Mechanisms of Platinum Chemoresistance in Lung Cancer
2019-08-22T01:16:56Z (GMT) by
Lung cancer is the leading cause of cancer-related death. Although platinum-based chemotherapy is the standard of care for most cases of advanced lung cancer, resistance limits its effectiveness. Initial treatments with platinum chemotherapies are effective in small cell lung cancer (SCLC); often resulting in a complete response with resistance being acquired after multiple rounds of chemotherapy. In contrast, initial adenocarcinoma response rates rarely exceed 20% suggesting that adenocarcinoma is innately resistant. I hypothesized that chemoresistance is mediated by one or more signalling pathways dependent on the expression of a single gene, and that these pathways could ultimately be targeted therapeutically. As such I set out to determine the mechanisms behind acquired resistance in SCLC and innate chemoresistance in lung adenocarcinoma. To address chemoresistance in SCLC, I first developed a cohort of patient derived xenografts, obtained using Endobronchial Ultrasound-Guided Transbronchial Needle Aspiration (EBUS-TBNA), a minimally invasive technique for biopsying lung cancer. From this cohort of PDXs, I generated an in vivo model of acquired resistance by treating mice with multiple rounds of chemotherapy. To identify mechanisms of chemoresistance, gene expression arrays comparing resistant and naïve tumours were performed, identifying differential expression in 767 genes. By comparing these genes to those identified in acute response to platinum, we identified Notch 3 as a potential target for the re-sensitization of acquired resistant SCLC to platinum. To address innate chemoresistance, I developed a synthetic-lethal high throughput xiv siRNA screen using the innately resistant A549 lung adenocarcinoma cell line. Optimisation of the screen was performed using a siRNA death control (PLK1), which induced cell death in the absence of platinum, and a sensitization control (MTOR), which enhanced cell death only in combination with a sublethal concentration of carboplatin. These independent controls revealed that the screening protocol performed within acceptable limits of variability, quality and reproducibility as determined by Z’ factor analysis. Screening was then performed using a pool of four siRNAs targeting a single gene in conjunction with vehicle treatment, or with carboplatin. After screening 18,000 siRNAs targeting coding sequences of the whole human genome, we identified 909 candidate targets based on fold change difference between platinum and vehicle treatments, and statistical significance determined by multiple t-test corrected for false discovery rate. From the screen I identified and validated several therapeutic targets. Of these Follistatin, an endogenous Activin/TGFβ superfamily ligand trap, was identified as a potent platinum sensitization agent. Importantly, Follistatin also has the potential to block Activin/TGBβ signaling in the setting of inflammation, fibrosis, renal injury, cachexia and anemia, all of which are commonly seen in lung cancer patients treated with platinum agents. I conclude that Follistatin therapy could improve the efficacy of platinum-based chemotherapy in lung adenocarcinoma, while at the same time ameliorate the systemic effects of both chemotherapy and malignancy. Additional material(s) submitted with thesis.