Standardization of a sample preparation and analytical workflow for proteomics of archival endometrial cancer tissue

The goal of the present study was to establish a standard operating procedure for mass spectrometry (MS)-based proteomic analysis of laser microdissected (LMD) formalin-fixed, paraffin-embedded (FFPE) uterine tissue. High resolution bioimage analysis of a large endometrial cancer tissue microarray immunostained for the breast cancer type 1 susceptibility protein enabled precise counting of cells to establish that there is an average of 600 cells/nL of endometrial cancer tissue. We sought to characterize the peptide recovery from various volumes of tissue gathered by LMD and processed/digested using the present methodology. We observed a nearly linear increase in peptide recovery amount with increasing tissue volume dissected. There was little discernible difference in the peptide recovery from stromal versus malignant epithelium, and there was no apparent difference in the day-to-day recovery. This methodology reproducibly results in 100 ng of digested peptides per nL of endometrial tissue, or ∼25 pg peptides/endometrial cancer cell. Results from liquid chromatography (LC)-MS/MS experiments to assess the impact of total peptide load on column on the total number of peptides and proteins identified from FFPE tissue digests prepared with the present methodology indicate a demonstrable increase in the total number of peptides identified up to 1000 ng, beyond which diminishing returns were observed. Furthermore, we observed no impact on the peptide identification rates from analyses of equivalent peptide amounts derived from lower volume LMD samples. These results show that this single-tube collection-to-injection proteomics (CTIP) workflow represents a straightforward, scalable, and highly reliable methodology for sample preparation to enable high throughput LMD-MS analysis of tissues derived from biopsy or surgery.