Development of PSB202, a bifunctional antibody pair that target CD20 and CD37, for the treatment of B-cell malignancies

Abstract CD20 and CD37 are co-expressed on most B-NHL and CLL tumors. Systemic depletion of normal and malignant B-cells by anti-CD20 antibodies (e.g. rituximab and obinutuzumab) and anti-CD37 antibodies (e.g. otlertuzumab and BI 836826) has been well tolerated in clinical studies. Depletion of B-cells is reversible, with the ability to repopulate B-cells from hematopoietic stem cells. Dual targeting CD20 and CD37 may improve the clinical efficacy and decrease drug resistance. PSB202 is a novel biological entity composed of two engineered monoclonal antibodies which are produced from a single stable CHO cell line - a humanized anti-CD20 antibody (PSB102) and a humanized anti-CD37 antibody (PSB107) at a 1:1 molecular ratio. In vitro binding studies demonstrated that PSB202 specifically binds to human CD20 and CD37. The antibodies’ binding to FcγRIIIa was enhanced by reducing the fucose level on each antibody component. PSB202 directly induced potent autonomous killing via target engagement. PSB202 mediated depletion of human and monkey blood B-cells and malignant human B-cell lines through ADCC activity at EC50 of double digit pM and CDC activity at EC50 of low single digit nM. Importantly, PSB202 effectively depleted B-cells in ex vivo cultures of blood cells from CLL and NHL patients who were refractive to rituximab treatment. The antitumor activity of PSB202 was demonstrated in human xenograft models in mice. PSB202 was able to reduce different human lymphoma tumors by up to ~97.9% in a dose-dependent manner, suggesting that PSB202 might be potentially efficacious against multiple types of B-cell malignancies. Synergy was demonstrated for PSB202 in combination with lenalidomide. Toxicokinetic assessment in cynomolgus monkeys showed a dose proportional exposure for both antibody components, with mean terminal elimination half-life (T1/2) of ~60 and ~68 hours for the anti-CD20 and anti-CD37 component, respectively. PBS202 was well tolerated, with observed toxicities mostly related to its activity as a B-cell depletion agent. As expected, PSB202 when administered at ≥ 10 mg/kg resulted in nearly complete depletion of B lymphocytes 24 hours following the 1st dose. B-cells returned to near baseline within 2 months after the last dose at 10 mg/kg. PSB202 can deplete normal and malignant B-cells by targeting two clinically validated targets through multiple distinct mechanisms including direct B-cell killing, enhanced ADCC activity, and CDC activity. PSB202 offers the potential to improve clinical efficacy, decrease drug resistance, provide administration convenience especially when combining with additional therapeutics, lower the cost for treatment, and reduce the unwanted side effects from chemotherapy. PSB202 is currently being evaluated in patients with previously treated, relapsed, indolent B-cell malignancies (NCT05003141). Citation Format: Paul Algate, Zhi Liu, Saying Yuan, Hua Liu, Cristina Domeier, Haiming Jiang, Yuanzhi Lao, Yanling Xu, William C. Fanslow, Ron Schoner, Wei Yan. Development of PSB202, a bifunctional antibody pair that target CD20 and CD37, for the treatment of B-cell malignancies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2902.