Tuberous sclerosis complex 1 is associated with primary resistance to osimertinib in a lung adenocarcinoma cell line

<p>【Introduction】Osimertinib, an epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI), is effective in the EGFR mutation positive lung cancer, but 5-15% of patients show primary resistance. Tuberous sclerosis complex 1 (TSC1) is a tumor suppressor gene that negatively regulates mammalian target of rapamycin (mTOR) and frequently mutated in lung adenocarcinoma. Autophagy, regulated by mTOR, is closely linked to EGFR-TKI resistance. Although the relationship between TSC1 and EGFR-TKI resistance remains to be unclear, we investigated the role of TSC1 in primary osimertinib resistance.【Methods】We utilized an EGFR mutation positive lung adenocarcinoma cell line (PC9). Western blotting was used to analyze TSC1 and LC3B-II (an autophagy marker) in PC9 cells treated with osimertinib (0.01-5 μM) for 24 hours. Knockdown of TSC1 was performed by transfection of PC9 cells with 10 nM TSC1 siRNAs (si-TSC1). In PC9 cells with si-TSCl, the proliferation rate with 1-5 μM osimertinib was monitored in real-time with the xCELLigence system. Cell viability was also assessed by ATP quantification with 1 μM osimertinib.【Results】TSC1 and LC3B-II in PC9 cells were increased in an osimertinib concentration-dependent manner. In PC9 cells with si-TSC1, LC3B-II was downregulated, indicating that the autophagy was decreased. Knockdown of TSC1 significantly reduced the proliferation rates and cell viability in the presence of 1-5 μM osimertinib. In contrast, knockdown of TSC1 in the absence of osimertinib had no significant effect on cell proliferation rates and cell viability. These results showed that inhibition of TSC1 was associated with improving sensitivity to osimertinib.【Conclusion】This study suggests that TSC1 could be involved in regulating autophagy and also lead to primary osimertinib resistance in a human lung adenocarcinoma cell line. TSC1 loss-of-function mutations could be a potential biomarker for osimertinib therapy and require further clinical study.</p>