Drug addiction is a serious problem affecting many countries. In 2016, there were 60,000 reported deaths in the US alone and half of those was due to opioid use. Several methods of therapy are available but vaccines are getting the limelight lately.
This past June, researchers from the Scripps Research Institute, California, led by first author Paul Bremer and senior author Kim Janda, published their study about an anti-heroin vaccine which they tested on monkeys and mice. This is the first anti-opioid vaccine to pass pre-clinical testing and researchers are hoping to start the human clinical trials soon. The paper can be read in the Journal of the American Chemical Society.
Opioids are a class of highly addictive drugs that target the nervous system and produce a narcotic, morphine-like effect. The class includes morphine, heroin, and synthetic opioids like methadone, oxycodone and fentanyl. Morphine is naturally extracted from opium plant (hence the name of the group) and is itself a potent pain reliever. Heroin, on the other hand, is made by mixing morphine with another chemical and the combination makes it three times more potent than morphine.
In the United States, morphine, methadone, oxycodone and fentanyl are classified as Schedule 2 drugs by the Drug Enforcement Agency. This means they have accepted medical use but have a high potential for severe psychological or physical dependence; acceptable levels of use are set for these drugs. Among opioids, only heroin is classified as a Schedule 1 drug: this means it has no medical use and has a high potential for abuse.
When a drug user takes heroin, the effect immediately kicks in, leading to euphoria (the “high” feeling) followed by a sense of tranquility. The new anti-heroin vaccine is designed to block the brain from feeling these mind-altering effects. The user will be “dissatisfied” not to experience what he is expecting to feel and this “dissatisfaction” is what researchers are counting on to make a user stop his or her addiction.
While opioids are notoriously known for their ability to give the “high” effect, they are medically used for treating chronic pain that can’t be managed with over-the-counter pain relievers like aspirin or ibuprofen. One thing of worry though is that the dose needs to be increased over time to achieve the original relieving effect and this causes the medication to be abused.
Attempts to make an anti-opioid vaccine started in the 1970s but development was slow. One reason was the wide acceptance of drug substitution therapy as an intervention for drug addiction. This is done by replacing heroin and other powerful narcotics with methadone and other opioids of lesser potency to create less euphoria and, in turn, less tendency to be abused. However, the therapy is expensive and unreliable: the user has to make frequent trips to the clinic to get his daily dose and one “taste” of heroin (or a more potent drug) is enough to send him or her into relapse.
Another reason for the slow development is that designing a vaccine against heroin (or any opioid) is tricky. A heroin molecule is so small that antibodies are ignoring its presence. In order for antibodies to take notice, the hapten (the vaccine’s part that binds to the antibodies) which contains part of the heroin molecule has to be connected to a protein to become large enough to elicit a reaction. The immune response must be long-lasting as well so that the antibodies can readily recognize heroin in its free state once the drug enters the body.
Unlike what they do to viruses and bacteria, antibodies do not destroy heroin ; they just make the drug too big to cross the blood-brain barrier. Based on the Bremer -Janda anti-heroine vaccine study, on mice, potency was reduced by more than 15-fold. On monkeys, additional booster shots of the vaccine enabled the effect to last for at least 8 months. Compared to drug substitution therapy, this vaccine showed fewer side effects. Furthermore, there was no shown dependence on other opioids or risk of overdose. Additionally, the cost is lower. Speaking of cost, according to the Guardian, heroin use costs the US about $50 billion annually.
Researchers, however, recommend vaccination only for drug users who really want to quit the habit. “Vaccines are meant to be used by people who want to quit taking drugs,” says Janda. “If you don’t want to stop then nothing will help. The idea is that if they have a moment of weakness, they won’t relapse and can continue with their therapy.” Also, experts agree that the vaccine has to be applied with psychotherapy as it only addresses the aspect of physical dependence.
Another drawback is that a vaccinated user can easily switch to another drug which will give the same effect and this vaccine is ineffective against other opioids. The opioid epidemic is not centered on heroin alone and it is also not uncommon to see heroin being mixed with other opioids, fentanyl. Fentanyl is up to ten times more potent than morphine and for drug users this is obviously, and unfortunately at the same time, a welcome treat. But this was also addressed.
Given that each opioid needs a unique design, the research team took the right steps when they developed separate vaccines for heroin as well as fentanyl. Their anti-fentanyl vaccine was made last year and yielded positive results on mice. In the future, researchers are aiming to combine the two for maximum effectiveness and wider coverage.