DuoBody®-FAPαxDR4 is a novel DR4 agonist that induces potent antitumor activity through FAPα-dependent, DR4-transactivation-mediated apoptosis.

Purpose Death receptor (DR) agonism is a promising strategy for cancer treatment, but clinical success has been limited by insufficient efficacy and/or on-target off-tumor toxicity, particularly hepatotoxicity. We hypothesized that restricting DR4 activation to the tumor microenvironment may enhance both therapeutic efficacy and safety. Fibroblast activation protein alpha (FAPα) is overexpressed on cancer-associated fibroblasts (CAFs) within the tumor stroma of several solid cancers, making it an attractive target for conditional activation of DR4 on tumor cells. Experimental Design DuoBody-FAPαxDR4 is an Fc-silenced IgG1 bispecific antibody that binds to DR4 on tumor cells and FAPα on CAFs. Functional activity of DuoBody-FAPαxDR4 was assessed in tumor cell lines and colorectal carcinoma (CRC) patient-derived organoids (PDOs) using viability and bioluminescent reporter assays. Toxicity was tested using human primary liver spheroids in vitro. In vivo, antitumor activity was evaluated in patient-derived xenograft (PDX) models and models for spontaneous multiorgan metastasis by implantation of CRC-derived organoids into the cecum. Results DuoBody-FAPαxDR4 localized to the fibroblast-tumor cell interface, where it induced conditional caspase-8 activation and cytotoxicity in DR4-expressing tumor cells while sparing the fibroblasts. DuoBody-FAPαxDR4 did not induce cytotoxicity in human primary liver spheroids. In vivo, DuoBody-FAPαxDR4 demonstrated potent antitumor activity in PDX models and in mouse models of multiorgan metastases of CRC. Conclusions DuoBody-FAPαxDR4 is a novel bispecific antibody that conditionally activates DR4 on cancer cells exclusively in the presence of FAPα-expressing cells, resulting in targeted apoptosis and antitumor activity. These findings supported the initiation of a first-in-human trial in patients with solid tumors.