Effects of a new steroidal aromatase inhibitor, TZA-2237, and/or chlormadinone acetate on hormone-induced and spontaneous canine benign prostatic hyperplasia.

OBJECTIVE: It has been known for many years that human benign prostatic hyperplasia (BPH) is composed predominantly of hyperplastic stromal cells rather than epithelial cells. In the present study the effects of a new steroidal aromatase inhibitor on hormone-induced and spontaneous canine BPH were investigated.
METHODS: (1) Effects of TZA-2237 on hormone-induced canine BPH. Ten castrated beagles were administered testosterone and androstenedione 6 days/week for 8 months, and divided randomly into three groups after 2 months of treatment as follows. Group I served as controls, Group II was given 0.5 and Group III was given 2.5 mg/kg/day TZA-2237 5 days/week for 6 months. (2) Effects of TZA-2237 on spontaneous canine BPH. Twenty aged beagles with BPH were divided into five groups, Group IV was untreated, Group V was treated with 1 and Group VI with 5mg/kg/day TZA-2237 5 days/week for 31 weeks. Group VII was treated with 5mg/kg/day Atamestane and Group VIII was treated with 0.3 mg/kg/day chlormadinone acetate (CMA) 5 days/week. (3) Effects of TZA-2237 combined with CMA on spontaneous canine BPH. Three aged beagles with BPH were treated with 1mg/kg/day TZA-2237 and 0.03 mg/kg/day CMA 5 days/week for 20 weeks (Group IX) and a further three aged beagles with BPH were treated with 0.3 mg/kg/day CMA alone 5 days/week (Group X).
RESULTS: Hormone-induced prostatic growth was significantly suppressed in group III compared with that in other groups. In Group III, the intraprostatic aromatase activity, estradiol level and androgen receptor content decreased significantly in comparison with the values in Group I. The prostatic weights in Groups V, VI and VII increased significantly in comparison with the weight in Group IV. Serum LH and testosterone levels in Groups V, VI, and VII increased significantly in comparison with the level in Group IV. The prostatic weight in Group IX was decreased only slightly, but the smooth muscle component was decreased significantly.
CONCLUSIONS: TZA-2237 is a new, unique and effective aromatase inhibitor that causes inhibition of both epithelial and stromal compartments in hormone-induced canine BPH. Dual inhibition of androgen and estrogen resulted in inhibition of smooth muscle growth, and should prove effective as a new method of treatment given the atrophic effects on not only the epithelium but also the stroma in human BPH.