The War Against Viruses: Part 2—Anti-viral Drugs

Last updated on April 23, 2020

            Last week, we discussed the immune system and vaccines—our armor and shield against viral invasion. But what happens when those defenses aren’t enough? As our immune system begins taking arms against an enemy horde, we must pivot from girding our defenses to looking for ways we can help our immune system achieve victory quickly with minimal cellular casualties. Just like Gandalf bringing the Riders of Rohan to aid at the battle of Helms Deep moments before the heroes’ glorious defeat (yes, I did use this metaphor to make a LOTR reference), anti-viral drugs can mean the difference between victory and crushing defeat for your immune system. But what sort of weapons do we build to fight an enemy that is constantly evolving to become stronger, smarter, and more resilient?

            Anti-viral drug is an umbrella term covering an enormous variety of drugs that researchers have developed to inhibit viral replication or to modulate the immune system’s response to a viral threat. The diversity, adaptability, and simplicity of viruses make them dangerous opponents. We have developed a whole slew of antibiotics, drugs designed to kill bacteria.  Antibiotics often work against a broad spectrum of bacterial strains. Such “broad spectrum antibiotics” are known to wipe out all the good, beneficial bacteria living in our body as well, because bacteria tend to have more in common with each other than they have with our cells. Viruses, on the other hand, are incredibly diverse in their genetic material, their outer shells, and their modes of replication and transmission. This diversity makes it near impossible to develop broad spectrum anti-viral drugs.

            And even as we develop anti-viral drugs, the ability of viruses to mutate and evolve relatively quickly help them to evade our attacks. Bacteria can also mutate, but at a much slower rate than viruses. Antibiotic resistant bacteria develop in response to antibiotic use, and while bacteria evolve slower than viruses, we still struggle to develop new drugs to keep bacteria at bay—over 35,000 people in the U.S. die each year as a result of antibiotic resistant bacteria. The quick adaptability of viruses prompts doctors to sometimes use cocktails of anti-viral drugs that attack different parts of the infection and replication process. The virus may evolve to evade one of these attacks, but remain vulnerable to all the others. 

            Perhaps counterintuitive, the simplicity of viruses actually makes them harder to fight. Because viruses are really just genetic material enveloped in proteins and occasionally lipids, there is less machinery for anti-virals to target. Viruses also replicate inside our own cells; in order to target any particular step of their replication, we have to target processes within our own cells. This can interrupt normal cellular functioning and/or harm our own cells, which may not be worth the risk unless the patient has a weakened immune system. 

            In general, anti-virals work by interrupting the viral replication cycle: (1) preventing the virus from binding to and entering a host cell, (2) blocking the virus from releasing its genetic material into the cell, (3) interfering with the synthesis of new virus parts, (4) hindering the assembly of new viruses, or (5) stopping the new viruses from leaving the infected cell. 

            Any of these processes can be interrupted by disabling certain proteins or enzymes that the virus hijacks to help it replicate. A virus that cannot replicate dies. Some of the viruses may evade death by thinking on their feet and adapting to the interruption (not literally—viruses have neither brains nor what one could reasonably call feet). But if the viral attack is weakened enough, then the immune system can usually take care of the remaining horde.

            In some cases, anti-virals can mean the difference between life and death. This is the case for HIV, which attacks a key immune cell called CD4 resulting in Acquired Immunodeficiency Syndrome (AIDS). Because HIV weakens the immune system, your body is unable to fight it off alone. The standard anti-viral treatment for HIV is antiretroviral therapy (ART), which includes multiple drugs that interrupt the viral replication at multiple different stages. Since ART is a long-term treatment, the cocktail of different anti-viral drugs is essential to keeping the virus on its toes (again, not actual toes). There is no cure for HIV, but ART can keep the virus at bay and allow infected individuals to live long, healthy lives.

            In the case of more tame viruses, anti-virals can be helpful to lessen the severity of an infection. This is the case with drugs like Tamiflu® (oseltamivir phosphate), a drug that blocks a key influenza enzyme preventing it from spreading from one cell to the next. For many, the immune system can overcome influenza on its own with some days of fever and sickness. But the use of an anti-viral can shorten that period significantly and lower the intensity of the symptoms. This is especially important for individuals with weak immune systems or those who are more sensitive to the symptoms of a flu.

            Between last week’s post on vaccines and this week’s post on anti-viral drugs, I hope I have given you some helpful information on how scientists have been fighting the war against viruses along with our immune system. Next week, we’ll turn our sights on Covid-19, and I’ll talk a bit about the drugs and vaccines that are being considered to hopefully beat back this dangerous virus and get us back to a sense of normalcy. Comment below or email me at contact@anyonecanscience.com to let me know what you think about this week’s blog post and tell me what sorts of topics you want me to cover in the future. And subscribe below for weekly science posts sent straight to your email!