Kiwi scientists closing in killer infectious disease

Otago University's Professor Greg Cook (pictured) and Dr Kiel Hards have been investigating one of the first new TB drugs approved in more than 40 years. Photo / Supplied

Kiwi scientists have discovered a novel property of a new anti-tuberculosis drug which may help develop more drugs to treat the world's biggest-killing infectious disease.

Globally, there are about 1.7 million deaths annually that are attributed to tuberculosis (TB) with rising incidents of drug-resistant TB.

Professor Greg Cook from the University of Otago's Department of Microbiology and Immunology, along with postdoctoral fellow Dr Kiel Hards, has been investigating one of the first new TB drugs approved in more than 40 years, Bedaquiline – which is sold under the brand name Sirturo.

Bedaquiline is the first new drug to be developed after four decades of searching for more effective drugs that combat TB and was only approved by the US Food and Drug Administration in 2012.

But Cook said one drug wouldn't be enough to reverse a 40-year lull in drug-development.

"So our lab is actively searching for new TB drugs to complement Bedaquiline and expand the treatment options available to clinicians worldwide."

To develop even better drugs to combat TB, it was important to understand why Bedaquiline was so good in the first place.

"The most promising aspects of the drug are its ability to shorten treatment timeframe to eight weeks and that its target is unconventional for an antimicrobial," Hards said.

"Bedaquiline disrupts the ability of M. tuberculosis to generate energy," he said.

"What we discovered is that the drug has a second activity or property that may explain how it is able to kill non-replicating cells."

This second activity, called "ionophoric", involved the movement or shutting of ions across the mycobacterial membrane, resulting in the dissipating of critical ion gradients needed for growth and survival.

Potentially, their finding may have ramifications for other antibiotics, as it be could be the case that many other antibiotics work by this mechanism.

"We believe that we can design more effective TB drugs if we include ionophore-like properties in a similar way to Bedaquiline," Cook said.

"The 'biological electricity' that these ions normally create is key to energy generation and a whole series of other incredibly important cellular processes.

"It was already known that disrupting these ion gradients is lethal to M. tuberculosis but before Bedaquiline there were no drugs that could do this and be safe in humans."

Cook said it was very rare to discover new properties about drugs as researchers frequently focus on the primary target of a drug and often the off-target or secondary effects of drugs are ignored.

"Subsequent discoveries are usually serendipitous, but in the case of Bedaquiline we realised the previous data didn't explain how it could kill non-replicating cells and so we kept pushing to find the answer," he said.

"Many researchers are now turning their attention back to focusing on how antimicrobials actually kill bacteria to uncover new pathways of cell death.

"These offer tremendous potential to develop new antimicrobials."

The Otago researchers worked in collaboration with colleagues from The University of Technology in the Netherlands, the University of Illinois in the United States and Vrije University in Amsterdam.

The study was supported with funding from the Marsden Fund, Royal Society and the Maurice Wilkins Centre for Molecular Biodiscovery.