Robyn L. Van Zyl

Structure-activity relationships and inhibitory effects of various purine derivatives on the in vitro growth of Plasmodium falciparum

The development of novel chemotherapeutic agents has become an urgent task due to the development and rapid spread of drug resistance in Plasmodium falciparum, the protozoan parasite responsible for cerebral malaria. Cyclin-dependent kinases (CDKs) are essential for the regulation of the eukaryotic cell cycle, and several enzymes of this family have been identified in P. falciparum. In recent years, a number of purine-derived kinase inhibitors have been synthesised, some of which display selective activity against CDKs. This report describes a study in which various purine derivatives were screened for in vitro antimalarial activity. The erythrocytic asexual stages of the chloroquine-resistant P. falciparum strain (FCR-3) were cultivated in vitro in the presence of the various purines, and their effect on parasite proliferation was determined by the [3H]hypoxanthine incorporation assay. Our results show considerable variation in the sensitivity of P. falciparum to the different purines, as well as a general independence from their effect on purified starfish CDK1/cyclin B activity, which has been the standard assay used to identify CDK-specific inhibitors. Two subfamilies of purines with moderate to poor activity against CDK1/cyclin B activity showed submicromolar activity against P. falciparum. Structure-activity analysis indicates that certain structural features are associated with increased activity against P. falciparum. These features can be exploited to synthesise compounds with higher activity and specificity towards P. falciparum.

Antiprotozoal activity of chloroquinoline based chalcones.

A new series of chloroquinoline based chalcones were synthesized and evaluated for in vitro antiamoebic and antimalarial activities. The results showed that out of fifteen compounds, four were found to be more active against the Entamoeba histolytica; while one compound was moderatively active compared to the standard drug metronidazole (IC50=1.46 μM). In contrast, in vitro antimalarial activity against the chloroquine-sensitive (3D7) strain of P. falciparum indicated relatively low activity when compared to controls such as chloroquine and quinine (IC50=0.0065 μM and 0.14 μM, respectively). The toxicological studies of these compounds on human breast cancer MCF-7 cell line showed that all the compounds were non-toxic at the concentration range of 1.56-50 μM.

The anti-diarrhoeal properties of Breonadia salicina, Syzygium cordatum and Ozoroa sphaerocarpa when used in combination in Swazi traditional medicine

AIM OF THE STUDY The aim of the study was to determine in vitro activity of the bark of Ozoroa sphaerocarpa R. Fern & A. Fern (Anacardiaceae), Breonadia salicina (Vahl) Hepper & J.I.R. Wood (Rubiaceae) and Syzygium cordatum Hochst ex C Krauss (Myrtaceae) against a diarrhoea-causing pathogen, Escherichia coli; as well as the pharmacological interactions present in their combination. MATERIALS AND METHODS In consultation with traditional healers, the plants were collected from the wild, dried and extracted with dichloromethane:methanol (1:1). Thereafter, antimicrobial activity of the individual plants and their different combinations was tested using a common diarrhoea pathogen, Escherichia coli by employing the minimum inhibitory concentration assay. RESULTS Ozoroa sphaerocarpa was the most potent inhibitor of antimicrobial growth (MIC value of 1.2 mg/ml), followed by Syzygium cordatum (MIC value of 1.44 mgl/ml) and lastly Breonadia salicina (MIC value of 10.89 mg/ml). The combination between Syzygium cordatum and Ozoroa sphaerocarpa gave the strongest synergistic interaction (MIC value of 0.33 mg/ml); whilst that between Syzygium cordatum and Breonadia salicina was mildly synergistic (MIC value of 1.00 mg/ml). The triple combination (1:1:1) was also very effective in inhibiting microbial growth (MIC value of 0.44 mg/ml). The combined effect of these plants on toxicity was predominantly synergistic except for the combination of Ozoroa sphaerocarpa and Syzygium cordatum which was predominantly antagonistic (ΣFIC value of 1.48 ± 0.25). The triple combination had a favourable toxicity profile with an IC(50) value of 155.76 ± 11.86 μg/ml. CONCLUSION This study supports the rationale by traditional healers to use the bark of Syzygium cordatum, Breonadia salicina and Ozoroa sphaerocarpa in combination for the treatment of diarrhoea.

Expeditious synthesis and biological evaluation of novel 2,N6-disubstituted 1,2-dihydro-1,3,5-triazine-4,6-diamines as potential antimalarials.

A small set of novel 2,N6-disubstituted 1,2-dihydro-1,3,5-triazine-4,6-diamines was prepared possessing a flexible tether between the exocyclic nitrogen bonded to C-6 of the 1,2-dihydro-1,3,5-triazine-4,6-diamine heterocycle and the distal aryl ring. Three zones were varied in this series of compounds, namely the nature of the substituent(s) on C-2; the nature of the substituent(s) on the distal aryl ring; as well as the nature and length of the flexible tether between the rings. The compound showing the best antimalarial activity (cycloguanil-resistant FCR-3 Plasmodium falciparum IC50=0.99 μM) was N6-(3-(4-chlorophenoxy)propyl)-2-(furan-2-yl)-1,2-dihydro-1,3,5-triazine-4,6-diamine hydrochloride.

Synthesis and biological evaluation of novel 4-substituted 1-{[4-(10,15,20-triphenylporphyrin-5-yl)phenyl]methylidene}thiosemicarbazides as new class of potential antiprotozoal agents.

A novel series of 4‐substituted 1‐{[4‐(10,15,20‐triphenylporphyrin‐5‐yl)phenyl]methylidene}thiosemicarbazide, 4a–4n, was synthesized in 9–21% yield by the condensation of 4‐(10,15,20‐triphenylporphyrin‐5‐yl)benzaldehyde (3) with various substituted thiosemicarbazides in presence of catalytic amount of AcOH. These compounds were assayed for in vitro antiamoebic activity, and the results showed that out of 14 compounds 9 were found with IC50 values lower than metronidazole corresponding to 1.05‐ to 4.7‐fold increase in activity. MTT Assay showed that all the compounds are nontoxic to human kidney epithelial cell line. 4‐(m‐Toluidinyl)‐1‐{[4‐(10,15,20‐triphenylporphyrin‐5‐yl)phenyl]methylidene}thiosemicarbazide (4h) showed the highest antiamoebic activity with least cytotoxicity. Some of the compounds were screened for their antimalarial activities and ability to inhibit β‐haematin formation, but none of them showed an activity better than chloroquine and quinine. Only one compound out of six showed an activity comparable to standard drug.

Chloroquinoline–acetamide hybrids: a promising series of potential antiprotozoal agents

In an endeavour to develop efficacious antiprotozoal agents 2-[4-(7-chloroquinolin-4-yl)piperazin-1-yl]acetamide derivatives were synthesized and screened in vitro against the HM1 : IMSS strain of E. histolytica and 3D7 strain of P. falciparum. Among the twenty-seven synthesized compounds, eleven evinced propitious anti-amoebic activity with IC50 values ranging from 0.41 to 1.80 μM) lower than the standard drug metronidazole (IC50 1.80 μM). All the compounds inhibited the in vitro growth of P. falciparum (IC50 range: 0.30–33.52 μM). Compounds A22 and A25 were found to be the most active antimalarial derivatives, and compound A16 the most active in inhibiting β-haematin formation; however compound A25 displayed the more favourable safety profile. The crystal structure for the compounds A7, A8, A12 and A21 was also determined. The molecular docking of crystal resolved inhibitors with PfDHFR allowed identification of stabilizing interactions within enzyme active sites. These compounds affirm the potential for further derivatives to enhance antiprotozoal activity whilst retaining their safety profile.

Synthesis, characterization, biological evaluation, and drug release study of polyamidoamine-containing neridronate

Abstract Polyamidoamines were synthesized by Michael-type polyaddition reaction and conjugates characterized by 1H NMR, 31P NMR, FTIR, SEM, and EDX. The biological evaluation of the new materials revealed 12–30% inhibition of the human breast cancer cells (MCF7) and 25% of the Plasmodium falciparum malaria parasites by the conjugates. The hemolysis assay revealed that these materials did not have any effect on the host red blood cell membrane. The release mechanism of neridronate followed Korsmeyer–Peppas model at pH 1.2 with a diffusion coefficient of 0.45 indicating a Fickian diffusion mechanism; Higuchi model at pH 6.0 thus indicating a diffusion mechanism. Graphical Abstract

Polymeric prodrugs containing neridronate and ferrocene: Synthesis, characterization, and antimalarial activity

ABSTRACT Polyamidoamine prodrugs containing ferrocene derivatives and neridronate were successfully synthesized and characterized by NMR, FTIR, SEM, and EDX analyses. Appearance of characteristic peaks in 1H and 31P NMR or EDX spectra were used to confirm the presence of neridronate or ferrocene in the conjugates and co-conjugates. In vitro evaluation of the new materials revealed improved antimalarial activity, especially for conjugate 5 and corresponding co-conjugate 8, when compared with chloroquine and quinine. Hemolysis studies revealed that synthesized prodrugs had no effect on the integrity of the host red blood cell membrane; a direct effect on the intra-erythrocytic parasite was, however, noted. GRAPHICAL ABSTRACT

Design and synthesis of polysapartamide co-drugs of platinum and methotrexate as anticancer agents

ABSTRACT Literature reports several recent attempts to load a single drug onto one carrier to improve drug efficacy. An ideal anticancer drug would result from anchoring two anticancer drugs on a single carrier to exploit the advantage of possible synergistic interactions between the drugs, whilst targeting different sites in the cancer cell. This work presents the results of the synthesis and analysis of water-soluble polyaspartamide carriers, which were loaded with platinum along with methotrexate. Platinum was anchored by coordination and methotrexate by amide bonds. In all cases, drug incorporation in the molecule was assessed to be 100%. NMR was used for methotrexate conjugate analysis, while platinum incorporation was evaluated by CHN analysis. The in vitro antiproliferative activity against breast cancer displayed a very good cytotoxic activity by the co-conjugates over the free drugs and their simple conjugates. GRAPHICAL ABSTRACT

New antiprotozoal agents: Synthesis and biological evaluation of different 4-(7-chloroquinolin-4-yl) piperazin-1-yl)pyrrolidin-2-yl)methanone derivatives

In an endeavor to develop efficacious antiprotozoal agents 4-(7-chloroquinolin-4-yl) piperazin-1-yl)pyrrolidin-2-yl)methanone derivatives (5-14) were synthesized, characterized and biologically evaluated for antiprotozoal activity. The compounds were screened in vitro against the HM1: IMSS strain of Entamoeba histolytica and NF54 chloroquine-sensitive strain of Plasmodium falciparum. Among the synthesized compounds six exhibited promising antiamoebic activity with IC50 values (0.14-1.26μM) lower than the standard drug metronidazole (IC50 1.80μM). All nine compounds exhibited antimalarial activity (IC50 range: 1.42-19.62μM), while maintaining a favorable safety profile to host red blood cells. All the compounds were less effective as an antimalarial and more toxic (IC50 range: 14.67-81.24μM) than quinine (IC50: 275.6±16.46μM) against the human kidney epithelial cells. None of the compounds exhibited any inhibitory effect on the viability of Anopheles arabiensis mosquito larvae.