Abstract
Enhanced ceramide glycosylation catalyzed by glucosylceramide synthase (GCS) limits therapeutic efficiencies of antineoplastic agents including doxorubicin in drug-resistant cancer cells. Aimed to determine the role of GCS in tumor response to chemotherapy, a new mixed-backbone oligonucleotide (MBO-asGCS) with higher stability and efficiency has been generated to silence human GCS gene. MBO-asGCS was taken up efficiently in both drug-sensitive and drug-resistant cells, but it selectively suppressed GCS overexpression, and sensitized drug-resistant cells. MBO-asGCS increased doxorubicin sensitivity by 83-fold in human NCI/ADR-RES, and 43-fold in murine EMT6/AR1 breast cancer cells, respectively. In tumor-bearing mice, MBO-asGCS treatment dramatically inhibited the growth of multidrug-resistant NCI/ADR-RE tumors, decreasing tumor volume to 37%, as compared with scrambled control. Furthermore, MBO-asGCS sensitized multidrug-resistant tumors to chemotherapy, increasing doxorubicin efficiency greater than 2-fold. The sensitization effects of MBO-asGCS relied on the decreases of gene expression and enzyme activity of GCS, and on the increases of C18-ceramide and of caspase-executed apoptosis. MBO-asGCS was accumulation in tumor xenografts was greater in other tissues, excepting liver and kidneys; but MBO-asGCS did not exert significant toxic effects on liver and kidneys. This study, for the first time in vivo, has demonstrated that GCS is a promising therapeutic target for cancer drug resistance, and MBO-asGCS has the potential to be developed as an antineoplastic agent.
Highlights
Chemotherapy remains a standard treatment for patients with metastatic cancers
We found that resistant NCI/ADR-RE cells took up approximately the same amount, 20% of total Cy3-Mixed-backbone oligonucleotide (MBO)-asGCS, as drug-sensitive MCF-7 cells (Fig. 1a) in 4 hr of transfection
We examine the effect of MBO against glucosylceramide synthase (GCS) on cancer drug resistance
Summary
Chemotherapy remains a standard treatment for patients with metastatic cancers. multidrug resistance (MDR) often occurs in more than 50% of patients with cancers during the course of chemotherapy, resulting in treatment failures [1,2]. Recent studies indicated that glucosylceramide synthase (GCS) is a gene for drug resistance in cancer cells [3,4,5,6]. Transfection of GCS gene confers cellular resistance to doxorubicin, tumor necrosis factor-a and daunorubicin in various cancer cell lines [11,12,13]. GCS overexpression has been identified in MDR cell lines of breast, ovarian, cervical, and colorectal cancers [14,15]. Suppressing GCS overexpression using small interfering RNA (siRNA), phosphorothioate antisense oligonucleotide (PS-oligo) and transfection of antisense sequence overcomes MDR in human breast, colon, cervical and ovarian cancer cell lines [3,15,20,23,24,26]. Inhibition of GCS enzyme with small molecules, such as D-threo-1phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP), sensitizes cancer cells to doxorubicin, paclitaxel and vincristine [19,21,22,25]
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