Ceramide synthase inhibitor fumonisin B1 inhibits apoptotic cell death in SCC17B human head and neck squamous carcinoma cells after Pc4 photosensitization

Abstract

The sphingolipid ceramide modulates stress-induced cell death and apoptosis. We have shown that ceramide generated via de novo sphingolipid biosynthesis is required to initiate apoptosis after photodynamic therapy (PDT). The objective of this study was to define the role of ceramide synthase (CERS) in PDT-induced cell death and apoptosis using fumonisin B1 (FB), a CERS inhibitor. We used the silicon phthalocyanine Pc4 for PDT, and SCC17B cells, as a clinically-relevant model of human head and neck squamous carcinoma. zVAD-fmk, a pan-caspase inhibitor, as well as FB, protected cells from death after PDT. In contrast, ABT199, an inhibitor of the anti-apoptotic protein Bcl2, enhanced cell killing after PDT. PDT-induced accumulation of ceramide in the endoplasmic reticulum and mitochondria was inhibited by FB. PDT-induced Bax translocation to the mitochondria and cytochrome c release were also inhibited by FB. These novel data suggest that PDT-induced cell death via apoptosis is CERS/ceramide-dependent.

C6-pyridinium ceramide sensitizes SCC17B human head and neck squamous cell carcinoma cells to photodynamic therapy

“…As depicted in Figure 2, combining PDT with LCL29 led to a significant reduction in survival. We have previously shown that FB and the pancaspase inhibitor zVAD protected cells from death after PDT [17]. Apoptosis is induced after LCL29 [25].…”

“…We have shown that PDT-induced mitochondrial ceramide accumulation is FB-sensitive [17]. Although it has been shown that LCL29 accumulates in mitochondria of HNSCC cells [6], it is not known whether mitochondrial ceramide accumulation is induced after LCL29 alone or in combination with PDT.…”

“…The mitochondrial apoptosis pathway, including cyt c release, is induced by PDT and LCL29 [17, 25, 27]. Both of these processes are inhibited by FB after PDT [17].…”

“…Ceramide is generated from dihydroceramide subsequently. FB rescues cells from mitochondrial apoptosis after radiation [16], as well as from cell death after PDT [17]. SCC17B cells were chosen for the study as a clinically-relevant HNSCC model because the cells were derived from a non-metastatic cancer of the larynx, a PDT-treatable HNSCC type [18].…”

Enhanced apoptotic cancer cell killing after Foscan photodynamic therapy combined with fenretinide via de novo sphingolipid biosynthesis pathway

“…Sphingolipids include membrane-bound bioactive lipids that can act as anticancer agents [2]. We and others have shown that stresses, including Pc4-mediated PDT, can perturb the de novo sphingolipid biosynthesis (DNS) pathway, leading to changes in the levels of its intermediates, which are potent regulators of cell death [3] [4]. The DNS pathway includes a ceramide synthase (CERS)-dependent addition of a fatty acyl group to dihydrosphingosine resulting in production of dihydroceramide, which is then converted in a desaturase (DES)-dependent reaction to ceramide.…”