Anti-proliferative activity of fenretinide in human hepatoma cells in vitro and in vivo

The potential roles of retinoids in combating drug resistance in cancer: implications of ATP-binding cassette (ABC) transporters

Multidrug resistance (MDR) means that tumour cells become unresponsive during or after the course of treatment to one or more of chemotherapeutic drugs. Chemotherapeutic resistance critically limits the treatment outcomes and remains a key challenge for clinicians. The alternation in intracellular drug concentration through the modulation of its transport across the plasma membrane is the major cause for MDR and is adopted by various mediators, including ATP-requiring enzymes (ATPases). Among these ATPases, ABC transporters have been extensively studied, and found to be highly implicated in tumorigenesis and MDR. The present review sheds light on the documented effects of retinoids on ABC enzymes to understand their mechanism in combating cancer cell resistance. This would open the gate to test the mechanism and applicability of different new synthetic retinoids in literature and market as modulators of ATP-dependent efflux pumping activity, and promote their applicability in diminishing anti-cancer drug resistance.

Flavonoids as putative modulators of Δ4-, Δ5-, and Δ6-desaturases: Studies in cultured hepatocytes, myocytes, and adipocytes

This study was conducted to screen flavonoids for affecting expression of desaturases involved in omega-3 fatty acid synthesis and ceramide (CER) metabolism. To this end, cultured HepG2 hepatocytes, C2C12 myocytes, and 3T3-L1 adipocytes were treated with nontoxic concentrations of 12 selected flavonoids and expression of Δ4-, Δ5-, and Δ6-desaturases (DEGS1, FADS1, and FADS2, respectively) was determined. The flavonoids tested were more cytotoxic to HepG2 and 3T3-L1 than to C2C12 cells. In HepG2 cells, FADS1 was induced by quercetin and FADS2 expression was increased by daidzein, genistein, and pratensein treatment. DEGS1 was increased by apigenin, luteolin, orobol, and quercetin administration. In differentiated C2C12 cells, substances had no inducing effect or even lowered target gene expression. Pratensein induced both FADS1 and FADS2 in differentiated 3T3-L1 cells and DEGS1 was increased by treatment with apigenin, genistein, luteolin, orobol, and quercetin. In conclusion, pratensein may be an interesting test compound for further studies in vitro and in vivo on omega-3 synthesis since it induces its rate-limiting enzyme FADS2. Apigenin, luteolin, orobol, and quercetin induced DEGS1 and thereby possibly synthesis of proapoptotic CER in malignant HepG2 cells and 3T3-L1. In contrast, in benign C2C12 cells, they did not elevate mRNA steady state levels of DEGS1. That may partly explain the higher resistance of C2C12 cells against flavonoids compared to the other cell lines. By affecting tumor cells and nontumor cells differently, these flavonoids may be promising substances for further research regarding anticancer properties. © 2018 BioFactors, 44(5):485-495, 2018.

Retinoic acid suppresses growth of lesions, inhibits peritoneal cytokine secretion, and promotes macrophage differentiation in an immunocompetent mouse model of endometriosis

OBJECTIVE

To determine the effects of all-trans-retinoic acid (RA) on establishment and growth of endometrial lesions, peritoneal interleukin-6 (IL-6) and macrophage chemotactic factor-1 (MCP-1) concentrations, and CD38, CD11b, and F4/80 expression on peritoneal macrophages in an immunocompetent mouse model of endometriosis.

DESIGN

Experimental transplantation study using mice.

SETTING

Academic medical center.

ANIMAL(S)

C57BL/6 recipient mice and syngeneic green fluorescent protein transgenic (GFP+) mice.

INTERVENTION(S)

Recipient mice were inoculated with GFP+ minced uterine tissue to induce endometriosis and treated with RA (400 nmol/day) or vehicle for 17 days (3 days before to 14 days after tissue injection).

MAIN OUTCOME MEASURE(S)

Total number of GFP+ implants in recipient mice, number of implants showing visible blood vessels, total volume of established lesions per mouse, concentrations of IL-6 and MCP-1 in peritoneal fluid, and expression of CD11b, F4/80, and CD38 on peritoneal macrophages.

RESULT(S)

Retinoic acid treatment for 17 days reduced the number of implants versus controls and decreased the frequency of lesions with vessels. Peritoneal washings in RA-treated animals had lower concentrations of IL-6 and MCP-1 than controls 3 days after endometrial inoculation and lower levels of IL-6 on day 14 after inoculation. Concomitant with these effects on day 14, CD38, CD11b, and F4/80 were higher on macrophages from RA-treated mice versus controls.

CONCLUSION(S)

The development of endometriotic implants is inhibited by RA. This effect may be caused, at least in part, by reduced IL-6 and MCP-1 production and enhanced differentiation of peritoneal macrophages.

Heterogeneous role of the glutathione antioxidant system in modulating the response of ESFT to fenretinide in normoxia and hypoxia

Glutathione (GSH) is implicated in drug resistance mechanisms of several cancers and is a key regulator of cell death pathways within cells. We studied Ewing's sarcoma family of tumours (ESFT) cell lines and three mechanistically distinct anticancer agents (fenretinide, doxorubicin, and vincristine) to investigate whether the GSH antioxidant system is involved in the reduced sensitivity to these chemotherapeutic agents in hypoxia. Cell viability and death were assessed by the trypan blue exclusion assay and annexin V-PI staining, respectively. Hypoxia significantly decreased the sensitivity of all ESFT cell lines to fenretinide-induced death, whereas the effect of doxorubicin or vincristine was marginal and cell-line-specific. The response of the GSH antioxidant system in ESFT cell lines to hypoxia was variable and also cell-line-specific, although the level of GSH appeared to be most dependent on de novo biosynthesis rather than recycling. RNAi-mediated knockdown of key GSH regulatory enzymes γ-glutamylcysteine synthetase or glutathione disulfide reductase partially reversed the hypoxia-induced resistance to fenretinide, and increasing GSH levels using N-acetylcysteine augmented the hypoxia-induced resistance in a cell line-specific manner. These observations are consistent with the conclusion that the role of the GSH antioxidant system in modulating the sensitivity of ESFT cells to fenretinide is heterogeneous depending on environment and cell type. This is likely to limit the value of targeting GSH as a therapeutic strategy to overcome hypoxia-induced drug resistance in ESFT. Whether targeting the GSH antioxidant system in conjunction with other therapeutics may benefit some patients with ESFT remains to be seen.