Q6, a novel hypoxia-targeted drug, regulates hypoxia-inducible factor signaling via an autophagy-dependent mechanism in hepatocellular carcinoma

Abstract

Tumor hypoxia underlies treatment failure and yields more aggressive and metastatic cancer phenotypes. Although therapeutically targeting these hypoxic environments has been proposed for many years, to date no approaches have shown the therapeutic value to gain regulatory approval. Here, we demonstrated that a novel hypoxia-activated prodrug, Q6, exhibits potent antiproliferative efficacy under hypoxic conditions and induces caspase-dependent apoptosis in 2 hepatocellular carcinoma (HCC ) cell lines, with no obvious toxicity being detected in 2 normal liver cell lines. Treatment with Q6 markedly downregulated HI F1A [hypoxia inducible factor 1, a subunit (basic helix-loop-helix transcription factor)] expression and transcription of the downstream target gene, VEGFA (vascular endothelial growth factor A). This dual hypoxia-targeted modulation mechanism leads to high potency in suppressing tumor growth and vascularization in 2 in vivo models. Intriguingly, it is the autophagy-dependent degradation pathway that plays a crucial role in Q6-induced attenuation of HI F1A expression, rather than the proteasome-dependent pathway, which is normally regarded as the predominant mechanism underlying posttranslational regulation of HI F1A. Inhibition of autophagy, either by short interfering RNA (siRNA) or by chemical inhibitors, blocked Q6-induced HI F1A degradation. Autophagic degradation of HI F1A was further confirmed by the observation that HI F1A coimmunoprecipitated with the ubiquitinbinding adaptor protein, SQSTM1, which is degraded through autophagy. Additionally, silencing of SQSTM1 inhibited Q6-induced HI F1A degradation. These findings suggest that the novel hypoxia-targeted agent, Q6, has potential clinical value in the therapy of HCC . Furthermore, the identification of autophagy as a crucial regulator of HI F1A provides new insights into hypoxia-related treatments.© 2014 Landes Bioscience.