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P3.02c-010 Resistance Mechanisms to PI3K-mTOR Inhibition in NSCLC

Topic: Targeted Therapy

      Background

      Non-small cell lung cancer (NSCLC) is a leading cause of cancer mortality globally, having a 5 year survival rate of less than 15%. PI3K-mTOR signaling has been implicated in various hallmarks of cancer and this pathway is often dysregulated in NSCLC. Efforts to therapeutically target the PI3K-mTOR pathway have been hindered by emerging drug resistance. In this study, mechanisms of drug resistance were investigated in a H1975 cell line model of acquired resistance, following chronic exposure to a phase II PI3K-mTOR inhibitor (GDC-0980), Additionally, short term exposure of BEZ235 (another phase II PI3K-mTOR inhibitor) and IBL-301 (a novel PIM/PI3K/mTOR inhibitor) were investigated for effects on cell viability/proliferation and downstream signaling pathways.

      Methods

      Alterations to the mRNA expression profile of GDC-0980 acquired resistant H1975 cells versus matched parent cells were examined using an 84-gene IL-6/STAT3 signaling-specific profiler array. Subsequently, selected genes were validated by qPCR. The effectiveness of BEZ235 and IBL-301 on cell viability of two lung cancer cell lines (H1975 and H1838) following 72 hour treatment were investigated by Cell Titre Blue. pAkt and p4E-BP1 expression were examined by Western blot analyses following treatment with BEZ235 and IBL-301 at 3, 6 and 24 hours.

      Results

      Thirty candidate gene alterations were identified from the array profile and six genes were chosen for validation by qPCR (n=3). The pro-proliferative and pro-metabolic regulator mTOR and the anti-apoptotic protein BCL-2 were increased in GDC-0980 resistant cells (p<0.05 and p<0.001). Similarly, TNF-α and its receptor co-stimulatory molecule CD40 were increased (p<0.05 and p<0.01). Furthermore, the cell cycle inhibitor, CDKN1, and JAK-signaling blocker, SOCS1 were downregulated (both p<0.01) in GDC-0980 resistant cells. BEZ235 and IBL-301 had a dose-dependent effect on the viability of NSCLC cell lines with respective IC50 values of 9.42nM and 136.55nM in H1975 cells and 103.35nM and 159.27nM in H1838 cells. Treatments of 250nM BEZ235 or IBL-301 inhibited pAKt at all-time points in the lung cancer cell lines. BEZ235 blocked translation repressor protein (p4E-BP1) across all 3 cell lines and time points while IBL-301 treatment resulted in a reduction in p4E-BP1 at 24 hours.

      Conclusion

      This study highlights a number of genes involved in IL-6/STAT3 signaling that may contribute to PI3K-mTOR inhibitor resistance. BEZ235 and IBL-301 both decrease cell viability and inhibit PI3K pathway signaling and cap-dependent translation in NSCLC cell lines that warrant further investigation.

      Keywords

      PI3K-mTOR, IL-6/STAT3 signaling, resistance, NSCLC