Frank P. LaCreta

Phase I trial of buthionine sulfoximine in combination with melphalan in patients with cancer.

PURPOSE AND METHODS Resistance to alkylating agents and platinum compounds is associated with elevated levels of glutathione (GSH). Depletion of GSH by buthionine sulfoximine (BSO) restores the sensitivity of resistant tumors to melphalan in vitro and in vivo. In a phase I trial, each patient received two cycles as follows: BSO alone intravenously (i.v.) every 12 hours for six doses, and 1 week later the same BSO as cycle one with melphalan (L-PAM) 15 mg/m2 i.v. 1 hour after the fifth dose. BSO doses were escalated from 1.5 to 17 g/m2 in 41 patients. RESULTS The only toxicity attributable to BSO was grade I or II nausea/vomiting in 50% of patients. Dose-related neutropenia required an L-PAM dose reduction to 10 mg/m2 at BSO 7.5 g/m2. We measured GSH in peripheral mononuclear cells (PMN), and in tumor biopsies when available, at intervals following BSO dosing. In PMNs, GSH content decreased over 36 to 72 hours to reach a nadir on day 3; at the highest dose, recovery was delayed beyond day 7. The mean PMN GSH nadirs were approximately 10% of control at BSO doses > or = 7.5 g/m2; at 13 and 17 g/m2, all but two patients had nadir values in this range. GSH was depleted in sequential tumor biopsies to a variable extent, but with a similar time course. At BSO doses > or = 13 g/m2, tumor GSH was < or = 20% of starting values on day 3 in five of seven patients; recovery had not occurred by day 5. We measured plasma concentrations of R- and S-BSO by high-performance liquid chromatography (HPLC) in 22 patients throughout the dosing period. Total-body clearance (CLt) and volume of distribution at steady-state (Vss) for both isomers were dose-independent. The CLt of S-BSO was significantly less than that of R-BSO at all doses, but no significant differences in Vss were observed between the racemates. Harmonic mean half-lives were 1.39 hours and 1.89 hours for R-BSO and S-BSO, respectively. CONCLUSION A biochemically appropriate dose of BSO for use on this schedule is 13 g/m2, which will be used in phase II trials to be conducted in ovarian cancer and melanoma.

Effect of renal impairment on the pharmacokinetics, pharmacodynamics, and safety of apixaban.

This open‐label study evaluated apixaban pharmacokinetics, pharmacodynamics, and safety in subjects with mild, moderate, or severe renal impairment and in healthy subjects following a single 10‐mg oral dose. The primary analysis determined the relationship between apixaban AUC∞ and 24‐hour creatinine clearance (CLcr) as a measure of renal function. The relationships between 24‐hour CLcr and iohexol clearance, estimated CLcr (Cockcroft‐Gault equation), and estimated glomerular filtration rate (modification of diet in renal disease [MDRD] equation) were also assessed. Secondary objectives included assessment of safety and tolerability as well as international normalized ratio (INR) and anti–factor Xa activity as pharmacodynamic endpoints. The regression analysis showed that decreasing renal function resulted in modestly increased apixaban exposure (AUC∞ increased by 44% in severe impairment with a 24‐hour CLcr of 15 mL/min, compared with subjects with normal renal function), but it did not affect Cmax or the direct relationship between apixaban plasma concentration and anti–factor Xa activity or INR. The assessment of renal function measured by iohexol clearance, Cockcroft‐Gault, and MDRD was consistent with that determined by 24‐hour CLcr. Apixaban was well tolerated in this study. These results suggest that dose adjustment of apixaban is not required on the basis of renal function alone.

Phase II multicenter evaluation of prolonged murine monoclonal antibody 17-1A therapy in pancreatic carcinoma.

Twenty-eight patients with unresectable, measurable pancreatic carcinoma and Eastern Oncology Cooperative Group (ECOG) performance status of 0 or 1 were treated with the murine monoclonal antibody 17-1A, planning to administer 500 mg i.v. three times weekly for 8 weeks. Treatment was well tolerated, with an 18% incidence (five patients) of hypersensitivity reactions. All hypersensitivity episodes occurred in the first 3 weeks of therapy and required treatment discontinuation. Six patients required early discontinuation of therapy due to symptomatic progressive disease and one patient was removed from the study due to a protocol violation. Sixteen patients received the full course of 12 g of antibody. One patient has exhibited a durable partial response. Antibody pharmacokinetics were determined in five patients. In four patients peak 17-1A levels averaged 100 micrograms/ml with mean harmonic t1/2 of 16.8 h in a one-compartment model. Neither pretreatment nor posttreatment levels of circulating 17-1A changed significantly during the 8 weeks of treatment. This study demonstrates the feasibility and acceptable toxicity of repetitive dosing with an unconjugated murine monoclonal antibody. The lack of efficacy of treatment suggests that factors other than prolonged exposure of tumor and cytotoxic effector cells to murine antibody are required for successful antibody therapy of pancreatic cancer.

The spontaneous and glutathione S-transferase-mediated reaction of chlorambucil with glutathione.

Incubation of 100 microM chlorambucil (CMB) with 1 mM glutathione (GSH) in 0.1 M potassium phosphate buffer yielded a mixture of GSH conjugates and hydrolytic products that were separable by HPLC. The appearance in HPLC analysis of four of these products was GSH-dependent. 35S-Label from 35S-GSH eluted with all four chemical species that also gave UV spectra characteristic of CMB-containing compounds. Mass spectral analysis of three of these compounds gave molecular weights consistent with the following adducts: adduct 2: diglutathionyl CMB; adduct 3: monohydroxy monochloroglutathionyl CMB; adduct 4: monochloro monoglutathionyl CMB. Purified GST alpha and partially pure GST pi and mu class protein prepared from adult male mouse liver cytosol significantly increased the formation of the monoglutathionyl CMB adduct. At 5 min incubations, this adduct was quantitatively most important and was increased 4.4-fold by the addition of GST alpha isozymes. At 1 hr incubations, all four adducts were measurable, although enzymes primarily affected the formation of adduct 4. At 1 hr, addition of GST alpha, pi, or mu protein increased the production of monochloro monoglutathionyl CMB 2-fold, 1.5-fold, and 1.7-fold, respectively, demonstrating that CMB is indeed a substrate for GST isozymes in vitro.

Technique, pharmacokinetics, toxicity, and efficacy of intratumoral etanidazole and radiotherapy for treatment spontaneous feline oral squamous cell carcinoma

The histologic appearance, locoregional recurrence, and rate/site of metastases of spontaneous feline oral squamous cell carcinoma are similar to head and neck cancer in humans. A feasibility study of intratumoral Etanidazole, a hypoxic cell sensitizer, and radiation therapy were instituted in this model. Eleven cats with feline squamous cell carcinoma were treated with intratumoral Etanidazole and radiation therapy. Total Etanidazole doses were 1.5-24.0 gms/m2 (0.5-6.9 gms). The tumor partial response rate was 100% (11/11); the median volume regression was 70%. All cats have died as a result of tumor recurrence or tumor-related complications. Median survival was 116 days. Ten cats have been autopsied. Non-necrotic and necrotic tumor cells were identified at the treatment site in all cats. Pharmacokinetic studies were performed in six cats. Following intravenous infusion, the plasma elimination of the Etanidazole was biexponential. The systemic availability following intratumoral administration was 61.2 +/- 21.1%. Peak plasma Etanidazole levels were observed 14 minutes following intratumoral injection, after which elimination was biexponential. Thirty minutes following intratumoral Etanidazole administration, tumor Etanidazole levels were 62.8% of plasma levels. Feline squamous cell carcinoma appears to be a useful model of human head and neck cancer. Cats tolerate substantial doses of intratumoral and intravenous Etanidazole. Etanidazole and radiation therapy cause rapid regression, but not cure, of feline squamous cell carcinoma. There is a similarity between the intravenous kinetics of Etanidazole in humans and cats. Further studies in this model are planned.

A randomized direct comparison of the pharmacokinetics and pharmacodynamics of apixaban and rivaroxaban.

Background Currently, there are no direct comparisons of apixaban and rivaroxaban, two new oral direct factor Xa inhibitors approved for management of thromboembolic disorders. Objective Compare the pharmacokinetics and anti-factor Xa activity (AXA) of apixaban and rivaroxaban. Methods In this randomized, open-label, two-period, two-treatment crossover study, healthy subjects (N=14) received apixaban 2.5 mg twice daily (BID) and rivaroxaban 10 mg once daily (QD) for 4 days with a ≥4.5-day washout. Plasma samples were obtained for pharmacokinetic and AXA assessments; parameters were calculated using noncompartmental methods. Results Median time-to-maximum concentration was 2 hours for both compounds, and the mean half-life was 8.7 and 7.9 hours for apixaban and rivaroxaban, respectively. Daily exposure, the area under the curve (AUC(0–24)), appeared similar for rivaroxaban (1,094 ng · h/mL) and apixaban (935 ng · h/mL), whereas mean peak-to-trough plasma concentration ratio was 3.6-fold greater for rivaroxaban (16.9) than apixaban (4.7). Coefficient of variation for exposure parameters (AUC0–24, Cmax, Cmin) was 20%–24% for apixaban versus 29%–46% for rivaroxaban. Peak AXA, AXA AUC(0–24), and AXA fluctuation were ~2.5-, 1.3-, and 3.5-fold higher for rivaroxaban than apixaban, respectively. Trough concentrations and AXA were lower for rivaroxaban (10 ng/mL and 0.17 IU/mL vs 17 ng/mL and 0.24 IU/mL for apixaban, respectively). Rivaroxaban exhibited a steeper concentration–AXA response (slope: 0.0172 IU/ng vs 0.0134 IU/ng for apixaban, P<0.0001). Conclusion Apixaban 2.5 mg BID demonstrated less intersubject variability in exposure, lower AXA AUC, and higher trough and smaller peak-to-trough fluctuations in plasma concentration and AXA, suggesting more constant anticoagulation compared with rivaroxaban 10 mg QD. However, the clinical impact of these differences on the relative efficacy and safety of apixaban and rivaroxaban remains to be determined.

Clinical, pharmacokinetic and biological studies of topotecan

The topoisomerase I inhibtor topotecan is a potent water-soluble camptothecin derivative with activity in a wide variety of preclinical models. Topotecan exhibits schedule dependency in vivo, with the greatest activity being observed on repeated dose schedules. On the basis of the initial clinical studies that showed a short plasma halflife, we attempted to prolong drug exposure by giving topotecan as a 24-h infusion weekly. In a phase I trial, we treated 32 patients at doses ranging from 1.0 to 2.0 mg/m2. The patient population had not been heavily pretreated with chemotherapy and was of good performance status. The incidence of neutropenia, which was dose-limiting, increased sharply with relative small increments in dose. Doses greater than 1.5 mg/m2 were associated with nadirs that developed after one to three weekly treatments. A patient with metastatic colorectal cancer had a prolonged partial response. The plasma pharmacokinetics of topotecan (lactone and open forms) was characterized in 21 patients. Mean plasma steady-state drug levels were proportional to the dose and were within the range required to exert cytotoxicity in preclinical models. Plasma elimination curves were fit to a one-compartment model, in which the harmonic mean half-life of topotecan was 3.5 h. The ratio of the lactone to the total drug concentrations was constant throughout, which suggests that for this schedule the total drug concentration may be used as a measure of active lactone exposure. This conclusion is supported by the pharmacodynamic analysis, which revealed a positive correlation of both lactone and total drug steady-state concentrations with bone marrow toxicity. The further investigation of this and other infusional schedules in phase II trials will be conducted. The steady-state concentrations of total drug will be measured in several of these trials to establish its potential role in adaptive dosing using this schedule. Such a strategy is justified by the interpatient variability in toxicity and the steep dose-response curve observed in this study. Preliminary evidence of interpatient variability in the mRNA expression of topoisomerase I in the peripheral mononuclear cells and colon mucosa is presented. Trials are under way using biological endpoints for further selection of patients in whom the use of topoisomerase inhibitors may be therapeutically beneficial.

Phase I trial of thiotepa in combination with recombinant human granulocyte-macrophage colony-stimulating factor.

PURPOSE The ability of growth factors to stimulate marrow recovery suggests their potential for use in dose intensification of cytotoxic drugs. We performed a phase I study of the alkylating agent thiotepa in combination with granulocyte-macrophage colony-stimulating factor (GM-CSF), with the goal of dose-escalation of thiotepa. Thiotepa was selected based on its capacity for dose escalation to more than 1 g/m2 in the marrow transplantation setting. PATIENTS AND METHODS The starting dose of thiotepa (75 mg/m2) was the highest dose evaluated in our previous phase I trial. Thirteen patients received 22 courses of thiotepa and GM-CSF. The dose of GM-CSF was 10 micrograms/kg subcutaneously daily in six patients and 5 micrograms/kg in seven patients. RESULTS Three patients (23%) developed grade 3 to 4 neutropenia on the first course, with a recovery to more than 1000/mm3 in 4.7 days (mean). Recovery was as rapid with the 5 micrograms/kg as it was with the 10 micrograms/kg GM-CSF dose. Thrombocytopenia grade 3 to 4 affected seven of 13 (54%) patients in the first course; counts recovered to more than 50,000/mm3 in a median of 15 days. GM-CSF at either dose did not influence markedly the severity or duration of thrombocytopenia, and did not permit dose escalation of thiotepa. Among the seven patients who received a second cycle of treatment, six of seven experienced grade 3 or 4 thrombocytopenia that lasted a median of 15.5 days. Five had thrombocytopenia that lasted more than 35 days after one to three cycles of treatment. Plasma concentrations of thiotepa and tepa were measured by gas chromatography in eight patients. The plasma elimination of thiotepa fit a two-compartment open model with a harmonic mean terminal half-life of 2.44 hours. The mean total body clearance was 217.9 mL/min/m2, and the mean steady-state volume of distribution (Vdss) was 36.8 L/m2. The half-life of tepa was 7.98 hours, and the ratio of the area under the plasma concentration versus time curve (AUC) of tepa to that of thiotepa was 0.79. CONCLUSIONS These data were consistent with our previous observations at this dose, and indicated that the severity of toxicity in these patients was not explained by aberrant pharmacokinetic indices. We conclude that, independent of effects on neutropenia, severe and cumulative platelet toxicity precludes further escalation of thiotepa dose despite the use of GM-CSF.

Safety, tolerability, pharmacokinetics, and pharmacodynamics of multiple doses of apixaban in healthy Japanese male subjects.

OBJECTIVE This was a randomized, placebo-controlled, double-blind, sequential, ascending-dose study to assess the safety, tolerability, pharmacokinetics, and pharmacodynamics of multiple oral doses of apixaban in healthy Japanese male subjects. METHODS The study was conducted using three sequential dose panels: apixaban 2.5 mg, 5 mg, and 10 mg given twice daily. For each dose panel, subjects were randomly assigned to receive oral apixaban (n = 6) or matching placebo (n = 2) for 7 days. The pharmacokinetics of apixaban and effect on pharmacodynamic variables (clotting assays and anti-Xa activity) were assessed on day 1 and day 7 of treatment. Safety was assessed throughout the study. Only after the preceding dose was confirmed to be safe and well-tolerated subjects were enrolled into the next-higher-dose panel. RESULTS Apixaban was safe and well-tolerated in these healthy Japanese male subjects across the doses evaluated. On day 7, peak plasma concentrations were reached ~ 3 hours postdose, and increases in peak plasma concentration (C(max)), trough plasma concentration, and area under the plasma concentration-time curve across one dosing interval (12 hours) were tested dose-proportional across the dose range. A modest degree of accumulation was observed that was similar for all doses (accumulation index of 1.7 to 2.0), and renal clearance was consistent across doses (0.91 L/h - 1.07 L/h). Exposure-dependent prolongation of prothrombin time, activated partial thromboplastin time, modified prothrombin time, and increases in anti-Xa activity were observed after single and multiple doses of apixaban. CONCLUSIONS Apixaban was safe and well-tolerated in healthy Japanese subjects. The pharmacokinetic profile of apixaban following multiple twice-daily doses was linear, and exposure parameters such as C(max), observed at ~ 3 hours post-dose, and area under the plasma concentration-time curve increased in a dose-proportional manner. Pharmacodynamic profiles closely followed the apixaban plasma concentration-time profiles.

Effect of famotidine on the pharmacokinetics of apixaban, an oral direct factor Xa inhibitor.

Background Apixaban is an oral, selective, direct factor Xa inhibitor approved for thromboprophylaxis after orthopedic surgery and stroke prevention in patients with atrial fibrillation, and under development for treatment of venous thromboembolism. This study investigated the effect of a gastric acid suppressant, famotidine (a histamine H2-receptor antagonist), on the pharmacokinetics of apixaban in healthy subjects. Methods This two-period, two-treatment crossover study randomized 18 healthy subjects to receive a single oral dose of apixaban 10 mg with and without a single oral dose of famotidine 40 mg administered 3 hours before dosing with apixaban. Plasma apixaban concentrations were measured up to 60 hours post-dose and pharmacokinetic parameters were calculated. Results Famotidine did not affect maximum apixaban plasma concentration (Cmax) or area under the plasma concentration-time curve from zero to infinite time (AUC∞). Point estimates for ratios of geometric means with and without famotidine were close to unity for Cmax (0.978) and AUC∞ (1.007), and 90% confidence intervals were entirely contained within the 80%–125% no-effect interval. Administration of apixaban alone and with famotidine was well tolerated. Conclusion Famotidine does not affect the pharmacokinetics of apixaban, consistent with the physicochemical properties of apixaban (lack of an ionizable group and pH-independent solubility). Apixaban pharmacokinetics would not be affected by an increase in gastrointestinal pH due to underlying conditions (eg, achlorhydria), or by gastrointestinal pH-mediated effects of other histamine H2-receptor antagonists, antacids, or proton pump inhibitors. Given that famotidine is also an inhibitor of the human organic cation transporter (hOCT), these results indicate that apixaban pharmacokinetics are not influenced by hOCT uptake transporter inhibitors. Overall, these results support that apixaban can be administered without regard to coadministration of gastric acid modifiers.