Science Spotlight

High’d and seek: drug-specific antibodies to treat addiction and prevent overdose

From the Pancera Lab, Vaccine and Infectious Disease Division

If I start explaining about how your immune system works—how your B cells recognize pathogens, identify little protein pieces of those pathogens called antigens, and produce neutralizing antibodies against these antigens to clear the invader—chances are you’re impatiently nodding along, having heard this story far too many times. If you’re anything like me, though, you’ve probably never stopped to ask yourself a few deep questions about this process: do antigens always have to be proteins? And do the invaders always have to be pathogens?

If you bring these questions to Dr. Marie Pancera, a structural biologist in Fred Hutch’s Vaccine and Infectious Disease Division, prepare to be amazed. Her lab uses a biophysical approach to understand host-pathogen immune interactions, hoping to use what they learn to prevent and treat diverse diseases of global health burden. The lab’s latest project, a collaboration with Dr. Marco Pravetoni at the University of Washington and spearheaded by former lab technician Justas Rodarte, characterizes interactions between monoclonal antibodies isolated from immunized hosts and opiate drugs—you read that right, drugs—which pose a significant public health concern in light of the ongoing opioid crisis.

The concept behind this approach is relatively straightforward: by binding these drugs in the bloodstream, the antibodies keep them from entering the brain and causing dependence or overdose. “The idea of using antibodies to treat drug-use disorders isn’t that new,” comments Rodarte. “Nicotine and cocaine, for example, were some of the early targets. The problem with nicotine was that its effective dose was so high that it would overwhelm your available antibodies after a single cigarette.” Indeed, while newer synthetic opiates like oxycodone and fentanyl are particularly dangerous due to their incredible potency, this same fact makes them promising targets for antibodies.
 

A cartoon depicts of a sea of red blood cells and drugs underneath an array of robotic arms with antibodies at the ends- these antibody arms are fishing the harmful drugs out of the sea of blood cells.
A cartoon depiction of drug-specific antibodies neutralizing harmful drugs in the bloodstream Image generated by the author.

Just as well, advances in vaccine and antibody development technologies now allow researchers like Dr. Pravetoni to elicit more potent antibodies by conjugating their drug targets to immunogenic carrier proteins. Focusing on common drugs—nicotine, heroin, morphine, oxycodone, fentanyl, and fentanyl analogs—Dr. Pravetoni’s group generated drug-specific antibodies which they showed to reduce drug concentrations in the brain and improve behavioral effects of drug use in several animal models. While they had evidence that these antibodies worked, the crucial piece of the puzzle they were missing—the piece which Dr. Pancera was able to provide—was exactly how they worked. Purifying these drug-specific antibodies, Rodarte and colleagues solved X-ray crystal structures of drug-antibody conjugates, which they analyzed to determine the mechanism of binding at atomic resolution.

To say that Rodarte and Pancera were surprised at what they found would be an understatement. “Since these are small molecules, they don’t have too many chemical groups which antibodies can bind in the first place,” Rodarte says. “But we were still pretty shocked at how similarly these diverse drugs were bound.” Thus, while each antibody was exquisitely specific to each drug, the chemical groups which were common among the drugs were bound in similar poses and by similar amino acids on the respective antibody. In stark contrast, when the team compared their structures to published structures of the drugs bound to their endogenous receptors in the brain, they found that the binding modes were completely different. “In hindsight, it makes sense—the drug-receptor pairs evolved promiscuity and rapid on-off binding according to their function,” Rodarte explains. “The kind of ‘high-affinity, low dissociation’ binding we look for in antibodies is distinct from that.”

This work highlights both the promises and novelty of a drug-specific antibody approach. When Rodarte and Pancera went to deposit their structure models into the Protein Data Bank (PDB) archive, which holds millions of protein structures determined by researchers worldwide, they were surprised to find that their oxycodone-bound antibody was the first oxycodone-bound protein structure in the entire database! And now that the exact mechanisms of binding for these antibodies are known, researchers can leverage protein and immune-engineering strategies to design more effective antibodies for eventual clinical use, either as acute interventions to prevent overdose (in combination with Naloxone and related treatments), as safer clinical treatments for opioid use disorder (replacing cumbersome and side-effect prone methadone regimes) or to design ‘drug vaccines’ which prevent accidental overdoses and make it easier for users to overcome their addictions. With opioid use disorders reaching record levels, these innovative approaches couldn’t be timelier.
 

The spotlighted research was funded by the National Institutes of Health and the J.B. Pendleton Charitable Trust.

Rodarte, J.V., Baehr, C., Hicks, D., Liban, T. L., Weidle, C., Ruper, P. B., Jahan, R., Wall, A., McGuire, A.T., Strong, R. K., Runyon, S., Pravetoni, M., Pancera, M. 2023. Structures of drug-specific monoclonal antibodies bound to opioids and nicotine reveal a common mode of binding. Structure. 31(1).