Abstract
It has been demonstrated previously that immune cell activation and proliferation were sensitive to the effects of naltrindole, a nonpeptidic δ-opioid receptor-selective antagonist; therefore, we hypothesized that human multiple myeloma (MM) would be a valuable model for studying potential antineoplastic properties of naltrindole. [3H]naltrindole exhibited saturable, low-affinity binding to intact human MM cells; however, the pharmacological profile of the binding site differed considerably from the properties of δ-, κ-, and μ-opioid receptors, and opioid receptor mRNA was not detected in MM cells by reverse transcriptase-polymerase chain reaction. Naltrindole inhibited the proliferation of cultured human U266 MM cells in a time- and dose-dependent manner with an EC50 of 16 μM. The naltrindole-induced inhibition of U266 cell proliferation was not blocked by a 10-fold molar excess of naltrexone, a nonselective opioid antagonist. Additive inhibition of MM cell proliferation was observed when using a combination of naltrindole with the histone deacetylase inhibitor sodium valproate, the proteasome inhibitor bortezomib, the glucocorticoid receptor agonist dexamethasone, and the HMG CoA reductase inhibitor simvastatin. Treatment of U266 cells with naltrindole significantly decreased the level of the active, phosphorylated form of the kinases, extracellular signal-regulated kinase and Akt, which may be related to its antiproliferative activity. The antiproliferative activity of naltrindole toward MM cells was maintained in cocultures of MM and bone marrow-derived stromal cells, mimicking the bone marrow microenvironment. In vivo, naltrindole significantly decreased tumor cell volumes in human MM cell xenografts in severe combined immunodeficient mice. We hypothesize that naltrindole inhibits the proliferation of MM cells through a nonopioid receptor-dependent mechanism.
Footnotes
This work was supported by the National Institutes of Health National Institute on Drug Abuse [Grant 09113]; the New Jersey Commission on Cancer Research; and the Foundation of the University of Medicine and Dentistry of New Jersey.
Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
ABBREVIATIONS:
- MM
- multiple myeloma
- ANOVA
- analysis of variance
- BNTX
- 7-benzylidenenaltrexone
- bp
- base pairs
- BTz
- bortezomib
- Dex
- dexamethasone
- DMEM
- Dulbecco's modified Eagle's medium
- DOR
- δ-opioid receptor
- DTNB
- 5,5′-dithiobis-2-nitrobenzoic acid
- DTT
- dithiothreitol
- ERK
- extracellular signal-regulated kinase
- FITC
- fluorescein isothiocyanate
- HDAC
- histone deacetylase
- HEK
- human embryonic kidney
- IL-6
- interleukin-6
- KOR
- κ-opioid receptor
- MAPK
- mitogen-activated protein kinase
- MG132
- N-(benzyloxycarbonyl)leucinylleucinylleucinal
- MOPS
- 4-morpholinepropanesulfonic acid
- MOR
- μ-opioid receptor
- NEM
- N-ethylmaleimide
- NF-κB
- nuclear factor-κB
- Nti
- naltrindole
- PBMC
- peripheral blood mononuclear cell
- PBS
- phosphate-buffered saline
- PCR
- polymerase chain reaction
- PI
- propidium iodide
- PS
- phosphatidylserine
- RBC
- red blood cell
- RT
- reverse transcriptase
- SCID
- severe combined immunodeficient
- Smvstn
- simvastatin
- SNC80
- 4-[(R)-[(2S,5R)-4-allyl-2,5-dimethylpiperazin-1-yl](3-methoxyphenyl)methyl]-N,N-diethylbenzamide
- VPA
- valproic acid.
- Received March 9, 2012.
- Accepted April 20, 2012.
- Copyright © 2012 by The American Society for Pharmacology and Experimental Therapeutics
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