Natural products play a key role in pharmaceutical research, as many medicines are either natural products or derivatives thereof. It is estimated that about 40% of all medicines are either natural products or their semi-synthetic derivatives, while about 60% of anti-cancer agents in clinical use are either natural products or their derivatives. Plants, marine organisms, amphibians and soil micro-organisms produce cytotoxic compounds to defend themselves against predators and/or to protect their ecological niche versus other species. It may be advantageous if such cytotoxic natural products affect target enzymes across a broad spectrum of species, rather than just a narrow range.

Guaiane-type sesquiterpene lactones are naturally occurring compounds which have attracted attention due to their array of biological activities. In this study, chlorinated guaianolides 1–8, isolated from plants of the genus Centaurea, were evaluated against the human leukemia cell lines HL-60, U-937, a specific U-937 cell line that overexpresses the anti-apoptotic Bcl-2 protein and the human melanoma cell line SK-MEL-1. This established the relevant structure-growth inhibition relationships. Chlorohyssopifolins A (1), C (3) and D (4) and linichlorin A (6) were the most potent compounds in terms of inducing growth inhibition in the four cell lines. IC50 values were below 10 μM in all cases. Chlorohyssopifolins A (1) and D (4) and linichlorin A (6) were potent apoptotic inducers in human U-937 leukemia cells, as determined by fluorescent microscopy and flow cytometry, and their mechanism of action was associated with cytochrome c release, caspase activation and poly(ADP-ribose)polyme...

Background and Objectives: The dichloromethane crude extract (P), and compounds, glyasperin A (1), propolin E (2), and propolin A (3), obtained from Philippine stingless bee (Tetragonula biroi Friese) nests, were evaluated for their cytotoxic potentials. Materials and Methods: The anti-proliferative activities of P and 1-3 against human cancer cell lines, breast (MCF-7) and colon (HT-29 and HCT-116), and a normal cell line, human dermal fibroblast neonatal (HDFn), were evaluated using the PrestoBlue® cell viability assay. Results: The crude extract (P) was most anti-proliferative against HCT-116 cells (IC50 = 1.410 μg/mL). Glyasperin A (1) exhibited the strongest effect on MCF-7 cells (IC50 = 2.378 μg/mL). Propolin E (2) was most cytotoxic against HCT-116 cells (IC50 = 2.279 μg/mL), while propolin A (3) was most inhibitory against MCF-7 cells (2.815). Comparing the colorectal cancer cell lines, HCT-116 was generally more susceptible under P, 2 and 3 (IC50 = 1.410, 2.279, 3.013 μg/mL, respectively) than HT-29 (5.620, 5.320, 5.359). Comparing propolin E and propolin A, significant difference was seen in HCT-116 cells where 2 (IC50 = 2.279 μg/mL) was more cytotoxic than 3 (3.013). The crude extract (P) was more cytotoxic than Zeocin against HCT-116 cells. Conclusion: The dichloromethane crude extract, glyasperin A, propolin E, and propolin A, from Philippine stingless bee (Tetragonula biroi Friese) nests, exhibited strong cytotoxic activities against MCF-7, HT-116, and HT-29 cells with IC50 values ranging from 1.410 to 5.620 μg/mL. This is the first report on the anti-proliferative properties of the crude extract and compounds from this source.

Abstract Euphorbia grandicornis Blanc is widely utilized in traditional medicine for a variety of ailments including body pains associated with skin irritations, inflammation, and snake or scorpion bites. Compounds from E. grandicornis were characterized using spectroscopic techniques, NMR, IR, MS, and melting points and alongside the extracts were evaluated for in vitro anticancer activity against several cancer cell lines. The root extract afforded known, β-glutinol (1), β-amyrin (2), 24-methylenetirucalla-8-en-3β-ol (3), tirucalla-8,25-diene-3β,24R-diol (4), stigmasterol (5), sitosterol (6), and hexyl (E)-3-(4‑hydroxy-3-methoxyphenyl)-2-propenoate (7) based on their NMR spectroscopic data for the first report in E. grandicornis. The extracts and isolated compounds were evaluated for anticancer activities against hormone receptor-positive breast cancer (MCF-7), triple-negative breast cancer (HCC70), and non-tumorigenic mammary epithelial (MCF-12A) cell lines. The CH2Cl2 extract exhibited potent, cytotoxicity against MCF-7, HCC70, and MCF-12A cells. The aerial extract exhibited IC50 values of 1.03, 0.301, and 1.68 µg/mL, and root extract displayed IC50 values of 0.83, 0.83 and 3.98 µg/mL against MCF-7, HCC70, and MCF-12A cells, respectively. The root extract thus showed selectivity for the cancer cell lines over the non-cancerous control cell line (SI = 4.80). Hexyl (E)-3-(4‑hydroxy-3-methoxyphenyl)-2-propenoate (7) showed significant activity with IC50 values of 23.41, 29.45 and 27.01 µM against MCF-7, HCC70 and MCF-12A cells, respectively, suggesting non-specific cytotoxicity.