2-methoxyestradiol inhibits hypoxia-inducible factor lot, tumor growth, and angiogenesis and augments paclitaxel efficacy in head and neck squamous cell carcinoma

Purpose: Head and neck squamous cell carcinomas have been reported to overexpress hypoxia-inducible factor (HIF)-1alpha, a transcription factor that promotes expression of angiogenesis factors and resistance to programmed and therapy-induced cell death. 2-Methoxyestradiol (2ME2) is a natural compound with HIF-1alpha inhibitory activity that is currently being evaluated in phase 1 and 2 clinical trials for advanced solid tumors and multiple myeloma. To our knowledge, this is the first study to evaluate the effects of 2ME2 in head and neck squamous cell carcinoma. Experimental Design: In the present study, we investigated the effects of 2ME2 alone and in combination with paclitaxel, an active agent in recurrent or advanced head and neck squamous cell carcinoma. Results: 2ME2 exhibited antiproliferative and cytotoxic effects in a panel of five head and neck squamous cell carcinoma cell lines in the 0.5 to 10 mumol/L range, including induction of G(2)-M blockade, caspase-3/7 activation, and apoptosis at 48 hours. 2ME2 resulted in decreased nuclear HIF-1alpha-binding activity and affected the expression of downstream genes, such as bid, a proapoptotic bcl-2 family member, and vascular endothelial growth factor, a proangiogenic cytokine. The up-regulation of Bid (57.5% at 12 hours, P < 0.0006) and inhibition of vascular endothelial growth factor secretion (57.7% at 24 hours, P < 0.015; and 50.3% at 48 hours, P < 0.0006) could be partially attributed to the effects on HIF-1alpha, because HIF-1alpha small interfering RNAs produced similar effects. Finally, in vivo, in a xenograft model of head and neck squamous cell carcinoma using UM-SCC-11A cells, 2ME2 exhibited antitumor and antiangiogenic activity, as measured by CD31 immuno-staining. Conclusions: These results provide support for the use of 2ME2 in combination with paclitaxel for the treatment of recurrent or advanced head and neck squamous cell carcinoma.