Potent Skin Cancer Chemopreventing Activity of Some Novel Semi-synthetic Cembranoids from Marine Sources

Sarcophine and (7S, 8R)-dihydroxydeepoxysarcophine from the Red Sea soft coral Sarcophyton glaucum as in vitro and in vivo modulators of glycine receptors

The inhibitory glycine receptor (GlyR) is a key mediator of synaptic signalling in spinal cord, brain stem, and higher centres of the central nervous system. We examined the glycinergic activity of sarcophine (SN), a marine terpenoid known for its various biological activities, and its trans-diol derivative (7S, 8R)-dihydroxy-deepoxysarcophine (DSN). SN was isolated from the Red Sea soft coral Sacrophyton glaucum, DSN was semisynthesized by hydrolysis of the epoxide ring. In cytotoxicity tests against HEK293 cells, SN and DSN had LD₅₀ values of 29.3 ± 3.0 mM and 123.5 ± 13.0 mM, respectively. Both compounds were tested against recombinant human α1 glycine receptors in HEK293 cells using whole-cell recording techniques. Both, SN and DSN were shown for the first time to be inhibitors of recombinant glycine receptors, with K_Ivalues of 2.1 ± 0.3 μM for SN, and 109 ± 9 μM for DSN. Receptor inhibition was also studied in vivo in a mouse model of strychnine toxicity. Surprisingly, in mouse experiments strychnine inhibition was not augmented by either terpenoid. While DSN had no significant effect on strychnine toxicity, SN even delayed strychnine effects. This could be accounted for by assuming that strychnine and sarcophine derivatives compete for the same binding site on the receptor, so the less toxic sarcophine can prevent strychnine from binding. The combination of modulatory activity and low level of toxicity makes sarcophines attractive structures for novel glycinergic drugs.

Purification and identification of novel cytotoxic oligopeptides from soft coral Sarcophyton glaucum

Globally, peptide-based anticancer therapies have drawn much attention. Marine organisms are a reservoir of anticancer peptides that await discovery. In this study, we aimed to identify cytotoxic oligopeptides from Sarcophyton glaucum. Peptides were purified from among the S. glaucum hydrolysates produced by alcalase, chymotrypsin, papain, and trypsin, guided by a methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay on the human cervical cancer (HeLa) cell line for cytotoxicity evaluation. Purification techniques adopted were membrane ultrafiltration, gel filtration chromatography, solid phase extraction (SPE), and reversed-phase high-performance liquid chromatography (RP-HPLC). Purified peptides were identified by de novo peptide sequencing. From papain hydrolysate, three peptide sequences were identified: AGAPGG, AERQ, and RDTQ (428.45, 502.53, and 518.53 Da, respectively). Peptides synthesized from these sequences exhibited cytotoxicity on HeLa cells with median effect concentration (EC₅₀) values of 8.6, 4.9, and 5.6 mmol/L, respectively, up to 5.8-fold stronger than the anticancer drug 5-fluorouracil. When tested at their respective EC₅₀, AGAPGG, AERQ, and RDTQ showed only 16%, 25%, and 11% cytotoxicity to non-cancerous Hek293 cells, respectively. In conclusion, AERQ, AGAPGG, and RDTQ are promising candidates for future development as peptide-based anticancer drugs.

New cytotoxic isoprenoid derivatives from the Red Sea soft coral Sarcophyton glaucum

Chemical investigation of the soft coral Sarcophyton glaucum collected from the Red Sea led to isolation of 11 isoprenoidal metabolites (1-11). A new sesquiterpenoid, 6-oxo-germacra-4(15),8,11-triene (1), a new natural cembranoid, sarcophinediol, along with two known sesquiterpenoids (2 and 3) and seven known cembranoids (5-11) was obtained. The structures of the compounds were established based on their NMR, MS, IR and UV spectral data. All compounds were evaluated for their cytotoxicity employing three cancer cell lines (HepG2, MCF-7 and HCT116). Compounds 4 and 6 showed significant cytotoxicity towards HepG2 with IC50 values of 18.8 ± 0.07 and 19.9 ± 0.02 μM; respectively. Compounds 5-7 exhibited potent cytotoxicity against MCF-7 cells with IC50 values of 9.9 ± 0.03, 2.4 ± 0.04 and 3.2 ± 0.02 μM, respectively. Compounds 1, 4 and 5 showed significant activities towards HCT116 cells with IC50 values of 29.4 ± 0.03, 19.4 ± 0.02 and 25.8 ± 0.03 μM, respectively.

Evaluation of Anti-melanoma Activities of (1S,2E,4R,6E,8R,11S,12R)-8,12-epoxy-2,6-cembradiene-4,11-diol, (1S,2E,4R,6E,8S,11R,12S)-8,11-epoxy-4,12-epoxy-2,6-cembradiene and (1S,4R,13S)-cembra-2E,7E,11E-trien-4,13-diol from the Red Sea soft coral Sarcophyton glaucum

Three natural cembranoids from the Red Sea soft coral Sarcophyton glaucum namely (1 S,2 E,4 R,6 E,8 R,11 S,12 R)-8,12-epoxy-2,6-cembradiene-4,11-diol, (1 S,2 E,4 R,6 E,8 S,11 R,12 S)-8,11-epoxy-4,12-epoxy-2,6-cembradiene and (1 S,4 R,13 S)-cembra-2 E,7 E,11 E-trien-4,13-diol were evaluated for their inhibitory effects on mouse melanoma B16F10 cell growth. Results show that all the cembranoids strongly inhibit viability of melanoma cells particularly during 48–72 hrs treatment and also inhibit de novo DNA synthesis and PARP activity and stimulate fragmentation of DNA. (1 S,2 E,4 R,6 E,8 R,11 S,12 R)-8,12-epoxy-2,6-cembradiene-4,11-diol was not cytotoxic to monkey kidney CV-1 cells at the concentration that produces the anti-melanoma effects which indicates that this compound may be a good candidate for further development. (1 S,2 E,4 R,6 E,8 S,11 R,12 S)-8,11-epoxy-4,12-epoxy-2,6-cembradiene and (1 S,4 R,13 S)-cembra-2 E,7 E,11 E-trien-4,13-diol were found to be cytotoxic to healthy cells.

Renoprotective effects of Moringa oleifera pods in 7,12-dimethylbenz [a] anthracene-exposed mice

OBJECTIVE

To investigate the potential of hydroethanolic extract of Moringa oleifera (MOHE) against 7, 12-dimethylbenz [a] anthracene (DMBA)-induced toxicity in male Swiss albino mice.

METHODS

Experimental mice were respectively pretreated with 200 and 400 mg/kg of MOHE, and 0.5% and 1% of butylated hydroxyanisole (BHA) for two weeks prior to the administration of 15 mg/kg of DMBA, respectively. Levels of xenobiotic metabolizing enzymes such as cytochrome (Cyt) P450 and Cyt b5, activities of reduced glutathione (GSH) and glutathione-S-transferase (GST) and renal aspartate amino transaminase (AST), alanine amino transaminase (ALT) and alkaline phosphatase (ALP), and content of protein and total cholesterol were measured to determine the nephrotoxicity caused by DMBA and to elucidate the ameliorating role of M. oleifera.

RESULTS

Single oral administration of 15 mg/kg of DMBA resulted in significant increases in Cyt P450 and Cyt b5 (P<0.01). The toxic effect of DMBA was justified by the significant decreases in the activities of GSH and GST in renal tissues (P<0.05). The levels of renal AST, ALT and ALP and protein content which are indicative of renocellular damage were also found decreased along with significant increase in total cholesterol content in DMBA-treated mice (P<0.01). The DMBA-induced alterations in the tissues were significantly reversed after pretreatment with 200 and 400 mg/kg of MOHE orally for 14 d (P<0.01).

CONCLUSION

The effects of MOHE in enhancing the levels of antioxidants and enhancing the levels of biochemical assays in DMBA-induced carcinogenesis are by reducing the formation of free radicals. This study rationalizes the ethnomedicinal use of M. oleifera for the protection against nephrotoxicity induced by chemical carcinogens.

Chemopreventive Effect of Sarcophine-diol on NOR-1-Induced TPA-Promoted Skin Carcinogenesis in Female HOS:HR-1 Mice

The cancer chemopreventive potential of sarcophine-diol in a chemical carcinogen initiation–promotion experimental tumor model in mice was evaluated. Sarcophine-diol, when given orally, afforded significant protection in the mouse skin cancer model initiated by the topical administration of (±)-( E)-4-methyl-2-[( E)-hydroxyamino]-5-nitro-6-methoxy-3-hexanamide (NOR-1) and promoted by 12- O-tetradecanoylphorbol-13-acetate (TPA). These findings, along with our initial reports, suggest that sarcophine-diol is an effective cancer chemopreventive agent, even when administered orally and at a very low dose and thus indicating possible potential human applications in the control of malignancy.

Dose-response on the chemopreventive effects of sarcophine-diol on UVB-induced skin tumor development in SKH-1 hairless mice

Sarcophine-diol (SD) is a lactone ring-opened analogue of sarcophine. It has shown chemopreventive effects on chemically-induced skin tumor development in female CD-1 mice, as well as in a UVB-induced skin tumor development model in hairless SKH-1 mice at a dose of 30 μg SD applied topically and 180 mJ/cm² UVB. The objective of this study was to determine the dose-response on the chemopreventive effects of SD on SKH-1 hairless mice when exposed to a UVB radiation dose of 30 mJ/cm². This UVB dose better represents chronic human skin exposure to sunlight leading to skin cancer than previous studies applying much higher UVB doses. Carcinogenesis was initiated and promoted by UVB radiation. Female hairless SKH-1 mice were divided into five groups. The control group was topically treated with 200 μL of acetone (vehicle), and the SD treatment groups were topically treated with SD (30 μg, 45 μg, and 60 μg dissolved in 200 μL of acetone) 1 h before UVB radiation (30 mJ/cm²). The last group of animals received 60 μg SD/200 μL acetone without UVB exposure. These treatments were continued for 27 weeks. Tumor multiplicity and tumor volumes were recorded on a weekly basis for 27 weeks. Weight gain and any signs of toxicity were also closely monitored. Histological characteristics and the proliferating cell nuclear antigen (PCNA) were evaluated in the mice skin collected at the end of the experiment. The dose-response study proved a modest increase in chemopreventive effects with the increase in SD dose. SD reduced the number of cells positively stained with PCNA proliferation marker in mice skin. The study also showed that SD application without UVB exposure has no effect on the structure of skin. The results from this study suggest that broader range doses of SD are necessary to improve the chemopreventive effects.

Sarcophine-diol, a skin cancer chemopreventive agent, inhibits proliferation and stimulates apoptosis in mouse melanoma B₁₆F₁₀ cell line

Sarcodiol (SD) is a semi-synthetic derivative of sarcophine, a marine natural product. In our previous work, we reported the significant chemopreventive effects of SD against non-melanoma skin cancer both in vitro and in vivo mouse models. In this investigation, we extended this work to study the effect of sarcodiol on melanoma development, the more deadly form of skin cancer, using the mouse melanoma B₁₆F₁₀ cell line. In this study we report that SD inhibits the de novo DNA synthesis and enhances fragmentation of DNA. We also evaluated the antitumor effect of SD on melanoma cell viability using several biomarkers for cell proliferation and apoptosis. SD inhibits the expression levels of signal transducers and activators of transcription protein (STAT-3) and cyclin D1, an activator of cyclin-dependent kinase 4 (Cdk4). SD treatment also enhances cellular level of tumor suppressor protein 53 (p53) and stimulates cleavage of the nuclear poly (ADP-ribose) polymerase (cleaved-PARP). SD also enhances cellular levels of cleaved Caspase-3, -8, -9 and stimulates enzymatic activities of Caspase-3, -8 and -9. These results, in addition to inhibition of cell viability, suggest that SD inhibits melanoma cell proliferation by arresting the cell-division cycle in a Go quiescent phase and activates programmed cell death (apoptosis) via extrinsic and intrinsic pathways. Finally, these studies demonstrate that SD shows a very promising chemopreventive effect in melanoma B₁₆F₁₀ tumor cells.

Matrix metalloproteinase inhibitors (MMPIs) from marine natural products: the current situation and future prospects

Matrix metalloproteinases (MMPs) are a family of more than twenty five secreted and membrane-bound zinc-endopeptidases which can degrade extracellular matrix (ECM) components. They also play important roles in a variety of biological and pathological processes. Matrix metalloproteinase inhibitors (MMPIs) have been identified as potential therapeutic candidates for metastasis, arthritis, chronic inflammation and wrinkle formation. Up to present, more than 20,000 new compounds have been isolated from marine organisms, where considerable numbers of these naturally occurring derivatives are developed as potential candidates for pharmaceutical application. Eventhough the quantity of marine derived MMPIs is less when compare with the MMPIs derived from terrestrial materials, huge potential for bioactivity of these marine derived MMPIs has lead to large number of researches. Saccharoids, flavonoids and polyphones, fatty acids are the most important groups of MMPIs derived from marine natural products. In this review we focus on the progress of MMPIs from marine natural products.

Sarcophine-diol, a Chemopreventive Agent of Skin Cancer, Inhibits Cell Growth and Induces Apoptosis through Extrinsic Pathway in Human Epidermoid Carcinoma A431 Cells

Sarcophine-diol (SD), a structural modifications of sarcophine, has shown chemopreventive effects on 7,12-dimethylbenz(a)anthracene-initiated and 12-O-tetradecanoylphorbol-13-acetate-promoted skin tumor developments in mice. Tumorigenesis is associated with uncontrolled cell growth and loss of apoptosis. In the present study, the effects of SD on cell growth and apoptosis in human epidermoid carcinoma A431 cells were determined to assess whether SD could inhibit cell growth and/or induce apoptosis, thus elucidating possible mechanism of action. MTT assay was used for cell viability; bromodeoxyuridine incorporation assay was used for cell proliferation; fluorescence-activated cell sorting analysis of annexin V/propidium iodide staining and TUNEL assay were used for determining apoptotic cells; Western blot analysis was used for determining the expression of caspase-3 and colorimetric caspase activity assays were used for determination of caspase-3, -8, and -9 activity. The results showed that SD treatment at concentration of 200 to 600 microM resulted in a concentration-dependent decrease in cell viability and cell proliferation in A431 cells, which largely inhibited cell growth. Sarcophine-diol treatment induced a strong apoptosis and significantly (P < .05) increased DNA fragmentation in A431 cells. Furthermore, SD treatment significantly (P < .05) increased the activity and expression of caspase-3 through activation of upstream caspase-8 in A431 cells rather than the activation of caspase 9. Sarcophine-diol treatment is relatively much less cytotoxic in monkey kidney normal CV-1 cells. These results suggest that SD decreases cell growth and induces apoptosis through caspase-dependent extrinsic pathway in A431 cells, and this may contribute to its overall chemopreventive effects in mouse skin cancer models.

Chemopreventive effects of sarcophine-diol on skin tumor development in CD-1 mice

The objective of this study was to determine the chemopreventive effects of sarcophine-diol (SD) on 7,12-dimethylbenz(a)anthracene initiated and 12-O-tetradecanoylphorbol-13-acetate promoted skin tumor development in mice and its possible mechanisms of action. SD pretreatment significantly (P<0.05) decreased skin papilloma development during promotion phase. SD significantly (P<0.05) increased caspase-3 and decreased cyclooxygenase-2 during initiation phase or promotion phase. SD significantly (P<0.05) increased caspase-8 during promotion phase. SD resulted in a 95% reduction in 12-O-tetradecanoylphorbol-13-acetate-induced DNA synthesis. SD could be an effective chemopreventive agent for skin cancer by enhancing apoptosis and decreasing cell proliferation.