Abstract 546: Selectively targeting CD47 with bispecific antibody to efficiently eliminate mesothelin-positive solid tumors

Abstract

Abstract The CD47- signal regulatory protein α (SIRPα) axis, originally discovered as a mechanism of self-recognition, has emerged as a novel innate immune check-point employed by cancer cells to escape immune surveillance. Over-expression of CD47 on a plethora of hematologic and solid cancers has been shown to be associated with poor prognosis. CD47 blockade is thus considered as an attractive strategy to retune the host immune system toward eliminating cancer cells. Clinical efficacy has been achieved in patients with Non-Hodgkin lymphoma (NHL) treated with a combination of the anti-CD20 monoclonal antibody (mAb), rituximab, and the anti-CD47 mAb, Hu5F9-G4. However, in parallel, due to the ubiquitous expression of CD47 on healthy cells, toxicity is observed limiting exposure which impairs clinical development of anti-CD47 mAbs. To harness the tumoricidal potential and avoid the liabilities of CD47 blockade, we have developed bispecific antibodies (bsAbs), co-targeting CD47 and a tumor associated antigen (TAA), for selective blockade of CD47 on malignant cells. Mesothelin (MSLN) has been selected as one of these TAAs as it is over-expressed on multiple types of solid tumors. An anti-CD47xMSLN bsAb with a fully functional IgG1 Fc domain has been generated and tested for efficacy and safety in vitro and in vivo using cell-based assays and animal models. With a panel of human MSLN+ target cells, the bsAb kills more efficiently through Ab-dependent cellular phagocytosis (ADCP) and cell-mediated cytotoxicity (ADCC) as compared to the anti-MSLN mAb, amatuximab. Efficacy of the bsAb was minimally affected by soluble MSLN as compared to amatuximab. Mechanistic studies demonstrated that the increased ADCP and ADCC were due to co-engagement-mediated blockade of both target proteins. In vivo using xenograft models, whereas amatuximab was unable, the bsAb inhibited tumor growth of OVCAR3 and MSLN-transfected HepG2 cell lines. Phenotypic analysis showed that treatment with the bsAb induced the accumulation of myeloid cells with increased F4/80 expression in the tumor microenvironment. Importantly, the bsAb was well-tolerated in an exploratory four-week repeated dose study at the highest dose tested (10 mg/kg) in cynomolgus monkeys. Conclusion: Selective CD47 targeting on tumor cells with an anti-CD47xMSLN bsAb showed efficient killing of MSLN+ tumor cells in vitro and in vivo. A study in non-human primates administered weekly a therapeutically relevant dose over 28 days was well tolerated demonstrating no adverse hematological profiles. Citation Format: Limin Shang, Vanessa Buatois, Eric Hatterer, Xavier Chauchet, Hasnaà Haddouk, Stefano Majocchi, Krzysztof Masternak, Marie H. Kosco-Vilbois, Nicolas Fischer, Walter G. Ferlin. Selectively targeting CD47 with bispecific antibody to efficiently eliminate mesothelin-positive solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 546.