Abstract 1770: Enavatuzumab (PDL192), a humanized monoclonal antibody to TweakR, displays broad anticancer activity which is dependent on NFκB signaling

TWEAK (TNFSF12) is a multifunctional cytokine that binds to the cell surface receptor TweakR (Fn14, TNFRSR12A). TweakR is overexpressed in many solid tumor types, including cancers of breast, pancreatic, and ovarian origin. The initial functional description of TWEAK described it as a weak inducer of apoptosis in certain cancer cell lines. TWEAK is also known to function in other diverse biological processes such as inflammation, tissue repair, angiogenesis, cell migration, and growth inhibition. The growth inhibitory activity of TWEAK observed in some cancer cell lines and the overexpression of its receptor in cancer led to investigation of targeting TweakR as a therapeutic modality. Enavatuzumab (PDL192), a humanized IgG1 mAb to TweakR, exhibits some of the same functional activities of TWEAK and is currently in clinical investigation for the treatment of solid tumors due to its significant in vitro and in vivo growth inhibitory activity in models of multiple solid tumor types. The purpose of the current study was to provide insight into the mechanism of action of enavatuzumab and to further our understanding of the biology of TweakR in tumor cell lines. A panel of 106 cancer cell lines was tested for the ability of enavatuzumab to inhibit in vitro cell growth to identify characteristics of response. Of the 106 cell lines tested, 33 cell lines had >25% growth inhibition in response to the drug. Using luciferase transcriptional reporter constructs, it was revealed that the NFκB pathway was activated in response to enavatuzumab treatment in responder cells. Both classical (p50/p65) and non-classical NFκB (p52/RelB) pathways were subsequently shown to be induced by enavatuzumab treatment using Western blot and functional ELISA in responder cell lines. Using Affymetrix™ microarrays, we observed that cell lines sensitive to enavatuzumab had a higher number of transcriptional changes compared with resistant cells and included many genes known to be regulated by NFκB. To confirm a role for NFκB in enavatuzumab-mediated signaling, we inhibited NFκB pathway induction using siRNAs to the individual NFκB subunits p50, p65, p52, and RelB as well as the upstream kinases IKKα and IKKβ. The siRNAs were able to block enavatuzumab9s growth inhibitory activity in multiple sensitive cell lines. Further confirmation of the importance of NFκB was obtained using a small molecule inhibitor of IKKα/β (IKK16) which significantly reduced the drug-induced growth inhibition. The finding that NFκB drives the growth inhibitory activity of enavatuzumab is a compelling function for a family of transcription factors that are more frequently associated with cancer growth and survival than inhibition of cell proliferation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1770. doi:10.1158/1538-7445.AM2011-1770