HETEROCELLULAR INTERACTION IN ORGAN SPECIFIC METASTASIS OF PROSTATE AND BREAST CANCER CELLS TO THE BONE: EXPLORING A ROLE FOR NUCLEOPHOSMIN-1

Abstract

Background: Metastasis remains the central feature of cancer malignancy and causes most of cancer-related deaths. Organo-tropic metastasis is defined as the preference of cancer cells to colonize select distant organs from the primary tumor. Breast and prostate cancers account for a high number of patients, and bone is their preferential site of metastasis. Nucleophosmin 1 (NPM1), a key regulator in multiple physiological processes including ribosomal biogenesis, is over expressed in solid tumors. NPM1 high expression correlates with invasiveness, metastasis, angiogenesis and poor survival outcomes in patients.

Aim: Unravelling NPM1 mediated cellular and molecular mechanisms and their potential to govern breast and prostate cancer cells’ colonization of bone presents an opportunity to target cancer metastasis.

Materials and Methods: Highly metastatic (MDA-MB-231 and PC3) and low metastatic (MCF-7 and LNCaP) breast and prostate cancer cells were utilized. NPM1 expression and its impact on ribosomal biogenesis were assessed by western blot and real time PCR respectively. EMT markers, and angiogenesis were assessed by real time PCR. Interaction of breast and prostate highly metastatic cancer cells with endothelial cells was assessed by adhesion and dye transfer assays screened by flow cytometry. To study the role of NPM1 in the extravasation of breast and prostate cancer cells to the bone, mesenchymal stem cells were differentiated into osteoblasts and co-cultured with MDA-MB-231 and PC3, before screening for NPM1 localization by confocal microscopy.

Results: Our findings indicate that breast and prostate cancer cells with high metastatic potential (MDA-MB 231 and PC3) proliferate at a higher rate than cells with low metastatic potential (MCF-7 and LNCaP). We also demonstrated that NPM1 expression is higher in high metastatic tumors than in low metastatic tumors. Low metastatic tumors exhibited a more differentiated phenotype (with higher expression of epithelial markers), while high metastatic tumors displayed an undifferentiated phenotype (higher expression of mesenchymal markers). The interaction between cancer cells and endothelial cells is regulated by adhesion molecules that facilitate i this interaction during extravasation. Finally, co-culture of differentiated mesenchymal stem cells with MDA-MB-231 or PC3 resulted in a shift in NPM1 localization from the cytoplasm to the nucleus, at day 21 of co-culture, indicating a role of NPM1 in metastasis.

Conclusion: These findings may provide insights into the molecular mechanisms underlying the metastatic progression of breast and prostate cancers in the context of NPM1, which may aid in the development of new therapies for these diseases.