Effect of obatoclax (GX15-070) on cell survival, apoptosis, and prosurvival autophagy in head and neck squamous cell carcinoma (HNSCC).

Abstract

e13587 Background: Approximately 500,000 new cases of head and neck cancer are diagnosed annually worldwide, with 300,000 deaths per year. Patients with recurrent and metastatic disease have a dismal prognosis with a median survival of less than one year. Current standard of care involves a platinum-based regimen for patients with good performance status, but is usually difficult to tolerate. Novel therapeutic approaches are in great need for this patient population. The antiapoptotic BCL-2 family proteins, including BCL-2, BCL-XL, and MCL-1 are involved in oncogenesis and chemoresistance and are overexpressed in HNSCC. Obatoclax is a pan-BCL2 inhibitor capable of inhibiting MCL-1, in addition to BCL-2 and BCL-XL. Methods: We determined the activity of obatoclax in 4 well-characterized HNSCC cell lines (UMSCC-1, Cal-33, 1483, UMSCC-22A). Cell viability was determined by MTT assay and apoptosis by Annexin-V binding, FACS analysis, and immunoblotting. Autophagy was assessed by immunofluorescence and immunoblotting. Results: All 4 HNSCC cell lines were highly sensitive to single-agent obatoclax with IC50’s ranging from 50-200 nM. Obatoclax induced apoptosis in all cell lines as evidenced by increased Annexin-V binding at 48 hours in a dose-dependent manner from less than 10% in vehicle treated cells to 30-60% in cells treated with obatoclax. Processing/activation of caspase-3 and cleavage of PARP protein was also observed. In addition, obatoclax induced prosurvival autophagy in all cell lines and the addition of the autophagy inhibitor chloroquine enhanced obatoclax cytotoxicity. In vivo studies of obatoclax using human HNSCC xenograft tumors is currently underway. Conclusions: This preclinical study suggests that obatoclax might have therapeutic value in HNSCC, as a single agent or in combination with an autophagy inhibitor.