Phase III Study Comparing a Reduced Dose of Cabazitaxel (20 mg/m2) and the Currently Approved Dose (25 mg/m2) in Postdocetaxel Patients With Metastatic Castration-Resistant Prostate Cancer—PROSELICA

To assess the feasibility of administering XRP6258, a new taxane with a low affinity for the multidrug resistance 1 protein, as a 1-hour i.v. infusion every 3 weeks. The study also sought to determine the maximum tolerated dose and the recommended dose, to describe the pharmacokinetic (PK) behavior of the compound, and to seek preliminary evidence of anticancer activity. Twenty-five patients with advanced solid malignancies were treated with 102 courses of XRP6258 at four dose levels ranging from 10 to 25 mg/m(2). Dose escalation was based on the occurrence of dose-limiting toxicity (DLT) at each dose level, provided that PK variables were favorable. The maximum tolerated dose was defined as the dose at which at least two patients developed a DLT at the first course. Neutropenia was the principal DLT, with one patient experiencing febrile neutropenia and two others showing prolonged grade 4 neutropenia at the 25 mg/m(2) dose level. Nonhematologic toxicities, including nausea, vomiting, diarrhea, neurotoxicity, and fatigue, were generally mild to moderate in severity. XRP6258 exhibited dose-proportional PK, a triphasic elimination profile, a long terminal half-life (77.3 hours), a high clearance (mean CL, 53.5 L/h), and a large volume of distribution (mean V(ss), 2,034 L/m(2)). Objective antitumor activity included partial responses in two patients with metastatic prostate carcinoma, one unconfirmed partial response, and two minor responses. The recommended phase II dose of XRP6258 on this schedule is 20 mg/m(2). The general tolerability and encouraging antitumor activity in taxane-refractory patients warrant further evaluations of XRP6258.

Taxanes are important chemotherapeutic agents with proven efficacy in human cancers, but their use is limited by resistance development. We report here the preclinical characteristics of cabazitaxel (XRP6258), a semisynthetic taxane developed to overcome taxane resistance. Cabazitaxel effects on purified tubulin and on taxane-sensitive or chemotherapy-resistant tumor cells were evaluated in vitro. Antitumor activity and pharmacokinetics of intravenously administered cabazitaxel were assessed in tumor-bearing mice. In vitro, cabazitaxel stabilized microtubules as effectively as docetaxel but was 10-fold more potent than docetaxel in chemotherapy-resistant tumor cells (IC50 ranges: cabazitaxel, 0.013-0.414 μmol/L; docetaxel, 0.17-4.01 μmol/L). The active concentrations of cabazitaxel in these cell lines were achieved easily and maintained for up to 96 hours in the tumors of mice bearing MA16/C tumors treated with cabazitaxel at 40 mg/kg. Cabazitaxel exhibited antitumor efficacy in a broad spectrum of murine and human tumors (melanoma B16, colon C51, C38, HCT 116, and HT-29, mammary MA17/A and MA16/C, pancreas P03 and MIA PaCa-2, prostate DU 145, lung A549 and NCI-H460, gastric N87, head and neck SR475, and kidney Caki-1). Of particular note, cabazitaxel was active in tumors poorly sensitive or innately resistant to docetaxel (Lewis lung, pancreas P02, colon HCT-8, gastric GXF-209, mammary UISO BCA-1) or with acquired docetaxel resistance (melanoma B16/TXT). Cabazitaxel is as active as docetaxel in docetaxel-sensitive tumor models but is more potent than docetaxel in tumor models with innate or acquired resistance to taxanes and other chemotherapies. These studies were the basis for subsequent clinical evaluation. ©2013 AACR

XRP6258 is a novel taxoid with a low affinity for P-glycoprotein. This multicenter phase II study assessed the activity of XRP6258 in the treatment of taxane-resistant metastatic breast cancer (MBC). XRP6258 was administered as a 1-h i.v. infusion every 3 weeks at 20 mg/m(2) (then, in the absence of severe toxicity, at 25 mg/m(2) from cycle 2). The primary end point was the objective response rate (ORR) assessed according to response evaluation criteria in solid tumours (RECIST) guidelines. Seventy-one patients were enrolled. The median relative dose intensity was 0.98. The ORR was 14% (two complete, eight partial responses). Eighteen patients (25%) had stable disease of >3 months duration. At a median follow-up of 20.0 months, the median time to progression was 2.7 months, and the median overall survival 12.3 months. The most common grade 3/4 adverse events (AEs) were neutropenia (73%) and leucopenia (55%), with a low febrile neutropenia rate (3%) and infrequent grade 3/4, treatment-related, non-hematological AEs (<5% patients for any AE). Two deaths were reported, one related to study drug and one to unknown cause. XRP6258 was active and well tolerated in this group of MBC patients with taxane-resistant disease. These results support the further clinical development of this agent.