Publications

Funding for clinical research |drugs, vaccines, microbicides, diagnostics | HIV/AIDS, tuberculosis, malaria, other infectious diseases |sub-Saharan Africa

Dr Marisa Klopper

South Africa

EDCTP portfolio: Career Development Fellowships

Dr Marisa Klopper is testing the hypothesis that Mycobacterium tuberculosis mutations causing drug resistance also contribute to retain the metabolic fitness of the pathogen.

Understanding mechanisms of TB drug resistance

Drug-resistant tuberculosis (TB) remains a world-wide crisis. Despite early work indicating that drug-resistant Mycobacterium tuberculosis is less fit than its drug-susceptible counterparts, M. tuberculosis resistant to increasing numbers of drugs continues to emerge and spread. It has been shown that compensatory mutations exist that may explain the ability of the resistant bacilli to retain fitness. The challenge is to understand this mechanism.

The challenge

Mutations in the inhA promoter are well known to cause resistance to at least two drugs. These mutations have been suggested to be a gateway to extensively drug-resistant TB (resistant to at least 4 key drugs). Dr Klopper proposes that, in addition to causing resistance, inhA promoter mutations act as compensatory mechanisms, overcoming negative effects of drug-resistance.

She will test this hypothesis by targeted mutagenesis and fitness assays. In particular, inhA promoter mutations cause the upregulation of two genes involved in mycolic acid synthesis (mabA and inhA), as well as one gene involved in haem biosynthesis (hemZ). Dr Klopper aims to show that this upregulation causes an increase in the number of mycolic acids synthesised, which in turn increases the functionality of mycolic acids. She will show that this function is to facilitate the sequestration of ferrous iron, nitric oxide or oxygen by isolation of mycolic acids and measurement of the concentration of these molecules in a solution containing mycolic acids.

The project

The study focuses on an important drug-resistance mechanism and will aid in elucidating additional functions of this mechanism. This will contribute to a better understanding of the physiology of the bacillus and may lead to novel insights for drug design.

The fellowship will not only allow Dr Klopper to conduct this study plan but also plan longer-term projects emanating from its results, including the investigation of further structure-function relationships of different mycolic acids, as well as the related role of haem in the utilisation of reactive oxygen or -nitrogen species. Building out the project will increase opportunities for postgraduate student supervision, as well as international collaborations and publications.

Impact


test the safety and efficacy of this new formulation in young children

Bringing antiretroviral drugs to children

The CHAPAS trials have ensured that many more children with HIV have benefited
from life-saving antiretrovirals.

EDCTP portfolio: HIV & HIV-associated infections

The challenge

Drug-resistant tuberculosis (TB) remains a world-wide crisis. Despite early work indicating that drug-resistant Mycobacterium tuberculosis is less fit than its drug-susceptible counterparts, M. tuberculosis resistant to increasing numbers of drugs continues to emerge and spread. It has been shown that compensatory mutations exist that may explain the ability of the resistant bacilli to retain fitness. The challenge is to understand this mechanism.

Mutations in the inhA promoter are well known to cause resistance to at least two drugs. These mutations have been suggested to be a gateway to extensively drug-resistant TB (resistant to at least 4 key drugs). Dr Klopper proposes that, in addition to causing resistance, inhA promoter mutations act as compensatory mechanisms, overcoming negative effects of drug-resistance.

She will test this hypothesis by targeted mutagenesis and fitness assays. In particular, inhA promoter mutations cause the upregulation of two genes involved in mycolic acid synthesis (mabA and inhA), as well as one gene involved in haem biosynthesis (hemZ). Dr Klopper aims to show that this upregulation causes an increase in the number of mycolic acids synthesised, which in turn increases the functionality of mycolic acids. She will show that this function is to facilitate the sequestration of ferrous iron, nitric oxide or oxygen by isolation of mycolic acids and measurement of the concentration of these molecules in a solution containing mycolic acids.

The project

The later CHAPAS-3 trial compared the efficacy and safety of three fixed-dose combinations including two without stavudine (found to have some long-term side effects in adults, leading to a recommendation that its use be discontinued in children). The trial the first of its kind in Africa studied nearly 500 children at four sites in two African countries.

The study focuses on an important drug-resistance mechanism and will aid in elucidating additional functions of this mechanism. This will contribute to a better understanding of the physiology of the bacillus and may lead to novel insights for drug design.

The fellowship will not only allow Dr Klopper to conduct this study plan but also plan longer-term projects emanating from its results, including the investigation of further structure-function relationships of different mycolic acids, as well as the related role of haem in the utilisation of reactive oxygen or -nitrogen species. Building out the project will increase opportunities for postgraduate student supervision, as well as international collaborations and publications.

ratios forfixed-dose combinations and on appropriatedosage according to weight. 

The CHAPAS-3 trial confirmed the effectiveness of fixed-dose combinations, providing further impetus to the rollout of antiretrovirals to children. Its evidence on abacavir informed the WHO recommendation of abacavir-containing combinations for first-line therapy in children. Trial data have also been used to support applications for regulatory approval for new scored efavirenz tablets.

Impact

L’homme RF et al. Nevirapine, stavudine and lamivudine pharmacokinetics in African children on paediatric fixed-dose combination tablets. AIDS. 2008;22(5):557–65.

Mulenga V et al. Abacavir, zidovudine, or stavudine as paediatric tablets for African HIVinfected children (CHAPAS-3): an open-label, parallel-group, randomised controlled trial. Lancet Infect Dis. 2016;16(2):169–79.

WHO. Guidelines on the use of antiretroviral drugs for treating and preventing HIV infection: recommendations for a public health approach. 2010.

WHO. Consolidated guidelines on the use of antiretroviral drugs
for treating and preventing

HIV infection: Recommendations for a public health approach
(second edition). 2016

Projects: Children with HIV in Africa Pharmacokinetics and Adherence of Simple Antiretroviral Regimens (CHAPAS): CHAPAS-1 and -3

Project lead: Professor Chifumbe Chintu, University Teaching Hospital, Zambia (CHAPAS-1); Dr Veronica Mulenga, University Teaching Hospital, Zambia (CHAPAS-3)

Target population(s): Children with HIV

Sample size: 71 (CHAPAS-1); 480 (CHAPAS-3)

Countries involved: Ireland, the Netherlands, the UK, the USA, Zambia (CHAPAS-1); Uganda, Zambia (CHAPAS-3)

Project duration: 2005–2009 (CHAPAS-1); 2010 –2011 (CHAPAS-3)

EDCTP funding: €1.2M (CHAPAS-1); €4.6M (CHAPAS-3)

Total project funding: €1.2M (CHAPAS-1); €5.0M