Type II 5α-reductase （IC50: 4.2 nM)

In PC-3 cells, finasteride (10 μM; 6–24 h) stimulates the expression of the proteins Nrf2 and HO-1[2]. Finasteride inhibits P. crustosum's ability to convert [3H]testosterone (T) to [3H]dihydrotestosterone (DHT)[1].

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A number of naturally-occurring or synthetic chemicals have been reported to exhibit prostate chemopreventive effects. Synthetic 5α-reductase (5-AR) inhibitors, e.g. finasteride and durasteride, gained special interests as possible prostate chemopreventive agents. Indeed, two large-scale epidemiological studies have demonstrated that finasteride or durasteride significantly reduced the incidence of prostate cancer formation in men. However, these studies have raised an unexpected concern; finasteride and durasteride increased the occurrence of aggressive prostate tumor formation. In the present study, researchers have observed that treatment of finasteride did not affect the growth of androgen-refractory PC-3 prostate cancer cells. Finasteride also failed to induce apoptosis or affect the expression of proto-oncogenes in PC-3 cells. Interestingly, it was found that treatment of finasteride induced the expression of Nrf2 and HO-1 proteins in PC-3 cells. In particular, basal level of Nrf2 protein was higher in androgen-refractory prostate cancer cells, e.g. DU-145 and PC-3 cells, compared with androgen-responsive prostate cancer cells, e.g. LNCaP cells. Also, treatment of finasteride resulted in a selective induction of Nrf2 protein in DU-145 and PC-3 cells, but not in LNCaP cells. In view of the fact that upregulation of Nrf2-mediated phase II cytoprotective enzymes contribute to attenuating tumor promotion in normal cells, but, on the other hand, confers a selective advantage for cancer cells to proliferate and survive against chemical carcinogenesis and other forms of toxicity, researchers propose that finasteride-mediated induction of Nrf2 protein might be responsible, at least in part, for an increased risk of high-grade prostate tumor formation in men.[2]

In dogs with BPH, finasteride (0.1–0.5 mg/kg; po once daily for 16 weeks) lowers prostatic size without negatively impacting the quality of the semen or the level of serum testosterone[3].

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Finasteride significantly decreased prostatic diameter (mean percentage decrease, 20%), prostatic volume (mean percentage decrease, 43%), and serum DHT concentration (mean percentage decrease, 58%). Finasteride decreased semen volume but did not adversely effect semen quality or serum testosterone concentration. No adverse effects were reported by owners of dogs in the study. Conclusions and clinical relevance: Results suggest that finasteride can be used to reduce prostatic size in dogs with BPH without adversely affecting semen quality or serum testosterone concentration. [3]

In order to develop the treatment for 5α-DHT associated diseases such as BPH and PCa, a simple test system has been required to screen for 5α-SR inhibitors. Because of its simplicity and high sensitivity, the present method is also applicable to the simple test system for screening 5α-SR inhibitors. After confirming that finasteride showed no effect on the enzyme cycling of 5α-DHT, we performed the inhibition experiments by finasteride of rat liver and prostate microsomal 5α-SR. From the results, the concentrations of finasteride required to inhibit 5α-SR activity by 50% (IC50) were estimated to be 21 nM for liver 5α-SR and 20 nM for prostate 5α-SR, respectively. The inhibitions of rat 5α-SR1 and 5α-SR2 by fenasteride have been investigated by using COS cells transiently expressing 5α-SR1 and 5α-SR2. The IC50 values of finasteride to 5α-SR1 and 5α-SR2 were evaluated to be and 5.2 nM respectively in whole cell assay, whereas those were 13 and 1.0 nM respectively in the assay with crude enzyme preparations.21 The IC50 value of finasteride to rat 5α-SR in prostate microsomes was also evaluated to be 11 nM by Häusler et al., 13 nM by Igarashi et al. and 237 nM by Mitamura et al. The reported IC50 values of fenasteride to rat 5α-SR in prostate homogenate were in the range from 6.8 to 147 nM. The reason for such a difference may be related to differences in experimental conditions of enzyme activity evaluation such as pH, testosterone concentration and enzyme preparation[4].

Western Blot Analysis[2]
Cell Types: PC-3, DU-145, and LNCaP cells
Tested Concentrations: 10 μM
Incubation Duration: 6, 12, 24 h
Experimental Results: Increased the expression of HO-1 protein in a time-dependent manner in PC-3 cells. Induced the expression of Nrf2 protein in DU-145 and PC-3 cells, but not in LNCaP cells.

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Trypan-blue exclusion assay [2]
PC-3 cells were seeded in 6-well plates at a density of 1×105 per well. Following an exposure to finasteride for 24 h and 48 h, cells were collected by trypsinization, followed by centrifugation at 1,000 g for 5 min. Collected cells were rinsed with ice-cold phosphate-buffer saline (PBS) solution (pH 7.4) 3 times and mixed with 100 μl of PBS together with an equal amount of 0.4% trypan blue reagent. After counting viable cell numbers that excluded trypan blue reagent by hemacytometer, total number of viable cells was calculated by doubling a dilution factor (×2).

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Western blot analysis [2]
For preparation of whole cell lysates, cells were harvested in whole cell lysis buffer [10 mmol/L Tris-HCl (pH 7.9), 250 mmol/L NaCl, 30 mmol/L sodium bisphosphate, 50 mmol/L sodium fluoride, 0.5% Triton X-100, 10% glycerol, 1×proteinase inhibitor mixture,] for 30 min on ice. Lysates were then collected by centrifugation at 14,800 g for 30 min. Protein concentrations were determined by the BCA protein assay kit. Aliquots of supernatant, containing 30 mg proteins were boiled in 1× SDS sample loading buffer for 2 min and resolved using 12% SDS-PAGE. Proteins in SDS-polyacrylamide gel were transferred to polyvinylidene difluoride (PVDF) membrane. The membrane was blocked with 5% fat-free milk in PBS-Tween 20 (PBST, 0.1% Tween 20) at room temperature for 2 h. The membrane was then probed with primary antibodies (1:1,000) in PBS overnight at 4℃. Blots were rinsed with PBST (PBS with 0.1% Tween-20) three times and then incubated with 1:5,000 dilution of horseradish peroxidase–conjugated second antibody at room temperature for 1 h. The blots were washed in PBST buffer for 5 min thee times and the transferred protein was visualized, using the enhanced chemiiluminescence (ECL).

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Measurement of dual luciferase activity [2]
U2OS cells were plated in six-well plates and allowed to grow around 70% confluency. 0.1 mg COX-2-, MMP2- and NF-kB-promoter-driven firefly luciferase constructs were cotransfected with 0.1 μg Renilla luciferase plasmid, using lipofectamine reagent. After transfection, cells were treated with DMSO or finasteride for additional 48 h. Cells were then collected and the dual luciferase activity was measured by the GLOMAX Multi-detection system. The measured firefly luciferase activity was normalized against the measured Renilla luciferase activity and the resulting value was expressed as a fold induction over the control. Values are expressed as mean ± SD of experiments and statistical analysis was performed, using Student t-test with n=6.

Animal/Disease Models: Male dogs with spontaneous BPH (2.7-11 years old ; 10.3-49 kg)[3]
Doses: 0.1-0.5 mg/kg
Route of Administration: Po one time/day for 16 weeks
Experimental Results: diminished prostatic diameter (20%), prostatic volume (43%), and serum DHT concentration (58%) . diminished semen volume but did not adversely effect on semen quality or serum testosterone concentration. No adverse effects on dogs.

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Objective: To determine the effect of the 5alpha-reductase inhibitor finasteride on prostatic diameter and volume, semen quality, and serum dihydrotestosterone (DHT) and testosterone concentrations in dogs with spontaneous benign prostatic hypertrophy (BPH).
Design: Double-blind placebo-controlled trial.
Animals: 9 dogs with BPH.
Procedure: Five dogs were treated with finasteride for 16 weeks (0.1 to 0.5 mg/kg [0.05 to 0.23 mg/lb] of body weight, PO, q 24 h); the other 4 received a placebo. Prostatic diameter, measured radiographically, prostatic volume, measured ultrasonographically, semen quality, and serum DHT and testosterone concentrations were evaluated before and during treatment. After receiving the placebo for 16 weeks, the 4 control dogs were treated with finasteride for 16 weeks, and evaluations were repeated.[3]

Absorption, Distribution and Excretion
Finasteride is well absorbed following oral administration and displays a slow accumulation phase after multiple dosing.[lablel] In healthy male subjects receiving oral finasteride, the mean oral bioavailability was 65% for 1 mg finasteride and 63% for 5 mg finasteride, and the values ranged from 26 to 170% for 1 mg dose and from 34 to 108% for 5 mg dose, respectively. It is reported that food intake does not affect the oral bioavailability of the drug. The peak plasma concentrations (Cmax) averaged 37 ng/mL (range, 27-49 ng/mL) and was reached 1-2 hours post administration. The AUC(0-24 hr) was 53 ngxhr/mL (range, 20-154 ngxhr/mL). The plasma concentrations and AUC are reported to be higher in elderly male patients aged 70 years or older.
In healthy subjects, about 32-46% of total oral dose of finasteride was excreted in the urine in the form of metabolites while about 51-64% of the dose was excreted in the feces. In patients with renal impairment, the extent of urinary excretion of finasteride is expected to be decreased while the fecal excretion is increased.
The volume of distribution is 76 L at steady state, ranging from 44 to 96 L. Finasteride has been shown to cross the blood brain barrier but does not appear to distribute preferentially to the CSF. It is not known whether finasteride is excreted in human milk.
In healthy young subjects (n=15), the mean plasma clearance of finasteride was 165 mL/min with the range between 70 and 279 mL/min.

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Metabolism / Metabolites
Finasteride undergoes extensive hepatic metabolism predominantly mediated by the cytochrome P450 3A4 (CYP3A4) enzyme to form the t-butyl side chain monohydroxylated and monocarboxylic acid metabolites. Theses metabolites retain less than 20% of the pharmacological activity of the parent compound.
Finasteride has known human metabolites that include N-(1-Hydroxy-2-methylpropan-2-yl)-9a,11a-dimethyl-7-oxo-1,2,3,3a,3b,4,5,5a,6,9b,10,11-dodecahydroindeno[5,4-f]quinoline-1-carboxamide.
Drug is extensively metabolized, primarily in the liver via CYP3A4. Two metabolites have been identified with дЉ_20% of the activity of finasteride.
Route of Elimination: Following an oral dose of 14C-finasteride in man (n = 6), a mean of 39% (range, 32 to 46%) of the dose was excreted in the urine in the form of metabolites; 57% (range, 51 to 64%) was excreted in the feces. Urinary excretion of metabolites was decreased in patients with renal impairment. This decrease was associated with an increase in fecal excretion of metabolites.
Half Life: 4.5 hours (range 3.3-13.4 hours)

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Biological Half-Life
In healthy young subjects receiving finasteride, the mean elimination half-life in plasma was 6 hours ranging from 3 to 16 hours. In elderly patients over the age of 70 years, the half-life is prolonged to 8 hours.

Toxicity Summary
The mechanism of action of Finasteride is based on its preferential inhibition of Type II 5a-reductase through the formation of a stable complex with the enzyme. Inhibition of Type II 5a-reductase blocks the peripheral conversion of testosterone to DHT, resulting in significant decreases in serum and tissue DHT concentrations, minimal to moderate increase in serum testosterone concentrations, and substantial increases in prostatic testosterone concetrations. As DHT appears to be the principal androgen responsible for stimulation of prostatic growth, a decrease in DHT concentrations will result in a decrease in prostatic volume (approximately 20-30% after 6-24 months of continued therapy). In men with androgenic alopecia, the mechanism of action has not been fully determined, but finasteride has shown to decrease scalp DHT concentration to the levels found in hairy scalp, reduce serum DHT, increase hair regrowth, and slow hair loss.

[1]. Steroid 5alpha-reductase inhibitors. Mini Rev Med Chem. 2003 May;3(3):225-37.

[2]. Finasteride Increases the Expression of Hemoxygenase-1 (HO-1) and NF-E2-Related Factor-2 (Nrf2) Proteins in PC-3 Cells: Implication of Finasteride-Mediated High-Grade Prostate Tumor Occurrence. Biomol Ther (Seoul). 2013 Jan;21(1):49-53.

[3]. Effects of finasteride on size of the prostate gland and semen quality in dogs with benign prostatic hypertrophy. J Am Vet Med Assoc. 2001 Apr 15;218(8):1275-80.

Therapeutic Uses
Enzyme Inhibitors
Treatment of benign prostatic hypertrophy
Antiandrogen therapy appears to produce a 30 to 40% decrease in the volume of the hyperplastic prostate after 3 to 6 months of therapy. Longer treatment may result in further prostatic regression, although this remains to be seen. Biopsy studies suggest that epithelial regression occurs to a much more significant degree than does stromal regression, but this finding may simply reflect the relatively longer turnover of the stromal cell population. The significant placebo effect of oral medication in patients with benign prostatic hyperplasia makes interpretation of clinical symptomatology and uro-flow data difficult. Analysis of symptom improvement is further complicated by the relatively slow improvement of patients on antiandrogen therapy, in contrast to surgery, in which relief is immediate. In addition to limited stromal involution and inadequate treatment duration, other biologic factors may limit the clinical efficacy of antiandrogen therapy. Most importantly, prostatic involution may not necessarily decrease urethral resistance. In addition, obstruction induced detrusor dysfunction may persist after relief of outflow obstruction in some patients, as it does after surgery. Incomplete antiandrogen action of the compounds, as well as compliance issues, may likewise limit efficacy. Although there are no data to suggest that the 5 alpha-reductase inhibitor finasteride will be more effective than other antiandrogen compounds in the treatment of benign prostatic hyperplasia, preliminary studies suggest that it has less toxicity. If long-term studies validate a modest but significant clinical response rate and preservation of sexual function, then finasteride therapy may well be acceptable to a subgroup of men presenting with the symptoms of benign prostatic hyperplasia.

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Pharmacodynamics
Finasteride is an antiandrogenic compound that works by suppressing the production of serum and intraprostatic dihydrotestosterone (DHT) in men via inhibiting the enzyme responsible for the biosynthesis of DHT. The maximum effect of a rapid reduction in serum DHT concentration is expected to be observed 8 hours following administration of the first dose. In a single man receiving a single oral dose of 5 mg finasteride for up to 4 years, there was a reduction in the serum DHT concentrations by approximately 70% and the median circulating level of testosterone increased by approximately 10-20% within the physiologic range. In a double-blind, placebo-controlled study, finasteride reduced intraprostatic DHT level by 91.4% but finasteride is not expected to decrease the DHT levels to castrate levels since circulating testosterone is also converted to DHT by the type 1 isoenzyme expressed in other tissues. It is expected that DHT levels return to normal within 14 days upon discontinuation of the drug. In a study of male patients with benign prostatic hyperplasia prior to prostatectomy, the treatment with finasteride resulted in an approximate 80% lower DHT content was measured in prostatic tissue removed at surgery compared to placebo. While finasteride reduces the size of the prostate gland by 20%, this may not correlate well with improvement in symptoms. The effects of finasteride are reported to be more pronounced in male patients with enlarged prostates (>25 mL) who are at the greatest risk of disease progression. In phase III clinical studies, oral administration of finasteride in male patients with male pattern hair loss promoted hair growth and prevented further hair loss by 66% and 83% of the subjects, respectively, which lasted during two years' treatment. The incidences of these effects in treatment groups were significantly higher than that of the group receiving a placebo. Following finasteride administration, the levels of DHT in the scalp skin was shown to be reduced by more than 60%, indicating that the DHT found in scalp is derived from both local DHT production and circulating DHT. The effect of finasteride on scalp DHT is likely seen because of its effect on both local follicular DHT levels as well as serum DHT levels.. There is evidence from early clinical observations and controlled studies that finasteride may reduce bleeding of prostatic origin.

C23H36N2O2

372.54

372.277

C, 74.15; H, 9.74; N, 7.52; O, 8.59

98319-26-7

Finasteride acetate;222989-99-3;Finasteride-d9;1131342-85-2

57363

White to off-white solid powder

1.1±0.1 g/cm3

576.6±50.0 °C at 760 mmHg

253 °C

177.4±30.3 °C

0.0±1.6 mmHg at 25°C

1.524

3.24

2

2

2

27

678

7

O=C([C@@]1([H])C([H])([H])C([H])([H])[C@@]2([H])[C@]3([H])C([H])([H])C([H])([H])[C@]4([H])[C@@](C([H])=C([H])C(N4[H])=O)(C([H])([H])[H])[C@@]3([H])C([H])([H])C([H])([H])[C@@]21C([H])([H])[H])N([H])C(C([H])([H])[H])(C([H])([H])[H])C([H])([H])[H]

DBEPLOCGEIEOCV-WSBQPABSSA-N

InChI=1S/C23H36N2O2/c1-21(2,3)25-20(27)17-8-7-15-14-6-9-18-23(5,13-11-19(26)24-18)16(14)10-12-22(15,17)4/h11,13-18H,6-10,12H2,1-5H3,(H,24,26)(H,25,27)/t14-,15-,16-,17+,18+,22-,23+/m0/s1

(4aR,4bS,6aS,7S,9aS,9bS,11aR)-N-(tert-butyl)-4a,6a-dimethyl-2-oxo-2,4a,4b,5,6,6a,7,8,9,9a,9b,10,11,11a-tetradecahydro-1H-indeno[5,4-f]quinoline-7-carboxamide

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Solubility in Formulation 1: ≥ 2.5 mg/mL (6.71 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.5 mg/mL (6.71 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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Solubility in Formulation 3: 2 mg/mL (5.37 mM) in 50% PEG300 50% Saline (add these co-solvents sequentially from left to right, and one by one), suspension solution; with ultrasonication.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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 (Please use freshly prepared in vivo formulations for optimal results.)