this version of the guideline, the Panel also recommends that full, approved doses of immunotherapy and targeted therapies be offered to obese adults with cancer. In the event of toxicity, the consensus of the Panel is that dose modifications of systemic antineoplastic therapies should be handled similarly for obese and nonobese patients. Important areas for future research include the impact of sarcopenia and other measures of body composition on optimal antineoplastic dosing, and more customized dosing based on pharmacokinetic or pharmacogenetic factors. Additional information is available at www.asco.org/supportive-care-guidelines .

Acute myeloid leukemia (AML) is characterized by the uncontrolled expansion of un-differentiated hematopoietic progenitor myeloblasts. AML treatment is very challenging owing to its complex heterogeneity resulting in a dismal 5-year overall survival rate particularly in elderly patients unfit for standard induction chemotherapy. The expansion of AML requires the availability of sufficient nucleotides supporting the anabolic processes required for AML growth thus, targeting nucleotide biosynthesis can halt AML progression. Indeed, targeting dihydroorotate dehydrogenase (DHODH), a critical rate-limiting step in the de novo pyrimidine synthesis pathway not only induced cytotoxicity but has been shown to promote blast differentiation in a HOXA9/MEIS1 over-expressing model. We sought to develop a DHODH inhibitor that had superior properties to those reported for AML therapy. Compound 41 (cmpd 41) demonstrates sub-nanomolar 50% inhibitory concentration for DHODH biochemical activity and potent in vitro activity across several AML cell lines and primary AML cells independent of mutational subtype, including mutated TP53. Cmpd 41 also demonstrated superior in vivo anti-leukemic activity in multiple AML xenograft models as monotherapy and demonstrated synergy with a hypomethylating agent, decitabine in TP53 mutated AML. Given the heterogeneity of AML and frequent emergence of resistant clones, we aimed to investigate ways to enhance response to DHODH inhibitors through combination. After in vitro treatment of AML cell lines and primary patient samples with DHODH inhibitors, we observed an increase in CD38 surface expression suggesting synergy with CD38 targeting monoclonal antibody (mAb) immunotherapies. Indeed, we are the first to report synergy between DHODH inhibitors and anti-CD38 mAb in AML which emphasizes the synergy between this promising novel class of agents with immunotherapies via recruiting innate immunity. Consequently, given the relevance of CD38 mAb therapy to multiple myeloma (MM), we extended these studies to MM and remarkably found that cmpd 41 was highly efficacious as a monotherapy and in combination with CD38 mAb, resulted in complete tumor regression in a subcutaneous MM xenograft model. In summary, we introduce a best in class DHODH inhibitor with a data-driven combination strategy for both AML and MM. Our studies suggest a highly synergistic combination strategy involving immunotherapy for AML and other hematologic malignancies. Citation Format: Ola A. Elgamal, Sandip Vibhute, Sydney Fobare, Abeera Mehmood, Mariah L. Johnson, Jean Truxall, Emily Stahl, Bridget Carmichael, Shelley J. Orwick, Ramasamy Santhanam, Kasey Hill, Susheela Tridandapani, Christopher C. Coss, Alice S. Mims, Karilyn T. Larkin, Mitch A. Phelps, Sharyn D. Baker, Alex Sparreboom, Thomas E. Goodwin, Gerard Hilinski, Chad E. Bennett, Erin Hertlein, John C. Byrd. Introducing a novel DHODH inhibitor with superior in vivo activity as monotherapy or in novel combination regimen with immunotherapy for hematological malignancies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1060.

Purpose: OATP1B1 (SLCO1B1) is the most abundant and pharmacologically relevant uptake transporter in the liver and a key mediator of xenobiotic clearance. However, the regulatory mechanisms that determine OATP1B1 activity remain uncertain, and as a result, unexpected drug–drug interactions involving OATP1B1 substrates continue to be reported, including several involving tyrosine kinase inhibitors (TKI). Experimental Design: OATP1B1-mediated activity in overexpressing HEK293 cells and hepatocytes was assessed in the presence of FDA-approved TKIs, while rosuvastatin pharmacokinetics in the presence of an OATP1B1 inhibiting TKI were measured in vivo. Tyrosine phosphorylation of OATP1B1 was determined by LC/MS-MS–based proteomics and transport function was measured following exposure to siRNAs targeting 779 different kinases. Results: Twenty-nine of 46 FDA-approved TKIs studied significantly inhibit OATP1B1 function. Inhibition of OATP1B1 by TKIs, such as nilotinib, is predominantly noncompetitive, can increase systemic concentrations of rosuvastatin in vivo, and is associated with reduced phosphorylation of OATP1B1 at tyrosine residue 645. Using genetic screens and functional validation studies, the Src kinase LYN was identified as a potential regulator of OATP1B1 activity that is highly sensitive to inhibition by various TKIs at clinically relevant concentrations. Conclusions: A novel kinase-dependent posttranslational mechanism of OATP1B1 activation was identified and interference with this process by TKIs can influence the elimination of a broad range of xenobiotic substrates.

Androgen receptor (AR) signalling drives neoplastic growth and therapy resistance in prostate cancer. Recent clinical data show that docetaxel combined with androgen deprivation therapy improves outcome in hormone-sensitive disease. We studied whether testosterone and AR signalling interferes with docetaxel treatment efficacy in castration-resistant prostate cancer (CRPC). We found that testosterone supplementation significantly impaired docetaxel tumour accumulation in a CRPC model, resulting in decreased tubulin stabilisation and antitumour activity. Furthermore, testosterone competed with docetaxel for uptake by the drug transporter OATP1B3. Irrespective of docetaxel-induced tubulin stabilisation, AR signalling by testosterone counteracted docetaxel efficacy. AR-pathway activation could also reverse long-term tumour regression by docetaxel treatment in vivo. These results indicate that to optimise docetaxel efficacy, androgen levels and AR signalling need to be suppressed. This study lends evidence for continued maximum suppression of AR signalling by combining targeted therapeutics with docetaxel in CRPC.

Purpose: AZD1775, a first-in-class, small-molecule inhibitor of the Wee1 tyrosine kinase, is under evaluation as a potential chemo- and radiosensitizer for treating glioblastoma. This study was to prospectively, quantitatively, and mechanistically investigate the penetration of AZD1775 across the human blood–brain barrier (BBB). Experimental Design: AZD1775 plasma and tumor pharmacokinetics were evaluated in 20 patients with glioblastoma. The drug metabolism, transcellular passive permeability, and interactions with efflux and uptake transporters were determined using human derived in vitro systems. A whole-body physiologically based pharmacokinetic (PBPK) model integrated with a four-compartment permeability-limited brain model was developed for predicting the kinetics of AZD1775 BBB penetration and assessing the factors modulating this process. Results: AZD1775 exhibited good tumor penetration in patients with glioblastoma, with the unbound tumor-to-plasma concentration ratio ranging from 1.3 to 24.4 (median, 3.2). It was a substrate for ABCB1, ABCG2, and OATP1A2, but not for OATP2B1 or OAT3. AZD1775 transcellular passive permeability and active efflux clearance across MDCKII–ABCB1 or MDCKII–ABCG2 cell monolayers were dependent on the basolateral pH. The PBPK model well predicted observed drug plasma and tumor concentrations in patients. The extent and rate of drug BBB penetration were influenced by BBB integrity, efflux and uptake active transporter activity, and drug binding to brain tissue. Conclusions: In the relatively acidic tumor microenvironment where ABCB1/ABCG2 transporter-mediated efflux clearance is reduced, OATP1A2-mediated active uptake becomes dominant, driving AZD1775 penetration into brain tumor. Variations in the brain tumor regional pH, transporter expression/activity, and BBB integrity collectively contribute to the heterogeneity of AZD1775 penetration into brain tumors. Clin Cancer Res; 23(24); 7454–66. ©2017 AACR. See related commentary by Peer et al., p. 7437

Resistance to xenobiotic nucleosides used to treat acute myeloid leukemia (AML) and other cancers remains a major obstacle to clinical management. One process suggested to participate in resistance is reduced uptake into tumor cells via nucleoside transporters, although precise mechanisms are not understood. Through transcriptomic profiling, we determined that low expression of the ergothioneine transporter OCTN1 (SLC22A4; ETT) strongly predicts poor event-free survival and overall survival in multiple cohorts of AML patients receiving treatment with the cytidine nucleoside analogue cytarabine. Cell biological studies confirmed OCTN1-mediated transport of cytarabine and various structurally related cytidine analogues, such as 2′deoxycytidine and gemcitabine, occurs through a saturable process that is highly sensitive to inhibition by the classic nucleoside transporter inhibitors dipyridamole and nitrobenzylmercaptopurine ribonucleoside. Our findings have immediate clinical implications given the potential of the identified transport system to help refine strategies that could improve patient survival across multiple cancer types where nucleoside analogues are used in cancer treatment. Cancer Res; 77(8); 2102–11. ©2017 AACR.

The use of multikinase inhibitors (MKI) in oncology, such as sorafenib, is associated with a cutaneous adverse event called hand–foot skin reaction (HFSR), in which sites of pressure or friction become inflamed and painful, thus significantly impacting quality of life. The pathogenesis of MKI-induced HFSR is unknown, and the only available treatment options involve dose reduction or discontinuation of therapy, which have negative effects on primary disease management. To investigate the underlying mechanisms by which sorafenib promotes keratinocyte cytotoxicity and subsequent HFSR induction, we performed a transporter-directed RNAi screen in human epidermal keratinocytes and identified SLC22A20 (OAT6) as an uptake carrier of sorafenib. Further investigations into the intracellular mechanism of sorafenib activity through in situ kinome profiling identified the mitogen-activated protein kinase MAP3K7 (TAK1) as a target of sorafenib that induces cell death. Finally, we demonstrate that sorafenib induced keratinocyte injury in vivo and that this effect could be reversed by cotreatment with the OAT6 inhibitor probenecid. Collectively, our findings reveal a novel pathway that regulates the entry of some MKIs into keratinocytes and explains the basis underlying sorafenib-induced skin toxicity, with important implications for the therapeutic management of HFSR. Cancer Res; 76(1); 117–26. ©2015 AACR.

Docetaxel is used for treatment of several solid malignancies. In this study, we aimed for predicting docetaxel clearance and docetaxel-induced neutropenia by developing several genetic models. Therefore, pharmacokinetic data and absolute neutrophil counts (ANCs) of 213 docetaxel-treated cancer patients were collected. Next, patients were genotyped for 1936 single nucleotide polymorphisms (SNPs) in 225 genes using the drug-metabolizing enzymes and transporters platform and thereafter split into two cohorts. The combination of SNPs that best predicted severe neutropenia or low clearance was selected in one cohort and validated in the other. Patients with severe neutropenia had lower docetaxel clearance than patients with ANCs in the normal range (P=0.01). Severe neutropenia was predicted with 70% sensitivity. True low clearance (1 s.d.

Background: Both taxanes, docetaxel and cabazitaxel, are effective treatments for metastatic castration-resistant prostate cancer (mCRPC). However, resistance to taxanes is common. Our objective was to investigate mechanisms of taxane resistance in prostate cancer. Methods: Two docetaxel-resistant patient-derived xenografts (PDXs) of CRPC were established (PC339-DOC and PC346C-DOC) in male athymic nude mice by frequent intraperitoneal administrations of docetaxel. Next-generation sequencing was performed on PDX tissue pre- and post-docetaxel resistance and gene expression profiles were compared. [14C]-docetaxel and [14C]-cabazitaxel uptake assays in vitro and cytotoxicity assays were performed to validate direct involvement of transporter genes in taxane sensitivity. Results: Organic anion-transporting polypeptide (SLCO1B3), an influx transporter of docetaxel, was significantly downregulated in PC346C-DOC tumours. In accordance with this finding, intratumoural concentrations of docetaxel and cabazitaxel were significantly decreased in PC346C-DOC as compared with levels in chemotherapy-naive PC346C tumours. In addition, silencing of SLCO1B3 in chemo-naive PC346C resulted in a two-fold decrease in intracellular concentrations of both taxanes. Overexpression of SLCO1B3 showed higher sensitivity to docetaxel and cabazitaxel. Conclusions: The SLCO1B3 determines intracellular concentrations of docetaxel and cabazitaxel and consequently influences taxane efficacy. Loss of the drug transporter SLCO1B3 may drive taxane resistance in prostate cancer.

TPS12128 Background: Chemotherapy-induced peripheral neuropathy (CIPN) is a debilitating adverse effect of paclitaxel, but convincing evidence for a preventative technique founded on mechanistic rationale is lacking. We previously report that paclitaxel accumulation is mediated by the murine organic anion transporting polypeptide, OATP1B2 in mice (OATP1B1 and OATP1B3 in humans) (Leblanc, J Clin Invest, 2018). We found that paclitaxel induces acute and chronic neurotoxicity in mice in an OATP1B2-dependent manner, which is reversed by pre-treatment with FDA-approved tyrosine kinase inhibitor, nilotinib. Methods: This phase Ib dose finding study of nilotinib in combination with weekly paclitaxel is investigating the hypothesis that intermittent dosing of nilotinib 24 hours before paclitaxel infusion (excluding C1D1) and again 30 minutes before paclitaxel infusion will inhibit OATP1B1 and prevent CIPN. This hypothesis will be assessed using an adaptive Bayesian method for dose finding based on efficacy-toxicity trade-offs in patients with breast cancer stages I-III who qualify for paclitaxel therapy. Patients with previous ≥ grade 2 neuropathy on breast cancer therapies will be excluded. The primary objectives are to find the recommended phase II dose of nilotinib in combination with paclitaxel for early stage breast cancer, defined as the lowest intermittent dose of nilotinib that temporarily inhibits OATP1B1 function without affecting paclitaxel plasma pharmacokinetics (PK), and to determine the toxicity profile of nilotinib in combination with paclitaxel. OATP1B1 inhibition by nilotinib will be assessed via validated surrogate endogenous substrates, glycochenodeoxycholate sulfate (GCDGA-S) and chenodeoxycholate-24-glucuronide (CDCA-24G). Effective OATP1B1 inhibition will be ≥5-fold increase in AUC of GCDCA-S from pre- to post- treatment or detectable CDCA-24G levels post-treatment. The 4 nilotinib dose levels are 50 mg (dose level -1), 100 mg (dose level 1), 200 mg (dose level 2), 300 mg (dose level 3). IV paclitaxel dose of 80 mg/m2 on D1,8,15 for 12 total weekly doses will be used. Oral nilotinib will be administered 24 hours before paclitaxel infusion on C1D7,D14 and again 30 minutes before infusion on C1D8,D15. Secondary objectives are to determine paclitaxel’s effect on PK of nilotinib and vice versa. Quality of life via CIPN-20 survey, disease free survival, event free survival, overall survival are exploratory objectives. NCT04205903 enrollment opened February 2020 and is accepting patients. Clinical trial information: NCT04205903 .

TPS12125 Background: Neurotoxicity is one of the most significant and disabling side effects of oxaliplatin and frequently limits the cumulative amount that can be used. The mechanism of oxaliplatin-induced neurotoxicity remains uncertain, although our preliminary studies suggest that oxaliplatin uptake by organic cation transporter 2 (OCT2) into mouse and rat dorsal root ganglion is a prerequisite for oxaliplatin-induced peripheral neuropathy. The activity of OCT2 is dependent on tyrosine phosphorylation by the SRC-kinase family member Yes1, which is highly sensitive to inhibition by several FDA-approved, small molecule kinase inhibitors such as dasatinib. We have previously shown that pre-treatment with oral dasatinib prevented acute and chronic oxaliplatin-induced peripheral neuropathy in mouse and rat models. Methods: This is a phase Ib dose-finding study of dasatinib given in combination with mFOLFOX6 with or without bevacizumab. The study explores the hypothesis that the addition of dasatinib prior to oxaliplatin will inhibit OCT2 activity and reduce oxaliplatin-induced neuropathy. This hypothesis will be tested in a Bayesian Phase 1b trial with adaptive dose selection using efficacy-toxicity trade-offs (modified toxicity-efficacy probability interval dose-finding design) in patients with confirmed stage IV colorectal cancer who are candidates for mFOLFOX6 with bevacizumab therapy. Patients who have documented peripheral neuropathy or prior exposure to oxaliplatin will be excluded. The primary objective is to determine the recommended Phase 2 dose which is defined as the lowest intermittent dose of dasatinib that affects serum biomarkers of OCT2, including methylnicotinamide and creatinine, by ≥2-fold without influencing the clearance of oxaliplatin by > 20%. The following doses will be used: oxaliplatin 85mg/m2 IV, 5FU bolus 400mg/m2 IV bolus with Leucovorin 400mg/m2, bevacizumab 5mg/kg, followed by infusional 5FU 2400mg/m2 IV over 46 hours given on a day 1 and 15 schedule every 28 days. Dasatinib will be administered at one of 2 dose levels – 100mg or 140mg po. Dasatinib will be given 24 hours and 30 mins prior to oxaliplatin on C1D14, C1D15 respectively and repeated on C1D28 and C2D1. Secondary objectives include evaluation of the influence of dasatinib on the pharmacokinetics of oxaliplatin and vice versa. Quality of life will be explored using the CIPN20 questionnaire. The trial opened to enrollment in Dec 2019 (NCT04164069) and is accepting patients. Clinical trial information: NCT04164069 .

Aim: Assuming that genetic variants of the SLC22A2 and SLC31A1 transporter affect patients’ susceptibility to cisplatin-induced ototoxicity, we compared the distribution of 11 SLC22A2 variants and the SLC31A1 variant rs10981694 between patients with and without cisplatin-induced ototoxicity. Patients & methods: Genotyping was performed in 64 pediatric patients and significant findings were re-evaluated in 66 adults. Results: The SLC22A2 polymorphism rs316019 (c.808G>T; Ser270Ala) was significantly associated with protection from cisplatin-induced ototoxicity in the pediatric (p = 0.022) and the adult cohort (p = 0.048; both: Fisher's exact test). This result was confirmed by multiple logistic regression analysis accounting for age which was identified as a relevant factor for ototoxicity as well (rs316019: OR [G/T vs G/G] = 0.12, p = 0.009; age: OR [per year]: 0.84, p = 0.02). Conclusion: These results identified rs316019 as potential pharmacogenomic marker for cisplatin-induced ototoxicity and point to a critical role of SLC22A2 for cisplatin transport in humans and its contribution to the organ specific side effects of this drug. Original submitted 17 September 2014; Revision submitted 19 December 2014

Cancer chemotherapy has transitioned from the use of cytotoxic drugs to the era of agents with an apparent selectivity for a cancer-specific target. The past decade has provided evidence that therapy with such agents can be curative in subsets of patients. It is anticipated that incorporation of pharmacological principles for novel therapeutics will result in further refinement of outcome measures as well as the discovery of new treatment modalities for multiple malignant diseases.

Item does not contain fulltext PURPOSE: Patients treated with sunitinib show substantial inter-patient variability in drug exposure (~30-40 %), which is largely unexplained. Since sunitinib is metabolized by cytochrome P450(CYP)3A4, variability in the activity of this enzyme may explain a considerable proportion of this inter-patient variability. Midazolam is widely used as a phenotyping probe to assess CYP3A4-activity. The objective of this study was to prospectively evaluate the relationship between midazolam and sunitinib exposure. Additionally, the correlation between sunitinib trough levels and exposure and the influence of sunitinib on midazolam exposure was determined. METHODS: Thirteen patients treated with sunitinib in a 4 weeks "on"-2 weeks "off" regimen received twice 7.5 mg midazolam; once with and once without sunitinib. Steady-state sunitinib, its active metabolite SU12662 and midazolam exposures were determined. RESULTS: A significant correlation between midazolam exposure (AUC(0-7h)) and steady-state sunitinib and sunitinib + SU12662 exposure (AUC(0-24h)) was found (p = 0.006 and p = 0.0018, respectively); midazolam exposure explained 51 and 41 % of the inter-patient variability in sunitinib and sunitinib + SU12622 exposure. Furthermore, C trough was highly correlated (r(2) = 0.94) with sunitinib AUC(0-24h). Sunitinib decreased midazolam exposure with 24 % (p = 0.034). CONCLUSION: Midazolam exposure is highly correlated with sunitinib exposure and explains a large proportion of the observed inter-patient variability in sunitinib pharmacokinetics. Consequently, midazolam could be used to identify patients that are at risk of under- or overtreatment, respectively, at the start of sunitinib therapy. Moreover, sunitinib and sunitinib + SU12662 trough levels are highly correlated with drug exposure and can thus be used in clinical practice to individualize sunitinib therapy. The decrease in midazolam exposure by sunitinib needs further investigation.

Identification of the optimal dose remains a key challenge in drug development. For cytotoxic drugs, the standard approach is based on identifying the maximum tolerated dose (MTD) in phase I trials and incorporating this to subsequent trials. However, this strategy does not take into account important aspects of clinical pharmacology. For targeted agents, the dose-effect relationships from preclinical studies are less obvious, and it is important to change the way these agents are developed to avoid recommending drug doses for different populations without evidence of differential antitumour effects in different diseases. The use of expanded cohorts in phase I trials to better define MTD and refine dose optimization should be further explored together with a focus on efficacy rather than toxicity-based predictions. Another key consideration in dose optimization is related to interindividual pharmacokinetic variability. High variability in intra-individual pharmacokinetics has been observed for many orally-administered drugs, especially those with low bioavailability, which might complicate identification of dose-effect relationships. End-organ dysfunction, interactions with other prescription drugs, herbal supplements, adherence, and food intake can influence pharmacokinetics. It is important these variables are identified during early clinical trials and considered in the development of further phase II and subsequent large-scale phase III studies.

Purpose: Paclitaxel is used in the treatment of solid tumors and displays high interindividual variation in exposure. Low paclitaxel clearance could lead to increased toxicity during treatment. We present a genetic prediction model identifying patients with low paclitaxel clearance, based on the drug-metabolizing enzyme and transporter (DMET)-platform, capable of detecting 1,936 genetic variants in 225 metabolizing enzyme and drug transporter genes. Experimental Design: In 270 paclitaxel-treated patients, unbound plasma concentrations were determined and pharmacokinetic parameters were estimated from a previously developed population pharmacokinetic model (NONMEM). Patients were divided into a training- and validation set. Genetic variants determined by the DMET platform were selected from the training set to be included in the prediction model when they were associated with low paclitaxel clearance (1 SD below mean clearance) and subsequently tested in the validation set. Results: A genetic prediction model including 14 single-nucleotide polymorphisms (SNP) was developed on the training set. In the validation set, this model yielded a sensitivity of 95%, identifying most patients with low paclitaxel clearance correctly. The positive predictive value of the model was only 22%. The model remained associated with low clearance after multivariate analysis, correcting for age, gender, and hemoglobin levels at baseline (P = 0.02). Conclusions: In this first large-sized application of the DMET-platform for paclitaxel, we identified a 14 SNP model with high sensitivity to identify patients with low paclitaxel clearance. However, due to the low positive predictive value we conclude that genetic variability encoded in the DMET-chip alone does not sufficiently explain paclitaxel clearance. Clin Cancer Res; 19(18); 5210–7. ©2013 AACR.

Purpose: Several oral multikinase inhibitors are known to interact in vitro with the human ATP-binding cassette transporter ABCC4 (MRP4), but the in vivo relevance of this interaction remains poorly understood. We hypothesized that host ABCC4 activity may influence the pharmacokinetic profile of dasatinib and subsequently affect its antitumor properties. Experimental Design: Transport of dasatinib was studied in cells transfected with human ABCC4 or the ortholog mouse transporter, Abcc4. Pharmacokinetic studies were done in wild-type and Abcc4-null mice. The influence of Abcc4 deficiency on dasatinib efficacy was evaluated in a model of Ph+ acute lymphoblastic leukemia by injection of luciferase-positive, p185(BCR-ABL)-expressing Arf(−/−) pre-B cells. Results: Dasatinib accumulation was significantly changed in cells overexpressing ABCC4 or Abcc4 compared with control cells (P < 0.001). Deficiency of Abcc4 in vivo was associated with a 1.75-fold decrease in systemic exposure to oral dasatinib, but had no influence on the pharmacokinetics of intravenous dasatinib. Abcc4 was found to be highly expressed in the stomach, and dasatinib efflux from isolated mouse stomachs ex vivo was impaired by Abcc4 deficiency (P < 0.01), without any detectable changes in gastric pH. Abcc4-null mice receiving dasatinib had an increase in leukemic burden, based on bioluminescence imaging, and decreased overall survival compared with wild-type mice (P = 0.048). Conclusions: This study suggests that Abcc4 in the stomach facilitates the oral absorption of dasatinib, and it possibly plays a similar role for other orally administered substrates, such as acetylsalicylic acid. This phenomenon also provides a mechanistic explanation for the malabsorption of certain drugs following gastric resection. Clin Cancer Res; 19(16); 4359–70. ©2013 AACR.

Retrospective and prospective preclinical and clinical data have demonstrated an association between chemotherapy dose intensity and both clinical efficacy and toxicity. The optimum tolerable and effective dose and schedule of chemotherapeutic agents is based on data from dose-finding studies and early clinical trials. There is considerable evidence that reductions in the recommended dose intensity often occurs in actual clinical practice, particularly among overweight and obese patients with cancer. With increasing rates of obesity, and variation and uncertainty about appropriate dosing of chemotherapy in obese patients, ASCO has generated clinical practice guidelines for appropriate chemotherapy dosing for obese adult patients with cancer. Without evidence of any increase in treatment-related toxicity among obese patients receiving chemotherapy, the guidelines recommend that, after considering any accompanying comorbidities, chemotherapy dosing should be calculated based on body surface area using actual weight, rather than an estimate or idealization of weight. While further research is needed, pharmacokinetic studies support the use of actual body weight to calculate chemotherapy doses for most chemotherapy drugs in obese patients. We highlight the issue of chemotherapy dosing in this population, how a more personalized approach can be achieved, as well as discussing areas for further research.

Purpose: Paclitaxel is used for the treatment of several solid tumors and displays a high interindividual variation in exposure and toxicity. Neurotoxicity is one of the most prominent side effects of paclitaxel. This study explores potential predictive pharmacokinetic and pharmacogenetic determinants for the onset and severity of neurotoxicity. Experimental Design: In an exploratory cohort of patients (n = 261) treated with paclitaxel, neurotoxicity incidence, and severity, pharmacokinetic parameters and pharmacogenetic variants were determined. Paclitaxel plasma concentrations were measured by high-performance liquid chromatography or liquid chromatography/tandem mass spectrometry, and individual pharmacokinetic parameters were estimated from previously developed population pharmacokinetic models by nonlinear mixed effects modeling. Genetic variants of paclitaxel pharmacokinetics tested were CYP3A4*22, CYP2C8*3, CYP2C8*4, and ABCB1 3435 C>T. The association between CYP3A4*22 and neurotoxicity observed in the exploratory cohort was validated in an independent patient cohort (n = 239). Results: Exposure to paclitaxel (logAUC) was correlated with severity of neurotoxicity (P < 0.00001). Female CYP3A4*22 carriers were at increased risk of developing neurotoxicity (P = 0.043) in the exploratory cohort. CYP3A4*22 carrier status itself was not associated with pharmacokinetic parameters (CL, AUC, Cmax, or T>0.05) of paclitaxel in males or females. Other genetic variants displayed no association with neurotoxicity. In the subsequent independent validation cohort, CYP3A4*22 carriers were at risk of developing grade 3 neurotoxicity (OR = 19.1; P = 0.001). Conclusions: Paclitaxel exposure showed a relationship with the severity of paclitaxel-induced neurotoxicity. In this study, female CYP3A4*22 carriers had increased risk of developing severe neurotoxicity during paclitaxel therapy. These observations may guide future individualization of paclitaxel treatment. Clin Cancer Res; 19(12); 3316–24. ©2013 AACR.

Purpose: Many tyrosine kinase inhibitors (TKI) undergo extensive hepatic metabolism, but mechanisms of their hepatocellular uptake remain poorly understood. We hypothesized that liver uptake of TKIs is mediated by the solute carriers OATP1B1 and OATP1B3. Experimental Design: Transport of crizotinib, dasatinib, gefitinib, imatinib, nilotinib, pazopanib, sorafenib, sunitinib, vandetanib, and vemurafenib was studied in vitro using artificial membranes (PAMPA) and HEK293 cell lines stably transfected with OATP1B1, OATP1B3, or the ortholog mouse transporter, Oatp1b2. Pharmacokinetic studies were conducted with Oatp1b2-knockout mice and humanized OATP1B1- or OATP1B3-transgenic mice. Results: All 10 TKIs were identified as substrates of OATP1B1, OATP1B3, or both. Transport of sorafenib was investigated further, as its diffusion was particularly low in the PAMPA assay ( Conclusions: These findings signify a unique role for OATP1B1 and OATP1B3 in the elimination of sorafenib-glucuronide and suggest a role for these transporters in the in vivo handling of glucuronic acid conjugates of drugs. Clin Cancer Res; 19(6); 1458–66. ©2013 AACR.

Tyrosine kinases have emerged as important tumor targets for the design of potent and selective inhibitors. Eighteen of these tyrosine kinase inhibitors (TKIs) have already been approved for the treatment of diseases that were previously essentially resistant to standard chemotherapy. Major efforts are ongoing that focus on the development of companion diagnostics for investigational and approved TKIs, as well as on integrating clinical pharmacology principles in clinical practice to decrease toxicity and improve efficacy. Clinical Pharmacology & Therapeutics (2013); 93 3, 215–219. doi:10.1038/clpt.2012.247

Purpose: Imatinib minimal (trough) plasma concentrations after one month of treatment have shown a significant association with clinical benefit in patients with gastrointestinal stromal tumors (GIST). Considering that a retrospective pharmacokinetic analysis has also suggested that imatinib clearance increases over time in patients with soft tissue sarcoma and GIST, the primary aim of this study was to assess systemic exposure to imatinib at multiple time points in a long-term prospective population pharmacokinetic study. As imatinib is mainly metabolized in the liver, our secondary aim was to elucidate the potential effects of the volume of liver metastases on exposure to imatinib. Experimental Design: Full pharmacokinetic blood sampling was conducted in 50 patients with GIST on the first day of imatinib treatment, and after one, six, and 12 months. In addition, on day 14, and monthly during imatinib treatment, trough samples were taken. Pharmacokinetic analysis was conducted using a compartmental model. Volume of liver metastases was assessed by computed tomographic (CT) imaging. Results: After 90 days of treatment, a significant decrease in imatinib systemic exposure of 29.3% compared with baseline was observed (P < 0.01). For every 100 cm3 increase of metastatic volume, a predicted decrease of 3.8% in imatinib clearance was observed. Conclusions: This is the first prospective pharmacokinetic study in patients with GIST, showing a significant decrease of approximately 30% in imatinib exposure after long-term treatment. This means that future "trough level – clinical benefit" analyses should be time point specific. GIST liver involvement, however, has a marginal effect on imatinib clearance. Clin Cancer Res; 18(20); 5780–7. ©2012 AACR.

BACKGROUND: Dose banding is a recently suggested dosing method that uses predefined ranges (bands) of body surface area (BSA) to calculate each patient's dose by using a single BSA-value per band. Thus, drugs with sufficient long-term stability can be prepared in advance. The main advantages of dose banding are to reduce patient waiting time and improve pharmacy capacity planning; additional benefits include reduced medication errors, reduced drug wastage, and prospective quality control. This study compares dose banding with individual BSA dosing and fixed dose according to pharmacokinetic criteria.METHODS: Three BSA bands were defined: BSARESULTS: For all six drugs, the per cent variation in individual dose obtained with dose banding compared with BSA dosing ranged between -14% and +22%, and distribution of AUC values was very similar with both dosing methods. In terms of reaching the target AUC, there was no significant difference in precision between dose banding and BSA dosing, except for paclitaxel (32.0% vs 30.7%, respectively; PCONCLUSION: For the studied drugs, implementation of dose banding should be considered as it entails no significant increase in interindividual plasma exposure.

OCTN2 is a bifunctional transporter that reabsorbs filtered carnitine in a sodium-dependent manner and secretes organic cations into urine as a proton antiport mechanism. We hypothesized that inhibition of OCTN2 by anticancer drugs can influence carnitine resorption. OCTN2-mediated transport inhibition by anticancer drugs was assessed using cells transfected with human OCTN2 (hOCTN2) or mouse Octn2 (mOctn2). Excretion of carnitine and acetylcarnitine was measured in urine collected from mice and pediatric patients with cancer before and after administration of etoposide. Five of 27 tested drugs (50–100 μmol/L) inhibited hOCTN2-mediated carnitine uptake by 42% to 85% (P < 0.001). Of these inhibitors, etoposide was itself a transported substrate of hOCTN2 and mOctn2. Etoposide uptake by hOCTN2 was reversed in the presence of excess carnitine. This competitive inhibitory mechanism was confirmed in an in silico molecular docking analysis. In addition, etoposide inhibited the transcellular apical-to-basolateral flux of carnitine in kidney cells. Etoposide was also associated with a significant urinary loss of carnitine in mice (∼1.5-fold) and in patients with cancer (∼2.4-fold). Collectively, these findings indicate that etoposide can inhibit hOCTN2 function, potentially disturb carnitine homeostasis, and that this phenomenon can contribute to treatment-related toxicities. Mol Cancer Ther; 11(4); 921–9. ©2012 AACR.

Members of the solute carrier family of transporters are responsible for the cellular uptake of a broad range of endogenous compounds and xenobiotics in multiple tissues. Several of these solute carriers are known to be expressed in cancer cells or cancer cell lines, and decreased cellular uptake of drugs potentially contributes to the development of resistance. As result, the expression levels of these proteins in humans have important consequences for an individual's susceptibility to certain drug-induced side effects, interactions, and treatment efficacy. In this review article, we provide an update of this rapidly emerging field, with specific emphasis on the direct contribution of solute carriers to anticancer drug uptake in tumors, the role of these carriers in regulation of anticancer drug disposition, and recent advances in attempts to evaluate these proteins as therapeutic targets.

Purpose To determine whether shortening the infusion duration of high-dose methotrexate (HDMTX; 1 g/m2) affects the in vivo accumulation of active methotrexate polyglutamates (MTXPG1-7) in leukemia cells and whether this differs among major acute lymphoblastic leukemia (ALL) subtypes. Methods From June 2000 through October 2007, 356 children with ALL were randomly assigned to receive initial single-agent treatment with HDMTX (1 g/m2) as either a 24-hour infusion or a 4-hour infusion at two pediatric hospitals in the United States. The primary outcome measures were the accumulation of MTXPG1-7 in leukemia cells and the antileukemic effects (eg, inhibition of de novo purine synthesis in bone marrow ALL cells, and decrease in circulating ALL cells). Results The 24-hour infusion resulted in significantly higher amounts of MTXPG1-7 in bone marrow leukemia cells (median: 1,695 v 1,150 pmol/109 cells, P = .0059), and better antileukemic effects. The 24-hour infusion had the greatest effect on MTXPG1-7 accumulation in hyperdiploid ALL (median: 3,919 v 2,417 pmol/109 cells, P = .0038); T-cell ALL exhibited smaller differences in MTXPG1-7 but greater antileukemic effects with the longer infusion (median decrease in leukemia cells: 88.4% v 51.8%, P = .0075). In contrast, infusion duration had no significant impact on MTXPG1-7 accumulation or antileukemic effects in ALL with the t(12;21)/(ETV6-RUNX1) chromosomal translocation. Conclusion Shortening the infusion time of HDMTX reduces accumulation of active methotrexate in leukemia cells and decreases antileukemic effects, with differing consequences among major ALL subtypes.

Purine nucleoside antimetabolites, such as clofarabine, are effective antileukemic agents. However, their effectiveness depends on an initial activation step in which they are monophosphorylated by deoxycytidine kinase (dCK). Some purine nucleoside antimetabolites and their monophosphate derivatives are exported by the ABC transporter ABCG2. Because clofarabine is a dCK substrate, and we show substantial variation in dCK and ABCG2 in myeloid leukemia, we hypothesized that the activity of dCK may modulate ABCG2-mediated resistance to clofarabine by regulating the formation of clofarabine monophosphate. We show that ABCG2 influence on clofarabine cytotoxicity was markedly influenced by dCK activity. When dCK expression was reduced by siRNA, clofarabine cytotoxicity was strongly reduced by enhanced ABCG2-mediated efflux. Conversely, dCK overexpression blunted ABCG2-mediated efflux of clofarabine by increasing the formation of clofarabine nucleotides. The use of an ABCG2 inhibitor confirmed that ABCG2 export of clofarabine is maximal when dCK levels are minimal. Analysis of intracellular clofarabine metabolites suggested that ABCG2 exported clofarabine more readily than clofarabine monophosphate. That ABCG2 primarily effluxes clofarabine, but not chlorfarabine-monophosphate, was confirmed by HPLC analysis of drug exported from ABCG2-overexpressing cells. Because the level and function of dCK and ABCG2 vary substantially among other types of cancer, these findings have important implications not only for clofarabine therapy but for purine nucleoside therapy in general. Therefore, we propose that addition of ABCG2 inhibitors would effectively increase the antitumor efficacy of purine nucleosides by blocking drug efflux that may be a significant mode of resistance when dCK levels are low. Cancer Res; 71(5); 1781–91. ©2011 AACR.

Purpose: Although the ABCB1 (P-glycoprotein) drug transporter is a constituent of several blood–tissue barriers (i.e., blood–brain and blood–nerve), its participation in a putative blood–heart barrier has been poorly explored. ABCB1 could decrease the intracardiac concentrations of drugs that cause QT prolongation and cardiotoxicity. Experimental Design: ABCB1-related romidepsin transport kinetics were explored in LLC-PK1 cells transfected with different ABCB1 genetic variants. ABCB1 plasma and intracardiac concentrations were determined in Abcb1a/1b (−/−) mice and wild-type FVB controls. These same mice were used to evaluate romidepsin-induced heart rate-corrected QT interval (QTc) prolongation over time. Finally, a cohort of 83 individuals with available QTcB and ABCB1 genotyping data were used to compare allelic variation in ABCB1 versus QTc-prolongation phenotype. Results: Here, we show that mice lacking the ABCB1-type P-glycoprotein have higher intracardiac concentrations of a model ABCB1 substrate, romidepsin, that correspond to changes in QT prolongation from baseline (ΔQTc) over time. Consistent with this observation, we also show that patients carrying genetic variants that could raise ABCB1 expression in the cardiac endothelium have lower ΔQTc following a single dose of romidepsin. Conclusions: To our knowledge, this is the first evidence that Abcb1-type P-glycoprotein can limit intracardiac exposure to a drug that mediates QT prolongation and suggests that certain commonly inherited polymorphisms in ABCB1 may serve as markers for QT prolongation following the administration of ABCB1-substrate drugs. Clin Cancer Res; 17(4); 937–46. ©2010 AACR.

Imatinib mesylate is approved for the treatment of chronic myeloid leukemia (CML) and advanced gastrointestinal stromal tumors (GIST). Unfortunately, in the course of treatment, disease progression occurs in the majority of patients with GIST. Lowered plasma trough levels of imatinib over time potentially cause disease progression, a phenomenon known as “acquired pharmacokinetic drug resistance.” This outcome may be the result of an altered expression pattern or activity of drug transporters. To date, the role of both efflux transporters (ATP-binding cassette transporters, such as ABCB1 and ABCG2) and uptake transporters [solute carriers such as organic cation transporter 1 (OCT1) and organic anion transporting polypeptide 1A2 (OATP1A2)] in imatinib pharmacokinetics and pharmacodynamics has been studied. In vitro experiments show a significant role of ABCB1 and ABCG2 in cellular uptake and retention of imatinib, although pharmacokinetic and pharmacogenetic data are still scarce and contradictory. ABCB1 and ABCC1 expression was shown in GIST, whereas ABCB1, ABCG2, and OCT1 were found in mononuclear cells in CML patients. Several studies have reported a clinical relevance of tumor expression or activity of OCT1 in CML patients. Further (clinical) studies are required to quantify drug transporter expression over time in organs involved in imatinib metabolism, as well as in tumor tissue. In addition, more pharmacogenetic studies will be needed to validate associations. Clin Cancer Res; 17(3); 406–15. ©2010 AACR.

Purpose To assess whether the low incidence of severe neutropenia in castrated men with prostate cancer treated with docetaxel is the result of changes in systemic clearance. Patients and Methods A total of 10 noncastrated and 20 castrated men with prostate cancer were studied to achieve 80% power (α = .05) to detect at least a 25% change in the clearance of docetaxel. The erythromycin breath test was evaluated to determine hepatic activity of cytochrome P450 3A4 (CYP3A4), the main docetaxel-metabolizing enzyme. Additional studies were performed in rats and transfected cells overexpressing human or rodent transporters. Results Docetaxel clearance was increased by approximately 100% in castrated men and was associated with a two-fold reduction in area under the curve (P = .0001), although hepatic activity of CYP3A4 was unchanged (P = .26). In rats, castration was associated with higher uptake of docetaxel in the liver and a concurrent increase in the expression of rOat2 (Slc22a7), an organic anion transporter that regulates, in part, the transfer of docetaxel from the circulation into hepatocytes. Conclusion It is recommended that castration- and/or hormone-related changes in the clearance of oncology drugs should be considered as a possible risk factor for treatment failure.

Purpose: Carnitine is an essential cofactor for mitochondrial fatty acid oxidation that is actively reabsorbed by the luminal transporter Octn2 (Slc22a5). Because the nephrotoxic agent cisplatin causes urinary loss of carnitine in humans, we hypothesized that cisplatin may affect Octn2 function. Experimental Design: Excretion of carnitine and acetylcarnitine was measured in urine collected from mice with or without cisplatin administration. The transport of carnitine was assessed in cells that were transfected with OCT1 or OCT2. The effect of cisplatin treatment on gene expression was analyzed using a mouse GeneChip array and validated using quantitative reverse transcriptase-PCR. Results: In wild-type mice, urinary carnitine excretion at baseline was ∼3-fold higher than in mice lacking the basolateral cisplatin transporters Oct1 and Oct2 [Oct1/2(−/−) mice], indicating that carnitine itself undergoes basolateral uptake into the kidney. Transport of carnitine by OCT2, but not OCT1, was confirmed in transfected cells. We also found that cisplatin caused an increase in the urinary excretion of carnitine and acetylcarnitine in wild-type mice but not in Oct1/2(−/−) mice, suggesting that tubular transport of cisplatin is a prerequisite for this phenomenon. Cisplatin did not directly inhibit the transport of carnitine by Octn2 but downregulated multiple target genes of the transcription factor peroxisome proliferator activated receptor α, including Slc22a5, in the kidney of wild-type mice that were absent in Oct1/2(−/−) mice. Conclusion: Our study shows a pivotal role of Oct1 and Oct2 in cisplatin-related disturbances in carnitine homeostasis. We postulate that this phenomenon is triggered by deactivation of peroxisome proliferator activated receptor α and leads to deregulation of carnitine-shuttle genes. Clin Cancer Res; 16(19); 4789–99. ©2010 AACR.

Purpose: This study aimed to test the influence of functional renal organic cation transporters (OCT2 in humans, Oct1 and Oct2 in mice) on biomarkers of cisplatin nephrotoxicity, such as urinary activity of N-acetyl-β-D-glucosaminidase (NAG). Experimental Design: Temporal cisplatin-induced nephrotoxicity was assessed by histopathology and biomarkers. Cisplatin-mediated NAG changes and survival were determined in wild-type and Oct1/2(-/-) mice. Identification of OCT2 inhibitors was done in transfected 293Flp-In cells, and the NCI60 cell line panel was used to assess contribution of OCT2 to cisplatin uptake in cancer cells. Results: Classical biomarkers such as blood urea nitrogen and serum creatinine were not elevated until 72 hours after cisplatin administration and substantial kidney damage had occurred. Oct1/2(-/-) mice had 2.9-fold lower NAG by 4 hours (P < 0.0001) and 2.3-fold increased survival (P = 0.0097). Among 16 agents, cimetidine strongly inhibited uptake of tetraethylammonium bromide (P = 0.0006) and cisplatin (P < 0.0001), but did not have an influence on cisplatin uptake in SK-OV-3 cells, the cancer line with the highest OCT2 mRNA levels. In wild-type mice, cimetidine inhibited cisplatin-induced NAG changes (P = 0.016 versus cisplatin alone) to a degree similar to that seen in Oct1/2(-/-) mice receiving cisplatin (P = 0.91). Cumulative NAG activity of >0.4 absorbance units (AU) was associated with 21-fold increased odds for severe nephrotoxicity (P = 0.0017), which was linked with overall survival (hazard ratio, 8.1; 95% confidence interval, 2.1-31; P = 0.0078). Conclusions: Cimetidine is able to inhibit OCT2-mediated uptake of cisplatin in the kidney, and subsequently ameliorate nephrotoxicity likely with minimal effect on uptake in tumor cells. Clin Cancer Res; 16(16); 4198–206. ©2010 AACR.

Purpose: Irinotecan, the prodrug of SN-38, is extensively metabolized by cytochrome P450-3A4 (CYP3A4). A randomized trial was done to assess the utility of an algorithm for individualized irinotecan dose calculation based on a priori CYP3A4 activity measurements by the midazolam clearance test. Experimental Design: Patients were randomized to receive irinotecan at a conventional dose level of 350 mg/m2 (group A) or doses based on an equation consisting of midazolam clearance, γ-glutamyl-transferase, and height (group B). Pharmacokinetics and toxicities were obtained during the first treatment course. Results: Demographics of 40 evaluable cancer patients were balanced between both groups, including UGT1A1*28 genotype and smoking status. The absolute dose of irinotecan ranged from 480 to 800 mg in group A and 380 to 1,060 mg in group B. The mean absolute dose and area under the curve of irinotecan and SN-38 were not significantly different in either group (P > 0.18). In group B, the interindividual variability in the area under the curve of irinotecan and SN-38 was reduced by 19% and 25%, respectively (P > 0.22). Compared with group A, the incidence of grades 3 to 4 neutropenia was >4-fold lower in group B (45 versus 10%; P = 0.013). The incidence of grades 3 to 4 diarrhea was equal in both groups (10%). Conclusions: Incorporation of CYP3A4 phenotyping in dose calculation resulted in an improved predictability of the pharmacokinetic and toxicity profile of irinotecan, thereby lowering the incidence of severe neutropenia. In combination with UGT1A1*28 genotyping, CYP3A4 phenotype determination should be explored further as a strategy for the individualization of irinotecan treatment. Clin Cancer Res; 16(2); 736–42

Purpose Methotrexate plasma concentration is related to its clinical effects. Our aim was to identify the genetic basis of interindividual variability in methotrexate pharmacokinetics in children with newly diagnosed acute lymphoblastic leukemia (ALL). Patients and Methods We performed a genome-wide analysis of 500,568 germline single-nucleotide polymorphisms (SNPs) to identify how inheritance affects methotrexate plasma disposition among 434 children with ALL who received 3,014 courses of methotrexate at 2 to 5 g/m2. SNPs were validated in an independent cohort of 206 patients. Results Adjusting for age, race, sex, and methotrexate regimen, the most significant associations were with SNPs in the organic anion transporter polypeptide, SLCO1B1. Two SNPs in SLCO1B1, rs11045879 (P = 1.7 × 10−10) and rs4149081 (P = 1.7 × 10−9), were in linkage disequilibrium (LD) with each other (r2 = 1) and with a functional polymorphism in SLCO1B1, T521C (rs4149056; r2 > 0.84). rs11045879 and rs4149081 were validated in an independent cohort of 206 patients (P = .018 and P = .017), as were other SLCO1B1 SNPs residing in different LD blocks. SNPs in SLCO1B1 were also associated with GI toxicity (odds ratio, 15.3 to 16.4; P = .03 to .004). Conclusion A genome-wide interrogation identified inherited variations in a plausible, yet heretofore low-priority candidate gene, SLCO1B1, as important determinants of methotrexate's pharmacokinetics and clinical effects.

Purpose: To compare side-by-side the uptake of sorafenib and sunitinib in vitro by human uptake solute carriers of the SLC22A and SLCO families, the transport by and inhibition of efflux ATP-binding cassette (ABC) transporters, and the role of ABCB1 in the plasma pharmacokinetics and brain penetration of these agents. Experimental Design: Uptake of [3H]sorafenib or [3H]sunitinib was assessed in Xenopus laevis oocytes or mammalian cells transfected with cDNAs coding for human OATP1A2, OATP1B1, OATP1B3, OCT1, OAT2, OAT3, OCTN1, or OCTN2. Efflux and inhibition experiments were conducted in cells transfected with human ABCB1, ABCG2, ABCC2, or ABCC4. In vivo pharmacokinetic studies were done in knockout mice lacking Abcb1-type transporters. Results: Intracellular uptake was not appreciably affected by any of the studied solute carriers and was minute relative to the respective prototypical substrates. Sorafenib and sunitinib showed concentration-dependent (1 and 10 μmol/L), low to moderate affinity for ABCB1 but were not affected by the other ABC transporters. Both agents inhibited all tested ABC transporters. The absence of Abcb1 had no affect on plasma pharmacokinetics, but brain penetration was moderately increased by 1.9- and 2.9-fold for sorafenib and sunitinib, respectively, in knockout animals versus controls. Conclusions: Unlike other tyrosine kinase inhibitors, sorafenib and sunitinib do not appear to rely on active transport to enter the cell nor are they high-affinity substrates for ABC efflux transporters. Based on these characteristics, these two drugs may be less susceptible to transporter-mediated alterations in systemic exposure and transporter-related resistance mechanisms. (Clin Cancer Res 2009;15(19):6062–9)

Purpose: Abraxane (ABI-007) is a 130-nm albumin-bound (nab) particle formulation of paclitaxel, devoid of any additional excipients. We hypothesized that this change in formulation alters the systemic disposition of paclitaxel compared with conventional solvent-based formulations (sb-paclitaxel; Taxol), and leads to improved tolerability of the drug. Patients and Methods: Patients with malignant solid tumors were randomized to receive the recommended single-agent dose of nab-paclitaxel (260 mg/m2 as a 30-minute infusion) or sb-paclitaxel (175 mg/m2 as a 3-hour infusion). After cycle 1, patients crossed over to the alternate treatment. Pharmacokinetic studies were carried out for the first cycle of sb-paclitaxel and the first two cycles of nab-paclitaxel. Results: Seventeen patients were treated, with 14 receiving at least one cycle each of nab-paclitaxel and sb-paclitaxel. No change in nab-paclitaxel pharmacokinetics was found between the first and second cycles (P = 0.95), suggesting limited intrasubject variability. Total drug exposure was comparable between the two formulations (P = 0.55) despite the dose difference. However, exposure to unbound paclitaxel was significantly higher after nab-paclitaxel administration, due to the increased free fraction (0.063 ± 0.021 versus 0.024 ± 0.009; P < 0.001). Conclusion: This study shows that paclitaxel disposition is subject to considerable variability depending on the formulation used. Because systemic exposure to unbound paclitaxel is likely a driving force behind tumoral uptake, these findings explain, at least in part, previous observations that the administration of nab-paclitaxel is associated with augmented antitumor efficacy compared with solvent-based paclitaxel.

Purpose: Cisplatin is predominantly eliminated in the urine through active secretion. As the solute carrier organic cation transporter 2 (OCT2) is highly expressed in the basolateral membrane of proximal tubules, we determined its contribution to cisplatin transport and assessed the relation of variation in the gene encoding OCT2 (SLC22A2) with the disposition of cisplatin. Experimental Design: Cell lines were transfected using the Flp-In 293 system with the full-length OCT2 cDNA, and platinum concentrations were measured using flameless atomic absorption spectrometry. Pharmacokinetic data were available from 106 cancer patients, and DNA was screened for eight nonsynonymous SLC22A2 variants using direct sequencing. Results: mRNA expression was 36-fold higher and uptake of the model substrate tetraethylammonium was significantly increased (P < 0.0001) in OCT2-transfected cells compared with empty vector-transfected controls. OCT2-mediated transport of cisplatin was saturable, and uptake was increased by ∼4-fold (P < 0.0001) relative to control cells. Cisplatin inhibited OCT2-mediated transport of tetraethylammonium by up to 97%. The mean ± SD systemic clearance of unbound cisplatin-derived platinum in the patient population was 29.2 ± 8.39 L/h, and renal clearance was particularly variable. Only one single nucleotide polymorphism (Ala270Se; rs316019) was identified (minor allele frequency, 7.6%), and it was not found to be associated with any of the studied pharmacokinetic variables (P > 0.05). Conclusion: These findings support the hypothesis that OCT2 is a key renal transporter involved in cisplatin elimination. However, known variants in SLC22A2 do not substantially contribute to explaining interindividual pharmacokinetic variability, suggesting that other mechanisms, controlling OCT2 expression, might be involved.

Purpose: The organic anion transporter OATP1B3, encoded by SLCO1B3, is involved in the transport of steroid hormones. However, its role in testosterone uptake and clinical outcome of prostatic cancer is unknown. This study examined (a) the SLCO1B3 genotype in cancer cells as well as the uptake of testosterone by cells transfected with genetic variants of SLCO1B3; (b) the expression of OATP1B3 in normal prostate, benign prostatic hyperplasia, and prostatic cancer; and (c) the role of SLCO1B3 haplotype on clinical outcome of Caucasian patients with androgen-independent prostatic cancer. Experimental Design: SLCO1B3 genotype was assessed in the NCI-60 panel of tumor cells by sequencing, whereas testosterone transport was analyzed in Cos-7 cells transfected with WT, 334G, and 699A SLCO1B3 variants. OATP1B3 expression in prostatic tissues was examined by fluorescence microscopy, and the relationship between SLCO1B3 haplotypes and survival was examined in patients. Results: Cells transfected with wild-type (334T/699G) SLCO1B3, or with a vector containing either the 334G or 699A variants, actively transported testosterone, whereas its uptake was impaired in cells transfected with a gene carrying both 334G and 699A single nucleotide polymorphisms. Prostatic cancer overexpresses OATP1B3 compared with normal or benign hyperplastic tissue; patients with SLCO1B3 334GG/699AA haplotype showed longer median survival (8.5 versus 6.4 years; P = 0.020) and improved survival probability at 10 years (42% versus 23%; P < 0.023) than patients carrying TT/AA and TG/GA haplotypes. Conclusions: The common SLCO1B3 GG/AA haplotype is associated with impaired testosterone transport and improved survival in patients with prostatic cancer.

The formulation excipient Cremophor EL (CrEL) is known to limit the absorption of oral paclitaxel given together with cyclosporin A. We hypothesized that the use of oral Genetaxyl, a paclitaxel formulation containing only 20% CrEL would have an improved oral bioavailability. Cohorts of six patients were treated with oral Genetaxyl at a dose of 60, 120, or 180 mg/m2 and 10 mg/kg of oral cyclosporin A in cycle 1. In cycle 2, patients received intravenous (i.v.) Genetaxyl (175 mg/m2, 3-h infusion). Three additional patients received one dose of generic i.v. paclitaxel (Genaxol, containing 50% CrEL; 175mg/m2, 3-h infusion). The median area under the plasma concentration-time curve (AUC) and peak concentration of total paclitaxel following i.v. Genetaxyl were lower than those for i.v. Genaxol, as a result of significantly increased clearance (P = 0.017), and the AUC ratio for unbound to total paclitaxel for i.v. Genetaxyl was about two times higher than that for i.v. Genaxol (P = 0.0077). After oral administration of Genetaxyl at doses of 60, 120, and 180 mg/m2, the median total paclitaxel AUCs were 1.29, 1.60, and 1.85 microg x h/ml, respectively, suggesting a less than proportional increase in systemic exposure with increasing doses. The corresponding median values for the apparent bioavailability of oral Genetaxyl were similar when compared with i.v. Genetaxyl, when calculated either on the basis of data for total paclitaxel (30.1%) or unbound paclitaxel (30.6%).

Using a single nucleotide polymorphism association study in 52 men with prostate cancer receiving docetaxel, we found that individuals carrying two copies of the CYP1B1*3 polymorphic variant had a poor prognosis after docetaxel-based therapies compared with individuals carrying at least one copy of the CYP1B1*1 allele (30.6 versus 12.8 months; P = 0.0004). The association between CYP1B1*3 and response to therapy was not observed in similar subjects receiving non-taxane-based therapy (P = 0.18). The systemic clearance of docetaxel was also unrelated to CYP1B1 genotype status (P = 0.39), indicating that the association of CYP1B1*3 with clinical response is not due to docetaxel metabolism. To explain these results, we hypothesized that an indirect gene-drug interaction was interfering with the primary mechanism of action of docetaxel, tubulin polymerization. We therefore conducted tubulin polymerization experiments with taxanes in the presence or absence of certain CYP1B1 estrogen metabolites, which are known to bind to nucleophilic sites in proteins and DNA, that revealed the primary estrogen metabolite of CYP1B1, 4-hydroxyestradiol (4-OHE2), when oxidized to estradiol-3,4-quinone strongly inhibits tubulin polymerization. The 4-OHE2 is also formed more readily by the protein encoded by the CYP1B1*3 allele, validating further our data in patients. Furthermore, estradiol-3,4-quinone reacted in vitro with docetaxel to form the 4-OHE2-docetaxel adduct. This pilot study provides evidence that CYP1B1*3 may be an important marker for estimating docetaxel efficacy in patients with prostate cancer. This link is likely associated with CYP1B1*3 genotype-dependent estrogen metabolism. [Mol Cancer Ther 2008;7(1):19–26]

Purpose Our published preclinical experiments have indicated that romidepsin mediates growth arrest and apoptosis in lung cancer cells (but not cultured normal bronchial epithelia) via chromatin remodeling mechanisms. Also, romidepsin has direct effects on survival and stress signal pathways. A phase II trial was performed to examine clinical and molecular responses mediated by this histone deacetylase (HDAC) inhibitor in patients with lung cancer. Patients and Methods Nineteen patients with neoplasms refractory to standard therapy received 4-hour romidepsin infusions (17.8 mg/m2) on days 1 and 7 of a 21-day cycle. Each full course of therapy consisted of 2 identical 21-day cycles. Plasma romidepsin levels were evaluated by liquid chromatography/mass spectrometry techniques. A variety of molecular endpoints were assessed in tumor biopsies via immunohistochemistry techniques. Long-oligo arrays were used to examine gene expression profiles in laser-captured tumor cells before and after romidepsin exposure, relative to lung cancer cells and adjacent normal bronchial epithelia from patients undergoing pulmonary resections. Results Nineteen patients were evaluable for toxicity assessment; 18 were evaluable for treatment response. Myelosuppression was dose limiting in 1 individual. No significant cardiac toxicities were observed. Maximum steady-state plasma romidepsin concentrations ranged from 384-1114 ng/mL. No objective responses were observed. Transient stabilization of disease was noted in 9 patients. Romidepsin enhanced acetylation of histone H3 (H3K9) as well as H4K16 and increased p21 expression in lung cancer cells. No obvious changes in phosho-extracellular signal–regulated kinase, ki67, or cleaved caspase-3 levels were noted. Although romidepsin appeared to induce a relatively small number of genes, this HDAC inhibitor diminished expression of > 1000 genes in laser-captured tumor cells. Interestingly, these genes, which appeared to be induced or repressed by romidepsin, were repressed or induced, respectively, in primary lung cancers relative to adjacent histologically normal bronchial epithelia, suggesting that romidepsin can reverse lung cancer gene expression in vivo. Conclusion Although exhibiting minimal clinical efficacy at this dose and schedule, romidepsin mediates biologic effects that might warrant further evaluation of this HDAC inhibitor in combination with novel agents targeting chromatin remodeling complexes, survival pathways, or death receptors in patients with lung cancer.

Purpose: To evaluate the effects of ritonavir, a potent inhibitor of CYP3A4, on the steady-state pharmacokinetics of imatinib. Experimental Design: Imatinib pharmacokinetics were evaluated in cancer patients receiving the drug for at least 2 months, after which ritonavir (600 mg) was administered daily for 3 days. Samples were obtained on the day before ritonavir (day 1) and on the third day (day 4). The in vitro metabolism of imatinib with or without ritonavir and the effect of imatinib on 1-OH-midazolam formation rate, a probe for CYP3A4 activity, were evaluated with human CYP3A4 and pooled liver microsomes. Results: In 11 evaluable patients, the geometric mean (95% confidence interval) area under the curve of imatinib on days 1 and 4 were 42.6 (33.0-54.9) μg·h/mL and 41.2 (32.1-53.1) μg·h/mL, respectively (P = 0.65). A population analysis done in NONMEM with a time-dependent covariate confirmed that ritonavir did not influence the clearance or bioavailability of imatinib. In vitro, imatinib was metabolized to the active metabolite CGP74588 by CYP3A4 and CYP3A5 and, to a lesser extent, by CYP2D6. Ritonavir (1 μmol/L) completely inhibited CYP3A4-mediated metabolism of imatinib to CGP74588 but inhibited metabolism in microsomes by only 50%. Imatinib significantly inhibited CYP3A4 activity in vitro. Conclusion: At steady state, imatinib is insensitive to potent CYP3A4 inhibition and relies on alternate elimination pathways. For agents with complex elimination pathways that involve autoinhibition, interaction studies that are done after a single dose may not be applicable when drugs are administered chronically.

Objectives To investigate the association between a cytochrome P450 17α-hydroxylase gene (CYP17) polymorphism and survival in Caucasian patients with androgen-independent prostate cancer (AIPC). Methods The study used 222 samples acquired from Caucasian patients with AIPC. The CYP17 polymorphism (−34T>C) was analyzed using polymerase chain reaction amplification followed by restriction fragment length polymorphism detection. Results No significant differences were observed in the frequencies of the CYP17 genotype in relation to categorized Gleason scores, age at diagnosis, or hormone therapy. The median survival was significantly longer in 126 patients with the CYP17 A2 allele (8.9 years) genotype than in 96 patients with the A1 allele (6.7 years) genotype ( P = 0.040 by log-rank test). Similarly, the estimated survival probability at 10 years (24% in A1 allele versus 43% in A2 allele) showed a statistically significant difference between the two groups ( P = 0.002 by the permutation test). Conclusions These results suggest that the CYP17 polymorphism is associated with overall survival in patients with AIPC.

The current practice of using body-surface area (BSA) in dosing anticancer agents was implemented in clinical oncology half a century ago. By correcting for BSA, it was generally assumed that cancer patients would receive a dose of a particular cytotoxic drug associated with an acceptable degree of toxicities without reducing the agent's therapeutic effect. More recently, doubt has arisen to this hypothesis, and for many drugs, the effects of BSA on the pharmacokinetics of these agents have therefore been studied retrospectively. In (by far) most cases, use of BSA does not reduce the interindividual variation in the pharmacokinetics of adults, and thus, a logical rationale for further use of this tool in dosing adults is lacking. As a result, alternative dosing strategies have been proposed in order to replace BSA-based dosing. Flat-fixed dosing regimens have been suggested, thereby avoiding potential dose calculation mistakes. As flat-fixed dosing does not typically lead to greater pharmacokinetic variability, it does not seem worse than using BSA-based dosing. While it provides a simplification, it can, however, be questioned whether to call this an improvement or not. The implementation of so-called genotyping and phenotyping strategies, and therapeutic drug monitoring, may probably be of more clinical value. In the end, the nonscientifically based BSA-based dosing strategy should be replaced by alternative strategies. Despite the lack of basic fundamentals, BSA-based dosing still seems "untouchable" in clinical oncology. Even when alternatives will be shown to be indisputably better, many hurdles will probably have to be overcome before physicians will be willing to ban BSA-based dosing. Disclosure of potential conflicts of interest is found at the end of this article.