Asmaa A. Sallam

Design, synthesis, and biological evaluation of dibromotyrosine analogues inspired by marine natural products as inhibitors of human prostate cancer proliferation, invasion, and migration

Bioactive secondary metabolites originating from dibromotyrosine are common in marine sponges, such as sponges of the Aplysina species. Verongiaquinol (1), 3,5-dibromo-1-hydroxy-4-oxocyclohexa-2,5-diene-1-acetamide, and aeroplysinin-1 are examples of such bioactive metabolites. Previous studies have shown the potent antimicrobial as well as cytotoxic properties of verongiaquinol and the anti-angiogenic activity of aeroplysinin-1. The work presented herein shows the design and synthesis of dibromotyrosine-inspired phenolic ester and ether analogues with anti-angiogenic, anti-proliferative and anti-migratory properties and negligible cytotoxicity. Several analogues were synthesized based on docking experiments in the ATP binding site of VEGFR2 and their anti-angiogenic potential and ability to inhibit angiogenesis and prostate cancer proliferation, migration and invasion were evaluated using the chick chorioallantoic membrane (CAM) assay, MTT, wound-healing, and Cultrex® BME cell invasion assay models, respectively. Analogues with high docking scores showed promising anti-angiogenic activity in the CAM assay. In general, ester analogues (5, 6, and 8-10) proved to be of higher anti-migratory activity whereas ether analogues (11-14) showed better anti-proliferative activity. These results demonstrate the potential of dibromotyrosines as promising inhibitory scaffolds for the control of metastatic prostate cancer proliferation and migration.

Discovery, Optimization, and Pharmacophore Modeling of Oleanolic Acid and Analogues as Breast Cancer Cell Migration and Invasion Inhibitors Through Targeting Brk/Paxillin/Rac1 Axis

Bioassay‐guided fractionation of Terminalia bentzoe L. leaves methanol extract identified the known triterpene oleanolic acid (1) as its major breast cancer cell migration inhibitor. Further chemical optimization afforded five new (9–12 and 15) and seven known (4–8, 13, and 14) semisynthetic analogues. All compounds were tested for their ability to inhibit human breast cancer MDA‐MB‐231 cells migration, proliferation, and invasion. The results revealed that 3‐O‐[N‐(3′‐chlorobenzenesulfonyl)‐carbamoyl]‐oleanolic acid (11) and 3‐O‐[N‐(5′‐fluorobenzenesulfonyl)‐carbamoyl]‐oleanolic acid (12) were the most active hits at low μm concentration. Western blot analysis indicated the activity of 1, 11, and 12 might be related, at least in part, to the suppression of Brk/Paxillin/Rac1 signaling pathway. Pharmacophore modeling study was conducted to better understand the common structural binding epitopes important for the antimigratory activity. The sulfonyl carbamoyl moiety with an optimal bulkiness electron‐deficient phenyl ring is associated with improved activity. This study is the first to discover the antimigratory and anti‐invasive activities of oleanolic acid and analogues through targeting the Brk/Paxillin/Rac1 axis.

Indole diterpene alkaloids as novel inhibitors of the Wnt/β-catenin pathway in breast cancer cells

Penitrems are indole diterpene alkaloids best known for their BK channel inhibition and tremorgenic effects in mammals. In a previous study, penitrems A-F (1-5), their biosynthetic precursors, paspaline (6) and emindole SB (7), and two brominated penitrem analogs 8 and 9 demonstrated promising in vitro antiproliferative, antimigratory, and anti-invasive effects in the MTT (MCF-7 and MDA-MB-231), wound-healing, and Cultrex BME cell invasion (MDA-MB-231) assays, respectively. The study herein reports the novel ability of penitrem A to suppress total β-catenin levels in MDA-MB-231 mammary cancer cells. Nine new penitrem analogs (10-18) were semisynthetically prepared, in an attempt to identify pharmacophores correlated with BK channel inhibition and tremorgenicity of penitrems and decrease their toxicity. The degree of BK channel inhibition was assessed using the nematode Caenorhabditis elegans, and in vivo tremorgenic EC₅₀ was calculated using CD-1 male mice following an Up-and-Down Procedure (UDP). Although new analogs were generally less active than parent compound 1, some showed no BK channel inhibition or tremorgenicity and retained the ability of penitrem A (1) to suppress total β-catenin levels in MDA-MB-231 cells. Paspaline (6) and emindole SB (7), both lacking BK channel inhibition and tremorgenicity, represent the simplest indole diterpene skeleton that retains the antiproliferative, antimigratory and total β-catenin suppressing effects shown by the more complex penitrem A (1).

Bioguided discovery and pharmacophore modeling of the mycotoxic indole diterpene alkaloids penitrems as breast cancer proliferation, migration, and invasion inhibitors

Marine-derived fungi have proven to be important sources of bioactive natural organohalides. The genus Penicillium is recognized as a rich source of chemically diverse bioactive secondary metabolites. This study reports the fermentation, isolation and identification of a marine-derived Penicillium species. Bioassay-guided fractionation afforded the indole diterpene alkaloids penitrems A, B, D, E and F as well as paspaline and emnidole SB (1-7). Supplementing the fermentation broth of the growing fungus with KBr afforded the new 6-bromopenitrem B (8) and the known 6-bromopenitrem E (9). These compounds showed good antiproliferative, antimigratory and anti-invasive properties against human breast cancer cells. Penitrem B also showed a good activity profile in the NCI-60 DTP human tumor cell line screen. The nematode Caenorhabditis elegans was used to assess the BK channel inhibitory activity and toxicity of select compounds. A pharmacophore model was generated to explain the structural relationships of 1-9 with respect to their antiproliferative activity against the breast cancer MCF-7 cells. The structurally less complex biosynthetic precursors, paspaline (6) and emindole SB (7), were identified as potential hits suitable for future studies.

Design of semisynthetic analogues and 3D-QSAR study of eunicellin-based diterpenoids as prostate cancer migration and invasion inhibitors

Prostrate cancer constitutes the second leading cause of cancer deaths in men in United States. Eunicellin-based diterpenoids are important bioactive marine natural products isolated from corals of alcyonaria species. The bioactivities of eunicellin diterpenes were correlated with their chemical structures. Recently eunicellin diterpenes from the Red Sea soft coral Cladiella pachyclados showed significant anti-migratory and anti-invasive activities against prostate cancer in wound-healing and Cultrex(®) invasion models. These results encouraged the semisynthetic and 3D-QSAR studies of this unique marine natural product class as possible hits for the control of metastatic prostate cancer. Ten new semisynthetic analogues of cladiellisin (1) were prepared. These include C-6 carbamoylation and ∆(11-17) epoxidation. Carbamate analogues of 1 showed potent anti-migratory and anti-invasive activities against PC-3 cells. Comparative Molecular Field Analysis (CoMFA) and Comparative Molecular Similarity Indices Analysis (CoMSIA) were performed using SYBYL 8.1 program package to create a valid 3D-QSAR model to guide future design of potent eunicellin diterpenes cancer migration inhibitors. Eunicellin-based diterpenes are potential marine natural hits appropriate for optimization as inhibitors of metastatic prostate cancer.

Semisynthetic analogues of the marine cembranoid sarcophine as prostate and breast cancer migration inhibitors.

Sarcophine (1) is a bioactive cembranoid diterpene isolated from the Red Sea soft coral Sarcophyton glaucum. Previous semisynthesis attempts resulted in decreased or complete loss of 1s anticancer activity. Sarcophine and analogues showed antimigratory activity against breast and prostate cancer cell lines. This encouraged further semisynthestic optimizations to improve its activity and establish a preliminary structure-activity relationship. Eight new and five known semisynthetic analogues were generated. These compounds were evaluated for their ability to inhibit growth, proliferation, and migration of the prostate and breast metastatic cancer cell lines PC-3 and MDA-MB-231, respectively. Most analogues exhibited enhanced antimigratory activity.

PEGylated γ-tocotrienol isomer of vitamin E: Synthesis, characterization, in vitro cytotoxicity, and oral bioavailability.

Vitamin E refers to a family of eight isomers divided into two subgroups, tocopherols and the therapeutically active tocotrienols (T3). The PEGylated α-tocopherol isomer of vitamin E (vitamin E TPGS) has been extensively investigated for its solubilizing capacity as a nonionic surfactant in various drug delivery systems. Limited information, however, is available about the PEG conjugates of the tocotrienol isomers of vitamin E. In this study two PEGylated γ-T3 variants with mPEG molecular weights of 350 (γ-T3PGS 350) and 1000 (γ-T3PGS 1000) were synthesized by a two-step reaction procedure and characterized by (1)H NMR, HPLC, and mass spectroscopy. The physical properties of their self-assemblies in water were characterized by zeta, CMC, and size analysis. Similar physical properties were found between the PEGylated T3 and vitamin E TPGS. PEGylated T3 were also found to retain the in vitro cytotoxic activity of the free T3 against the MCF-7 and the triple-negative MDA-MB-231 breast cancer cells. PEGylated γ-T3 also increased the oral bioavailability of γ-T3 by threefolds when compared to the bioavailability of γ-T3 formulated into a self-emulsified drug delivery system. No significant differences in biological activity were found between the PEG 350 and 100 conjugates. Results from this study suggest that PEGylation of γ-T3 represents a viable platform for the oral and parenteral delivery of γ-T3 for potential use in the prevention of breast cancer.

Mannich- and Lederer–Manasse-based analogues of the natural product S-(+)-curcuphenol as cancer proliferation and migration inhibitors

The Mannich-based analogues of S-(+)-curcuphenol (1), 3a–5a, and 3b potently inhibited the growth of several NCIs human cancer cell lines. In addition, 7a showed a 12-fold antimigratory activity (IC50 3.1 μM) against the human breast cancer cell line MDA-MB-231 compared to its parent 1 (IC50 37.2 μM).

Discovery and Computer-Aided Drug Design Studies of the Anticancer Marine Triterpene Sipholanes as Novel P-gp and Brk Modulators

Sipholane triterpenes are marine natural products isolated from the Red Sea sponge Callyspongia siphonella. Based on their structure similarity to the marine polyepoxysqualene terpenoids sodwanones, sipholanes were tested for various anticancer activities. Sipholenone A showed cytotoxicity and anti-angiogenic activity against human and mouse breast cancer cells. Sipholenols A and L, sipholenone E, and siphonellinol D showed potential activity in multi-drug resistant (MDR) tumors overexpressing P-glycoprotein (P-gp) and their in-silico binding mode justified their activity order. Recently, a kinase assay profiling platform was used to identify the breast tumor kinase, Brk (also known as protein tyrosine kinase 6, PTK6) as a potential target for 19,20-anhydrosipholenol A 4-β-benzoate (28), a semisynthetic ester analog of sipholenol A. Brk has recently emerged as an attractive therapeutic target for controlling breast cancer proliferation and migration. Additional semisynthetic modifications afforded sipholenol A 4β-4′,5′-dichlorobenzoate as a potent breast cancer migration inhibitor, with an IC50 of 1.3 µM in the wound-healing assay, without any cytotoxicity to the non-tumorigenic breast cells MCF10A. Pharmacophore modeling and 3D-QSAR studies highlighted the important pharmacophoric features responsible for the antimigratory activity and Brk phosphorylation inhibition. Those features are restricted to rings A and B (perhydrobenzoxepine) together with the substituted aromatic ester moiety, thus resulting in a much simpler structure and eliminating rings C and D ([5,3,0] bicyclodecane system). This will open new horizons for the future design and synthesis of novel sipholane-inspired active compounds with perhydrobenzoxepine-aromatic cores, both feasibly and cost-effectively. These results demonstrate the potential of marine natural products for the discovery of novel scaffolds for the control and management of metastatic breast cancer.