PO-460 Targeting Endoplasmic Reticulum Stress Using Thiosemicarbazones to Suppress Cancer Progression

Introduction Endoplasmic reticulum (ER) stress and its corresponding response, namely, the unfolded protein response (UPR), are activated in cancer cells due to genetic mutations and the hostile microenvironment of tumours. This UPR activation has been demonstrated to be a crucial step in oncogenic transformation and cancer development; even eliciting activity of cancer supporting stromal cells. An innovative strategy is to induce lethal activation of the UPR via the use of novel thiosemicarbazone anti-cancer agents (TCs) developed in my lab. TCs form cellular redox active metal complexes and demonstrate potent and selective anti-tumour and anti-metastatic activity in vivo. Importantly, these agents overcome drug resistance. The most potent of these agents is currently being examined in clinical trials for the treatment of patients with advanced solid tumours in Australia. Material and methods Studies assessed the mechanisms by which the potent TC, di-2-pyridylketone 4,4-dimethyl-3-thiosemicarbazones (Dp44mT), alters the UPR in SKNMC neuroepthelioma and PANC1 pancreatic cancer cells using a range of techniques, including western blotting, q-RT-PCR, gene silencing and cell migration assays. Results and discussions Our studies demonstrate that Dp44mT significantly:1 increased activation of ER stress-associated pro-apoptotic signalling (i.e., p-eIF2α, ATF4 and CHOP);2 increased phosphorylation of IRE1α and XBP1 splicing;3 reduced the expression of molecules involved in ER stress-associated cell survival signalling (e.g., XBP1s and p58IPK);4 activated the transcription factor, ATF6, and its downstream targets (i.e., CHOP and BiP); and5 activated pro-apoptotic p-CaMKII. Moreover, it was demonstrated that anti-oxidants could inhibit TC-mediated activation of the UPR, while pro-oxidants enhanced activity. Moreover, PERK or IRE1α silencing reduced Dp44mT-mediated migration inhibition, demonstrating that PERK or IRE1α can regulate cell migration and the anti-cancer activity of Dp44mT. Conclusion Collectively, these results demonstrate that Dp44mT activates the pro-apoptotic pathways of the UPR, re-sensitising cancer cells to UPR-induced apoptosis while inhibiting cell survival signals. Considering UPR activation in cancers, it is crucial to characterise the effect of cancer therapeutics on the UPR to better predict clinical outcomes and the sub-populations of patients that will benefit from this type of therapy.