Skip to main content
NCBI home page
ACS Medicinal Chemistry Letters logoLink to ACS Medicinal Chemistry Letters
. 2024 Aug 5;15(9):1526–1532. doi: 10.1021/acsmedchemlett.4c00257

Synthesis and Optimization of Small Molecule Inhibitors of Prostate Specific Antigen

Jeffery A Erickson †, Ravikumar Jimmidi ‡, Prashanth Anamthathmakula §, Xuan Qin ‡, Jian Wang ‡, Leyi Gong ∥, Jaehyeon Park ∥, Gary Koolpe ∥, Caitlin Tan ∥, Martin M Matzuk ‡,⊥, Feng Li ‡,⊥, Srinivas Chamakuri ‡,*, Wipawee Winuthayanon †,*
PMCID: PMC11403753  PMID: 39291021

Abstract

graphic file with name ml4c00257_0009.jpg

Semen liquefaction is a postejaculation process that transforms semen from a gel-like (coagulated) form to a water-like consistency (liquefied). This process is primarily regulated by serine proteases from the prostate gland, most prominently, prostate-specific antigen (PSA; KLK3). Inhibiting PSA activity has the potential to impede liquefaction of human semen, presenting a promising target for nonhormonal contraception in the female reproductive tract. This study employed triazole B1 as a starting compound. Through systematic design, synthesis, and optimization, we identified compound 20 (CDD-3290) as a 216 nM inhibitor of PSA with better stability in media than triazole B1. Further, we also evaluated the selectivity profile of compound 20 (CDD-3290) by testing against closely related proteases and demonstrated excellent inhibition of PSA versus α-chymotrypsin and elastase and similar potency versus thrombin. Thus, compound 20 is an improved PSA inhibitor that can be tested for efficacy in vitro or in the female reproductive tract.

Keywords: kallikrein-related peptidase 3, KLK3, prostate-specific antigen, PSA, structure−activity relationship, small molecule inhibitors

The world population now has exceeded 8 billion, which has a huge impact on public health as well as the global environment.1 In North America, unintended pregnancy rates are higher than in any other developed countries.2 In the U.S., many unintended pregnancies occur among teenagers,3 a population that primarily relies on over-the-counter (OTC) methods.4 Nonhormonal OTCs, however, have two major drawbacks: (1) high failure rates5 (19% for condoms and 28% for spermicides) and (2) some spermicides damage the vaginal epithelial barrier,6 leading to an increased risk of viral infection in certain populations.6 Hormonal methods of contraception, including oral contraceptive pills (OCPs), dermal patches, injections, implants, or other devices, are highly effective and reversible. However, hormonal-based contraceptives are contraindicated for many women due to concerns over the long-term effects of hormones on patient health.7 For instance, estrogen-containing OCPs have been linked to an increased risk of venous thrombosis8 and breast cancer,9 among other pathologies.10 Moreover, there are only two choices for reversible male contraceptives: condoms and withdrawal. Therefore, there is an urgent need to develop new contraceptive options for both men and women to alleviate family planning issues.

Semen liquefaction is a postejaculation process that changes semen from a gel-like (coagulated) state to a water-like consistency (liquefied). This process is governed by serine proteases from the prostate gland, most prominently, prostate-specific antigen (PSA), encoded by the KLK3 (kallikrein-related peptidase 3) gene, which is a member of the tissue KLK family. Note that plasma KLK (encoded by KLKB1) is a liver-derived KLK, involved in the kallikrein–kinin system, and has different biological functions from tissue KLKs.11 In the ejaculate, PSA hydrolyzes its substrate, a gel-forming protein called semenogelin (SEMG), and liquefies semen within 30 min of ejaculation.12 If left unhydrolyzed, intact SEMG prevents sperm capacitation, causes the ejaculate to remain viscous, and inhibits sperm motility.13 The KLK family has a catalytic triad (His57, Asp102, and Ser195)14 that is highly conserved among mammalian species. Although KLK2,15 KLK5,16 and KLK1417 can hydrolyze SEMG in vitro, PSA (KLK3) is secreted at 0.5–3 g/L in seminal plasma,18 whereas other prostate-derived KLKs are secreted at significantly lower levels (μg/L to mg/L).19 In addition, PSA is expressed only in the male reproductive tract. In humans, the presence of a naturally occurring antibody against PSA in seminal plasma is associated with infertility and hyperviscous semen.20 In addition, men with low concentrations of seminal PSA have reduced sperm motility.21 Moreover, SNPs in the PSA gene are associated with infertility in men,22 and two of the SNPs that cause amino acid changes are only found in infertile men.22

Further support for this novel contraceptive method emanates from studies by Robert et al., showing that a pan serine protease inhibitor, benzenesulfonyl fluoride (AEBSF), attenuates PSA enzymatic activity.23 Although there is no known KLK3 ortholog in mice, there are multiple KLK1b subclasses expressed in mouse prostate glands.24 We demonstrated that AEBSF treatment (transvaginal) before mating reduced SEMG cleavage and severely disrupted sperm transport to the mouse oviduct.25 Moreover, AEBSF inhibited sperm motility in mice in vitro,26 and human semen.27 Female mice treated with AEBSF became severely subfertile, and the contraceptive effect of AEBSF was reversible.26 Our work verifies that AEBSF disrupts human semen liquefaction, resulting in hyperviscous semen.26 Importantly, we show that the direct inhibition of PSA activity using polyclonal PSA-inhibiting antibody (pAb αPSA) prevents the liquefaction process in human semen.26 Thus, direct inhibition of PSA using a pAb αPSA mechanistically blocks human semen liquefaction by preventing SEMG cleavage,27 and blocking semen liquefaction using a pan-inhibitor (AEBSF) to inhibit multiple serine proteases is on par with preventing semen liquefaction using a pAb αPSA.

PSA inhibitors have generally been developed as a therapeutic strategy for prostate cancer by targeting the enzymatic activity of PSA. Various inhibitors, such as peptide-based compounds, boronic acids,28 certain β-lactam derivatives,29 and triazole derivatives27 have been reported in the literature (Figure 1). However, many of these inhibitors have encountered challenges with selectivity. Koistinen et al. presented notable selective compounds for inhibiting PSA activity. Through their investigation, Koistinen et al. evaluated different triazole derivatives and identified triazole B1 (Table 1) as the most promising small molecule drug-like compound.27 The study revealed that the triazole inhibitor disrupted histidine and/or serine residues near the catalytic pocket of PSA, leading to competitive inhibition against the SEMG-binding site and hindering SEMG hydrolysis.27,28 In this study, compared to boronic acid peptide and β-lactam derivatives, triazole B1 was selected as a prime candidate for structure–activity relationship (SAR) analysis due to its drug-like properties that follow Lipinski’s rule of 5,30 such as a low molecular weight of 325.32, preferred CLogP value of 1.89 (Table 1), and a moderate selectivity for PSA inhibition. However, the potency of triazole B1 in the reported literature is 0.5 μM.27 Its modest potency, in addition to its low solubility in water, prevented us from using it as an effective tool molecule to study its contraceptive effect. This prompted us to identify more potent, selective, and drug-like PSA inhibitors to study the relationship between PSA inhibition and the semen liquefaction effect.

Figure 1.

Figure 1

Open in a new tab

Known inhibitors of prostate-specific antigen (PSA).

Table 1. Modification of the R1, X, Y, and R2 Groups and Its Inhibitory Activities against PSAa.

graphic file with name ml4c00257_0004.jpg

graphic file with name ml4c00257_0005.jpg

Open in a new tab
a

N/A= not active (concentrations tested ranged 1 pm, 100 nM, 1 μM, 10 μM, 100 μM, 500 μM); CLogP values generated from Chemdraw software.

With the objective of developing a potent and selective PSA inhibitor possessing favorable pharmacological attributes, we selected triazole B1 (Figure 1, Table 1, compound 1) as a starting point and embarked on detailed SAR studies. First, we validated the inhibitory activity of compound 1 on PSA and found that the Ki was 13.8 μM. This is likely due to differences in the PSA (recombinant protein vs purified from human semen) used in the assay. Initially, we delved into the significance of the amide linkage within the N1-triazole moiety. Upon replacing the amide linkage with an alkyl linkage with N1-3,4-dimethoxybenzyl substitution (compound 2, Table 1) and with simple hydrogen (compound 3), we observed a complete loss of activity, underscoring the pivotal role of the amide carbonyl in maintaining PSA inhibition. Subsequently, we maintained the amide linkage and examined the length between the amide carbonyl group and the aryl group by incorporating one methylene center (compound 4), which led to diminished potency (Ki = 308 μM). This highlighted the necessity of the aryl amide on the N1-triazole ring for PSA inhibition. Continuing our investigation, we analyzed the significance of the triazole ring (X = N). Substituting it with a pyrazole unit (X = CH) resulted in a 2-fold decrease in activity (compound 5, Ki = 33 μM).

Despite being 2-fold less potent, the pyrazole core allowed us to explore a number of variations of R1 groups to assess the significance of the nitrogen position in pyridine (Table 1). We shifted from the third (compound 5) to the fourth position in compound 6 (Ki = 104 μM) and from the third to the second position (with respect to the pyrazole position on pyridine) in compound 7 (Ki = 37 μM), leading to diminished activity. Furthermore, the introduction of an extra nitrogen into the ring, pyrimidine derivative, and pyrazine derivative (compounds 8 and 9, with Ki values of 68 and 51 μM, respectively) yielded similar outcomes. Complete replacement of the pyridine unit with a methoxyphenyl group (compound 10) resulted in a Ki value of 50 μM. Next, we introduced a 3-methoxy substitution onto the pyridine unit (compound 11), rendering the compound inactive, whereas a 2-methoxy pyridine analog (compound 12) remained as active as the parent triazole B1. Next, we validated the importance of the 2-amino functionality of the pyrazole ring (Y = NH2) in maintaining PSA inhibition. We introduced monomethyl substitution (compound 13) and dimethyl substitutions (compound 14), both of which were inactive in our experiments. However, these results underscore the crucial role of the amine functional group in engaging the PSA inhibition.

After thoroughly investigating the importance of the X, R1, and Y groups, we redirected our focus to the R2 modifications (Table 2). Trimethoxy substitution in compound 15 resulted in a less active compound with a Ki of 367 μM. Next, we introduced different heteroatom-containing bicyclic aryl substitutions, substituting benzoxazole-6-carboxamide (compound 16) resulted in a Ki of 4.79 μM, which is 3-fold better than triazole B1. Subsequently, we tested benzoxazole-6-carboxamide (compound 17) to validate the significance of the regio positions of oxygen and nitrogen in the benzoxazole ring. This resulted in a slight decrease in potency, indicating that the positions of the heteroatoms are indeed important. Furthermore, when we introduced a methyl substitution onto the second position of the benzoxazole (compounds 18 and 19), we observed a drop in potency. When we incorporated benzimidazole (compound 20, CDD-3290) instead of the benzoxazole unit, we fortuitously observed a 60-fold improvement in potency (Ki = 0.216 μM).

Table 2. Modification of the R2 Group and Its Inhibitory Activities against PSA.

graphic file with name ml4c00257_0006.jpg

graphic file with name ml4c00257_0007.jpg

Open in a new tab

After systematic evaluation of SAR based on compound 1, we focus on compound 20 to determine its selectivity toward other serine proteases such as α-chymotrypsin, elastase, and thrombin (Figure 2A). We found that compound 20 shows minimal inhibitory activity against elastase (Ki = 1.18 mM) and is 12.7-fold less potent against α-chymotrypsin (Ki = 2.74 μM) in comparison to that against PSA (Ki = 0.216 μM). Unfortunately, compound 20 still exhibited similar inhibition against thrombin (Ki = 0.411 μM), thus, warranting further structural studies to enhance our compound selectivity toward PSA. However, we observed that the modification of structure from compound 1 to 20 improved compound stability after the incubation in Dulbecco’s Modified Eagle Medium/Nutrient Mixture F-12 (DMEM/F12) media at 37 °C (Figure 2B) as indicated by the percentage of compound left at 8 h (∼47% for compound 20 compared to ∼4% of compound 1). Nevertheless, both compounds were almost completely degraded at 24 h, suggesting the need for further stability improvement in compound 20. We also evaluated the cellular uptake and solubility of compound 20. We observed low accumulation in HepG2 cells, with an intracellular concentration of 3.41 ± 1.76 nmol per 109 cells (n = 4) and 27 μM aqueous solubility.

Figure 2.

Figure 2

Open in a new tab

Improvement of specificity and stability of compound 20. (A) Biochemical enzyme assays for compound 20 on the inhibition of serine proteases including elastase, α-chymotrypsin, thrombin, and PSA. (B) Compound stability after incubation in DMEM/F12 media at 37 °C for 0, 8, or 24 h.

As the intended usage for PSA inhibitor as contraceptives would be intravaginal delivery, local cellular toxicity was evaluated in the human ectocervical (Ect1/E6E7) cell line using the MTT assay. Nonoxynol-9 (N9), an active pharmaceutical ingredient in the spermicide was used as a positive control as it was previously shown to have cytotoxicity in the female reproductive tract.31 We found that the exposure of compound 20 for either 1 or 3 h had no impact on Ect1/E6E7 cell viability, unlike N9 (Supporting Information, Figure S1).

To understand the mode of inhibition of compound 20 compared to other compounds with moderate potency (compounds 1, 5, and 10), weak potency (compound 15), or inactive compound (compound 13), we utilized AutoDock Vina (a Chimera Extension) to predict the location of ligands binding to PSA crystal structure.32 As AutoDock Vina outputs ten possible conformations with each analysis, the scoring and a general overview for all outputs of docked ligand location for compound 1 and compounds 5, 10, 13, 15, and 20 were illustrated in Figure 3, Supporting Information, Figure S2 and Table S1. Note that some conformations of compounds were docked outside of the binding pocket of PSA (Supporting Information, Figure S2).

Figure 3.

Figure 3

Open in a new tab

Compounds 1 and 20 docked to the PSA crystal structure. Compounds (A) 1 and (B) 20 docked to the PSA (2ZCH) crystal structure using AutoDock Vina. Both conformation versions are the top predictions (V1) (Table 3). (C) The superimposition of compounds 1 and 20 in the PSA binding pocket. Residues colored by heteroatom (blue = N; white = H; red = O) have at least one atom within 3.5 Å of the ligand, with some PSA residues labeled for reference and a mesh surface to depict the van der Waals (VDW) radii of the compound. Hydrogen bonds were assessed for all compounds and marked as bold dashed black lines when applicable. (D) Top prediction (V1) of compounds 5, 10, 13, and 15 to PSA using AutoDock Vina.

Further analysis focused on comparing the top version out of 10 for each compound docked to PSA. In agreement with previous studies, compound 1 docked near the S1 pocket, with one of the catalytic residues, His57, being close to its aryl carboxamide group (R2). R1 group of compound 1 occupied the S3 pocket, with residues such as Thr190 and Ser226 nearby (Figure 3A and Table 3). In comparison, the depth within the S2 pocket (Tyr94) and proximity to S1 (Glu218) were not observed for compound 20, resulting in the possible formation of a hydrogen bond with Val41 (Figure 3B and Table 3) Specifically, the R1 group of compound 20 was near S1 while its midpiece (aminopyrazole) rested above His57 and the R2 group points toward Val41 (Figure 3B). These differences in the conformations of compounds 1 and 20 could be observed clearly when both compounds were superimposed (Figure 3C).

Table 3. Residues near Compounds Docked to PSAa.

compound PSA residues with an atom within 3.5 Å total residues
1 H57; Y94; L95D; F95H; L95I; T190; C191; S192; W215; G216; E218; S226 12
5 H57; Y94; L95C; L95D; R95G; F95H; L95I; W215; G216; E218 10
10 H57; Y94; D102; L95C; L95D; S99; F95H; L95I; W215; G216; S192; G193; S195 13
13 V41; H57; F95H; L95I; F149; T190; C191; S192; G193; S195; T213; W215; G216; C220; S226 15
15 H57; Y94; L95C; L95D; R95G; F95H; L95I; S192; G193; S195; S214; W215; G216 13
20 V41; H57; F149; T190; C191; S192; G193; S195; S214; W215; G216; S226 12
Open in a new tab
a

Residues listed represent annotation from the top conformation of each compound. Residue numbering follows the description from the authors who crystallized PSA (2ZCH)32 to retain the chymotrypsinogen-based numbering system (i.e., His57; Asp 102; Ser195). Highlighted residues correspond to ones shared with compound 20 (CDD-3290).

Previous studies indicate that the kallikrein loop (spanning the 95A-95K residues) restricted the access of substrate to the active site of PSA.27,32,33 Therefore, compounds preferentially binding near or interacting with this loop could result in a lower inhibition potency. Proximity to the kallikrein loop of PSA (L95D, F95H, L95I) was lost when comparing all other compounds (1, 5, 10, 13, and 15) to compound 20 (Table 3). Specifically, residues contained within the kallikrein loop (near S2) were close to compounds 5 (L95C, R95G, F95H, L95I), 10 (L95C, L95D, F95H, L95I), 13 (F95H, L95I), and 15 (L95C, L95D, R95G, F95H, L95I) (Table 3). Notably, hydrogen bonds were detected with compound 10 at Tyr94 (Figure 3B) as well as compound 13 at Ser192 (Figure 3C). These interactions highlight the depth of compound 10 into the S2 pocket and compound 13’s abundant coverage over the general active site of PSA.

In summary, our research has focused on enhancing the efficacy of a known small molecule inhibitor through systematic structure–activity relationship (SAR) evaluations. Through this process, we have successfully identified compound 20 with improved pharmacological properties, potently targeting prostate-specific antigen (PSA) inhibition while maintaining off-target selectivity. As compound 20 also has inhibitory toward thrombin, its off-target impact in vivo is needed to be further evaluated. Our ongoing efforts in the laboratory are dedicated to further exploring and refining these promising PSA inhibitors and their potential applications as contraceptives. We anticipate sharing the results of these studies as our research progresses.

Acknowledgments

This work was supported in part by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), National Institutes of Health Award Numbers R01HD108198, X01HD104425, and X01HD106634 to W.W., R01HD108198-03S1 to J.A.E., R33HD099995 to F.L., and R01HD088412 to M.M.M. The work conducted by the SRI International team was supported by the contract awarded from the NICHD (Contract Number HHSN275201800007I, SRI Project Number: p25681).

Glossary

Abbreviations

AEBSF

benzenesulfonyl fluoride

DMEM/F12

Dulbecco’s modified Eagle medium/nutrient mixture F-12

KLK3

kallikrein-related peptidase 3

MTT

(3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide

PSA

prostate-specific antigen

SEMG

semenogelin

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsmedchemlett.4c00257.

  • Detailed experimental procedures and compound characterization data of all new compounds (PDF)

Author Contributions

# These authors with equally contributed (J.A.E. and R.J.).

The authors declare no competing financial interest.

Supplementary Material

ml4c00257_si_001.pdf (3.9MB, pdf)

References

  1. United_States_Cencus_Bureau . U.S. and World Population Clock 2024. https://www.census.gov/popclock/ (accessed 2019 September 8). [Google Scholar]; Jensen J. T. Why family planning matters. Reviews in Endocrine and Metabolic Disorders 2011, 12 (2), 55–62. 10.1007/s11154-011-9179-z. [DOI] [PubMed] [Google Scholar]
  2. Singh S.; Sedgh G.; Hussain R. Unintended pregnancy: worldwide levels, trends, and outcomes. Stud Fam Plann 2010, 41 (4), 241–250. 10.1111/j.1728-4465.2010.00250.x. [DOI] [PubMed] [Google Scholar]; Sedgh G.; Singh S.; Hussain R. Intended and unintended pregnancies worldwide in 2012 and recent trends. Stud Fam Plann 2014, 45 (3), 301–314. 10.1111/j.1728-4465.2014.00393.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Finer L. B.; Zolna M. R. Declines in Unintended Pregnancy in the United States, 2008–2011. N Engl J. Med. 2016, 374 (9), 843–852. 10.1056/NEJMsa1506575. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Abma J. C.; Martinez G. M. Sexual Activity and Contraceptive Use Among Teenagers in the United States, 2011–2015. National Health Statistics Reports 2017, (104), 1–22. [PubMed] [Google Scholar]; Bailey M. J.; Lindo J. M.. Access and Use of Contraception and Its Effects on Women’s Outcomes in the U.S.; National Bureau of Economic Research: Cambridge, MA, 2017. [Google Scholar]
  5. Trussell J. Contraceptive failure in the United States. Contraception 2011, 83 (5), 397–404. 10.1016/j.contraception.2011.01.021. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Roddy R. E.; Cordero M.; Cordero C.; Fortney J. A. A dosing study of nonoxynol-9 and genital irritation. Int. J. STD AIDS 1993, 4 (3), 165–170. 10.1177/095646249300400308. [DOI] [PubMed] [Google Scholar]; Niruthisard S.; Roddy R. E.; Chutivongse S. The effects of frequent nonoxynol-9 use on the vaginal and cervical mucosa. Sex Transm Dis 1991, 18 (3), 176–179. 10.1097/00007435-199107000-00010. [DOI] [PubMed] [Google Scholar]; Raymond E. G.; Lien Chen P.; Luoto J. Contraceptive effectiveness and safety of five nonoxynol-9 spermicides: a randomized trial. Obstetrics and gynecology 2004, 103 (3), 430–439. 10.1097/01.AOG.0000113620.18395.0b. [DOI] [PubMed] [Google Scholar]; Van Damme L.; Ramjee G.; Alary M.; Vuylsteke B.; Chandeying V.; Rees H.; Sirivongrangson P.; Tshibaka L. M.; Ettiegne-Traore V.; Uaheowitchai C.; et al. Effectiveness of COL-1492, a nonoxynol-9 vaginal gel, on HIV-1 transmission in female sex workers: a randomised controlled trial. Lancet 2002, 360 (9338), 971–977. 10.1016/S0140-6736(02)11079-8. [DOI] [PubMed] [Google Scholar]
  7. Peipert J. F.; Gutmann J. Oral contraceptive risk assessment: a survey of 247 educated women. Obstetrics and gynecology 1993, 82 (1), 112–117. [PubMed] [Google Scholar]
  8. Gronich N.; Lavi I.; Rennert G. Higher risk of venous thrombosis associated with drospirenone-containing oral contraceptives: a population-based cohort study. Canadian Medical Association Journal 2011, 183 (18), E1319 10.1503/cmaj.110463. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. La Vecchia C.; Altieri A.; Franceschi S.; Tavani A. Oral Contraceptives and Cancer. Drug Safety 2001, 24 (10), 741–754. 10.2165/00002018-200124100-00003. [DOI] [PubMed] [Google Scholar]
  10. Cushman M.; Kuller L. H.; Prentice R.; Rodabough R. J.; Psaty B. M.; Stafford R. S.; Sidney S.; Rosendaal F. R. Estrogen plus progestin and risk of venous thrombosis. Jama 2004, 292 (13), 1573–1580. 10.1001/jama.292.13.1573. [DOI] [PubMed] [Google Scholar]; Group, T. E. C. W. Hormones and cardiovascular health in women. Human Reproduction Update 2006, 12 ( (5), ), 483–497. 10.1093/humupd/dml028 (acccessed 9/9/2019). [DOI] [PubMed]
  11. Pathak M.; Wong S. S.; Dreveny I.; Emsley J. Structure of plasma and tissue kallikreins. Thromb Haemost 2013, 110 (9), 423–433. 10.1160/TH12-11-0840. [DOI] [PubMed] [Google Scholar]
  12. Lilja H.; Oldbring J.; Rannevik G.; Laurell C. B. Seminal vesicle-secreted proteins and their reactions during gelation and liquefaction of human semen. J. Clin Invest 1987, 80 (2), 281–285. 10.1172/JCI113070. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. de Lamirande E.; Yoshida K.; Yoshiike T. M.; Iwamoto T.; Gagnon C. Semenogelin, the main protein of semen coagulum, inhibits human sperm capacitation by interfering with the superoxide anion generated during this process. Journal of andrology 2001, 22 (4), 672–679. 10.1002/j.1939-4640.2001.tb02228.x. [DOI] [PubMed] [Google Scholar]
  14. Harvey T. J.; Hooper J. D.; Myers S. A.; Stephenson S. A.; Ashworth L. K.; Clements J. A. Tissue-specific expression patterns and fine mapping of the human kallikrein (KLK) locus on proximal 19q13.4. J. Biol. Chem. 2000, 275 (48), 37397–37406. 10.1074/jbc.M004525200. [DOI] [PubMed] [Google Scholar]
  15. Deperthes D.; Frenette G.; Brillard-Bourdet M.; Bourgeois L.; Gauthier F.; Tremblay R. R.; Dube J. Y. Potential involvement of kallikrein hK2 in the hydrolysis of the human seminal vesicle proteins after ejaculation. Journal of Andrology 1996, 17 (6), 659–665. 10.1002/j.1939-4640.1996.tb01850.x. [DOI] [PubMed] [Google Scholar]
  16. Michael I. P.; Pampalakis G.; Mikolajczyk S. D.; Malm J.; Sotiropoulou G.; Diamandis E. P. Human tissue kallikrein 5 is a member of a proteolytic cascade pathway involved in seminal clot liquefaction and potentially in prostate cancer progression. J. Biol. Chem. 2006, 281 (18), 12743–12750. 10.1074/jbc.M600326200. [DOI] [PubMed] [Google Scholar]
  17. Emami N.; Deperthes D.; Malm J.; Diamandis E. P. Major role of human KLK14 in seminal clot liquefaction. J. Biol. Chem. 2008, 283 (28), 19561–19569. 10.1074/jbc.M801194200. [DOI] [PubMed] [Google Scholar]
  18. Wang M. C.; Valenzuela L. A.; Murphy G. P.; Chu T. M. Purification of a human prostate specific antigen. Invest Urol 1979, 17 (2), 159–163. [PubMed] [Google Scholar]
  19. Veveris-Lowe T. L.; Kruger S. J.; Walsh T.; Gardiner R. A.; Clements J. A. Seminal fluid characterization for male fertility and prostate cancer: kallikrein-related serine proteases and whole proteome approaches. Semin Thromb Hemost 2007, 33 (1), 87–99. 10.1055/s-2006-958467. [DOI] [PubMed] [Google Scholar]
  20. Cuppett V. A.; Sikka S. C.; Naz R. K. Presence of PSA antibodies in seminal plasma of infertile men. Front. Biosci. (Elite Ed) 2017, 9, 258–265. 10.2741/e800. [DOI] [PubMed] [Google Scholar]
  21. Ahlgren G.; Rannevik G.; Lilja H. Impaired secretory function of the prostate in men with oligo-asthenozoospermia. Journal of andrology 1995, 16 (6), 491–498. 10.1002/j.1939-4640.1995.tb00569.x. [DOI] [PubMed] [Google Scholar]
  22. Gupta N.; Sudhakar D. V. S.; Gangwar P. K.; Sankhwar S. N.; Gupta N. J.; Chakraborty B.; Thangaraj K.; Gupta G.; Rajender S. Mutations in the prostate specific antigen (PSA/KLK3) correlate with male infertility. Sci. Rep. 2017, 7 (1), 11225. 10.1038/s41598-017-10866-1. [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. Robert M.; Gibbs B. F.; Jacobson E.; Gagnon C. Characterization of prostate-specific antigen proteolytic activity on its major physiological substrate, the sperm motility inhibitor precursor/semenogelin I. Biochemistry 1997, 36 (13), 3811–3819. 10.1021/bi9626158. [DOI] [PubMed] [Google Scholar]
  24. Lawrence M. G.; Lai J.; Clements J. A. Kallikreins on steroids: structure, function, and hormonal regulation of prostate-specific antigen and the extended kallikrein locus. Endocr Rev. 2010, 31 (4), 407–446. 10.1210/er.2009-0034. [DOI] [PubMed] [Google Scholar]
  25. Li S.; Garcia M.; Gewiss R. L.; Winuthayanon W. Crucial role of estrogen for the mammalian female in regulating semen coagulation and liquefaction in vivo. PLoS Genet 2017, 13 (4), e1006743 10.1371/journal.pgen.1006743. [DOI] [PMC free article] [PubMed] [Google Scholar]
  26. Barton B. E.; Rock J. K.; Willie A. M.; Harris E. A.; Finnerty R. M.; Herrera G. G.; Anamthathmakula P.; Winuthayanon W. Serine protease inhibitor disrupts sperm motility leading to reduced fertility in female mice. Biol. Reprod. 2020, 103, 400. 10.1093/biolre/ioaa049. [DOI] [PMC free article] [PubMed] [Google Scholar]
  27. Koistinen H.; Wohlfahrt G.; Mattsson J. M.; Wu P.; Lahdenpera J.; Stenman U. H. Novel small molecule inhibitors for prostate-specific antigen. Prostate 2008, 68 (11), 1143–1151. 10.1002/pros.20773. [DOI] [PubMed] [Google Scholar]
  28. LeBeau A. M.; Singh P.; Isaacs J. T.; Denmeade S. R. Potent and selective peptidyl boronic acid inhibitors of the serine protease prostate-specific antigen. Chem. Biol. 2008, 15 (7), 665–674. 10.1016/j.chembiol.2008.05.020. [DOI] [PMC free article] [PubMed] [Google Scholar]
  29. Singh P.; Williams S. A.; Shah M. H.; Lectka T.; Pritchard G. J.; Isaacs J. T.; Denmeade S. R. Mechanistic insights into the inhibition of prostate specific antigen by beta-lactam class compounds. Proteins 2008, 70 (4), 1416–1428. 10.1002/prot.21676. [DOI] [PubMed] [Google Scholar]
  30. Lipinski C. A.; Lombardo F.; Dominy B. W.; Feeney P. J. Experimental and computational approaches to estimate solubility and permeability in drug discovery and development settings. Adv. Drug Delivery Rev. 1997, 23 (1), 3–25. 10.1016/S0169-409X(96)00423-1. [DOI] [PubMed] [Google Scholar]
  31. Fichorova R. N.; Tucker L. D.; Anderson D. J. The Molecular Basis of Nonoxynol-9-Induced Vaginal Inflammation and Its Possible Relevance to Human Immunodeficiency Virus Type 1 Transmission. Journal of Infectious Diseases 2001, 184 (4), 418–428. 10.1086/322047. [DOI] [PubMed] [Google Scholar]
  32. Ménez R.; Michel S.; Muller B. H.; Bossus M.; Ducancel F.; Jolivet-Reynaud C.; Stura E. A. Crystal Structure of a Ternary Complex between Human Prostate-specific Antigen, Its Substrate Acyl Intermediate and an Activating Antibody. J. Mol. Biol. 2008, 376 (4), 1021–1033. 10.1016/j.jmb.2007.11.052. [DOI] [PubMed] [Google Scholar]
  33. LeBeau A. M.; Singh P.; Isaacs J. T.; Denmeade S. R. Prostate-Specific Antigen Is a “Chymotrypsin-like” Serine Protease with Unique P1 Substrate Specificity. Biochemistry 2009, 48 (15), 3490–3496. 10.1021/bi9001858. [DOI] [PMC free article] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

ml4c00257_si_001.pdf (3.9MB, pdf)

Articles from ACS Medicinal Chemistry Letters are provided here courtesy of American Chemical Society

RESOURCES