Amino acid containing thapsigargin analogues deplete androgen receptor protein via synthesis inhibition and induce the death of prostate cancer cells.

Abstract

There are quantitative and/or qualitative mechanisms allowing androgen receptor (AR) growth signaling in androgen ablation refractory prostate cancer cells. Regardless of the mechanism, agents that deplete AR protein expression prevent such AR growth signaling. Thapsigargin (TG) is a highly cell-penetrant sequiterpene-lactone that once inside cells inhibits (IC(50), ∼ 10 nmol/L) critically important housekeeping SERCA 2b calcium pumps in the endoplasmic reticulum. Using a series of five genetically diverse androgen ablation refractory human prostate cancer lines (LNCaP, LAPC-4, VCaP, MDA-PCa-2b, and CWR22Rv1), TG inhibition of SERCA pumps consistently results in depletion of the endoplasmic reticulum Ca(+2) coupled with μmol/L elevation in the intracellular free Ca(+2) initiating a molecular cascade that: (a) inhibits Cap-dependent AR protein synthesis resulting in 90% depletion of AR protein by 24 hours of TG exposure, (b) arrests the cells in G(0), and (c) induces their apoptotic death. Unfortunately, due to its highly lipophilic nature, TG is not deliverable as a systemic agent without host toxicity. Therefore, TG analogues containing amino acids were developed, which retain ability to deplete AR protein and induce cell death and which can be covalently linked to peptide carriers producing water soluble prodrugs for systemic delivery. Specific amino acid sequences are used to restrict the liberation of cytotoxic amino acid containing TG analogues from the peptide prodrug by prostate-specific proteases, such as prostate-specific antigen and prostate-specific membrane antigen, or cancer-specific proteases, such as fibroblast activation protein, so that toxicity of these prodrugs is selectively targeted to metastatic sites of prostate cancer. Based on these results, these prodrugs are undergoing clinical development.

• Authors: Donald J Vander Griend, Lizamma Antony, Susan L Dalrymple, Yi Xu, S Brogger Christensen, Samuel R Denmeade, John T Isaacs
• Journal: Molecular cancer therapeutics (Mol Cancer Ther) Vol. 8 Issue 5 Pg. 1340-9 (May 2009) ISSN: 1538-8514 [Electronic] United States
• PMID: 19417145 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Chemical References

• Adaptor Proteins, Signal Transducing
• Cell Cycle Proteins
• DNA-Binding Proteins
• EIF4EBP1 protein, human
• ELF4 protein, human
• Phosphoproteins
• Receptors, Androgen
• Transcription Factors
• Thapsigargin
• Calcium

Topics

• Adaptor Proteins, Signal Transducing (metabolism)
• Animals
• Calcium (metabolism)
• Cell Cycle Proteins
• Cell Death (drug effects)
• Cell Line, Tumor
• DNA-Binding Proteins (metabolism)
• Endoplasmic Reticulum (metabolism)
• Gene Expression Regulation, Neoplastic (drug effects)
• Humans
• Male
• Mice
• Mice, Nude
• Phosphoproteins (metabolism)
• Phosphorylation (drug effects)
• Prostatic Neoplasms (drug therapy, metabolism)
• Rabbits
• Receptors, Androgen (genetics, metabolism)
• Signal Transduction (drug effects)
• Thapsigargin (chemistry, pharmacology)
• Transcription Factors (metabolism)