HPV Photodynamic Therapy
by Luke Nearhood | published Oct. 17th, 2019
The future of human papillomavirus (HPV) treatment may reside not in a pill or cream, but in the power of light.
Back in February there were claims that researchers in Mexico found a “cure” for HPV. This is, however, a bit of an overstatement. Using photodynamic therapy (PDT), they have developed what appears to be an effective treatment. It is important to note that a treatment, though exciting to discover, is not a cure.
Maureen Ferran, an associate professor of Biology at RIT who has studied HPV, talked about the news she saw circulating.
“Any time an article comes out saying, ‘HPV’s cured,’ or just like a month ago there was a big one saying, ‘Cancer’s been cured, in a year there will be no more cancer,’ I was like, 'Hmm really?'” she asked.
Ferran is not alone — many are asking the same question.
Why All the Excitement?
HPV is known as a common sexually transmitted disease that causes genital warts and can lead to cervical cancer. But it also is the cause of most common warts that humans experience.
“It’s a DNA virus that causes pretty much every wart that humans get,” said Ferran.
With over 300 strains of HPV and approximately 100 that infect humans, researchers like Dr. Ferran break down the latter into two main categories.
“Some of them are high risk, associated with the development of cancer. Others we call low risk, that very, very rarely or never cause cancer. For example, HPV type 1 appears to be the strain that causes plantar warts [low risk] ... and the virus is everywhere, it’s ubiquitous,” said Ferran.
The ubiquity and uniqueness of HPV makes seeking treatments for it a valuable endeavor, especially for the STD form of the disease — which, despite being as damaging as many other STDs, is often overlooked.
“In terms of the genital warts, [the] sexually transmitted part ... it’s one of the most common STDs out there, we think; depending on what paper you read, 60 to 80 percent of young people have been, or are currently infected with HPV,” said Ferran.
There’s already been great success with the Gardasil vaccine in reducing the number of HPV cases among the population. This is specific to HPV types 16 and 18, the sexually transmitted varieties which can lead to cervical cancer.
“And now of course we have this amazing vaccine against HPV [Gardasil], which has done miracles, honestly, in terms of reducing the number of infections,” said Ferran.
Despite the maximum recommended age for getting the vaccine being raised from 26 to 45, there are still many vulnerable in the population who would benefit from a post facto treatment, as Dr. Sandi Connelly, the principal Biology lecturer at RIT, explained.
“ ... there are lots of folks that either didn’t get the HPV vaccine, it didn’t exist when they contracted HPV, or were exposed,” Connelly said.
The gap between current immunization rates and the risk of exposure means a new treatment, like PDT, still has value in treating those who are already infected and at risk of developing cancer. It can also help treat future infections until heard immunity gets high enough to significantly reduce the infection rate. But, how exactly does this new treatment work?
How It Works
PDT has a long history of being used to treat superficial — in the literal sense of the word — ailments, such as acne.
“Probably it’s been 30 or 40 years since the first papers came out on phototherapies. Early phototherapies were used to treat things like acne and psoriasis. So, it started out as an external sort of treatment,” said Connelly.
The use of PDT to treat HPV types 16 and 18 is the next logical step in recent developments attempting to use PDT on internal aliments, such as prostate and colon cancer.
For treating HPV, PDT presents a much less invasive form of treatment as it is generally faster and requires fewer treatments than the alternatives, as Connelly explained.
“On medication regimes, or anything like that, you’re talking about really long term — like if you’re treating something like hepatitis, it’s years of medication. And if you have something that can be a very focused therapy very quickly, people are all for that,” said Connelly.
However, PDT also presents some challenges. Since it's only able to penetrate the top few layers of skin, it is currently unable to completely eliminate HPV from an individual.
Ferran explained, “It only can penetrate about one centimeter of tissue, and that’s a concern because we know that the virus sets up a persistent, long-term infection.”
When used to treat skin ailments, PDT can also result in several side effects, such as skin photosensitivity which usually lasts about 24 hours, where the skin becomes irritated when exposed to light. Phototoxicity can also occur, which can lead to skin lesions and other uncomfortable, but manageable side effects. These side effects are a result from the medium used to make the area treated receptive to the application of light, usually in the form of a topical gel or cream.
“The deal with phototherapy is that you need something that is photosensitive,” said Connelly. “They actually have to coat the area in something that will react with the light wavelengths. When they do that, you get reactions occurring in the cells, that actually decrease the health of the cells.”
PDT is a promising treatment. However, due to the high tech appearance of the treatment, there are still a number of misconceptions and misinterpretations about it.
Misconceptions and Recent Developments
A study in Mexico is the second from Eva Ramon Gallegos's group on the use of PDT to treat HPV. The first study published in 2017 showed promising results for PDT as a treatment, with no HPV detected after 12 months in 83 percent of the 30 patients. The results of this recent and larger study have yet to be published.
“Well, there’s not a paper, that’s the problem. But there was a big news release recently that HPV’s been cured, which of course is unfortunately ... an overstatement,” said Ferran.
As such it will likely be a while before we see widespread clinical application of PDT as a treatment for HPV. Even if or when PDT does become a viable treatment option, treatment will still be less effective than prevention.
“An ounce of prevention is worth a pound of cure,” said Connelly. “So prevention is always our first and foremost.”