C-type lectin domain family 12 member A (CLEC12A, CLL-1) is a single-pass transmembrane protein of 265 amino acids that is found on monocytes and AML blasts. We have created and characterized antibody-drug conjugates (ADCs) based on a humanized CLEC12A specific antibody to determine whether CLEC12A may be exploited as a therapeutic target for AML. The payload is a proprietary PBD prodrug with a beta-glucuronide trigger, and the linker-payload was conjugated through farnesyltransferase-mediated functionalization. The ADC demonstrated sub-nM cytotoxicity in vitro against several CLEC12A-positive cell lines including HL-60 and PL21. Leu234Ala/Leu235Ala (LALA) mutations were employed to reduce Fc gamma receptor binding and to avoid on-target toxicity. The LALA mutation-bearing ADC displayed a nearly 50-fold decrease in cytotoxicity towards CD34+ hematopoietic stem cells. Its potency was reduced but still sufficient with IC50 values of 61 pM and 15 pM against HL60 and PL21, respectively. Regardless of LALA mutation, the ADCs demonstrated potent antitumor activities with a complete regression at a dose of 0.5 mpk against a subcutaneous HL-60 SCID mouse xenograft model. When the LALA-mutated ADC was tested against a disseminated NSGA mouse model of HL-60-luc, all treated animals survived without clinical symptoms for three weeks after treatment, whereas vehicle-treated animals exhibited morbidity 19 days after treatment or 35 days after tumor implantation. The bone marrow of ADC-treated animals appeared to have nearly fully recovered, whereas that of vehicle-treated animals showed necrosis or tumor growth. In cynomolgus monkeys, the LALA-mutated ADC had a half-life of 82 hours at a dose of 0.2 mpk, and target-mediated drug disposition appeared weak or negligible. Our preclinical studies have shown that CLEC12A targeting ADC can be used as a therapeutics for treating AML.

Citation Format: Jinwon Jung, Juhee Kim, Bora Lee, Jung A Kwon, Suyoun Lee, Byeongmin Yoo, Minji Ko, Ilhwan Ryu, Donghoon Yeom, Kyoungjae Lee, Jaehyun Eom, Hanbyul Lee, Jinhyung Ahn, Eunsil Sung, Weonkyoo You, Sang Hoon Lee, Myeong Joo Kim, Keon Woo Kwon, Hyun Joo Bae, Yun-Hee Park, Ho Young Song, Chul-Woong Chung. Preclinical study of a novel anti-CLEC12A antibody-drug conjugate with a glucuronide-protected pyrrolobenzodiazepine payload [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 6296.