Hypoxic human cancer cells are sensitized to BH-3 mimetic–induced apoptosis via downregulation of the Bcl-2 protein Mcl-1
Luke R.E. Harrison, Dimitra Micha, Martin Brandenburg, Kathryn L. Simpson, Christopher J. Morrow, Olive Denneny, Cassandra Hodgkinson, Zaira Yunus, Clare Dempsey, Darren Roberts, Fiona Blackhall, Guy Makin, Caroline Dive
Luke R.E. Harrison, Dimitra Micha, Martin Brandenburg, Kathryn L. Simpson, Christopher J. Morrow, Olive Denneny, Cassandra Hodgkinson, Zaira Yunus, Clare Dempsey, Darren Roberts, Fiona Blackhall, Guy Makin, Caroline Dive
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Research Article Oncology

Hypoxic human cancer cells are sensitized to BH-3 mimetic–induced apoptosis via downregulation of the Bcl-2 protein Mcl-1

Abstract

Solid tumors contain hypoxic regions in which cancer cells are often resistant to chemotherapy-induced apoptotic cell death. Therapeutic strategies that specifically target hypoxic cells and promote apoptosis are particularly appealing, as few normal tissues experience hypoxia. We have found that the compound ABT-737, a Bcl-2 homology domain 3 (BH-3) mimetic, promotes apoptotic cell death in human colorectal carcinoma and small cell lung cancer cell lines exposed to hypoxia. This hypoxic induction of apoptosis was mediated through downregulation of myeloid cell leukemia sequence 1 (Mcl-1), a Bcl-2 family protein that serves as a biomarker for ABT-737 resistance. Downregulation of Mcl-1 in hypoxia was independent of hypoxia-inducible factor 1 (HIF-1) activity and was consistent with decreased global protein translation. In addition, ABT-737 induced apoptosis deep within tumor spheroids, consistent with an optimal hypoxic oxygen tension being necessary to promote ABT-737–induced cell death. Tumor xenografts in ABT-737–treated mice also displayed significantly more apoptotic cells within hypoxic regions relative to normoxic regions. Synergies between ABT-737 and other cytotoxic drugs were maintained in hypoxia, suggesting that this drug may be useful in combination with chemotherapeutic agents. Taken together, these findings suggest that Mcl-1–sparing BH-3 mimetics may induce apoptosis in hypoxic tumor cells that are resistant to other chemotherapeutic agents and may have a role in combinatorial chemotherapeutic regimens for treatment of solid tumors.

Authors

Luke R.E. Harrison, Dimitra Micha, Martin Brandenburg, Kathryn L. Simpson, Christopher J. Morrow, Olive Denneny, Cassandra Hodgkinson, Zaira Yunus, Clare Dempsey, Darren Roberts, Fiona Blackhall, Guy Makin, Caroline Dive

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Figure 2

Western blot analysis of CC3 and CPARP in response to ABT-737 in cancer cell lines under hypoxic and normoxic conditions.

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Western blot analysis of CC3 and CPARP in response to ABT-737 in cancer ...
Cells were preincubated in normoxia or hypoxia (1% O2) for 18 hours prior to treatment with ABT-737, after which cells were harvested for protein analysis by Western blot. (A) H146 cells (treated with 89.1 nM ABT-737). (B) H82 cells (treated with 12.2 μM ABT-737). “Time” indicates the number of hours exposed to ABT-737 or control (DMSO). (C) HCT116 cells were treated with ABT-737 for 24 hours; concentration of ABT-737 is shown. Actin was used as a protein loading control.