CHICAGO--Although interferon-alfa 2b (Intron A) has been used for some time to treat malignant melanoma patients at high risk for relapse after surgery, little has been known about the way in which it works.
A study from Roswell Park Cancer Institute suggests a possible mechanism. The research, reported at the Society for Surgical Oncology cancer symposium, shows that interferon-alfa 2b activates STAT (signal transducer and activator of transcription) proteins in malignant melanoma cell lines and tumor specimens.
Using a gel electrophoresis assay, the researchers found that STAT activation was rapid in melanoma cell lines treated with interferon-alfa 2b, occurring within 30 seconds of administration of a radiolabeled DNA probe, said Roswell Park surgeon William Carson, MD.
Pretreatment with genistein, a tyrosine kinase inhibitor, completely blocked interferon's DNA-binding activity, he added, showing that tyrosine kinase activity is needed for signaling to occur.
Previously frozen melanoma specimens responded to interferon-alfa 2b with a gel shift on electrophoresis, signaling activation of STAT proteins. Fresh specimens also responded to interferon by generating DNA-binding activity.
Interferon-alfa 2b concentrations as low as 102 U/mL activated STAT 1 and STAT 2 proteins. A signaling maximum was achieved with a concentration of 105 U/mL, revealing a distinct dose- response curve for activation of these specific STAT proteins.
Pretreatment with interferon-gamma for 18 hours decreased by more than 1,000-fold the amount of interferon-alfa 2b needed to activate STAT proteins. The researchers believe interferon-gamma is able to enhance the subsequent response to interferon-alfa 2b by acting on the STAT chaperon molecule.
"Interferon-gamma pretreatment has been used with other cytokines without much rationale," he said. "The way it is probably working in this system is by up-regulating levels of the protein chaperon molecule that carries STAT proteins into the nucleus. There is a gene transcription response to interferon-gamma, and protein levels come up within a few hours."