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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.

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

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.

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.

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.

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: 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: 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.

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.

Purpose: To evaluate the effect of naturally occurring variants in genes encoding the cytochrome P450 (CYP) isoforms CYP3A4 and CYP3A5 in patients with cancer receiving midazolam as a phenotyping probe. Experimental Design: Five variants in CYP3A4 and CYP3A5 were evaluated in 58 patients (21 women and 37 men) receiving a short i.v. bolus of midazolam (dose, 0.0145 or 0.025 mg/kg). Midazolam concentrations in plasma were determined using liquid chromatography-mass spectrometry, and pharmacokinetic variables were calculated using noncompartmental analysis. Genomic DNA was characterized for the variants by PCR-RFLP, and all genotypes were confirmed by direct nucleotide sequencing. Results: The mean clearance of midazolam was 24.4 ± 9.12 L/h, and phenotypic CYP3A activity varied about 4-fold in this population (range, 10.8-44.3 L/h). There were six carriers of the CYP3A4*1B allele (allele frequency, 0.061). No variant alleles for CYP3A4*17, CYP3A4*18A, or CYP3A5*6 were identified. Forty-eight of the 58 patients were homozygous variant for CYP3A5*3C, eight were heterozygous, and two were homozygous wild type (allele frequency, 0.897). No associations were noted between any of the studied genotypes and the phenotypic measures (P ≥ 0.16). Likewise, a common variant in exon 26 in the gene encoding P-glycoprotein [i.e., ABCB1 (MDR1) 3435C>T] that was previously reported to be linked to CYP3A4 mRNA levels was unrelated to any of the studied phenotypic measures (P ≥ 0.49). Conclusions. The studied genetic variants in CYP3A4 and CYP3A5 are unlikely to have an important functional significance to phenotypic CYP3A activity in patients with cancer.

Purpose: The purpose is to identify the demographic, physiologic, and inheritable factors that influence CYP3A activity in cancer patients Experimental Design: A total of 134 patients (62 females; age range, 26 to 83 years) underwent the erythromycin breath test as a phenotyping probe of CYP3A. Genomic DNA was screened for six variants of suspected functional relevance in CYP3A4 (CYP3A4*1B, CYP3A4*6, CYP3A4*17, and CYP3A4*18) and CYP3A5 (CYP3A5*3C and CYP3A5*6). Results: CYP3A activity (AUC0–40min) varied up to 14-fold in this population. No variants in the CYP3A4 and CYP3A5 genes were a significant predictor of CYP3A activity (P > 0.2954). CYP3A activity was reduced by ∼50% in patients with concurrent elevations in liver transaminases and alkaline phosphatase or elevated total bilirubin (P < 0.001). In a multivariate analysis, CYP3A activity was not significantly influenced by age, sex, and body size measures (P > 0.05), but liver function combined with the concentration of the acute-phase reactant, α-1 acid glycoprotein, explained ∼18% of overall variation in CYP3A activity (P < 0.001). Conclusions: These data suggest that baseline demographic, physiologic, and chosen genetic polymorphisms have a minor impact on phenotypic CYP3A activity in patients with cancer. Consideration of additional factors, including the inflammation marker C-reactive protein, as well as concomitant use of other drugs, food constituents, and complementary and alternative medicine with inhibitory and inducible effects on CYP3A, is needed to reduce variation in CYP3A and treatment outcome to anticancer therapy.

Purpose: The ATP-binding cassette transporter ABCG2 (breast cancer resistance protein) is an efflux protein that plays a role in host detoxification of various xenobiotic substrates, including the irinotecan metabolite 7- ethyl-10-hydroxycamptothecin (SN-38). The ABCG2 421C>A polymorphism has been associated with reduced protein expression and altered function in vitro. The aim of this study was to evaluate the ethnic distribution and potential functional consequence of the ABCG2 421C>A genotype in cancer patients treated with irinotecan. Experimental Design: ABCG2 genotyping was performed using Pyrosequencing on DNA from 88 American Caucasians, 94 African Americans, 938 Africans, and 95 Han Chinese, as well as in 84 European Caucasian patients treated with irinotecan undergoing additional blood sampling for pharmacokinetic studies. Results: Significant differences in allele frequencies were observed between the given world populations (P < 0.001), the variant allele being most common in the Han Chinese population with a frequency as high as 34%. The mean area under the curve of irinotecan and SN-38 were 19,851 and 639 ng × hour/mL, respectively. The frequency of the variant allele (10.7%) was in line with results in American Caucasians. No significant changes in irinotecan pharmacokinetics were observed in relation to the ABCG2 421C>A genotype, although one of two homozygous variant allele carriers showed extensive accumulation of SN-38 and SN-38 glucuronide. Conclusions: The ABCG2 421C>A polymorphism appears to play a limited role in the disposition of irinotecan in European Caucasians. It is likely that the contribution of this genetic variant is obscured by a functional role of other polymorphic proteins.

Purpose: The purpose of this study was to determine the toxicities and characterize the pharmacokinetics of docetaxel and flavopiridol in patients with metastatic breast cancer. Experimental Design: Docetaxel was administered at an initial dose of 60 mg/m2 followed in 24 hours by a 72-hour infusion of flavopiridol at 50 mg/m2/d every 3 weeks. Because dose-limiting myelosuppression occurred, the schedule was amended to docetaxel, 50 mg/m2, followed by escalating doses of flavopiridol (starting dose, 26 mg/m2/d) as a 1-hour infusion daily for 3 days. Pharmacokinetic studies were performed. Ki67, p53, and phosphorylated retinoblastoma protein (phospho-Rb) in paired tumor and buccal mucosa biopsies (obtained pre- and posttreatment) were examined by immunohistochemistry. Results: Eleven patients were enrolled. Five patients received docetaxel and 72-hour flavopiridol. Dose-limiting toxicity was grade 4 neutropenia. Six patients received docetaxel and 1-hour flavopiridol, and the dose-limiting toxicity was grade 3 hypotension. Pharmacokinetics of flavopiridol and docetaxel were consistent with historical data. Nuclear staining with p53 increased and phospho-Rb decreased in 10 pairs of buccal mucosa biopsies posttreatment (P = 0.002 and P = 0.04, respectively). No significant changes in Ki67, p53, or phospho-Rb were detected in six paired tumors. Two patients sustained stable disease for >3 months (72-hour flavopiridol), and one partial response was observed (1-hour flavopiridol). Conclusions: Docetaxel combined with 72-hour flavopiridol was not feasible because of dose-limiting neutropenia. Dose escalation of a 1-hour infusion of flavopiridol with docetaxel was also not possible. The changes in p53 and phospho-Rb in buccal mucosa suggest that a biological effect with flavopiridol was achieved.

Purpose: In a previous analysis, it was shown that body-surface area (BSA) is not a predictor of irinotecan pharmacokinetic parameters. Here, we prospectively evaluated the effects of administering a flat-fixed irinotecan dose to cancer patients, regardless of BSA. Experimental Design: Twenty-six cancer patients (12 females) received a fixed irinotecan dose of 600 mg, given as a 90-min i.v. infusion. Plasma concentrations of irinotecan and its metabolites SN-38 (7-ethyl-10-hydroxycamptothecin) and SN-38G (SN-38 glucuronide) were measured during the first cycle and analyzed using nonlinear mixed-effect modeling. Data were compared with those obtained in 47 cancer patients (19 females) who received irinotecan at a BSA-normalized dose of 350 mg/m2. Results: The interindividual variability in irinotecan clearance (25.9% versus 25.1%; P = 0.93), in relative extent of conversion to SN-38 (47.8% versus 42.7%; P = 0.24), and in relative extent of SN-38 glucuronidation (71.2% versus 72.4%; P = 0.95) were not significantly different between the two dose groups. Variance differences in irinotecan-mediated hematological side effects were also similar between the 600 mg and 350 mg/m2 groups (P > 0.14). Conclusions: These findings suggest that flat-fixed dosing of irinotecan does not result in increased pharmacokinetic/pharmacodynamic variability and could be safely used to supplant current dosing strategies based on BSA.

Purpose: To determine the maximum-tolerated dose, toxicity profile, and pharmacokinetics of a fixed dose of paclitaxel followed by increasing doses of carboplatin, given weekly to patients with advanced esophageal or gastric junction cancer. Experimental Design: Paclitaxel was administered on day 1 as a 1-h infusion at a fixed dose of 100 mg/m2 followed by a 1-h infusion of carboplatin targeting an area under the curve (AUC) of 2–5 mg × min/ml, with cycles repeated on days 8, 15, 29, 36, and 43. Results: Forty patients [36 males; median (range) age, 57 (40–74) years] were enrolled. Dose-limiting toxicity was observed at a carboplatin AUC of 5 mg × min/ml and consisted of treatment delay attributable to myelosuppression. No grade 3/4 treatment-related nonhematological toxicity was observed. The highest dose intensity (>95% of the planned dose over time) was achieved with a carboplatin AUC of 4 mg × min/ml. The mean (±SD) AUCs of unbound (Cu) and total paclitaxel were 0.662 ± 0.186 and 7.37 ± 1.33 μm × h, respectively. Clearance of Cu was 188 ± 44.6 liter/h/m2, which is not significantly different from historical data (P = 0.52). Cremophor EL clearance was 123 ± 23 ml/h/m2, similar to previous findings. Of 37 patients evaluable for response, 1 had complete response, 19 had partial response, and 10 had stable disease, accounting for an overall response rate of 54%. Conclusions: This regimen is very tolerable and effective, and the recommended doses for additional studies are paclitaxel (100 mg/m2), with carboplatin targeting an AUC of 4 mg × min/ml.

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