Summary
Breakdown of the extracellular matrix is crucial for cancer invasion and metastasis.
It is accomplished by the concerted action of several proteases, including the serine
protease plasmin and a number of matrix metalloproteases. The activity of each of
these proteases is regulated by an array of activators, inhibitors and cellular receptors.
Thus, the generation of plasmin involves the pro-enzyme plasminogen, the urokinase
type plasminogen activator uPA and its pro-enzyme pro-uPA, the uPA inhibitor PAI-1,
the cell surface uPA receptor uPAR, and the plasmin inhibitor α2-antiplasmin. Furthermore, the regulation of extracellular proteolysis in cancer involves
a complex interplay between cancer cells and non-malignant stromal cells in the expression
of the molecular components involved. For some types of cancer, this cellular interplay
mimics that observed in the tissue of origin during non-neoplastic tissue remodelling
processes. We propose that cancer invasion can be considered as uncontrolled tissue
remodelling. Inhibition of extracellular proteases is an attractive approach to cancer
therapy. Because proteases have many different functions in the normal organism, efficient
inhibition will have toxic side effects. In cancer invasion, like in normal tissue
remodelling processes, there appears to be a functional overlap between different
extracellular proteases. This redundancy means that combinations of protease inhibitors
must be used. Such combination therapy, however, is also likely to increase toxicity.
Therefore for each type of cancer, a combination of protease inhibitors that is optimised
with respect to both maximal therapeutic effect and minimal toxic side effects need
to be identified.
Keywords
Cancer invasion - plasminogen activation - matrix degradation - tissue remodelling
- cancer therapy