Abstract

As the paradigm of treating patients in the clinic shifts towards precision medicine, new strategies are needed to test clinical samples at the level of individual molecules. We developed a new approach to perform quantitative single molecule localization microscopy (qSMLM) on two types of clinical samples: patient tissues and extracellular vesicles secreted by patient cells. We optimized methodology for preparing the clinical samples, performing qSMLM imaging, and analyzing the resulting data sets. The approach allowed us to 1) quantify the density of biomolecules, and 2) define how individual molecules are organized in the patient specimen. Specifically, we assessed human epidermal growth factor receptor 2 (HER2) in tissues from breast cancer patients. Using an anti-HER2 therapeutic antibody called trastuzumab, we quantified both the density and nano-organization of HER2; the results provided a readout on receptors with an available drug binding site [1]. Importantly, we observed a significant positive correlation between the detected densities from qSMLM and HER2 copy numbers from a clinical assay. In addition to assessing tissue samples, we used qSMLM to quantify both the size and molecular content of extracellular vesicles from plasma of pancreatic cancer patients. Compared to healthy controls, patients with pancreatic cancer exhibited a distinct population of larger extracellular vesicles enriched in two biomarkers: epidermal growth factor receptor and carbohydrate antigen 19-9 [2]. Altogether, these results support pairing qSMLM with clinical assays to ultimately advance precision medicine.