In vivo monitoring of intranuclear p27kip1 protein expression in breast cancer cells during trastuzumab (Herceptin) therapy

[111In]-Anti-p27kip1-tat may be useful for monitoring changes in the expression of the intranuclear protein, p27kip1. Up-regulation of p27kip1 resulted in increased retention of [111In]-anti-p27kip1-tat in cells treated with trastuzumab. Modest, but statistically significantly higher, retention was also observed in tumours in mice treated with trastuzumab. Since responsiveness to trastuzumab correlated to up-regulation of p27kip1, it may be possible to use [111In]-anti-p27kip1-tat to guide treatment with Herceptin and other drugs which alter p27kip1 expression.