We found that the combined use of Q, a natural inhibitor of both catechol-O-methyltransferase (COMT) and multidrug resistance-associated proteins (MRPs), with GT significantly increased the bioavailability and cellular uptake of GTPs and decreased their methylation in vitro and in vivo, leading to a synergistically enhanced inhibition of xenograft prostate tumor growth in SCID mice [16–18]. This evidence concerns the gene COMT and prostate neoplasm.