Zebrafish phenotypic screen identifies novel Notch antagonists

Canthin-6-One Inhibits Developmental and Tumour-Associated Angiogenesis in Zebrafish

Tumour-associated angiogenesis play key roles in tumour growth and cancer metastasis. Consequently, several anti-angiogenic drugs such as sunitinib and axitinib have been approved for use as anti-cancer therapies. However, the majority of these drugs target the vascular endothelial growth factor A (VEGFA)/VEGF receptor 2 (VEGFR2) pathway and have shown mixed outcome, largely due to development of resistances and increased tumour aggressiveness. In this study, we used the zebrafish model to screen for novel anti-angiogenic molecules from a library of compounds derived from natural products. From this, we identified canthin-6-one, an indole alkaloid, which inhibited zebrafish intersegmental vessel (ISV) and sub-intestinal vessel development. Further characterisation revealed that treatment of canthin-6-one reduced ISV endothelial cell number and inhibited proliferation of human umbilical vein endothelial cells (HUVECs), suggesting that canthin-6-one inhibits endothelial cell proliferation. Of note, canthin-6-one did not inhibit VEGFA-induced phosphorylation of VEGFR2 in HUVECs and downstream phosphorylation of extracellular signal-regulated kinase (Erk) in leading ISV endothelial cells in zebrafish, suggesting that canthin-6-one inhibits angiogenesis independent of the VEGFA/VEGFR2 pathway. Importantly, we found that canthin-6-one impairs tumour-associated angiogenesis in a zebrafish B16F10 melanoma cell xenograft model and synergises with VEGFR inhibitor sunitinib malate to inhibit developmental angiogenesis. In summary, we showed that canthin-6-one exhibits anti-angiogenic properties in both developmental and pathological contexts in zebrafish, independent of the VEGFA/VEGFR2 pathway and demonstrate that canthin-6-one may hold value for further development as a novel anti-angiogenic drug.

Protective effect of curcumin on zebrafish liver under ethanol-induced oxidative stress

Oxidative stress has an important role in determining severe damage to the liver, including steatosis. Curcumin (CUR) is a natural polyphenol compound with antioxidant potential but its mechanism is still unclear. In this study, 2% ethanol (ETH) was used to establish a liver injury model in Tg (fabp10: Ps Red) transgenic zebrafish with the fluorescent liver. Ethanol-treated zebrafish had an increased vacuole rate at 144 h post-fertilization (hpf), thus confirming the effectiveness of the proposed model in inducing liver damage. However, when ethanol was submitted to co-exposure with curcumin, fluorescence area and signal intensity, as well as vacuole rate, were similar to the levels found in the control group. RNA-seq results showed that ethanol and CUR affected the regulation of catalytic activity and phenylalanine metabolism, biosynthesis of amino acids, and arginine and proline metabolism signaling pathways. QRT-PCR analysis also showed that treatment with CUR led to the downregulation of genes involved in the Nrf2-Keap1 signaling pathway and altered the expression pattern of genes related to glutathione metabolism (gsr, gpx1a, gstp1, gsto1, and idh1a). CUR also induced an increase in GSH content and recovered decreased GSH caused by ethanol exposure. The findings discussed herein indicate that CUR can promote glutathione synthesis, which aided in the recovery from ethanol-induced liver damage in zebrafish larvae.

Differential toxicity and teratogenic effects of the hot water and cold water extracts of Lignosusrhinocerus (Cooke) Ryvarden sclerotium on zebrafish (Danio rerio) embryos

ETHNOPHARMACOLOGICAL RELEVANCE

The sclerotium of Lignosusrhinocerus (Cooke) Ryvarden is highly valued for its purported medicinal properties. The decoction and macerated materials prepared from the sclerotium are used for treating cancer and other ailments based on extensive traditional knowledge. Scientific evidence from in vitro cytototoxicity, anti-inflammatory and immunomodulatory analyses showed the effectiveness of sclerotial water extracts but toxicity assessment of such preparations has not been reported.

AIM OF THE STUDY

This study aimed to compare the differential toxicity and teratogenicity (if any) of the hot water (HW) and cold water (CW) extracts of both wild and cultivated sclerotium on zebrafish (Danio rerio) embryos.

MATERIALS AND METHODS

Zebrafish embryos were treated with varying concentrations of the sclerotial HW and CW extracts (0.3-500 μg/mL) for 72 h until hatching. The hatching, mortality and heartbeat rate of the embryos as well as the potential teratogenic effect of the extracts were assessed in embryos post-treatment with the extracts.

RESULTS

While the sclerotial HW extracts were nontoxic (LC₅₀ > 500 μg/mL), the sclerotial CW extracts delayed the hatching of the embryos up to 48 h and showed slight toxicity with LC₅₀ values of 398.4 μg/mL and 428.3 μg/mL for the cultivated and wild sclerotium, respectively. The sclerotial CW extracts also induced minor tachycardia in zebrafish larvae. Phenotypic assessment revealed that, while yolk sac edema was observed at high concentrations (300 and 500 μg/mL) of all extracts, curved trunk and bent tail were only observed in the embryos treated with CW extracts of wild sclerotium (300 and 500 μg/mL) but not for CW extracts of cultivated sclerotium at similar concentrations.

CONCLUSION

The sclerotial water extracts of L.rhinocerus prepared using different methods have varying degree of toxicity and teratogenicity in zebrafish embryos with the sclerotial CW extracts showed higher toxicity than the HW extracts.

3,4-Difluorobenzocurcumin Inhibits Vegfc-Vegfr3-Erk Signalling to Block Developmental Lymphangiogenesis in Zebrafish

Lymphangiogenesis, the formation of new lymphatic vessels from pre-existing vasculature, plays critical roles in disease, including in cancer metastasis and chronic inflammation. Preclinical and recent clinical studies have now demonstrated therapeutic utility for several anti-lymphangiogenic agents, but optimal agents and efficacy in different settings remain to be determined. We tested the anti-lymphangiogenic property of 3,4-Difluorobenzocurcumin (CDF), which has previously been implicated as an anti-cancer agent, using zebrafish embryos and cultured vascular endothelial cells. We used transgenic zebrafish labelling the lymphatic system and found that CDF potently inhibits lymphangiogenesis during embryonic development. We also found that the parent compound, Curcumin, does not inhibit lymphangiogenesis. CDF blocked lymphatic and venous sprouting, and lymphatic migration in the head and trunk of the embryo. Mechanistically, CDF impaired VEGFC-VEGFR3-ERK signalling in vitro and in vivo. In an in vivo pathological model of Vegfc-overexpression, treatment with CDF rescued endothelial cell hyperplasia. CDF did not inhibit the kinase activity of VEGFR3 yet displayed more prolonged activity in vivo than previously reported kinase inhibitors. These findings warrant further assessment of CDF and its mode of action as a candidate for use in metastasis and diseases of aberrant lymphangiogenesis.

Assessment of Potential Anticancer Activity of Brown Seaweed Compounds Using Zebrafish Phenotypic Assay

Despite the extensive work on anticancer drug discovery, the number of potent lead compounds that enter the preclinical and clinical trials thus far is still low due to the poor selectivity and understanding in pharmacodynamics. In view of the homology between zebrafish embryogenesis and carcinogenesis in human, zebrafish embryos can be used in the screening platform to elucidate the molecular targets of potential anticancer compounds. In the present study, the possible targets modulating the potential anticancer effects of selected brown seaweed-derived compounds (ie alginate, fucoidan, phloroglucinol, fucosterol, and fucoxanthin) were examined. Teratogenic effects induced by the compounds were observed after 72 hours post-fertilization. Fucoidan, phloroglucinol, and fucosterol were observed to significantly reduce the pigmentation of the zebrafish in a dose-dependent manner at low concentrations (fucoidan, <60 µg/mL; phloroglucinol, <10 µg/mL; fucosterol, <3 µg/mL). On the other hand, embryos treated with fucoxanthin at 200 µg/mL and 300 µg/mL exhibited either phenotypes of curved trunk or bent tail. Further validation work using dual antiplatelet therapy (DAPT) and dorsomorphin as positive controls suggest that fucoxanthin might target the Notch and bone morphogenetic protein (BMP) pathways, respectively. Findings from this exploratory study henceforth have demonstrated the utility of zebrafish embryo to accelerate the discovery of potential compounds for targeted anticancer therapy.

Novel 2-Benzoyl-6-(2,3-Dimethoxybenzylidene)-Cyclohexenol Confers Selectivity toward Human MLH1 Defective Cancer Cells through Synthetic Lethality

DNA mismatch repair (MMR) deficiency has been associated with a higher risk of developing colorectal, endometrial, and ovarian cancer, and confers resistance in conventional chemotherapy. In addition to the lack of treatment options that work efficaciously on these MMR-deficient cancer patients, there is a great need to discover new drug leads for this purpose. In this study, we screened through a library of commercial and semisynthetic natural compounds to identify potential synthetic lethal drugs that may selectively target MLH1 mutants using MLH1 isogenic colorectal cancer cell lines and various cancer cell lines with known MLH1 status. We identified a novel diarylpentanoid analogue, 2-benzoyl-6-(2,3-dimethoxybenzylidene)-cyclohexenol, coded as AS13, that demonstrated selective toxicity toward MLH1-deficient cancer cells. Subsequent analysis suggested AS13 induced elevated levels of oxidative stress, resulting in DNA damage where only the proficient MLH1 cells were able to be repaired and hence escaping cellular death. While AS13 is modest in potency and selectivity, this discovery has the potential to lead to further drug development that may offer better treatment options for cancer patients with MLH1 deficiency.

Asymmetrical meta-methoxylated diarylpentanoids: Rational design, synthesis and anti-cancer evaluation in-vitro

In the present study, a series of forty-five asymmetrical meta-methoxylated diarylpentanoids have been synthesized, characterized and evaluated for their in-vitro anti-cancer potential. Among the forty-five analogs, three compounds (20, 33 and 42) have been identified as lead compounds due to their excellent inhibition against five human cancer cell lines including SW620, A549, EJ28, HT1080 and MCF-7. Structure-activity relationship study on cytotoxicity of tested compounds suggested that the presence of meta-oxygenated phenyl ring played a critical role in enhancing their cytotoxic effects. Compounds 33 and 42 in particular, exhibited strongest cytotoxicity against tested cell lines with the IC₅₀ values ranging from 1.1 to 4.3 μM. Subsequent colony formation assay on SW620 cell line showed that both compounds 33 and 42 possessed strong anti-proliferative activity. In addition, flow cytometry based experiments revealed that these compounds could trigger intracellular ROS production thus inducing G2/M-phase cell arrest and apoptosis. All these results suggested that poly meta-oxygenated diarylpentnoid is a promising scaffold which deserved further modification and investigation in the development of natural product-based anti-cancer drug.

Interference Potential of Tannins and Chlorophylls in Zebrafish Phenotypic-Based Assays

Natural products are prolific producers of diverse chemical scaffolds, which have yielded several clinically useful drugs. However, the complex features of natural products present challenges for identifying bioactive molecules using high-throughput screens. For most assays, measured endpoints are either colorimetric or luminescence based. Thus, the presence of the major metabolites, tannins, and chlorophylls, in natural products could potentially interfere with these measurements to give either false-positive or false-negative hits. In this context, zebrafish phenotypic assays provide an alternative approach to bioprospect naturally occurring bioactive compounds. Whether tannins and/or chlorophylls interfere in zebrafish phenotypic assays, is unclear. In this study, we evaluated the interference potential of tannins and chlorophylls against efficacy of known small-molecule inhibitors that are known to cause phenotypic abnormalities in developing zebrafish embryos. First, we fractionated tannin-enriched fraction (TEF) and chlorophyll-enriched fraction (CEF) from Camellia sinensis and cotreated them with PD0325901 [mitogen-activated protein kinase-kinase (MEK) inhibitor] and sunitinib malate (SM; anti-[lymph]angiogenic drug). While TEF and CEF did not interfere with phenotypic or molecular endpoints of PD0325901, TEF at 100 μg/mL partially masked the antiangiogenic effect of SM. On the other hand, CEF (100 μg/mL) was toxic when treated up to 6 dpf. Furthermore, CEF at 100 μg/mL potentially enhanced the activity of γ-secretase inhibitors, resulting in toxicity of treated embryos. Our study provides evidence that the presence of tannin and/or chlorophyll in natural products do interfere with zebrafish phenotype assays used for identifying potential hits. However, this may be target/assay dependent and thus requiring additional optimization steps to assess interference potential of tannins and chlorophylls before performing any screening assay.

Quo natas, Danio?-Recent Progress in Modeling Cancer in Zebrafish

Over the last decade, zebrafish has proven to be a powerful model in cancer research. Zebrafish form tumors that histologically and genetically resemble human cancers. The live imaging and cost-effective compound screening possible with zebrafish especially complement classic mouse cancer models. Here, we report recent progress in the field, including genetically engineered zebrafish cancer models, xenotransplantation of human cancer cells into zebrafish, promising approaches toward live investigation of the tumor microenvironment, and identification of therapeutic strategies by performing compound screens on zebrafish cancer models. Given the recent advances in genome editing, personalized zebrafish cancer models are now a realistic possibility. In addition, ongoing automation will soon allow high-throughput compound screening using zebrafish cancer models to be part of preclinical precision medicine approaches.