Rationale and preclinical development of LEAF-1401 and LEAF-1701: A novel class of potent next generation antifolates

e14515 Background: Polyglutamation of antifolates by folylpolyglutamate synthase (FPGS) greatly enhances their activity, e.g. pentaglutamated pemetrexed is 80-fold more potent at inhibiting thymidylate synthase than pemetrexed. Polyglutamated antifolates however, do not readily cross the cell membrane, due to high negative charge and molecular mass. The resulting poor intracellular bioavailability greatly limits their therapeutic potential. Gamma glutamyl hydrolase (GGH) enzyme removes the glutamate residues from polyglutamates, which then are subject to efflux pumps. Resistance to pemetrexed has been linked to downregulation of both FPGS and folate transporters and upregulation of both GGH and the efflux pumps. We have been developing a novel class of nanoliposomal polyglutamated-antifolates including: LEAF-1401; nanoliposomal gamma-L pentaglutamated antifolate LEAF-1701; nanoliposomal alpha-L pentaglutamated antifolate These were designed to address key challenges of currently used antifolates namely: Bypassing the need for intracellular endogenous FPGS Direct delivery of the much more active polyglutamates through nanoliposome technology Minimizing toxicity to normal cells Mitigating against key antifolate resistance mechanisms such as downregulation of FPGS and folate transporters, and upregulation of GGH and efflux pumps Methods: In vitro testing in cell lines and in vivo testing in mice were performed using LEAF-1701 and LEAF-1401 in various tumor types. Results: Compared to pemetrexed: In vitro, LEAF-1701 and LEAF-1401 were more potent, in various cell lines while sparing normal neutrophils, colon and liver cells. In vivo, in H292 lung cancer xenografts, treatment with LEAF-1701 improved survival to 59 days vs 39 days for pemetrexed. In A549 lung cancer mouse orthotopic models, treatment with LEAF-1401 reduced metastatic tumor burden and prevented new metastases. In vivo, in mice doses of up to 80 mg/kg IV weekly were tolerated with little impact on blood counts and chemistry. Conclusions: LEAF-1701 and LEAF-1401 are innovative new chemical entities with promising preclinical activity and improved safety profiles and are now advancing to the clinic.