[Show abstract][Hide abstract] ABSTRACT: Sipholenol A, a sipholane triterpene isolated from the Red Sea sponge Callyspongia siphonella, has the ability to reverse multidrug resistance in cancer cells that overexpress P-glycoprotein (P-gp). Here, the antimigratory activity of sipholenol A and analogues are reported against the highly metastatic human breast cancer cell line MDA-MB-231 in a wound-healing assay. Sipholenol A and sipholenone A were semisynthetically optimized using ligand-based strategies to generate structurally diverse analogues in an attempt to maximize their antimigratory activity. A total of 22 semisynthetic ester, ether, oxime, and carbamate analogues were generated and identified by extensive one- and two-dimensional NMR spectroscopy and high-resolution mass spectrometry analyses. Sipholenol A 4β-4-chlorobenzoate and 19,20-anhydrosipholenol A 4β-4-chlorobenzoate esters were the most potent of all tested analogues in the wound-healing assay, with IC(50) values of 5.3 and 5.9 μM, respectively. Generally, ester derivatives showed better antimigratory activities than the carbamate analogues. A KINOMEscan of 19,20-anhydrosipholenol A 4β-benzoate ester against 451 human protein kinases identified protein tyrosine kinase 6 (PTK6) as a potential target. In breast tumor cells, PTK6 promotes growth factor signaling and migration, and as such the semisynthetic sipholanes were evaluated for their ability to inhibit PTK6 phosphorylation in vitro. The two analogues with the highest antimigratory activities, sipholenol A 4β-4-chlorobenzoate and 19,20-anhydrosipholenol A 4β-4-chlorobenzoate esters, also exhibited the most potent inhibition of PTK6 phosphorylation inhibition. None of the compounds exhibited cytotoxicity in a normal epithelial breast cell line. These derivatives were evaluated in an in vitro invasion assay, where sipholenol A succinate potently inhibited MDA-MB-231 cell invasion at 10 μM. These results highlight sipholane triterpenoids as novel antimigratory marine natural products with potential for further development as agents for the control of metastatic breast malignancies.
[Show abstract][Hide abstract] ABSTRACT: Previously, we reported sipholenol A, a sipholane triterpenoid from the Red Sea sponge Callyspongia siphonella, as a potent reversal of multidrug resistance (MDR) in cancer cells that overexpressed P-glycoprotein (P-gp). Through extensive screening of several related sipholane triterpenoids that have been isolated from the same sponge, we identified sipholenone E, sipholenol L and siphonellinol D as potent reversals of MDR in cancer cells. These compounds enhanced the cytotoxicity of several P-gp substrate anticancer drugs, including colchicine, vinblastine and paclitaxel, and significantly reversed the MDR-phenotype in P-gp-overexpressing MDR cancer cells KB-C2 in a dose-dependent manner. Moreover, these three sipholanes had no effect on the response to cytotoxic agents in cells lacking P-gp expression or expressing MRP1 (ABCC1) or MRP7 (ABCC10) or breast cancer resistance protein (BCRP/ABCG2). All three sipholanes (IC(50) >50 μM) were not toxic to all the cell lines that were used. [(3)H]-Paclitaxel accumulation and efflux studies demonstrated that all three triterpenoids time-dependently increased the intracellular accumulation of [(3)H]-paclitaxel by directly inhibiting P-gp-mediated drug efflux. Sipholanes also inhibited calcein-AM transport from P-gp-overexpressing cells. The Western blot analysis revealed that these three triterpenoids did not alter the expression of P-gp. However, they stimulated P-gp ATPase activity in a concentration-dependent manner and inhibited the photolabeling of this transporter with its transport substrate [(125)I]-iodoarylazidoprazosin. In silico molecular docking aided the virtual identification of ligand binding sites of these compounds. In conclusion, sipholane triterpenoids efficiently inhibit the function of P-gp through direct interactions and may represent potential reversal agents for the treatment of MDR.
[Show abstract][Hide abstract] ABSTRACT: This study reports the isolation of nine new terpenoids (2-10), possessing two novel skeletons, from the Red Sea sponge Callyspongia (=Siphonochalina) siphonella. The identity of these novel skeletons was based on X-ray crystallography and extensive spectral analyses. These compounds were evaluated for their ability to reverse P-glycoprotein (P-gp)-mediated multidrug resistance in human epidermoid cancer cells. Sipholenone E (3) was better than sipholenol A (1), a known P-gp modulator from this sponge, in reversing the P-gp-mediated multidrug resistance. Sipholenol L (6) and siphonellinol D (8) were nearly as active as sipholenol A. On the basis of X-ray crystallographic data and the established identity of 3-7, the structure of sipholenol I (11) is revised. A pharmacophore model of three hydrophobic points and two H-bond acceptors was generated for the active sipholane P-gp modulators.
Journal of Natural Products 07/2009; 72(7):1291-8. · 3.95 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Through extensive screening of marine sponge compounds, the authors have found that sipholenol A, a sipholane triterpene isolated from the Red Sea sponge, Callyspongia siphonella, potently reversed multidrug resistance (MDR) in cancer cells that overexpressed P-glycoprotein (P-gp). In experiments, sipholenol A potentiated the cytotoxicity of several P-gp substrate anticancer drugs, including colchicine, vinblastine, and paclitaxel, but not the non-P-gp substrate cisplatin, and significantly reversed the MDR of cancer cells KB-C2 and KB-V1 in a concentration-dependent manner. Furthermore, sipholenol A had no effect on the response to cytotoxic agents in cells lacking P-gp expression or expressing MDR protein 1 or breast cancer resistance protein. Sipholenol A (IC(50) > 50 microM) is not toxic to all the cell lines that were used, regardless of their membrane transporter status. Accumulation and efflux studies with the P-gp substrate [(3)H]-paclitaxel demonstrated that sipholenol A time-dependently increased the intracellular accumulation of [(3)H]-paclitaxel by directly inhibiting P-gp-mediated drug efflux. In addition, sipholenol A did not alter the expression of P-gp after treating KB-C2 and KB-V1 cells for 36 h and 72 h. However, it efficaciously stimulated the activity of ATPase of P-gp and inhibited the photolabeling of this transporter with its transport substrate [(125)I]-iodoarylazidoprazosin. Overall, the present results indicate that sipholenol A efficiently inhibits the function of P-gp through direct interactions, and sipholane triterpenes are a new class of potential reversing agents for treatment of MDR in P-gp-overexpressing tumors.
Cancer Science 10/2007; 98(9):1373-80. · 3.48 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The Red Sea sponge Callyspongia (= Siphonochalina) siphonella is a rich source of sipholane triterpenoids. Biocatalysis of the major sipholanes, sipholenol A (1) and sipholenone A (2), respectively, by Mucor ramannianus ATCC 9628 and Cunninghamella elegans ATCC 7929 afforded four new metabolites 3 - 6 along with sipholenol G and 28-hydroxysipholenol A. Major sipholanes along with their biocatalytic products were investigated for their antiproliferative activity against the highly malignant +SA mouse mammary epithelial cell line. Sipholenone A (2) was the most active sipholane inhibiting +SA cell proliferation with an IC(50) value of 20 - 30 microM. Sipholenone A, also, showed cytotoxicity against MCF-7 at a dose of 0.9 microM and antiangiogenic activity in the CAM (chorio-allantoic membrane) assay. This is the first report on anticancer activity of these triterpenoids.
[Show abstract][Hide abstract] ABSTRACT: Nineteen triterpenoids, possessing four different skeletons, have been reported so far from the Red Sea sponge Siphonochalina siphonella. However, no biological activity of these compounds was ever reported. This study describes the isolation of two new triterpenoids, siphonellinol C (3) and sipholenol I (4), along with several known sipholane triterpenoids from the Red Sea sponge Callyspongia (=Siphonochalina) siphonella. Allylic oxidation of the major sipholane triterpenoids, sipholenol A (1) and sipholenone A (2), by selenium dioxide afforded four C-28-oxidized derivatives. Sipholane triterpenoids along with their semisynthetic derivatives were evaluated for their cytotoxicity and effect on reversing P-glycoprotein-mediated MDR to colchicine. Sipholenol A was found to be the most potent, and it increased the sensitivity of resistant KB-C2 cells by 16 times toward colchicine. This is the first report related to reversal of cancer chemotherapy resistance using these triterpenoids.
Journal of Natural Products 07/2007; 70(6):928-31. · 3.95 Impact Factor