title: Iterative design of emetine-based prodrug targeting fibroblast activation protein (FAP) and dipeptidyl peptidase IV DPPIV using a tandem enzymatic activation strategy.
abstract: BACKGROUND
  There is an urgent need to develop new agents for treating metastatic prostate cancer to overcome multiple drug resistance to the current standard targeted cancer therapy. Emetine is a highly cytotoxic natural product protein synthesis inhibitor, which is toxic to all cell types. Its cytotoxicity can be blocked by derivatizing its N-2' position. Thus emetine can be selectively delivered to cancer cells in the region of metastatic cancer as a prodrug that will be activated by an enzyme selectively overexpressed within the metastatic tumor microenvironment. In this work, we convert emetine to a prodrug activatable by the fibroblast activation protein (FAP), a serine protease overexpressed by the carcinoma associated fibroblasts.
  
  
  METHODS
  By using an iterative structure-activity relationship strategy, several peptidyl emetine prodrug analogs (1-11) were synthesized by chemical derivatization of emetine at its N-2' position and tested for in-vitro activation by FAP. The lead prodrug 11 is made up of a DPPIV activatable prodrug precursor 10 (Ala-Pro-PABC-Emetine) coupled to FAP substrate (Ala-Ser-Gly-Pro-Ala-Gly-Pro). Activation assays of the prodrugs were performed in purified FAP, DPPIV, FBS, and human serum and were analyzed by LCMS. In vitro cytotoxicity assays of these prodrugs are carried out in prostate (LNCaP, PC3) and breast (MCF7 and MDA-MB-231) cancer cell lines. The prodrugs are also tested in normal immortalized human prostatic epithelial cell line (PrEC).
  
  
  RESULTS
  The lead FAP activated emetine prodrug 11 is activated to emetine in tandem by FAP and DPPIV in about 70% conversion within 24 hr. In prostate and breast cancer cell lines treated with prodrug 11, it is found to be equipotent with emetine in the presence of FAP and DPPIV. However, in the PrEC cell line grown in serum free media, prodrug 11 is more than 200-fold less cytotoxic than emetine in the absence of FAP and DPPIV.
  
  
  CONCLUSIONS
  This FAP activated prodrug of cytotoxic agent emetine further shows the crucial role of the N-2' position of emetine in controlling its cytotoxicity. Significantly reduced toxicity observed in the PrEC cell line in the absence of FAP and DPPIV shows that prodrug 11 could be systemically delivered to regions of metastatic prostate cancer or other solid tumor for activation by cancer selective enzymes within the cancer microenvironment, such as FAP that is overexpressed by the carcinoma-associated fibroblasts. The two-step tandem enzymatic activation of prodrug 11 by FAP and DPPIV is a strategy for overcoming steric hindrance.
authors.affiliation: Department of Oncology, Chemical Therapeutic Program, Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Johns Hopkins University School of Medicine, Baltimore, Maryland.
authors.forename: Emmanuel S
authors.initials: ES
authors.lastname: Akinboye
authors.affiliation: Department of Oncology, Chemical Therapeutic Program, Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Johns Hopkins University School of Medicine, Baltimore, Maryland.
authors.forename: W Nathaniel
authors.initials: WN
authors.lastname: Brennen
authors.affiliation: Department of Oncology, Chemical Therapeutic Program, Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Johns Hopkins University School of Medicine, Baltimore, Maryland.
authors.forename: D Marc
authors.initials: DM
authors.lastname: Rosen
authors.affiliation: Department of Chemistry, Howard University, District of Columbia, Washington.
authors.forename: Oladapo
authors.initials: O
authors.lastname: Bakare
authors.affiliation: Department of Oncology, Chemical Therapeutic Program, Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Johns Hopkins University School of Medicine, Baltimore, Maryland.
authors.forename: Samuel R
authors.initials: SR
authors.lastname: Denmeade
mesh_terms: D000970:Antineoplastic Agents / Q000627:therapeutic use*; D045744:Cell Line, Tumor; D018819:Dipeptidyl Peptidase 4 / Q000378:metabolism*; D015195:Drug Design; D004640:Emetine / Q000627:therapeutic use*; D010450:Endopeptidases; D018093:Gelatinases / Q000378:metabolism*; D006801:Humans; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D011355:Prodrugs / Q000627:therapeutic use*; D011471:Prostatic Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D012697:Serine Endopeptidases / Q000378:metabolism*; D013329:Structure-Activity Relationship; D000099167:Fibroblast Activation Protein Alpha
chemical_list: D000970:Antineoplastic Agents; D018819:Dipeptidyl Peptidase 4; D004640:Emetine; D010450:Endopeptidases; D018093:Gelatinases; D008565:Membrane Proteins; D011355:Prodrugs; D012697:Serine Endopeptidases; D000099167:Fibroblast Activation Protein Alpha
keywords: dipeptidyl peptidase IV (DPPIV); emetine; fibroblast activation protein (FAP); linker; para-aminobenzyloxycarbonyl (PABC); prodrug
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