Research-based pharmaceuticals developer iThemba Pharmaceuticals has sent one of its scientists, Dr Darren Riley, to the University of Cambridge to vali- date the use of a new production technique, called continuous flow chemistry, in ultimately producing frontline HIV medicines for South Africa, says iThemba Pharmaceuticals chief scientific officer Dr Chris Edlin.
In flow chemistry, a chemical reaction is run in a continuously flowing stream, rather than intermittently, as in batch production. In other words, pumps move fluid into a tube and, where tubes join, the fluids come into contact and a reaction occurs.
“This technology is beginning to make an impact among European and North American active pharmaceutical ingredient (API) manufacturers but is largely absent in, for example, India and China. Establishing this capability in South Africa will create a significant competitive advantage over other traditional low-cost producers,” says Edlin.
Riley, who will be in Cambridge for three months, will study at the university’s Department of Chemistry under flow chemistry expert Professor Steve Ley and, if successful, iThemba hopes to use this proof of concept to establish a flow chemistry laboratory in South Africa. In the longer term, the company also hopes to establish local antiretroviral (ARV) pro- duction using this technique.
“Our efforts in HIV-medicine research are directed towards the low-cost production of ARV APIs. Currently, South Africa imports, at an estimated cost of around R4-billion a year, all bulk drug substances to manufacture HIV medicines and does not have any local production capacity for constituent substances,” he notes.
Further, the company has prepared and submitted grant proposals to several organisations, totalling more than R140-million, and is working towards establishing an ARV API production facility.
“The objective in the next five years is to establish a robust revenue stream that will support the continued expansion of the scientific capabilities of the organisation,” Edlin adds.
iThemba develops new pharmaceuticals for the prevention and treatment of neglected infectious diseases. It does so through international collaboration and has a board of international chemistry and pharmaceutical experts that advises the company.
The company is also focused on building local capacity in pharmaceutical research and development, particularly in medicinal chemistry, in South Africa.
“Within the company, we recruit science graduates from South African universities and expose them to techniques and research methods that are used in international pharmaceutical research organisations. Experience gained internationally by the management team and the exposure of staff members to the scientific advisory board also provide training mechanisms,” says Edlin.
Collaborations and TB
Meanwhile, in collaboration with Emory University, in Atlanta, US, iThemba has used a computational technique called virtual screening to identify potential inhibitors of the enzyme isocitrate lyase, which plays a role in the persistence of Mycobacterium tuberculosis (MTB) says Edlin.
This technique involves building a computational model of the enzyme, ‘docking’ potential molecules into this model (determining if a molecule will fit into an enzyme) and assigning a score based on its predicted fit. In this way, tens of thousands of molecules can be assessed rapidly and the compounds predicted to be most active selected, bought and tested against the actual enzyme, he explains.
Several of the compounds show good activity against the enzyme, but do not show any activity against MTB, the causative agent of most cases of TB. However, iThemba took these starting points and modified the chemical structures in a logical and systematic manner to try to resolve the lack of activity seen with MTB.
“After synthesising several hundred compounds in our laboratories and testing them against live TB at the University of Chicago, the team eventually managed to demonstrate activity similar to the current TB medicines rifampicin and isoniazid,” he notes.
“The next steps in the process involve assessing the compounds for their suitability to be tested in animal models (in vivo) of the disease. However, before this, there are a number of in vitro techniques that can be used to prioritise and refine the final selection for in vivo assessment. This avoids the use of animals at this early stage of research.”
The company is currently addressing some of the issues highlighted through testing by designing and synthesising new analogues that will be suitable for in vivo assessment, he adds.
iThemba is developing an analogue of a compound in phase-two clinical trials for TB that are being developed by nonprofit medicine development partnership Global Alliance for TB Drug Development, based in New York. The compound, called PA-824, is a nitroimidazole, a new class of antibacterial agent.
“As a potential TB therapy, it has many attractive characteristics – most notably its mechanism of action, its activity in vitro against all tested drug-resistant clinical isolates and its activity as both a potent bactericidal agent and a sterilising agent in mice,” Edlin says.
Further, PA-824 has been demonstrated to be safe for humans and has no effect on metabolising enzymes, which is important for coadministration with HIV medication.
Clinical results are encouraging, with positive phase-two data generated in TB patients, he notes.
“iThemba’s project has identified new chemical spaces that can be exploited without affecting the ‘warhead’ portion of the molecule (which is active in treating the disease) and that may improve the physical and metabolic characteristics of this class of molecule. The company has also completed the first set of synthetic analogues and demonstrated anti-TB activity in vitro.”
TB and HIV
The frequent coinfection of TB in HIV patients creates significant problems for the development of new TB therapy because increased pill burden (of around 15 pills a day for HIV/TB coinfections) diminishes compliance; and rifampicin, one of the frontline TB drugs, modifies a number of crucial metabolising enzymes in the liver, which leads to a significant reduction in the concentration of HIV drugs and renders some of this therapy inactive, Edlin explains.
“All our TB projects are being investigated with these two key points in mind and, by using a number of in vitro tests, new compounds are being designed and synthesised,” Edlin concludes.