Enhancement of cyclopamine via conjugation with nonmetabolic sugars

Novel MeON-glycosides of ursolic acid: Synthesis, antitumor evaluation, and mechanism studies

Ursolic acid (UA) is a pentacyclic triterpenoid widely found in in medicinal plants, edible plants, fruits, and flowers. The great interest in this bioactive compound is related to the positive effects in human health. However, its limited solubility, moderate biological activity and poor bioavailability limit the potential and further applications of UA. Here, we explored the efficacy of MeON-Glycosides of UA in inhibiting tumor cell proliferation. A number of compounds showed significant antitumor activity against tested five cancer cell lines. Among them, compound 2a exhibited the most potent activity against HepG2 cells with IC50 values of 3.1 ± 0.5 μM. Especially, compound 2a could induce HepG2 cells apoptosis and reduce mitochondrial membrane potential. Western blot analysis showed that compound 2a up-regulated Bax, cleaved caspase-3/9, cleaved PARP levels and down-regulated Bcl-2 level of HepG2 cells. These results indicated that compound 2a could obviously induce the apoptosis of HepG2 cells. At the same time, compound 2a significantly decreased the expression of p-AKT and p-mTOR, which indicated that compound 2a might exert its cytotoxic effect by targeting PI3K/AKT/mTOR signaling pathway. Moreover, the in silico ADME predictions showed that compound 2a has improved water solubility and other properties. Thus, compound 2a may be a promising antitumor candidate, which may be potentially used to prevent or treat cancers.

Discovery of highly potent and selective 7-ethyl-10-hydroxycamptothecin-glucose conjugates as potential anti-colorectal cancer agents

7-Ethyl-10-hydroxycamptothecin (SN38), a highly potent metabolite of irinotecan, has an anticancer efficacy 100-1000 folds more than irinotecan in vitro. However, the clinical application of SN38 has been limited due to the very narrow therapeutic window and poor water solubility. Herein, we report the SN38-glucose conjugates (Glu-SN38) that can target cancer cells due to their selective uptake via glucose transporters, which are overexpressed in most cancers. The in vitro antiproliferative activities against human cancer cell lines and normal cells of Glu-SN38 were investigated. One of the conjugates named 5b showed high potency and selectivity against human colorectal cancer cell line HCT116. Furthermore, 5b remarkably inhibited the growth of HCT116 in vivo. These results suggested that 5b could be a promising drug candidate for treating colorectal cancer.

Jerveratrum-Type Steroidal Alkaloids Inhibit β-1,6-Glucan Biosynthesis in Fungal Cell Walls

The limited number of available effective agents necessitates the development of new antifungals. We report that jervine, a jerveratrum-type steroidal alkaloid isolated from Veratrum californicum, has antifungal activity. Phenotypic comparisons of cell wall mutants, K1 killer toxin susceptibility testing, and quantification of cell wall components revealed that β-1,6-glucan biosynthesis was significantly inhibited by jervine. Temperature-sensitive mutants defective in essential genes involved in β-1,6-glucan biosynthesis, including BIG1, KEG1, KRE5, KRE9, and ROT1, were hypersensitive to jervine. In contrast, point mutations in KRE6 or its paralog SKN1 produced jervine resistance, suggesting that jervine targets Kre6 and Skn1. Jervine exhibited broad-spectrum antifungal activity and was effective against human-pathogenic fungi, including Candida parapsilosis and Candida krusei. It was also effective against phytopathogenic fungi, including Botrytis cinerea and Puccinia recondita. Jervine exerted a synergistic effect with fluconazole. Therefore, jervine, a jerveratrum-type steroidal alkaloid used in pharmaceutical products, represents a new class of antifungals active against mycoses and plant-pathogenic fungi. IMPORTANCE Non-Candida albicans Candida species (NCAC) are on the rise as a cause of mycosis. Many antifungal drugs are less effective against NCAC, limiting the available therapeutic agents. Here, we report that jervine, a jerveratrum-type steroidal alkaloid, is effective against NCAC and phytopathogenic fungi. Jervine acts on Kre6 and Skn1, which are involved in β-1,6-glucan biosynthesis. The skeleton of jerveratrum-type steroidal alkaloids has been well studied, and more recently, their anticancer properties have been investigated. Therefore, jerveratrum-type alkaloids could potentially be applied as treatments for fungal infections and cancer.

Potential of Steroidal Alkaloids in Cancer: Perspective Insight Into Structure-Activity Relationships

Steroidal alkaloids contain both steroidal and alkaloid properties in terms of chemical properties and pharmacological activities. Due to outstanding biological activities such as alkaloids and similar pharmacological effects to other steroids, steroidal alkaloids have received special attention in anticancer activity recently. Substituted groups in chemical structure play markedly important roles in biological activities. Therefore, the effective way to obtain lead compounds quickly is structural modification, which is guided by structure-activity relationships (SARs). This review presents the SAR of steroidal alkaloids and anticancer, including pregnane alkaloids, cyclopregnane alkaloids, cholestane alkaloids, C-nor-D-homosteroidal alkaloids, and bis-steroidal pyrazine. A summary of SAR can powerfully help to design and synthesize more lead compounds.

Synthesis of MeON-Glycoside Derivatives of Oleanolic Acid by Neoglycosylation and Evaluation of Their Cytotoxicity Against Selected Cancer Cell Lines

A series of C-3 and C-28 MeON-neoglycosides of oleanolic acid were designed and synthesized by neoglycosylation as potential antiproliferative agents. Their cytotoxicity was evaluated in vitro against five human cancer cell lines: human non-small cell lung cancer cell line (A549), human melanoma cell line (A375), human colon cancer cell line (HCT116), human liver carcinoma cell line (HepG2), human breast adenocarcinoma cell line (MCF-7) by the Cell Counting Kit-8 (CCK-8) assay. Most of C-3 and C-28 MeON-neoglycosides of oleanolic acid exhibited notably inhibitory effects against the tested cancer cells and more sensitive to HepG2 cells than 5-Fluorouracil (5-FU). Structure-activities relationship (SAR) analysis revealed that sugar types and the d/l configuration of sugars would significantly affect their antiproliferative activities of neoglycosides. Among them, compound 8a (28-N-methoxyaminooleanane-β-d-glucoside) exhibited the most potent antiproliferative activities against HepG2 cells with IC₅₀ values of 2.1 µM. Further pharmacological experiments revealed that compound 8a could cause morphological changes and cell cycle arrest at G0/G1 phase and induce apoptosis in HepG2 cells. These results suggested that neoglycosylation could provide a rapid strategy for the discovery of potential antiproliferative agents and their possible pharmacological mechanisms need more further research.

Glycorandomization: A promising diversification strategy for the drug development

Glycorandomization is a natural product derivatization strategy in which different sugar moieties are linked to the aglycone part of the naturally existing glycosides to create glycorandomized libraries. Sugars attached to the natural products are responsible for affecting their solubility, mechanism of action, target recognition, and toxicity and thus, by changing the sugar part, these properties could be modified. Glycorandomization can be done via two approaches (i) a synthetic approach known as neoglycorandomization, and (ii) chemoenzymatic approach including in-vitro and in-vivo glycorandomization. Glycorandomization can be a promising technology for the drug discovery that has proved its potential to improve pharmacokinetic (solubility) and pharmacodynamic profile (mechanism of action, toxicity, and target recognition) of the parent compounds. The substrate flexibility of glycosyltransferases and other enzymes towards sugars and/or aglycone substrates has made this technique versatile. Further, the enzymes can be altered by genetic engineering to generate glycorandomized libraries of diverse natural product scaffolds. This technique has the potential to produce new compounds that can be helpful to the mankind by treating the threatening disease states. This review covers the different strategies for glycorandomization as a tool in drug discovery and development. The fundamentals of glycorandomization, different types, and further development of differentially glycorandomized libraries of natural products and small molecule based drugs have been discussed.

Synthesis of tigogenin MeON-Neoglycosides and their antitumor activity

To discover new potent cytotoxic steroidal saponins, a series of tigogenin neoglycosides were synthesized via oxyamine neoglycosylation for the first time. The preliminary bioassays for their in vitro antitumor activities against five human cancer cell lines (A375, A-549, HCT-116, HepG2 and MCF-7) were conducted. The results revealed a sugar-dependent activity profile of their cytotoxicity, the glycoconjugation converted the non-active tigogenin to the most potential product Tg29 ((3R)-N-methoxyamino-tigogenin-β-2-deoxy-d-galactoside) with IC₅₀ value of 2.7μM and 4.6μM against HepG2 and MCF-7 cells respectively. And the 3R-tigogenin neoglycosides exhibited enhanced antitumor activity while the 3S-tigogenin almost showed no activity. Among the five cell lines, HepG2 and MCF-7 cells showed more sensitive cytotoxic responses to the products. Therefore, the neoglycosylation could be a promising strategy for the synthesis of antitumor steroidal saponins and it also proved the essential role of carbohydrate moiety of steroidal saponins in the biological activity.

Development of anticancer agents targeting the Hedgehog signaling

Hedgehog signaling is an evolutionarily conserved pathway which is essential in embryonic and postnatal development as well as adult organ homeostasis. Abnormal regulation of Hedgehog signaling is implicated in many diseases including cancer. Consequently, substantial efforts have made in the past to develop potential therapeutic agents that specifically target the Hedgehog signaling for cancer treatment. Here, we review the therapeutic agents for inhibition of the Hedgehog signaling and their clinical advances in cancer treatment.

Small Molecules for Active Targeting in Cancer

For the purpose of this review, active targeting in cancer research encompasses strategies wherein a ligand for a cell surface receptor expressed on tumor cells is used to deliver a cytotoxic or imaging cargo. This area of research is more than two decades old, but in those 20 and more years, how many receptors have been studied extensively? What kinds of the ligands are used for active targeting? Are they mostly naturally occurring molecules such as folic acid, or synthetic substances developed in campaigns for medicinal chemistry efforts? This review outlines the most important receptor or ligand combinations that have been used in active targeting to answer these questions, and therefore to address the most important one of all: is research in active targeting affording diminishing returns, or is this an area for which the potential far exceeds progress made so far?

The identification of perillyl alcohol glycosides with improved antiproliferative activity

A facile route to perillyl alcohol (POH) differential glycosylation and the corresponding synthesis of a set of 34 POH glycosides is reported. Subsequent in vitro studies revealed a sugar dependent antiproliferative activity and the inhibition of S6 ribosomal protein phosphorylation as a putative mechanism of representative POH glycosides. The most active glycoside from this cumulative study (4′-azido-d-glucoside, PG9) represents one of the most cytotoxic POH analogues reported to date.

Neoglycosylation and neoglycorandomization: Enabling tools for the discovery of novel glycosylated bioactive probes and early stage leads

This review focuses upon the development, scope, and utility of the highly versatile chemoselective alkoxyamine-based 'neoglycosylation' reaction first described by Peri and Dumy. The fundamentals of neoglycosylation and the subsequent development of a 'neoglycorandomization' platform to afford differentially-glycosylated libraries of plant-based natural products, microbial-based natural products, and small molecule-based drugs for drug discovery applications are discussed.

A fast entry to furanoditerpenoid-based Hedgehog signaling inhibitors: identifying essential structural features

New, small molecule Hedgehog (Hh) pathway inhibitors, such as the furanoditerpenoid taepeenin D, are of high medicinal importance. To establish key structure-activity relationships (SARs) for this lead, a synthetic sequence has been developed for the expedient preparation of several derivatives and their evaluation as Hh inhibitors exploiting its structural similarity to abietic acid. While C(14) substitution is not essential for biological activity, the presence of a hydrogen bond acceptor at C(6) and an intact benzofuran moiety are.

Dual targeting of the Warburg effect with a glucose-conjugated lactate dehydrogenase inhibitor

Effective glucose diet: We report the development and activity of glucose-conjugated LDH-A inhibitors designed for dual targeting of the Warburg effect (elevated glucose uptake and glycolysis) in cancer cells. Glycoconjugation could be applied to inhibitors of many enzymes involved in glycolysis or tumor metabolism.

Synthesis and antibacterial activity of doxycycline neoglycosides

A set of 37 doxycycline neoglycosides were prepared, mediated via a C-9 alkoxyamino-glycyl-based spacer reminiscent of that of tigecycline. Subsequent in vitro antibacterial assays against representative drug-resistant Gram negative and Gram positive strains revealed a sugar-dependent activity profile and one doxycycline neoglycoside, the 2'-amino-α-D-glucoside conjugate, to rival that of the parent pharmacophore. In contrast, the representative tetracycline-susceptible strain E. coli 25922 was found to be relatively responsive to a range of doxycycline neoglycosides. This study also extends the use of aminosugars in the context of neoglycosylation via a simple two-step strategy anticipated to be broadly applicable for neoglycorandomization.

Glucose conjugation for the specific targeting and treatment of cancer

Cancers of diverse origins exhibit marked glucose avidity and high rates of aerobic glycolysis. Increased understanding of this dysfunctional metabolism known as the Warburg effect has led to an interest in targeting it for cancer therapy. One promising strategy for such targeting is glycoconjugation, the linking of a drug to glucose or another sugar. This review summarizes the most salient examples of glycoconjugates, in which known cytotoxins or targeted anticancer therapeutics have been linked to glucose (or another glucose transporter substrate sugar) for improved cancer targeting and selectivity. Building on these examples, this review also provides a series of guidelines for the design and mechanistic evaluation of future glycoconjugates.

Natural product disaccharide engineering through tandem glycosyltransferase catalysis reversibility and neoglycosylation

A two-step strategy for disaccharide modulation using vancomycin as a model is reported. The strategy relies upon a glycosyltransferase-catalyzed 'reverse' reaction to enable the facile attachment of an alkoxyamine-bearing sugar to the vancomycin core. Neoglycosylation of the corresponding aglycon led to a novel set of vancomycin 1,6-disaccharide variants. While the in vitro antibacterial properties of corresponding vancomycin 1,6-disaccharide analogs were equipotent to the parent antibiotic, the chemoenzymatic method presented is expected to be broadly applicable.