Arginine methylation of EGFR in circulating tumor cells: A new biomarker for predicting resistance to anti-EGFR agents.

Abstract

3590 Background: Arginine methylation of the epidermal growth factor receptor (meEGFR) increases binding affinity of EGF and other EGFR ligands, reduces the efficacy of anti-EGFR agents in vivo, and is reported to have a role in predicting response to anti-EGFR agents. This study aimed to investigate the predictive impact of meEGFR in metastatic colorectal cancer (mCRC) patients (pts) treated with anti-EGFR agents using blood-based testing. Methods: 15 mL of blood were collected from mCRC pts with documented disease progression following anti-EGFR treatment (Rx). Circulating tumor cells (CTCs) were isolated using antibody (ab)-independent micro-fluidic cassette-based technology (Parsortix system), which separates CTCs on the basis of size and deformability. CTCs were identified based on negative staining for CD45ab and positive staining for EpCAMab. meEGFR was identified based on positive staining for me-R198/200ab on CTCs. Associations between meEGFR-CTCs and total CTCs with progression free survival (PFS) were determined by Kaplan-Meier method and compared by the log-rank test. Results: A total of 47 mCRC pts were prospectively included in this study. CTCs were identified in 30 out of 47 cases (64%). Of those 30, meEGFR-CTCs were identified in 19 cases (63%). Mean total CTCs and meEGFR-CTCs counts were 3.6 (range 0-52) and 2.3 (range 0-30) cells per 7.5ml, respectively. There was no association between meEGFR-CTCs and clinic-pathological features (age, sex, tumor site & grade), line of anti-EGFR Rx, previous irinotecan used, or NRAS, BRAF, PIK3CA, and MSI status. However, in RASwt/BRAFwtmCRC pts, high levels of meEGFR ratio (defined as > 0.25 meEGFR-CTCs per total CTCs) was associated with significantly inferior PFS with anti-EGFR Rx (median PFS 5.4 mo vs. 8 mo, HR 3.4, 95% CI of 1.5-7.9, P = 0.004). By contrast, high levels of total CTCs ( > 3 cells/per 7.5 ml) had no impact on PFS with anti-EGFR Rx. Conclusions: We have successfully isolated CTCs from mCRC pts’ blood using Parsortix system. Elevated levels of arginine methylated EGFR is associated with a shorter PFS with anti-EGFR-based Rx. Assessment of meEGFR-CTCs may provide a “liquid biopsy” biomarker for reduced efficacy from anti-EGFR Rx.