TY - JOUR
T1 - Anti-leukemic activity and mechanisms underlying resistance to the novel immunoproteasome inhibitor PR-924
AU - Niewerth, Denise
AU - Van Meerloo, Johan
AU - Jansen, Gerrit
AU - Assaraf, Yehuda G.
AU - Hendrickx, Tessa C.
AU - Kirk, Christopher J.
AU - Anderl, Janet L.
AU - Zweegman, Sonja
AU - Kaspers, Gertjan J.L.
AU - Cloos, Jacqueline
N1 - Funding Information:
This study was supported by research funding from the Netherlands Organization for Scientific Research (YGA), KiKa (Children cancer-free) (GJLK), and Fonds Stimulans (JC, GJ, SZ). PR-924 was provided by Onyx Pharmaceuticals, Inc. Specific β5, β5i, and β1i subunit activity probes were kindly provided by Millennium Pharmaceuticals Inc. We thank Tonia Buchholz and Peter Morello from Onyx Pharmaceuticals, Inc. for critical reading of the manuscript.
PY - 2014/5/1
Y1 - 2014/5/1
N2 - PR-924 is a novel prototypic immunoproteasome inhibitor bearing markedly enhanced specificity for the β5i immunoproteasome subunit, compared to the classical proteasome inhibitor bortezomib. Here, we assessed the growth inhibitory potential of PR-924 in three human hematologic malignancy cell lines (CCRF-CEM, THP1, and 8226) and their bortezomib-resistant sublines. Parental cells displayed equal sensitivity to PR-924 (IC50: 1.5-2.8 μM), whereas their bortezomib-resistant tumor lines displayed a 10-12 fold cross-resistance to PR-924. However, PR-924 cross-resistance factors for bortezomib-resistant sublines were markedly lower compared to the resistance factors to bortezomib. Proteasome inhibition experiments confirmed that PR-924 specifically inhibited β5i activity, even far below concentrations that exerted anti-proliferative activity. We further determined whether PR-924 activity might be compromised by acquisition of drug resistance phenomena. Indeed, CEM cells rendered stepwise resistant to 20 μM PR-924 (CEM/PR20) displayed 13-fold PR-924-resistance and 10-fold cross-resistance to bortezomib. CEM/PR20 cells were devoid of mutations in the PSMB8 gene (encoding β5i), but acquired Met45Ile mutation in the PSMB5 gene (encoding constitutive β5), consistent with β5 mutations observed in bortezomib-resistant cells. Furthermore, compared to parental CEM cells, CEM/PR20 cells exhibited 2.5-fold upregulation of constitutive proteasome subunit expression, whereas immunoproteasome subunit expression was 2-fold decreased. In conclusion, PR-924 displayed potent anti-leukemic activity including toward bortezomib-resistant leukemia cells. Despite the specificity of PR-924 to the β5i immunoproteasome subunit, its anti-leukemic effect required concentrations that blocked both β5 and β5i subunits. This is underscored by the emergence of mutations in PSMB5 rather than in PSMB8.
AB - PR-924 is a novel prototypic immunoproteasome inhibitor bearing markedly enhanced specificity for the β5i immunoproteasome subunit, compared to the classical proteasome inhibitor bortezomib. Here, we assessed the growth inhibitory potential of PR-924 in three human hematologic malignancy cell lines (CCRF-CEM, THP1, and 8226) and their bortezomib-resistant sublines. Parental cells displayed equal sensitivity to PR-924 (IC50: 1.5-2.8 μM), whereas their bortezomib-resistant tumor lines displayed a 10-12 fold cross-resistance to PR-924. However, PR-924 cross-resistance factors for bortezomib-resistant sublines were markedly lower compared to the resistance factors to bortezomib. Proteasome inhibition experiments confirmed that PR-924 specifically inhibited β5i activity, even far below concentrations that exerted anti-proliferative activity. We further determined whether PR-924 activity might be compromised by acquisition of drug resistance phenomena. Indeed, CEM cells rendered stepwise resistant to 20 μM PR-924 (CEM/PR20) displayed 13-fold PR-924-resistance and 10-fold cross-resistance to bortezomib. CEM/PR20 cells were devoid of mutations in the PSMB8 gene (encoding β5i), but acquired Met45Ile mutation in the PSMB5 gene (encoding constitutive β5), consistent with β5 mutations observed in bortezomib-resistant cells. Furthermore, compared to parental CEM cells, CEM/PR20 cells exhibited 2.5-fold upregulation of constitutive proteasome subunit expression, whereas immunoproteasome subunit expression was 2-fold decreased. In conclusion, PR-924 displayed potent anti-leukemic activity including toward bortezomib-resistant leukemia cells. Despite the specificity of PR-924 to the β5i immunoproteasome subunit, its anti-leukemic effect required concentrations that blocked both β5 and β5i subunits. This is underscored by the emergence of mutations in PSMB5 rather than in PSMB8.
KW - Immunoproteasome
KW - Leukemia
KW - PR-924
KW - Proteasome
KW - Proteasome inhibitor
UR - http://www.scopus.com/inward/record.url?scp=84897975846&partnerID=8YFLogxK
U2 - 10.1016/j.bcp.2014.02.005
DO - 10.1016/j.bcp.2014.02.005
M3 - Article
C2 - 24552657
AN - SCOPUS:84897975846
SN - 0006-2952
VL - 89
SP - 43
EP - 51
JO - Biochemical Pharmacology
JF - Biochemical Pharmacology
IS - 1
ER -