Antiproliferative activity of novel rhenium complexes and medicinal plant extracts
- Authors: Oosthuizen, Kenneth Thomas , Venables, Luanne
- Date: 2021-04
- Subjects: Gqeberha (South Africa) , Eastern Cape (South Africa) , Medicinal plants -- South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/52028 , vital:43441
- Description: Cancer is a complex, multifactorial disease that affects millions of individuals every year. The adverse side effects and escalating costs of current therapies coupled with the increased incidence of resistance to these therapies make it imperative that we explore novel treatments for the disease. This study investigated two avenues for novel drug design namely, novel synthetic compounds and medicinal plant extracts. The benzimidazole ring system has shown potential as a scaffold for designing novel anticancer agents. Conjugation of the metal rhenium to novel variants of this ring system open up the possibility of designing novel drugs that serve both a diagnostic and a therapeutic function. This study investigated the in vitro anticancer potential of ten such complexes against selected breast and cervical cancer cell lines. The selectivity of the complexes for cancer cells over normal cells was also investigated while the mechanism of action of effective complexes was determined by exploring cell cycle arrest, biochemical markers of apoptosis and mitochondrial membrane disruption. All ten complexes were screened against MCF7 breast and HeLa cervical cancer cell lines with four showing antiproliferative activity against both cancer cell lines and one showing cell line specific toxicity against MCF7 breast cancer cells. When looking at the SAR of the compounds it was noted that activity was higher in compounds which contain two potentially bidentate benzothiazole ligands, while compounds with potentially tridentate ligands show good activity, but only if the benzothiazole moiety is not involved in coordination. The complexes showed greater antiproliferative activity against the MCF7 breast cancer cells with IC50 values ranging from 3.2 to 7.0 µM versus a range of 7.6 to 24.4 µM being obtained on the HeLa cervical cancer cells. Antiproliferative complexes were tested against confluent and log phase Vero cells at their respective IC50 values to determine their effect on “normal” cells. Confluent Vero cells showed less cell death than those in log phase indicating that the complexes show preference for proliferating cells. The mechanism of action of the complexes was studied on both cancer cell lines via cell cycle analysis and apoptosis assays investigating phosphatidylserine translocation, caspase -3 and -8 activation and mitochondrial membrane potential with most complexes inducing cell cycle arrest followed by cell death via both the extrinsic and intrinsic pathways of apoptosis. Since 1940, 49% of all the available anticancer drugs approved for cancer treatment were natural products or directly derived from natural products. Plants are an excellent source of secondary metabolites, many of which are unique chemical compounds that cannot be synthesized in a laboratory. Ethnobotanical surveys conducted in conjunction with Traditional Health Practitioners of the Mkuranga and Same districts in Tanzania identified 25 plants that are used for the treatment of cancer. Four of these plants (A. mossambicensis, C. adenocaule, C. pseudopulchelusis and R. natalensis) with ethnobotanically reported anticancer usage showed cytotoxic activity against brine shrimp and were selected for further in vitro anticancer studies. All four plants were found to have antiproliferative activity against HeLa cervical cancer cells with IC50 values ranging from 3.4 to 50.8 µg/mL. This study was also tasked with investigating the mechanism of action of C. pseudopulchelus on HeLa cervical cancer cells by exploring cell cycle arrest, biochemical markers of apoptosis and mitochondrial membrane x disruption. C. pseudopulchelus caused early M phase arrest followed by slippage and subsequent cell death via the extrinsic pathway of apoptosis. In conclusion, this study showed that both novel complexes as well as medicinal plant extracts represent an interesting avenue for the development of novel anticancer drugs that are cheaper and produce less side effects than current therapies. , Thesis (MSc) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2021
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- Date Issued: 2021-04
In vitro induction of cell death pathways by artemisia afra extract and isolation of an active compound, isoalantolactone
- Authors: Venables, Luanne
- Date: 2014
- Subjects: Medicinal plants -- South Africa , Cell death
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10363 , http://hdl.handle.net/10948/d1021087
- Description: Artemisia afra is one of the oldest, most well known and widely used traditional medicinal plants in South Africa. It is used to treat many different medical conditions, particularly respiratory and inflammatory ailments. There is no reported evidence of its use for the treatment of cancer but due to its reported cytotoxicity, an investigation of the mode of cell death induced by an ethanol A. afra extract using two cancer cell lines was done. IC50 values of 18.21 and 31.88 μg/mL of ethanol extracts were determined against U937 and HeLa cancer cells, respectively. An IC50 value of the aqueous extract was greater than 250 μg/mL. The ethanol extract was not cytotoxic against confluent control cell lines, Chang Liver and Vero cells. The effect of the cytotoxic ethanol A. afra extract on U937 and HeLa cells and their progression through the cell cycle, apoptosis and mitochondrial membrane potential was investigated. After 12 hours of treatment with A. afra a delay in G2/M phase of the cell cycle was evident. Apoptosis was confirmed using the TUNEL assay for DNA fragmentation, as well as fluorescent staining with annexin V-FITC. Apoptosis was evident with the positive control and A. afra treatment at 24 and 48 hours. JC-1 staining showed a decrease in mitochondrial membrane potential at 24 hours. It was deduced that A. afra ethanol extract induces caspase-dependent apoptosis in a mitochondrial dependent manner. Plants harbour many compounds that are not only useful to the plants but also to mankind. Many metabolites have been isolated from A. afra and their biological activity characterised. Due to observed apoptosis induction, isolation of cytotoxic compounds was done and a new sesquiterpene lactone from A. afra was isolated. Structural elucidation of the compound was done by IR, 1D and 2D NMR, CD and mass spectrometry and it was identified as isoalantolactone. HeLa cancer cells were treated with isoalantolactone and cytotoxicity was exhibited in a dose-dependent manner. A low IC50 value of 8.15 ± 1.16 μM was achieved. This study showed that isoalantolactone is partly responsible for the observed A. afra cytotoxicity. Due to the evidence of G2/M arrest, the anti-mitotic potential and the possible onset of mitotic catastrophe by A. afra and isoalantolactone was investigated. It was evident from various flow cytometric analysis of cyclin B1 and phospho-H3 and confocal microscopy that A. afra does possess anti-mitotic activity by causing hyperpolymerisation of tubulin and cells progress into the mitotic phase where M arrest is experienced. The anti-inflammatory activity of sesquiterpene lactones is well documented; however, the anti-inflammatory activity of A. afra is not. Here, it is reported that the production of NO and COX-2 protein levels in RAW 264.7 cells decrease in the presence of A. afra and isoalantolactone after stimulation with LPS. The activated NF-κB subunit, p65 was also investigated. The results suggest that A. afra and isoalantolactone inhibit p65 activation as a decrease in the activated subunit was evident. Thus, the results indicate that exposure to A. afra and isoalantolactone induces an anti-inflammatory response. In conclusion, this study shows, for the first time, the mechanism of induced apoptosis, the anti-mitotic and anti-inflammatory activity of A. afra and its isolated compound, isoalantolactone. It also proves that although extensive research may have been done on a particular plant, as with A. afra, more can be discovered leading to the identification of new compounds and integration of signalling pathways that can be exploited for the treatment of various diseases and ailments.
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- Date Issued: 2014