Antileukemic Activity and Mechanism of Drug Resistance to the Marine Salinispora tropica Proteasome Inhibitor Salinosporamide A (Marizomib)

• Published in: Molecular pharmacology 2014-07, Vol.86 (1), p.12-19
• Main Authors: Niewerth, Denise, Jansen, Gerrit, Riethoff, Lesley F.V., van Meerloo, Johan, Kale, Andrew J., Moore, Bradley S., Assaraf, Yehuda G., Anderl, Janet L., Zweegman, Sonja, Kaspers, Gertjan J.L., Cloos, Jacqueline
• Format: Article
• Language: English
• Subjects: Actinobacteria - metabolism; Boronic Acids - pharmacology; Bortezomib; Catalysis - drug effects; Cell Line, Tumor; Drug Resistance, Neoplasm - drug effects; Drug Resistance, Neoplasm - genetics; Humans; Lactones - pharmacology; Leukemia - drug therapy; Leukemia - genetics; Leukemia - metabolism; Mutation - drug effects; Mutation - genetics; Proteasome Endopeptidase Complex - genetics; Proteasome Endopeptidase Complex - metabolism; Proteasome Inhibitors - pharmacology; Pyrazines - pharmacology; Pyrroles - pharmacology; Up-Regulation - drug effects; Up-Regulation - genetics
• ISSN: 0026-895X; 1521-0111
• DOI: 10.1124/mol.114.092114

Salinosporamide A (NPI-0052, marizomib) is a naturally occurring proteasome inhibitor derived from the marine actinobacterium Salinispora tropica, and represents a promising clinical agent in the treatment of hematologic malignancies. Recently, these actinobacteria were shown to harbor self-resistance properties to salinosporamide A by expressing redundant catalytically active mutants of the 20S proteasome β-subunit, reminiscent of PSMB5 mutations identified in cancer cells with acquired resistance to the founding proteasome inhibitor bortezomib (BTZ). Here, we assessed the growth inhibitory potential of salinosporamide A in human acute lymphocytic leukemia CCRF-CEM cells, and its 10-fold (CEM/BTZ7) and 123-fold (CEM/BTZ200) bortezomib-resistant sublines harboring PSMB5 mutations. Parental cells displayed sensitivity to salinosporamide A (IC50 = 5.1 nM), whereas their bortezomib-resistant sublines were 9- and 17-fold cross-resistant to salinosporamide A, respectively. Notably, combination experiments of salinosporamide A and bortezomib showed synergistic activity in CEM/BTZ200 cells. CEM cells gradually exposed to 20 nM salinosporamide A (CEM/S20) displayed stable 5-fold acquired resistance to salinosporamide A and were 3-fold cross-resistant to bortezomib. Consistent with the acquisition of a PSMB5 point mutation (M45V) in CEM/S20 cells, salinosporamide A displayed a markedly impaired capacity to inhibit β5-associated catalytic activity. Last, compared with parental CEM cells, CEM/S20 cells exhibited up to 2.5-fold upregulation of constitutive proteasome subunits, while retaining unaltered immunoproteasome subunit expression. In conclusion, salinosporamide A displayed potent antileukemic activity against bortezomib-resistant leukemia cells. β-Subunit point mutations as a common feature of acquired resistance to salinosporamide A and bortezomib in hematologic cells and S. tropica suggest an evolutionarily conserved mechanism of resistance to proteasome inhibitors.