Purpose: Drug resistance in melanoma is commonly attributed to ineffective apoptotic pathways. Inhibiting antiapoptotic BCL-2 and its relatives is an attractive strategy for sensitizing lymphoid malignancies to drugs but it has been largely unsuccessful for melanoma and other solid tumors. ABT-737, a small-molecule BH3-mimetic, selectively inhibits BCL-2, BCL-XL, and BCL-w and shows promise for treating leukemia, lymphoma, and small-cell lung cancer. Melanoma cells are insensitive to ABT-737, but MCL-1 inhibition reportedly increases the sensitivity of other tumors to the compound.
Experimental Design: The efficacy of MCL-1 and BFL-1 inhibition for sensitizing melanoma cells to ABT-737 was investigated by short hairpin RNA–mediated knockdown or overexpression of their antagonist NOXA in two-dimensional cell culture, a three-dimensional organotypic spheroid model, and an in vivo model.
Results: MCL-1 downregulation or NOXA overexpression strongly sensitized melanoma cells to ABT-737 in vitro. NOXA-inducing cytotoxic drugs also strongly sensitized melanomas to ABT-737 but, surprisingly, not vice versa. The drugs most suitable are not necessarily those normally used to treat melanoma. Resistance to ABT-737 occurred quickly in three-dimensional melanoma spheroids through reduced NOXA expression, although experiments with both xenografts and three-dimensional spheroids suggest that penetration of ABT-737 into tumor masses may be the principal limitation, which may be obviated through use of more diffusible BH3-mimetics.
Conclusion: Sensitization of tumors to BH3-mimetics by cytotoxic drugs that induce NOXA is a therapeutic strategy worth exploring for the treatment of melanoma and other solid cancers. Clin Cancer Res; 18(3); 1–13. ©2011 AACR.
Note: Supplementary data for this article are available at Clinical Cancer Research Online (http://clincancerres.aacrjournals.org/).
- Received May 3, 2011.
- Revision received November 5, 2011.
- Accepted December 6, 2011.
- ©2011 American Association for Cancer Research.