XPO1 inhibition by selinexor induces potent cytotoxicity against high grade bladder malignancies

Abstract

Treatment options for high grade urothelial cancers are limited and have remained largely unchanged for several decades. Selinexor (KPT-330), a first in class small molecule that inhibits the nuclear export protein XPO1, has shown efficacy as a single agent treatment for numerous different malignancies, but its efficacy in limiting bladder malignancies has not been tested. In this study we assessed selinexor-dependent cytotoxicity in several bladder tumor cells and report that selinexor effectively reduced XPO1 expression and limited cell viability in a dose dependent manner. The decrease in cell viability was due to an induction of apoptosis and cell cycle arrest. These results were recapitulated in in vivo studies where selinexor decreased tumor growth. Tumors treated with selinexor expressed lower levels of XPO1, cyclin A, cyclin B, and CDK2 and increased levels of RB and CDK inhibitor p27, a result that is consistent with growth arrest. Cells expressing wildtype RB, a potent tumor suppressor that promotes growth arrest and apoptosis, were most susceptible to selinexor. Cell fractionation and immunofluorescence studies showed that selinexor treatment increased nuclear RB levels and mechanistic studies revealed that RB ablation curtailed the response to the drug. Conversely, limiting CDK4/6 dependent RB phosphorylation by palbociclib was additive with selinexor in reducing bladder tumor cell viability, confirming that RB activity has a role in the response to XPO1 inhibition. These results provide a rationale for XPO1 inhibition as a novel strategy for the treatment of bladder malignancies.

p27/Kip1 functions as a tumor suppressor and oncoprotein in osteosarcoma

“…S15). Decreases in the expression levels of XPO1 protein by Selinexor are reported in other studies 24 and are associated with decreased cell proliferation and apoptosis, mediated by survivin. Immunofluorescence staining confirmed that p27 was localized predominantly in the nucleus in cells that were exposed to Selinexor, Fig.…”

“…Using the approach of selective inhibition of nuclear export (SINE) with siRNA mediated knockdown of XPO1, our results show that in order to execute its anti-apoptotic function, p27 protein must be stabilized in the nucleus and the combined inhibition of cell cycle progression and XPO1 activity, maintains p27 nuclear localization and promotes tumor suppressor function. These findings are of interest as SINE agents such as Selinexor show promising clinical activity against multiple myeloma growth 32 , bladder cancer 24 as well as other types of cancer that is mediated through the survivin pathway. Of note, Selinexor did not achieve single agent activity against the Pediatric Preclinical Testing Consortium osteosarcoma xenograft tumor panel 33 .…”

The selective inhibitor of nuclear export (SINE) verdinexor exhibits biologic activity against canine osteosarcoma cell lines

“…To assess if canine OS cells responded similarly, we treated four cell lines with 0.1% DMSO, 0.1 μM verdinexor, or 1 μM verdinexor for 24 hours and evaluated XPO1 expression via quantitative real‐time PCR and Western blotting (Figure 4). Similar to previously published results, we found that treatment with verdinexor caused a reduction in XPO1 protein expression 35,36 . Additionally, XPO1 mRNA was significantly increased in all cell lines tested.…”

“…Concordant with our data, XPO1 is overexpressed in human OS compared with normal tissues 19 . Similarly, XPO1 is overexpressed in a number of human cancers such as gastric, oesophageal, bladder, and multiple myeloma and increased XPO1 expression has been associated with poor survival outcome 22,34‐36 . Although the prognostic impact of XPO1 expression in canine OS was not evaluated in this study, we demonstrated that XPO1 overexpression is common event in canine OS cells and as such, XPO1 may represent a relevant target for therapeutic intervention.…”

Characterization of mRNA Expression and Endogenous RNA Profiles in Bladder Cancer Based on The Cancer Genome Atlas (TCGA) Database

“…Molecular and genetic alterations in bladder cancer have been extensively studied in the past decades. Clinicopathological features, including tumor grade and stage have been shown to be linked to biological and genetic mechanisms [22–24]. However, clinical challenges still exist for bladder cancer making it crucial to focus on new prediction methods based on the molecular targets.…”