Wing-Ping Fong

Anti-human immunodeficiency virus (anti-HIV) natural products with special emphasis on HIV reverse transcriptase inhibitors

This review article aims at summarizing research findings concerning natural products which are endowed with the ability to inhibit human immunodeficiency virus (HIV). An emphasis is placed on HIV reverse transcriptase inhibitors because the bulk of the literature is focused on these compounds. It was found that a spectacular diversity of chemical structures encompassing proteins, terpenoids, coumarins, xanthones, alkaloids, flavonoids, polyphenols, and polysaccharides, which are elaborated by plant species as phylogenetically remote as the algae, gymnosperms and angiosperms, were capable of rendering the retroviral enzyme less active. The literature pertaining to natural products with HIV protease and integrase inhibitory activities is less voluminous.

The plant ribosome inactivating proteins luffin and saporin are potent inhibitors of HIV-1 integrase

The ribosome inactivating proteins (RIPs) are a group of proteins that are able to inactivate eukaryotic protein synthesis by attacking the 28S ribosomal RNA. Recent studies have shown that some RIPs possess strong anti‐human immunodeficiency virus (HIV) activity. In this study, several common plant RIPs including agrostin, gelonin, luffin, α‐momorcharin, β‐momorcharin, saporin and trichosanthin were examined for the ability to interfere with HIV‐1 replication in a variety of mechanistic assays in vitro. These assays included the CD4/gp120 interaction assay, HIV‐1 reverse transcriptase (RT) assay, HIV‐1 protease assay and HIV‐1 integrase assay. At the concentration of 100 nM, all RIPs appeared to enhance the CD4/gp120 interaction by about 50%. These RIPs exhibited a very weak suppressive effect on HIV‐1 RT and on HIV‐1 protease. In contrast, with the exception of agrostin, all the RIPs tested could strongly inhibit HIV‐1 integrase, the extent of inhibition ranging from 26.1 to 96.3% in an ELISA‐based assay. Two RIPs, saporin and luffin, which licited over 90% inhibition in the ELISA‐based assay, were further characterized in a radiometric assay. Both of these two RIPs evoked a strong dose‐dependent inhibition in the 3′‐end processing and strand‐transfer activities of integrase. The results from this study suggest that the anti‐HIV property of RIPs may be due to inhibition of HIV‐1 integrase.

Phthalocyanine−Polyamine Conjugates as Highly Efficient Photosensitizers for Photodynamic Therapy

A series of silicon(IV) phthalocyanines substituted axially with different polyamine moieties have been prepared. Their fluorescence quantum yields (Φ(F) = 0.03-0.08) in N,N-dimethylformamide are low because of reductive quenching by the amino moieties. The values are significantly increased in aqueous media (Φ(F) = 0.12-0.21) as a result of protonation of the amino substituents. All the compounds are highly photocytotoxic against human colon adenocarcinoma HT29 cells and Chinese hamster ovary cells with IC(50) values as low as 1.1 nM. Flow cytometric studies of two selected compounds (2 and 5) against HT29 cells have shown that they induce apoptosis extensively. As shown by confocal microscopy, these two compounds also show high affinity toward the lysosomes, but not the mitochondria, of the cells. Their in vivo photodynamic activity has also been investigated using HT29 tumor bearing nude mice. Both of them can effectively inhibit the growth of the tumor without causing apparent injury to the liver of the mice.

A comparison of human immunodeficiency virus type 1 inhibition by partially purified aqueous extracts of chinese medicinal herbs

A multiple screening approach to detect compounds inhibitory to various aspects of the human immunodeficiency virus type 1 (HIV-1) life-cycle has been applied to aqueous extracts of 19 herbs traditionally used in Chinese medicine as anti-viral agents. The extracts were tested for their ability to inhibit HIV-1 in a series of in vitro assays. The extracts were tested for inhibition of the interaction between HIV-1 gp120 and immobilized CD4 receptor, inhibition of recombinant HIV-1 reverse transcriptase and for inhibition of three glycohydrolase enzymes that contribute to viral protein glycosylation. Six of the herb extracts (30%) were potent inhibitors of the interaction between HIV-1 gp120 and the CD4 receptor (ID50 5.6 - 79.4 microg/ml), two extracts (10%) contained potent reverse transcriptase inhibitors (ID50 16.9 - 26.0 microg/ml) and 14 extracts (75%) were able to inhibit at least one of the glycohydrolase enzymes.

Preparation of unsymmetrical distyryl BODIPY derivatives and effects of the styryl substituents on their in vitro photodynamic properties

A series of unsymmetrical distyryl BODIPYs have been prepared which function as highly potent photosensitisers with in vitro IC(50) values as low as 15 nM. Their cellular uptake, subcellular localisation and photocytotoxicity depend greatly on the styryl substituents.

Momordica Charantia Lectin, a Type II Ribosome Inactivating Protein, Exhibits Antitumor Activity toward Human Nasopharyngeal Carcinoma Cells In Vitro and In Vivo

The incidence of nasopharyngeal carcinoma (NPC) remains high in endemic regions, including southern China, northern Africa, and North America. One of the promising therapeutic approaches on NPC is drug screening from natural products, such as components from traditional Chinese medicine. In this study, the antitumor activity of Momordica charantia lectin (MCL), a type II ribosome inactivating protein from bitter gourd, on NPC was investigated. MCL evinced potent cytotoxicity toward NPC CNE-1 (IC50 = 6.9) and CNE-2 (IC50 = 7.4) cells but minimally affected normal NP 69 cells. Further investigation disclosed that MCL induced apoptosis, DNA fragmentation, G1-phase arrest, and mitochondrial injury in both types of NPC cells. The reduction of cyclin D1 and phosphoretinoblastoma (Rb) protein expression contributed to arrest at G1-phase of the cell cycle. These events were associated with regulation of mitogen-activated protein kinases (MAPK; including p38 MAPK, JNK, and ERK) phosphorylation and promoted downstream nitric oxide (NO) production. Concurrent administration of the p38 MAPK inhibitor SB-203580 significantly diminished NO production and lethality of MCL toward NPC cells. Further studies revealed that MCL increased cytochrome c release into the cytosol, activated caspases-8, -9, and -3, and enhanced production of cleaved PARP, subsequently leading to DNA fragmentation and apoptosis. Finally, an intraperitoneal injection of MCL (1.0 mg/kg/d) led to an average of 45% remission of NPC xenograft tumors subcutaneously inoculated in nude mice. This is the first article that unveils the potential of a type II RIP, MCL, for prevention and therapy of NPC. Cancer Prev Res; 5(1); 109–21. ©2011 AACR.

A Zinc(II) Phthalocyanine Conjugated with an Oxaliplatin Derivative for Dual Chemo- and Photodynamic Therapy

A novel zinc(II) phthalocyanine substituted with an oxaliplatin derivative via a triethylene glycol linker has been synthesized. The two components work in a cooperative manner in the antitumor action. The conjugate shows a cytotoxic effect in the dark due to the cytostatic oxaliplatin moiety and an enhanced cytotoxicity upon illumination due to the photosensitizing phthalocyanine unit against the HT29 human colon adenocarcinoma cells. The IC(50) value of the conjugate is as low as 0.11 μM, which is 5-fold lower than that of the reference compound without the platinum complex. The high photodynamic activity of the conjugate can be attributed to its high cellular uptake and efficiency in generating intracellular reactive oxygen species. The conjugate also shows preferential localization in the lysosomes of the cells and induces cell death mainly through apoptosis.

Phthalocyanine–Polyamine Conjugates as pH‐Controlled Photosensitizers for Photodynamic Therapy

A series of aryl hydroxyamines prepared by reductive amination were treated with silicon(IV) phthalocyanine dichloride in the presence of pyridine to give the diaxially substituted phthalocyanine-polyamine conjugates 1-5. The electronic absorption, fluorescence emission, and efficiency at generating reactive oxygen species of these compounds were all sensitive to the pH environment. Under acidic conditions, the fluorescence quantum yields and the singlet oxygen quantum yields of these compounds were greatly enhanced in DMF as a result of protonation of the amino moieties, which inhibited the photoinduced electron-transfer deactivation pathway. The Q band was diminished and broadened, and the fluorescence intensity decreased as the pH increased in citrate buffer solutions. The rate of superoxide radical formation was also reduced in a higher pH environment. Compound 3, containing a terminal 4-chlorophenyl group at the axial substituent, showed the most desirable pH-responsive properties, which makes it a promising tumor-selective fluorescence probe and photosensitizer for photodynamic therapy. All of the phthalocyanines 1-5 were highly photocytotoxic against HT29 and HepG2 cells with IC(50) values as low as 0.03 microM. Compound 3 was highly selective toward lysosomes, but not mitochondria of HT29 cells.

Halogenated silicon(IV) phthalocyanines with axial poly(ethylene glycol) chains. Synthesis, spectroscopic properties, complexation with bovine serum albumin and in vitro photodynamic activities

A new series of unsubstituted and halogenated silicon(IV) phthalocyanines with two axial poly(ethylene glycol) (PEG) chains having an average molecular weight of 550 or 750 (PEG550 or PEG750) have been synthesised by treating the corresponding silicon phthalocyanine dichloride with PEG methyl ether in the presence of NaH. The compounds have been unambiguously characterised with 1H NMR and MALDI-TOF mass spectrometry. With two bulky polymeric substituents, the compounds are essentially non-aggregated in common organic solvents. The longer PEG750 chain enhances the hydrophilicity of the phthalocyanine ring and is more effective to prevent aggregation and fluorescence quenching by Cu(OAc)2. Substitution with heavier halogen atoms on the periphery of the ring leads to a reduction in fluorescence emission and an increase in singlet oxygen quantum yield, as a result of heavy atom effect. The compounds Si(PcX8)(PEG750)2 [X = H (4b), Cl (4c), Br (4d)] are photocytotoxic towards HepG2 human hepatocarcinoma cells and J774 mouse mammary tumour cells. Although halogenation results in an increase in singlet oxygen quantum yield, the general photocytotoxicity follows the order 4b > 4d > 4c. This can be attributed to the opposite effect of aggregation, which follows the order 4a < 4b < 4c in the growth medium. The interactions of 4b–d with bovine serum albumin (BSA) have also been investigated by a fluorescence quenching method and a non-covalent conjugate of 4b and BSA has been prepared. Conjugation with BSA leads to a higher photocytotoxicity against J774 cells, which have a BSA-loving macrophage origin.

Purpurin Suppresses Candida albicans Biofilm Formation and Hyphal Development

A striking and clinically relevant virulence trait of the human fungal pathogen Candida albicans is its ability to grow and switch reversibly among different morphological forms. Inhibition of yeast-to-hypha transition in C. albicans represents a new paradigm for antifungal intervention. We have previously demonstrated the novel antifungal activity of purpurin against Candida fungi. In this study, we extended our investigation by examining the in vitro effect of purpurin on C. albicans morphogenesis and biofilms. The susceptibility of C. albicans biofilms to purpurin was examined quantitatively by 2,3-bis(2-methoxy-4-nitro-5-sulfo-phenyl)-2H-tetrazolium-5-carboxanilide reduction assay. Hyphal formation and biofilm ultrastructure were examined qualitatively by scanning electron microscopy (SEM). Quantitative reverse transcription-PCR (qRT-PCR) was used to evaluate the expression of hypha-specific genes and hyphal regulator in purpurin-treated fungal cells. The results showed that, at sub-lethal concentration (3 µg/ml), purpurin blocked the yeast-to-hypha transition under hypha-inducing conditions. Purpurin also inhibited C. albicans biofilm formation and reduced the metabolic activity of mature biofilms in a concentration-dependent manner. SEM images showed that purpurin-treated C. albicans biofilms were scanty and exclusively consisted of aggregates of blastospores. qRT-PCR analyses indicated that purpurin downregulated the expression of hypha-specific genes (ALS3, ECE1, HWP1, HYR1) and the hyphal regulator RAS1. The data strongly suggested that purpurin suppressed C. albicans morphogenesis and caused distorted biofilm formation. By virtue of the ability to block these two virulence traits in C. albicans, purpurin may represent a potential candidate that deserves further investigations in the development of antifungal strategies against this notorious human fungal pathogen in vivo.