Abstract P5-09-03: Intrinsic heterogeneity of triple-negative breast cancer cells triggers vascular mimicry in 3D matrigel matrix environment

Within the same tumor microenvironment phenotypic and functional heterogeneity arise among cancer cells as a consequence of genetic change, environmental differences, and reversible epigenetic changes in cellular properties. However, it is thought that cancer stem cells are drivers of drug resistance and metastasis. Individual tumor cells growing in culture also display heterogeneity in their intrinsic ability to progress and metastasize. It remains unclear whether intrinsic and extrinsic heterogeneity contribute to the emergence of distinct progressive phenotypes that contribute more to cancer stem cells to disseminate. To this study, we have examined the ability of matrigel to stimulate complex cell behavior that is a consequence of its heterogeneous composition. We have observed that mixing matrigel with metastatic triple negative breast cancer MDA-MB-231 cells, which mimic in vivo tumor microenvironment, around 80-90% cells created network like structures resembling a clinical phenotype known as vascular mimicry (VM) and around 10-20% cells form spheroids. BT549 another triple-negative breast cancer cells also responded similarly, forming cellular networks and spheroids when mixing with matrigel. Since CD44, a marker of epithelial-to-mesenchymal transition has shown enhances tumor aggressiveness by promoting cell plasticity, we decided to examine CD44 expression in MDA-MB-231 cells grown in 3D matrigel matrix environment. We have observed that VM forming cells are showing CD44 positive staining compared to spheroid forming cells which showed negative staining in formaldehyde-fixed 3D matrigel culture of MDA-MB-231 cells, while both group of cells stained positive for VEGFC. Next, we sought to isolate two phenotypically different groups of cells (VM and Tumorsphere forming cells) from the 3D matrigel culture by using microscopic suction procedure for gene expression analysis by qPCR. Our gene expression data suggested that VM forming cells have more expression of VM inducer genes such as CD44 and HIF1α compared to spheroid forming cells isolated from the same 3D matrigel culture of MDA-MB-231 cells. Spheroid forming cells express significant level of endothelial cell adhesion marker, CD31 compared to VM forming cells. Epigenetic mechanisms mediated suppression of tumor suppressors or anti-angiogenesis marker genes are hall mark of VM formation and cancer progression, we examine whether re-expression of those genes with Entinostat (MS-275), a selective inhibitor of class I histone deacetylase (HDAC) can abolish VM structures in 3D matrigel cell culture. Data suggested that MS-275 treatment in 3D culture drastically reduced VM structure by epigenetically re-expression of anti-angiogenic genes; SERPINF1, THBS1 and THBS2 and tumor suppressor genes; APC, PTEN and p21. While MS-275 treatment also downregulated Vimentin, VEGF-A and CD44. Our results suggest that the VM phenotype arises in a subpopulation of cells from a conserved transcriptional response in 3D matrigel environment. Epigenetically re-expression of anti-angiogenic gene expression could be a mechanism to control VM formation in triple-negative breast cancer cells.

Citation Format: Maiti A, Takabe K, Hait NC. Intrinsic heterogeneity of triple-negative breast cancer cells triggers vascular mimicry in 3D matrigel matrix environment [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P5-09-03.

L-myo-Inositol 1-phosphate synthase from Entamoeba histolytica

L-myo-Inositol 1-phosphate synthase (I-1-P synthase) catalyses the primary reaction for the synthesis of inositol in a variety of prokaryotes, eukaryotes and in the chloroplasts of algae and higher plants. Inositol is a precursor of essential macromolecules like membrane phospholipids, GPI anchor proteins and lipophosphoglycans, which play a determinant role in the pathogenesis of protozoan parasites such as Leishmania and Entamoeba. However, there is no report of I-1-P synthase or its gene from these organisms. The gene INO1 coding for this enzyme was first cloned from Saccharomyces cerevisiae and subsequently from several plants. Using molecular cloning techniques we have isolated and characterised the INO1 gene coding for the enzyme I-1-P synthase from Entamoeba histolytica. Simultaneously, we have purified and characterised the native enzyme from E. histolytica trophozoites and the cloned gene product from Escherichia coli. The gene product and the purified enzyme were both shown to be recognised by a heterologous anti-I-1-P synthase antibody from the phytoflagellate Euglena gracilis. Phylogenetic analysis of I-1-P synthase sequences from different eukaryotes suggest that it is highly conserved across species and the origin of this enzyme precedes the evolutionary divergence of modern eukaryotes.

L-myo-lnositol 1-Phosphate Synthase from Plant Sources (Characteristics of the Chloroplastic and Cytosolic Enzymes)

L-myo-inositol 1-phosphate synthase (EC 5.5.1.4) from cyanobacterial (Spirulina platensis), algal (Euglena gracilis), and higher plant (Oryza sativa, Vigna radiata) sources was purified to electrophoretic homogeneity, biochemically characterized, and compared. Both chloroplastic and cytosolic forms of the enzyme were detected in E. gracilis, O. sativa, and V. radiata, whereas only the cytosolic form was detected in streptomycin-bleached or chloroplastic mutants of E. gracilis and in S. platensis. Both the chloroplastic and cytosolic forms from different sources could be purified following the same three-step chromatographic protocol. L-myo-inositol 1-phosphate synthases purified from these different sources do not differ significantly with respect to biochemical and kinetic parameters except for the molecular mass of the chloroplastic and cytosolic native holoenzymes, which appear to be homotetrameric and homotrimeric associations of their constituent subunits, respectively. Monovalent and divalent cations, sugar alcohols, and sugar phosphates are inhibitory to the enzyme activity. N-ethylmaleimide inhibition of synthase activity could be protected by the combined presence of the substrate glucose-6-phosphate and cofactor NAD+. Antibody raised against the cytosolic enzyme from E. gracilis immunoprecipitates and cross-reacts with both chloroplastic and cytosolic forms from the other sources studied.