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INTRODUCTION: This Phase Ib trial investigated the safety, tolerability, and recommended phase 2 dose for the pan-PI3K/mTOR inhibitor, GSK2126458 (GSK458), and trametinib combination when administered to patients with advanced solid tumors. PATIENTS AND METHODS: Patients with advanced solid tumors received escalating doses of GSK458 (once or twice daily, and continuous or intermittent) and trametinib following a zone-based 3 + 3 design to determine the maximum tolerated dose (MTD). Assessments included monitoring for adverse events and response, and evaluating pharmacokinetic (PK) measures. Archival tissue and circulating free DNA samples were collected to assess biomarkers of response in the PI3K and RAS pathways. RESULTS: 57 patients were enrolled onto the continuous dosing cohort and 12 patients onto an intermittent BID dosing cohort. Two MTDs were established for the continuous daily dosing: 2 mg of GSK458 with 1.0 mg of trametinib or 1.0 mg of GSK458 with 1.5 mg of trametinib; no MTD was determined in the intermittent dosing cohort. The most frequent adverse events were rash (74 %) and diarrhea (61 %). Dose interruptions due to adverse events occurred in 42 % of patients. No significant PK interaction was observed. One patient achieved partial response and 12 patients had stable disease >16 weeks. Mutations in RAS/RAF/PI3K were detected in 70 % of patients, but no pattern emerged between response and mutational status. CONCLUSION: GSK458 plus trametinib is poorly tolerated, due to skin and GI-related toxicities. Responses were minimal, despite enrichment for PI3K/RAS pathway driven tumors, which may be due to overlapping toxicities precluding sufficient dose exposure.

The potential for an interaction between lapatinib and absorption of the P-glycoprotein (ABCB1) substrate digoxin at a therapeutic dose in breast cancer patients was characterized. Seventeen women with HER2-positive metastatic breast cancer received a single oral 0.5-mg dose of digoxin on days 1 and 9 and oral lapatinib 1500 mg once daily on days 2 through 9. Digoxin pharmacokinetic parameters were determined on day 1 (digoxin administration alone) and on day 9 (coadministration of lapatinib and digoxin), and parameters were compared to determine the effects of lapatinib on digoxin absorption. Concomitant medications that could affect ABCB1 were accounted for. Lapatinib 1500 mg/day increased digoxin absorption approximately 80%, implicating lapatinib inhibition of intestinal ABCB1-mediated efflux. In summary, coadministration of lapatinib with narrow therapeutic index drugs that are substrates of ABCB1 should be undertaken with caution and dose adjustment should be considered.

Lapatinib is approved for use in various therapeutic combinations for treating metastatic breast cancers that over-express HER2. To deliver the approved doses, up to six large tablets need to be ingested with the current 250-mg tablets. For ease of ingestion, a powder for oral suspension was developed. This study was an open-label, randomized, adaptive design, two-period crossover bioequivalence study of the powder for suspension relative to the commercial tablet at steady state following once daily dosing for 7 days in patients with advanced cancer. To minimize the number of cancer patients required for a pivotal bioequivalence study (144 in this case), a four-stage adaptive group sequential design with interim analyses after every 36 subjects was implemented to allow for early termination. Bioequivalence for the oral suspension relative to the commercial tablet was demonstrated in both the first (and only) interim analysis and the final analysis, as the 90% confidence intervals for the treatment comparison ratios for both AUC0-24 and Cmax were contained within the acceptance criteria (0.80, 1.25). Additionally, there was no statistical difference in tlag or tmax , suggesting no difference in the absorption rate between treatments. There were no unexpected safety findings during this study.

The aqueous solubility of lapatinib declines significantly at pH >4, suggesting that its bioavailability might be lowered by acid-reducing drugs. A study was therefore conducted to assess the effects of esomeprazole on lapatinib pharmacokinetics (PK). Women with metastatic human epidermal growth factor receptor 2 positive (HER2(+) ) breast cancer were enrolled. Patients received 1,250 mg lapatinib once daily (QD) in the morning on Days 1-7 (Period 1) and Days 8-14 (Period 2) with 40 mg esomeprazole QD at bedtime 3 hours after dinner on Days 8-14. Lapatinib PK sampling occurred during the 24-hour steady-state dosing intervals on Day 7 (lapatinib alone) and Day 14 (lapatinib with esomeprazole). Esomeprazole treatment resulted in decreased lapatinib bioavailability (mean 26%, range 6-49%) that was inversely associated with patient age as a significant covariate.

Purpose The paradigm shift in cancer treatment from cytotoxic drugs to tumor targeted therapies poses new challenges, including optimization of dose and schedule based on a biologically effective dose, rather than the historical maximum tolerated dose. Optimal dosing is currently determined using concentrations of tyrosine kinase inhibitors in plasma as a surrogate for tumor concentrations. To examine this plasma-tumor relationship, we explored the association between lapatinib levels in tumor and plasma in mice and humans, and those effects on phosphorylation of human epidermal growth factor receptors (HER) in human tumors. Experimental Design Mice bearing BT474 HER2+ human breast cancer xenografts were dosed once or twice daily (BID) with lapatinib. Drug concentrations were measured in blood, tumor, liver, and kidney. In a randomized phase I clinical trial, 28 treatment-naïve female patients with early stage HER2+ breast cancer received lapatinib 1000 or 1500 mg once daily (QD) or 500 mg BID before evaluating steady-state lapatinib levels in plasma and tumor. Results In mice, lapatinib levels were 4-fold higher in tumor than blood with a 4-fold longer half-life. Tumor concentrations exceeded the in vitro IC90 (~ 900 nM or 500 ng/mL) for inhibition of HER2 phosphorylation throughout the 12-hour dosing interval. In patients, tumor levels were 6- and 10-fold higher with QD and BID dosing, respectively, compared to plasma trough levels. The relationship between tumor and plasma concentration was complex, indicating multiple determinants. HER receptor phosphorylation varied depending upon lapatinib tumor concentrations, suggestive of changes in the repertoire of HER homo- and heterodimers. Conclusion Plasma lapatinib concentrations underestimated tumor drug levels, suggesting that optimal dosing should be focused on the site of action to avoid to inappropriate dose escalation. Larger clinical trials are required to determine optimal dose and schedule to achieve tumor concentrations that maximally inhibit HER receptors. Trial Registration Clinical Trial Registration: NCT00359190

Reverset™ (2′,3′-didehydro-2′,3′-dideoxy-5-fluorocyti-dine, RVT) is a potent inhibitor of HIV-1 replication in cell culture, with a 90% effective concentration at or below 1 μM. In vitro, RVT retains its activity against isolates harbouring mutations in the reverse transcriptase (RT) gene that otherwise confer resistance to lamivudine and/or zidovudine. The pharmacokinetics and safety of single oral doses of RVT (10–200 mg) were evaluated in an initial Phase I clinical trial. The viral load changes were determined on 18 HIV-1-infected antiretroviral therapy-naive subjects that were randomized into three cohorts, each cohort consisting of three study periods. The subjects received up to two oral doses of active drug and one placebo dose with a 1-week washout period separating the three study periods. Quantification of viral RNA was performed on the pre-dose, 12, 24 and 48 h post-dose plasma samples. A single oral dose of RVT to antiretroviral-naive subjects significantly reduced plasma viral load by 0.45 ±0.10 log10 copies/ml ( P=0.0003). A mean drop of 0.37 ±0.12 log10 copies/ml ( P=0.001) was obtained at the lowest dose of 10 mg. Sequence analysis of the HIV-1 RT gene performed before and after RVT dosing detected no genotypic changes in this short-term study. The viral RT gene of one subject had at predose the following genotype: L41 + N103 + C181 + W210 + D215, indicating prior exposure to zidovudine and non-nucleoside analogues, and anticipating high-level resistance against these agents. A single 10 mg RVT dose resulted in a viral load drop of 0.61 ±0.05 log10 providing evidence that a viral strain with the indicated genotype is susceptible to RVT.

The potential for an interaction between lapatinib and absorption of the P-glycoprotein (ABCB1) substrate digoxin at a therapeutic dose in breast cancer patients was characterized. Seventeen women with HER2-positive metastatic breast cancer received a single oral 0.5-mg dose of digoxin on days 1 and 9 and oral lapatinib 1500 mg once daily on days 2 through 9. Digoxin pharmacokinetic parameters were determined on day 1 (digoxin administration alone) and on day 9 (coadministration of lapatinib and digoxin), and parameters were compared to determine the effects of lapatinib on digoxin absorption. Concomitant medications that could affect ABCB1 were accounted for. Lapatinib 1500 mg/day increased digoxin absorption approximately 80%, implicating lapatinib inhibition of intestinal ABCB1-mediated efflux. In summary, coadministration of lapatinib with narrow therapeutic index drugs that are substrates of ABCB1 should be undertaken with caution and dose adjustment should be considered.

Lapatinib is approved for use in various therapeutic combinations for treating metastatic breast cancers that over-express HER2. To deliver the approved doses, up to six large tablets need to be ingested with the current 250-mg tablets. For ease of ingestion, a powder for oral suspension was developed. This study was an open-label, randomized, adaptive design, two-period crossover bioequivalence study of the powder for suspension relative to the commercial tablet at steady state following once daily dosing for 7 days in patients with advanced cancer. To minimize the number of cancer patients required for a pivotal bioequivalence study (144 in this case), a four-stage adaptive group sequential design with interim analyses after every 36 subjects was implemented to allow for early termination. Bioequivalence for the oral suspension relative to the commercial tablet was demonstrated in both the first (and only) interim analysis and the final analysis, as the 90% confidence intervals for the treatment comparison ratios for both AUC0-24 and Cmax were contained within the acceptance criteria (0.80, 1.25). Additionally, there was no statistical difference in tlag or tmax , suggesting no difference in the absorption rate between treatments. There were no unexpected safety findings during this study.

(2000). Protein Kinase C Modulation and Anticancer Drug Response. Cancer Investigation: Vol. 18, No. 8, pp. 731-739.

Purpose: Cytosine arabinoside induces apoptosis and this cell death process is influenced by protein kinase C signaling events in leukemic cells. We present findings that extend these observations to include another deoxycytidine analog, gemcitabine, which is more potent in solid tumors. Methods and results: Gemcitabine induced programmed cell death in BG-1 human ovarian cancer cells based on biochemical and morphologic analyses. The DNA was fragmented in BG-1 cells exposed to gemcitabine (0.5 μM, 1.0 μM and 10 μM ) for 8 h, but gemcitabine treatment did not induce internucleosomal DNA degradation. Scanning and transmission electron microscopy of BG-1 cells showed morphologic changes associated with apoptosis in response to gemcitabine: membrane blebbing, the formation of apoptotic bodies and chromatin condensation. Thus, BG-1 cells undergo programmed cell death in response to gemcitabine treatment without internucleosomal DNA fragmentation. Furthermore, gemcitabine (10 μM) activated protein kinase C in BG-1 cells and the phosphorylation of the endogenous protein kinase C substrate, myristoylated alanine-rich C kinase substrate, was increased following exposure of BG-1 cells to gemcitabine for up to 6 h. Clonogenicity studies with gemcitabine in combination with various protein kinase C-modulating agents demonstrated that gemcitabine cytotoxicity was influenced by protein kinase C signaling events in BG-1 cells. Short-term (1 h) exposure to TPA (1 or 10 nM ) followed by gemcitabine (0.5 μM for 4 h) did not alter the response to gemcitabine. However, a 24-h exposure to TPA followed by gemcitabine resulted in synergistic cytotoxicity, while coincubation of TPA with a PKC inhibitor (e.g. bisindolylmaleimide or calphostin-C) in this regimen abrogated the synergistic response. Conclusions: Based on our findings, it is plausible that gemcitabine therapy could be improved by modulating PKC signaling events linked to drug-induced apoptosis/cytotoxicity.

Uncontrolled clinical trials have shown that parenteral administration of GM-CSF reduces the frequency of chemotherapy-induced mucositis. The mechanism of this effect could be related to acceleration of haematopoiesis and/or increase in functional activation of WBC. We conducted a double-blind, placebo-controlled, dose ranging study of GM-CSF (mol-gramostim) mouthwash in patients with breast cancer during the first treatment cycle of a combination chemotherapy regimen which has historically produced dose-limiting (grade > or = 3) mucositis in approximately 39% of patients. Subjects were randomized to receive either placebo mouthwash (0.1 percent albumin) or one of four concentrations of GM-CSF mouthwash (0.01, 0.1, 1.0 or 10 mcg/ml). The primary endpoint was to evaluate the relationship between dose of GM-CSF mouthwash received and probability of grade > or = 3 mucositis using a logistic model. Solutions were administered four times daily starting within 24 hours of chemotherapy initiation and continuing until the end of the cycle (day 21). Mucositis was assessed on days 1-6, 10, 15 and 21. Day 6 plasma samples were assayed for GM-CSF. Forty-five patients were evaluable for response (nine per dosing group). A 42% risk (15/36) of mucositis grade > or = 3 was evident on day 15 in patients receiving GM-CSF compared to 2 of 9 patients on the placebo arm. No evidence of dose response was found by logistic regression. Five patients had a detectable plasma concentration of GM-CSF (56-209 pg/ml). A positive correlation between GM-CSF dose and leukocyte recovery was noted (P = 0.04).

The aqueous solubility of lapatinib declines significantly at pH4, suggesting that its bioavailability might be lowered by acid-reducing drugs. A study was therefore conducted to assess the effects of esomeprazole on lapatinib pharmacokinetics (PK). Women with metastatic human epidermal growth factor receptor 2 positive (HER2(+) ) breast cancer were enrolled. Patients received 1,250 mg lapatinib once daily (QD) in the morning on Days 1-7 (Period 1) and Days 8-14 (Period 2) with 40 mg esomeprazole QD at bedtime 3 hours after dinner on Days 8-14. Lapatinib PK sampling occurred during the 24-hour steady-state dosing intervals on Day 7 (lapatinib alone) and Day 14 (lapatinib with esomeprazole). Esomeprazole treatment resulted in decreased lapatinib bioavailability (mean 26%, range 6-49%) that was inversely associated with patient age as a significant covariate.

Objectives: The primary objectives were to assess safety, tolerability and the maximum tolerated dose (MTD) for the combination of the PI3K/mTOR inhibitor GSK458 and the MEK inhibitor T. Methods: Pts with selected advanced solid tumors enriched for MAPK and PI3K pathway alterations, ECOG PS 0/1, with no history of diabetes, retinopathy or uncontrolled CNS disease were eligible. Three dosing schedules were evaluated: continuous (cont) once daily (QD) GSK458 and T; cont twice daily (BID) GSK458 and QD T; and intermittent (int) BID GSK458 (4 days on/10 days off) and cont QD T. Dose escalation followed a 3+3 design with dose limiting toxicity (DLT) evaluation during the first 28 days (NCT01248858). Results: From Dec/10-Oct/13, 69 pts were enrolled. The most frequent tumor types were colorectal (CRC) 29%, breast 16%, non-small cell lung (NSCLC) 10%, and pancreas 10%. A total of 12 dose levels were explored and 8 pts experienced DLTs that were reversible (Table). The MTD was exceeded at 0.5mg QD GSK458/2.0mg QD T and 0.5mg BID GSK458/1.5 mg QD T. Dose escalation was stopped before the MTD was defined for int GSK458 dosing because the tolerability of the combination was not improved. The most commonly reported drug-related AEs (≥20%) included rash 72%, diarrhea 54%, vomiting 33%, fatigue 30%, decreased appetite 23%, and stomatitis 22%, with dose interruptions for 51% of pts treated. No RECIST responses were observed. Stable disease >22 weeks occurred in 7 pts (KRASmt CRC, ocular melanoma, renal cell, KRASmt ovary (2), KRASmt small bowel, and KRASmt NSCLC). Conclusion: The MTDs of cont QD dosing are 1.0mg GSK458/1.5mg T and 2.0mg GSK458/1.0mg T. Tolerability of the combination was limited by rash, GI toxicity, fatigue and anorexia. A recommended phase 2 dose and schedule was not defined despite exploring alternative schedules including twice daily and intermittent dosing of GSK458. No further clinical development of the combination is planned. CohortGSK458TDLT(s)/EvaluableDLT event(s)10.5mg QD0.5mg QD0/320.5mg QD1.0mg QD0/431.0mg QD0.5mg QD0/440.5mg QD1.5mg QD0/551.0mg QD1.0mg QD1/6G2 folliculitis61.5mg QD1.0mg QD1/8G3 diarrhea70.5mg QD2.0mg QD3/5G3 stomatitis; G3 hypertension & G1 elevated troponin; G3 hypophosphatemia & G2 diarrhea82.0mg QD1.0mg QD0/691.0mg QD1.5mg QD0/7100.5mg BID1.5mg QD2/6Asymptomatic20% decrease LVEF; G3 mucositis110.5mg BID int1.5mg QD1/7G3 central serousretinopathy120.75mg BID int1.5mg QD0/5 Citation Format: Philippe L. Bedard, Juneko E. Grilley-Olson, Mark Cornfeld, Leanne Cartee, Susan Warwick, Albiruni A.R. Razak, Lee-Anne Stayner, Yuehui Wu, Rebecca Greenwood, Veronica Viana-Gilmartin, Carrie B. Lee, Johanna Bendell, Howard A. Burris, Luca Gianni, Cristiana Sessa, Jeffrey R. Infante, Angelica Fasolo. A phase I dose-escalation study of trametinib (T) in combination with continuous or intermittent GSK2126458 (GSK458) in patients (pts) with advanced solid tumors. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr CT205. doi:10.1158/1538-7445.AM2014-CT205

Racivir [RCV; (+/−)-β-2′,3′-dideoxy-5-fluoro-3′-thiacytidine], a 50:50 racemic mixture of the two β nucleoside enantiomers, is currently in development for the treatment of human immunodeficiency virus type 1 (HIV-1) infections. RCV was administered once a day orally for 14 days at doses of 200, 400, or 600 mg in combination with stavudine and efavirenz to HIV-1-infected treatment-naïve male volunteers in a phase Ib/IIa study. Six volunteers at each dose were monitored for a total of 35 days for tolerance, pharmacokinetics, and plasma HIV RNA levels. RCV in combination with stavudine and efavirenz was well tolerated at all doses tested. Pharmacokinetic parameters were dose proportional, and the maximum concentration of drug in serum at all doses exceeded the 90% effective concentration for wild-type HIV-1. Viral loads dropped as expected in all dosage groups, with mean reductions from 1.13 to 1.42 log 10 by day 4 and 2.02 to 2.43 log 10 by day 14. HIV RNA levels remained suppressed for more than 2 weeks in the absence of any additional therapy, with mean viral loads ranging from 2.1 to 2.6 log 10 below baseline through day 28. By day 35, HIV RNA levels began to increase but still remained >1 log 10 below baseline levels.

Reverset (2',3'-didehydro-2',3'-dideoxy-5-fluorocytidine, RVT) is a potent inhibitor of HIV-1 replication in cell culture, with a 90% effective concentration at or below 1 microM. In vitro, RVT retains its activity against isolates harbouring mutations in the reverse transcriptase (RT) gene that otherwise confer resistance to lamivudine and/or zidovudine. The pharmacokinetics and safety of single oral doses of RVT (10-200 mg) were evaluated in an initial Phase I clinical trial. The viral load changes were determined on 18 HIV-1-infected antiretroviral therapy-naive subjects that were randomized into three cohorts, each cohort consisting of three study periods. The subjects received up to two oral doses of active drug and one placebo dose with a 1-week washout period separating the three study periods. Quantification of viral RNA was performed on the pre-dose, 12, 24 and 48 h post-dose plasma samples. A single oral dose of RVT to antiretroviral-naive subjects significantly reduced plasma viral load by 0.45 +/- 0.10 log10 copies/ml (P=0.0003). A mean drop of 0.37 +/- 0.12 log10 copies/ml (P=0.001) was obtained at the lowest dose of 10 mg. Sequence analysis of the HIV-1 RT gene performed before and after RVT dosing detected no genotypic changes in this short-term study. The viral RT gene of one subject had at predose the following genotype: L41 + N103 + C181 + W210 + D215, indicating prior exposure to zidovudine and non-nucleoside analogues, and anticipating high-level resistance against these agents. A single 10 mg RVT dose resulted in a viral load drop of 0.61 +/- 0.05 log10 providing evidence that a viral strain with the indicated genotype is susceptible to RVT.

Antimicrobial resistance in hospital and community settings is growing at an alarming rate and has been attributed to such organisms as methicillin-resistant staphylococcus aureus, staphylococci with decreased susceptibility to vancomycin, vancomycin-resistant enterococci, multi-drug resistant pseudomonas spp., klebsiella spp., enterobacter spp, and acinetobacter spp., as well as Streptococcus pneumoniae with decreased susceptibility to penicillin and other antibacterials. To address the need for new therapies to combat resistant organisms, drug companies are refocusing their discovery efforts on developing novel agents with new mechanisms of action. The hope is that rapidly emerging technologies including combinatorial chemistry, high throughput screening, proteomics and microbial genomics will have a positive impact on antimicrobial drug discovery. These technologies should aid in the identification of novel drug targets and compounds with unique mechanisms of action other than those currently provided by the traditional antibiotics. Nucleosides are one class of compounds worthy of further investigation as antibacterials since some derivatives have shown moderate to good activity against specific bacterial strains. For example, 5'-peptidyl nucleoside derivatives can inhibit peptide deformylase, an enzyme essential for bacterial survival that is not vital to human cells. This review also includes a list of miscellaneous nucleosides that have been synthesized as potential antibacterials. More detailed investigations on structure, as it relates to the antimicrobial activity of the various classes of nucleosides, need to be conducted in order to maximize the potential of developing a potent nucleoside for the treatment of bacterial infections. This review begins with an introduction to terms followed by discussions regarding the general background and relevance for developing novel antimicrobial agents. Challenges facing the antimicrobial drug discovery process are discussed along with relevant drug targets. An overview of nucleoside chemistry as it relates to antimicrobial activity is presented, followed by a discussion of the evidence which supports the potential of this class of compounds to yield the novel antimicrobial therapies needed in the new millennium.

2′-Deoxy-2′-fluorocytidine (FdC) is a potent inhibitor of the hepatitis C virus RNA replicon in culture, and FdC-5′-triphosphate is an effective inhibitor of the NS5B polymerase. Dynamic profiling of cell growth in an antiviral assay showed that FdC caused cytostasis due to an S-phase arrest. These observations demonstrate that FdC treatment is affecting both a viral target and a cellular target.

Interactions between the protein kinase C activator bryostatin 1 and the cyclin-dependent kinase (CDK) inhibitor flavopiridol (FP) have been examined in human myeloid leukemia cells (U937 and HL-60). Previous studies have demonstrated synergistic induction of apoptosis in leukemic cells exposed to the potent differentiation-inducer phorbol 12-myristate 13-acetate (PMA) in conjunction with FP [L. Cartee et al., Cancer Res., 61: 2583-2591, 2001]. Although bryostatin 1 (10 nM) is a very weak inducer of differentiation compared with PMA in these cells, coadministration of a minimally toxic concentration of FP (100 nM) did not promote bryostatin 1-related maturation but instead caused a marked increase in mitochondrial damage (e.g., cytochrome c release; loss of Deltapsi(m)), caspase activation, poly(ADP-ribose) polymerase cleavage, and apoptosis. Bryostatin 1/FP-induced apoptosis was significantly diminished in cells ectopically expressing dominant-negative Fas-associated death domain or by coadministration of tumor necrosis factor (TNF)-alpha soluble receptors, implicating the extrinsic pathway in bryostatin 1/FP actions. Enhanced apoptosis in bryostatin 1/FP-treated cells was accompanied by down-regulation of Mcl-1 and a sustained increase in TNF-alpha release. The selective protein kinase C inhibitor GFX blocked TNF-alpha and cytochrome c release in bryostatin 1/FP-treated cells and attenuated apoptosis. Finally, coadministration of bryostatin 1 (or PMA) with FP induced a marked increase in apoptosis in U937 cells ectopically expressing an NH(2)-terminal phosphorylation loop-deleted Bcl-2 protein, which are otherwise highly resistant to FP-mediated lethality. Taken together, these findings suggest that synergistic induction of apoptosis by bryostatin 1 and FP does not stem from disruption of the leukemic cell maturation process but instead results from enhanced release of TNF-alpha and activation of the extrinsic apoptotic cascade, culminating in cell death.

Interactions between the cyclin-dependent kinase inhibitor flavopiridol (FP) and the histone deacetylase inhibitor sodium butyrate (SB) have been examined in human leukemia cells (U937) in relation to differentiation and apoptosis. Whereas 1 mM of SB or 100 nM of FP minimally induced apoptosis (4% and 10%, respectively) at 24 h, simultaneous exposure of U937 cells to these agents dramatically increased cell death (e.g., approximately 60%), reflected by both morphological and Annexin/propidium iodide-staining features, procaspase 3 activation, and poly(ADP-ribose) polymerase cleavage. Similar interactions were observed in human promyelocytic (HL-60), B-lymphoblastic (Raji), and T-lymphoblastic (Jurkat) leukemia cells. Coadministration of FP opposed SB-mediated accumulation of cells in G0G1 and differentiation, reflected by reduced CD11b expression, but instead dramatically increased procaspase-3, procaspase-8, Bid, and poly(ADP-ribose) polymerase cleavage, as well as mitochondrial damage (e.g., loss of mitochondrial membrane potential and cytochrome c release). FP also blocked SB-related p21WAF1-CIP1 induction through a caspase-independent mechanism and triggered the caspase-mediated cleavage of p27KIP1 and retinoblastoma protein. The latter event was accompanied by a marked reduction in retinoblastoma protein/E2F1 complex formation. However, FP did not modify the extent of SB-associated acetylation of histones H3 and H4. Treatment of cells with FP/SB also resulted in the caspase-mediated cleavage of Bcl-2 and caspase-independent down-regulation of Mcl-1. Levels of cyclins A, D1, and E, and X-linked inhibitor of apoptosis also declined in SB/FP-treated cells. Finally, FP/SB coexposure potently induced apoptosis in two primary acute myelogenous leukemia samples. Together, these findings demonstrate that FP, when combined with SB, induces multiple perturbations in cell cycle and apoptosis regulatory proteins, which oppose leukemic cell differentiation but instead promote mitochondrial damage and apoptosis.

A clinically relevant dose (2.0 Gy) of ionizing radiation (IR) was employed to determine if subsequent exposure to the protein kinase C (PKC) and Chk 1 inhibitor UCN-01 for 24 h could abrogate IR-induced G 2 /M arrest and promote apoptosis in U937 leukemic cells ectopically expressing Bcl-2 (U937/Bcl-2). To this end, empty-vector control (U937/pCEP4) and U937/Bcl-2 cells were exposed to two UCN-01 concentrations following IR: i) a 50 nM concentration, which by itself was minimally toxic to both cell lines, and ii) a 150 nM concentration, which modestly induced apoptosis (e.g., ∼19%) in control cells after 24 h. The effects of UCN-01 on IR responses were examined in relation to apoptosis induction, suspension culture growth inhibition, loss of clonogenic survival, and cell cycle perturbations. IR (2 Gy) alone minimally induced apoptosis in both U937 transfectant cell lines (e.g.

Previous studies have shown that coexposure to marginally toxic concentrations of phorbol 12-myristate 13-acetate (PMA; 10 nM) and the cyclin-dependent kinase inhibitor flavopiridol (FP; 100-200 nM) synergistically induces apoptosis in human myeloid leukemia cells U937 and HL-60 (i.e.,50% apoptotic at 24 h). Attempts have now been made to characterize the cell death pathway(s) involved in this phenomenon. In contrast to cytochrome c release and caspase-3 activation, which occur within 2.5 h of PMA/FP coexposure, caspase-8 activation and Bid cleavage appeared as later events. Such findings implicate the mitochondria-dependent pathway in the initial induction of apoptosis by PMA/FP. However, U937 cells ectopically expressing CrmA, dominant-negative caspase-8, or dominant-negative Fas-associated death domain that were highly resistant to tumor necrosis factor (TNF)/cycloheximide-induced lethality displayed significant, albeit incomplete, resistance to PMA/FP-induced apoptosis after 24 h. Furthermore, coadministration of TNF soluble receptor significantly attenuated PMA/FP-induced apoptosis in U937 (p0.02) and HL-60 (p0.03) cells at 24 h. PMA/FP coadministration also triggered substantial increases in TNFalpha mRNA and protein secretion compared with the effects of PMA administered alone. The protein kinase C (PKC) inhibitor bisindolylmaleimide (1 microM) completely blocked PMA/FP-induced TNFalpha secretion in U937 cells and attenuated apoptosis. Taken together, these results suggest that coadministration of PMA with FP in myeloid leukemia cells initially triggers mitochondrial damage, an event followed by the PKC-dependent induction and release of TNFalpha, supporting a model in which the synergistic induction of leukemic cell apoptosis by this drug combination proceeds via both mitochondrial- and TNF receptor-related apoptotic pathways.

Ionizing radiation (IR) produced a dose-dependent increase in apoptosis in U937/pCEP4 cells which was attenuated by the stable over expression of Bcl-2 (U937/Bcl-2). A dose of 2 Gy IR was selected for further analyses to determine if subsequent exposure to 10nM bryostatin- would overcome the resistance to IR-induced apoptosis conferred by Bcl-2 over expression.Although bryostatin- did not increase IR-induced apoptosis in U937/pCEP4 or U937/Bcl-2 cells, it impaired mitochondrial function and increased the antiproliferative effects of IR in both cell lines. The effects were more pronounced in U937/Bcl-2 cells. Bryostatin-1 also exerted differential effects on cell-cycle distributions of U937 transfectant cells, producing a significant G0/G1 arrest in U937/Bcl-2 cells, while decreasing IR-induced G2/M arrest in U937/pCEP4 cells. Although Bcl-2 over expression attenuated IR-induced apoptosis, clonogenic survival was similar in U937/pCEP4 and U937/Bcl-2 cells following 2 Gy IR treatment. Treatment with 10nM bryostatin-1 after 2 Gy IR further reduced clonogenic survival in both cell lines. Moreover, U937/Bcl-2 cells were more susceptible to the growth-inhibitory effects of IR/bryostatin-1 than U937/pCEP4 cells.Bryostatin-1 increased the radiosensitivity of U937 transfectant cell lines without enhancing apoptosis; furthermore, U937/Bcl-2 cells were more susceptible to IR/bryostatin-1-mediated antiproliferative effects than their empty-vector counterparts.

The ability of low dose ionizing radiation (2 Gy) to modulate the activities of the mitogen activated protein kinase (MAPK) and c-Jun NH2-terminal kinase (JNK1) cascades in human monocytic leukemia (U937/pREP4) cells and in cells over-expressing dominant negative c-Jun (TAM67) (U937/TAM67) was investigated. Radiation exposure caused prolonged ( approximately 1 h) MAPK activations in U937 cells. In contrast, low dose irradiation weakly modulated JNK1 activity in these cells. Inhibition of the MAPK pathway by use of the specific MEK1/2 inhibitor (10 microM PD98059) in both U937/pREP4 and U937/TAM67 cells prior to radiation exposure permitted strong prolonged radiation-induced activations of JNK1. Expression of TAM67 decreased the ability of radiation to cause apoptosis compared to control transfected cells. However, combined MEK1/2 inhibition and radiation exposure in both cell types caused a large decrease in suspension culture growth and a large increase in apoptosis, when compared to either treatment alone. Reduced proliferation after combined irradiation and PD98059 treatment in both cell types correlated with prolonged cell cycle arrest in G2/M phase. Prolonged growth arrest was abolished when MEK1/2 inhibitor was removed 6 h following irradiation, which was associated with a reduction in apoptosis. The ability of MEK1/2 inhibition to cause prolonged G2/M growth arrest was reduced in U937 cells stably transfected with a p21Cip-1/WAF1 antisense construct (U937/p21AS). This data correlated with an enhancement of radiation-induced apoptosis and a reduced ability of MEK1/2 inhibition to potentiate apoptosis. Collectively our data demonstrate that inhibition of MEK1/2 function increases the radiation sensitivity of U937 cells, independently of c-Jun function, and decreases the ability of these cells to recover from the radiation-induced G2/M cell cycle checkpoint arrest. In addition, our data also demonstrate that the ability of MEK1/2 inhibition to potentiate radiation-induced cell death in U937 cells in part requires an ability of cells to express low levels of p21Cip-1/WAF1.

Background: This is a Phase I, open-label, dose escalation, pharmacokinetic (PK), pharmacodynamic (PD) and safety study in patients (pts) with advanced solid tumors exploring the combination of the investigational drugs GSK458 and GSK212. GSK212 is a reversible, highly selective, allosteric inhibitor of mitogen-activated extracellular signal regulated kinases 1 and 2 (MEK1 and MEK2). GSK458 is a potent, reversible, ATP-competitive, pan-phosphoinositide-3 kinase (PI3K) inhibitor, which also inhibits the mammalian target of rapamycin (mTOR), and the common activating mutations of catalytic isoform p110α. The MTD for daily, continuous dosing of monotherapy GSK458 is 2.5mg and GSK212 is 2.0mg. Methods: The study consists of two parts: dose escalation in Part 1 (ongoing) uses a zone design (3+3 rules) to study safety, tolerability, PK, PD and clinical activity, and to establish the maximum tolerated doses (MTDs) and schedules for the combination. Adult pts with relapsed or refractory solid tumors are receiving oral doses of GSK458+GSK 212 once daily until disease progression or toxicity. Efficacy is assessed using RECIST 1.1. Part 2 will examine safe dose combinations from Part 1 in patients with tumors likely to respond to MEK/PI3K pathway inhibition. Genetic and protein profiles collected from blood and tumor samples will be used to explore relationships between predictive biomarkers of response and efficacy. Results: 34 pts(45% female) with a mean age of 58y (range 37–82y) have enrolled. Safety data includes31 subjects who have received ≥1 dose of GSK458+GSK212. Most commonly reported drug-related AEs >10%, n=31) include rash (68%; G3/4, 3%), diarrhea (42%; G3/4, 6%), nausea (29%; G3/4, 0%), vomiting (23%; G3/4, 3%), decreased appetite (19%; G3/4, 0%), stomatitis (13%; G3/4, 3%) and fatigue (13%; G3/4; 3%). Of 21 serious adverse events (SAEs) reported in 14 pts, 3 were considered related to study drug. Stable disease has been observed in several patients with the longest being at 6 months (renal cell carcinoma and colorectal cancer). The combination of GSK458 0.5 mg + GSK212 2.0 mg exceeded the MTD. However, once daily and continuous combination dosing of GSK458 (0.5, 1.0 or 1.5mg) + GSK212 ≤ 2.0 mg were well tolerated. Conclusions: The preliminary safety profile and anti-tumor activity of this combination warrants further investigation in continued dose escalation and planned expansion cohorts. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B155.

The phosphoinositide 3-kinase (PI3K) signalling pathway is activated in a broad spectrum of human cancers. Activation of this pathway often occurs indirectly by somatic aberrations of receptor tyrosine kinases, or directly by mutations in PI3K genes, such as PIK3CA. GSK2126458 is a novel, orally administered inhibitor of wild type phosphoinositide 3-kinase alpha (PI3K) and the common activation mutants of p110 found in human cancers that has recently entered Phase I clinical trials. In order to determine histological and genetic profiles of patients that are more likely to gain clinical benefit from GSK2126458, the compound was tested in a 3-day continuous exposure proliferation assay on a panel of 198 genetically characterized human cancer cell lines derived from a diversity of tissue types. Cells originating from bladder, breast, and ovarian cancers are most responsive based on growth inhibition metrics (gIC50's). Breast cancer cell lines harboring activating mutations of PIK3CA are associated with increased levels of response (p = 0.027); an observation which was validated in an independent cohort of 53 breast cell lines (p = 0.021). While colon cancers exhibit an intermediate level of sensitivity compared to other tumor types, specific exon 5 G12/13 hotspot mutations of the KRAS gene are predictive of decreased cellular response (p = 0.025). Additionally, a comparison of these cell line proliferation data to a similarly-assayed panel of 19 compounds of diverse target class shows that while the overall pattern of cellular response to GSK2126458 resembles other inhibitors or the PI3K/AKT/mTOR pathway, distinctions emerge that correlate with pathway targeting strategy. For example, while breast cancers are preferentially responsive to GSK2126458 and other inhibitors of this pathway, cell lines harboring PTEN mutations are less responsive to GSK2126458 than to compounds directly targeting AKT. Collectively these data suggest a unique profile for GSK2126458 among compounds that inhibit the PI3K/AKT/mTOR pathway. Positive predictors of response, such as PIK3CA mutations in breast cancer, may identify patients who are most likely to benefit from GSK2126458. The use of this predictor to select patients has the potential to reduce the size of a clinical registration trial for GSK2126458 by approximately 25%, thereby limiting cost and accelerating the development of this compound. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B140.