Tivozanib mediated inhibition of c-Kit/SCF signaling on Tregs and MDSCs and reversal of tumor induced immune suppression correlates with survival of HCC patients

The immune modulatory effect of tivozanib, a tyrosine kinase inhibitor, and the underlying immune mechanisms impacting survival of HCC patients have not been investigated. Pre-clinical studies have shown that tivozanib reduces Tregs and MDSCs accumulation through inhibition of c-Kit/SCF axis. We rationalized that c-Kit/SCF axis antagonism by tivozanib may reverse tumor-induced immune suppression in HCC patients. The frequency of circulating Tregs, MDSCs, CTLA-4(+)Tregs, PD-1(+)T cells, c-Kit(+)pERK-2(+)Tregs, and c-Kit(+)pERK-2(+)MDSCs were quantified in HCC patients at baseline and two time points during tivozanib treatment. We report for the first time that reduction in Tregs after tivozanib treatment and increased levels of baseline CD4(+)PD-1(+)T cells correlated with significant improvement in overall survival (OS) of the patients and these signatures may be potential biomarkers of prognostic significance. This immune modulation resulted from tivozanib-mediated blockade of c-Kit/SCF signaling, impacting ERK2 phosphorylation on Tregs and MDSCs. Low pre-treatment CD4(+)T cells: Treg ratio and reduction in the frequencies of Foxp3(+)c-Kit(+)pERK(+)Tregs after tivozanib treatment correlated significantly with progression free survival. In a comparative analysis of tivozanib vs sorafenib treatment in HCC patients, we demonstrate that decrease in the baseline numbers or frequencies of Foxp3(+)Tregs, MDSCs and exhausted T cells was significantly greater following tivozanib treatment. Additionally, greater increase in CD4(+)T cell: Treg ratio after tivozanib treatment was associated with significant improvement in OS compared to sorafenib treatment, highlighting the greater efficacy of tivozanib. These insights may help identify patients who likely would benefit from c-Kit/SCF antagonism and inform efforts to improve the efficacy of tivozanib in combination with immunotherapy.