mTORC1 inhibition and ECM-cell adhesion-independent drug resistance via PI3K-AKT and PI3K-RAS-MAPK feedback loops.

Abstract

Mammalian target of rapamycin (mTOR) serine threonine kinase is the enzyme that regulates cancer cell growth by altering nutrient supplies to cancer cells. The neuropeptide (proline-rich peptide 1 (PRP-1)), galarmin, produced by the brain neurosecretory cells is a mTOR kinase inhibitor with powerful 80% antiproliferative cytostatic effect in a high-grade chondosarcoma and other mesenchymal tumors. However, the negative feedback loop of phosphatidylinositol 3 kinase-Protein kinase B (PKB), PI3K-AKT and PI3K-rat sarcoma (RAS)-mitogen-activated protein kinase (MAPK) activation is well documented for mTOR inhibitors. This study explored the involvement of those loops in drug resistance after the treatment with mTOR complex 1 (mTORC1) inhibitor, PRP-1. Multidrug resistance assay (MDR) demonstrated that this cytokine did not inhibit permeability glycoprotein-mediated MDR in chondrosarcoma. Phospho-MAPK array in human chondrosarcoma cell line treated with galarmin (10 μg/ml,) showed a strong upregulation of phosphorylated glycogen synthase kinase 3β (GSK3β) via activation of PI3K-AKT and MAPK feedback loops. Such GSK3β inactivation leads to β-catenin accumulation that entails drug resistance. The ability of cells to metastasize is reflected in their capacity to adhere to extracellular matrix and endothelium. Laminin cell adhesion assay demonstrated that PRP-1 in the same concentrations that inhibit mTOR kinase inhibited JJ012 chondrosarcoma cell adhesion. The neuropeptide did not have any effect on the expression of total focal adhesion kinase and its phosphorylated form. Thus, it was not accompanied by total HAT downregulation and total HDAC upregulation. Combinatorial treatments of PRP-1 with MAPK and PI3K/AKT inhibitors most probably will lead to full cytotoxicity overcoming drug resistance.

• Authors: Karina Galoian, H T Temple, Armen Galoyan
• Journal: Tumour biology : the journal of the International Society for Oncodevelopmental Biology and Medicine (Tumour Biol) Vol. 33 Issue 3 Pg. 885-90 (Jun 2012) ISSN: 1423-0380 [Electronic] Netherlands
• PMID: 22246604 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Antimicrobial Cationic Peptides
• Multiprotein Complexes
• PRP-1 peptide
• Peptides
• Proteins
• Histone Acetyltransferases
• Mechanistic Target of Rapamycin Complex 1
• Proto-Oncogene Proteins c-akt
• TOR Serine-Threonine Kinases
• Mitogen-Activated Protein Kinases
• Histone Deacetylases
• ras Proteins

Topics

• Antimicrobial Cationic Peptides
• Cell Adhesion (drug effects)
• Cell Line, Tumor
• Drug Resistance, Neoplasm (drug effects)
• Extracellular Matrix (metabolism)
• Histone Acetyltransferases (metabolism)
• Histone Deacetylases (metabolism)
• Humans
• Mechanistic Target of Rapamycin Complex 1
• Mitogen-Activated Protein Kinases (metabolism)
• Multiprotein Complexes
• Peptides (pharmacology)
• Phosphatidylinositol 3-Kinases (metabolism)
• Proteins (antagonists & inhibitors)
• Proto-Oncogene Proteins c-akt (metabolism)
• Signal Transduction (drug effects)
• TOR Serine-Threonine Kinases
• ras Proteins (metabolism)