Abstract
Lung cancer is the largest cause of cancer-related mortality worldwide and is the second most common cancer in New Zealand. By disproportionality impacting Māori and those who are most vulnerable in our community, lung cancer is a significant burden to New Zealand’s health system.
Despite advancements in lung cancer treatment, relapse remains common in patients undergoing therapy. In recent years, our understanding of the drug resistance mechanisms that lead to relapse has been challenged by the discovery of the phenomenon of drug tolerance driven by a rare subpopulation of cells called “drug tolerant persisters” (DTPs). A growing body of literature suggests that non-genetic mechanisms allow DTPs to change their identity to evade therapy by assuming a lung progenitor cell phenotype. We aimed to investigate the role of lung progenitor and stem cell genes in DTPs induced by three distinct targeted agents, and to identify genes as markers to determine whether DTPs exist prior to treatment or are induced upon addition of drug.
We generated DTPs in PC9, H3122 and H358 lung cancer cell lines with which contain oncogenic mutations in EGFR, ALK and KRAS, respectively. We found that the stem cell genes OCT3/4 and NANOG were upregulated by 4-fold (P<0.0005) and 2.5-fold (P<0.005) respectively in PC9 DTPs and by 6-fold (P<0.005) and 5-fold (P<0.0005) in respectively in H358 DTPs. SOX2, another stem cell gene, was found to be upregulated by 13-fold (P<0.005) in H3122 DTPs. Furthermore, our findings suggest that DTPs gain pluripotency by dedifferentiating back to a progenitor lung cell state, with the expression of the surfactant genes SFTPC and SFTPD being upregulated 5-fold (P<0.005), and 2.5-fold (P<0.05) in PC9 DTPs, 2-fold (P<0.05) and 5-fold (P<0.005) in H3122 DTPs and 5-fold (P<0.0005) and 9-fold (P<0.0005) in H358 DTPs respectively. Significantly, we identified AQP4 to be consistently upregulated in all three cell lines by at least 5-fold. AQP4 is a cell surface marker and thus will allow future studies to isolate DTPs from treated and untreated cell populations to determine whether DTPs are pre-existing or induced.
The information generated throughout this project has provided insight into the establishment of the DTP phenotype, which will inform future studies to exploit these findings. By understanding the mechanisms that underpin drug tolerance in lung cancer, it is hoped that we will eventually be able to prevent drug tolerance and the subsequent development of stable resistance in patients.