Effect of selinexor on lipogenesis in virus-positive Merkel cell carcinoma cell lines

Abstract

Background: Merkel cell carcinoma (MCC) is a highly aggressive neuroendocrine cutaneous carcinoma aetiologically linked to the Merkel cell polyomavirus (MCPyV). Immune checkpoint inhibitors are currently the first-line therapy for metastatic MCC; however, the treatment is effective in only about half of patients, highlighting the need for alternative therapies. Selinexor (KPT-330) is a selective inhibitor of nuclear exportin 1 (XPO1) and has been shown to inhibit MCC cell growth in vitro, but the pathogenesis has not been established. Decades of research have established that cancer cells significantly upregulate lipogenesis to meet an increased demand for fatty acids and cholesterol. Treatments that inhibit lipogenic pathways may halt cancer cell proliferation.

Aim: To determine the effect of increasing doses of selinexor on fatty acid and cholesterol synthesis in MCPyV-positive MCC (MCCP) cell lines and aid in elucidating the mechanism by which selinexor prevents and reduces MCC growth.

Methods: MKL-1 and MS-1 cell lines were treated with increasing doses of selinexor for 72 h. Protein expression quantification was determined using chemiluminescent Western immunoblotting and densitometric analysis. Fatty acids and cholesterol were quantified using free fatty acid assay and cholesterol ester detection kits.

Results: Selinexor causes statistically significant reductions of the lipogenic transcription factors sterol regulatory element-binding proteins 1 and 2, and lipogenic enzymes acetyl-CoA carboxylase, fatty acid synthase, squalene synthase and 3β-hydroxysterol Δ-24-reductase in a dose-dependent manner in two MCCP cell lines. Although inhibiting the fatty acid synthesis pathway results in meaningful decreases in fatty acids, the cellular cholesterol levels did not demonstrate such reductions.

Conclusion: For patients with metastatic MCC refractory to immune checkpoint inhibitors, selinexor may provide clinical benefit through the inhibition of the lipogenesis pathway; however, further research and clinical trials are needed to evaluate these findings.