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Inhibition of deubiquitinase (DUB) activity is a promising strategy for cancer therapy. VLX1570 is an inhibitor of proteasome DUB activity currently in clinical trials for relapsed multiple myeloma. Here we show that VLX1570 binds to and inhibits the activity of ubiquitin-specific protease-14 (USP14) in vitro, with comparatively weaker inhibitory activity towards UCHL5 (ubiquitin-C-terminal hydrolase-5). Exposure of multiple myeloma cells to VLX1570 resulted in thermostabilization of USP14 at therapeutically relevant concentrations. Transient knockdown of USP14 or UCHL5 expression by electroporation of siRNA reduced the viability of multiple myeloma cells. Treatment of multiple myeloma cells with VLX1570 induced the accumulation of proteasome-bound high molecular weight polyubiquitin conjugates and an apoptotic response. Sensitivity to VLX1570 was moderately affected by altered drug uptake, but was unaffected by overexpression of BCL2-family proteins or inhibitors of caspase activity. Finally, treatment with VLX1570 was found to lead to extended survival in xenograft models of multiple myeloma. Our findings demonstrate promising antiproliferative activity of VLX1570 in multiple myeloma, primarily associated with inhibition of USP14 activity., Funding Agencies|Cancerfonden; Radiumhemmets forskningsfonder; Vetenskapsradet; Barncancerfonden

Inhibition of deubiquitinase (DUB) activity is a promising strategy for cancer therapy. VLX1570 is an inhibitor of proteasome DUB activity currently in clinical trials for relapsed multiple myeloma. Here we show that VLX1570 binds to and inhibits the activity of ubiquitin-specific protease-14 (USP14) in vitro, with comparatively weaker inhibitory activity towards UCHL5 (ubiquitin-C-terminal hydrolase-5). Exposure of multiple myeloma cells to VLX1570 resulted in thermostabilization of USP14 at therapeutically relevant concentrations. Transient knockdown of USP14 or UCHL5 expression by electroporation of siRNA reduced the viability of multiple myeloma cells. Treatment of multiple myeloma cells with VLX1570 induced the accumulation of proteasome-bound high molecular weight polyubiquitin conjugates and an apoptotic response. Sensitivity to VLX1570 was moderately affected by altered drug uptake, but was unaffected by overexpression of BCL2-family proteins or inhibitors of caspase activity. Finally, treatment with VLX1570 was found to lead to extended survival in xenograft models of multiple myeloma. Our findings demonstrate promising antiproliferative activity of VLX1570 in multiple myeloma, primarily associated with inhibition of USP14 activity., Funding Agencies|Cancerfonden; Radiumhemmets forskningsfonder; Vetenskapsradet; Barncancerfonden

Inhibition of deubiquitinase (DUB) activity is a promising strategy for cancer therapy. VLX1570 is an inhibitor of proteasome DUB activity currently in clinical trials for relapsed multiple myeloma. Here we show that VLX1570 binds to and inhibits the activity of ubiquitin-specific protease-14 (USP14) in vitro, with comparatively weaker inhibitory activity towards UCHL5 (ubiquitin-C-terminal hydrolase-5). Exposure of multiple myeloma cells to VLX1570 resulted in thermostabilization of USP14 at therapeutically relevant concentrations. Transient knockdown of USP14 or UCHL5 expression by electroporation of siRNA reduced the viability of multiple myeloma cells. Treatment of multiple myeloma cells with VLX1570 induced the accumulation of proteasome-bound high molecular weight polyubiquitin conjugates and an apoptotic response. Sensitivity to VLX1570 was moderately affected by altered drug uptake, but was unaffected by overexpression of BCL2-family proteins or inhibitors of caspase activity. Finally, treatment with VLX1570 was found to lead to extended survival in xenograft models of multiple myeloma. Our findings demonstrate promising antiproliferative activity of VLX1570 in multiple myeloma, primarily associated with inhibition of USP14 activity., Funding Agencies|Cancerfonden; Radiumhemmets forskningsfonder; Vetenskapsradet; Barncancerfonden

Inhibition of deubiquitinase (DUB) activity is a promising strategy for cancer therapy. VLX1570 is an inhibitor of proteasome DUB activity currently in clinical trials for relapsed multiple myeloma. Here we show that VLX1570 binds to and inhibits the activity of ubiquitin-specific protease-14 (USP14) in vitro, with comparatively weaker inhibitory activity towards UCHL5 (ubiquitin-C-terminal hydrolase-5). Exposure of multiple myeloma cells to VLX1570 resulted in thermostabilization of USP14 at therapeutically relevant concentrations. Transient knockdown of USP14 or UCHL5 expression by electroporation of siRNA reduced the viability of multiple myeloma cells. Treatment of multiple myeloma cells with VLX1570 induced the accumulation of proteasome-bound high molecular weight polyubiquitin conjugates and an apoptotic response. Sensitivity to VLX1570 was moderately affected by altered drug uptake, but was unaffected by overexpression of BCL2-family proteins or inhibitors of caspase activity. Finally, treatment with VLX1570 was found to lead to extended survival in xenograft models of multiple myeloma. Our findings demonstrate promising antiproliferative activity of VLX1570 in multiple myeloma, primarily associated with inhibition of USP14 activity., Funding Agencies|Cancerfonden; Radiumhemmets forskningsfonder; Vetenskapsradet; Barncancerfonden

Inhibition of deubiquitinase (DUB) activity is a promising strategy for cancer therapy. VLX1570 is an inhibitor of proteasome DUB activity currently in clinical trials for relapsed multiple myeloma. Here we show that VLX1570 binds to and inhibits the activity of ubiquitin-specific protease-14 (USP14) in vitro, with comparatively weaker inhibitory activity towards UCHL5 (ubiquitin-C-terminal hydrolase-5). Exposure of multiple myeloma cells to VLX1570 resulted in thermostabilization of USP14 at therapeutically relevant concentrations. Transient knockdown of USP14 or UCHL5 expression by electroporation of siRNA reduced the viability of multiple myeloma cells. Treatment of multiple myeloma cells with VLX1570 induced the accumulation of proteasome-bound high molecular weight polyubiquitin conjugates and an apoptotic response. Sensitivity to VLX1570 was moderately affected by altered drug uptake, but was unaffected by overexpression of BCL2-family proteins or inhibitors of caspase activity. Finally, treatment with VLX1570 was found to lead to extended survival in xenograft models of multiple myeloma. Our findings demonstrate promising antiproliferative activity of VLX1570 in multiple myeloma, primarily associated with inhibition of USP14 activity., Funding Agencies|Cancerfonden; Radiumhemmets forskningsfonder; Vetenskapsradet; Barncancerfonden

Although more traditionally associated with degradation and maintenance of protein homeostasis, the ubiquitin-proteasome system (UPS) has emerged as a critical component in the regulation of cancer cell growth and survival. The development of inhibitors that block the proteolytic activities of the proteasome have highlighted its suitability as a bona fide anti-cancer drug target. However, key determinants including the development of drug resistance and dose-limiting toxicity call for the identification of alternative components of the UPS for novel drug targeting. Recently the deubiquitinases (DUBS), a diverse family of enzymes that catalyze ubiquitin removal, have attracted significant interest as targets for the development of next generation UPS inhibitors. In particular, pharmacological inhibition of the proteasomal cysteine DUBs (i.e., USP14 and UCHL5) has been shown to be particularly cytotoxic to cancer cells and inhibit tumour growth in several in vivo models. In the current review we focus on the modes of action of proteasome DUB inhibitors and discus the potential of DUB inhibitors to circumvent acquired drug resistance and provide a therapeutic option for the treatment of cancer. (C) 2015 Elsevier Ltd. All rights reserved., Funding Agencies|Cancerfonden; Vetenskapsradet; Radiumhemmets forskningsfonder; Barncancerfonden; Mary Beves Foundation; Alex and Eva Wallstroms Foundation; Ake Olssons Foundation

Although more traditionally associated with degradation and maintenance of protein homeostasis, the ubiquitin-proteasome system (UPS) has emerged as a critical component in the regulation of cancer cell growth and survival. The development of inhibitors that block the proteolytic activities of the proteasome have highlighted its suitability as a bona fide anti-cancer drug target. However, key determinants including the development of drug resistance and dose-limiting toxicity call for the identification of alternative components of the UPS for novel drug targeting. Recently the deubiquitinases (DUBS), a diverse family of enzymes that catalyze ubiquitin removal, have attracted significant interest as targets for the development of next generation UPS inhibitors. In particular, pharmacological inhibition of the proteasomal cysteine DUBs (i.e., USP14 and UCHL5) has been shown to be particularly cytotoxic to cancer cells and inhibit tumour growth in several in vivo models. In the current review we focus on the modes of action of proteasome DUB inhibitors and discus the potential of DUB inhibitors to circumvent acquired drug resistance and provide a therapeutic option for the treatment of cancer. (C) 2015 Elsevier Ltd. All rights reserved., Funding Agencies|Cancerfonden; Vetenskapsradet; Radiumhemmets forskningsfonder; Barncancerfonden; Mary Beves Foundation; Alex and Eva Wallstroms Foundation; Ake Olssons Foundation

Although more traditionally associated with degradation and maintenance of protein homeostasis, the ubiquitin-proteasome system (UPS) has emerged as a critical component in the regulation of cancer cell growth and survival. The development of inhibitors that block the proteolytic activities of the proteasome have highlighted its suitability as a bona fide anti-cancer drug target. However, key determinants including the development of drug resistance and dose-limiting toxicity call for the identification of alternative components of the UPS for novel drug targeting. Recently the deubiquitinases (DUBS), a diverse family of enzymes that catalyze ubiquitin removal, have attracted significant interest as targets for the development of next generation UPS inhibitors. In particular, pharmacological inhibition of the proteasomal cysteine DUBs (i.e., USP14 and UCHL5) has been shown to be particularly cytotoxic to cancer cells and inhibit tumour growth in several in vivo models. In the current review we focus on the modes of action of proteasome DUB inhibitors and discus the potential of DUB inhibitors to circumvent acquired drug resistance and provide a therapeutic option for the treatment of cancer. (C) 2015 Elsevier Ltd. All rights reserved., Funding Agencies|Cancerfonden; Vetenskapsradet; Radiumhemmets forskningsfonder; Barncancerfonden; Mary Beves Foundation; Alex and Eva Wallstroms Foundation; Ake Olssons Foundation

Although more traditionally associated with degradation and maintenance of protein homeostasis, the ubiquitin-proteasome system (UPS) has emerged as a critical component in the regulation of cancer cell growth and survival. The development of inhibitors that block the proteolytic activities of the proteasome have highlighted its suitability as a bona fide anti-cancer drug target. However, key determinants including the development of drug resistance and dose-limiting toxicity call for the identification of alternative components of the UPS for novel drug targeting. Recently the deubiquitinases (DUBS), a diverse family of enzymes that catalyze ubiquitin removal, have attracted significant interest as targets for the development of next generation UPS inhibitors. In particular, pharmacological inhibition of the proteasomal cysteine DUBs (i.e., USP14 and UCHL5) has been shown to be particularly cytotoxic to cancer cells and inhibit tumour growth in several in vivo models. In the current review we focus on the modes of action of proteasome DUB inhibitors and discus the potential of DUB inhibitors to circumvent acquired drug resistance and provide a therapeutic option for the treatment of cancer. (C) 2015 Elsevier Ltd. All rights reserved., Funding Agencies|Cancerfonden; Vetenskapsradet; Radiumhemmets forskningsfonder; Barncancerfonden; Mary Beves Foundation; Alex and Eva Wallstroms Foundation; Ake Olssons Foundation

Although more traditionally associated with degradation and maintenance of protein homeostasis, the ubiquitin-proteasome system (UPS) has emerged as a critical component in the regulation of cancer cell growth and survival. The development of inhibitors that block the proteolytic activities of the proteasome have highlighted its suitability as a bona fide anti-cancer drug target. However, key determinants including the development of drug resistance and dose-limiting toxicity call for the identification of alternative components of the UPS for novel drug targeting. Recently the deubiquitinases (DUBS), a diverse family of enzymes that catalyze ubiquitin removal, have attracted significant interest as targets for the development of next generation UPS inhibitors. In particular, pharmacological inhibition of the proteasomal cysteine DUBs (i.e., USP14 and UCHL5) has been shown to be particularly cytotoxic to cancer cells and inhibit tumour growth in several in vivo models. In the current review we focus on the modes of action of proteasome DUB inhibitors and discus the potential of DUB inhibitors to circumvent acquired drug resistance and provide a therapeutic option for the treatment of cancer. (C) 2015 Elsevier Ltd. All rights reserved., Funding Agencies|Cancerfonden; Vetenskapsradet; Radiumhemmets forskningsfonder; Barncancerfonden; Mary Beves Foundation; Alex and Eva Wallstroms Foundation; Ake Olssons Foundation