Background
The αvβ6- and αvβ8-integrins, two cell-adhesion receptors upregulated in many solid tumors, can promote the activation of transforming growth factor-β (TGFβ), a potent immunosuppressive cytokine, by interacting with the RGD sequence of the latency-associated peptide (LAP)/TGFβ complex. We have previously described a chromogranin A-derived peptide, called "peptide 5a", which recognizes the RGD-binding site of both αvβ6 and αvβ8 with high affinity and selectivity, and efficiently accumulates in αvβ6- or αvβ8-positive tumors. This study aims to demonstrate that peptide 5a can inhibit TGFβ activation in tumors and suppress tumor growth.
Conclusion
Peptide 5a is an efficient tumor-homing inhibitor of αvβ6- and αvβ8-integrin that after coupling to HSA, can be used as a drug to block integrin-dependent TGFβ activation in tumors and promote immunotherapeutic responses.
Methods
Peptide 5a was chemically coupled to human serum albumin (HSA) to prolong its plasma half-life. The integrin recognition properties of this conjugate (called 5a-HSA) and its capability to block TGFβ activation by αvβ6+ and/or αvβ8+ cancer cells or by regulatory T cells (Tregs) were tested in vitro. The in vivo anti-tumor effects of 5a-HSA, alone and in combination with S-NGR-TNF (a vessel-targeted derivative of tumor necrosis factor-a), were investigated in various murine tumor models, including pancreatic ductal adenocarcinoma, fibrosarcoma, prostate cancer, and mammary adenocarcinoma.
Results
In vitro assays showed that peptide 5a coupled to HSA maintains its capability of recognizing αvβ6 and αvβ8 with high affinity and selectivity and inhibits TGFβ activation mediated by αvβ6+ and/or αvβ8+ cancer cells, as well as by αvβ8+ Tregs. In vivo studies showed that systemic administration of 5a-HSA to tumor-bearing mice can reduce TGFβ signaling in neoplastic tissues and promote CD8-dependent anti-tumor responses. Combination therapy studies showed that 5a-HSA can enhance the anti-tumor activity of S-NGR-TNF, leading to tumor eradication.