Targeting of BMI-1 with PTC-209 shows potent anti-myeloma activity and impairs the tumour microenvironment.

Abstract

BACKGROUND:

The polycomb complex protein BMI-1 (BMI-1) is a putative oncogene reported to be overexpressed in multiple myeloma (MM). Silencing of BMI-1 was shown to impair the growth and survival of MM cells. However, therapeutic agents specifically targeting BMI-1 were not available so far. Here, we investigated PTC-209, a novel small molecule inhibitor of BMI-1, for its activity in MM.

METHODS:

BMI-1 expression was analysed in human MM cell lines and primary MM cells by using publically available gene expression profiling (GEP) data. The anti-MM activity of PTC-209 was investigated by viability testing, cell cycle analysis, annexin V and 7-AAD staining, quantification of cleaved poly(ADP-ribose) polymerase (PARP), JC-1 as well as colony formation assays. Deregulation of central myeloma growth and survival genes was studied by quantitative PCR and flow cytometry, respectively. In addition, the impact of PTC-209 on in vitro osteoclast, osteoblast and tube formation was analysed.

RESULTS:

We confirmed overexpression of BMI-1 in MM patients by using publically available GEP datasets. Of note, BMI-1 expression was further increased at relapse which translated into significantly shorter overall survival in relapsed/refractory patients treated with bortezomib or dexamethasone. Treatment with PTC-209 significantly decreased viable cell numbers in human MM cell lines, induced a G1 cell cycle arrest, promoted apoptosis and demonstrated synergistic activity with pomalidomide and carfilzomib. The anti-MM activity of PTC-209 was accompanied by a significant decrease of cyclin D1 (CCND1) and v-myc avian myelocytomatosis viral oncogene homolog (MYC) expression as well as upregulation of cyclin-dependent kinase inhibitor 1A (CDKN1A) and cyclin-dependent kinase inhibitor 1B (CDKN1B). We also observed upregulation of NOXA (up to 3.6 ± 1.2-fold induction, P = 0.009) and subsequent downregulation of myeloid cell leukemia 1 (MCL-1) protein levels, which likely mediates the apoptotic effects of PTC-209. Importantly, the anti-MM activity was upheld in the presence of stromal support or myeloma growth factors insulin-like growth factor 1 (IGF-1) and interleukin 6 (IL-6). In the MM microenvironment, PTC-209 impaired tube formation, impaired osteoclast development and decreased osteoblast formation in a dose-dependent manner (P < 0.01 at 1 μM, respectively). The latter might be attributed to an induction of DKK1 and was reversed by concurrent anti-DKK1 antibody treatment.

CONCLUSIONS:

We confirmed overexpression of BMI-1 in MM highlighting its role as an attractive drug target and reveal therapeutic targeting of BMI-1 by PTC-209 as a promising novel therapeutic intervention for MM.

• Authors: Arnold Bolomsky, Karin Schlangen, Wolfgang Schreiner, Niklas Zojer, Heinz Ludwig
• Journal: Journal of hematology & oncology (J Hematol Oncol) Vol. 9 Pg. 17 (Mar 02 2016) ISSN: 1756-8722 [Electronic] England
• PMID: 26935956 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• BMI1 protein, human
• Heterocyclic Compounds, 2-Ring
• Oligopeptides
• PTC-209
• Thiazoles
• Thalidomide
• carfilzomib
• Dexamethasone
• pomalidomide
• Polycomb Repressive Complex 1

Topics

• Apoptosis (drug effects, genetics)
• Cell Line, Tumor
• Cell Proliferation (drug effects, genetics)
• Cell Survival (drug effects, genetics)
• Cells, Cultured
• Dexamethasone (pharmacology)
• Drug Synergism
• Gene Expression Profiling (methods)
• Gene Expression Regulation, Neoplastic (drug effects)
• Heterocyclic Compounds, 2-Ring (pharmacology, therapeutic use)
• Human Umbilical Vein Endothelial Cells (drug effects, metabolism, physiology)
• Humans
• Multiple Myeloma (drug therapy, genetics, metabolism)
• Neovascularization, Physiologic (drug effects, genetics)
• Oligopeptides (pharmacology)
• Osteogenesis (drug effects, genetics)
• Polycomb Repressive Complex 1 (antagonists & inhibitors, genetics, metabolism)
• Reverse Transcriptase Polymerase Chain Reaction
• Thalidomide (analogs & derivatives, pharmacology)
• Thiazoles (pharmacology, therapeutic use)
• Tumor Microenvironment (drug effects, genetics)