Overexpression and activating mutations of cKIT are associated with tumor aggressiveness and poor prognosis in various cancer patients such as small cell lung cancer (SCLC), gastrointestinal stromal tumor (GIST), acute myeloid leukemia (AML), and mastocytoma. Since small molecule inhibitors including imatinib frequently have a limited therapeutic application due to eventual drug resistance and severe adverse events, we developed the cKIT-directed antibody-drug conjugate (ADC), NN3201, for the treatment of wild-type and mutant cKIT-positive cancers. NN3201 is an ADC conjugate of the antimitotic payload MMAE to the fully human 2G4 antibody, directed against cKIT, via the cysteine re-bridging technology ThioBridge® at a drug-to-antibody ratio (DAR) of 4. NN3201 displayed preferable biophysical properties and broadly potent in vitro antitumor activities across various cKIT-positive tumor cell lines. NN3201 exhibited potent in vivo antitumor activities in cKIT-positive tumor cell line xenograft and patient-derived tumor xenograft models of SCLC and AML, representing robust and durable antitumor responses. Furthermore, in a single-dose toxicity study with cynomolgus monkey, no significant or severe clinical toxicity signs were observed in animals dosed at 1, 2, and 3 mg/kg. Even though a decrease in reticulocyte, red cell mass (hemoglobin and red blood cell), neutrophil, and monocyte counts, along with bone marrow recovery and reticulocyte compensatory mechanism, red blood cell and white blood cell recovery were observed from day 14 in the low and medium dose groups and day 21 in the high dose group, dose-dependently. These preclinical results suggest that NN3201 is a potential therapeutic agent for the treatment of cKIT-positive cancers and support the further clinical evaluation in SCLC and AML.

Citation Format: Han-Jik Ko, Sung Tae Kim, Jin Gu Cho, Jin-Ock Kim, Jung Tae Lee, Sang Gyu Park. In vivo efficacy and preclinical safety profile of NN3201, an anti-cKIT antibody-drug conjugate, for treating SCLC and AML [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2648.