Identification and Characterization of the Anticancer Potential of Indigenous Medicinal Plants of the Arabian Peninsula
Indigenous plant species historically used for their medicinal properties are a tremendous source for bringing newer and safer drugs to the market. A concerted effort is needed to characterize their medicinal potential and identify new molecules that could be exploited in modern medicine. The current study was undertaken to study the anticancer properties of several indigenous plants that are used by the local population of the Arabian Peninsula and beyond for various medicinal purposes. Towards this end, we acquired different plant extracts from five plants, namely Boswellia sacra (BS), Cleome droserifolia (CD), Terbium muscatensis (TM), Orchadenus arabicus (OA), and Acredocarpus orientalis (AO) that were screened for their anticancer properties and mechanism of action. Of these, only the essential oil from Boswellia sacra has recently been shown to have anticancer activity Thirty-two different organic extracts were obtained from these native plants. Essential oil from Boswellia sacra was used as a control as well as to expand upon its anticancer activity profile. Initially, the essential oil and the extracts were screened for their anti-proliferation potential in two different human cancer cell lines, MCF-7 and HeLa, to ensure that their anticancer potential was not missed. The cell proliferation assay, MTT (3-(4, 5-dimethylthiazol-2-yl)-2-5-diphenyltetrazolium bromide]), was used to study the effect of the oil and various extracts on cell viability in a time and dose-dependent manner. Once all the extracts had been screened, select groups of effective extracts were chosen from each plant for a more in-depth analysis in a full panel of human breast cancer cell lines comprising of MCF -7 and MDA-MB-231 and their normal counterpart, MCF-10A, as well as the prototypic human cervical cancer cell line, HeLa. MCF -7 represents a hormone-responsive breast cancer cell line, while MDA-MB-231 represents a non-hormone responsive (triple receptor negative) breast cancer cell line. The mechanism of cell death induced by these extracts was explored by testing the activities of various caspase enzymes induced during apoptosis, a major pathway of programmed cell death, using caspase-specific glow assays and western blot analysis. Finally, a few isolated compounds and their derivatives obtained from these extracts were acquired from our collaborators and tested to determine whether they could demonstrate the anti- proliferative effects observed using the crude extracts and if so, whether it was due to apoptosis.
Test of the extracts using these assays revealed that some of the extracts exhibited anti-proliferative activity against the targeted cancer cell lines. The anti- proliferative effects of some of these extracts were found to be selectively more active against breast cancer cell line than HeLa cells. The ATP-dependent Cell Titer Glow® Luminescent Cell Viability Assay further confirmed the effect of the extracts on cell viability. Test of the activity of different caspase enzymes revealed that some of the effective extracts had the capability of inducing apoptosis. Western blotting was used to confirm the role of various caspases in the activation of apoptosis. Finally, isolated compounds from these extracts and their derivatives were screened with the MTT assay for their effect on cell viability. One of these isolated compounds has shown promising anti-proliferative activity and could induce a specific caspase, suggesting activation of caspase-dependent apoptosis. Thus, analyses from these multi-pronged approaches have resulted in the identification and characterization of extracts having anticancer potential from five indigenous plant species. We are further characterizing their mechanism(s) of action as well as exploring other cell death pathways that may be induced. Overall, our results demonstrate that traditional medicinal plants can provide an excellent source of natural raw material to isolate novel anticancer agents, enlarging the arsenal of new molecules available to fight cancer.