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
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."