Synthesis and in vitro anticancer evaluation of novel flavonoid-based amide derivatives as regulators of the PI3K/AKT signal pathway for TNBC treatment.

Aberrant activation of the PI3K/AKT pathway is considered in many malignant tumors and plays a crucial role in mediating malignancy progression, metastasis, and chemoresistance. Consequently, development of PI3K/AKT pathway targeted drugs is currently an attractive research field for tumor treatment. In this study, twenty-six flavonoid-based amide derivatives were synthesized and evaluated for their antiproliferation effects against seven cancer cell lines, including MDA-MB-231, MCF-7, HCC1937, A549, HepG2, GTL-16 and HeLa. Among them, compound 7t possessed the best specific cytotoxicity against triple negative breast cancer MDA-MB-231 cells with an IC50 value of 1.76 ± 0.91 µM and also presented inhibitory ability on clonal-formation, migration and invasion of MDA-MB-231 cells. Further cell-based mechanistic studies demonstrated that compound 7t caused cell cycle arrest of MDA-MB-231 cells at the G0/G1 phase and induced apoptosis. Meanwhile, the western blot assay revealed that compound 7t could down-regulate the expression of p-PI3K, p-AKT, and Bcl-2 and up-regulate the production of PTEN, Bax, and caspase-3. Molecular docking also showed a possible binding mode of 7t with PI3Kα. Together, compound 7t was eligible as a potential TNBC therapeutic candidate for further development.

Pharmacological characterization of a novel metal-based proteasome inhibitor Na-AuPT for cancer treatment.

The ubiquitin-proteasome system (UPS) is essential for maintaining cell homeostasis by orchestrating the protein degradation, but is impaired in various diseases, including cancers. Several proteasome inhibitors, such as bortezomib, are currently used in cancer treatment, but associated toxicity limits their widespread application. Recently metal complex-based drugs have attracted great attention in tumor therapy; however, their application is hindered by low water-solubility and poor absorbency. Herein, we synthesized a new type of gold (I) complex named Na-AuPT, and further characterized its anticancer activity. Na-AuPT is highly water-soluble (6 mg/mL), and it was able to potently inhibit growth of a panel of 11 cancer cell lines (A549, SMMC7721, H460, HepG2, BEL7402, LNCap, PC3, MGC-803, SGC-7901, U266, and K562). In A549 and SMMC7721 cells, Na-AuPT (in a range of 2.5-20 µM) inhibited the UPS function in a dose-dependent fashion by targeting and inhibiting both 20 S proteasomal proteolytic peptidases and 19 S proteasomal deubiquitinases. Furthermore, Na-AuPT induced caspase-dependent apoptosis in A549 and SMMC7721 cells, which was prevented by the metal chelator EDTA. Administration of Na-AuPT (40 mg · kg-1 · d-1, ip) in nude mice bearing A549 or SMMC7721 xenografts significantly inhibited the tumor growth in vivo, accompanied by increased levels of total ubiquitinated proteins, cleaved caspase 3 and Bax protein in tumor tissue. Moreover, Na-AuPT induced cell death of primary mononuclear cells from 5 patients with acute myeloid leukemia ex vivo with an average IC50 value of 2.46 µM. We conclude that Na-AuPT is a novel metal-based proteasome inhibitor that may hold great potential for cancer therapy.

Regulation of Bax-dependent apoptosis by mitochondrial deubiquitinase USP30.

Deubiquitinates (DUBs) have been suggested as novel promising targets for cancer therapies. Accumulating experimental evidence suggests that some metal compounds have the potential to induce cancer cell death via inhibition of DUBs. We previously reported that auranofin, a gold(I)-containing agent used for the treatment of rheumatoid arthritis in clinics, can induce cell death by inhibiting proteasomal DUBs in a series of cancer cell lines. Unfortunately, currently available gold compounds are not potent in inhibiting DUBs. Here, we report that: (i) aumdubin, a synthetic derivative of auranofin, exhibited stronger DUB-inhibiting and apoptosis-inducing activities than auranofin in lung cancer cells; (ii) aumdubin shows high affinity for mitochondrial DUB USP30; (iii) aumdubin induces apoptosis by increasing the ubiquitination and mitochondrial location of Bax protein; and (iv) USP30 inhibition may contribute to Bax-dependent apoptosis induced by aumdubin in lung cancer cells. These results suggest that gold(I)-containing agent aumdubin induces Bax-dependent apoptosis partly through inhibiting the mitochondrial DUB USP30, which could open new avenues for lung cancer therapy.

MiR-142-3p enhances chemosensitivity of breast cancer cells and inhibits autophagy by targeting HMGB1.

MiR-142-3p has been reported to act as a tumor suppressor in breast cancer. However, the regulatory effect of miR-142-3p on drug resistance of breast cancer cells and its underlying mechanism remain unknown. Here, we found that miR-142-3p was significantly downregulated in the doxorubicin (DOX)-resistant MCF-7 cell line (MCF-7/DOX). MiR-142-3p overexpression increased DOX sensitivity and enhanced DOX-induced apoptosis in breast cancer cells. High-mobility group box 1 (HMGB1) is a direct functional target of miR-142-3p in breast cancer cells and miR-142-3p negatively regulated HMGB1 expression. Moreover, overexpression of HMGB1 dramatically reversed the promotion of apoptosis and inhibition of autophagy mediated by miR-142-3p up-regulation. In conclusion, miR-142-3p overexpression may inhibit autophagy and promote the drug sensitivity of breast cancer cells to DOX by targeting HMGB1. The miR-142-3p/HMGB1 axis might be a novel target to regulate the drug resistance of breast cancer patients.

Broad Spectrum Deubiquitinase Inhibition Induces Both Apoptosis and Ferroptosis in Cancer Cells.

Proteasomal deubiquitinase (DUB) inhibition has been found to be effective in experimental cancer therapy by inducing proteasome inhibition and apoptosis. Ferroptosis is a form of regulated cell death characterized by an iron-dependent lipid peroxidation. Antioxidant enzyme glutathione peroxidase 4 (GPX4) plays a key role in blocking ferroptosis through directly reducing phospholipid hydroperoxides production. Since cytoplasmic DUB inhibition can promote protein degradation in the cell, we hypothesize that DUB inhibition induces GPX4 degradation. Here we used palladium pyrithione complex (PdPT), a broad spectrum deubiquitinase inhibitor, to explore its cell death induction and anti-cancer effect in vitro, ex vivo, and in vivo. Mechanically, caspase activation and GPX4 protein degradation are required for PdPT-induced apoptosis and ferroptosis, respectively. Notably, PdPT-induced multiple deubiquitinase inhibition is essential for proteasomal degradation of GPX4. These findings not only identify a novel mechanism of post-translational modification of GPX4 in ferroptosis, but also suggest a potential anti-caner therapeutic strategy using Pan-DUB inhibition.

Autophagy Induced by Proteasomal DUB Inhibitor NiPT Restricts NiPT-Mediated Cancer Cell Death.

Ubiquitin-proteasome system (UPS) and autophagy-lysosome pathway (ALP) are two major systems for protein quality control (PQC) in eukaryotic cells. Interconnectivity between these two pathways has been suggested, but the molecular detail of how they impact each other remains elusive. Proteasomal deubiquitinase (DUB) is an important constituent in the UPS and has proved to be a novel anticancer target. We have previously found that a novel DUB inhibitor, nickel complex NiPT, induces apoptosis in both cultured tumor cell lines and cancer cells from acute myeloid leukemia human patients. In this study, we found that NiPT triggered autophagy both in vitro and in vivo. Mechanistically, NiPT targets two DUBs, USP14, and UCHL5, and increased the total cellular level of polyubiquitination. Deletion of the Ubiquitin Associated (UBA) domain of P62 that is required for polyubiquitin binding prevented NiPT-induced autophagy. NiPT-induced autophagy is through either concomitant activation of AMP-activated protein kinase (AMPK) and inhibition of mechanistic target of rapamycin (mTOR) signaling, or eliciting endoplasmic reticulum (ER)-stress by activating activating transcription factor 4 (ATF4) and C/EBP-homologous protein (CHOP). Moreover, NiPT could induce more lung cancer cells undergoing apoptosis if it synergistically uses autophagy inhibitors, suggesting that NiPT-induced autophagy protects cancer cell from death. Collectively, our findings demonstrate that autophagy inhibition enhances the anticancer effects of proteasomal DUB inhibitor and might be an effective treatment strategy for lung cancer.

Costunolide induces apoptosis and inhibits migration and invasion in H1299 lung cancer cells.

Costunolide being a sesquiterpene lactone, is known to have anticancer properties. The present study investigated the anticancer effects of costunolide against the H1299 human non­small­cell lung cancer (NSCLC) cell line. Inhibition of cell viability by costunolide was assessed via a MTT assay. Furthermore, the apoptotic rate was detected using Annexin V/propidium iodide labeling. A colony forming cell assay was performed to investigate the antiproliferative effects of costunolide. Wound healing and Transwell assays were performed to determine the inhibitory effects of costunolide on migration and invasion, respectively. Western blot analysis was undertaken to determine protein expression, and reverse transcription­quantitative PCR was performed to assess mRNA expression levels. The results demonstrated that costunolide inhibited the viability of H1299 cells, with a half maximal inhibitory concentration value of 23.93±1.67 µM and induced cellular apoptosis in a dose­dependent manner. Furthermore, the colony formation, migrative and invasive abilities of the H1299 cells were inhibited in a dose­ or time­dependent manner. The protein expression levels of E­cadherin increased and those of N­cadherin decreased following treatment with costunolide, which suggested that costunolide inhibited epithelial­to­mesenchymal transition. The mRNA levels of B­Raf, E­cadherin, N­cadherin, integrins α2 and ß1, as well as matrix metalloproteinases 2 were also found to be regulated costunolide. These findings indicate the potential of costunolide in the treatment of NSCLC.

Synthesis and Activity Evaluation of Nasopharyngeal Carcinoma Inhibitors Based on 6-(Pyrimidin-4-yl)-1H-indazole.

Human nasopharyngeal carcinoma is a common head and neck malignancy with high incidence in Southeast Asia and Southern China. It is necessary to develop safe, effective and inexpensive anticancer agents to improve the therapeutics of patients with nasopharyngeal carcinoma. A series of small molecular compounds based on 6-(pyrimidin-4-yl)-1H-indazole were synthesized and evaluated for antiproliferative activities against human nasopharyngeal carcinoma cell lines SUNE1. Compounds 6b, 6c, 6e and 6l showed potent antiproliferative activities similar to positive control drug cisplatin in vitro with lower nephrotoxicity than it. N-[4-(1H-Indazol-6-yl)pyrimidin-2-yl]benzene-1,3-diamine (6l) was selected for further study. It was found that 6l induced mitochondria-mediated apoptosis and G2 /M phase arrest in SUNE1 cells. Furthermore, compound 6l at 10 mg/kg can suppress the growth of an implanted SUNE1 xenograft with a TGI% (tumor growth inhibition) value of 50 % and did not cause serious side effects in BALB/c nude mice. This study suggests that 6-(pyrimidin-4-yl)-1H-indazole derivatives are a series of small molecule compounds with anti-nasopharyngeal carcinoma activities.

A new gold(I) complex-Au(PPh3)PT is a deubiquitinase inhibitor and inhibits tumor growth.

BACKGROUND: Ubiquitin-proteasome system (UPS) is integral to cell survival by maintaining protein homeostasis, and its dysfunction has been linked to cancer and several other human diseases. Through counteracting ubiquitination, deubiquitinases (DUBs) can either positively or negatively regulate UPS function, thereby representing attractive targets of cancer therapies. Previous studies have shown that metal complexes can inhibit tumor growth through targeting the UPS; however, novel metal complexes with higher specificity for cancer therapy are still lacking. METHODS: We synthesized a new gold(I) complex, Au(PPh3)PT. The inhibitory activity of Au(PPh3)PT on the UPS and the growth of multiple cancer cell types were tested in vitro, ex vivo, and in vivo. Furthermore, we compared the efficacy of Au(PPh3)PT with other metal compounds in inhibition of UPS function and tumor growth. FINDINGS: Here we report that (i) a new gold(I) complex-pyrithione, i.e., Au(PPh3)PT, induced apoptosis in two lung cancer cell lines A549 and NCI-H1299; (ii) Au(PPh3)PT severely impaired UPS proteolytic function; (iii) Au(PPh3)PT selectively inhibited 19S proteasome-associated DUBs (UCHL5 and USP14) and other non-proteasomal DUBs with minimal effects on the function of 20S proteasome; (iv) Au(PPh3)PT induced apoptosis in cancer cells from acute myeloid leukemia patients; (v) Au(PPh3)PT effectively suppressed the growth of lung adenocarcinoma xenografts in nude mice; and (vi) Au (PPh3)PT elicited less cytotoxicity in normal cells than several other metal compounds. INTERPRETATION: Together, this study discovers a new gold(I) complex to be an effective inhibitor of the DUBs and a potential anti-cancer drug. FUND: The National High Technology Research and Development Program of China, the project of Guangdong Province Natural Science Foundation, the projects from Foundation for Higher Education of Guangdong, the project from Guangzhou Medical University for Doctor Scientists, the Medical Scientific Research Foundation of Guangdong Province, and the Guangzhou Key Medical Discipline Construction Project Fund.

Inhibition of Proteasomal Deubiquitinase by Silver Complex Induces Apoptosis in Non-Small Cell Lung Cancer Cells.

BACKGROUND/AIMS: The ubiquitin proteasome system (UPS) is responsible for the degradation of most intracellular proteins, and proteasomal deubiquitinases (DUBs) have recently been highlighted as novel anticancer targets. It is well documented that copper complexes can inhibit UPS function through targeting both 20S proteasome and proteasomal DUBs. The antineoplastic activities of silver complexes have received much attention, but the exact mechanisms are not fully elucidated. In this study, we aim to investigate the effects of a novel silver complex [Ag(S2CN(C2H5)2)]6 (AgDT) on UPS function and its anticancer potential in non-small cell lung cancer (NSCLC). METHODS: Cell viability assay (i.e., the MTS assay) and flow cytometry assay were used to analyze the cell viability and apoptosis. Proteasome inhibition was measured using 20S proteasome activity assay and 19S proteasomal DUBs activity assay. Western blot analysis and immunohistochemistry were performed to detect protein levels. The in vivo antitumor activity of AgDT was assessed with nude xenografts. RESULTS: Silver ions, alone or in combination with disulfiram (DSF), induced UPS inhibition in NSCLC cells mainly through inhibition of proteasomal DUBs activities. Silver complex AgDT triggered intracellular accumulation of ubiquitinated proteins, and prevented the degradation of surrogate substrate GFPu. Mechanistically, AgDT potently inhibited the activities of proteasomal DUBs USP14 and UCHL5, without altering the 20S proteasome peptidases. Moreover, AgDT induced apoptosis in NSCLC cells and significantly inhibited tumor growth in xenografts. CONCLUSION: Our findings suggest that silver complex AgDT is a novel metal-based proteasomal DUBs inhibitor, and pharmacologic inhibition of USP14 and UCHL5 could prove to be an effective therapeutic strategy for NSCLC.

Cadmium pyrithione suppresses tumor growth in vitro and in vivo through inhibition of proteasomal deubiquitinase.

The ubiquitin-proteasome system (UPS) is indispensable to the protein quality control in eukaryotic cells. Due to the remarkable clinical success of using proteasome inhibitors for clinical treatment of multiple myeloma, it is anticipated that targeting the UPS upstream of the proteasome step be an effective strategy for cancer therapy. Deubiquitinases (DUB) are proteases that remove ubiquitin from target proteins and therefore regulate multiple cellular processes including some signaling pathways altered in cancer cells. Thus, targeting DUB is a promising strategy for cancer drug discovery. Previously, we have reported that metal complexes, such as copper and gold complexes, can disrupt the UPS via suppressing the activity of 19S proteasome-associated DUBs and/or of the 20S proteasomes, thereby inducing cancer cell death. In this study, we found that cadmium pyrithione (CdPT) treatment led to remarkable accumulation of ubiquitinated proteins in cultured cancer cells and primary leukemia cells. CdPT potently inhibited the activity of proteasomal DUBs (USP14 and UCHL5), but slightly inhibited 20S proteasome activity. The anti-cancer activity of CdPT was associated with triggering apoptosis via caspase activation. Moreover, treatment with CdPT inhibited proteasome function and repressed tumor growth in animal xenograft models. Our results show that cadmium-containing complex CdPT may function as a novel proteasomal DUB inhibitor and suggest appealing prospects for cancer treatment.

Hinokitiol copper complex inhibits proteasomal deubiquitination and induces paraptosis-like cell death in human cancer cells.

The ubiquitin-proteasome system (UPS) plays a central role in the regulation of proteins that control cell growth and apoptosis and has therefore become an important target for anticancer therapy. Several constitutive subunits of the 19S proteasome display deubiquitinase (DUB) activity, suggesting that ubiquitin modification of proteins is dynamically regulated. Our study and others have shown that metal complexes, such as copper complexes, can induce cancer cell apoptosis through inhibiting 19S proteasome-associated DUBs and/or 20S proteasome activity. In this study, we found that (1) Hinokitiol copper complex (HK-Cu) induces striking accumulation of ubiquitinated proteins in A549 and K562 cells (2) HK-Cu potently inhibits the activity of the 19S proteasomal DUBs much more effectively than it does to the chymotrypsin-like activity of the 20S proteasome (3) HK-Cu effectively induces caspase-independent and paraptosis-like cell death in A549 and K562 cells, and (4) HK-Cu-induced cell death depends on ATF4-assosiated ER stress but is apparently not related to ROS generation. Altogether, these data indicate that HK-Cu can inhibit the activity of the 19S proteasomal DUBs and induce paraptosis-like cell death, representing a new drug candidate for cancer treatment.

Platinum pyrithione induces apoptosis in chronic myeloid leukemia cells resistant to imatinib via DUB inhibition-dependent caspase activation and Bcr-Abl downregulation.

Chronic myelogenous leukemia (CML) is characterized by the chimeric tyrosine kinase Bcr-Abl. T315I Bcr-Abl is the most notorious point mutation to elicit acquired resistance to imatinib (IM), leading to poor prognosis. Therefore, it is urgent to search for additional approaches and targeting strategies to overcome IM resistance. We recently reported that platinum pyrithione (PtPT) potently inhibits the ubiquitin-proteasome system (UPS) via targeting the 26 S proteasome-associated deubiquitinases (DUBs), without effecting on the 20 S proteasome. Here we further report that (i) PtPT induces apoptosis in Bcr-Abl wild-type and Bcr-Abl-T315I mutation cells including the primary mononuclear cells from CML patients clinically resistant to IM, as well as inhibits the growth of IM-resistant Bcr-Abl-T315I xenografts in vivo; (ii) PtPT downregulates Bcr-Abl level through restraining Bcr-Abl transcription, and decreasing Bcr-Abl protein mediated by DUBs inhibition-induced caspase activation; (iii) UPS inhibition is required for PtPT-induced caspase activation and cell apoptosis. These findings support that PtPT overcomes IM resistance through both Bcr-Abl-dependent and -independent mechanisms. We conclude that PtPT can be a lead compound for further drug development to overcome imatinib resistance in CML patients.

Repurposing an antidandruff agent to treating cancer: zinc pyrithione inhibits tumor growth via targeting proteasome-associated deubiquitinases.

The ubiquitin-proteasome system (UPS) plays a central role in various cellular processes through selectively degrading proteins involved in critical cellular functions. Targeting UPS has been validated as a novel strategy for treating human cancer, as inhibitors of the 20S proteasome catalytic activity are currently in clinical use for treatment of multiple myeloma and other cancers, and the deubiquitinase activity associated with the proteasome is also a valid target for anticancer agents. Recent studies suggested that zinc pyrithione, an FDA-approved antidandruff agent, may have antitumor activity, but the detailed molecular mechanisms remain unclear. Here we report that zinc pyrithione (ZnPT) targets the proteasome-associated DUBs (USP14 and UCHL5) and inhibits their activities, resulting in a rapid accumulation of protein-ubiquitin conjugates, but without inhibiting the proteolytic activities of 20S proteasomes. Furthermore, ZnPT exhibits cytotoxic effects against various cancer cell lines in vitro, selectively kills bone marrow cells from leukemia patients ex vivo, and efficiently inhibits the growth of lung adenocarcinoma cancer cell xenografts in nude mice. This study has identified zinc pyrithione, an FDA-approved pharmacological agent with potential antitumor properties as a proteasomal DUB inhibitor.

Nickel pyrithione induces apoptosis in chronic myeloid leukemia cells resistant to imatinib via both Bcr/Abl-dependent and Bcr/Abl-independent mechanisms.

BACKGROUND: Acquired imatinib (IM) resistance is frequently characterized by Bcr-Abl mutations that affect IM binding and kinase inhibition in patients with chronic myelogenous leukemia (CML). Bcr-Abl-T315I mutation is the predominant mechanism of the acquired resistance to IM. Therefore, it is urgent to search for additional approaches and targeting strategies to overcome IM resistance. We recently reported that nickel pyrithione (NiPT) potently inhibits the ubiquitin proteasome system via targeting the 19S proteasome-associated deubiquitinases (UCHL5 and USP14), without effecting on the 20S proteasome. In this present study, we investigated the effect of NiPT, a novel proteasomal deubiquitinase inhibitor, on cell survival or apoptosis in CML cells bearing Bcr-Abl-T315I or wild-type Bcr-Abl. METHODS: Cell viability was examined by MTS assay and trypan blue exclusion staining assay in KBM5, KBM5R, K562, BaF3-p210-WT, BaF3-p210-T315I cells, and CML patients' bone marrow samples treated with NiPT. Cell apoptosis in CML cells was detected with Annexin V-FITC/PI and rhodamine-123 staining followed by fluorescence microscopy and flow cytometry and with western blot analyses for apoptosis-associated proteins. Expression levels of Bcr-Abl in CML cells were analyzed by using western blotting and real-time PCR. The 20S proteasome peptidase activity was measured using specific fluorogenic substrate. Active-site-directed labeling of proteasomal DUBs, as well as the phosphorylation of USP14 was used for evaluating the inhibition of the DUBs activity by NiPT. Mouse xenograft models of KBM5 and KBM5R cells were analyzed, and Bcr-Abl-related proteins and protein biomarkers related to proliferation, differentiation, and adhesion in tumor tissues were detected by western blots and/or immunohistological analyses. RESULTS: NiPT induced apoptosis in CML cells and inhibited the growth of IM-resistant Bcr-Abl-T315I xenografts in nude mice. Mechanistically, NiPT induced decreases in Bcr-Abl proteins, which were associated with downregulation of Bcr-Abl transcription and with the cleavage of Bcr-Abl protein by activated caspases. NiPT-induced ubiquitin proteasome system inhibition induced caspase activation in both IM-resistant and IM-sensitive CML cells, and the caspase activation was required for NiPT-induced Bcr-Abl downregulation and apoptotic cell death. CONCLUSIONS: These findings support that NiPT can overcome IM resistance through both Bcr-Abl-dependent and Bcr-Abl-independent mechanisms, providing potentially a new option for CML treatment.

Platinum-containing compound platinum pyrithione is stronger and safer than cisplatin in cancer therapy.

DNA is the well-known molecular target of current platinum-based anticancer drugs; consequently, their clinical use is severely restricted by their systemic toxicities and drug resistance originating from non-selective DNA damage. Various strategies have been developed to circumvent the shortcomings of platinum-based chemotherapy but the inherent problem remains unsolved. Here we report that platinum pyrithione (PtPT), a chemically well-characterized synthetic complex of platinum, inhibits proteasome function and thereby exhibits greater and more selective cytotoxicity to multiple cancer cells than cisplatin, without showing discernible DNA damage both in vitro and in vivo. Moreover, unlike the classical proteasome inhibitor bortezomib/Velcade which inhibits the proteasome via blocking the peptidase activity of 20S proteasomes, PtPT primarily deactivates 26S proteasome-associated deubiquitinases USP14 and UCHL5. Furthermore, PtPT can selectively induce cytotoxicity and proteasome inhibition in cancer cells from leukemia patients but not peripheral blood mononuclear cells from healthy humans. In nude mice, PtPT also remarkably inhibited tumor xenograft growth, without showing the adverse effects that were induced by cisplatin. Hence, we have discovered a new platinum-based anti-tumor agent PtPT which targets 26S proteasome-associated deubiquitinases rather than DNA in the cell and thereby exerts safer and more potent anti-tumor effects, identifying a highly translatable new platinum-based anti-cancer strategy.

Gambogic acid induces apoptosis in diffuse large B-cell lymphoma cells via inducing proteasome inhibition.

Resistance to chemotherapy is a great challenge to improving the survival of patients with diffuse large B-cell lymphoma (DLBCL), especially those with activated B-cell-like DLBCL (ABC-DLBCL). Therefore it is urgent to search for novel agents for the treatment of DLBCL. Gambogic acid (GA), a small molecule derived from Chinese herb gamboges, has been approved for Phase II clinical trial for cancer therapy by Chinese FDA. In the present study, we investigated the effect of GA on cell survival and apoptosis in DLBCL cells including both GCB- and ABC-DLBCL cells. We found that GA induced growth inhibition and apoptosis of both GCB- and ABC-DLBCL cells in vitro and in vivo, which is associated with proteasome malfunction. These findings provide significant pre-clinical evidence for potential usage of GA in DLBCL therapy particularly in ABC-DLBCL treatment.

A novel proteasome inhibitor suppresses tumor growth via targeting both 19S proteasome deubiquitinases and 20S proteolytic peptidases.

The successful development of bortezomib-based therapy for treatment of multiple myeloma has established proteasome inhibition as an effective therapeutic strategy, and both 20S proteasome peptidases and 19S deubiquitinases (DUBs) are becoming attractive targets of cancer therapy. It has been reported that metal complexes, such as copper complexes, inhibit tumor proteasome. However, the involved mechanism of action has not been fully characterized. Here we report that (i) copper pyrithione (CuPT), an alternative to tributyltin for antifouling paint biocides, inhibits the ubiquitin-proteasome system (UPS) via targeting both 19S proteasome-specific DUBs and 20S proteolytic peptidases with a mechanism distinct from that of the FDA-approved proteasome inhibitor bortezomib; (ii) CuPT potently inhibits proteasome-specific UCHL5 and USP14 activities; (iii) CuPT inhibits tumor growth in vivo and induces cytotoxicity in vitro and ex vivo. This study uncovers a novel class of dual inhibitors of DUBs and proteasome and suggests a potential clinical strategy for cancer therapy.