A Discovery Puts the Brakes on a Cancer-Inducing Virus

“Almost everyone becomes infected with human papillomavirus (HPV) during their lifetime, but in many cases it happens in a relatively harmless way. Often the symptoms never manifest at all”, says Mart Toots, a fresh PhD in biomedical technology at the University of Tartu. His doctoral thesis focuses on the oncogenic types of the virus.

Mart Toots

Fresh PhD in biomedical technology Mart Toots discovered novel inhibitors of the cancer-causing papillomavirus. Photo by Mart Ustav Junior

During his study, Toots half-incidentally discovered many previously undescribed chemical compounds which can hinder the viral infection.

By now, we know about 205 or more types of HPV, 13 of them considered dangerous. The virus is spread by contact transmission, including sexual transmission. Unlike infections with most HPV types that may result in benign growths – typically manifesting as warts and disappearing, thanks to the immune system, by themselves – when a malign type of the virus is present, the persistent, long-lasting infection might lead to cancer.

HPV most frequently causes cervical cancer. More than half a million women receive the diagnosis each year, most often in Africa and South America, where there are up to 60 cases per 100,000 women. In Estonia the number is 20 on average. The virus can cause genital cancers in men as well, but it doesn’t happen nearly as often.

the spread of papilloma virus

On the left: The global number of cervical cancer cases per 100,000 women. 
On the right: The percentage in the grey circle shows the proportion of women infected with viruses causing cervical cancer. The circles represent various regions. The small circles represent the three most wide-spread cancer-causing virus type per each region.
The figures are from Mart Toots’ PhD and are based on the following sources: Ferlay et al. 2010, Crow 2012, Jung et al. 2015.

HPV infects the basal dividing cells in the deepest layer of epithelial tissue through microwounds or abrasions.

HPV infection can be prevented with vaccination, but until now there’s no efficient cure that can stop the disease once the infection has caused it. There are three vaccines available, but they work only when the vaccination happens before sexual initiation. In Estonia, the vaccine is allowed for girls aged 9–12 and boys aged 9–15.

“Chance favors the prepared mind”

These words belong to Louis Pasteur, the French chemist and microbiologist, affirming that just noticing a lucky discovery, as well as moving on to conclusions that have results, takes an attentive mind paired with the necessary skills.

Mart Toots’ search for possibilities to stop the pathogen began with constructing an easily usable model to study the replication of the HPV genome. In the laboratory of Professor Mart Ustav, the research team including Toots built a model that made it possible to evaluate how thousands of chemical compounds impact HPV. This was achieved by using the cells derived from osteosarcoma, marked as U2OS in the study.

“At first, we modified the genome of the virus a little, so it would be easier to measure it. As a result, when the virus replicated, a certain protein – luciferaze – emanated, through which it was possible to measure bioluminescence”, Toots explains. The working mechanism of the “target protein” is simple: the greater the presence of virus, the greater the bioluminescence.

In fact, luciferase is usually known because of firefly larvae that it causes to have a blue glow on summer nights. Using such light as an indicator, the research team managed to recognize five inhibitors (compounds that put brakes on the infection from cancer-causing HPV) from 1,600 chemical compounds.

“We got terribly lucky”, Mart Toots says. “At first, I had neither much faith nor any deep knowledge about how some of these numerous compounds could relate to HPV”.

Did you know?
 The most well-known researcher of HPV comes from 
Germany – Harald zur Hausen, who started looking for links between 
the virus and cancer already in the 1970s, leading to the Nobel 
Prize in Medicine in 2008.

Two patented discoveries from a single study

Toots brings attention to the original results of the joint research in the laboratory. “First, no one has succeeded in creating a similar system, something that would enable us to model the whole DNA synthesis of the virus and, at the same time in a extremely precise but really simple way – through measuring light – to analyze a great amount of chemical compounds, all of this with very small consumption of materials.

Popular models used to study HPV up to now don’t let you research all types of the virus, let alone the impact of thousands of chemical compounds. Some of them enable measurement of just a certain part of the life cycle of the virus, not the whole”, the researcher explains.

Toots assures that there’s already a patent pending for the modelled system, developed for seeking cures for HPV and novel inhibitors. When it comes to the compounds inhibiting the infection, recognized in the bank of 1,600, then, surprisingly, the impact of the five compounds described manifested itself with the dangerous forms of the virus.

“The inhibitors worked on types of the virus that cause cancer without influencing the harmless types”, the molecular biologist explains. He’s not yet ready to state to the public why it is so, but there is a hypothesis. Experiments must lead to final, controlled results.

According to Toots, 99.7 per cent of the cancer cases caused by HPV can be traced back to types 18, 16, 31, 33 and 45. All five inhibitors suppressed replication of those types. Allegedly, in some other lab, one of those had made it into the phase of clinical trials as a potential cure for cancer.

Generally, dangerous and non-dangerous forms of HPV are distinguishable by the capability of two proteins – E6 and E7. These proteins influence cells in such a way that the virus can procreate in the organism and retain the sickness during a longer period of time. Because of that, mutations arise in DNA, developing into cancer.

Speaking of a future scenario, when it comes to developing medicine, a suitable animal model should be discovered first – something that doesn’t yet exist – so further research of human papillomavirus could be performed. Because of that, Mart Toots would like to begin experimenting with bovine papillomavirus and find out if some of the novel inhibitors found during the doctoral study could first be used for curing cattle.

Signe Opermann is a senior specialist for science communication at the University of Tartu and an author at ERR Novaator.

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