Microtubule inhibitors containing immunostimulatory agents promote cancer immunochemotherapy by inhibiting tubulin polymerization and tryptophan-2,3-dioxygenase

A combination therapeutic regimen via introducing tryptophan 2,3-dioxygenase inhibitors into microtubule inhibitors was performed and evaluated for their antitumor activity. Thereinto, HT2, composed of combretastatin A-4 (CA-4) and tryptophan-2,3-dioxygenase (TDO) inhibitor by a linker, displayed the most potent activity with 10-fold higher than its parent CA-4 against HepG2, A549 and HCT-116 Cancer cell lines. Mechanism studies suggested that HT2 inhibited tubulin polymerization and cell migration, caused G2 phase arrest, induced Apoptosis by mitochondrial mediated apoptotic pathway, concurrent depolarized the mitochondria membrane potentials and caused Reactive Oxygen Species (ROS) production in HepG2 cells. Moreover, HT2 could enhance T-cell immune responses in vitro by releasing a TDO inhibitor to suppress TDO expression and blockade kynurenine production. As expected, HT2 could remarkably promote the antitumor activity of CA-4 in either immunocompetent H22 or immunodeficient A549 tumor xenograft models without observable toxic effects. More importantly, HT2 increased the level of splenic and tumor-infiltrated T cells and in turn effectively boosted the inhibition effect in H22 xenografted tumor growth. Collectively, this immunochemotherapeutic strategy can be applied to promote chemotherapeutic effect.