A topoisomerase II poison screen of ethnomedicinal Thai plants using a yeast cell-based assay

Anticancer Effects and Molecular Action of 7-α-Hydroxyfrullanolide in G2/M-Phase Arrest and Apoptosis in Triple Negative Breast Cancer Cells

Triple negative breast cancer (TNBC) is a breast cancer subtype characterized by the absence of estrogen receptor, progesterone receptor and human epidermal growth factor receptor 2 expression. TNBC cells respond poorly to targeted chemotherapies currently in use and the mortality rate of TNBC remains high. Therefore, it is necessary to identify new chemotherapeutic agents for TNBC. In this study, the anti-cancer effects of 7-α-hydroxyfrullanolide (7HF), derived from Grangea maderaspatana, on MCF-7, MDA-MB-231 and MDA-MB-468 breast cancer cells were assessed using MTT assay. The mode of action of 7HF in TNBC cells treated with 6, 12 and 24 µM of 7HF was determined by flow cytometry and propidium iodide (PI) staining for cell cycle analysis and annexin V/fluorescein isothiocyanate + PI staining for detecting apoptosis. The molecular mechanism of action of 7HF in TNBC cells was investigated by evaluating protein expression using proteomic techniques and western blotting. Subsequently, 7HF exhibited the strongest anti-TNBC activity toward MDA-MB-468 cells and a concomitantly weak toxicity toward normal breast cells. The molecular mechanism of action of low-dose 7HF in TNBC cells primarily involved G2/M-phase arrest through upregulation of the expression of Bub3, cyclin B1, phosphorylated Cdk1 (Tyr 15) and p53-independent p21. Contrastingly, the upregulation of PP2A-A subunit expression may have modulated the suppression of various cell survival proteins such as p-Akt (Ser 473), FoxO3a and β-catenin. The concurrent apoptotic effect of 7HF on the treated cells was mediated via both intrinsic and extrinsic modes through the upregulation of Bax and active cleaved caspase-7-9 expression and downregulation of Bcl-2 and full-length caspase-7-9 expression. Notably, the proteomic approach revealed the upregulation of the expression of pivotal protein clusters associated with G1/S-phase arrest, G2/M-phase transition and apoptosis. Thus, 7HF exhibits promising anti-TNBC activity and at a low dose, it modulates signal transduction associated with G2/M-phase arrest and apoptosis.

Anti-breast cancer potential of frullanolide from Grangea maderaspatana plant by inducing apoptosis

Breast cancer is the leading cause of female mortality worldwide. Although there are several modern treatments for breast cancer, there is a high rate of recurrence for the majority of treatments; therefore, the search for effective anticancer agents continues. The present study aimed to investigate the anti-breast cancer potential of frullanolide, a compound which is isolated and purified from the Grangea maderaspatana plant, for selected human breast cancer cell lines (MCF-7, MDA-MB-468 and MDA-MB-231). The MTT assay was used to assess cytotoxic activity in breast cancer cell lines of treatment with frullanolide at 1.25, 2.5, 5.0, 10.0 and 20.0 µg/ml. Additionally, the apoptotic induction ability of frullanolide at various concentrations [0.5×, 1× and 2× half maximal inhibitory concentration (IC₅₀)] was investigated by flow cytometry and western blot analysis. Frullanolide exhibited strong anti-breast cancer activity against MDA-MB-468 (IC₅₀, 8.04±2.69 µg/ml) and weak cytotoxicity against the MCF-7 (IC₅₀, 10.74±0.86 µg/ml) and MDA-MB-231 (IC₅₀, 12.36±0.31 µg/ml) cell lines. The IC₅₀ of frullanolide was high in the human normal epithelial breast cell line (MCF-12A) and mouse fibroblast cell line (L-929). Density plot diagrams revealed that frullanolide induced apoptosis in MCF-7, MDA-MB-468 and MDA-MB-231 cells. Notably, a plausible anticancer mechanism was elucidated via cellular apoptosis by p53-independence in the treated MCF-7 cell line and p53-dependence in the treated MDA-MB-468 and MDA-MB-231 cell lines. In conclusion, the present study demonstrated that frullanolide may exert anticancer activity on breast cancer cell lines by inducing apoptosis. Frullanolide offers a possible novel approach to breast cancer therapy.

Interrogation of ethnomedicinal plants for synthetic lethality effects in combination with deficiency in the DNA repair endonuclease RAD1 using a yeast cell-based assay

ETHNOPHARMACOLOGICAL RELEVANCE

Plant materials used in this study were selected based on the ethnobotanical literature. Plants have either been utilized by Thai practitioners as alternative treatments for cancer or identified to exhibit anti-cancer properties.

AIM OF THE STUDY

To screen ethnomedicinal plants using a yeast cell-based assay for synthetic lethal interactions with cells deleted for RAD1, the yeast homologue of human ERCC4 (XPF) MATERIALS AND METHODS: Ethanolic extracts from thirty-two species of medicinal plants utilized in Thai traditional medicine were screened for synthetic lethal/sick interactions using a yeast cell-based assay. Cell growth was compared between the parental strain and rad1∆ yeast following exposure to select for specific toxicity of plant extracts. Candidate extracts were further examined for the mode of action using genetic and biochemical approaches.

RESULTS

Screening a library of ethanolic extracts from medicinal plants identified Bacopa monnieri and Colubrina asiatica as having synthetic lethal effects in the rad1∆ cells but not the parental strain. Synthetic lethal effects for B. monneiri extracts were more apparent and this plant was examined further. Genetic analysis indicates that pro-oxidant activities and defective excision repair pathways do not significantly contribute to enhanced sensitivity to B. monneiri extracts. Exposure to B. monneiri extracts resulted in nuclear fragmentation and elevated levels of ethidium bromide staining in rad1∆ yeast suggesting promotion of an apoptosis-like event. Growth inhibition also observed in the human Caco-2 cell line suggesting the effects of B. monnieri extracts on both yeast and human cells may be similar.

CONCLUSIONS

B. monneiri extracts may have utility in treatment of colorectal cancers that exhibit deficiency in ERCC4 (XPF).

Anti-cancer drug discovery: update and comparisons in yeast, Drosophila, and zebrafish

Discovery of novel cancer chemotherapeutics focuses on screening and identifying compounds that can target 'cancer-specific' biological processes while causing minimal toxicity to non-tumor cells. Alternatively, model organisms with highly conserved cancer-related cellular processes relative to human cells may offer new opportunities for anticancer drug discovery when combined with chemical screening. Some organisms used for chemotherapeutic discovery include yeast, Drosophila, and zebrafish which are similar in important ways relevant to cancer study but offer distinct advantages as well. Here, we describe these model attributes and the rationale for using them in cancer drug screening research.