Autophagy Inhibition Sensitizes Colon Cancer Cells to Antiangiogenic and Cytotoxic Therapy

Abstract

Purpose: Autophagy is a critical survival pathway for cancer cells under conditions of nutrient or oxygen limitation, or cell stress. As a consequence of antiangiogenic therapy, solid tumors encounter hypoxia induction and imbalances in nutrient supply. We wished to determine the role of autophagy in protection of tumor cells from the effects of antiangiogenic therapy and chemotherapy. We examined the effect of inhibiting autophagy on hypoxic colon cancer cells in vitro and on bevacizumab-and oxaliplatin-treated mouse xenografts in vivo.Experimental Design: The autophagic response to hypoxia and DNA-damaging agents was assessed by fluorescent microscopic imaging, autophagy-related gene expression, and by electron microscopic ultrastructural analysis. Pharmacologic and molecular approaches to autophagy inhibition were taken in a panel of colon cancer cell lines. Mouse xenograft models were treated with combinations of oxaliplatin, bevacizumab, and chloroquine to assess effects on tumor growth reduction and on pharmacodynamic markers of autophagy inhibition.Results: Autophagy was induced in colon cancer models by exposure to both hypoxia and oxaliplatin. Inhibition of autophagy, either with chloroquine or by downregulation of beclin1 or of ATG5, enhanced sensitivity to oxaliplatin under normal and hypoxic conditions in a synergistic manner. Both bevacizumab and oxaliplatin treatments activate autophagy in HT29 murine xenografts. The addition of chloroquine to bevacizumab-based treatment provided greater tumor control in concert with evidence of autophagy inhibition.Conclusions: These findings implicate autophagy as a mechanism of resistance to antiangiogenic therapies and support investigation of inhibitory approaches in the management of this disease.

Autophagy in colorectal cancer: An important switch from physiology to pathology

“…ATG5 expression was down regulated in 95% of CRC patients and, interestingly, increased ATG5 expression was associated with lymp hovascular invasion [92] . Other research showed that ATG5 is downregulated in colorectal carcinoma, in both tissue samples and cell lines, and that downregulation of ATG5 in CRC enhanced sensitivity to oxaliplatin [93] . Heterozygous deletion of ATG5 predisposed mice to intestinal adenoma growth and enhanced the antitumor effect of interferon gamma.…”

“…Furthermore, CQ inhibits phospholipase A2 and lysophospholipid acylhydrolase, enzymes that are required for the acidification of lysosomes [124] . Treating human colon carcinoma HT29 cells with CQ sensitized mouse colon cancers to antiangiogenic and cytotoxic therapy [93] . Moreover, the combination of CQ and 5FU displayed a significant advantage over treatment with 5FU alone in inhibiting tumor growth in colon 26 cells, which are a CRC cell line [125] .…”

Role of autophagy in the maintenance and function of cancer stem cells

“…The survival of CML stem/ progenitor cells was also impaired by the depletion of ATG4B (Rothe et al, 2014). Along similar lines, the inhibition of autophagy via the administration of chloroquine (CQ, a lysosomotropic agent arresting the fusion between autophagosomes and lysosomes (Firat et al, 2012, O'Donovan et al, 2011, Sasaki et al, 2010, Selvakumaran et al, 2013) depleted the CD44 + /CD24…”

Phase I clinical trial and pharmacodynamic evaluation of combination hydroxychloroquine and doxorubicin treatment in pet dogs treated for spontaneously occurring lymphoma

“…6,7 A number of preclinical cancer therapy mouse xenograft models have been used to demonstrate the enhanced efficacy of cancer therapies when combined with the autophagy inhibitors chloroquine (CQ) or hydroxychloroquine (HCQ). [8][9][10] Thus, autophagy appears to be an attractive pathway to target. However, autophagy has been shown to have a protective role in a variety of organs including the gut, kidneys, and liver and combining HCQ with other drugs may exacerbate the toxicities of chemotherapy especially in these tissues.…”