nifuroxazide and Multiple-Myeloma

Cyclophilin A (Cyp A), a member of the peptidyl-prolyl isomerase (PPI) family, may function as a molecular signalling switch. Comparative proteomic studies have identified Cyp A as a potential downstream target of protein kinase B (Akt). This study confirmed that Cyp A is a downstream effector of the phosphatidylinositide 3-kinase (PI3K)/Akt signalling pathway. Cyp A was highly phosphorylated in response to interleukin-6 treatment, which was consistent with the accumulation of phosphorylated Akt, suggesting that Cyp A is a phosphorylation target of Akt and downstream effector of the PI3K/Akt pathway. Cyclosporine A (CsA), a PPI inhibitor, inhibited the growth of multiple myeloma (MM) U266 cells. Moreover, CsA treatment inhibited the activation of the signal transducer and activator of transcription 3 (STAT3) in MM U266 cells. Several Cyp A mutants were generated. Mutants with mutated AKT phosphorylation sites increased the G1 phase arrest in MM U266 cells. The other mutants that mimicked the phosphorylated state of Cyp A decreased the percentage of G1 phase. These results demonstrated that the states of phosphorylation of Cyp A by Akt can influence the progress of the cell cycle in MM U266 cells and that this effect is probably mediated through the Janus-activated kinase 2/STAT3 signalling pathway.

Topics: Amino Acid Sequence; Base Sequence; Cell Cycle; Cell Line, Tumor; Cell Proliferation; Cyclophilin A; Cyclosporine; DNA Mutational Analysis; Humans; Hydroxybenzoates; Molecular Sequence Data; Multiple Myeloma; Mutant Proteins; Nitrofurans; Phosphatidylinositol 3-Kinases; Phosphorylation; Proto-Oncogene Proteins c-akt; Signal Transduction; STAT3 Transcription Factor

Constitutive activation of the transcription factor STAT3 contributes to the pathogenesis of many cancers, including multiple myeloma (MM). Since STAT3 is dispensable in most normal tissue, targeted inhibition of STAT3 is an attractive therapy for patients with these cancers. To identify STAT3 inhibitors, we developed a transcriptionally based assay and screened a library of compounds known to be safe in humans. We found the drug nifuroxazide to be an effective inhibitor of STAT3 function. Nifuroxazide inhibits the constitutive phosphorylation of STAT3 in MM cells by reducing Jak kinase autophosphorylation, and leads to down-regulation of the STAT3 target gene Mcl-1. Nifuroxazide causes a decrease in viability of primary myeloma cells and myeloma cell lines containing STAT3 activation, but not normal peripheral blood mononuclear cells. Although bone marrow stromal cells provide survival signals to myeloma cells, nifuroxazide can overcome this survival advantage. Reflecting the interaction of STAT3 with other cellular pathways, nifuroxazide shows enhanced cytotoxicity when combined with either the histone deacetylase inhibitor depsipeptide or the MEK inhibitor UO126. Therefore, using a mechanistic-based screen, we identified the clinically relevant drug nifuroxazide as a potent inhibitor of STAT signaling that shows cytotoxicity against myeloma cells that depend on STAT3 for survival.

Topics: Butadienes; Cell Line, Tumor; Cell Survival; Depsipeptides; Humans; Hydroxybenzoates; Janus Kinases; Multiple Myeloma; Myeloid Cell Leukemia Sequence 1 Protein; Nitriles; Nitrofurans; Phosphorylation; Proto-Oncogene Proteins c-bcl-2; STAT3 Transcription Factor