Abstract 1697: Role of intra-tumoral bacteria in EGFR-tyrosine kinase inhibitor resistance

Abstract Although most lung cancers with EGFR-mutation respond to osimertinib, resistance eventually develops, and there are no approved targeted therapies once resistance to osimertinib occurs. Intra-tumoral bacteria are emerging as a cause of therapy resistance in cancer. In order to determine if intra-tumoral bacteria play a role in the resistance of EGFR-mutant lung cancers to EGFR-TKIs, including osimertinib, we used a bacterial pre-conditioned medium (PCM) screening system which utilized various bacteria identified in lung cancer specimens. We used a cell viability evaluation method in GFP-labeled PC9 cells (EGFR Ex19del) to identify the bacterial PCM that may lead to resistance to EGFR-TKIs. We found that PCM from Chryseobacterium indologenes (C-PCM) markedly rescued PC9 from osimertinib. Furthermore, we found that C-PCM also could increase cell viability in other EGFR-mutated cell lines HCC4006, HCC827, and H1650. We found that proteinase K treatment eliminated the rescue of C-PCM on EGFR-TKI treatment, indicating that proteins within C-PCM are responsible for its effect of EGFR-TKI treatment. Mass spectrometry (MS) analysis showed that C-PCM does not degrade osimertinib, suggesting that C-PCM mediated resistance does not occur through drug degradation. To understand the mechanism by which C-PCM meditates resistance to osimertinib in NSCLC, we performed phosphor-Receptor Kinase Array to detect changes in phosphorylation between C-PCM and non-C-PCM treatment in PC9 cells. This showed no change in phosphorylation levels of EGFR, indicating that rescue from osimertinib is not through re-activation of EGFR pathway. However, phosphorylation levels of MET and IGF1R were significantly increased when C-PCM was applied to PC9 cells regardless of the presence or absence of osimertinib. Knockdown of IGF1R significantly increased the sensitivity of PC9 cell to osimertinib. Similar results were observed in siMET-PC9 cells. Interestingly, we found that C-PCM lost its ability to rescue PC9 cells from osimertinib when IGF1R was knocked down. Also, inhibition of IGF1R activation by the IGF1R inhibitor linsitinib increased PC9 cell sensitivity to osimertinib, and C-PCM rescue ability decreased with increased linsitinib concentration. Even though MET knockdown increased PC9 cell sensitivity to osimertinib, C-PCM still could increase cell viability with MET knockdown. These results together indicate that activation of IGF1R may be the main pathway that mediates Chryseobacterium indologenes resistance to osimertinib. Further mechanistic studies of C-PCM mediated resistance are underway to understand the precise mechanism of bacterial-mediated EGFR-TKI resistance. Additional research on the clinical relevance of these findings may lead to new strategies to overcome EGFR-TKI-resistance. Citation Format: Wendong Li, Keqiang Zhang, Aviva Rotter-Maskowitz, Deborah Nejman, Ravid Straussman, Dan Raz. Role of intra-tumoral bacteria in EGFR-tyrosine kinase inhibitor resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1697.