Thesis (PhD)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The prevalence of multi-drug resistant (MDR) and extensively drug-resistant (XDR) Mycobacterium
tuberculosis has been increasing to alarming levels globally. This has been exacerbated by
tuberculosis (TB) co-infection with HIV where the epidemic is endemic. South Africa as a developing
country is hit hard by TB and efforts to develop TB drugs that are compatible with anti-retroviral
medication and also effective against MDR/XDR, could help shorten the treatment duration of the
current TB treatment regimens. This thesis presents the identification and characterisation of a novel
furanone based compound (F1082) and its derivatives as leads for anti-TB drug development.
Furanones are generally known for an array of biological activities ranging from antibacterial,
antifungal and antitumor. F1082 has an aromatic benzene structure and was identified from screening synthetic compounds
against M. tuberculosis. It is potent against M. tuberculosis at minimum inhibitory concentration
(MIC) of 8 μg/ml. It is selective for mycobacteria since it did not inhibit the growth of Gram-positive
and Gram-negative bacteria at concentrations five times the MIC for M. tuberculosis. F1082 is
generally bacteriostatic around MIC concentrations in its effects against M. tuberculosis however; it
may be bactericidal at higher concentrations. It is as effective against MDR, XDR and clinical isolates
of M. tuberculosis at the same concentration as the M. tuberculosis H37Rv reference strain. This
suggests that F1082 may have a different mechanism of action compared to current TB drugs. It has
been shown to have no antagonistic effect with the first-line anti-TB drugs and it has been shown to
synergize with rifampicin by reducing the MIC of rifampicin. A drawback of F1082 is that it is
cytotoxic to human cell lines, but this is presently being addressed through the synthesis of analogues
that have shown improved activity and less cytotoxicity. The synthesis of more than 40 analogues has
led to identification of 4 compounds that have more than five times higher activity and more than 100
times less cytotoxicity against human cell-lines. Microarray analyses have identified possible metabolic pathway/s in M. tuberculosis that is/are
affected by F1082. One subset of genes which showed the most prominent alteration encodes the
siderophores, which are involved with iron homeostasis in the M. tuberculosis bacillus. Of these
genes, 7 were of interest (mbtB, mbtC, mbtD, mbtE, mbtF, mbtH and bfrB) as they all fall in the same
cluster and are involved in iron acquisition. Due to the involvement of iron we also show that F1082
generates oxidative stress that is metal (iron) dependent. From the results we conclude that F1082 is a
promising antituberculosis lead compound with unique target properties and also specificity against
mycobacteria. / AFRIKAANSE OPSOMMING: Die voorkoms van veelvuldige middelweerstandige M.tuberculosis (MDR) en uiters
middelweerstandige M.tuberculosis (XDR) is besig om toe te neem teen ‘n kommerwekkende tempo
wêreldwyd. Hierdie situasie word vererger met die ko-infektering van M.tuberculosis en HIV. Suid-
Afrika, as ontwikkelende land, word sleg benadeel met tuberkulose siekte. Antituberkulose middels
wat kan saamwerk met bestaande antiretrovirale middels en ook effektief is teen MDR en XDR
stamme, kan alles meewerk om die behandelingstyd van tuberkulose te verkort. In hierdie tesis
identifiseer en karakteriseer ons ‘n furanoon-gebaseerde verbinding (F1082) en derivate daarvan as
voorloper-middels vir anti-tuberkulose middelontwikkeling. Furanone is algemeen bekend vir ‘n
verskeidenheid van biologiese aktiwiteite insluitende antibakteriële-, antifungale- en antitumor
aktiwiteite.
F1082 bevat ‘n aromatiese benseenstruktuur en is oorspronklik geïdentifiseer gedurende die
skandering van sintetiese middels teen M.tuberculosis. Dit het ‘n sterk werking teen M.tuberculosis
met ‘n minimum inhibitoriese konsentrasie (MIC) van 8ug/ml. Dit is baie selektief vir mikobakterieë
aangesien dit nie gram-positiewe of gram-negatiewe bakterieë teen 5 maal die MIC, soos vir
M.tuberculosis, geïnhibeer het nie. F1082 is bevind om, by laer konsentrasies, bakteriostaties te wees in sy aktiwiteit teen M.tuberculosis maar by hoër konsentrasies word ‘n meer bakteriosidiese effek
waargeneem. F1082 is effektief teen MDR, XDR en kliniese isolate van M.tuberculosis en teen
dieselfde konsentrasie soos vir die M. tuberculosis H37Rv verwysingstam waargeneem is. Dit
impliseer dat F1082 dalk ‘n alternatiewe meganisme van werking het in vergelyking met die van die
huidige TB teenmiddels. F1082 toon geen antagonistiese werking in kombinasie met die voorste anti-
TB middels nie, maar toon wel sinergistiese werking in kombinasie met rifampisien. F1082 toon nog
sitotoksiese aktiwiteit teenoor menslike sellyne, maar die sintese van derivate van F1082 toon tot
dusvêr groter anti-TB aktiwiteit en verminderde sitotoksisiteit. Die sintese van meer as 40 homoloë
het gelei tot die identifisering van vier verbindings met vyf keer hoër anti-TB aktiwiteit en honderd
keer verminderde sitotoksisiteit teen menslike sellyne as F1082 self.
“Microarray” ontledings het ‘n aantal metabolise paaie geïdentifiseer waar F1082 ‘n effek kan
uitoefen. Een stel gene wat die mees uitstaande effek toon kodeer vir siderofore wat betrokke is by
yster homeostase in M.tuberculosis. Van hierdie gene was daar sewe van belang omdat hulle in
dieselfde groep voorkom en almal betrokke is by ysteropname (mbtB, mbtC, mbtD, mbtE, mbtF,
mbtH, bfrB). Weens die rol wat F1082 in ysterhomeostase speel, toon ons ook dat F1082
intrasellulêre oksidatiewe stres bevorder wat yster afhanklik is. Al ons resultate dui daarop dat F1082
‘n belowende ant-TB voorloper verbinding is met spesifisiteit teen M.tb en unieke teikeneienskappe in
M. tuberculosis.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/71976 |
| Date | 12 1900 |
| Creators | Ngwane, Andile Happyboy |
| Contributors | Van Helden, Paul, Wiid, Ian J. F., Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Biomedical Sciences. Division of Molecular Biology and Human Genetics. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
| Format | xvii, 180 p. : ill. , some col., map |
| Rights | Stellenbosch University |
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