Targeting surface receptors overexpressed on
cancer cells is one way to specifically treat
cancer versus normal cells.
Vintafolide (
EC145), which consists of
folate linked to a cytotoxic small molecule, desacetylvinblastine
hydrazide (DAVLBH), takes advantage of the overexpression of
folate receptor (FR) on
cancer cells. Once bound to FR,
vintafolide enters the cell by endocytosis, and the reducing environment of the endosome cleaves the linker, releasing DAVLBH to destabilize microtubules.
Vintafolide has shown efficacy and improved tolerability compared with DAVLBH in FR-positive preclinical models. As the first FR-targeting
drug to reach the clinic,
vintafolide has achieved favorable responses in phase II clinical trials in FR-positive ovarian and
lung cancer. However, some FR-positive patients in these clinical trials do not respond to
vintafolide. We sought to identify potential
biomarkers of resistance to aid in the future development of this and other FR-targeting drugs. Here, we confirm that high
P-glycoprotein (P-gp) expression was the strongest predictor of resistance to DAVLBH in a panel of 359
cancer cell lines. Furthermore, targeted delivery of DAVLBH via the FR, as in
vintafolide, fails to overcome P-gp-mediated efflux of DAVLBH in both in vitro and in vivo preclinical models. Therefore, we suggest that patients whose
tumors express high levels of P-gp be excluded from future clinical trials for
vintafolide as well as other FR-targeted
therapeutics bearing a P-gp substrate. Mol
Cancer Ther; 15(8); 1998-2008. ©2016 AACR.