Photodynamic Attack: Defeating Biowarfare with Light

Biowarfare and bioterrorism are terms that describe the use of biological weapons such as infectious organisms or toxins.  Though we tend to think of biowarfare as a modern phenomenon, it’s actually quite old.  As far back as 400 B.C., Scythian archers infected their arrows by dipping them in decomposing bodies or in blood mixed with manure.  Records from ancient Persia, Greece, and Rome speak of dead animals deliberately placed in wells to contaminate drinking water supplies.  These days, acts of bioterrorism are of course more sophisticated, usually linked with the specific use of microbes or toxins found in nature that can be used to kill or injure people.

Among the most insidious bioweapons in this regard are bacterial strains resistant to all known antibiotics.  For example, the bacterium known as Streptococcus pyogenes is highly virulent, and systemic infection can lead to death in only 48 hours.  The Ebola virus (pictured in the above image) causes severe hemorrhagic fever and results in mortality rates up to 90%.  Anthrax and smallpox are other well-known examples.

Such microbes can serve as effective biological weapons because no security screening is effective or in place.  In many cases, they can be spread by air, water or food.  Even if detected, the antibiotic-resistant nature of the microorganism typically would stay hidden, and no alarms would be triggered until widespread contamination and infection already had occurred.  Owing to the steady worldwide increase in antibiotic resistance, it is imperative that we develop alternative anti-infective strategies to which microbes will be unable to develop resistance.

Photodynamic or light-based methods may offer a powerful countermeasure against these biological weapons, according to Dr. Michael Hamblin and his research team from the Wellman Center for Photomedicine, based at Harvard Medical School.  Hamblin is among the world’s leading authorities on the use of photodynamic therapy (PDT), and he has published dozens of scientific papers on how PDT and related methods can be used to overcome treatment-resistant microbial infections.  (Dr. Hamblin also provided a glowing endorsement for our book, The Medicine of Light.)

Hamblin’s team has identified three major ways in which photodynamic methods can be used in this way: (1) to destroy or neutralize the agent in a wide range of environments before the agent has had a chance to come into contact with humans; (2) to kill or neutralize the agent after it has come into contact with humans, either before or after an established infection or intoxication; and (3) to vaccinate or immunize people who have been exposed to the agent, or who are at risk of being exposed.

In the 25 September 2013 issue of Virulence, Hamblin and his colleagues coauthored an extensive review paper titled “Can biowarfare agents be defeated with light?”  They identify the following advantages of using light-based methods instead of the usual disinfectants, biocides, and anti-infectives:

• Light is relatively cheap, safe and non-toxic.
• Light is non-polluting and thus environmentally friendly.
• Light does not cause excessive damage to the tissue or material surrounding the biological agent.
• Light acts rapidly, typically within seconds.
• Light can be applied to human skin, mucosa, wounds and other sites of exposure without causing undue injury.
• At this juncture, there have been no reports of microbial cells developing resistance to light-based anti-infectives.

Once the potential of different light-based methods to kill microbes was understood, there emerged a growing interest to improve the utilization of light.  This led to the development of even more sophisticated strategies for photodynamic inactivation, or PDI.  One widely studied example is the use of blue light to inactivate antibiotic-resistant bacteria.

In a report published in the October 2013 issue of Current Opinion in Pharmacology, Hamblin’s group notes,  “Many microbial cells are highly sensitive to killing by blue light (400-470nm) due to accumulation of naturally occurring photosensitizers…”  These substances become concentrated in the microbes, making them far more vulnerable to destruction by light.  At the same time, the immune system is activated to help eliminate them more effectively.

Another compelling strategy is what’s called photocatalytic inactivation, which essentially uses light as a way to oxidize toxins or pollutants.  Commercial uses for this technology already include self-cleaning windows and self-cleaning glass covers for road lights.

Speaking of peacetime applications, it is likely that photodynamic methods will prove useful in knocking out the deadly MRSA infections that currently kill tens of thousands of people each year.  “The use of light-based technology to prevent and treat actual infections suggests that they may be useful to decontaminate humans that have already received exposure to biological agents, without causing undue harm to host tissue,” the Harvard authors write.  They also cite research showing that light-based inactivation could prove highly suitable for forming vaccines that can destroy otherwise lethal pathogens.

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Sources

Vatansever F, Ferraresi C, de Sousa MV, Yin R, Rineh A, Sharma SK, Hamblin MR. Can biowarfare agents be defeated with light? Virulence. 2013 Sep 25;4(8). [Epub ahead of print]

Yin R, Dai T, Avci P, Jorge AE, de Melo WC, Vecchio D, Huang YY, Gupta A, Hamblin MR. Light based anti-infectives: ultraviolet C irradiation, photodynamic therapy, blue light, and beyond. Curr Opin Pharmacol. 2013;13(5):731-762

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