By Nana O 
An experimental drug, currently undergoing clinical trials for cancer treatment, has demonstrated significant potential to bolster the efficacy of first-line tuberculosis (TB) therapies by promoting a gentler, more controlled cell death in infected cells. This groundbreaking research, conducted by investigators at Johns Hopkins Medicine, utilized mouse models to explore the mechanisms behind the lung-damaging effects of TB. The findings, published on March 27 in the esteemed journal Nature Communications and supported by funding from the National Institutes of Health (NIH), offer a beacon of hope for developing more effective and less burdensome treatments. These advancements could not only reduce immediate lung damage in TB survivors but also prevent the onset of debilitating post-TB lung disease, a growing concern affecting tens of millions worldwide.
A Novel Approach to Combatting a Global Health Crisis
Tuberculosis, a disease that has plagued humanity for centuries, remains a formidable global health challenge. Despite being preventable and treatable, it has re-emerged as the leading cause of death worldwide, with the World Health Organization (WHO) estimating 1.25 million deaths and 10.8 million new cases in 2023 alone. The rise of drug-resistant strains further complicates recovery efforts, underscoring the urgent need for innovative therapeutic strategies.
"Current treatment regimens for TB are lengthy, expensive, and leave patients vulnerable to relapse and lung scarring. Our research shows that adding in a host-directed therapy has extraordinary promise to solve these problems," stated Dr. Sanjay Jain, the study’s senior author, a pediatric infectious diseases specialist at Johns Hopkins Children’s Center, and professor of pediatrics at the Johns Hopkins University School of Medicine. This sentiment highlights the paradigm shift proposed by the research: moving beyond solely targeting the bacteria to actively supporting the host’s cellular defenses.
Understanding TB’s Destructive Mechanism: Apoptosis vs. Necrosis
Mycobacterium tuberculosis (M.tb), the bacterium responsible for TB, employs a sophisticated strategy to evade the host’s immune system and wreak havoc on the lungs. In the early stages of infection, the body’s infected lung cells attempt to contain the spread of the pathogen through apoptosis, a programmed and orderly process of cell death. This can be metaphorically likened to a controlled demolition of a building, where the structure is dismantled in a precise and contained manner.
However, as the infection progresses, M.tb manipulates this delicate cellular balance. The bacterium prompts infected "host cells" to overproduce Bcl-2, a family of anti-apoptotic proteins. This intervention effectively hijacks a crucial molecular pathway, tipping the scales away from controlled apoptosis and towards necrosis. Necrosis, in contrast to apoptosis, is a chaotic and uncontrolled form of cell death, akin to destruction by a bomb. This uncontrolled cellular demise triggers widespread inflammation and leads to extensive damage to surrounding lung tissue.
"This hijack of a typically healthy molecular pathway has significant advantages for M. tuberculosis," explained Dr. Medha Singh, the study’s first author and a pediatric infectious diseases fellow at the school of medicine. "It promotes necrotic niches within the lung that prevent immune system attacks and allow the bacteria to multiply." These necrotic pockets serve as a sanctuary for the bacteria, shielding them from immune surveillance and facilitating their proliferation.
Navitoclax: A Cancer Drug’s Unexpected Role in TB Treatment
While previous research had explored the concept of inhibiting Bcl-2 as a potential strategy against TB, this approach, known as host-directed therapy, had not been rigorously tested in conjunction with established TB treatments. Host-directed therapies focus on modulating the host’s response to infection rather than directly attacking the pathogen.
To investigate this promising avenue, the Johns Hopkins researchers designed an experiment involving mice infected with M.tb. The study commenced with a control group receiving the standard first-line TB treatment regimen: rifampin, isoniazid, and pyrazinamide (RHZ). A separate group of mice received the same RHZ treatment, but with the crucial addition of navitoclax. Navitoclax is a potent Bcl-2 inhibitor that is currently undergoing clinical trials for various types of cancer, where its ability to accelerate programmed cell death is exploited to eliminate cancerous cells.
Promising Results: Reduced Damage, Enhanced Bacterial Clearance
The results of the study were compelling. Mice that received the combination of RHZ and navitoclax exhibited a significant 40% reduction in necrotic lesions within their lungs compared to those treated with RHZ alone. Furthermore, the spread of infection to other organs, such as the spleen, was notably less frequent in the combined treatment group over the four-week study period.
Advanced imaging techniques, including clinically translatable positron emission tomography (PET), provided further insights. These non-invasive methods allowed researchers to assess apoptosis and fibrosis in live animals. The imaging revealed that the addition of navitoclax not only doubled the amount of pulmonary apoptosis but also reduced lung scarring by an impressive 40% when compared to standard TB treatments.
"Although navitoclax had no effect alone on M. tuberculosis, animals that received the drug along with RHZ decreased their bacterial burden 16 times more effectively," noted Dr. Laurence Carroll, a study author and assistant professor of radiology at the school of medicine. This synergistic effect is particularly significant, demonstrating that navitoclax doesn’t just mitigate damage; it actively enhances the body’s ability to clear the infection when combined with existing antibiotics.
Implications for TB and Beyond: A Broader Impact
The implications of these findings extend beyond the realm of TB. Dr. Jain suggested that navitoclax could potentially offer similar benefits for patients suffering from other chronic bacterial infections, including those caused by Staphylococcus aureus and non-TB mycobacteria, which are prevalent in the United States.
"This idea would need to be tested in clinical trials," Dr. Jain emphasized, underscoring the necessity of further human studies. He envisioned future trials leveraging novel PET imaging approaches developed at the Johns Hopkins Center for Infection and Inflammation Imaging Research. These advanced imaging tools could provide early indicators of the effectiveness of host-directed therapies and offer real-time visualization of lung scarring, enabling more precise treatment monitoring and adjustments.
If subsequent clinical trials prove successful, the integration of navitoclax or similar Bcl-2 inhibitors into standard TB treatment could revolutionize patient care. Potential benefits include shortening the arduous six-month daily antibiotic course, significantly reducing the incidence of lung scarring and post-TB lung disease, and improving outcomes for individuals battling drug-resistant TB. This could represent a monumental step forward in alleviating the long-term burden of TB on individuals and healthcare systems globally.
A Collaborative Effort and Future Directions
This significant research was the product of a dedicated team of scientists at Johns Hopkins, including Mona Sarhan, Nerketa Damiba, Alok Singh, Andres Villabona-Rueda, Oscar Nino-Meza, Xueyi Chen, Yuderleys Masias-Leon, Carlos Ruiz-Gonzalez, Alvaro Ordonez, and Franco D’Alessio. Their collective expertise and commitment were instrumental in advancing this promising field.
The study received vital financial support from several grants from the National Institutes of Health (NIH), specifically R01-AI153349, R01-AI145435-A1, R56-AI179012-A1, R01-AI190038, and S10-OD030381-A1. This funding underscores the NIH’s commitment to addressing critical public health challenges like tuberculosis. Importantly, the researchers declared no conflicts of interest under the Johns Hopkins University School of Medicine policies, ensuring the integrity and objectivity of their findings.
The path forward involves rigorous clinical trials to translate these promising preclinical findings into tangible benefits for patients. The development of host-directed therapies, exemplified by the investigation of navitoclax in TB, signifies a critical evolution in infectious disease treatment, offering a more nuanced and potentially more effective approach to combating long-standing and emerging health threats. The potential to not only cure infections but also to mitigate their devastating long-term consequences marks a new era in medical research.
