Integrin α5β1 plays an important role in tumor angiogenesis, invasion, and metastasis. Overexpression of α5β1 has been associated with poor prognosis in various types of cancers, and also plays a critical role in the resistance of cancers to radiotherapy and chemotherapy. We have previously reported that PF-04605412 (PF-5412), a fully human Fc-engineered IgG1 mAb against human α5β1, displayed robust and dose-dependent antitumor efficacy in multiple preclinical tumor models. Assessment of PF-5412 mechanism of action (MOA) in standard mouse xenograft models has been limited, however, because this antibody does not cross-react with murine integrin α5. To further our understanding of PF-5412 MOAs, we generated human integrin α5 knock-in mice (ITGA5 KI) in which the entire murine coding sequence of integrin α5 was replaced with the corresponding human coding sequence. Mice that were homozygous for human integrin α5 were viable and no abnormal phenotype or behavior was observed. qPCR and FACS analyses showed that human integrin α5 was expressed in various types of tissues and peripheral blood in ITGA5 KI mice, whereas no mouse integrin α5 was detected. Murine integrin β1 expression in ITGA5 KI mice was comparable to wild type mice. Growth of MC38 murine CRC tumors engineered to express human α5 was inhibited by treatment with PF-5412 in a dose-dependent manner. Tumor regression was observed at high doses of PF-5412 but not at comparable dose levels of α5 antibodies lacking ADCC activity (IgG4). IHC analyses of CD31 positive vessels showed that PF-5412 significantly inhibited blood vessel density and induced greater macrophages infiltration into tumors than non-ADCC-inducing antibodies. Notably, parental MC38 tumors lacking endogenous human α5 expression were also controlled by PF-5412 treatment (60% TGI) in ITGA5 KI mice. PF-5412 efficacy in this model also exceeded that of non-ADCC-inducing antibodies. Immunohistochemistry (IHC) analyses showed that PF-5412 treatment significantly decreased blood vessel density in the parental MC38 tumors. These results demonstrate that PF-5412 benefit does not depend on integrin α5β1 expression by the tumor cell itself, and support the hypothesis that ADCC-mediated killing of tumor endothelium will confer clinical benefit. The results showed here indicate that ITGA5 KI mouse is a relevant model for evaluating anti-human integrin α5 antibody MOA.

Citation Format: Lianglin Zhang, Jeffrey L. Stock, Mark W. Elliott, Enhong Chen, Thao Nguyen, Anthony Wong, Craig B. Davis, James G. Christensen. Assessment of mechanisms of action (MOAs) of the Fc-engineered integrin α5β1 targeting antibody PF-04605412 in human integrin α5 knock-in mice. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2336. doi:10.1158/1538-7445.AM2013-2336