epothilone-a and Carcinoma--Squamous-Cell

Ixabepilone is a tubulin-polymerizing agent with potential activity in squamous cell carcinoma of the head and neck (SCCHN). Patients were eligible who had incurable, measurable SCCHN and less than two prior regimens for metastatic/recurrent disease. Eastern Cooperative Oncology Group performance status of less than or equal to one and adequate renal/hepatic/hematological function were required. Patients were randomly assigned to receive ixabepilone 6 mg/m(2)/day x 5 days every 21 days (arm A) or 20 mg/m(2) on days 1, 8, and 15 of a 28-day cycle (arm B). Each arm accrued taxane-naive and -exposed strata in a two-stage design. The primary end point was response. Eighty-five eligible patients entered; there was one response in a taxane-exposed patient among 32 patients on arm A. Five of 35 taxane-naive patients on arm B had partial responses (14%). No taxane-exposed patient on arm B responded. Common grades 3 and 4 toxic effects were fatigue, neutropenia, and sensory/motor neuropathy. Median survival for arm A taxane-naive and taxane-exposed patients is 5.6 and 6.5 months; for arm B, taxane-naive and taxane-exposed patients is 7.8 and 6.5 months. Weekly ixabepilone 20 mg/m(2) is active in taxane-naive patients with SCCHN. A high incidence of motor and sensory grade 3 neuropathy resulted at this dose and schedule. Further development of ixabepilone in previously treated head and neck cancer is not warranted on the basis of these data.

Topics: Adult; Aged; Antibiotics, Antineoplastic; Antineoplastic Combined Chemotherapy Protocols; Carcinoma, Squamous Cell; Combined Modality Therapy; Disease-Free Survival; Docetaxel; Drug Administration Schedule; Drug Resistance, Neoplasm; Epothilones; Female; Head and Neck Neoplasms; Hematologic Diseases; Humans; Infusions, Intravenous; Male; Middle Aged; Paclitaxel; Peripheral Nervous System Diseases; Recurrence; Salvage Therapy; Survival Analysis; Taxoids

Ixabepilone (BMS-247550) is a semi-synthetic, microtubule stabilizing epothilone B analogue which is more potent than taxanes and has displayed activity in taxane-resistant patients. The human plasma pharmacokinetics of ixabepilone have been described. However, the excretory pathways and contribution of metabolism to ixabepilone elimination have not been determined. To investigate the elimination pathways of ixabepilone we initiated a mass balance study in cancer patients. Due to autoradiolysis, ixabepilone proved to be very unstable when labeled with conventional [14C]-levels (100 microCi in a typical human radio-tracer study). This necessitated the use of much lower levels of [14C]-labeling and an ultra-sensitive detection method, Accelerator Mass Spectrometry (AMS). Eight patients with advanced cancer (3 males, 5 females; median age 54.5 y; performance status 0-2) received an intravenous dose of 70 mg, 80 nCi of [14C]ixabepilone over 3 h. Plasma, urine and faeces were collected up to 7 days after administration and total radioactivity (TRA) was determined using AMS. Ixabepilone in plasma and urine was quantitated using a validated LC-MS/MS method. Mean recovery of ixabepilone-derived radioactivity was 77.3% of dose. Fecal excretion was 52.2% and urinary excretion was 25.1%. Only a minor part of TRA is accounted for by unchanged ixabepilone in both plasma and urine, which indicates that metabolism is a major elimination mechanism for this drug. Future studies should focus on structural elucidation of ixabepilone metabolites and characterization of their activities.

Topics: Adenocarcinoma; Antineoplastic Agents; Carcinoma, Non-Small-Cell Lung; Carcinoma, Squamous Cell; Chromatography, Liquid; Colonic Neoplasms; Epothilones; Feces; Female; Humans; Lung Neoplasms; Male; Middle Aged; Neoplasms; Ovarian Neoplasms; Pancreatic Neoplasms; Sigmoid Neoplasms; Tandem Mass Spectrometry

Resistance to paclitaxel-based therapy is frequently encountered in the clinic. The mechanisms of intrinsic or acquired paclitaxel resistance are not well understood. We sought to characterize the resistance mechanisms that develop upon chronic exposure of a cancer cell line to paclitaxel in the presence of the P-glycoprotein reversal agent, CL-347099. The epidermoid tumor line KB-3-1 was exposed to increasing concentrations of paclitaxel and 5 micromol/L CL-347099 for up to 1 year. Cells grown in 15 nmol/L paclitaxel plus CL-347099 (KB-15-PTX/099) developed 18-fold resistance to paclitaxel and were dependent upon paclitaxel for maximal growth. They grew well and retained resistance to paclitaxel when grown in athymic mice. Cross-resistance (3- to 5-fold) was observed in tissue culture to docetaxel, the novel taxane MAC-321, and epothilone B. Collateral sensitivity (approximately 3-fold) was observed to the depolymerizing agents vinblastine, dolastatin-10, and HTI-286. KB-15-PTX/099-resistant cells did not overexpress P-glycoprotein nor did they have an alteration of [14C]paclitaxel accumulation compared with parental cells. However, a novel point mutation (T to A) resulting in Asp26 to glutamate substitution in class I (M40) beta-tubulin was found. Based on an electron crystallography structure of Zn-stabilized tubulin sheets, the phenyl ring of C-3' NHCO-C6H5 of paclitaxel makes contact with Asp26 of beta-tubulin, suggesting a ligand-induced mutation. Optimized model complexes of paclitaxel, docetaxel, and MAC-321 in beta-tubulin show a novel hydrogen bonding pattern for the glutamate mutant and rationalize the observed resistance profiles. However, a mutation in the paclitaxel binding pocket does not explain the phenotype completely. KB-15-PTX/099 cells have impaired microtubule stability as determined by a reduced percentage of tubulin in microtubules and reflected by less acetylated tubulin. These results suggest that a mutation in tubulin might affect microtubule stability as well as drug binding and contribute to the observed resistance profile.

Topics: Amino Acid Substitution; Animals; Antineoplastic Agents, Phytogenic; Aspartic Acid; ATP Binding Cassette Transporter, Subfamily B, Member 1; Carcinoma, Squamous Cell; Cell Line, Tumor; Docetaxel; Drug Resistance, Neoplasm; Epothilones; Glutamic Acid; Humans; Mice; Mice, Nude; Microtubules; Paclitaxel; Point Mutation; Protein Conformation; Taxoids; Tubulin; Verapamil