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.