Phase I and Pharmacokinetic Study of the Dolastatin-15 Analogue Tasidotin ( ILX 651 ) Administered Intravenously on Days 1 , 3 , and 5 Every 3 Weeks in Patientswith Advanced Solid Tumors

To determine the maximum tolerated dose (MTD), dose-limiting toxicity (DLT), and pharmacokinetics of tasidotin (ILX651), a dolastatin-15 analogue, when administered on days 1, 3, and 5 every 3 weeks in patients with advanced solid tumors. Thirty-two patients were treated with 92 courses of tasidotin through seven dose levels determined by a modified Fibonacci scheme ranging from 3.9 to 45.7 mg/m. Pharmacokinetic samples were collected during the first course.  Neutropenia was the principal DLTat the 45.7 mg/m/d dose level. In addition, one patient also experienced grade 3 neutropenia complicated with grade 3 esophageal candidiasis and grade 3 dehydration. Only 1of 11patients treated at the MTD, 34.4 mg/m, experienced dose-limiting neutropenia. Other common, drug-related toxicities included mild to moderate fatigue, anemia, nausea, anorexia, emesis, alopecia, and diarrhea. The best observed antitumor response consisted of stable disease andwas noted in10 patients (31%); the median duration on study for those patients with stable disease was 99.5 days compared with 37.5 days for those patients with progressive disease. Tasidotin plasma concentrations declined biphasically with an effective half-life of V55 minutes, andf11%was excreted unchanged in the urine. The recommended dose for phase II studies and the MTDwhen tasidotin is administered on days1, 3, and 5 every 3 weeks is 34.4 mg/m.The favorable toxicity profile of tasidotin comparedwith other antitubulin agents, includingother dolastatin analogues, and its novelmechanism of action support further disease-directed evaluation of this agent. Tubulin is a well-established target for anticancer agents. Although available antitubulin agents, including the taxanes and Vinca alkaloids, are highly effective in cancer therapy, their clinical usefulness is limited by intrinsic or acquired resistance and systemic toxicity (1). Thus, it is important to develop new agents that target the tubulin/microtubule system with efficacy against resistant tumors and an improved side effect profile. The dolastatins, a group of peptides isolated from the Indian Ocean sea hare Dolabella auricularia (2–5), bind to tubulin subunits and inhibit tubulin-dependent GTP hydrolysis in vitro (6). In vivo , these actions inhibit the assembly of new microtubules, induce the depolymerization of existing microtubules, and inhibit cell cycle progression in mitosis (7, 8). However, initial clinical evaluation of dolastatin-10 and cemadotin, a synthetic analogue of dolastatin-15, showed disappointing results (9–11), possibly due, in part, to poor cellular uptake. In addition, cemadotin is rapidly converted to a metabolite with dose-limiting cardiovascular toxicities, including hypertension, angina, and myocardial infarction, that limited its therapeutic efficacy (12–15). To address these problems, a new generation of dolastatins, represented by tasidotin (Genzyme Corp., San Antonio, TX), has been created that offer several advantages over most other antitubulins. Tasidotin is a pentapeptide (N,N-dimethylL-valyl-L-valyl-N -methyl-L-valyl-L-prolyl-L-proline-tert -butylamide hydrochloride; , chemically modified to improve the pharmacologic properties of cemadotin resulting in a more metabolically stable compound. Tasidotin induces a prolonged lag phase in microtubule assembly at concentrations of 25 to 40 Amol/L (16-26 Ag/mL) followed by recovery with microtubule assembly returning to normal levels (16). These effects are in contrast to those seen with other antitubulins, such as podophyllotoxin and vinblastine (17–21), and produce cell cycle arrest in the G2 and M cell cycle phases. At concentrations z50 Amol/L (32 Ag/mL), tasidotin inhibits the extent of microtubule assembly, which is also an atypical finding for antitubulins. Finally, in addition to its potentially enhanced therapeutic window, tasidotin is orally bioavailable (22).  Tyler Cancer Center, Tyler, Texas; Dana-Farber Cancer Institute, Massachusetts General Hospital, Boston, Massachusetts ; and Genzyme Corp., San Antonio, Texas Received1/10/05; revised 7/19/05; accepted 8/8/05. The costs of publication of this article were defrayed in part by the payment of page charges.This article must therefore be hereby marked advertisement in accordance with18 U.S.C. Section1734 solely to indicate this fact. Requests for reprints: Peter L. Bonate, Genzyme Corp., 4545 Horizon Hill Boulevard, San Antonio,TX 78229.  210-949-6662; Fax: 210-949-6219;  peter.bonate@genzyme.com.  American Association for Cancer Research. doi:10.1158/1078-0432.CCR-05-0058 www.aacrjournals.org Clin Cancer Res 2005;11(21) November1, 2005 7825 Research. on April 15, 2017.  nervous system, and leukemia cell lines); GI50 values ranged from <10 nmol/L (6 ng/mL) to >1 mmol/L (0.6 mg/mL; ref. 23). Complete responses were documented in early-stage and late-stage breast carcinoma (MX-1), melanoma (LOX), and prostate (PC-3) cancer mouse models, and survival time was significantly increased in the P388 murine leukemia model. In the MX-1 model, tasidotin induced tumor growth delays ranging from 20 to >90 days compared with 15 days for paclitaxel (23). Of note, repetitive dosing schedules of tasidotin showed superior activity compared with single dosing schedules (24). Toxicology studies in rats and dogs showed that tasidotin principally affects the bone marrow, gonads, lymphoid tissues, and kidney. Administration of tasidotin i.v. in dogs resulted in emesis, diarrhea, and neutropenia. Neutropenia was maximal at days 6 to 13, and recovery occurred during days 15 to 29. Mesangioproliferative glomerulopathy was only observed in rats treated at the highest dose of tasidotin (30 mg/kg i.v. 5 days). When administered to mongrel dogs, tasidotin induced dose-dependent decreases in cardiac output and increases in coronary, femoral, and total peripheral vascular resistance that were 10-fold less than cemadotin (24). After both i.v. and oral administration of tasidotin in dogs, the plasma concentrations showed a linear increase and a half-life of f2.3 hours (22). The mean bioavailability was 23%. Studies with [C]tasidotin using a single i.v. dose of tasidotin in rats revealed that 55% to 60.5% of drug was recovered in the feces, whereas 22.8% to 30.6% was excreted renally (internal data). Given its novel mechanism of action, impressive preclinical antineoplastic activity, favorable preclinical pharmacologic properties, and reduction in toxicities over previous dolastatins, a phase I trial of tasidotin given i.v. to patients with advanced solid tumors refractory to standard treatment was conducted. To mimic the repetitive dosing schedules associated with superior antitumor activity in the preclinical studies, tasidotin was administered i.v. over 30 minutes on days 1, 3, and 5 every 3 weeks. The principal objectives of this study were to determine the maximum tolerated dose (MTD) of tasidotin administered i.v. on this schedule, determine the toxicities of tasidotin, characterize the pharmacokinetic behavior of tasidotin, seek preliminary evidence of antitumor activity, and recommend a dose of tasidotin for phase II studies.  Patients with histologically documented, advanced solid tumors refractory to conventional therapy, or for whom no effective therapy existed, were candidates. Eligibility criteria also required the following: age, z18 years; Eastern Cooperative Oncology Group performance status, V2; life expectancy, z12 weeks; no prior chemotherapy, radiation therapy, or major surgical procedures within 4 weeks of study entry (6 weeks for mitomycin C or nitrosourea); adequate hematopoietic [absolute neutrophil count (ANC), z1,500/AL; platelet count, z100,000/AL; and hemoglobin, z9.0 g/d], hepatic (total bilirubin, <2.0 mg/dL; aspartate amino transaminase and alanine amino transaminase levels, V2 upper limit of normal or <5 upper limit of normal for patients with liver metastases), metabolic (calcium within institutional limits of normal), and renal (serum creatinine, V1.5 mg/dL or creatinine clearance, z60 mL/min; ref. 25) variables; prior radiotherapy to <25% of bone marrow reserves; no active infection or coexisting medical problems of sufficient severity to limit compliance with the study; no apparent central nervous system metastases; no prior stem cell or bone marrow transplantation; and no cardiac functional capacity of class III or IV, using the New York Heart Association Classification. All patients gave written informed consent in accordance with federal and local institutional guidelines before treatment. Dosage and drug administration. The starting dose of tasidotin was 3.9 mg/m/d (one tenth of the MTD in rat studies ref. 24) administered i.v. over 30 minutes on days 1, 3, and 5 of each 21-day treatment course. Successive cohorts of patients were dose escalated per a modified Fibonacci scheme from the initial dose of 3.9 to 7.8, 13.0, 19.5, 25.9, 34.4, and 45.7 mg/m. Dose reduction to the previous dose level was permitted for patients experiencing dose-limiting toxicity (DLT); however, a maximum of two dose reductions per patient was permitted. The MTD, or recommended phase II dose, was defined as the highest dose level that induced DLT in less than two of six new patients treated in the first course. At least three new patients were treated at each escalated dose level, except at the MTD where the cohort was expanded to 11 patients to gain greater safety data at that dose level. DLT was defined during the first course for determination of MTD as follows: ANC, <500/A