A Boston University (BU)-led research team has found that two compounds acting in synergy could help the body more effectively fight tuberculosis (TB) by tweaking the activation of key macrophage immune cells. To develop their host-directed therapeutic approach the investigators identified the genetic signatures of TB-susceptible and TB-resistant immune system macrophage cells, and then tested the ability of different compounds to transform vulnerable macrophages into those that were more resilient against Mycobacterium tuberculosis (Mtb), the bacterium that causes tuberculosis.
Their lab-based studies demonstrated that the two identified molecules, Rocaglamide A (RocA) and a c-Jun N-terminal kinase (JNK) inhibitor—which have shown promise as cancer treatments—acted in partnership to improve the control of virulent Mtb in TB-susceptible macrophages. They suggested that with the right backing and funding, their treatment strategy could be ready for clinical trials in 2024.
“We hope that our research will contribute to the development of more effective treatments for TB by better understanding how to fine tune the activation states of immune cells,” said Shivraj M. Yabaji, PhD, a BU’s National Emerging Infectious Diseases Laboratories (NEIDL) postdoctoral researcher. “This could potentially lead to therapies that target host immunity to tuberculosis.” Yabaji is lead author of the team’s published paper in Science Advances, titled “Cell state transition analysis identifies interventions that improve control of Mycobacterium tuberculosis infection by susceptible macrophages.” The studies combined lab-based work at BU’s NEIDL with a big data audit of potential compounds by scientists at University College Dublin, Ireland.
Tuberculosis is an infectious bacterial disease that has co-evolved with humans for millenia and is “arguably the most successful human bacterial pathogen,” the authors wrote. And while TB has been stunted by vaccinations, antibiotics, and public health measures such as isolation, there is no cure, and more than a million people around the world still die from TB every year.
“Tuberculosis, as one of my colleagues used to say, has studied us much longer than we have studied it,” said Kramnik, who is also a NEIDL investigator. “It’s a serious and complex disease and our standard interventions are only partially efficient—none of them are sufficient to eradicate the disease.” Added research lead and co-corresponding author Igor Kramnik, MD, PhD, “The TB vaccine is not really 100 percent efficient and antibiotic resistance is becoming more prevalent,” Kramnik is a BU Chobanian & Avedisian School of Medicine associate professor of medicine.
The tiny rod-shaped bacterium, Mycobacterium tuberculosis that is the cause of TB is less than 0.5 micrometers in diameter. Spread by a cough, a sneeze, or even just a conversation, M. tuberculosis infection can cause symptoms including fever, weight loss, and chest pain with the disease typically concentrating its attack on their lungs. There were more than 10 million infections worldwide in 2021, the authors stated.
For 100 years, the bacille Calmette-Guérin (BCG) vaccine has represented the first line of defense against TB, but vaccination is not infallible. A recent study from Boston University showed that BCG has limited impact, with researchers suggesting that the vaccine was only about 37% effective in children under five years of age and offered no protection for adolescents and adults. And antibiotics, the fallback for those who do become infected, are losing their power. The authors cite WHO statistics indicating that some 500,000 people die every year from drug-resistant TB.
Kramnik has been studying TB for 30 years. “It’s a disease that’s very different from others,” he said. “Thinking about tuberculosis as a battle between a pathogen and a host isn’t really productive. What we’re probably dealing with is an evolutionarily refined coexistence of a pathogen and a host that eventually leads to incurable disease at its terminal stage.”
One of the key mysteries about TB is why some infected people get sick while most others don’t, and in particular, why so many patients initially ward off infection, then eventually succumb to it. Kramnik is also interested in why the M. tuberculosispathogen is so intent on destroying the lung, which enables its transmission via infectious aerosols. The Kramnike lab’s studies in experimental mouse models, mimicking what happens to humans when they contract TB, have been attempting to provide some answers.
“It all led us to identify the importance of macrophage cells as major determinants, and regulators and controllers, of local immune response in the lung,” he said, “and a major cell that affects susceptibility in cases of growing infection.”
Macrophages typically have two disease fighting states, said Kramnik, an active one that takes on and eliminates pathogenic intruders, and a regenerative one that helps to rebuild tissue after infection. The lab’s studies discovered that in the case of TB, the macrophages can get stuck in a hyperactive, but ineffective fight mode, resulting in a persistent and damaging inflammatory response that hurts the body, but doesn’t take down the pathogen. In their newly reported study Kramnik, Yabaji, and colleagues used the mouse models to look for ways to shut this response off and help the macrophages work more effectively.
They carried out RNA sequencing to zero in on the genetic signature that differentiates the normal/resistant and aberrant/susceptible activation macrophage states. Using a test developed in collaboration with study coauthor Alexander A. Gimelbrant, PhD, an investigator at the Seattle-based Altius Institute for Biomedical Sciences, the team then simultaneously measured the expression of 46 different genes that represented this signature. “This allowed us to look at gene expression patterns rather than individual genes to characterize the cell states and their changes in response to treatments,” Kramnick explained. The team then tested a range of drugs to see if any would perturb the expression of these genes.
They found that while some molecules worked better than others, no single compound could shift a macrophage from a TB-vulnerable to a TB-resistant state. To uncover a potential combination that would work in synergy, the lab-based team sent their data to researchers at University College Dublin, Ireland, who had developed a machine learning algorithm that they could use to predict whether particular combinations of drugs would be more effective. “We then went back to the bench and tested those predictions,” Kramnik said.
They found two molecules that have shown promise as cancer treatments—Rocaglamide A (RocA) and a c-Jun N-terminal kinase (JNK) inhibitor—formed an especially good partnership. Together, the two drugs helped to hinder cell signalling related to inflammation and stress, while boosting the pathways that carry stress resistance signals. “Our findings suggested perturbations for switching from TB-susceptible to TB-resistant transcriptional states, such that the susceptible macrophages showed improved control of Mtb,” the investigators noted. “We have experimentally validated
the following: (i) The RocA treatment increased macrophage resilience to oxidative stress, and (ii) low concentrations of RocA and JNKi acted synergistically to improve the control of virulent Mtb by the TB-susceptible macrophages.” Kramnik added, “They would be good candidates for clinical trials, so it could change the medical treatment of tuberculosis.”
The researchers discovered that using the two drugs together allowed them to dial back on the effective dose of RocA, which can be potentially toxic at higher levels. Kramnik suggests that their results show how to increase “therapeutic efficacy at lower drug doses and decrease toxic side effects. This is particularly important for chronic diseases that require long course treatments, such as tuberculosis.”
The new approach could add a host-directed treatment approach to the TB-fighting arsenal, as a way of helping the body better control infection and reduce disease-related inflammation. “Our findings indicate that targeting unresolving stress pathways associated with TB susceptibility is a promising strategy for host-directed TB therapies and provide candidates for the drug development,” the investigators stated. “It’s a way of treating the host, the patient, rather than focusing on the pathogen,” Kramnik noted.
Although the team is ready to move the research forward, bringing any therapy to trial would require fresh backing. “We will be in position,” pointed out Kramnik, “to partner with people who can bring it to the clinic. This is our goal.”
The same strategy, the team suggested, may also be applied to identify drug-based treatments for other diseases. “This study outlines the design and implementation of a complete path from molecular characterization of macrophage transcriptional states to pharmaceutical interventions, an approach that is broadly applicable to diseases driven by pathological cell states.”