Abstract 6318: Preclinical characterization of ARX305, a next-generation anti-CD70 antibody drug conjugate for the treatment of CD70-expressing cancers
Authors: Skidmore Lillian , Zhu Jingjing , Mills David , Jin Ting , Li Suqin , Tatsukawa Keith , Knudsen Nick A. , Gong Liying , Nelson Jay , Cox Kari , Hewet Amha G. , Wang Jianing , Buss Tim , Tian Feng , Xia Gang , Zhang Shawn 
Published: June 2023

Abstract
CD70 has emerged as an attractive tumor target with its over-expression in multiple solid and hematological cancers, yet tightly controlled and limited expression in normal cells. In the last decade, multiple anti-CD70 antibody drug conjugates (ADCs) have been developed, but most, if not all, of these ADC programs have been discontinued. Using an expanded genetic code to create Engineered Precision Biologics (EPBs), Ambrx has developed ARX305, a CD70-targeted next-generation antibody drug conjugate (ADC) to potentially overcome the challenges associated with earlier ADCs and treat patients with cancers over-expressing CD70. ARX305 is comprised of a proprietary, high-affinity, humanized anti-CD70 antibody stably and site-specifically conjugated to AS269, a potent microtubule inhibitor. After binding to CD70 expressed on target tumor cells, ARX305 internalizes and releases the cytotoxic payload pAF-AS269 which inhibits cellular proliferation. In vitro testing across a panel of solid and liquid tumor cell lines showed ARX305 elicited highly potent and specific cell killing across multiple tumor types with medium to high CD70 expression levels. In multiple in vivo CD70-expressing xenograft or disseminated models, ARX305 induced significant tumor growth inhibition or regression whereas unconjugated antibody exhibited poor activity. ARX305 utilizes stable oxime conjugation chemistry, a non-cleavable PEG linker, and a membrane-impermeable payload to minimize premature payload release in circulation and associated off-target toxicity. These properties of ARX305 result in high serum stability, with rodent pharmacokinetic studies confirming a similar exposure profile of ARX305 compared to unconjugated antibody and a long serum half-life. Repeat dose toxicokinetic studies in cynomolgus monkeys demonstrated ARX305 was tolerated at exposures well above therapeutic exposures in mouse pharmacology studies, indicating a wide therapeutic index. In summary, the highly potent anti-tumor activity in multiple tumor types and wide therapeutic index of ARX305 support clinical evaluation of this next generation anti-CD70 ADC. ARX305 is currently in a Phase 1 dose escalation study in China, and the IND in the United States is open.
Citation Format: Lillian Skidmore, Jingjing Zhu, David Mills, Ting Jin, Suqin Li, Keith Tatsukawa, Nick A. Knudsen, Liying Gong, Jay Nelson, Kari Cox, Amha G. Hewet, Jianing Wang, Tim Buss, Feng Tian, Gang Xia, Shawn Zhang. Preclinical characterization of ARX305, a next-generation anti-CD70 antibody drug conjugate for the treatment of CD70-expressing cancers [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 6318.