Effect of overexpression of ERK1/2 and MDR1 on chemoresistance in advanced gastric cancer patients

e16051 Background: Gastric cancer (GC) is late diagnosed disease with a poor prognosis. The emergence of multidrug resistance (MDR) increases the disease burden, and treatment failure in the patients. Several molecular and circulating biomarkers have been identified and evaluated for the clinical relevance in the management of gastric cancer. The aim of this study is to decipher the involvement of ERK1/2 and MDR1 in relation to MDR phenotype and major clinicopathological characteristics in gastric cancer patients. This will help to select effective drug combinations to improve the treatment success rate. Methods: This study recruited 64 individuals with newly diagnosed gastric cancer between 2019 and 2022. Patients were recommended for surgery or neoadjuvant chemotherapy (NACT). NACT group treated with docetaxel (60 mg/m2), oxaliplatin (85 mg/m2), leucovorin (200 mg/m2), and 5-fluorouracil (2,600 mg/m2 as a 24 hr infusion), all given on day 1 and administered every 2 weeks before surgery. Based on CECT report, patients were categorized as responders (CRs), partial responders (PRs), and non-responders (NRs). Tissue and blood samples were analyzed for ERK1/2 and MDR1expression using IHC, immuno-blotting and qRT-PCR analyses. Rhodamine123 (Rh123) accumulation assay and flowcytometry was performed to measure the degree of resistance among patients. Descriptive statistics, and Pearson’s Chi-square test was carried out to evaluate the expression distribution of ERK1/2 and MDR1. Results: Out of 64 patients, between the ages of 41-60 (53.08±10.51), 54.5% have ≥5 cm tumor size in the antrum site (56.1%) and diagnosed with stage III (56.1%). Majority of observations were intestinal type (60.6%) with lymphovascular invasion (71.2%). Among all 29.4%, 20.6% and 50.0% were CRs, PRs, & NRs respectively and 36.5% patients underwent NACT. The IHC scoring analysis revealed 25 (37.9%) & 18 (28.6%) individuals for ERK1/2 and 18 (27.3%) and 26 (39.4%) individuals for MDR1 had moderate to strong expressions respectively. Simultaneously, the expressions were highly significant with tumor site (antrum), tumor size (≥5 cm), wall thickening (radiological finding), signet ring cell carcinoma, grade 3, stage III (T3N2), NRs, lymphovascular, peritoneal and serosal invasions (p=0.000). ERK1/2 was more prevalent in diffuse type patients (p=0.000). Also, protein and mRNA level for both genes were more pronounced in NACT group (p<0.005). Flowcytometry showed FLOT receivers had lower Rh123 accumulation, indicating MDR1overexpression (11.5± 8.9) compared to baseline (49.5 ±38.3). The Pearson χ 2 test revealed positive correlation between ERK1/2 and MDR1 (p=0.000). Conclusions: ERK1/2 and MDR1 found to over-express in stage III, predicts the degree of resistance and MDR phenotype in the GC patients.