RO7297089 is a bispecific antibody (IgG-scFv) targeting Bcell maturation antigen (BCMA) and CD16a (FcγRIIIA) that is being developed for the treatment of multiple myeloma (MM). BCMA is exclusively expressed on plasmablasts and differentiated plasma cells (PCs), and is overexpressed on malignant PCs in MM patients. CD16a is expressed on natural killer (NK) cells, monocytes, mast cells, and macrophages. Herein, we characterized the mode of action and safety profile of RO7297089 in vitro and in vivo. RO7297089 showed potent cell killing when using BCMA+ MM tumor cell lines as target cells and human peripheral blood mononuclear cells, NK cells or macrophages as effector cells. Minimal increases in TNFα (2x) and IFNγ (4x), but not other cytokines/chemokines, were observed compared to the vehicle control treatment only in the presence of the BCMA+ MM tumor cell line up to the concentration tested. This suggests that, unlike T-cell engagers, the risk of cytokine release syndrome in patients receiving RO7297089 is low. Cynomolgus monkey is the only relevant nonclinical species for RO7297089 as it showed binding to both recombinant CD16 and BCMA with comparable affinity to human antigens. Following five weekly intravenous administrations to monkeys at 0, 15, and 50 mg/kg, RO7297089 was well tolerated. In line with the mechanism of action, there were no test article-related cytokine increases or adverse findings observed in both dose levels. Systemic exposure of RO7297089 was approximately dose proportional from 15 to 50 mg/kg. Anti-drug antibodies (ADA) were observed in some animals at both dose levels, and ADA-related decreases in concentrations were observed at only 15 mg/kg. To evaluate in vivo activity, RO7297089-related effects on total plasma sBCMA and PCs were assessed. Elevations of sBCMA levels (100x) were observed post dose at both dose levels, and these effects returned to predose levels in animals that did not maintain concentrations at 15 mg/kg, suggesting that RO7297089 bound to and stabilized circulating cynomolgus sBCMA. Time- and dose-dependent reductions in serum IgM levels were observed at both dose levels. Changes in PC numbers were not detected by immunophenotyping; however, gene expression analysis of PC markers was included and demonstrated clear reductions in mRNA expression levels of PC markers including BCMA and J-chain in blood at both dose levels, suggesting reductions in BCMA+ cells. Collectively, these studies suggest that RO7297089 selectively kills BCMA+ cells by engaging CD16a-positive immune cells and has a favorable safety profile. Citation Format: Satoko Kakiuchi-Kiyota, Melissa M. Schutten, Adeyemi O. Adedeji, Hao Cai, Robert Hendricks, Luna Liu, Sivan Cohen, Aaron M. Fullerton, Nicholas Corr, Lanlan Yu, Denise de Almeida Nagata, Shelly Zhong, Michael Dillon, Christoph Spiess, Steve R. Leong, Bing Zheng, Susanne Wingert, Uwe Reusch, Stefan Knackmuss, Thorsten Ross, Andrew Polson, Ayse M. Ovacik. Preclinical pharmacology and safety of RO7297089, a novel anti-BCMA/CD16a bispecific antibody for the treatment of multiple myeloma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4556.

For antibody-drug conjugates (ADCs) that carry a cytotoxic drug, doses that can be administered in preclinical studies are typically limited by tolerability, leading to a narrow dose range that can be tested. For molecules with non-linear pharmacokinetics (PK), this limited dose range may be insufficient to fully characterize the PK of the ADC and limits translation to humans. Mathematical PK models are frequently used for molecule selection during preclinical drug development and for translational predictions to guide clinical study design. Here, we present a practical approach that uses limited PK and receptor occupancy (RO) data of the corresponding unconjugated antibody to predict ADC PK when conjugation does not alter the non-specific clearance or the antibody-target interaction. We used a 2-compartment model incorporating non-specific and specific (target mediated) clearances, where the latter is a function of RO, to describe the PK of anti-CD33 ADC with dose-limiting neutropenia in cynomolgus monkeys. We tested our model by comparing PK predictions based on the unconjugated antibody to observed ADC PK data that was not utilized for model development. Prospective prediction of human PK was performed by incorporating in vitro binding affinity differences between species for varying levels of CD33 target expression. Additionally, this approach was used to predict human PK of other previously tested anti-CD33 molecules with published clinical data. The findings showed that, for a cytotoxic ADC with non-linear PK and limited preclinical PK data, incorporating RO in the PK model and using data from the corresponding unconjugated antibody at higher doses allowed the identification of parameters to characterize monkey PK and enabled human PK predictions.