The characterization of GTP Cyclohydrolase I and 6-Pyruvoyl Tetrahydropterin Synthase enzymes as potential anti-malarial drug targets
- Authors: Khairallah, Afrah Yousif Huseein
- Date: 2022-04-08
- Subjects: Antimalarials , Plasmodium falciparum , Malaria Chemotherapy , Malaria Africa , Drug resistance , Drug development , Molecular dynamics
- Language: English
- Type: Doctoral thesis , text
- Identifier: http://hdl.handle.net/10962/233784 , vital:50127 , DOI 10.21504/10962/233784
- Description: Malaria remains a public health problem and a high burden of disease, especially in developing countries. The unicellular protozoan malaria parasite of the genus Plasmodium infects about a quarter of a billion people annually, with an estimated 409 000 death cases. The majority of malaria cases occurred in Africa; hence, the region is regarded as endemic for malaria. Global efforts to eradicate the disease led to a decrease in morbidity and mortality rates. However, an enormous burden of malaria infection remains, and it cannot go unnoticed. Countries with limited resources are more affected by the disease, mainly on its public health and socio-economic development, due to many factors besides malaria itself, such as lack of access to adequate, affordable treatments and preventative regimes. Furthermore, the current antimalarial drugs are losing their efficacy because of parasite drug resistance. The emerged drug resistance has reduced the drug efficacy in clearing the parasite from the host system, causing prolonged illness and a higher risk of death. Therefore, the emerged antimalarial drug resistance has hindered the global efforts for malaria control and elimination and established an urgent need for new treatment strategies. When the resistance against classical antimalarial drugs emerged, the class of antifolate antimalarial medicines became the most common alternative. The antifolate antimalarial drugs target the malaria parasite de novo folate biosynthesis pathway by limiting folate derivates, which are essential for the parasite cell growth and survival. Yet again, the malaria parasite developed resistance against the available antifolate drugs, rendering the drugs ineffective in many cases. Given the previous success in targeting the malaria parasite de novo folate biosynthesis pathway, alternative enzymes within this pathway stand as good targets and can be explored to develop new antifolate drugs with novel mechanisms of action. The primary focus of this thesis is to contribute to the existing and growing knowledge of antimalarial drug discovery. The study aims to characterise the malaria parasite de novo folate synthesis pathway enzymes guanosine-5'-triphosphate (GTP) cyclohydrolase I (GCH1) and 6-pyruvoyl tetrahydropterin synthase (PTPS) as alternative drug targets for malaria treatment by using computational approaches. Further, discover new allosteric drug targeting sites within the two enzymes' 3D structures for future drug design and discovery. Sequence and structural analysis were carried out to characterise and pinpoint the two enzymes' unique sequence and structure-based features. From the analyses, key sequence and structure differences were identified between the malaria parasite enzymes relative to their human homolog; the identified sites can aid significantly in designing and developing new antimalarial antifolate drugs with good selectivity toward the parasites’ enzymes. GCH1 and PTPS contain a catalytically essential metal ion in their active site; therefore, force field parameters were needed to study their active sites accurately during all-atom molecular dynamic simulations (MD). The force field parameters were derived through quantum mechanics potential energy surface scans of the metals bonded terms and evaluated via all-atom MD simulations. Proteins structural dynamics is imperative for many biological processes; thus, it is essential to consider the structural dynamics of proteins whilst understanding their function. In this regard, the normal mode analysis (NMA) approach based on the elastic network model (ENM) was employed to study the intrinsic dynamics and conformations changes of GCH1 and PTPS enzymes. The NMA disclosed essential structural information about the protein’s intrinsic dynamics and mechanism of allosteric modulation of their binding properties, further highlighting regions that govern their conformational changes. The analysis also disclosed hotspot residues that are crucial for the proteins' fold stability and function. The NMA was further combined with sequence motif results and showed that conserved residues of GCH1 and PTPS were located within the identified key structural sites modulating the proteins' conformational rearrangement. The characterized structural features and hotspot residues were regarded as potential allosteric sites of important value for the design and development of allosteric drugs. Both GCH1 and PTPS enzymes have never been targeted before and can provide an excellent opportunity to overcome the antimalarial antifolate drug resistance problem. The data presented in this thesis contribute to the understanding of the sequence, structure, and global dynamics of both GCH1 and PTPS, further disclose potential allosteric drug targeting sites and unique structural features of both enzymes that can establish a solid starting point for drug design and development of new antimalarial drugs of a novel mechanism of actions. Lastly, the reported force field parameters will be of value for MD simulations for future in-silico drug discovery studies involving the two enzymes and other enzymes with the same Zn2+ binding motifs and coordination environments. The impact of this research can facilitate the discovery of new effective antimalarial medicines with novel mechanisms of action. , Thesis (PhD) -- Faculty of Science, Biochemistry and Microbiology, 2022
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- Date Issued: 2022-04-08
Antimalarial activity of quinoline thiosemicarbazones: synthesis and antiplasmodial evaluation
- Authors: Nqeno, Lukhanyiso Khanyisile
- Date: 2022-04-06
- Subjects: Antimalarials , Quinoline , Thiosemicarbazones , Malaria Chemotherapy , Plasmodium falciparum , Malaria Africa, Sub-Saharan , Iron chelates Therapeutic use
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/291292 , vital:56841
- Description: Africa is one of the regions that is most affected by malaria, as 90% of all malaria deaths occur in sub-saharan Africa. Malaria is a life threatening disease responsible for an estimated 800000 deaths each year, the majority of these deaths occurred in children under the age of five. The disease is a mosquito-borne, and it is transmitted to humans by the female Anopheles mosquito. The parasite responsible for this disease belong to the Plasmodium genus with Plasmodium falciparum causing the most severe cases of the disease in humans. The most widely available anti-malarials were designed to specifically target the pathogenic blood stage in humans, however, in order to completely eradicate malaria there is a need for the development of medicines that not only target the pathogenic blood stage of the parasite but also block parasite transmission and eliminate asymptomatic and cryptic hepatic forms of the parasite. Iron chelators have recently gained importance as potent antimalarials, to cause infection nearly all protozoa obtain growth essential iron from their hosts. Iron is required for the development of the parasite. Deprivation of utilizable iron by chelation is a proficient approach to arrest parasite growth and associated infection. Thiosemicarbazones are known iron chelating agents by bonding through the sulfur and azomethine nitrogen atoms. This study is aimed at the identification of thiosemicarbazone based derivatives as possible antimalarial agents. Due to their iron chelation abilities there has been increasing interest in the investigation of thiosemicarbazones as possible antimalarials. During the course of this project, several thiosemicarbazone derivatives were synthesized and their structure confirmed using routine analytical techniques (NMR, FTIR, and HRMS). The synthesized compounds were evaluated in vitro against the chloroquine sensitive strain (3D7) of P. falciparum for antimarial activity. The compounds were also evaluated agsinst Hela cells for overt cytotoxicity. The compounds generally showed poor antimalarial activity. One compound (LKN11) was identified to possess intrinsic and moderate antimalarial activity of 6.6 μM. The compounds were generally not cytotoxic against Hela cell at concentrations of up to 20 μM, with only compound LKN10 showing modest cytotoxic activity of 9.5 μM. This research went on to identify two thiosemicarbazone based derivatives which had a significant effect on HeLa and pLDH cells. , Thesis (MSc) -- Faculty of Science, Chemistry, 2022
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- Date Issued: 2022-04-06
Synthesis and in vitro biological evaluation of 2,3-substituted quinoline derivatives
- Authors: Bokosi, Fostino Raphael Bentry
- Date: 2020
- Subjects: Quinoline , Malaria Chemotherapy , Tuberculosis Chemotherapy , African trypanosomiasis Chemotherapy
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/163193 , vital:41017
- Description: The urgent need for new systemic pharmacological entities prompted us to report a library of 2,3-substituted quinoline derivatives. Considering the ubiquity of quinoline-containing compounds in pharmacologically active small molecules, synthesized 2,3-substituted quinoline derivatives were in vitro biologically evaluated for their potential antitubercular, antimalarial and antitrypanosomal activities. Quinoline scaffold was achieved by the Vilsmeier-Haack methodology, affording synthetically useful chloro and formyl substituents on C-2 and C-3 respectively. These two substituents acted as handles in expanding the chemical space around the quinoline ring. Target compounds were synthesized in six to seven steps, employing conventional synthetic organic protocols adapted from various literature. The final compounds were accessed in moderate to good yields. The structural identity of each compound was confirmed by common spectroscopic techniques. Aryl quinoline carboxamide derivatives 3.113 – 3.126 were isolated as rotamers, hence, Variable-Temperature Nuclear Magnetic Resonance (VT-NMR) was employed in resolving 1H splitting. At elevated temperature (~328 K); N-methylene carbons were not visible on 13C NMR due to signal line broadening effects. The presence of these nuclei in such cases was, however, supported by 2-dimensional NMR and high-resolution MS data. Most of the compounds achieved in this study displayed promising antimalarial activity against chloroquine-sensitive 3D7 strain of Plasmodium falciparum compared to antitrypanosomal activity against Trypanosoma brucei brucei 427 strain. In particular, compounds 3.80 and 3.108 showed superior activity against chloroquine-sensitive 3D7 P. falciparum strain with IC50 values < 1 μM. More importantly, most of the compounds were non-toxic as determined by HeLa cells, indicating their selectivity towards the parasites. Exploring the space provided on the quinoline scaffold revealed that methoxy incorporation on C-2 is very critical in enhancing antimalarial activity of this class of quinoline compounds. The preliminary SAR of compounds 3.57 – 3.72 showed that compounds containing the 3-cinnamate exhibited enhanced antimalarial activity compared to 2 and 4-cinnamates. Finally, benzamide compounds 3.113 − 3.126 showed poor activity against Mycobacterium tuberculosis H37Rv strain with only compounds 3.113, 3.117 – 3.120 and 3.126 showing appreciable MIC90 values in the range of 40 – 85 μM. , Thesis (MSc) -- Faculty of Science, Chemistry, 2020
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- Date Issued: 2020
Exploring para-thiophenols to expand the SAR of antimalarial 3-indolylethanones
- Authors: Chisango, Ruramai Lissa
- Date: 2018
- Subjects: Antimalarials , Malaria Chemotherapy , Thiols , Plasmodium falciparum , Blood-brain barrier
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/63515 , vital:28428
- Description: According to the WHO, malaria is responsible for over half a million deaths annually especially in populations from disadvantaged settings. Although there has been a documented improvement in the mortality rates, malaria has proved to be a global emergency. Mostly affecting the poor population, this disease is perpetuating a vicious cycle of poverty in the developing world as current preventive measures are not adequate unless adopted in addition to effective treatment. However, there has been a worldwide increase in resistance to available treatment which presents a need for novel, affordable treatment. A study conducted in our laboratory identified two hit thiophenol containing compounds 2.24 and 2.25. These molecules provided initial insight into the SAR and potential pharmacophore of this class of compounds. We decided to further explore these compounds by making bioisosteric replacements to optimize the structure as we monitor the effect of these modifications on the anti-plasmodial activity. The synthetic pathway to form the target compounds of our study comprised of three steps which were initiated by the Friedel-Crafts acetylation of the indoles resulting in compounds 3.5 - 3.7. A bromination step followed which yielded the -bromo ketones (3.8 - 3.11). Some of the thiophenols (3.14 and 3.16) were not readily available in our laboratory and so were synthesized for the final synthetic step. This step involved the nucleophilic displacement of the -bromine to generate the -aryl substituted 3-indolylethanones (3.17 - 3.27). The thioethers displayed improved antimalarial activity from 2.24 and 2.25 against the chloroquine sensitive 3D7 Plasmodium falciparum strain. In addition, these compounds were non-toxic against HeLa cells which indicated this potential novel class of antimalarials is selective for the malaria parasite as hypothesized in the previous study conducted in our laboratory. In an attempt to predict the bioavailability of some of our compounds, in silico studies were conducted revealing that these compounds could be passively absorbed by the gastrointestinal tract, a positive result for bioavailability purposes. However, results from these studies indicate that modifications of these compounds would be necessary to allow for permeation through the blood brain barrier (BBB) for instances when the patient has cerebral malaria. , Thesis (MSc) -- Faculty of Pharmacy, Pharmacy, 2018
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- Date Issued: 2018
Synthesis, characterisation and evaluation of benzoxaborole-based hybrids as antiplasmodial agents
- Authors: Gumbo, Maureen
- Date: 2017
- Subjects: Malaria Chemotherapy , Antimalarials , Boron compounds , Drug resistance , Plasmodium falciparum , Drug development
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/59193 , vital:27456
- Description: Malaria is a mosquito-borne disease, which continues to pose a threat to the entire humanity. About 40% of the world population is estimated to be at risk of infections by malaria. Despite efforts undertaken by scientific community, government entities and international organizations, malaria is still rampant. The major problem is drug resistance, where the Plasmodium spp have over the past decades developed drug resistance against available drugs. In order to counter this problem, novel antimalarial drugs that are efficacious and with novel mode of action are of great necessity. Benzoxaborole derivatives have been shown to exhibit promising antimalarial activity against Plasmodium falciparum strains. Previous studies reported on the compounds such as 6-(2- (alkoxycarbonyl)pyrazinyl-5-oxy)-1,3-dihydro-1-hydroxy-2,1-benzoxaboroles, which showed good antimalarial activity against both W7 and 3D7 strains without significant toxicity. On the other hand, chloroquine (CQ) and cinnamic acids have a wide variety of biological activity including antimalarial activity. Herein, a hybridisation strategy was employed to synthesise new CQ-benzoxaborole and cinnamoyl-benzoxaborole hybrids. CQ-Benzoxaborole 2.12a-c and cinnamoylbenzoxaborole 2.11a-g hydrid molecules were synthesised in low to good yields. Their structural identities were confirmed using conventional spectroscopic techniques (1H and 13C NMR, and mass spectrometry). CQ-benzoxaborole compounds, however, showed instability, and only 2.12b was used for in vitro biological assay and showed activity comparable to CQ. Furthermore, in vitro biological assay revealed that compounds 2.11a-g poorly inhibited the growth of P. falciparum parasites. Interestingly, these compounds, however, exhibited satisfactory activity against Trypanosoma brucei with IC50 = 0.052 μM for compound 2.11g. The cell cytotoxicity assay of all final compounds confirmed that all CQ-benzoxaborole 2.12b and cinnamoyl-benzoxaborole 2.11a-g hybrids were non-toxic against HeLa cell lines. However, efforts to further expand the structure-activity relationship (SAR) of CQbenzoxaborole by increasing the length of the linker with one extra carbon (Scheme 2.10) were not possible as an important precursor 6-formylbenzoxaborole 2.29 could not be synthesized in sufficient yields. , Thesis (MSc) -- Faculty of Faculty of Science, Chemistry, 2017
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- Date Issued: 2017