PO-233 Chemoresistant NSCLC cells are hypersensitive to metabolic drugs due to mTOR-mediated inhibition of autophagy

Abstract

IntroductionIn non-small cell lung cancer (NSCLC) cisplatin is the first line chemotherapy and triggers a strong apoptotic response mainly by inducing DNA interstrand crosslinks. However, the effectiveness of cytotoxic cancer therapy is often limited by the emergence of drug resistant tumour cells. Here, we identify strategies for overcoming resistance to DNA interstrand crosslinkers such as cisplatin.Material and methodsWe treated the NSCLC cell line H460 continuously with DNA crosslinking agents resulting in resistant subclones that displayed cross-resistance to multiple DNA-damaging cancer drugs, which are commonly used in the clinic.Results and discussionsDrug resistance was found to be mediated by mTOR-dependent upregulation of DNA repair via the Fanconi anaemia pathway. Strikingly, despite being multidrug-resistant, resistant cells were highly sensitive to treatment with the metabolic drugs 2-deoxyglucose (2-DG) and dichloroacetate (DCA), whereas parental H460 cells failed to respond. Moreover, xenograft studies in mice revealed, that DCA preferentially reduces growth of resistant tumour cells. Interestingly, mTOR inhibition by RNAi or pharmacological inhibitors not only reversed resistance to crosslinking drugs but in parallel mitigated the apoptotic response to metabolic drugs, thereby linking sensitivity to metabolic drugs with mTOR signalling in chemoresistant cells. Mechanistically, inhibition of autophagy by mTOR was found to be decisive. We observed elevated levels of the mTOR-induced inhibitory S757 phosphorylation of the central autophagy-initiating kinase Ulk1 in chemoresistant tumour cells. Matching these observations, autophagosome formation was detected only in parental, but was abrogated in resistant tumour cells upon DCA treatment. In line, knockout of ATG7 using the CRISPR/Cas9 system or direct inhibition of different steps of autophagy with pharmacological autophagy inhibitors was sufficient to render parental cells sensitive to metabolic drugs. Failure to initiate autophagy resulted in lethal energy stress indicating that autophagy is absolutely required to survive metabolic drug treatment.ConclusionTogether these results demonstrate that mTOR-triggered resistance to DNA-damaging cancer drugs generates a therapeutic vulnerability to metabolic drugs due to mTOR-mediated inhibition of autophagy.