Increased drug resistance is associated with reduced glucose levels and an enhanced glycolysis phenotype

Abstract

BACKGROUND AND PURPOSEThe testing of anticancer compounds in vitro is usually performed in hyperglycaemic cell cultures, although many tumours and their in vivo microenvironments are hypoglycaemic. Here, we have assessed, in cultures of tumour cells, the effects of reduced glucose levels on resistance to anticancer drugs and investigated the underlying cellular mechanisms. EXPERIMENTAL APPROACHPIK3CA mutant (AGS, HGC27), and wild-type (MKN45, NUGC4) gastric cancer cells were cultured in high-glucose (HG, 25 mM) or low-glucose (LG, 5 mM) media and tested for sensitivity to two cytotoxic compounds, 5-fluorouracil (5-FU) and carboplatin, the PI3K/mTOR inhibitor, PI103 and the mTOR inhibitor, Ku-0063794. KEY RESULTSAll cells had increased resistance to 5-FU and carboplatin when cultured in LG compared with HG conditions despite having similar growth and cell cycle characteristics. On treatment with PI103 or Ku-0063794, only the PIK3CA mutant cells displayed increased resistance in LG conditions. The PIK3CA mutant LG cells had selectively increased p-mTOR, p-S6, p-4EBP1, GLUT1 and lactate production, and reduced reactive oxygen species, consistent with increased glycolysis. Combination analysis indicated PI103 and Ku-0063794 were synergistic in PIK3CA mutant LG cells only. Synergism was accompanied by reduced mTOR signalling and increased autophagy. CONCLUSIONS AND IMPLICATIONSHypoglycaemia increased resistance to cytotoxic agents, especially in tumour cells with a high dependence on glycolysis. Dual inhibition of the PI3K/mTOR pathway may be able to attenuate such hypoglycaemia-associated resistance. Abbreviations

Hypoglycemia Enhances Epithelial‐Mesenchymal Transition and Invasiveness, and Restrains the Warburg Phenotype, in Hypoxic HeLa Cell Cultures and Microspheroids

“…HeLa cell proliferation was arrested under HH. Similar results have been reported for breast MCF‐7 and several metastatic cells (human prostate DU 145 and gastric MKN45 and NUGC4) (Singh et al, ; Sedoris et al, ; Bhattacharya et al, ). It is known that low glucose (≤ 2.5 mM) arrests the cell cycle through a mechanism associated with down‐regulation of both cyclins and CDK4 in non‐cancer and cancer cells (Zang et al, ; Salpeter et al, ; Cheng et al, ; Roy and Banerjee, ).…”

miR‑30 decreases multidrug resistance in human gastric cancer cells by modulating cell autophagy

“…It is believed that autophagy can play both positive and negative roles in promoting apoptosis. Previous research demonstrated the cytoprotective role of autophagy in response to 5-FU treatment in gastric cancer cells (27,28), while a different study showed that 5-FU may suppress miR-30 to upregulate beclin-1 and thus induce autophagic cell death and cell proliferation arrest in gastric cancer cells (29). Nevertheless, many studies have shown that autophagy protects various tumor cells against apoptosis induced by chemotherapeutic drugs (23,30,31).…”

“…Chemotherapeutic drugs can induce both apoptosis and autophagy in the treatment of cancer, and it was previously reported that autophagy helps cancer cells evade apoptosis, and thus contributes to chemoresistance (24). Additionally, cancer cells that respond to drugs by inducing autophagy are more drug-resistant (25): For example, in response to 5-fluorouracil (5-FU) and cisplatin, chemosensitive cell lines were found to undergo apoptosis, whereas chemoresistant populations underwent autophagy (25)(26)(27)(28). It is believed that autophagy can play both positive and negative roles in promoting apoptosis.…”

The Warburg effect and drug resistance

“…Indeed, GLUT1 up‐regulation has been reported in numerous malignancies (Wang et al ., ). Increased GLUT1 is associated with the activation of mTOR leading to an increase in glycolysis and reduction in autophagy (Bhattacharya et al ., ; Buller et al ., ). Increased mTOR activation may also lead to increased GLUT1 expression, forming a positive feedback loop (Buller et al ., ).…”