Sorafenib but not sunitinib affects the induction of immune responses
3504 Background: The tyrosine kinase inhibitors (TKIs) sorafenib and sunitinib are approved for the treatment of patients with metastatic renal cell cancer. To analyze the possible use of these compounds in combination with immunotherapeutic approaches we investigated the effects of both TKIs on function of human dendritic cells (DCs) and induction of primary immune responses in vitro and in vivo. Methods: Human monocytes-derived DCs were treated with DMSO, sorafenib or sunitinib. Functional and phenotypic analyses as well as the possible impact on signal transduction pathways were performed. Furthermore, induction of immune responses in vivo was analyzed in animals treated with both compounds. Results: Sorafenib but not sunitinib inhibits function of DCs. Exposure of DCs to sorafenib reduces expression of CD1a, MHC and costimulatory molecules in response to stimuli via TLR ligands. Sorafenib reduces cytokine production by DCs as well as their ability to migrate and stimulate T cell (TC) responses. We found that these inhibitory effects of sorafenib are mediated via inhibition of PI3K, MAP kinases and NFκB signaling. The TKIs have no influence on phenotype and proliferation of TCs. To analyze the effects of TKIs on the generation of immune responses in vivo, induction of TC responses was assessed by peptide vaccination with the model antigen OVA-001 in C57BL/6 mice. When mice were pretreated with both TKIs which were also given during vaccination, it was observed that sorafenib, but not sunitinib significantly reduces the generation of vaccine-specific CD8+ TCs. Numbers of CD4+ CD25+ regulatory TCs are reduced in sunitinib-treated mice, but not in sorafenib-treated animals. All effects of the TKIs are reversible, and the immune responses go back to normal levels if mice are immunized after discontinuation of treatment. Conclusions: In summary, sunitinib represents an interesting compound to be used in combination with immunotherapeutic approaches to treat cancer patients. No significant financial relationships to disclose.