Ceramide glycosylation, through glucosylceramide synthase (GCS), allows cellular escape from ceramide‐induced programmed cell death. This glycosylation event confers cancer cell resistance to cytotoxic anticancer agents [Liu, Y. Y., Han, T. Y., Giuliano, A. E., and M. C. Cabot. (1999) J. Biol. Chem . 274, 1140–1146]. We previously found that glucosylce‐ramide, the glycosylated form of ceramide, accumulates in adriamycin‐resistant breast carcinoma cells, in vinblastine‐resistant epithelioid carcinoma cells, and in tumor specimens from patients showing poor response to chemotherapy. Here we show that multidrug resistance can be increased over baseline and then totally reversed in human breast cancer cells by GCS gene targeting. In adriamycin‐resistant MCF‐7‐AdrR cells, transfection of GCS upgraded multidrug resistance, whereas transfection of GCS antisense markedly restored cellular sensitivity to anthracyclines, Vinca alkaloids, taxanes, and other anticancer drugs. Sensitivity to the various drugs by GCS antisense transfection increased 7‐ to 240‐fold and was consistent with the resumption of ceramide‐caspase‐apoptotic signaling. GCS targeting had little influence on cellular sensitivity to either 5‐FU or cisplatin, nor did it modify P‐glyco‐protein expression or rhodamine‐123 efflux. GCS anti‐sense transfection did enhance rhodamine‐123 uptake compared with parent MCF‐7‐AdrR cells. This study reveals that GCS is a novel mechanism of multidrug resistance and positions GCS antisense as an innovative force to overcome multidrug resistance in cancer chemotherapy.—Liu, Y.‐Y., Han, T.‐Y., Giuliano, A. E., and Cabot, M. C. Ceramide glycosylation potentiates cellular multidrug resistance. FASEB J. 15, 719‐730 (2001)

Multidrug-resistant cancer cells display elevated levels of glucosylceramide (Lavie, Y., Cao, H. T., Volner, A., Lucci, A., Han, T. Y., Geffen, V., Giuliano, A. E., and Cabot, M. C. (1997) J. Biol. Chem. 272, 1682–1687). In this study, we have introduced glucosylceramide synthase (GCS) into wild type MCF-7 breast cancer cells using a retroviral tetracycline-on expression system, and we developed a cell line, MCF-7/GCS. MCF-7/GCS cells expressed an 11-fold higher level of GCS activity compared with the parental cell line. Interestingly, the transfected cells demonstrated strong resistance to adriamycin and to ceramide, whereas both agents were highly cytotoxic to MCF-7 cells. The EC₅₀ values of adriamycin and ceramide were 11-fold (p < 0.0005) and 5-fold (p < 0.005) higher, respectively, in MCF-7/GCS cells compared with MCF-7 cells. Ceramide resistance displayed by MCF-7/GCS cells closely paralleled the activity of expressed GCS with a correlation coefficient of 0.99. In turn, cellular resistance and GCS activity were dependent upon the concentration of the expression mediator doxycycline. Adriamycin resistance in MCF-7/GCS cells was related to the hyperglycosylation of ceramide and was not related to shifts in the levels of either P-glycoprotein or Bcl-2. This work demonstrates that overexpression of GCS, which catalyzes ceramide glycosylation, induces resistance to adriamycin and ceramide in MCF-7 breast cancer cells.

The mammalian or mechanistic target of rapamycin (mTOR) and associated phosphatidyl-inositiol 3-kinase (PI3K)/protein kinase B (Akt) pathways regulate cell growth, differentiation, migration, and survival, as well as angiogenesis and metabolism. Dysregulation of these pathways is frequently associated with genetic/epigenetic alterations and predicts poor treatment outcomes in a variety of human cancers including cutaneous malignancies like melanoma and non-melanoma skin cancers. Recently, the enhanced understanding of the molecular and genetic basis of skin dysfunction in patients with skin cancers has provided a strong basis for the development of novel therapeutic strategies for these obdurate groups of skin cancers. This review summarizes recent advances in the roles of PI3K/Akt/mTOR and their targets in the development and progression of a broad spectrum of cutaneous cancers and discusses the current progress in preclinical and clinical studies for the development of PI3K/Akt/mTOR targeted therapies with nutraceuticals and synthetic small molecule inhibitors.

Curcumin, the active component of turmeric, has been shown to protect against carcinogenesis and prevent tumor development. However, little is known about its anti-tumor mechanism in small cell lung cancer (SCLC). In this study, we found that curcumin can inhibit SCLC cell proliferation, cell cycle, migration, invasion and angiogenesis through suppression of the STAT3. SCLC cells were treated with curcumin (15 µmol/L) and the results showed that curcumin was effective in inhibiting STAT3 phosphorylation to downregulate of an array of STAT3 downstream targets ,which contributed to suppression of cell proliferation, loss of colony formation, depression of cell migration and invasion. Curcumin also suppressed the expression of proliferative proteins (Survivin, Bcl-X_L and Cyclin B1), and invasive proteins (VEGF, MMP-2, MMP-7 and ICAM-1).Knockdown of STAT3 expression by siRNA was able to induce anti-invasive effects in vitro. In contrast, activation of STAT3 upstream of interleukin 6 (IL-6) leads to the increased cell proliferation ,cell survival, angiogenesis, invasion, migration and tumor growth. Our findings illustrate the biologic significance of IL-6/JAK/STAT3 signaling in SCLC progression and providenovel evidence that the pathway may be a new potential target for therapy of SCLC. It was concluded that curcumin is a potent agent in the inhibition of STAT3 with favorable pharmacological activity,and curcumin may have translational potential as an effective cancer therapeutic or preventive agent for SCLC.

Drug resistance is the outcome of multiple-gene interactions in cancer cells under stress of anticancer agents. MDR1 overexpression is most commonly detected in drug-resistant cancers and accompanied with other gene alterations including enhanced glucosylceramide synthase (GCS). MDR1 encodes for P-glycoprotein that extrudes anticancer drugs. Polymorphisms of MDR1 disrupt the effects of P-glycoprotein antagonists and limit the success of drug resistance reversal in clinical trials. GCS converts ceramide to glucosylceramide, reducing the impact of ceramide-induced apoptosis and increasing glycosphingolipid (GSL) synthesis. Understanding the molecular mechanisms underlying MDR1 overexpression and how it interacts with GCS may find effective approaches to reverse drug resistance.