Treating Cancer as an Infectious Disease
Worldwide, some 20 percent of all human cancers can be traced to prior infection with a virus. Both hepatitis B virus and hepatitis C virus, for example, can lead to liver cancer, while cervical cancer sometimes follows human papillomavirus infection. Now, NIAID grantees at the Albert Einstein College of Medicine of Yeshiva University in Bronx, NY, have used an experimental therapy to attack and destroy virus-infected cells before they turn cancerous. In effect, the researchers have shown that it may be possible to treat some cancers like an infectious disease by aiming key weapons of the immune system, antibodies, against them.
The technique used by Arturo Casadevall, M.D., Ph.D., and Ekaterina Dadachova, Ph.D., and their colleagues is called radioimmunotherapy (RIT), which involves tailor-made antibodies bound to radioisotopes. RIT capitalizes on the ability of antibodies to home in on antigens, molecules that signal the immune system to the presence of infectious or other foreign agent. Once an antibody attaches to an antigen, the “radio” part of RIT kicks in as the radioactive isotope destroys the diseased cell.
Aiming RIT at a New Target
RIT already is used in the clinic to treat a kind of non-viral cancer called lymphoma. Drs. Casadevall and Dadachova have previously used the technique in the lab to treat mice with fungal or bacterial infections. In those studies, RIT has been directed at antigens that are on the surface of infected cells and are thus easily accessible to antibodies. But because the viral antigens associated with cancers typically stay inside infected cells, up to now, scientists had assumed that antibodies could not reach them.
The Einstein scientists hypothesized that rapidly growing tumor cells might outgrow their blood supply, resulting in dead tumor cells—and viral antigens spilled amongst the living cancer cells. “We hoped that by injecting antibodies hitched to isotopes into the blood, that they’d be carried deep into the tumor mass and would latch onto these now-exposed antigens,” said Dr. Casadevall. “The blast of radiation emitted by the radioisotope would then destroy the live tumor cells nearby.”
Impressive Initial Results
The scientists tested their theory on mice that had developed cancerous tumors after being infected with either human papillomavirus or hepatitis B virus. When RIT directed at viral antigens was applied to mice with liver tumors, the treatment slowed the tumors’ growth, the researchers found. In mice with cervical cancer tumors, RIT not only halted the tumor growth, it also caused the tumors to shrink. Significantly, notes Dr. Dadachova, the radioactive effects of the treatment were confined entirely to the tumor masses, leaving the surrounding healthy tissue undamaged.
Reference
Wang, X. G. et al. Treating cancer as an infectious disease—viral antigens as novel targets for treatment and potential prevention of tumors of viral etiology. PLoS ONE 2(10): e1114. DOI:10.1371/journal.pone.0001114 (2007).
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