Yong-Yu Liu

Glucosylceramide Synthase, a Key Enzyme in Sphingolipid Metabolism, Regulates Expression of Genes Accounting for Cancer Drug Resistance

Emergent cancer drug resistance and further metastasis can mainly be attributed to altered expression levels and functional activities of multiple genes of cancer cells under chemotherapy. In response to challenge with anticancer drugs, enhanced ceramide glycosylation catalyzed by glucosylceramide synthase (GCS) confers drug resistance and enrichment with cancer stem cells. p53 mutations, which gain function in tumor progression, are prevalently extant in ovarian cancers. Via integrated gene expression assessments, we characterized GCS-responsive genes in ovarian cancer cells treated with dactinomycin. NCI/ADR-RES cells dominantly expressed a p53 mutant (7 aa deleted in exon-5) and displayed anti-apoptosis; however, silencing GCS expression rendered these cells sensitive to dactinomycin-induced apoptosis. Microarray analyses of NCI/ADR-RES and its GCS transfected sublines found that elevated GCS expression or ceramide glycosylation was associated with altered expression of 41 genes, notably coding for ABCB1, FGF2, ALDH1A3, apolipoprotein E, laminin 2, chemokine ligands, and IL6, with cellular resistance to induced apoptosis and enrichment with cancer stem cells, promoting cancer progression. These findings were further corroborated through integrated genomic analyses of ovarian cancer from The Cancer Genome Atlas (TCGA) and cancer resistance to platinum-based chemotherapy. Altogether, our present study indicates that altered ceramide glycosylation can modulate expression of these GCS-responsive genes and alter cancer cell attributes under chemotherapy.

Ceramide–Rubusoside Nanomicelles, a Potential Therapeutic Approach to Target Cancers Carrying p53 Missense Mutations

Abstract Ceramide (Cer) is an active cellular sphingolipid that can induce apoptosis or proliferation-arrest of cancer cells. Nanoparticle-based delivery offers an effective approach for overcoming bioavailability and biopharmaceutics issues attributable to the pronounced hydrophobicity of Cer. Missense mutations of the protein p53, which have been detected in approximately 42% of cancer cases, not only lose the tumor suppression activity of wild-type p53, but also gain oncogenic functions promoting tumor progression and drug resistance. Our previous works showed that cellular Cer can eradicate cancer cells that carry a p53 deletion-mutation by modulating alternative pre-mRNA splicing, restoring wild-type p53 protein expression. Here, we report that new ceramide–rubusoside (Cer–RUB) nanomicelles considerably enhance Cer in vivo bioavailability and restore p53-dependent tumor suppression in cancer cells carrying a p53 missense mutation. Natural RUB encapsulated short-chain C6-Cer so as to form Cer–RUB nanomicelles (∼32 nm in diameter) that substantially enhanced Cer solubility and its levels in tissues and tumors of mice dosed intraperitoneally. Intriguingly, Cer–RUB nanomicelle treatments restored p53-dependent tumor suppression and sensitivity to cisplatin in OVCAR-3 ovarian cancer cells and xenograft tumors carrying p53 R248Q mutation. Moreover, Cer–RUB nanomicelles showed no signs of significant nonspecific toxicity to noncancerous cells or normal tissues, including bone marrow. Furthermore, Cer–RUB nanomicelles restored p53 phosphorylated protein and downstream function to wild-type levels in p53 R172H/+ transgenic mice. Altogether, this study, for the first time, indicates that natural Cer–RUB nanomicelles offer a feasible approach for efficaciously and safely targeting cancers carrying p53 missense mutations.