PO-325 Topological-proteomics of breast cancer intra-tumour heterogeneity reveals metabolic diversity within single tumours

Abstract

IntroductionOne of the major obstacles in breast cancer treatment is its high degree of heterogeneity and ambiguous classification. The molecular subtypes and histological subtypes are routinely defined in the clinic to determine treatment modalities; however often these distinct subtypes co-exist in single tumours and therefore lead to treatment resistance. Here, we aim to delineate the proteomic landscapes of breast cancer intratumoral diversity based on clinical-pathological parameters using mass spectrometry-based microproteomics.Material and methodsUsing histopathological analysis of immunostained formalin fixed paraffin embedded (FFPE) tissues, we assembled a cohort of more than 200 tumour regions comprising of different histopathological and molecular subtypes that originate from 22 patients. Cancer cell subpopulations were harvested using laser-capture microdissection (LCM) and labelled by TMT 10-plex. After protein digestion, peptides were analysed using high resolution quantitative mass spectrometry followed by computational analysis with MaxQuant.Results and discussionsTopological proteomic analysis revealed the proteomic portraits that are associated with each cancer cell subpopulation, with the association to its receptor expression level and histological characteristics. We found a clear proteomic distinction between moderately and poorly differentiated regions: moderately differentiated regions were primarily segregated based on their histological subtypes such as micropapillary vs. invasive ductal carcinoma-no special type, while poorly differentiated tumour regions were distinct based on the differential expression of the oestrogen, progesterone and Her2 receptors. We identified the significantly changing proteins between these subtypes, including significant differences in metabolic enzyme profiles between co-existing subtypes. For example, we found upregulated pentose-phosphate pathway in progesterone receptor positive regions and upregulated proline/arginine biosynthesis pathways in tumour regions with micropapillary features.ConclusionThese findings suggest that integrated topo-proteomic landscape of inter- and intratumoral heterogeneity can serve as a platform for deciphering the mechanisms underlying tumorigenesis, distinct metabolic profiles of cancer cell subpopulations, cancer evolution, and therapy resistance.