We have seen the ability of androgen deprivation to increase the efficacy of high dose IMRT in controlling prostate cancer (see this commentary). A new study from Johns Hopkins turns conventional logic on its head by demonstrating that sequential androgen deprivation and androgen repletion may be optimal for enhancing the therapeutic efficacy of radiation in prostate cancer… at least in mice.
I don’t often comment on lab studies because what works in the mouse world often does not work when tested in humans. Johns Hopkins has been a leader in exploring the possibility of androgen sequencing, and is currently conducting a trial of “bipolar androgen therapy (BAT)” in men undergoing lifelong ADT for advanced cancer (see this commentary).
Haffner et al. discovered that androgens, like testosterone or DHT, can activate an enzyme (TOP2B) that induces double-strand breaks (breaks on both sides of the double helix) in the DNA of prostate cancer cells that express the TMPRSS2:ERG fusion gene. This gene has been implicated in prostate cancer development and has been detected in about half the cases of prostate cancer. Coincidentally, double-strand breaking is exactly how radiation kills cancer cells. They hypothesized that after androgen deprivation is used to kill off those cancer cells susceptible to it, that restoring androgens combined with ionizing radiation might increase the therapeutic potential over radiation alone. Hedayati et al. report that this is exactly what happened in mice.
This may or may not eventually translate into protocol changes in radiation therapy, but at the very least it gives us a healthy appreciation for the very complex biochemical machinery involved in cancer genesis and therapeutics.
Written February 4. 2016