Preclinical pharmacology of epothilone-folate conjugate BMS-753493, a tumor-targeting agent selected for clinical development

2326 Human folate receptor alpha (FR) is selectively overexpressed in certain tumor types, including ovarian, endometrial, renal, lung and breast carcinomas. Folic acid (FA) is a high affinity ligand which upon binding is internalized by endocytosis; therefore conjugation of a therapeutic to FA is a promising strategy for targeting agents to tumors while limiting exposure to normal tissues. The epothilones (e.g. ixabepilone) are a new class of microtubule agents with broad-spectrum antineoplastic activity and proven efficacy against taxane-resistant diseases. The epothilone-folate conjugate BMS-753493 was developed as a therapeutic strategy to specifically target a highly potent epothilone to human tumors.
 METHODS: Clonogenic assays were used to assess the cytotoxicity of BMS-753493 in vitro . Antitumor activity was evaluated in the KB nasopharyngeal, IGROV ovarian, HeLa cervical, and murine 98M109 lung models. The combinability of BMS-753493 with bevacizumab, cisplatin, or ixabepilone was evaluated in tumor xenografts in vivo . Proof of concept in vitro and in vivo was assessed by testing the activity of BMS-753493 in the presence of excess folate-analog against FR positive cancer cell lines and in FR negative tumors. Enteropathy was assessed by histopathology and neuropathy by the plantar test and the rotorod motor function test.
 RESULTS: The epothilone-folate conjugate BMS-753493 induced potent cytotoxicity in a panel of FR positive human tumor cells, including human KB and IGROV models in vitro . The cell-killing effect of BMS-753493 was abolished when excess folic acid was present; moreover BMS-753493 was inactive against FR negative cells. In several different FR positive tumor models, BMS-753493 demonstrated antitumor activity in vivo and showed excellent combinability with other chemotherapeutic agents. Similar to the in vitro experiments, antitumor activity of BMS-753493 was significantly reduced by the co-administration of 20-fold excess folate analog (EC-20) and the growth of FR negative tumors was unaffected by BMS-753493 at all doses tested. BMS-753493 combined synergistically with bevacizumab, cisplatin and ixabepilone in vivo against FR positive human tumor xenografts. Finally, rodents treated with BMS-753493 at the maximum tolerated dose did not demonstrate clinical signs of neuropathy and displayed minimal enteropathy, side-effects that are frequently associated with anti-microtubule cytotoxic agents.
 CONCLUSION: These data provide strong proof of concept that the antitumor activity of BMS-753493 is mediated mainly through the FR. Furthermore, these data support the notion that BMS-753493 would be cytotoxic against FR positive tumors but would have reduced adverse effects on normal tissues that do not express the FR. BMS-753493 thus represents a promising novel targeted-cytotoxic agent for the treatment of FR positive malignancies.