Proteomic profiling of antibody-drug conjugate (ADC) biomarkers in pancreatic cancer.

671 Background: Pancreatic cancer (PaC) is a highly fatal disease with a 5-year survival rate of 5-10%. Effective screening is not available, and most patients (50-55%) present with metastatic (50%-55%) disease at diagnosis. For patients with advanced PaC, the standard chemotherapy combinations include FOLFIRINOX and/or gemcitabine/nab-paclitaxel which has results in a overall survival of 7-11 months. The lack of effective therapies underscores the importance of exploring other agents. We propose that quantitating therapy-associated protein biomarkers including markers of antibody-drug conjugates (ADC) can improve treatment personalization for PaC. Methods: FFPE tumor tissues from 185 clinical PaC patients were microdissected and solubilized for mass spectrometry-based targeted proteomic analysis. We quantified biomarkers for ADCs simultaneously from 2-3 section of FFPE. These biomarkers include antibody targets such as EGFR, HER2, HER3, FRalpha, and Trop2 and payload biomarkers of sensitivity (TOPO1) and resistance (TUBB3). The multiplexed assay also quantified additional 65 clinically relevant protein biomarkers for chemotherapy, immunotherapy and targeted therapy. Results: Expression of EGFR was observed in majority of samples (88%) while only overexpressed ( > 1000 amol/µg) in 3% of samples. HER2 was expressed in half of patients (52%) and overexpressed ( > 750 amol/µg) in 5% of cases while the rest of HER2 protein expression ranged from 300 -750 amol/µg which corresponds to low Her2 expression. Trop2 was expressed in majority of patients (91%) with a 25x distribution between lowest and highest expressor. Other ADC biomarkers include HER3(55%, 5x), Axl (24%, 12x), Mesothelin (65%, 58x), Folate receptor alpha (10%, 17x). Expression of TUBB3 (77%, 8x) and TOPO1 (92%, 8x) in antibody target-positive subset may suggest resistance or response for several known payloads, such as taxanes and irinotecan/deruxtecan/govitecan, respectively. Conclusions: There is currently no approved ADC for pancreatic cancer, but several ADC clinical trials are underway. Quantitative proteomics identified antibody targets as well as markers of resistance or response to payloads for a variety of approved and investigational ADC therapies, which could aid in patient stratification in ADC clinical trials.