The Sphingosine Kinase 2 Inhibitor ABC294640 Restores the Sensitivity of BRAFV600E Mutant Colon Cancer Cells to Vemurafenib by Reducing AKT-Mediated Expression of Nucleophosmin and Translationally-Controlled Tumour Protein

Abstract

Vemurafenib (PLX4032), small-molecule inhibitor of mutated BRAFV600E protein, has emerged as a potent anti-cancer agent against metastatic melanoma harboring BRAFV600E mutation. Unfortunately, the effect of PLX4032 in the treatment of metastatic BRAF mutated colorectal cancer (CRC) is less potent due to high incidence of fast-developing chemoresistance. It has been demonstrated that sphingolipids are important mediators of chemoresistance to various therapies in colon cancer. In this study, we will explore the role of major regulators of sphingolipid metabolism and signaling in the development of resistance to vemurafenib in BRAF mutant colon cancer cells. The obtained data revealed significantly increased expression levels of activated sphingosine kinases (SphK1 and SphK2) in resistant cells concomitant with increased abundance of sphingosine-1-phosphate (S1P) and its precursor sphingosine, which was accompanied by increased expression levels of the enzymes regulating the ceramide salvage pathway, namely ceramide synthases 2 and 6 and acid ceramidase, especially after the exposure to vemurafenib. Pharmacological inhibition of SphK1/SphK2 activities or modulation of ceramide metabolism by exogenous C6-ceramide enhanced the anti-proliferative effect of PLX4032 in resistant RKO cells in a synergistic manner. It is important to note that the inhibition of SphK2 by ABC294640 proved effective at restoring the sensitivity of resistant cells to vemurafenib at the largest number of combinations of sub-toxic drug concentrations with minimal cytotoxicity. Furthermore, the obtained findings revealed that enhanced anti-proliferative, anti-migratory, anti-clonogenic and pro-apoptotic effects of a combination treatment with ABC294640 and PLX4032 relative to either drug alone were accompanied by the inhibition of S1P-regulated AKT activity and concomitant abrogation of AKT-mediated cellular levels of nucleophosmin and translationally-controlled tumour protein. Collectively, our study suggests the possibility of using the combination of ABC294640 and PLX4032 as a novel therapeutic approach to combat vemurafenib resistance in BRAF mutant colon cancer, which warrants additional preclinical validation studies.

Therapeutic Potential for Sphingolipids in Inflammatory Bowel Disease and Colorectal Cancer

“…In addition, ABC294640 has been shown to result in degradation of DES1 and SK1 [66]. Human CRC cell lines dosed with ABC294640 in combination with Vemurafenib, a common chemotherapeutic used in melanoma, demonstrated significant inhibition of SK2, reduced S1P content, and induction of apoptosis [67]. Further analysis revealed significant reductions in the phosphorylation and/or protein content of AKT, ERK1/2, and MEK1/2, suggesting that treatment restricted aberrant cell signaling.…”

Natural Products and Small Molecules Targeting Cellular Ceramide Metabolism to Enhance Apoptosis in Cancer Cells

“…However, ABC294640 has recently been reported to have an off-target effect of acting as a tamoxifen-like molecule with the estrogen receptor [ 69 ]. A recent study has shown that the sensitivity of BRAFV600E mutant colon cancer cells to Vemurafenib can be increased by reducing the AKT-mediated expression of nucleophosmin and translationally controlled tumor protein [ 70 ]. This study highlights the significance of sphingolipid biochemistry and targeting multiple pathways in combination in order to achieve effective cancer therapies.…”

Venetoclax resistance induced by activated T cells can be counteracted by sphingosine kinase inhibitors in chronic lymphocytic leukemia

“…In addition, others found that safingol, a known SPHK1 inhibitor which was recently found to be a substrate for SPHK2 ( 20 ), potentiates the anti-cancer effect of a botanical drug called Polyphenon E™ ( 21 ). In solid tumors, opaganib, an orally active, isozyme-selective inhibitor of SPHK2 with antitumor and anti-inflammatory activity, which can be safely administered to severely compromised patients with solid and hematological tumors or Covid-19 ( 22 ), restores the sensitivity of BRAFV600E mutant colon cancer cells to vemurafenib ( 23 ) and it has being studied in clinical trials with patients with metastatic castration-resistant prostate cancer progressing on abiraterone or enzalutamide (NCT04207255) and with advanced cholangiocarcinoma patients in combination with hydroxychloroquine sulfate (NCT03377179). The combination of SPHK inhibitors and venetoclax in CLL cells was not evaluated yet.…”