Amphiphilic desmuramyl peptides for the rational design of new vaccine adjuvants: Synthesis, in vitro modulation of inflammatory response and molecular docking studies.

Nucleotide-binding oligomerization domain 2 (NOD2) is cytosolic surveillance receptor of the innate immune system capable of recognizing the bacterial and viral infections. Muramyl dipeptide (MDP) is the minimal immunoreactive unit of murein. NOD2 perceives MDP as pathogen-associated molecular pattern, thereby triggering an immune response with undesirable side-effects. Beneficial properties of MDP, such as pro-inflammatory characteristics for the rational design of new vaccine adjuvants, can be harnessed by strategically re-designing the molecule. In this work, a new class of amphiphilic desmuramylpeptides (DMPs) were synthesized by replacing the carbohydrate moiety (muramic acid) of the parent molecule with hydrophilic arenes. A lipophilic chain was also introduced at the C-terminus of dipeptide moiety (alanine-isoglutamine), while conserving its L-D configuration. These novel DMPs were found to set off the release of higher levels of tumour necrosis factor alpha (TNF-α) than Murabutide, which is a well-known NOD2 agonist. Molecular docking studies indicate that all these DMPs bind well to NOD2 receptor with similar dock scores (binding energy) through a number of hydrogen bonding and hydrophobic/π interactions with several crucial residues of the receptor. More studies are needed to further assess their immunomodulatory therapeutic potential, as well as the possible involvement of NOD2 activation.

Synthesis and Cytotoxic Property of Annonaceous Acetogenin Glycoconjugates.

BACKGROUND: Annonaceous acetogenins (ACGs) are secondary metabolites produced by the Annonaceae family and display potent anticancer activity against various cancer cell lines. Squamocin and bullatacin are two examples of ACGs that show promising antitumor activity; however, preclinical data are not sufficient partly due to their being highly lipophilic and poorly soluble in water. These compounds also display high toxicity to normal cells. Due to these disadvantageous properties, the therapeutic potential of squamocin and bullatacin as antitumor agents has not been fully evaluated. METHODS: In order to enhance their water solubility and potentially improve their cancer targeting, squamocin and bullatacin were conjugated to a glucose or galactose to yield glycosylated derivatives by direct glycosylation or the Cu(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC) reaction (the click reaction). The synthesized compounds were evaluated for their anticancer property against HeLa, A549 and HepG2 cancer cell lines using MTT assay. RESULTS: Nine glycosyl derivatives were synthesized and structurally characterized. Most of them show comparable in vitro cytotoxicity against HeLa, A549 and HepG2 cancer cell lines as their parent compounds squamocin and bullatacin. It appears that the type of sugar residue (glucose or galactose), the position at which the sugar residue is attached, and whether or not a linking spacer is present do not affect the potency of these derivatives much. The solubility of galactosylated squamocin 13 in phosphate buffer saline (PBS, pH = 7) is greatly improved (1.37 mg/mL) in comparison to squamocin (not detected in PBS). CONCLUSION: The conjugation of a glucose or galactose to squamocin and bullatacin yields glycosyl derivatives with similar level of anticancer activity in tested cell lines. Further studies are needed to demonstrate whether or not these compounds show reduced toxicity to normal cells and their therapeutic potential as antitumor agents.

Synthesis and antitumor activity of camptothecin- 4ß-triazolopodophyllotoxin conjugates.

Two new compounds (9 and 10) having a camptothecin (CPT) analog conjugated to the 4ß-azido-4-deoxypodophyllotixin analog by untilizing the copper-catalyzed azide-alkyne cycloadditon (CuAAC) reaction, and were evaluated for their cytotoxicity against a panel of five human cancer cell lines (HL-60, SMMC-7721, A-549, MCF-7 and SW480) using the MTT (3-(4,5-dimethyl-thiahiazo-2-yl)-2,5-diphenyltetrazolium bromide) assay. Two novel conjugates shown weak cytotoxicity, compound 10 showed highly potent against HL-60 cell line tested, with IC50 value 17.69 ± 0.19 µM. This compound suggested its potential as anticancer agents for further development. [Formula: see text].

Glucoside Derivatives Of Podophyllotoxin: Synthesis, Physicochemical Properties, And Cytotoxicity.

BACKGROUND: Widespread concern of the side effects and the broad-spectrum anticancer property of podophyllotoxin as an antitumor agent highlight the need for the development of new podophyllotoxin derivatives. Although some per-butyrylated glucosides of podophyllotoxin and 4ß-triazolyl-podophyllotoxin glycosides show good anticancer activity, the per-acetylated/free of podophyllotoxin glucosides and their per-acetylated are not well studied. METHODS: A few glucoside derivatives of PPT were synthesized and evaluated for their in vitro cytotoxic activities against five human cancer cell lines, HL-60 (leukemia), SMMC-7721 (hepatoma), A-549 (lung cancer), MCF-7 (breast cancer), and SW480 (colon cancer), as well as the normal human pulmonary epithelial cell line (BEAS-2B). In addition, we investigated the structure-activity relationship and the physicochemical property-anticancer activity relationship of these compounds. RESULTS: Compound 6b shows the highest cytotoxic potency against all five cancer cell lines tested, with IC50 values ranging from 3.27±0.21 to 11.37±0.52 µM. We have also found that 6b displays higher selectivity than the etoposide except in the case of HL-60 cell line. The active compounds possess similar physicochemical properties: MSA > 900, %PSA < 20, ClogP > 2, MW > 700 Da, and RB > 10. CONCLUSION: We synthesized several glucoside derivatives of PPT and tested their cytotoxicity. Among them, compound 6b showed the highest cytotoxicity. Further studies including selectivity of active compounds have shown that the selectivity indexes of 6b are much greater than the etoposide except in the case of HL-60 cell line. The active compounds possessed similar physicochemical properties. This study indicates that active glucoside analogs of podophyllotoxin have potential as lead compounds for developing novel anticancer agents.

Design, Synthesis, and Biological Evaluation of Novel Biotinylated Podophyllotoxin Derivatives as Potential Antitumor Agents.

Podophyllotoxin has long been used as an active substance for cytotoxic activity. Fourteen novel biotinylated podophyllotoxin derivatives were designed, synthesized, and evaluated for cytotoxic activity for this study. The synthesized compounds were evaluated for cytotoxic activity in the following human cancer cell lines, SW480, MCF-7, A-549, SMMC-7721, and HL-60 by MTT assay. Most of them exhibited potent cytotoxic effects and compound 15 showed the highest cytotoxic activity among the five cancer cell lines tested, having its IC50 values in the range of 0.13 to 0.84 µM. Apoptosis analysis revealed that compound 15 caused obvious induction of cell apoptosis. Compound 15 significantly down-regulated the expression level of the marker proteins (caspase-3 and PARP) in H1299 and H1975 cells, activated the transcription of IRE1α, increased the expression of GRP78 and XBP-1s, and finally induced apoptosis of H1299 cells. In vivo studies showed that 15 at a dose of 20 mg/kg suppressed tumor growth of S180 cell xenografts in icr mice significantly. Further molecular docking studies suggested that compound 15 could bind well with the ATPase domain of Topoisomerase-II. These data suggest that compound 15 is a promising agent for cancer therapy deserving further research.

Synthesis and antitumor activity of biotinylated camptothecin derivatives as potent cytotoxic agents.

A series of biotinylated camptothecin derivatives were designed and synthesized. The key to the synthesis was achieved by employing an esterification reaction and click chemistry. All of the new derivatives were tested for cytotoxicity against five human tumor cell lines, including HL-60, SMMC-7721, A-549, MCF-7, and SW480 with IC50 values ranging from 0.13 to 21.53 µM. Most of the derivatives exhibited potent cytotoxicity, especially compound 17 (IC50 = 0.13-3.31 µM) and compound 18 (IC50 = 0.23-1.48 µM), which exhibited the highest potencies. The structure-activity relationships (SARs) of the biotinylated camptothecin derivatives were discussed for exploring novel anticancer agents.

Synthesis and anticancer activity of dimeric podophyllotoxin derivatives.

BACKGROUND: Podophyllotoxin is a potent cytotoxic agent and serves as a useful lead compound for the development of antitumor drugs. Several podophyllotoxin-derived antitumor agents, including etoposide, are currently in clinical use; however, their therapeutic efficacy is often limited due to side effects and the development of resistance by cancer cells. Previous studies have shown that 4ß-1,2,3-triazole derivatives of podophyllotoxin exhibit more potent anticancer activity and better binding to topoisomerase-II than etoposide. The effect of dimerization of such derivatives on the anticancer activity has not been studied. METHODS: Two moieties of podophyllotoxin were linked at the C-4 position via 1,2,3-triazole rings to give a series of novel dimeric podophyllotoxin derivatives. 4ß-Azido-substituted podophyllotoxin derivatives (23 and 24) were coupled with various dipropargyl functionalized linkers by utilizing the copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction to provide dimeric products in very good yield. The in vitro anticancer activity of the synthesized compounds was evaluated by MTT assay against a panel of five human cancer cell lines (HL-60, SMMC-7721, A-549, MCF-7, and SW480). The normal BEAS-2B (lung) cell line was also included for study in order to evaluate the cancer selectivity of the most active compound as compared with normal cells. RESULTS: A group of 16 dimeric podophyllotoxin derivatives with different linkers were synthesized and structurally characterized. Most compounds do not show significant cytotoxicity (IC50 > 40 mM) against all five cancer cell lines. However, one compound (29) which bears a perbutyrylated glucose residue on the glycerol linker is highly potent against all five cancer cell lines tested, with IC50 values ranging from 0.43 to 3.50 µM. This compound (29) also shows good selectivity towards cancer cell lines as compared with the normal BEAS-2B (lung) cell line, showing selectivity indexes from 4.4 to 35.7. CONCLUSION: The anticancer activity of dimeric podophyllotoxin derivatives is generally speaking not improved as compared to their monomeric counterparts, and the potency of these dimeric derivatives can be largely affected by the nature of the linker between the two moieties. Among the synthesized derivatives, compound 29 is significantly more cytotoxic and selective towards cancer cells than etoposide and cisplatin, which are currently in clinical use. Compound 29 is a promising anticancer drug and needs further studies.

Synthesis and Cytotoxic Activity of Novel Tetrahydrocurcumin Derivatives Bearing Pyrazole Moiety.

Tetrahydrocurcumin (THC) is a major metabolite of curcumin and plays an important role in curcumin-induced biological effects. THC is a promising preventive and chemotherapeutic agent for cancer. A series of new pyrazole derivatives of THC have been synthesized as potent anticancer agents. Direct condensation of THC with various substituted hydrazines leads to new pyrazole derivatives of THC (1-18). The prepared compounds have been evaluated via in vitro MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay for their cell proliferation-inhibitory activity against human lung adenocarcinoma (A549), human cervical carcinoma (HeLa) and human breast carcinoma (MCF-7) cells. Most derivatives show significantly higher anticancer activity against all three tested cancer cell lines than the parent compound THC. Several compounds (7, 8, 12, 13 and 15) display promising anticancer activity against MCF-7 cell line with IC50 values ranging from 5.8 to 9.3 µM. The most active compound (8) is substituted with 4-bromophenyl group at the pyrazole ring and inhibits the growth of all three tested cancer cell lines with an IC50 values of (8.0 µM, A549), (9.8 µM, HeLa) and (5.8 µM, MCF-7). The obtained compounds can be a good starting point for the development of new lead molecules in the fight against cancer.

Design, synthesis and immunological evaluation of novel amphiphilic desmuramyl peptides.

Muramyl dipeptide (MDP) - an essential bacterial cell wall component - is recognized by our immune system as pathogen-associated molecular pattern (PAMP) which results in immune responses with adverse toxic effects. In order to harness the beneficial properties from the pro-inflammatory characteristics of the bacterial cell wall motif, MDP was strategically re-designed while conserving the L-D configurations of the dipeptide moiety. The muramic acid was replaced with a hydrophilic arene and lipophilic chain was introduced at peptide end to give the amphiphilic desmuramyl peptides (DMPs). The novel DMPs were found to modulate the immune response by amplifying the LPS-induced surface glycoprotein (ICAM-1) expression in THP-1 cells without showing significant toxicity. Furthermore, these compounds were able to trigger the secretion of higher levels of pro-inflammatory cytokine (TNF-α) than the well-studied NOD2 agonist, Murabutide.

Synthesis and cancer cell growth inhibitory activity of icaritin derivatives.

A series of icaritin derivatives bearing carboxylic acid or carboxylic ester groups are synthesized, and their in vitro cytotoxic activity against three cancer cell lines, MCF-7, MDA-MB-435s, and A549, are evaluated by MTT assay. Several derivatives including 2h, 2j, 5b and 5d show higher cytotoxic activity than the parent compound icaritin against these cancer cell lines. Compounds 5b and 5d are even more cytotoxic to MCF-7 cells than the clinic drug tamoxifen. Moreover, compound 5b is found to be non-toxic to normal cells (Vero) and both 5b and 5d exhibit good selectivity towards estrogen receptor positive MCF-7 breast cancer cells over estrogen receptor negative MDA-MB-435s breast cancer cells. The structure activity relationship analysis has revealed that mono-substitution at either C-3 or C-7 hydroxyl group of icaritin could improve the cytotoxicity of icaritin, and the C-3 hydroxyl group may be a preferable site for chemical modification. In addition, the length, the flexibility and the additional branching substituent group of the substitution chain(s) at both C-3 and C-7 hydroxyl groups can all affect the anti-cancer activity of these derivatives.

Synthesis and Anticancer Activity of 4ß-Triazole-podophyllotoxin Glycosides.

A series of novel 4ß-triazole-podophyllotoxin glycosides were synthesized by utilizing the Click reaction. Evaluation of cytotoxicity against a panel of five human cancer cell lines (HL-60, SMMC-7721, A-549, MCF-7, SW480) using MTT assay shows that most of these compounds show weak cytotoxicity. It was observed that compound 16 shows the highest activity with IC50 values ranging from 2.85 to 7.28 µM, which is more potent than the control drugs etoposide and cisplatin against four of five cancer cell lines tested. Compound 16 is characterized with an α-D-galactosyl residue directly linked to the triazole ring and a 4'-OH group on the E ring of the podophyllotoxin scaffold. HPLC investigation of representative compound indicates that incorporation of a sugar moiety seems to improve the chemical stability of the podophyllotoxin scaffold.

Synthesis and antitumor activity of novel per-butyrylated glycosides of podophyllotoxin and its derivatives.

A series of perbutyrylated glycosides of podophyllotoxin and its derivatives were synthesized and evaluated for their antitumor activity in vitro. Most of them exhibit cytotoxic activity against a panel of five human cancer cell lines (HL-60, SMMC-7721, A-549, MCF-7, SW480) using MTT assays. Among the synthesized compounds, epipodophyllotoxin α-d-galactopyranoside 8b, epipodophyllotoxin α-d-arabinopyranoside 8e, and podophyllotoxin ß-d-glucopyranoside 11a show the highest potency of anticancer activity with their IC50 values ranging from 0.14 to 1.69µM. Structure activity relationship analysis indicates that the type of glycosidic linkage, the configuration at C-4 of the podophyllotoxin scaffold, and the substitution at 4'-position (OH vs OCH3) can all have significant effect on the potency of their anticancer activity. Several compounds are more active than the control drugs Etoposide and Cisplatin, suggesting their potential as anticancer agents for further development.

Design, synthesis, and cytotoxicity of perbutyrylated glycosides of 4ß-triazolopodophyllotoxin derivatives.

A series of novel perbutyrylated glycosides of 4ß-triazolopodophyllotoxin derivatives were synthesized by utilizing the copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. Evaluation of cytotoxicity against a panel of five human cancer cell lines (HL-60, SMMC-7721, A-549, MCF-7, SW480) using the MTT assay shows that some of these glycosylated derivatives have good anticancer activity. Among the synthesized compounds, compound 21a shows the highest activity, with IC50 values ranging from 0.49 to 6.70 µM, which is more potent than the control drugs etoposide and cisplatin. Compound 21a is characterized by a perbutyrylated α-D(+)-galactosyl residue, the absence of an additional linking spacer between the sugar residue and the triazole ring, as well as a 4'-OH group on the E ring of the podophyllotoxin scaffold.

Synthesis and tumor cell growth inhibitory activity of biotinylated annonaceous acetogenins.

Nineteen biotinylated squamocin/bullatacin derivatives have been synthesized for targeted delivery to biotin receptor overexpressed tumor cells. Most biotinylated squamocin and bullatacin derivatives show similar in vitro cytotoxicity against the biotin receptor non-overexpressed L1210 cells as squamocin and bullatacin, respectively, while against biotin receptor overexpressed 4T1 and P815 tumor cells, several derivatives show significantly higher potency and better selectivity. Among all the synthesized compounds, 15,28-di-O-(6-biotinylamidohexanoyl)squamocin (16) is the most potent, which is 10 and 26 times more active than squamocin against 4T1 and P815 cells, respectively. Compound 16 also appears to be six and fifteen times more selective than squamocin towards 4T1 and P815 cells, respectively, against L1210 cells. The structure activity relationship analysis has revealed that the preferred site for biotinylation is different for squamocin and bullatacin, and it also depends on whether a linking spacer is present.

Synthesis and anticancer activity of glucosylated podophyllotoxin derivatives linked via 4ß-triazole rings.

A series of 4ß-triazole-linked glucose podophyllotoxin conjugates have been designed and synthesized by employing a click chemistry approach. All the compounds were evaluated for their anticancer activity against a panel of five human cancer cell lines (HL-60, SMMC-7721, A-549, MCF-7, SW480) using MTT assays. Most of these triazole derivatives have good anticancer activity. Among them, compound 35 showed the highest potency against all five cancer cell lines tested, with IC50 values ranging from 0.59 to 2.90 µM, which is significantly more active than the drug etoposide currently in clinical use. Structure-activity relationship analysis reveals that the acyl substitution on the glucose residue, the length of oligoethylene glycol linker, and the 4'-demethylation of podophyllotoxin scaffold can significantly affect the potency of the anticancer activity. Most notably, derivatives with a perbutyrylated glucose residue show much higher activity than their counterparts with either a free glucose or a peracetylated glucose residue.

Synthesis of a dimeric monosaccharide lipid A mimic and its synergistic effect on the immunostimulatory activity of lipopolysaccharide.

Bacterial endotoxin lipopolysaccharide (LPS) is a potent immune stimulant, with the recognition of LPS and its active principal lipid A mediated by the Toll-like receptor 4 (TLR4)/MD-2 receptor complex. Due to the broad downstream implications of TLR4-mediated signalling, TLR4 ligands show great potential for immunotherapeutic manipulations. In this paper a dimeric monosaccharide lipid A mimic (3) has been designed as a potential TLR4 ligand. The chemical synthesis and the preliminary biological studies are described. Compound 3 shows a significant synergistic effect on LPS-induced ICAM-1 expression in human monocytic THP-1 cells.

Structural analogues of diosgenyl saponins: synthesis and anticancer activity.

Saponins display various biological activities including anti-tumor activity. Recently intensive research has been focused on developing saponins for tumor therapies. The diosgenyl saponin dioscin is one of the most common steroidal saponins and exhibits potent anticancer activity in several human cancer cells through apoptosis-inducing pathways. In this paper, we describe the synthesis of several diosgenyl saponin analogues containing either a 2-amino-2-deoxy-beta-d-glucopyranosyl residue or an alpha-l-rhamnopyranosyl-(1-->4)-2-amino-2-deoxy-beta-d-glucopyranosyl residue with different acyl substituents on the amino group. The cytotoxic activity of these compounds was evaluated in MCF-7 breast cancer cells and HeLa cervical cancer cells. Structure-activity relationship studies show that the disaccharide saponin analogues are in general less active than their corresponding monosaccharide analogues. The incorporation of an aromatic nitro functionality into these saponin analogues does not exhibit significant effect on their cytotoxic activity.

Synthesis and cytotoxic activity of diosgenyl saponin analogues.

Diosgenyl saponins are steroidal glycosides that are often found as major components in many traditional oriental medicines. Recently, a number of naturally occurring diosgenyl saponins have been shown to exert cytotoxic activity against several strains of human cancer cells. Use of these saponin compounds for cancer treatment is hampered due to the lack of understanding of their action mechanism as well as limited access to such structurally complicated molecules. In the present paper, we have prepared a group of diosgenyl saponin analogues which contain a beta-D-2-amino-2-deoxy-glucopyranose residue having different substituents at the amino group. Moderate cytotoxic activity is found for most analogues against neuroblastoma (SK-N-SH) cells, breast cancer (MCF-7) cells, and cervical cancer (HeLa) cells. The analogue 13 that contains an alpha-lipoic acid residue exhibits the highest potency against all three cancer cell lines with IC(50) ranging from 4.8 microM in SK-N-SH cells to 7.3 microM in HeLa cells. Preliminary mechanistic investigation with one saponin analogue (10) shows that the compound induces cell cycle arrest at G(1) phase in SK-N-SH cells, but the same compound induces cell cycle arrest at G(2) phase in MCF-7 cells. This result suggests that the cytotoxic activity of these saponin analogues may involve different action mechanisms in cell lines derived from different cancer sites.

Synthesis of beta-(1-->4)-oligo-D-mannuronic acid neoglycolipids.

Mammalian Toll-like receptors (TLRs) play important roles in host immune defense. The activation of TLR and down-stream signaling pathways have great impact on human physiology. Chemically diverse microbial products as well as synthetic ligands serve as agonists for these receptors. Recently, synthetic TLR ligands are being exploited as useful therapeutic agents for a variety of diseases including infections, inflammatory diseases, and cancers. Alginate polymers and oligosaccharides are strong immune stimulants mediated by TLR2/4, but synthesis of alginate oligomers is rarely studied. Reported here are the design and chemical synthesis of two beta-(1-->4)-di- and beta-(1-->4)-tri-d-mannuronic acid neoglycolipids 1 and 2 as potential TLR ligands. By using 4,6-di-O-benzylidene-protected 1-thio mannoside 7 as a glycosyl donor, the diastereoselective beta-d-mannosylation protocol provides the beta-(1-->4)-d-mannobiose and beta-(1-->4)-d-mannotriose derivatives, which upon regioselective oxidation with TEMPO/BAIB oxidation system yield the corresponding beta-(1-->4)-d-mannuronic acid containing neoglycolipids 1 and 2.

Synthetic vaccines: the role of adjuvants in immune targeting.

A clear understanding of the mechanism of function of immune stimulatory adjuvants, which commonly accompany vaccines, is beginning to emerge. Recent investigations have demonstrated that Toll-like receptors (TLRs) are the critical link between the innate and the adaptive immunity. This link, which is normally activated as a result of collaboration between adjuvants and TLRs in triggering adaptive immunity, has been a subject of several recent investigations. With the advent of well-defined synthetic small molecules, which are designed to either mimic the adjuvants or, as in many cases, to structurally represent pathogen associated molecular patterns, it is now possible to design reproducible experiments and to draw credible conclusions. An adjuvant alerts the host immune system through a mechanism similar to that of an infection by a pathogen, which involves interaction with a TLR followed by a lsqou;danger signal' to the immune system. Secretion of cytokines and regulation of the expression of co-stimulatory molecules induced by innate response shape the magnitude and quality of adaptive response. Synthetic vaccines containing specific epitopes to which immune responses are desired, are expected to be far superior in target specificity while the benefits may be long-lasting. The immune responses by therapeutic vaccines are generally adaptive in nature and such responses often require the participation of the components of innate immunity, most importantly the TLRs and their pathogen-associated binding compliments. Structurally well-defined synthetic molecules derived from lipid A, muramyl di-peptide (MDP), and CpG motifs from bacterial DNA offer a wide range of immune stimulants for the development of fully synthetic vaccines. Lipo-peptide and self-adjuvanted antigens, in combination with additional immune stimulatory adjuvants in liposome delivery system, may be important in vaccine design. Combinations of synthetic mimics of microbial products are known to display synergistic effects in stimulating the immune system. Either alone or in combination with chemotherapy, innate immune therapy using TLR ligands to stimulate the immune system may offer an alternate therapeutic approach against rapidly mutating viral infections-(HIV/AIDS), and cancers.