GLUCOSYLCERAMIDE SYNTHASE IN A NOVEL TARGET FOR CANCER TREATMENT

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Characterizing gene underlying drug resistance, as a novel therapeutic target can significantly improve cancer treatment. Glucosylceramide synthase (GCS), a key enzyme for ceramide glycosylation, is overexpressed in various drug-resistant cancer cell lines and in metastatic tumors. High GCS activity confers cell resistance by disrupting ceramide-induced apoptosis that is tightly associated with the efficiency of anthracycline, vinca alkaloids and taxanes. To determine whether GCS is a target for the reversal of drug resistance, we evaluated the effects of antisense approach against GCS in vitro and in vivo. MBO-asGCS (mixed-backbone oligonucleotide, 20-mer) was designed to silence human GCS gene. MBO-asGCS substantially increased doxorubicin sensitivity in drug-resistant human (MCF-7-AdrR) and murine breast cancer cells (EMT6/AR1) by 83-fold and 43-fold, respectively. In contrast, MBO-asGCS only increased the doxorubicin cytotoxicity by twofold in drug-sensitive cells and did not affect that cytotoxicity in human bone marrow mononuclear cells. In the orthotopic tumor model for drug-resistant breast cancer (MCF-7-AdrR), we found that MBO-asGCS significantly inhibited tumor growth and sensitized tumors to chemotherapy. The administration of MBO-asGCS (1 mg/kg/3-day, 42 days) inhibited tumor growth more than 64% (356 vs 983 mm3, N=10) and increased doxorubicin-sensitivity by 58% (187 vs. 432 mm3, N=10), compared to MBO-scrambled alone and the combination of MBO-scrambled with doxorubicin (2 mg/kg/week), respectively. Further assessments of GCS gene expression levels, ceramide glycosylation, and apoptosis demonstrated that the effects of MBO-asGCS in vivo rely on the suppression of endogenous GCS overexpressed and the enhancement of ceramide-induced apoptosis. These evidences pinpoint that GCS is a novel target for the reversal of drug resistance in cancers.