Cancer Agent Uses Immune System Against Tumors

The new study suggests that when treating cancer, it is not just killing the cancer cells that is important. How they are destroyed may be just as significant in determining the effectiveness of a cancer treatment.

In the study, published online February 22, 2007, in the journal Blood, investigators from Rockefeller University (New York, NY, USA) evaluated the effects of the chemotherapy drug bortezomib in tissue culture containing multiple myeloma cells. Multiple myeloma is a cancer of immune cells in the bone marrow.

The researchers discovered that bortezomib's action on cancer cells may enable the immune system to recognize them, which could potentially help cancer patients' fight the disease more successfully. After exposure to bortezomib, the multiple myeloma cells died in such a way that a heat shock protein, called hsp90, migrated to their surfaces. A group of immune cells, called dendritic cells, were activated when they encountered hsp90 on the dying tumor cells. This caused the dendritic cells to ingest the dying cancer cells and deliver them to memory and killer T-cells. If replicated in humans, this progression could potentially lead to enhanced immunity.

"If you could directly target the drug to these cells, it may be sufficient enough to create a vaccine. The exposure of heat shock proteins on dying cells represents an immunogenic form of cell death,” Dr. Madhav Dhodapkar, head of the Laboratory of Tumor Immunology and Immunotherapy at Rockefeller University, said in a prepared statement.

The immunity-enhancing effects of bortezomib also seem to extend to other types of cancers. When the researchers treated lymphoma and breast cancer cells with bortezomib, the dying cells experienced the same increase in hsp90. What is unclear is whether these findings will extend to actual immune responses in humans. If it does, the researchers hope to directly target tumors in cancer patients.

"A simple experiment that hasn't been done yet is simply injecting bortezomib directly into tumors. By directly targeting the tumor, rather than injecting the drug intravenously, we may be able to take better advantage of bortezomib's distinct properties,” said Dr. Dhodapkar.


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