title: Pharmacokinetics, biodistribution, and antitumor efficacy of a human glandular kallikrein 2 (hK2)-activated thapsigargin prodrug.
abstract: BACKGROUND
  Prostate cancer cells secrete unique proteases such as prostate-specific antigen (PSA) and human glandular kallikrein 2 (hK2) that represent targets for the activation of prodrugs as systemic treatment of metastatic prostate cancer. Previously, a combinatorial peptide library was screened to identify a highly active peptide substrate for hK2. The peptide was coupled to an analog of the potent cytotoxin thapsigargin, L12ADT, to generate an hK2-activated prodrug that was efficiently hydrolyzed by purified hK2, stable to hydrolysis in human and mouse plasma in vitro and selectively toxic to hK2 producing prostate cancer cells in vitro.
  
  
  METHODS
  In the current study, toxicology, pharmacokinetics, prodrug biodistribution, and antitumor efficacy studies were performed to evaluate the hK2-activated prodrug in vivo.
  
  
  RESULTS
  The single intravenous maximally tolerated dose of prodrug was 6 mg/kg (i.e., 3.67 micromole/kg) which produced peak serum concentration of approximately 36 microM and had a half-life of approximately 40 min. In addition, over a 24 hr period <0.5% of free L12ADT analog was observed in plasma. The prodrug demonstrated significant antitumor effect in vivo while it was being administered, but prolonged intravenous administration was not possible due to local toxicity to tail veins. Subcutaneous administration of equimolar doses produced lower plasma AUC compared to intravenous dosing but equivalent intratumoral levels of prodrug following multiple doses.
  
  
  CONCLUSIONS
  The hK2-activated prodrug was stable in vivo. The prodrug, however, was rapidly cleared and difficult to administer over prolonged dosing interval. Additional studies are underway to assess antitumor efficacy with prolonged administration of higher subcutaneous doses of prodrug. Second-generation hK2-activated thapsigargin prodrugs with increased half-lives and improved formulations are also under development.
authors.affiliation: The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21231, USA.
authors.forename: Samuel
authors.initials: S
authors.lastname: Janssen
authors.forename: D Marc
authors.initials: DM
authors.lastname: Rosen
authors.forename: Rebecca M
authors.initials: RM
authors.lastname: Ricklis
authors.forename: Craig A
authors.initials: CA
authors.lastname: Dionne
authors.forename: Hans
authors.initials: H
authors.lastname: Lilja
authors.forename: Soeren B
authors.initials: SB
authors.lastname: Christensen
authors.forename: John T
authors.initials: JT
authors.lastname: Isaacs
authors.forename: Samuel R
authors.initials: SR
authors.lastname: Denmeade
mesh_terms: D000818:Animals; D019540:Area Under Curve; D006801:Humans; D007262:Infusions, Intravenous; D008297:Male; D020714:Maximum Tolerated Dose; D051379:Mice; D008807:Mice, Inbred BALB C; D011355:Prodrugs / Q000493:pharmacokinetics* / Q000494:pharmacology*; D011471:Prostatic Neoplasms / Q000473:pathology*; D019284:Thapsigargin / Q000031:analogs & derivatives / Q000493:pharmacokinetics* / Q000494:pharmacology*; D020840:Tissue Kallikreins / Q000493:pharmacokinetics* / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
chemical_list: D011355:Prodrugs; D019284:Thapsigargin; D020840:Tissue Kallikreins