Abstract 4438: Bypassing immune evasion in colorectal cancer by integrin inhibition-mediated downregulation of PD-L1

Integrin receptors have long posed a potentially attractive target for disrupting cancer hallmarks. Promising preliminary findings with integrin inhibition as an adjuvant to chemotherapy have not translated to clinical success. However, the effect of integrin inhibition on tumor-immune cell interactions remains largely unexplored. Further investigation could shed light on a connection between integrin signaling and immune checkpoint expression, opening the path for using integrin inhibitors to sensitize otherwise resistant tumors to immunotherapy. Fluorescently labeled wild-type HCT-116 colorectal cancer cells and TALL-104 T-cells were co-cultured and treated with GLPG0187, a small molecule integrin inhibitor, at various doses. Co-cultures were observed at different time points using fluorescence microscopy and cell counts were quantified using ImageJ software. The co-culture included the cell viability marker ethidium homodimer so the number of viable cells of each type could be determined using colocalization. This assay revealed synergistic cancer cell killing, indicating that integrin inhibition may be sensitizing cancer cells to immune cells. The hypothesized mechanism involves TGF-beta-mediated PD-L1 expression in cancer cells. GLPG0187 has been shown to inhibit the ɑvβ6 integrin receptor, which is responsible for the activation of latent-TGFβ into the active form. By blocking this receptor, there would potentially be a reduction of TGFβ signaling and therefore a reduced expression of PD-L1 leading to an enhanced immune response. To investigate this mechanism, both WT and p53-/- HCT-116 cells were pre-treated with GLPG0187 and subsequently with latent-TGFβ. Western blot analysis demonstrated that the addition of latent-TGFβ increased the expression of PD-L1 in cancer cells. Additionally, a low dose of integrin inhibitor rescued these effects, returning PD-L1 expression back to control levels. However, the higher dose of the drug did not reduce PD-L1 expression. This could potentially be due to off-target effects conflicting with the proposed pathway, however, these findings are still under active investigation. Ongoing proteomic experiments include a larger range of both drug and latent-TGFβ doses. Probing for additional downstream markers of TGFβ and up-stream markers of PD-L1 will help to further elucidate the mechanism. Further co-culture experiments include anti-PD-L1 and anti-PD-1 therapy to investigate the viability of integrin inhibition as an