1682P Development of an ex vivo RNA-based predictive assay for tumor tissue explants

Abstract

Tumor tissue explants are an attractive tool for personalized predictive tests, however their use is compromised by subjective nature of morphological assessment of drug response. We aimed to identify reporter genes, which rapidly change their level of expression in drug-sensitive but not in drug-resistant tumors. Fresh tumor tissues were obtained from patients with non-small cell lung cancer (NSCLC) undergoing surgery. Tumor 0.4-mm-thick slices were generated with a tissue chopper. NSCLC explants were cultured for 24 hours in a standard media containing either 8 or 16 mkg/ml of gefitinib or no drug (control). NGS-based transcriptome analysis was performed for explants from EGFR-mutated (n = 4) and non-mutated (n = 5) tumors before and after gefitinib exposure. Thirty genes were responsive to gefitinib exposure in EGFR-mutant but not in the EGFR wild-type tumor tissue explants. There were several genes demonstrating evident up-regulation in drug responders, e.g., HSPA1A (a member of the heat shock protein 70 family), RSPO3 (a component of receptor tyrosine kinase signaling pathways) and CDKN1C (a tumor suppressor gene capable of causing cell cycle arrest). Some genes were downregulated in response to gefitinib in drug-sensitive tumors, e.g., MUC13, which contributes to lung cancer progression via activation of the ERK/JNK/p38 signaling cascade. The obtained data were replicated by PCR tests both in samples analyzed by RNAseq and in additional lung tumors. This study revealed a number of gefitinib-responsive genes, which may serve as RNA markers of drug sensitivity in an ex vivo assay. Appropriately designed PCR tests can potentially be used for the analysis of small tumor samples, e.g., tissue biopsies. It remains to be studied, whether the suggested approach is feasible for the prediction of tumor sensitivity to other targeted and cytotoxic drugs.