According to the researchers, their findings also raise the possibility of preventing cancer by destroying virus-infected cells before they turn cancerous.
The research team used a technique called radioimmunotherapy, in which radioisotopes are piggybacked onto antibodies. Once these precision-made molecules are injected into the body, the antibodies home in on a specific protein target...and the radioisotope "warhead" destroys the cell to which the protein is attached.
In this research the targets were viral antigens: proteins expressed by virus-infected cells that can cause those cells to multiply out of control and become cancerous.
But while antigens on the surface of cells are susceptible to attack by antibodies, the viral antigens associated with cancers typically lurk inside infected cells, so researchers had assumed that antibodies couldn't reach them.
"We had a hunch that rapidly growing tumours can "outgrow" their blood supply, resulting in dead tumour cells that might spill their viral antigens amongst the living cancer cells," said Dr. Arturo Casadevall, Forchheimer Professor and Chair of Microbiology & Immunology at Einstein and co-senior author of the study.
"So we hoped that by injecting antibodies hitched to isotopes into the blood that they'd be carried deep into the tumour mass and would latch onto these now-exposed antigens. Then the blast of radiation emitted by the radioisotope would destroy the live tumour cells nearby," he added.
The research team tested their theory in mice. They attached the radioisotope rhenium-18 to monoclonal antibodies made against E6, a viral antigen expressed by virtually all cervical-cancer cells.
Similarly, they prepared radioimmunotherapy for liver cancer by attaching rhenium-18 to monoclonal antibodies against HBx, a viral antigen made by liver-cancer cells. Then, mice bearing human cervical-cancer tumours or human liver tumours were treated with the appropriate therapy.
The team found that for both types of cancer, the radioimmunotherapy resulted in significant slowing of tumour growth compared with tumours in untreated mice. For the cervical-cancer mice, the therapy not only stopped the growth of tumours but also caused them to regress.
"Radioimmunotherapy not only worked against these cancers, but in addition the radioactivity was confined entirely to the tumour masses, leaving healthy tissues undamaged," said Dr. Ekaterina Dadachova, Associate Professor of Nuclear Medicine and of Microbiology & Immunology at Einstein and the study's other senior co-author.
"Virus-associated cancers account for some 1.3 million cancer cases each year, so the need for new strategies in treating them is obvious and urgent.
Our study has shown in principle that radioimmunotherapy can help in treating cancers caused by virusesand, just as exciting, the approach also holds promise for cancer prevention.
In people chronically infected with hepatitis B or C, human papillomaviruses, or other viruses known to cause cancer, radioimmunotherapy could potentially eliminate virus-infected cells before they're able to transform into cancer cells," she added.
The findings are published in the October 31 issue of PloS One.