A CD79b Targeting ADC with Superior Anti-Tumor Activity and Safety Resulting in Significantly Improved Therapeutic Index (TI): Safe and Efficacious CD79b ADC

Abstract

The Araris' site-specific and 1-step enzymatic linker conjugation technology aims at generating safe and highly potent ADCs without the need for antibody engineering prior to linker-payload conjugation. We developed a very stable anti-CD79b-MMAE ADC (ARC-02) with this technology showing a higher therapeutic index (TI) compared to the approved ADC polatuzumab-vedotin (Polivy®) in different preclinical models. Therefore, ARC-02 is considered a promising next generation treatment alternative for patients suffering from Non-Hodgkin lymphoma (NHL). Using native polatuzumab as the targeting antibody and monomethyl auristatin E (MMAE) as payload, we generated within 24 hours the highly homogeneous and pure ARC-02 development candidate with a well-defined drug-to-antibody ratio (DAR) of 1.9 and with high purity (monomer content > 98%). ARC-02 is highly stable under stressed conditions at elevated temperatures and maintains the FcyR/FcRn-binding properties of the parental mAb. In-vitro ARC-02 demonstrated potent cytotoxicity in four different NHL cell lines tested so far with similar potency (EC50 values) compared to the approved Polivy® ADC despite of the lower toxin load of ARC-02 (DAR of 1.9) compared to Polivy® (DAR of 3.5). ARC-02 clearly differentiates from Polivy® by extraordinary stability in mouse, cynomolgus monkey and human sera exemplified by the absence of payload deconjugation or linker cleavage under physiological conditions (at 37°C) and long-term incubation (>2 weeks). Exceptional stability could also be confirmed in vivo in pharmacokinetic studies in mice, rats and cynomolgus monkeys demonstrating an antibody-like exposure profile comparable to the unmodified polatuzumab parental antibody without premature toxin deconjugation in the circulation resulting in improved pharmacokinetics of ARC-02 compared to Polivy® (half-life in mice 10 days for ARC-02 vs 5 days for Polivy®). Despite the excellent stability of ARC-02 in vitro and in vivo, the MMAE toxin is still efficiently released from ARC-02 in lysosomal human Cathepsin B cleavage or human liver-lysosome release assays which is providing the foundation for the observed robust anti-tumor activity in vivo: ARC-02 was compared head-to-head to Polivy® in two different CD79b-expressing established tumor models in vivo (Granta-519 and Ramos). Single dose treatment of ARC-02 at very low payload doses induced effective and long-lasting anti-tumor responses with complete tumor eradication achieved at about half of the Polivy® payload dose in both NHL established tumor models. Based on these in vivo efficacy experiments, the minimal effective dose (MED) of ARC-02 that is still inducing eradication of established tumors is determined to be as low as 10 μg/kg based on the MMAE payload dose or 1 mg/kg based on the total ADC dose. Finally, the highest non-severely toxic dose (HNSTD) of ARC-02 in repeat dose toxicology studies was determined to be ≥30 mg/kg and ≥24 mg/kg in rats and cynomolgus monkeys, respectively, which is substantially higher than the HNSTD reported for Polivy® (i.e. 10 mg/kg in the rat and 3 mg/kg in the cynomolgus monkey as described in the Polivy® Biologic License Application). Therefore, the tolerability in rodents and non-human primates is at least 3 and 8 times higher when compared to historical safety data of Polivy®. Using the HNSTD derived from repeat dose non-human primate toxicity study (24 mg/kg) and the MED calculated from single dose rodent efficacy studies (1 mg/kg) an impressive TI of 24 can be calculated for ARC-02 which is substantially higher than the TI of Polivy®. These encouraging results obtained so far indicate that ARC-02 a) has very favorable biophysical properties, b) shows a consistent and highly defined DAR, c) is highly stable in vitro and in vivo, d) is highly potent and efficacious in multiple tumor models and e) has improved tolerability in rodents and non-human primates and f) shows an impressive improvement in TI and ultimately warrant further development of ARC-02.