GRK5 and the aggressive growth of prostate cancer tumors

An article published on line in the Journal of Urology last Friday suggests that an enzyme known as G-protein-coupled receptor kinase 5 or GRK5 may have an important role in the regulation of the growth of prostate cancer. The good news is that this finding may represent an important new opportunity to explore ways to slow or even stop the growth of prostate cancer (by selectively blockading the activity of this enzyme). The bad news is that so far evidence for this finding has been limited to cell cultures in Petri dishes and mouse models of prostate cancer.

We aren’t going to try to get into a lot of detail here. The paper by Kim et al. is very technical. Here is what is important from a patient’s point of view:

  • G-protein-coupled receptor molecules (GPCRs) are known to have significance in the development and progression of a number of cancers. 
  • When they are improperly activated (“expressed”), there is an increase in the likelihood of things like the initial spread of cancers, tumor growth, and metastasis.
  • The transition from hormone-sensitive to castration-resistant forms prostate cancer is known to be associated with higher levels of expression of GPCRs.
  • GRK5 seems to be ” a previously unknown critical regulator of prostate tumor growth.
  • Blockade of the activity of GRK5 in models of late stage prostate cancer using small “interfering” molecules of ribonucleic acid (siRNAs) appears to be possible.
  • Such blockade of GRK5 activity appears to significantly reduce the growth of aggressive forms of prostate cancer tumors (in laboratory and mouse models).

Clearly there is a lot more work that will need to be done:

  • We need to be sure that blockade of the GRK5 enzyme actually does significantly lower the risk for spread of prostate cancer in other mouse models
  • We will have to identify highly effective and potentially safe types of molecule that could be tested in humans
  • We must conduct initial tests of such molecules in man to see if they hold real clinical potential.

We do know that siRNA molecules can potentially be used as drugs. Several such molecules have been tested in clinical trials … but as yet no siRNA has actually been been proven safe and effective in Phase III clinical trials or submitted to the U.S. Food & Drug Administration for approval as a prescription medicine (that we are aware of). But then there may be other, more traditional ways to lower the level of activity of GRKs in men with prostate cancer.

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