Preclinical Anti-Tumor Efficacy of a Novel Anti-c-Kit Antibody Drug Conjugate, NN3201, in c-Kit Positive Tumors

Abstract Overexpression and gain-of-function mutations of c-Kit have been implicated in cancers including gastrointestinal stromal tumors (GIST), small cell lung cancer (SCLC), acute myeloid leukemia, and systematic mastocytosis. In clinics, small molecule c-Kit inhibitors often result in secondary c-Kit mutations or are ineffective despite c-Kit overexpression. We developed NN3201, a novel c-Kit targeting antibody-drug conjugate (ADC), via rational design to evaluate its anticancer activity in c-Kit-positive tumors, and preclinical pharmacologic profiles. A fully human c-Kit antibody NN2101 was conjugated to monomethyl auristatin E (MMAE) as DAR of 4 utilizing ThioBridge linker to generate NN3201. Anti-tumor efficacies of NN3201 were evaluated in c-Kit-positive cancer cell lines, cell line derived xenografts and patient-derived xenografts. NN3201 selectively binds to c-Kit and is rapidly internalized. By its design, NN3201 exhibits no antibody-dependent cell mediated cytotoxicity and complement-dependent cytotoxicity and possessed decreased binding to FcγRs. Inhibition of SCF/c-Kit downstream signaling pathways, cell cycle arrest and bystander effect were demonstrated as mechanism of action for NN3201. In xenograft models, NN3201 showed superior efficacy regardless of c-Kit mutations. Repeated intravenous administration of NN3201 was well tolerated in cynomolgus monkeys, confirming No Observed Adverse Effect Level of NN3201 to be 2 mg/kg and Highest Non-Severely Toxic Dose over 2 mg/kg. NN3201 exhibited significant c-Kit-dependent anti-tumor efficacies in various tumor models, followed by favorable pharmacokinetic and toxicity profile in cynomolgus monkeys. These data suggest that NN3201 is a promising therapeutic in SCLC and GIST, and warrants evaluation in a phase 1 clinical study.