Abstract 1842: CD79b targeting ADC with superior pharmacokinetic profile and anti-tumor activity
Authors: Spycher Philipp René , Probst Philipp , Bertrand Romain , Stark Ramona , Santimaria Roger , Grabulovski Dragan , Attinger-Toller Isabella 
Published: July 2021

Abstract
Araris' site-specific conjugation technology is improving the safety and efficacy of ADCs without antibody engineering. Our technology is using transglutaminase for site-specific enzymatic payload conjugation to ‘off-the-shelf' antibodies, i.e., without the need to reduce or engineer the antibody. The functionalization takes place site-specifically and stoichiometrically (drug-to-antibody ratio, DAR = 2) at the glutamine residue Q295 in the Fc-part of antibodies. The resulting ADCs show favorable biophysical properties such as high solubility and stability. Additionally, initial data show that linker conjugation does not interfere with Fc-gamma receptor and FcRn binding.
Using native polatuzumab (non-engineered, same antibody sequence as present in approved polatuzumab-vedotin) as the targeting antibody and monomethyl auristatin E (MMAE) as payload, we generated within 24 hours highly homogeneous and pure ADCs with a well-defined DAR of 1.9 (LC-MS). Size exclusion chromatography analysis showed a highly monomeric ADC product (&gt; 96% monomer content) that remained stable under stressed conditions at elevated temperatures. In in-vitro assays our ADCs demonstrated potent cytotoxicity in four tested cell-lines, similar to the approved polatuzumab-vedotin (Polivy®). Moreover, our anti-CD79b ADC (termed ARC-01) is highly stable in mouse, cynomolgus and human sera and is resistant to mouse Ces1c cleavage but is cleaved by the lysosomal human Cathepsin B. Most importantly, the resulting ADC is extremely stable as shown in pharmacokinetic studies in mice demonstrating a very long exposure comparable to the unmodified polatuzumab antibody and twice as long as the approved polatuzumab-vedotin (half-life 10d vs 5d).
Most importantly, the in vivo efficacy of our ARC-01 (DAR 1.9) as compared with approved polatuzumab-vedotin (DAR 3.5) was assessed in the Granta-519 tumor model. Animals received a single injection of 0.53 or 2.1 mg/kg polatuzumab-vedotin (Polivy®) and either 0.53, 1 or 2.1 mg/kg of ARC-01. ARC-01 provided equal tumor growth inhibition and survival at about half the payload dose relative to polatuzumab-vedotin (comparison of the 2mg/kg doses and 0.53 mg/kg doses). At an approximately equal payload dose, ARC-01 treatment led to a greater antitumor efficacy and a considerable survival advantage with 6/8 complete tumor remissions over polatuzumab-vedotin with 0/8 complete tumor remission (comparison of the 0.53mg/kg dose of polatuzumab-vedotin and 1mg/kg dose of ARC-01).
These encouraging results obtained so far indicate that our linker technology a) allows for fast (&lt; 24 hours) and straightforward manufacturing of ADCs without protein engineering efforts, b) results in ADCs with favorable biophysical properties and a clear defined drug-to-antibody ratio, and c) enables the generation of highly potent and stable, thus safer, next-generation ADCs.
Citation Format: Philipp René Spycher, Philipp Probst, Romain Bertrand, Ramona Stark, Roger Santimaria, Dragan Grabulovski, Isabella Attinger-Toller. CD79b targeting ADC with superior pharmacokinetic profile and anti-tumor activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1842.