Susan M. Christner

ABCB1, ABCG2, and PTEN determine the response of glioblastoma to temozolomide and ABT-888 therapy.

Purpose: Little is known about the optimal clinical use of ABT-888 (veliparib) for treatment of glioblastoma. ABT-888 is a PARP inhibitor undergoing extensive clinical evaluation in glioblastoma, because it may synergize with the standard-of-care temozolomide (TMZ). We have elucidated important factors controlling ABT-888 efficacy in glioblastoma. Experimental Design: We used genetically engineered spontaneous glioblastoma mouse models and allograft models that were orthotopically transplanted into wild-type (WT) and Abcb1/Abcg2-deficient (KO) recipients. Results: ABT-888/TMZ is not efficacious against p53;p16Ink4a/p19Arf;K-Rasv12;LucR allografts in wild-type recipients, indicating inherent resistance. Abcb1/Abcg2 mediated efflux of ABT-888 at the blood–brain barrier (BBB) causes a 5-fold reduction of ABT-888 brain penetration (P < 0.0001) that was fully reversible by elacridar. Efficacy studies in WT and KO recipients and/or concomitant elacridar demonstrate that Abcb1/Abcg2 at the BBB and in tumor cells impair TMZ/ABT-888 combination treatment efficacy. Elacridar also markedly improved TMZ/ABT-888 combination treatment in the spontaneous p53;p16Ink4a/p19Arf;K-Rasv12;LucR glioblastoma model. Importantly, ABT-888 does enhance TMZ efficacy in Pten deficient glioblastoma allografts and spontaneous tumors, even in Abcb1/Abcg2 proficient wild-type mice. Loss of PTEN occurs frequently in glioblastoma (36%) and in silico analysis on patient with glioblastoma samples revealed that it is associated with a worse overall survival (310 days vs. 620 days, n = 117). Conclusions: The potential of ABT-888 in glioblastoma can best be demonstrated in patients with PTEN null tumors. Therefore, clinical trials with ABT-888 should evaluate these patients as a separate group. Importantly, inhibition of ABCB1 and ABCG2 (by elacridar) may improve the efficacy of TMZ/ABT-888 therapy in all glioblastoma patients. Clin Cancer Res; 20(10); 2703–13. ©2014 AACR.

Effect of a proton pump inhibitor on the pharmacokinetics of imatinib

AIMS Imatinib mesylate (Gleevec/Glivec), which has revolutionized the treatment of chronic myeloid leukemias (CML) and gastrointestinal stromal tumours (GIST), has been reported to cause gastric upset. Consequently, proton pump inhibitors (PPI) are frequently co-administered with imatinib. Because PPI can elevate gastric pH and delay gastric emptying or antagonize ATP-binding-cassette transporters, they could influence imatinib absorption and pharmacokinetics. We aimed to evaluate whether use of omeprazole has a significant effect on imatinib pharmacokinetics. METHODS Twelve healthy subjects were enrolled in a two-period, open-label, single-institution, randomized cross-over, fixed-schedule study. In one period, each subject received 400 mg imatinib orally. In the other period, 40 mg omeprazole (Prilosec) was administered orally for 5 days, and on day 5 it was administered 15 min before 400 mg imatinib. Plasma concentrations of imatinib and its active N-desmethyl metabolite CGP74588 were assayed by LC-MS, and data were analyzed non-compartmentally. RESULTS PPI administration did not significantly affect the imatinib area under the plasma concentration vs time curve (AUC) (34.1 microg ml(-1) h alone vs 33.1 microg ml(-1) h with omeprazole, P= 0.64; 80% power), maximum plasma concentration (C(max)) (2.04 microg ml(-1) alone vs 2.02 microg ml(-1) with omeprazole, P= 0.97), or half-life (13.4 h alone vs 14.1 h with omeprazole, P= 0.13). CONCLUSIONS Our results indicate that the use of omeprazole does not significantly affect the pharmacokinetics of imatinib, as opposed to, for example, dasatinib where PPI decreased AUC and C(max) two-fold.

A phase 1 trial of imatinib, bevacizumab, and metronomic cyclophosphamide in advanced colorectal cancer

Background:This phase 1 clinical trial was conducted to determine the safety, maximum-tolerated dose (MTD), and pharmacokinetics of imatinib, bevacizumab, and metronomic cyclophosphamide in patients with advanced colorectal cancer (CRC).Methods:Patients with refractory stage IV CRC were treated with bevacizumab 5 mg kg−1 i.v. every 2 weeks (fixed dose) plus oral cyclophosphamide q.d. and imatinib q.d. or b.i.d. in 28-day cycles with 3+3 dose escalation. Response was assessed every two cycles. Pharmacokinetics of imatinib and cyclophosphamide and circulating tumour, endothelial, and immune cell subsets were measured.Results:Thirty-five patients were enrolled. Maximum-tolerated doses were cyclophosphamide 50 mg q.d., imatinib 400 mg q.d., and bevacizumab 5 mg kg−1 i.v. every 2 weeks. Dose-limiting toxicities (DLTs) included nausea/vomiting, neutropaenia, hyponatraemia, fistula, and haematuria. The DLT window required expansion to 42 days (1.5 cycles) to capture delayed toxicities. Imatinib exposure increased insignificantly after adding cyclophosphamide. Seven patients (20%) experienced stable disease for >6 months. Circulating tumour, endothelial, or immune cells were not associated with progression-free survival.Conclusion:The combination of metronomic cyclophosphamide, imatinib, and bevacizumab is safe and tolerable without significant drug interactions. A subset of patients experienced prolonged stable disease independent of dose level.

Phase 2 trial of dasatinib in target-selected patients with recurrent glioblastoma (RTOG 0627).

BACKGROUND We conducted a phase II trial to evaluate the efficacy of dasatinib, a multitargeted tyrosine kinase inhibitor, for adults with recurrent glioblastoma (GBM). METHODS Eligibility requirements were Karnofsky performance status ≥ 60%; no concurrent hepatic enzyme-inducing anticonvulsants; prior treatment with surgery, radiotherapy, and temozolomide exclusively; and activation or overexpression of ≥ 2 putative dasatinib targets in GBM (ie, SRC, c-KIT, EPHA2, and PDGFR). Using a 2-stage design, 77 eligible participants (27 in stage 1, if favorable, and then 50 in stage 2) were needed to detect an absolute improvement in the proportion of patients either alive and progression-free patients at 6 months (6mPFS) or responding (any duration) from a historical 11% to 25%. RESULTS A high rate of ineligibility (27%) to stage 1 precluded a powered assessment of efficacy, but there was also infrequent treatment-related toxicity at 100 mg twice daily. Therefore, the study was redesigned to allow intrapatient escalation by 50 mg daily every cycle as tolerated (stage 1B) before determining whether to proceed to stage 2. Escalation was tolerable in 10 of 17 (59%) participants evaluable for that endpoint; however, among all eligible patients (stages 1 and 1B, n = 50), there were no radiographic responses, median overall survival was 7.9 months, median PFS was 1.7 months, and the 6mPFS rate was 6%. The clinical benefit was insufficient to correlate tested biomarkers with efficacy. The trial was closed without proceeding to stage 2. CONCLUSIONS Intraparticipant dose escalation was feasible, but dasatinib was ineffective in recurrent GBM. Clinical trials.gov identified. NCT00423735 (available at http://clinicaltrials.gov/ct2/show/NCT00423735).

A phase II trial of dasatinib in patients with metastatic castration-resistant prostate cancer treated previously with chemotherapy.

There is a need for efficacious therapies for metastatic castration-resistant prostate cancer (mCRPC) after disease progression on docetaxel. The SRC tyrosine kinase and its related family members may be important drivers of prostate cancer and can be inhibited by dasatinib. mCRPC patients, after one previous chemotherapy, started dasatinib at 70 mg twice daily, amended to 100 mg daily. The primary endpoint was the disease control (DC) rate, defined as complete response (CR), partial response (PR), or stable disease (SD) in prostate specific antigen (PSA), RECIST, bone scan, and FACT-P score. Up to 41 patients were to be accrued (two-stage design, 21+20) to rule out a null-hypothesized effect of 5 versus 20% (&agr;=0.05, &bgr;=0.1). Secondary endpoints included progression-free survival, toxicity, and pharmacokinetic and pharmacodynamic correlatives. Of 38 patients, 27 were evaluable for response or toxicity. The median duration of therapy was 55 days (6–284). Five patients showed DC after 8 weeks of therapy (18.5% DC, 95% CI: 6.3–38.1%). One PR (3.7% response rate, 95% CI: 0.1–19.0%) was observed in a patient treated for 284 days. Twelve patients (43%) discontinued treatment for toxicity. Dasatinib induced a decrease in phytohemagglutinin-stimulated CSF2, CD40L, GZMB, and IL-2 mRNAs in blood cells, indicating target engagement. Decreases in plasma IL-6 and bone alkaline phosphatase, and in urinary N-telopeptide, were associated with DC. Dasatinib has definite but limited activity in advanced mCRPC, and was poorly tolerated. The observation of a patient with prolonged, objective, clinically significant benefit warrants molecular profiling to select the appropriate patient population.

Safety and efficacy of decitabine in combination with temozolomide in metastatic melanoma: a phase I/II study and pharmacokinetic analysis

BACKGROUND Temozolomide (TMZ) is widely used for chemotherapy of metastatic melanoma. We hypothesized that epigenetic modulators will reverse chemotherapy resistance, and in this article, we report studies that sought to determine the recommended phase 2 dose (RP2D), safety, and efficacy of decitabine (DAC) combined with TMZ. PATIENTS AND METHODS In phase I, DAC was given at two dose levels: 0.075 and 0.15 mg/kg intravenously daily × 5 days/week for 2 weeks, TMZ orally 75 mg/m(2) qd for weeks 2-5 of a 6-week cycle. The phase II portion used a two-stage Simon design with a primary end point of objective response rate (ORR). RESULTS The RP2D is DAC 0.15 mg/kg and TMZ 75 mg/m(2). The phase II portion enrolled 35 patients, 88% had M1c disease; 42% had history of brain metastases. The best responses were 2 complete response (CR), 4 partial response (PR), 14 stable disease (SD), and 13 progressive disease (PD); 18% ORR and 61% clinical benefit rate (CR + PR + SD). The median overall survival (OS) was 12.4 months; the 1-year OS rate was 56%. Grade 3/4 neutropenia was common but lasted >7 days in six patients. CONCLUSIONS The combination of DAC and TMZ is safe, leads to 18% ORR and 12.4-month median OS, suggesting possible superiority over the historical 1-year OS rate, and warrants further evaluation in a randomized setting.

A high-performance liquid chromatography-mass spectrometry assay for quantitation of the tyrosine kinase inhibitor nilotinib in human plasma and serum.

Nilotinib (AMN-107, Tasigna) is a small-molecule inhibitor of BCR/ABL, approved for chronic myelogenous leukemia. We developed and validated, according to FDA-guidelines, an LC-MS assay for sensitive, accurate and precise quantitation of nilotinib in 0.2 mL human plasma or serum. After acetonitrile protein precipitation, separation is achieved with a hydro-Synergi column and a 0.1% formic acid in methanol/water-gradient. Detection uses electrospray, positive-mode ionization mass spectrometry. Between 5 (LLOQ) and 5000 ng/mL, accuracy (92.1-109.5%), intra-assay precision (2.5-7.8%), and inter-assay precision (0-5.6%)) were within FDA limits. We demonstrated the suitability of this assay by quantitating plasma concentrations of nilotinib in a healthy volunteer after oral administration of 400 mg nilotinib.

Poly (ADP) ribose polymerase enzyme inhibitor, veliparib, potentiates chemotherapy and radiation in vitro and in vivo in small cell lung cancer.

Poly (ADP) ribose polymerase (PARP) plays a key role in DNA repair and is highly expressed in small cell lung cancer (SCLC). We investigated the therapeutic impact of PARP inhibition in SCLC. In vitro cytotoxicity of veliparib, cisplatin, carboplatin, and etoposide singly and combined was determined by MTS in 9 SCLC cell lines (H69, H128, H146, H526, H187, H209, DMS53, DMS153, and DMS114). Subcutaneous xenografts in athymic nu/nu mice of H146 and H128 cells with relatively high and low platinum sensitivity, respectively, were employed for in vivo testing. Mechanisms of differential sensitivity of SCLC cell lines to PARP inhibition were investigated by comparing protein and gene expression profiles of the platinum sensitive and the less sensitive cell lines. Veliparib showed limited single‐agent cytotoxicity but selectively potentiated (≥50% reduction in IC50) cisplatin, carboplatin, and etoposide in vitro in five of nine SCLC cell lines. Veliparib with cisplatin or etoposide or with both cisplatin and etoposide showed greater delay in tumor growth than chemotherapy alone in H146 but not H128 xenografts. The potentiating effect of veliparib was associated with in vitro cell line sensitivity to cisplatin (CC = 0.672; P = 0.048) and DNA‐PKcs protein modulation. Gene expression profiling identified differential expression of a 5‐gene panel (GLS, UBEC2, HACL1, MSI2, and LOC100129585) in cell lines with relatively greater sensitivity to platinum and veliparib combination. Veliparib potentiates standard cytotoxic agents against SCLC in a cell‐specific manner. This potentiation correlates with platinum sensitivity, DNA‐PKcs expression and a 5‐gene expression profile.

Phase I study investigating the safety and feasibility of combining imatinib mesylate (Gleevec) with sorafenib in patients with refractory castration-resistant prostate cancer.

Background:Determining the maximum tolerated dose (MTD) and the dose-limiting toxicity (DLT) of sorafenib (S) plus imatinib (IM) in castration-resistant prostate cancer (CRPC) patients.Methods:Refractory CRPC patients were enrolled onto this 3+3 dose escalation designed study. Imatinib pharmacokinetics (PK) were determined on day 15, 4 h post dose with a validated LC–MS assay.Results:Seventeen patients were enrolled; 10 evaluable (6 at 400 mg S qd with 300 mg IM qd (DL0) and 4 at 400 mg S bid with 300 mg IM qd (DL1)); inevaluable patients received <1 cycle. The median age was 73 (57–89); median prostatic serum antigen was 284 ng ml−1 (11.7–9027). Median number of prior non-hormonal therapies was 3 (1–12). Dose-limiting toxicities were diarrhoea and hand-foot syndrome. Maximum tolerated dose was 400 mg S and 300 mg IM both daily. No biochemical responses were observed. Two patients had stable disease by RECIST. Median time to progression was 2 months (1–5). Median OS was 6 months (1–30+) with 3/17 patients (17%) alive at 21 months median follow-up. Ten patients had PK data suggesting that S reduced IM clearance by 55%, resulting in 77% increased exposure (P=0.005; compared with historical data).Conclusion:This is the first report showing that S+IM can be administered in CRPC at a dose of 400 mg S and 300 mg IM, daily.

Ritonavir and Efavirenz Significantly Alter the Metabolism of Erlotinib—an Observation in Primary Cultures of Human Hepatocytes That Is Relevant to HIV Patients with Cancer

Erlotinib is approved for the treatment of non–small cell lung and pancreatic cancers, and is metabolized by CYP3A4. Inducers and inhibitors of CYP3A enzymes such as ritonavir and efavirenz, respectively, may be used as part of the highly active antiretroviral therapy drugs to treat patients with human immunodeficiency virus (HIV). When HIV patients with a malignancy need treatment with erlotinib, there is a potential of as-yet-undefined drug-drug interaction. We evaluated these interactions using human hepatocytes benchmarked against the interaction of erlotinib with ketoconazole and rifampin, the archetype cytochrome P450 inhibitor and inducer, respectively. Hepatocytes were treated with vehicle [0.1% dimethylsulfoxide, ritonavir (10 μM)], ketoconazole (10 μM), efavirenz (10 μM), or rifampin (10 μM) for 4 days. On day 5, erlotinib (5 μM) was incubated with the above agents for another 24–48 hours. Concentrations of erlotinib and O-desmethyl erlotinib were quantitated in collected samples (combined lysate and medium) using liquid chromatography and tandem mass spectrometry. The half-life (t1/2) of erlotinib increased from 10.6 ± 2.6 to 153 ± 80 and 23.9 ± 4.8 hours, respectively, upon treatment with ritonavir and ketoconazole. The apparent intrinsic clearance (CLint, app) of erlotinib was lowered 16-fold by ritonavir and 1.9-fold by ketoconazole. Efavirenz and rifampin decreased t1/2 of erlotinib from 10.3 ± 1.1 to 5.0 ± 1.5 and 3.4 ± 0.2 hours, respectively. Efavirenz and rifampin increased the CLint, app of erlotinib by 2.2- and 2-fold, respectively. Our results suggest that to achieve desired drug exposure, the clinically used dose (150 mg daily) of erlotinib may have to be significantly reduced (25 mg every other day) or increased (300 mg daily), respectively, when ritonavir or efavirenz is coadministered.