Induction of apoptosis by streptochlorin isolated from Streptomyces sp. in human leukemic U937 cells

Resistomycin Suppresses Prostate Cancer Cell Growth by Instigating Oxidative Stress, Mitochondrial Apoptosis, and Cell Cycle Arrest

Globally, prostate cancer is among the most threatening and leading causes of death in men. This study, therefore, aimed to search for an ideal antitumor strategy with high efficacy, low drug resistance, and no or few adverse effects. Resistomycin is a natural antibiotic derived from marine actinomycetes, and it possesses various biological activities. Prostate cancer cells (PC3) were treated with resistomycin (IC12.5: 0.65 or IC25: 1.3 µg/mL) or 5-fluorouracil (5-FU; IC25: 7 µg/mL) for 24 h. MTT assay and flow cytometry were utilized to assess cell viability and apoptosis. Oxidative stress, apoptotic-related markers, and cell cycle were also assessed. The results revealed that the IC50 of resistomycin and 5-FU on PC3 cells were 2.63 µg/mL and 14.44 µg/mL, respectively. Furthermore, treated cells with the high dose of resistomycin showed an increased number of apoptotic cells compared to those treated with the lower dose. Remarkable induction of reactive oxygen species generation and lactate dehydrogenase (LDH) leakage with high malondialdehyde (MDA), carbonyl protein (CP), and 8-hydroxyguanosine (8-OHdG) contents were observed in resistomycin-treated cells. In addition, marked declines in glutathione (GSH), superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) in PC3 cells subjected to resistomycin therapy were observed. Resistomycin triggered observable cell apoptosis by increasing Bax, caspase-3, and cytosolic cytochrome c levels and decreasing Bcl-2 levels. In addition, notable downregulation of proliferating cell nuclear antigen (PCNA) and cyclin D1 was observed in resistomycin-treated cancerous cells. According to this evaluation, the antitumor potential of resistomycin, in a concentration-dependent manner, in prostate cancer cells was achieved by triggering oxidative stress, mitochondrial apoptosis, and cell cycle arrest in cancer cells. In conclusion, our investigation suggests that resistomycin can be considered a starting point for developing new chemotherapeutic agents for human prostate cancer.

Discovery of Novel Benzoxaborole-Containing Streptochlorin Derivatives as Potential Antifungal Agents

Streptochlorin is a kind of indole alkaloid derived from marine microorganisms. It is a promising lead compound due to its potent bioactivity in preventing many phytopathogens, as shown in our previous study. To explore the potential applications of this natural product, a series of novel benzoxaborole-containing streptochlorin derivatives were designed and synthesized through a one-step and catalyst-free reaction in water at room temperature. All target compounds were first screened for their antifungal profiles in vitro against six common phytopathogenic fungi. The results of bioassay revealed that most of the designed compounds exhibited more significant antifungal activities against Botrytis cinrea, Gibberella zeae, Rhizoctorzia solani, Colletotrichum lagenarium, and alternaria leaf spot under the concentration of 50 μg/mL, and this is highlighted by compounds 4i and 5f, which demonstrated impressive antifungal effects against G. zeae and R. solani, with their corresponding EC₅₀ values 0.2983 and 0.2657 μg/mL, which are obviously better than positive control flutriafol and boscalid (5.2606 and 1.2048 μg/mL, respectively). Scanning electron microscopy on the hyphae morphology showed that compound 5b might cause mycelial abnormalities of G. zeae. 3D-QSAR studies of CoMFA and CoMSIA were carried out on 29 target compounds with antifungal activity against B. cinrea. The analysis results indicated that introducing appropriate electronegative groups at the 5-position of benzoxaborole and the 4,5-positions of the indole ring could effectively improve the anti-B. cinrea activity. Moreover, compound 5b showed good antifungal activities in vivo against Phytophthora capsici. Molecular docking was further explored to ascertain the practical value of the active compound as a potential inhibitor of LeuRS. The abovementioned results indicate that the designed benzoxaborole-containing streptochlorin derivatives could be further studied as template molecules of novel antifungal agents.

Design, Synthesis, Antifungal Activity, and Molecular Docking of Streptochlorin Derivatives Containing the Nitrile Group

Based on the structures of natural products streptochlorin and pimprinine derived from marine or soil microorganisms, a series of streptochlorin derivatives containing the nitrile group were designed and synthesized through acylation and oxidative annulation. Evaluation for antifungal activity showed that compound 3a could be regarded as the most promising candidate-it demonstrated over 85% growth inhibition against Botrytis cinerea, Gibberella zeae, and Colletotrichum lagenarium, as well as a broad antifungal spectrum in primary screening at the concentration of 50 μg/mL. The SAR study revealed that non-substituent or alkyl substituent at the 2-position of oxazole ring were favorable for antifungal activity, while aryl and monosubstituted aryl were detrimental to activity. Molecular docking models indicated that 3a formed hydrogen bonds and hydrophobic interactions with Leucyl-tRNA Synthetase, offering a perspective for the possible mechanism of action for antifungal activity of the target compounds.

Discovery of Novel Pimprinine and Streptochlorin Derivatives as Potential Antifungal Agents

Pimprinine and streptochlorin are indole alkaloids derived from marine or soil microorganisms. In our previous study, they were promising lead compounds due to their potent bioactivity in preventing many phytopathogens, but further structural modifications are required to improve their antifungal activity. In this study, pimprinine and streptochlorin were used as parent structures with the combination strategy of their structural features. Three series of target compounds were designed and synthesized. Subsequent evaluation for antifungal activity against six common phytopathogenic fungi showed that some of thee compounds possessed excellent effects, and this is highlighted by compounds 4a and 5a, displaying 99.9% growth inhibition against Gibberella zeae and Alternaria Leaf Spot under 50 μg/mL, respectively. EC₅₀ values indicated that compounds 4a, 5a, 8c, and 8d were even more active than Azoxystrobin and Boscalid. SAR analysis revealed the relationship between 5-(3'-indolyl)oxazole scaffold and antifungal activity, which provides useful insight into the development of new target molecules. Molecular docking models indicate that compound 4a binds with leucyl-tRNA synthetase in a similar mode as AN2690, offering a perspective on the mode of action for the study of its antifungal activity. These results suggest that compounds 4a and 5a could be regarded as novel and promising antifungal agents against phytopathogens due to their valuable potency.

Studies on the Mechanism of Alloimperatorin on the Proliferation and Apoptosis of HeLa Cells

Alloimperatorin is a compound extracted from the traditional Chinese medicine (Angelica dahurica), which has exhibited anticancer activity. However, its precise molecular mechanism of anticancer remains unclear. Alloimperatorin-induced apoptosis of cervical cancer cells and its molecular mechanism were investigated in the present study. Cholecystokinin octapeptide (CCK-8) was employed to evaluate the cytotoxicity of alloimperatorin on HeLa, SiHa, and MS-751 cells. Flow cytometry was used to assess apoptosis induced by alloimperatorin. The mechanism of apoptosis was verified by mitochondrial membrane potential, Western blotting, and fluorescent PCR. The results of the study showed that alloimperatorin reduced the activity of HeLa cells. The calculated IC50 at 48 hours was 116.9 μM. Compared with the control group, alloimperatorin increased the apoptotic rate of HeLa cells and reduced the mitochondrial membrane potential of HeLa cells. The Western blot results showed that alloimperatorin promotes the expression of caspase3, 8, 9 and that Bax apoptotic proteins reduce PARP expression, procaspase3, 8, 9, and BCL-2 proteins and reduces the cyt-c in the mitochondria expression. The results demonstrated that alloimperatorin can induce HeLa cell apoptosis through mitochondria and extrinsic apoptotic pathways.

Streptochlorin analogues as potential antifungal agents: Design, synthesis, antifungal activity and molecular docking study

Streptochlorin is a small molecule of indole alkaloid isolated from marine Streptomyces sp., it is a promising lead compound due to its potent bioactivity in preventing many phytopathogens in our previous study, but further structural modifications are required to improve its antifungal activity. Our work in this paper focused on the replacement of oxazole ring in streptochlorin with the imidazole ring, to discover novel analogues. Based on this design strategy, three series of streptochlorin analogues were efficiently synthesized through sequential Vilsmeier-Haack reaction, Van Leusen imidazole synthesis and halogenation reaction. Some of the analogues displayed excellent activity in the primary assays, and this is highlighted by compounds 4g and 4i, the growth inhibition against Alternaria Leaf Spot and Rhizoctorzia solani under 50 μg/mL are 97.5% and 90.3%, respectively, even more active than those of streptochlorin, pimprinine and Osthole. Molecular docking models indicated that streptochlorin binds with Thermus thermophiles Leucyl-tRNA Synthetase in a similar mode to AN2690, offering a perspective on the mode of action study for antifungal activities of streptochlorin derivatives. Further study is still ongoing with the aim of discovering synthetic analogues, with improved antifungal activity and clear mode of action.

Antiangiogenic molecules from marine actinomycetes and the importance of using zebrafish model in cancer research

Blood vessel sprouting from pre-existing vessels or angiogenesis plays a significant role in tumour progression. Development of novel biomolecules from marine natural sources has a promising role in drug discovery specifically in the area of antiangiogenic chemotherapeutics. Symbiotic actinomycetes from marine origin proved to be potent and valuable sources of antiangiogenic compounds. Zebrafish represent a well-established model for small molecular screening and employed to study tumour angiogenesis over the last decade. Use of zebrafish has increased in the laboratory due to its various advantages like rapid embryo development, optically transparent embryos, large clutch size of embryos and most importantly high genetic conservation comparable to humans. Zebrafish also shares similar physiopathology of tumour angiogenesis with humans and with these advantages, zebrafish has become a popular model in the past decade to study on angiogenesis related disorders like diabetic retinopathy and cancer. This review focuses on the importance of antiangiogenic compounds from marine actinomycetes and utility of zebrafish in cancer angiogenesis research.

Design and synthesis of novel 4-thiazolidinone derivatives with promising anti-breast cancer activity: Synthesis, characterization, in vitro and in vivo results

Novel lead compounds as anticancer agents with the ability to circumvent emerging drug resistance have recently gained a great deal of interest. Thiazolidinones are among such compounds with well-established biological activity in the field of oncology. Here, we designed, synthesized and characterized a series of thiazolidinone structures (8a-8k). The results of anti-proliferative assay led to the discovery of compound 8j with a high potent cytotoxic effect using colon, liver and breast cancer cells. Furthermore, MDA-MB-231 and 4T1 cell lines were used to represent triple negative breast cancer (TNBC). Next, a number of in vitro and in vivo evaluations were carried out to demonstrate the potential activity against TNBC and also elucidate the possible mechanism of cell death induction. Our in vitro outcomes exhibited an impressive anticancer activity for compound 8j toward MDA-MB-231 cells through inducing apoptosis and a remarkable anti-metastatic feature via suppressing MMP-9 expression as well. Consistently, the in vivo and immunohistopathologic evaluations demonstrated that this compound significantly inhibited the 4T1 induced tumor growth and its metastasis to the lung. Altogether, among numerous thiazolidinone derivatives, compound 8j might represent a promising anticancer agent for TNBC, which is a major concern in the developed and developing countries.

Diversity-oriented synthesis and antifungal activities of novel pimprinine derivative bearing a 1,3,4-oxadiazole-5-thioether moiety

Based on the strategy of diversity-oriented synthesis and the structures of natural product pimprinine and streptochlorin, two series of novel pimprinine derivatives containing 1,3,4-oxadiazole-5-thioether moieties were efficiently synthesized under the optimized reaction conditions. Biological assays conducted at Syngenta showed the designed derivatives displayed an altered pattern of biological activity, of which 5h was identified as the most promising compound with strong activity against Pythium dissimile and also a broad antifungal spectrum in primary screening. Further structural optimization of pimprinine and streptochlorin derivatives is well under way, aiming to discover synthetic analogues with improved antifungal activity. Two series of novel pimprinine derivatives containing 1,3,4-oxadiazole-5-thioether moieties were efficiently synthesized through diversity-oriented synthesis strategy under the optimized conditions. Biological assays showed the designed derivatives exhibited potential activity.

The effects and mechanism of peiminine-induced apoptosis in human hepatocellular carcinoma HepG2 cells

Peiminine is a compound isolated from Bolbostemma paniculatum (Maxim) Franquet (Cucurbitaceae family), which has demonstrated antitumor activities. But its precise molecular mechanism underlying antitumor activity remain elusive. In this study, peiminine-induced apoptosis towards human hepatocellular carcinoma and its molecular mechanism were investigated. MTT assay was employed to assess anticancer effects of peiminine upon Hela, HepG2, SW480 and MCF-7 cell lines. Nuclear staining and flow cytometry were carried out to detect apoptosis induced by peiminine. Mitochondrial membrane potential evaluation and Western blot analysis were performed to investigate the mechanism of peiminine-induced apoptosis. The results showed peiminine reduced the viability of HepG2 cells in a time- and dose-dependent manner and had an IC50 of 4.58 μg/mL at 24h. Peiminine significantly increased the percentage of apoptotic cells and the mitochondrial membrane potential dose-dependently in HepG2 cells. The results of Western blotting indicated the expressions of Bcl-2, procaspase-3, procaspase-8, procaspase-9, and PARP decreased in HepG2 cells treated with peiminine, while the expressions of Bax, caspase-3, caspase-8, caspase-9, and cleaved PARP1 increased. The result suggests that peiminine can induce apoptosis in human hepatocellular carcinoma HepG2 cells through both extrinsic and intrinsic apoptotic pathways.

An efficient synthesis and antifungal evaluation of natural product streptochlorin and its analogues

Streptochlorin, a small indole alkaloid isolated from marine Streptomyces sp., exhibits a wide range of potent biological activities. An efficient and economic synthetic protocol for streptochlorin has been developed and validated, 4 steps from indole in a total yield of 45%, and further applied for the synthesis of its analogues. Biological testing showed that most of the target compounds exhibited potential antifungal activity in the primary assays, especially compounds 6, 7 and 9c were the most active ones, representing effective activity against the phytopathogenic fungi screened in preliminary test and might be explored for the study of mode of action in the future.

Anticancer activity of streptochlorin, a novel antineoplastic agent, in cholangiocarcinoma

BACKGROUND

The aim of this study is to investigate the anticancer activity of streptochlorin, a novel antineoplastic agent, in cholangiocarcinoma.

METHODS

The anticancer activity of streptochlorin was evaluated in vitro in various cholangiocarcinoma cell lines for apoptosis, proliferation, invasiveness, and expression of various protein levels. A liver metastasis model was prepared by splenic injection of HuCC-T1 cholangiocarcinoma cells using a BALB/c nude mouse model to study the systemic antimetastatic efficacy of streptochlorin 5 mg/kg at 8 weeks. The antitumor efficacy of subcutaneously injected streptochlorin was also assessed using a solid tumor xenograft model of SNU478 cells for 22 days in the BALB/c nude mouse.

RESULTS

Streptochlorin inhibited growth and secretion of vascular endothelial growth factor by cholangiocarcinoma cells in a dose-dependent manner and induced apoptosis in vitro. In addition, streptochlorin effectively inhibited invasion and migration of cholangiocarcinoma cells. Secretion of vascular endothelial growth factor and activity of matrix metalloproteinase-9 in cholangiocarcinoma cells were also suppressed by treatment with streptochlorin. Streptochlorin effectively regulated metastasis of HuCC-T1 cells in a mouse model of liver metastasis. In a tumor xenograft study using SNU478 cells, streptochlorin significantly inhibited tumor growth without changes in body weight when compared with the control.

CONCLUSION

These results reveal that streptochlorin is a promising chemotherapeutic agent to the treatment of cholangiocarcinoma.

Synthesis and antifungal activity of novel streptochlorin analogues

Streptochlorin, first isolated as a new antibiotic in 1988 from the lipophilic extracts of the mycelium of a Streptomyces sp, is an indole natural products with a variety of biological activities. Based on the methods developed for the synthesis of pimprinine in our laboratory, we have synthesized a series of indole-modified streptochlorin analogues and measured their activities against seven phytopathogenic fungi. Some of the analogues displayed good activity in the primary assays, and the seven compounds 10b, 10c, 11e, 13e, 21, 22c and 22e (shown in Figure 1) were identified as the most promising candidates for further study. Structural optimization is still ongoing with the aim of discovering synthetic analogues with improved antifungal activity.

Gliotoxin isolated from marine fungus Aspergillus sp. induces apoptosis of human cervical cancer and chondrosarcoma cells

Gliotoxin, a secondary metabolite produced by marine fungus Aspergillus sp., possesses various biological activities including anticancer activity. However, the mechanism underlying gliotoxin-induced cytotoxicity on human cervical cancer (Hela) and human chondrosarcoma (SW1353) cells remains unclear. In this study, we focused on the effect of gliotoxin induction on apoptosis, the activating expressions of caspase family enzymes in the cells. Apoptotic cell levels were measured through DAPI and Annexin V/Propidium Iodide (PI) double staining analysis. The apoptotic protein expression of Bcl-2 and caspase family was detected by Western blot in Hela and SW1353 cells. Our results showed that gliotoxin treatment inhibited cell proliferation and induced significant morphological changes. Gliotoxin induced apoptosis was further confirmed by DNA fragmentation, chromatin condensation and disrupted mitochondrial membrane potential. Gliotoxin-induced activation of caspase-3, caspase-8 and caspase-9, down-regulation of Bcl-2, up-regulation of Bax and cytochromec (cyt c) release showed evidence for the gliotoxin activity on apoptosis. These findings suggest that gliotoxin isolated from marine fungus Aspergillus sp. induced apoptosis in Hela and SW1353 cells via the mitochondrial pathway followed by downstream events leading to apoptotic mode of cell death.

Physcion from marine-derived fungus Microsporum sp. induces apoptosis in human cervical carcinoma HeLa cells

Recently, the relationship between apoptosis and cancer has been emphasized and the induction of apoptosis is recognized as one of the key mechanisms of anti-cancer agents. Marine-derived fungi are valuable sources of structurally diverse bioactive anticancer agents. In the present study, a marine-derived fungus, Microsporum sp. was cultured and an anthraquinone derivative, physcion (11.8 mg) was isolated from the culture broth extract (1710 mg). Physcion has shown cytotoxic effect on human cervical carcinoma HeLa cells and its apoptosis induction in HeLa cells was investigated by the expressions of p53, p21, Bax, Bcl-2, caspase-9, and caspase-3 proteins. The Western blot analysis has revealed that physcion could significantly induce cell apoptosis through down-regulating of Bcl-2 expression, up-regulating of Bax expression, and activating the caspase-3 pathway. Furthermore, physcion induced the formation of reactive oxygen species (ROS) in HeLa cells. Collectively, these results suggest that physcion could be a potential candidate in the field of anticancer drug discovery against human cervical cancer.

Cell survival and apoptosis signaling as therapeutic target for cancer: marine bioactive compounds

Inhibition of apoptosis leads to activation of cell survival factors (e.g., AKT) causes continuous cell proliferation in cancer. Apoptosis, the major form of cellular suicide, is central to various physiological processes and the maintenance of homeostasis in multicellular organisms. A number of discoveries have clarified the molecular mechanism of apoptosis, thus clarifying the link between apoptosis and cell survival factors, which has a therapeutic outcome. Induction of apoptosis and inhibition of cell survival by anticancer agents has been shown to correlate with tumor response. Cellular damage induces growth arrest and tumor suppression by inducing apoptosis, necrosis and senescence; the mechanism of cell death depends on the magnitude of DNA damage following exposure to various anticancer agents. Apoptosis is mainly regulated by cell survival and proliferating signaling molecules. As a new therapeutic strategy, alternative types of cell death might be exploited to control and eradicate cancer cells. This review discusses the signaling of apoptosis and cell survival, as well as the potential contribution of marine bioactive compounds, suggesting that new therapeutic strategies might follow.

Synthesis and fungicidal activity of novel pimprinine analogues

A simple and efficient synthetic protocol for 5-(3-indolyl)-oxazoles has been developed and further used to synthesize a series of novel analogues of natural product pimprinine. All new compounds were identified by (1)H NMR, high resolution mass spectrometry, and the structures of 10 and 18o were further confirmed by X-ray crystallographic diffraction analysis. Bioassay conducted at Syngenta showed that several of the synthesized compounds exhibited fungicidal activity. Compounds 10, 17, 18 h, 18o, 19 h, 19i and 19 l all showed effective control of three out of the seven tested phytopathogenic fungi at the highest rate screened. Compounds 17 and 19 h in particular showed activity against the four pathogens screened in artificial media; Pythium dissimile, Alternaria solani, Botryotinia fuckeliana and Gibberella zeae.

Physicochemical characters of a tyrosinase inhibitor produced by Streptomyces roseolilacinus NBRC 12815

We examined the biological activities present in Streptomyces strains preserved at the National Institute of Technology and Evaluation Biological Resource Center, and found a metabolite of Streptomyces roseolilacinus NBRC 12815 that showed a potent anti-tyrosinase activity. The compounds with anti-tyrosinase activity were purified by several chromatographic procedures. Final HPLC analysis revealed at least two anti-tyrosinase compounds with different retention times (12815A and B). The identification of two anti-tyrosinase compounds was performed with instrumental analysis and database search. The results obtained suggest that the active compounds are SF 2583A and B. Compound 12815A (IC(50) values; about 9 microM) showed more potent tyrosinase inhibition than compound 12815B (IC(50) values; about 1086 microM). The only structural difference between 12815A and B is the presence of an additional chloric atom. In addition, the activity of 12815A was markedly decreased under acidic conditions, resulting in irreversible inactivation. However, the inactivated 12815A still exhibited residual activity when exposed to detergent, Tween 80. These results suggest that the chlorine and the hydration water are very important in the exertion of anti-tyrosinase activity by 12815A.

Antitumor compounds from marine actinomycetes

Chemotherapy is one of the main treatments used to combat cancer. A great number of antitumor compounds are natural products or their derivatives, mainly produced by microorganisms. In particular, actinomycetes are the producers of a large number of natural products with different biological activities, including antitumor properties. These antitumor compounds belong to several structural classes such as anthracyclines, enediynes, indolocarbazoles, isoprenoides, macrolides, non-ribosomal peptides and others, and they exert antitumor activity by inducing apoptosis through DNA cleavage mediated by topoisomerase I or II inhibition, mitochondria permeabilization, inhibition of key enzymes involved in signal transduction like proteases, or cellular metabolism and in some cases by inhibiting tumor-induced angiogenesis. Marine organisms have attracted special attention in the last years for their ability to produce interesting pharmacological lead compounds.