Nucleophosmin-1: A Potential Therapeutic Target in Metastatic Breast Cancer

Abstract

Background: Despite the advent of novel cancer therapeutics, metastasis remains the primary cause of cancer patient mortality. Metastasis is the colonization of secondary organs from a tumor's primary site. According to international databases, breast cancer (BC) is classified among the most prevalent cancers, with an alarming rise in the mortality-to-incidence ratio in the Middle East. We and others highlighted the significant role of Nucleophosmin-1 (NPM1) in various cancers. NPM1, a multifunctional chaperone protein, is overexpressed in triple-negative breast cancer (TNBC), a highly aggressive metastatic subtype of BC. The overexpression of NPM1 in this cancer is linked to poor patient survival. Methods: The TNBC MDA-MB-231 cell line was used in our study. Short hairpin RNA was used to downregulate NPM1 expression. The effect of NPM1 downregulation on cell proliferation and transcriptomic changes was assessed by the trypan blue exclusion dye assay and RNA sequencing, respectively. The impact of NPM1 silencing in MDA MB-231 on tumor size and metastasis to the liver, lung, and brain was also evaluated in vivo. Targeting the NPM1 downstream AKT/mTOR pathway was also performed using Arsenic trioxide (ATO), all-trans-retinoic acid (RA), and Everolimus (EV). The effect on proliferation and molecular components of this pathway were investigated in vitro by trypan blue exclusion assay and in vivo by monitoring mice survival. Results: Our findings revealed that stable knockdown of NPM1 in MDA-MB-231 cells reduced cell proliferation and reversed the mesenchymal phenotype of these cells towards a more epithelial phenotype. Knocking down NPM1 impaired tumor growth in vivo and abrogated the metastasis of TNBC cells into the lungs, livers, and brains. Pharmaceutical targeting of the NPM1 downstream AKT/mTOR pathways with ATO/RA/EV drug drastically decreased cell proliferation and inactivated this pathway in vitro, with a higher sensitivity to drugs in MDA-shNPM1 cells. Finally, this triple combination significantly prolonged the survival of MDA-MB-231 xenografted mice and resulted in a total cure of 20% of the treated mice. Conclusion: Our findings reveal that NPM1 plays a role in TNBC metastasis and supports the potential of using the combination of ATO, RA, and EV as a combination treatment to combat TNBC metastasis.