An αvβ6/αvβ8-targeting peptibody inhibits integrin-dependent TGFβ activation, enables tumor-selective cytotoxic delivery, and synergizes with PD-L1 immune checkpoint blockade.

BACKGROUND: The αvβ6 and αvβ8 integrins are upregulated in many solid-tumors and drive local activation of transforming growth factor-β (TGFβ), promoting immune evasion and resistance to immune checkpoint blockade. The chromogranin A-derived peptide 4Δ targets the RGD-binding site of αvβ6/αvβ8 and inhibits integrin-dependent TGFβ-activation. We investigated whether 4Δ-derived peptibodies can deliver cytotoxic drugs to cancer cells and enhance immune checkpoint inhibitors (ICIs) activity. METHODS: Peptide 4Δ was genetically fused to the Fc domains of murine and human IgG1 to generate the peptibodies 4ΔmFc and 4ΔhFc. Integrin-binding properties and inhibition of TGFβ activation were characterized using biochemical and cell-based assays. Peptibody internalization and lysosomal trafficking were analyzed by live-cell/confocal microscopy. Cytotoxic activity of peptibodies complexed with anti-Fc antibodies coupled to anticancer drugs was evaluated using αvβ6/αvβ8-positive and -negative cancer cells. Pharmacokinetics and antitumor activity of 4ΔmFc, alone or in combination with an anti-PD-L1 antibody, were evaluated in murine fibrosarcoma and mammary carcinoma models. RESULTS: 4ΔmFc and 4ΔhFc bound αvβ6 and αvβ8 with sub-nanomolar affinity. Both compounds selectively recognized αvβ6/αvβ8-positive tumor cells, as well as human pancreatic, lung, and colon carcinomas sections. 4ΔmFc and 4ΔhFc efficiently inhibited TGFβ activation, underwent efficient internalization, and trafficked to lysosomes. 4ΔhFc enabled delivery of cytotoxic payloads to αvβ6/αvβ8-positive cells, including MMAE, MMAF, DM1, PBD, or DX8951. 4ΔmFc delayed the growth of fibrosarcomas and improved mice survival in the mammary adenocarcinoma model when combined with an anti-PD-L1 mAb (immune checkpoint inhibitor), without overt toxicity. CONCLUSION: These peptibodies represent a dual-selective αvβ6/αvβ8-targeting platform that couples potent blockade of integrin-dependent TGFβ activation with efficient, selective delivery of cytotoxic payloads to cancer cells. These properties, together with the observed synergism with anti-PD-L1 mAbs, suggest their potential use as ligands for delivering cytotoxic agents to tumors, while concomitantly modulating the TGFβ-driven immunosuppressive microenvironment, either alone or in combination with ICIs.