Cytotoxic and cell cycle arrest properties of two steroidal alkaloids isolated from Holarrhena floribunda (G. Don) T. Durand & Schinz leaves

Abstract

Background The plant Holarrhena floribunda ( H. floribunda ; G. Don) is indigenous to sub-Saharan Africa and is traditionally used to treat several ailments. The present study was carried out to isolate and characterize bioactive compounds with anti-proliferative activity present in H. floribunda extracts. Methods Compounds were isolated from H. floribunda using the bioassay-guided fractionation technique of repeated column chromatography and the step-wise application of the MTT reduction assay to assess antiproliferative bioactivity. The structures of the compounds were identified mainly using NMR. The effects of the isolated compounds on the viability, cell cycle and proliferation of human cancer cell lines (MCF-7, HeLa and HT-29) as well as the non-cancerous human fibroblast cell line (KMST-6) were investigated. Results Bioassay-guided fractionation yielded two steroidal alkaloids: holamine ( 1) and funtumine ( 2 ). The MTT reduction assay shows that both compounds exhibited selective dose-dependent cytotoxicity against the cancer cell lines studied. The isolated compounds induced cell cycle arrest at the G 0 /G 1 and G 2 /M phases in the cancer cell lines with significant reduction in DNA synthesis. The results obtained show that the cancer cells (MCF-7, HeLa and HT-29) used in this study were more sensitive to the isolated compounds compared to the noncancerous fibroblast cells (KMST-6). Conclusion The ability of the isolated compounds to cause cell cycle arrest and reduce DNA synthesis raises hopes for their possible development and use as potent anticancer drugs. However, more mechanistic studies need to be done for complete validation of the efficacy of the two compounds.

An Insight into the Mechanism of Holamine- and Funtumine-Induced Cell Death in Cancer Cells

“…We have previously shown, using the MTT and bromodeoxyuridine (BrdU) incorporation assays, that holamine and funtumine ( Figure 1) inhibit the growth of the MCF-7, HeLa, HT-29, and KMST-6 cell lines [11]. This study also showed that both compounds block cell cycle progression in cancer cells, thus demonstrating promising anticancer properties [11].…”

“…We have previously shown, using the MTT and bromodeoxyuridine (BrdU) incorporation assays, that holamine and funtumine ( Figure 1) inhibit the growth of the MCF-7, HeLa, HT-29, and KMST-6 cell lines [11]. This study also showed that both compounds block cell cycle progression in cancer cells, thus demonstrating promising anticancer properties [11]. This study further explored the effects of holamine and funtumine on cancer cells by evaluating the induction of apoptosis, the activation of caspase-3/7, ROS production (oxidative stress induction), the perturbation of mitochondrial functions, actin filament disorganization, and the inhibition of topoisomerase-I.…”

“…Some of the known mechanisms of action of steroidal alkaloids include the initiation of apoptosis (through the induction of Bax expression, Bcl-2 suppression, and PARP-1 initiation), cell cycle arrest (at G0/G1 and G2/M check points), inhibition of cell-signaling protein (MMP-2/9 and AKT), and activation of transcriptional factors (p21WAF1/CIP1 and checkpoint kinase-2) [9]. Holamine and funtumine are pregnene-type steroidal alkaloids commonly found in the Apocynaceae family of Holarrhena with strong and diverse pharmacological activities [10][11][12]. These alkaloids have demonstrated a significant selective cytotoxicity against human cancer cells (HeLa, MCF-7 and HT-29) when compared with non-cancerous cells (i.e., normal KMST-6 fibroblasts).…”

“…These alkaloids have demonstrated a significant selective cytotoxicity against human cancer cells (HeLa, MCF-7 and HT-29) when compared with non-cancerous cells (i.e., normal KMST-6 fibroblasts). Both compounds were found to reduce cancer cell viability to 50% at concentrations ranging from 22 to 53 µM [11]. Their cytotoxicity in cancer cell lines was associated with cell cycle arrest at the G0/G1 and G2/M phases [11].…”

“…Both compounds were found to reduce cancer cell viability to 50% at concentrations ranging from 22 to 53 µM [11]. Their cytotoxicity in cancer cell lines was associated with cell cycle arrest at the G0/G1 and G2/M phases [11]. Compounds from some medicinal plants are known to induce cytotoxicity through the induction of apoptotic pathways triggered by mitochondrial dysfunction, the increased production of reactive oxygen species (ROS), and the inhibition of topoisomerase-I activity in tumor cells [13,14].…”