Cancer Science & Therapy

Objective: Despite advances in cancer treatment, chemotherapy resistance and metastasis are major hurdles in curative cancer treatment. Studies involving drug resistance and cancer metastasis have generally proceeded along separate pathways of research. Current interest has focused on a possible relationship between drug resistance and cancer metastasis, since the molecular basis for drug resistance with an aggressive metastatic phenotype remains to be elucidated. We aim to show that histone deacetylase (HDAC) involvement in hypoxia-inducible factor-1α (HIF-1α) regulation may connect drug resistance to cancer invasiveness in osteosarcoma and breast cancer.

Methods: We created a doxorubicin resistant (DoxR) cell line from wildtype (WT) human osteosarcoma (SJSA-1) and breast cancer (MCF-7) cells. Matrigel in vitro invasion assay and colony formation assay were used to compare invasiveness of WT to DoxR cells. Western blot assay was used to determine HDAC and HIF-1α expression. Invasiveness and expression of HDACs and HIF-1α between WT and DoxR cells were also compared after treatment with vorinostat, an HDAC inhibitor, and in small interfering RNA (siRNA)-mediated knockdowns of HDAC-6 and HIF-1α.

Results: Both DoxR SJSA-1 and MCF-7 cells were more invasive than their doxorubicin-sensitive WT cells. Expression of HDAC-6 and HIF- 1α was increased in DoxR compared to WT cells. Inhibition of HDAC-6, either by the HDAC inhibitor (HDACi) vorinostat or small interfering RNA (siRNA)-mediated knockdown, decreased HIF-1α expression and the invasiveness of DoxR cells. Small hairpin RNA (shRNA)-mediated knockdown of HIF-1α also suppressed the invasiveness of DoxR cells and sensitized the DoxR Cell to doxorubicin.

Conclusion: These findings demonstrate that HDAC6 is involved in the regulation of HIF-1α and might connect drug resistance and cancer invasion.