New photodynamic therapy mechanism described
March 18, 2015
By Karina Toledo
Agência FAPESP – Photodynamic therapy, which uses drugs activated by light to generate oxidizing substances capable of causing cell death, is considered an important candidate treatment for cancer and several types of infection.
A research group led by Mauricio da Silva Baptista at the University of São Paulo’s Chemistry Institute (IQ-USP) is investigating the action mechanisms of various photosensitive molecules. The aim of the project, which is supported by FAPESP, is to find compounds that are more effective in terms of requiring lower doses and less light while acting on deeper layers of the skin.
One of the molecules investigated, an inorganic complex comprising the metal ruthenium and several types of ligands, was recently described in a paper published in the Journal of the American Chemical Society.
“This study was innovative in two ways – first, because most photosensitive drugs are organic, and we described a mixture of organic and inorganic elements, and second, because the action mechanism described is different and more powerful than others that are already known,” Baptista said.
According to Baptista, a professor at IQ-USP, most photosensitive drugs induce cell death by generating molecules of singlet oxygen, a highly oxidizing substance that can damage proteins, nucleic acids and cell membranes.
There are also substances that, when photoactivated, bind with the DNA in the nucleus of a target cell and prevent it from dividing.
“The ruthenium complex acts in two ways simultaneously. In tests using cells cultured in the lab, it proved four times more effective than a compound that only generates singlet oxygen. And it was 170 times more effective than a substance capable only of binding with DNA,” Baptista said.
The inorganic ruthenium complex is one of 50 substances synthesized by a group of researchers at Ohio State University in the United States that are being tested at IQ-USP.
“We wanted to kill the cells of a tumor or pathogen with a smaller amount of photosensitive dye and less light,” Baptista said. “But the skin, acting as a barrier, stopped most of the light from penetrating the tissues.”
So far, the compounds investigated at IQ-USP have been tested only in cell cultures. According to Baptista, for the research to advance to the stage of in vivo experiments, there must be interest on the part of the pharmaceutical industry.
“Hundreds of photosensitive drugs that are more effective than those currently used have been described worldwide, but fewer than ten have advanced to the clinical trial stage so far. The pharmaceutical companies are resistant because they aren’t accustomed to dealing with light. New partnerships are needed to create something entirely different for their production pipelines,” Baptista said.
While prospecting for new compounds, Baptista is partnering with physicians to study the effect of phototherapy using well-known substances like methylene blue on diseases such as melanoma, leishmaniasis, mycosis, Kaposi’s sarcoma (a form of cancer that affects connective tissue and is frequently associated with HIV infection), gynecological cancer and diabetic foot.
More than 200 patients with diabetic foot have been treated through a partnership with Dr. João Paulo Tardivo, an angiologist at Hospital de Ensino Padre Anchieta, the ABC Medical School’s teaching hospital in São Bernardo do Campo, São Paulo State. Diabetic foot is a complication of diabetes that can involve ulceration, infection, osteomyelitis (bone infection), neuropathy (loss of nerve sensitivity), ischemia and thrombosis.
Conventional treatment relies on antibiotics, but these are often ineffective because damage to the patient’s microcirculation prevents the drug from reaching the focus of infection.
According to Tardivo, photodynamic therapy was applied to more than 200 people attending the outpatient clinic in São Bernardo do Campo. Seventy had already developed osteomyelitis and if treated only with conventional therapy would probably have required amputation. Thanks to photodynamic therapy, 62 were discharged and only eight required amputation.
“Diabetic foot is a condition with varying degrees of severity. We’ve developed an index and an algorithm to help determine the cases in which photodynamic therapy can avoid amputation of a toe or even the entire foot, taking into account such factors as whether there are ulcers and, if so, where, whether there is infection or ischemia, and so on. Overall, I think I can say that we’re able to avoid amputation in 65% of cases,” Tardivo said.
In a study published in 2014 in the journal Photodiagnosis and Photodynamic Therapy, researchers compared the results of photodynamic therapy for 18 patients who suffered from osteomyelitis with those for a control group of 16 patients treated solely with antibiotics.
All patients in the control group had at least one toe amputated. Only one patient in the phototherapy group required amputation.
“On ethical grounds, I felt unable to refrain from treating patients who might benefit from photodynamic therapy according to the algorithm we developed. So, in forming the control group, we chose 16 cases from the previous year who had the same diagnosis as the group to be treated but had already reached a clinical endpoint,” Tardivo said.
X-ray exams showed that phototherapy apparently promoted bone tissue regeneration in one of the patients, but the causal mechanism of the improvement still needs to be investigated, according to the researchers.
Baptista and Tardivo now plan to perform a multicentric trial to obtain stronger evidence in favor of the use of photodynamic therapy to treat diabetic foot so that it can cease to be considered experimental and become part of routine clinical practice.
“If the results are uniform across the different participating centers, I believe we’ll have sufficient evidence. It’s an effective, low-cost method,” Tardivo said.
Since 2013, Baptista and his group have conducted their research under the aegis of the Center for Research on Redox Processes in Biomedicine (Redoxoma), one of FAPESP’s Research, Innovation and Dissemination Centers (RIDCs).
Their latest findings were presented on February 5 during the first meeting of Redoxoma’s researchers with the international advisory committee responsible for assessment of the RIDCs.
“At this meeting, all the RIDCs’ ongoing research projects and goals were presented together for the first time. That’s very positive because it reinforces our team spirit,” said Ohara Augusto, a professor at IQ-USP and Redoxoma’s principal investigator.
Advisory committee member Rafael Radi, a professor at the University of the Republic’s Medical School in Uruguay, said that the progress made by the research group was “very good in every dimension.”
“The researchers in this group are outstanding and work very well as a team,” he told Agência FAPESP. “Moreover, the subjects they’re researching are highly relevant topics in biomedicine and biotechnology. The students are engaged in very good projects. Some of them devote all their time to the education and innovation components, and this has produced solid progress in these areas.”
The only negative point expressed by Radi was a need for better animal experiment facilities.
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