gx-15-070 and Colonic-Neoplasms

Activation of hypoxia-inducible factor (HIF)-1 is a feature of hypoxic solid tumors that has been associated with drug resistance, mainly due to disruption of Bcl-2 family dynamics. Resetting the balance in favor of proapoptotic family members is an attractive therapeutic goal that has been pursued by developing BH3-mimetic compounds. In the present study we evaluated the response of human colon adenocarcinoma cells to the BH3-mimetic obatoclax (OBX), in terms of growth arrest, apoptosis and autophagy, in the presence or absence of HIF-1α-stabilizing conditions; its possible effect on HIF-1α expression and HIF-1 activity; and the possibility to improve the response of colon cancer cells to cytotoxic chemotherapeutics by combining them with OBX. Colon cancer cell response to the BH3-mimetic was unmodified by HIF-1 activation and OBX induced a decrease in HIF-1α protein levels and HIF-1 transcriptional activity, probably by decreasing HIF-1α synthesis and facilitating a VHL-independent proteasomal degradation pathway. Finally, a chemosensitizing effect of OBX with respect to 5-fluorouracil or oxaliplatin treatment was observed, highlighting the possibility that patients with hypoxic colon tumors might benefit from combined regimens including OBX.

Topics: Adenocarcinoma; Antineoplastic Combined Chemotherapy Protocols; Apoptosis; Cell Hypoxia; Cell Proliferation; Colonic Neoplasms; Down-Regulation; Drug Synergism; Fluorouracil; HCT116 Cells; HT29 Cells; Humans; Hypoxia-Inducible Factor 1; Hypoxia-Inducible Factor 1, alpha Subunit; Indoles; Pyrroles; Transcriptional Activation

The Notch signaling pathway plays a significant role in differentiation, proliferation, apoptosis, and stem cell processes. It is essential for maintenance of the normal colon crypt and has been implicated in colorectal cancer oncogenesis. Downregulation of the Notch pathway through gamma-secretase inhibitors (GSIs) has been shown to induce apoptosis and enhance response to chemotherapy in a variety of malignancies. In this study, we analyzed the effect of MRK-003 (Merck), a potent inhibitor of gamma-secretase, on oxaliplatin-induced apoptosis in colon cancer. Unexpectedly, gamma-secretase inhibition reduced oxaliplatin-induced apoptosis while GSI treatment alone was shown to have no effect on growth or apoptosis. We determined that the underlying mechanism of action involved an increase in protein levels of the anti-apoptotic Bcl-2 family members Mcl-1 and/or Bcl-xL which resulted in reduced Bax and Bak activation. Blocking of Mcl-1 and/or Bcl-xL through siRNA or the small molecule inhibitor obatoclax restored the apoptotic potential of cells treated with both oxaliplatin and MRK-003. Moreover, obatoclax synergized with MRK-003 alone to induce apoptosis. Our findings warrant caution when treating colon cancer with the combination of GSIs and chemotherapy, whereas other drug combinations, such as GSIs plus obatoclax, should be explored.

Topics: Adenocarcinoma; Amyloid Precursor Protein Secretases; Antineoplastic Agents; Apoptosis; bcl-X Protein; Cell Line, Tumor; Colonic Neoplasms; Cyclic S-Oxides; Drug Synergism; Humans; Indoles; Myeloid Cell Leukemia Sequence 1 Protein; Organoplatinum Compounds; Oxaliplatin; Pyrroles; RNA, Small Interfering; Signal Transduction; Thiadiazoles

Topics: Antineoplastic Combined Chemotherapy Protocols; Autophagy; Cell Death; Colonic Neoplasms; HCT116 Cells; Humans; Indoles; Lapatinib; Proto-Oncogene Proteins c-bcl-2; Pyrroles; Quinazolines