Combined effect of proteasome and calpain inhibition on cisplatin-resistant human melanoma cells

Different Strategies to Overcome Resistance to Proteasome Inhibitors-A Summary 20 Years after Their Introduction

Proteasome inhibitors (PIs), bortezomib, carfilzomib, and ixazomib, are the first-line treatment for multiple myeloma (MM). They inhibit cytosolic protein degradation in cells, which leads to the accumulation of misfolded and malfunctioned proteins in the cytosol and endoplasmic reticulum, resulting in cell death. Despite being a breakthrough in MM therapy, malignant cells develop resistance to PIs via different mechanisms. Understanding these mechanisms drives research toward new anticancer agents to overcome PI resistance. In this review, we summarize the mechanism of action of PIs and how MM cells adapt to these drugs to develop resistance. Finally, we explore these mechanisms to present strategies to interfere with PI resistance. The strategies include new inhibitors of the ubiquitin-proteasome system, drug efflux inhibitors, autophagy disruption, targeting stress response mechanisms, affecting survival and cell cycle regulators, bone marrow microenvironment modulation, and immunotherapy. We list potential pharmacological targets examined in in vitro, in vivo, and clinical studies. Some of these strategies have already provided clinicians with new anti-MM medications, such as panobinostat and selinexor. We hope that further exploration of the subject will broaden the range of therapeutic options and improve patient outcomes.

New gold(III) complexes TGS 121, 404, and 702 show anti-tumor activity in colitis-induced colorectal cancer: an in vitro and in vivo study

BACKGROUND

Chronic inflammation in the course of inflammatory bowel disease may result in colon cancer, or colitis-associated colorectal cancer (CACRC). It is well established that CACRC is associated with oxidative stress and secretion of multiple pro-inflammatory cytokines, e.g. tumor necrosis factor-α. Recently, we proved that the administration of gold(III) complexes resulted in the alleviation of acute colitis in mice. The aim of the current study was to assess the antitumor effect of a novel series of gold(III) complexes: TGS 121, 404, 512, 701, 702, and 703.

MATERIALS

Analyzed gold(III) complexes were screened in the in vitro studies using colorectal cancer and normal colon epithelium cell lines, SW480, HT-29, and CCD 841 CoN, and in vivo, in the CACRC mouse model.

RESULTS

Of all tested complexes, TGS 121, 404, and 702 exhibited the strongest anti-tumor effect in in vitro viability assay of colon cancer cell lines and in in vivo CACRC model, in which these complexes decreased the total number of colonic tumors and macroscopic score. We also evidenced that the mechanism of action was linked to the enzymatic antioxidant system and inflammatory cytokines.

CONCLUSIONS

TGS 121, 404, and 702 present anti-tumor potential and are an attractive therapeutic option for colorectal cancer.

Proteasome inhibition potentiates Kv1.3 potassium channel expression as therapeutic target in drug-sensitive and -resistant human melanoma cells

Primary and acquired therapy resistance is a major problem in patients with BRAF-mutant melanomas being treated with BRAF and MEK inhibitors (BRAFI, MEKi). Therefore, development of alternative therapy regimes is still required. In this regard, new drug combinations targeting different pathways to induce apoptosis could offer promising alternative approaches. Here, we investigated the combination of proteasome and Kv1.3 potassium channel inhibition on chemo-resistant, BRAF inhibitor-resistant as well as sensitive human melanoma cells. Our experiments demonstrated that all analyzed melanoma cell lines were sensitive to proteasome inhibitor treatment at concentrations that are not toxic to primary human fibroblasts. To further reduce proteasome inhibitor-associated side effects, and to foster apoptosis, potassium channels, which are other targets to induce pro-apoptotic effects in cancer cells, were blocked. In support, combined exposure of melanoma cells to proteasome and Kv1.3 channel inhibitor resulted in synergistic effects and significantly reduced cell viability. On the molecular level, enhanced apoptosis correlated with an increase of intracellular Kv1.3 channels and pro-apoptotic proteins such as Noxa and Bak and a reduction of anti-apoptotic proteins. Thus, use of combined therapeutic strategies triggering different apoptotic pathways may efficiently prevent the outgrowth of drug-resistant and -sensitive BRAF-mutant melanoma cells. In addition, this could be the basis for an alternative approach to treat other tumors expressing mutated BRAF such as non-small-cell lung cancer.

Proteasome inhibitors as anticancer agents

INTRODUCTION

The therapeutic targeting of the ubiquitin-proteasome pathway (UPP) through inhibitors of the 20S proteasome core proteolytic activities has revolutionized the treatment of hematological malignancies and is paving the way for its extension to solid tumors.

AREAS COVERED

This review covers the progress made in the field of proteasome inhibitors, ranging from the first-generation bortezomib to the latest second-generation inhibitors such as carfilzomib and ixazomib as well as the proteasome inhibitors in clinical phase such as oprozomib and marizomib. The development of selective and potent proteasome inhibitors with improved pharmacological properties is described from the synthesis to their basic biological, and clinical validation.

EXPERT OPINION

Proteasome inhibitors have transformed the treatment landscape for hematological malignancies and hold great promise for cancer therapy. Combination therapies targeting multiple pathways, the development of novel inhibitors or 'hybrid-inhibitors,' and the optimization of treatment protocols are key areas for future exploration. The extension of proteasome inhibitors for the treatment of solid tumors, and their ability to pass the blood-brain barrier open new possibilities for treating central nervous system cancers. However, managing adverse effects, particularly those affecting the central nervous system, remains a critical consideration and a strategic 'working on' aspect for the near future.

Activity and Selectivity of Novel Chemical Metallic Complexes with Potential Anticancer Effects on Melanoma Cells

Human malignant melanoma cells from lymph node metastatic site (MeWo) were selected for testing several synthesized and purified silver(I) and gold(I) complexes stabilized by unsymmetrically substituted N-heterocyclic carbene (NHC) ligands, called L20 (N-methyl, N'-[2-hydroxy ethylphenyl]imidazol-2-ylide) and M1 (4,5-dichloro, N-methyl, N'-[2-hydroxy ethylphenyl]imidazol-2-ylide), having halogenide (Cl^- or I^-) or aminoacyl (Gly=N-(tert-Butoxycarbonyl)glycinate or Phe=(S)-N-(tert-Butoxycarbonyl)phenylalaninate) counterion. For AgL20, AuL20, AgM1 and AuM1, the Half-Maximal Inhibitory Concentration (IC₅₀) values were measured, and all complexes seemed to reduce cell viability more effectively than Cisplatin, selected as control. The complex named AuM1 was the most active just after 8 h of treatment at 5 μM, identified as effective growth inhibition concentration. AuM1 also showed a linear dose and time-dependent effect. Moreover, AuM1 and AgM1 modified the phosphorylation levels of proteins associated with DNA lesions (H2AX) and cell cycle progression (ERK). Further screening of complex aminoacyl derivatives indicated that the most powerful were those indicated with the acronyms: GlyAg, PheAg, AgL20Gly, AgM1Gly, AuM1Gly, AgL20Phe, AgM1Phe, AuM1Phe. Indeed, the presence of Boc-Glycine (Gly) and Boc-L-Phenylalanine (Phe) showed an improved efficacy of Ag main complexes, as well as that of AuM1 derivatives. Selectivity was further checked on a non-cancerous cell line, a spontaneously transformed aneuploid immortal keratinocyte from adult human skin (HaCaT). In such a case, AuM1 and PheAg complexes resulted as the most selective allowing HaCaT viability at 70 and 40%, respectively, after 48 h of treatment at 5 μM. The same complexes tested on 3D MeWo static culture induced partial spheroid disaggregation after 24 h of culture, with almost half of the cells dead.

New gold (III) cyanide complex TGS 121 induces ER stress, proteasome inhibition and death of Ras-hyperactivated cells

Metal-based agents in cancer therapy, like cisplatin and its derivates, have established clinical applications but also can induce serious side effects. Thus, metallotherapeutic alternatives for platinum derivatives are developed and intensively studied. Platinum is replaced by several transition metals including gold. Especially gold (III) complexes can have the same square-planar structure and are isoelectric with platinum (II). Hence, they are developed as potential anti-cancer drugs. Thus, our group projected and developed a group of novel cyanide-based gold (III) complexes. Within this work, we aimed to characterize the safety and effectivity of one of them, TGS 121. TGS 121 in our preliminary work was selective for Ras-hyperactivated cells. Here we studied the effects of the novel complex in cancerous Ras-3 T3 and non-cancerous NIH-3 T3 cells. The complex TGS 121 turned out to be non-toxic for NIH-3 T3 cells and to induce death and alternations in Ras-hyperactivated cells. We found induction of ER stress, mitochondria swelling, proteasome inhibition, and cell cycle block. Moreover, TGS 121 inhibited cell migration and induced the accumulation of perinuclear organelles that was secondary to proteasome inhibition. Results presented in this report suggest that stable gold-cyanide TGS 121 complex is non-toxic, with a targeted mechanism of action and it is promising in anticancer drug discovery.

Novel podophyllotoxin and benzothiazole derivative induces transitional morphological and functional changes in HaCaT cells

Podophyllotoxin (PPT) is an antimitotic drug used topically in the treatment of anogenital warts. Due to its toxicity it cannot be administered systemically as an anticancer agent. However, modified PPT derivatives such as etoposide and teniposide are used clinically as systemic agents. Thus, we invented novel PPT derivative KL3 that was synthesized by photocyclization. Earlier we have shown that KL3 has an anticancer effect in various cell lines. Here we compared the toxicity of KL3 vs PPT on non-cancerous normal human keratinocytes (HaCaT) and peripheral blood mononuclear cells (PBMC) showing that KL3 is less toxic than PPT to non-cancerous cells. At concentrations that neither induced cell death, nor affected cell cycle, KL3 in HaCaT cells evoked transient ultrastructural features of ER stress, swelling of mitochondria and elongation of cytoplasmic processes. Those changes partially reversed with prolonged incubation while features of autophagy were induced. PPT in equivalent concentrations induced HaCaT cell death by cell cycle arrest, intrinsic apoptosis and finally disintegration of cell membranes followed by secondary necrosis. In conclusion, we show that the KL3 derivative of PPT in contrast to PPT allows repair of normal keratinocytes and triggers mechanisms that restore non-tumor cell homeostasis.

A potential role of calpains in sulfonylureas (SUs) -mediated death of human pancreatic cancer cells (1.2B4)

Sulfonylureas (SUs) are suggested to accelerate the pancreatic β-cells mass loss via apoptosis. However, little is known whether calpains mediate this process. The aim of the present study is to evaluate the involvement of calpains in SUs-induced death of human pancreatic cancer (PC) cell line 1.2B4. The cells were exposed to: glibenclamide, glimepiride and gliclazide for 72 h. The expression analysis of caspase-3 (CASP-3), TP53, calpain 1 (CAPN-1), calpain 2 (CAPN-2) and calpain 10 (CAPN-10) was detected using RT-PCR method. Intracellular Ca²⁺ concentrations, CASP-3 activity and total calpain activity were also evaluated. Our results have shown that glibenclamide and glimepiride decrease 1.2B4 cells viability with accompanied increase in intracellular Ca²⁺ concentration and increased expression of apoptosis-related CASP-3 and TP53. Gliclazide did not affect 1.2B4 cell viability and Ca²⁺ concentration, however, it downregulated CASP-3 and upregulated TP53. Interestingly, 50 μM glimepiride increased expression of CAPN-1, CAPN-2 and CAPN-10 whereas 50 μM glibenclamide solely upregulated CAPN-2 expression. We have shown that 10 μM and 50 μM glibenclamide and glimepiride increased the activity of CASP-3, but decreased total calpain activity. Our results suggest that calpains may be involved in glibenclamide- and glimepiride-induced death of PC cells. However, further investigation is required to confirm the engagement of calpains in SUs-mediated death of PC cells, especially studies on protein level of particular isoforms of calpains should be conducted.

Targeting of Cisplatin-Resistant Melanoma Using a Multivalent Ligand Presenting an Elastin-like Polypeptide

Acquired drug resistance is a common occurrence and the main cause of melanoma treatment failure. Melanoma cells frequently developed resistance against cisplatin during chemotherapy, and thus, targeting delivery systems have been devised to decrease drug resistance, increase therapeutic efficacy, and reduce side effects. We genetically engineered a macromolecular carrier using the recursive directional ligation method that specifically targets cisplatin-resistant (Cis-R) melanoma. This carrier is composed of an elastin-like polypeptide (ELP) and multiple copies of Cis-R melanoma-targeting ligands (M-peptide). The designed M₁₆E₁₀₈ contains 16 targeting ligands incorporated within an ELP and has an ideal thermal phase transition at 39 °C. When treated to melanoma cells, M₁₆E₁₀₈ specifically accumulated in Cis-R B16F10 melanoma cells and accumulated to a lesser extent in parental B16F10 cells. Consistently, M₁₆E₁₀₈ exhibited efficient homing and longer retention in tumor tissues in Cis-R melanoma-bearing mice than in parental B16F10 melanoma-bearing mice. Thus, M₁₆E₁₀₈ was found to display considerable potential as a novel agent that specifically targets cisplatin-resistant melanoma.

High calpain-1 expression predicts a poor clinical outcome and contributes to tumor progression in pancreatic cancer patients

BACKGROUND

Pancreatic cancer (PC) is a highly aggressive and metastatic disease, with an elevated mortality rate. It is, therefore, crucial to assess factors affecting the prognosis of PC patients. Meanwhile, calpain-1 is associated with malignant tumor progression and metastasis. Thus, it is meaningful to evaluate the relationship between calpain-1 and PC.

MATERIALS AND METHODS

Calpain-1 protein expression was assessed by immunohistochemistry in 96 pancreatic cancer samples and paired adjacent non-cancerous specimens. In addition, calpain-1 protein levels were assessed in six PC cell lines by western blot (WB). Next, PC cells were transfected with calpain-1 siRNA, and silencing was confirmed by WB. Finally, cell proliferation, colony formation, migration and invasion assays, and cell apoptosis analysis were performed to examine the effects of calpain-1 knockdown on proliferation, growth, apoptosis, migration, and invasion in PC cells.

RESULTS

The results showed that calpain-1 was overexpressed in PC tissues and cells. Meanwhile, calpain-1 overexpression was associated with tumor site (P = 0.029), metastasis (P = 0.000), and TNM stage (P = 0.000), but showed no associations with histological grade (P = 0.396), age (P = 0.809), sex (P = 1.000), and lesion size (P = 0.679). The Kaplan-Meier method demonstrated that the low calpain-1 expression group had increased overall survival (OS) compared with patients expressing high calpain-1 levels (28.7 ± 4.1 vs. 17.0 ± 2.3 months) (P = 0.005). Besides, calpain-1 in PC cells was successfully silenced by liposome-mediated RNA interference, resulting in reduced cell growth, invasion, and metastasis in PC cells, with no effect on apoptosis.

CONCLUSION

The above findings suggest that calpain-1 should be considered a potential biomarker for PC prognosis and therapy.

Calpain system protein expression and activity in ovarian cancer

Purpose

Expression of members of the calpain system are associated with clinical outcome of patients with, amongst others, breast and ovarian cancers, with calpain-2 expression in ovarian cancer being implicated in chemo-resistance and survival. This study aimed, using a large patient cohort and in vitro models, to verify its importance and further investigate the role in ovarian cancer chemoresponse.

Methods

Calpain-1, calpain-2, calpain-4 and calpastatin expression were evaluated in primary ovarian carcinomas (n = 575) by immunohistochemistry. Protein expression was assessed, via western blotting, in five ovarian cancer cell lines with various sensitivities towards cisplatin/carboplatin. In vitro calpain activity was inhibited by calpeptin treatment to assess changes in platinum sensitivity by proliferation assay, with expression of genes associated with epithelial–mesenchymal transition being examined by RT² Profiler™ PCR Array.

Results

The current study confirmed previous data that high calpain-2 expression is associated with poor overall survival (P = 0.026) and that calpain-1 was not associated with overall survival or progression-free survival. Low expression of calpastatin (P = 0.010) and calpain-4 (P = 0.003) were also associated with adverse survival. Such prognostic associations do not seem to be linked with altered tumour sensitivity towards platinum-based chemotherapy. Interestingly, low calpain-1 expression was more frequent in patients with confined tumours (stage 1) (χ² = 11.310, df = 1, P = 0.001). Calpain and calpastatin expression varied among ovarian cancer cell lines yet their expression levels were similar between chemo-sensitive cells and resistant counterparts. Moreover, calpeptin treatment did not alter cellular response to platinum-based chemotherapy or epithelial–mesenchymal transition-related gene expression.

Conclusions

The conventional calpains and calpastatin have been confirmed to play an important role in ovarian cancer; however, the precise mechanisms whereby they exert effects remain to be elucidated.

Electronic supplementary material

The online version of this article (10.1007/s00432-018-2794-2) contains supplementary material, which is available to authorized users.

Downregulated TRPV1 Expression Contributes to Melanoma Growth via the Calcineurin-ATF3-p53 Pathway

Melanoma is the most lethal form of skin cancer with increasing incidence over the years. Because of its rapid proliferative and drastic metastatic capacity, the prognosis of melanoma remains dismal, although the targeted therapy and immunotherapy have gained revolutionary progress recently. Therefore, it is of necessity to further clarify the mechanism of melanoma pathogenesis for developing an alternative treatment strategy. Transient receptor potential vanilloid 1 (TRPV1) is a nonselective Ca²⁺ channel greatly involved in regulating cell apoptosis, proliferation, metabolism, and cancer development, but its role in melanoma remains unknown. Herein, we first found that TRPV1 expression was significantly decreased in melanoma tissues and cell lines, compared with nevus tissues and normal melanocytes, respectively. We then proved that TRPV1 overexpression or its agonist capsaicin treatment inhibited melanoma growth by activating p53 and inducing cell apoptosis. A subsequent mechanistic study revealed that TRPV1 induced Ca²⁺ influx to regulate p53 activation via calcineurin-ATF3 transcriptional cascade. Finally, the effect of TRPV1 on melanoma growth was proved in vivo. Altogether, our study demonstrates that TRPV1 is a potential tumor suppressor in melanoma.

Effect of cisplatin on proteasome activity

Cisplatin is a widely used chemotherapy drug which exerts cytotoxic activity by affecting both nuclear and cytosolic pathways. Herewith, we report, for the first time, that cisplatin inhibits proteasome activity in vitro. Cisplatin induces a dose dependent inhibition of the three enzymatic activities of proteasome (i.e., the chymotrypsin-like activity, the trypsin-like activity and the caspase-like activity). Moreover, cisplatin administration to neuroblastoma cells brings about a fast loss of proteasome particle activity, which is followed by a de novo synthesis of proteasome. Lastly, we report that the simultaneous administration of lactacystin and cisplatin enhances the cytotoxicity of cisplatin alone. The overall bulk of data opens to an intriguing scenario, concerning the biological effects of cisplatin in the control of cellular life, which goes beyond the well established genotoxic effect.

Calpain-2 Inhibitor Therapy Reduces Murine Colitis and Colitis-associated Cancer

BACKGROUND

An important role has emerged for calpain enzymes in regulating inflammation with one isoform, calpain-2, particularly important for macrophage activation. The goal of this study was to determine the therapeutic potential of a synthetic calpain-2 inhibitor, zLLY-CH2F, for colitis and inflammation-associated colorectal cancer.

METHODS

Mice were then subjected to the azoxymethane/dextran sulfate sodium model of colitis and colitis-associated cancer incorporating intervention with daily injections of 0.75 mg/kg calpain-2 inhibitor beginning after the first signs of colitis.

RESULTS

Calpain-2 inhibitor treatment alleviated weight loss and bloody diarrhea, and reduced inflammatory infiltration into colon tissues and inflammatory cytokine mRNA. Calpain-2 inhibitor intervention also reduced total colitis-associated cancer tumor volume by up to 70% in vehicle control mice and decreased cancer pathology scores of blinded histological colon tissue analyses. Mechanistic investigations showed that calpain-2 inhibition during macrophage activation reduced inhibitor of kappa beta (IκB) degradation and nuclear factor kappa beta (NFκB) nuclear localization as well as secretion of specific inflammatory cytokines. In addition, calpain-2 inhibitor treatment of CT26.WT mouse and HT-29 human colorectal cancer cells decreased proliferation and reduced IκB degradation and NFκB translocation.

CONCLUSIONS

Overall, these findings suggest that intervention with a calpain-2 inhibitor may reduce colitis and colitis-associated cancer through a two-hit process of limiting macrophage activation and inhibiting growth of the colorectal cancer cells themselves.

Anti-tumor activity of the proteasome inhibitor BSc2118 against human multiple myeloma

Introduction of bortezomib, the first generation of proteasome inhibitor, has significantly improved the median overall survival of patients with multiple myeloma (MM). However, the dose-limiting adverse events and acquired drug resistance limit its long-term usage. Here, we report in vitro and in vivo anti-MM activity of the irreversible proteasome inhibitor BSc2118. BSc2118 inhibited the chymotrypsin-like (CT-L) proteasome activity, accompanied by accumulation of ubiquitinated proteins. BSc2118 suppressed tumor cell growth through induction of G2/M phase arrest and induced apoptosis via activation of the apoptotic signaling cascade, in association with up-regulation of p53 and p21. Importantly, BSc2118 was active in vitro against MM cells' acquired bortezomib resistance. Of note, BSc2118 also displayed a novel anti-angiogenesis activity both in vitro and in vivo. Lastly, BSc2118 exhibited a broader safety dose range and higher anti-tumor efficacy in vivo in a human MM xenograft mouse model, compared to bortezomib. Together, these findings indicate the in vitro and in vivo anti-MM activities of BSc2118 through induction of cell cycle arrest and apoptosis, as well as inhibition of tumor angiogenesis. They also suggest that BSc2118 might, at least in vitro, partially overcome acquired bortezomib resistance, likely associated with inhibition of autophagy.

Biodistribution and Efficacy Studies of the Proteasome Inhibitor BSc2118 in a Mouse Melanoma Model

Inhibition of the proteasome offers many therapeutic possibilities in inflammation as well as in neoplastic diseases. However, clinical use of proteasome inhibitors is limited by the development of resistance or severe side effects. In our study we characterized the anti-tumor properties of the novel proteasome inhibitor BSc2118. The sensitivity of tumor lines to BSc2118 was analyzed in comparison to bortezomib using crystal violet staining in order to assess cell viability. The In Vivo distribution of BSc2118 in mouse tissues was tracked by a fluorescent-modified form of BSc2118 (BSc2118-FL) and visualized by confocal microscopy. Inhibition of the 20S proteasome was monitored both in cultured cell lines and in mice, respectively. Finally, safety and efficacy of BSc2118 was evaluated in a mouse melanoma model. BSc2118 inhibits proliferation of different tumor cell lines with a similar potency as compared with bortezomib. Systemic administration of BSc2118 in mice is well tolerated, even when given in a dose of 60 mg/kg body weight. After systemic injection of BSc2118 or bortezomib similar proteasome inhibition patterns are observed within the murine organs. Detection of BSc2118-FL revealed correlation of distribution pattern of BSc2118 with inhibition of proteasomal activity in cells or mouse tissues. Finally, administration of BSc2118 in a mouse melanoma model shows significant local anti-tumor effects. Concluding, BSc2118 represents a novel low-toxic agent that might be alternatively used for known proteasome inhibitors in anti-cancer treatment.

Towards combinatorial targeted therapy in melanoma: from pre-clinical evidence to clinical application (review)

Over the last few years, clinical trials with BRAF and mitogen-activated protein/extracellular signal-regulated kinase (MEK) inhibitors have shown significant clinical activity in melanoma, but only a fraction of patients respond to these therapies, and development of resistance is frequent. This has prompted a large set of preclinical studies looking at several new combinatorial approaches of pathway- or target-specific inhibitors. At least five main drug association strategies have been verified in vitro and in preclinical models. The most promising include: i) vertical targeting of either MEK or phosphoinositide-3 kinase (PI3K)/mammalian target of rapamycin (mTOR) pathways, or their combined blockade; ii) association of receptor tyrosine kinases (RTKs) inhibitors with other pro-apoptotic strategies; iii) engagement of death receptors in combination with MEK-, mTOR/PI3K-, histone deacetylase (HDAC)-inhibitors, or with anti-apoptotic molecules modulators; iv) strategies aimed at blocking anti-apoptotic proteins belonging to B-cell lymphoma (Bcl-2) or inhibitors of apoptosis (IAP) families associated with MEK/BRAF/p38 inhibition; v) co-inhibition of other molecules important for survival [proteasome, HDAC and Signal transducers and activators of transcription (Stat)3] and the major pathways activated in melanoma; vi) simultaneous targeting of multiple anti-apoptotic molecules. Here we review the anti-melanoma efficacy and mechanism of action of the above-mentioned combinatorial strategies, together with the potential clinical application of the most promising studies that may eventually lead to therapeutic benefit.

Synthesis of novel, peptidic kinase inhibitors with cytostatic/cytotoxic activity

The utility of a novel, chemoenzymatic procedure for the stereocontrolled synthesis of small peptides is presented in the preparation and structure optimisation of dipeptides with cytostatic/cytotoxic activity. The method uses Passerini multicomponent reaction for the preparation of racemic scaffold which is then enantioselectively hydrolysed by hydrolytic enzymes. Products of these transformations are further functionalised towards title compounds. Both activity and selectivity towards tumor cells is optimised. Final compound is shown to be an inhibitor of the protein kinase signaling pathway.

MGMT expression and pituitary tumours: relationship to tumour biology

Over the past half decade, temozolomide, an oral akylating chemotherapeutic agent, has been shown to have significant activity in the management of aggressive pituitary tumours. The expression of 06-methylguanine-DNA methyltransferase (MGMT), a DNA repair enzyme, is an important predictor of response to therapy. Low MGMT expression has been reported with a higher frequency amongst more aggressive pituitary tumours, suggesting MGMT may play a role in pituitary tumour progression. In this study, we performed a microarray analysis to determine whether there was a distinct gene expression profile between tumours with low MGMT and high MGMT expression. Overall, 1,403 differentially expressed genes were identified with raw p values less than 0.05. Gene set enrichment analysis (GSEA) revealed significant differences in the gene expression profile between high and low MGMT expressing pituitary tumours. High MGMT expressing pituitary tumours were found to have upregulation of components of the FGFR family and downstream signaling cascades such as PI3 K/Akt and MAPK pathways. Activation of genes involved in the DNA damage response and DNA repair pathways, as well as genes involved in transcription, were identified in pituitary tumours with low MGMT expression. These results form the basis of our proposed model to describe the role of MGMT in pituitary tumorigenesis.

Pathophysiological roles of aldo-keto reductases (AKR1C1 and AKR1C3) in development of cisplatin resistance in human colon cancers

Cisplatin (cis-diamminedichloroplatinum, CDDP) is widely used for treatment of patients with solid tumors formed in various organs including the lung, prostate and cervix, but is much less sensitive in colon and breast cancers. One major factor implicated in the ineffectiveness has been suggested to be acquisition of the CDDP resistance. Here, we established the CDDP-resistant phenotypes of human colon HCT15 cells by continuously exposing them to incremental concentrations of the drug, and monitored expressions of aldo-keto reductases (AKRs) 1A1, 1B1, 1B10, 1C1, 1C2 and 1C3. Among the six AKRs, AKR1C1 and AKR1C3 are highly induced with the CDDP resistance. The resistance lowered the sensitivity toward cellular damages evoked by oxidative stress-derived aldehydes, 4-hydroxy-2-nonenal and 4-oxo-2-nonenal that are detoxified by AKR1C1 and AKR1C3. Overexpression of AKR1C1 or AKR1C3 in the parental HCT15 cells mitigated the cytotoxicity of the aldehydes and CDDP. Knockdown of both AKR1C1 and AKR1C3 in the resistant cells or treatment of the cells with specific inhibitors of the AKRs increased the sensitivity to CDDP toxicity. Thus, the two AKRs participate in the mechanism underlying the CDDP resistance probably via detoxification of the aldehydes resulting from enhanced oxidative stress. The resistant cells also showed an enhancement in proteolytic activity of proteasome accompanied by overexpression of its catalytic subunits (PSMβ9 and PSMβ10). Pretreatment of the resistant cells with a potent proteasome inhibitor Z-Leu-Leu-Leu-al augmented the CDDP sensitization elicited by the AKR inhibitors. Additionally, the treatment of the cells with Z-Leu-Leu-Leu-al and the AKR inhibitors induced the expressions of the two AKRs and proteasome subunits. Collectively, these results suggest the involvement of up-regulated AKR1C1, AKR1C3 and proteasome in CDDP resistance of colon cancers and support a chemotherapeutic role for their inhibitors.

Calpain4 is required for activation of HER2 in breast cancer cells exposed to trastuzumab and its suppression decreases survival and enhances response

Overactivation of HER2 and crosstalk of other HER family members contribute to a survival pathway of breast cancer cells exposed to trastuzumab, the therapeutic inhibitor of HER2 and thus, decrease response and promote resistance. We have explored the involvement of the intracellular cysteine protease calpain4, the common partner of isoforms calpain1 and calpain2, in the regulation of cell survival and trastuzumab-response. Increase of calpain4 expression and isoform activities were detected in breast cancer cells and HER2-positive tumors. Molecular analyses of parent and resistant cells suggested that perturbation of regulations, induced by calpain4 and of activities of HER2 and HER3, was associated with trastuzumab-resistance. The suppression of calpain4 destabilized calpain1 and calpain2, however, did not prevent the activation of HER2 and HER3 or cell proliferation in the absence of trastuzumab. To understand the significance, the survival of parent and trastuzumab-resistant cells in which calpain4 was suppressed, was assessed in the presence of trastuzumab; survival in each cell type was decreased and associated with a loss of HER2 and HER3 activity. Taken together, by contributing to the activation and the crosstalk of HER2, calpain4 promotes the survival pathway of breast cancer cells, and therefore, its suppression enhances trastuzumab-response and decreases resistance.

Induction of apoptosis in Eμ-myc lymphoma cells in vitro and in vivo through calpain inhibition

Calpains are cysteine proteases that have been implicated as both effectors and suppressors of apoptosis. Previously, we showed that c-myc transformation regulated calpain activity and sensitized cells to apoptosis induced by calpain inhibition. The objective of this study was to investigate the role of calpain in the Eμ-myc transgenic model of B-cell lymphoma. Calpain activity assays, apoptosis, cell cycle assays, and expression measurements were used to determine the activity and role of calpain in vitro and in vivo. We found that Eμ-myc transgenic cells have highly elevated calpain activity. Calpastatin, the negative calpain regulator, was expressed at much lower levels in Eμ-myc lymphoma cells compared to normal splenic B cells. The primary isoform in Eμ-myc lymphoma is calpain 1. Treatment of Eμ-myc lymphoma cells with the calpain inhibitors PD150606 or calpain inhibitor III induced caspase-3-dependent apoptosis in vitro. General caspase inhibitors or caspase-3/7 inhibitor protected cells from death induced by calpain inhibitor, whereas caspase-9 inhibitors failed to rescue cells. Human Burkitt's lymphoma (BL2) cells display a pattern of sensitivity and caspase-3 dependence similar to calpain inhibition. Treatment of Eμ-myc lymphoma-bearing mice with PD150606 inhibited calpain activity in vivo and induced cell death in these cells as determined by terminal deoxynucleotide transferase-mediated dUTP nick-end labeling staining. Multiple daily treatments resulted in reduced tumor load, particularly in combination with etoposide. In conclusion, calpain is highly elevated in the Eμ-myc lymphoma and calpain inhibition has therapeutic potential.

Protein-based identification of quantitative trait loci associated with malignant transformation in two HER2+ cellular models of breast cancer

BACKGROUND

A contemporary view of the cancer genome reveals extensive rearrangement compared to normal cells. Yet how these genetic alterations translate into specific proteomic changes that underpin acquiring the hallmarks of cancer remains unresolved. The objectives of this study were to quantify alterations in protein expression in two HER2+ cellular models of breast cancer and to infer differentially regulated signaling pathways in these models associated with the hallmarks of cancer.

RESULTS

A proteomic workflow was used to identify proteins in two HER2 positive tumorigenic cell lines (BT474 and SKBR3) that were differentially expressed relative to a normal human mammary epithelial cell line (184A1). A total of 64 (BT474-184A1) and 69 (SKBR3-184A1) proteins were uniquely identified that were differentially expressed by at least 1.5-fold. Pathway inference tools were used to interpret these proteins in terms of functionally enriched pathways in the tumor cell lines. We observed "protein ubiquitination" and "apoptosis signaling" pathways were both enriched in the two breast cancer models while "IGF signaling" and "cell motility" pathways were enriched in BT474 and "amino acid metabolism" were enriched in the SKBR3 cell line.

CONCLUSION

While "protein ubiquitination" and "apoptosis signaling" pathways were common to both the cell lines, the observed patterns of protein expression suggest that the evasion of apoptosis in each tumorigenic cell line occurs via different mechanisms. Evidently, apoptosis is regulated in BT474 via down regulation of Bid and in SKBR3 via up regulation of Calpain-11 as compared to 184A1.

New therapeutic targets in melanoma

Research into molecular targets for drug development in melanoma is starting to bear fruit. Of the drugs tested to date in patients with metastatic melanoma, those that have yielded the best results are V600E BRAF inhibitors in melanomas carrying the V600E mutation; c-kit tyrosine kinase activity inhibitors in melanomas carrying c-kit mutations; and anti-cytotoxic T lymphocyte antigen 4 (CTLA-4) antibodies, which block the mechanisms involved in immune tolerance. Many problems have yet to be resolved in these areas, however, such as the rapid development of resistance to BRAF and c-kit inhibitors and the lack of biomarkers to predict treatment response in the case of CTLA-4 blockers. We review the results of targeted therapy with these and other drugs in metastatic melanoma and discuss what the future holds for this field.

Inhibition of activated receptor tyrosine kinases by Sunitinib induces growth arrest and sensitizes melanoma cells to Bortezomib by blocking Akt pathway

Despite the use of multiple therapeutic strategies, metastatic melanoma remains a challenge for oncologists. Thus, new approaches using combinational treatment may be used to try to improve the prognosis of this disease. In this report, we have analyzed the expression of receptor tyrosine kinases (RTKs) in melanoma specimens and in four metastatic melanoma cell lines. Both melanoma specimens and cell lines expressed RTKs, suggesting that they may represent eventual targets for multitargeted tyrosine kinase inhibitor, Suntinib. Sunitinib reduced the proliferation of two melanoma cell lines (M16 and M17) and increased apoptosis in one of them (M16). Moreover, the two metastatic melanoma cell lines harbored an activated receptor (PDGFRα and VEGFR, respectively), and Sunitinib suppressed the phosphorylation of the RTKs and their downstream targets Akt and ribosomal protein S6, in these two cell lines. Similar results were obtained when either PDGFRα or VEGFR2 expression was silenced by lentiviral-mediated short-hairpin RNA delivery in M16 and M17, respectively. To evaluate the interaction between Sunitinib and Bortezomib, median dose effect analysis using MTT assay was performed, and combination index was calculated. Bortezomib synergistically enhanced the Sunitinib-induced growth arrest in Sunitinib-sensitive cells (combination index < 1). Moreover, LY294002, a PI3K inhibitor, sensitized melanoma cells to Bortezomib treatment, suggesting that downregulation of phospho-Akt by Sunitinib mediates the synergy obtained by Bortezomib + Sunitinib cotreatment. Altogether, our results suggest that melanoma cells harboring an activated RTK may be clinically responsive to pharmacologic RTK inhibition by Sunitinib, and a strategy combining Sunitinib and Bortezomib, may provide therapeutic benefit.

The calpain system and cancer

The calpains are a conserved family of cysteine proteinases that catalyse the controlled proteolysis of many specific substrates. Calpain activity is implicated in several fundamental physiological processes, including cytoskeletal remodelling, cellular signalling, apoptosis and cell survival. Calpain expression is altered during tumorigenesis, and the proteolysis of numerous substrates, such as inhibitors of nuclear factor-κB (IκB), focal adhesion proteins (including, focal adhesion kinase and talin) and proto-oncogenes (for example, MYC), has been implicated in tumour pathogenesis. Recent evidence indicates that the increased expression of certain family members might influence the response to cancer therapies, providing justification for the development of novel calpain inhibitors.

Diagnostic value and prognostic significance of plasmatic proteasome level in patients with melanoma

Plasmatic proteasome (p-proteasome) also called circulating proteasome has recently been described as a tumor marker. We investigated the diagnostic and prognostic accuracies of p-proteasome levels in a melanoma population classified according to the American Joint Committee on Cancer staging system. Using an ELISA test, we measured p-proteasome levels in 90 patients and 40 controls between March 2003 and March 2008. The subunit composition of p-proteasomes was determined in metastatic melanoma by proteomic analysis. The mean p-proteasome levels were correlated with stages (P < 0.0001; r(S) = 0.664). They were significantly higher in patients with stage IV and stage III with lymph node metastasis (9187 ± 1294 and 5091 ± 454 ng/ml, respectively) compared to controls (2535 ± 187 ng/ml; P < 0.001), to stage I/II (2864 ± 166 ng/ml; P < 0.001) and to stage III after curative lymphadenectomy (2859 ± 271 ng/ml; P < 0.001). The diagnostic accuracy of p-proteasome was evaluated by receiver operating characteristic analysis. With a cut-off of 4300 ng/ml, diagnostic specificity and sensitivity of p-proteasome for regional or visceral metastases were respectively 96.3% and 72.2%. In univariate analysis, high p-proteasome levels (>4300 ng/ml) were significantly correlated with an increased risk of progression [hazard ratio (HR) = 7.34; 95% CI 3.54-15.21, P < 0.0001] and a risk of death (HR = 5.92; 95% CI 2.84-12.33, P < 0.0001). In multivariate analysis, high p-proteasome levels were correlated with a poorer clinical outcome in the subgroup analysis limited to patients with disease stages I, II and III. Proteomic analysis confirmed the presence of all proteasome and immunoproteasome subunits. Taken together, these results indicate that p-proteasomes are a new marker for metastatic dissemination in patients with melanoma.

Inhibition of nuclear factor kappa B transcription activity drives a synergistic effect of pyrrolidine dithiocarbamate and cisplatin for treatment of renal cell carcinoma

One of the impeding factors in the effective treatment of metastatic renal cell carcinoma (RCC) is their intrinsic and acquired resistance to chemotherapeutics. Many studies have shown that drug resistance, at least in part, is mediated by the upregulation of anti-apoptotic (Bcl-2) and multidrug resistance molecules (MDR-1 and MRP-1) by the transcription factor nuclear factor kappa B (NF-kappaB). Combining NF-kappaB inhibitors with conventional chemotherapeutics could overcome resistance of cancer cells. In this study, we examined the synergistic effect of pyrrolidine dithiocarbamate (PDTC), a NF-kappaB inhibitor, and cisplatin, on two human metastatic RCC cell lines ACHN and SN12K1. Individual non-toxic concentrations of PDTC and cisplatin, when combined, synergistically induced a significant increase in apoptosis of the two RCC cell lines. In ACHN cells, the groups with nuclear translocation of NF-kappaB showed resistance to apoptosis, but in SN12K1 cells, the groups with NF-kappaB translocation were susceptible to apoptosis. The combination treatment significantly decreased the transcription activity of all NF-kappaB subunits in both cell lines. Anti-apoptotic proteins Bcl-2 and Bcl-(XL) were significantly decreased in the combination therapy group of both cell lines, but MDR-1 was decreased only in the ACHN cells. No changes in MRP-1 were observed in any of the treatment groups. The results demonstrate the potential of PDTC to be an adjunct therapeutic agent. The major mechanism of the synergistic effect appears to be mediated by the inhibition of transcription activity of NF-kappaB rather than its expression, and the resultant decrease in the anti-apoptotic proteins Bcl-2 and Bcl-(XL).

BSc2118 is a novel proteasome inhibitor with activity against multiple myeloma

OBJECTIVES

The ubiquitin-proteasome system emerged as a new therapeutic target in cancer treatment. The purpose of this study was to elucidate the effects of the novel proteasome inhibitor BSc2118 on t(4;14) positive and negative multiple myeloma (MM) cells and normal peripheral blood mononuclear cells (PBMNC).

METHODS

Human MM cell lines OPM-2, RPMI-8226, and U266 and primary MM cells from bone marrow aspirates were exposed to BSc2118. Cytotoxicity levels were evaluated using the MTT-test. BSc2118-induced apoptosis was analyzed by annexin-V assay. Further methods used included proteasomal activity determination, cell cycle analysis, western blot, and transcription factor assays.

RESULTS

In OPM-2, RPMI-8226, U266 cell lines and primary MM cells, BSc2118 caused dose-dependent growth inhibitory effects. After 48 h, dose-dependent apoptosis occurred both in cell lines and primary myeloma cells irrespective of t(4;14). A significant G2-M cell cycle arrest occurred after 24 h. Furthermore, we observed a marked inhibition of intracellular proteasome activity, an increase in intracellular p21 levels, and an inhibition of NF-kappaB activation. The toxicity against PBMNC remained low, suggesting a broad therapeutic range of this agent.

CONCLUSION

Taken together, BSc2118 shows significant antimyeloma activity and may be considered as a promising agent in cancer drug development.

Proteasome inhibition: a new therapeutic strategy to cancer treatment

The ubiquitin-proteasome system is a major pathway for protein degradation. Targeting this pathway using proteasome inhibitors represents a novel approach for the treatment of cancer. Proteasome inhibitors lower cell proliferation and induce apoptosis in solid and hematologic malignancies through multiple mechanisms, including stabilization of cell cycle regulators and pro-apoptotic factors, stimulation of bone morphogenetic protein signaling, inhibition of protein translation, and sensitization to ligand-induced apoptosis. In this connection, proteasome inhibition activates macroautophagy, a compensatory protein degradation system, as well as other pro-survival signaling pathways. Inhibition of these auto-protective responses sensitizes cancer cells to the anti-proliferative effects of proteasome inhibitors.

Calpain regulates sensitivity to trastuzumab and survival in HER2-positive breast cancer

Resistance to anti-HER2 (human epithelial growth factor receptor 2) trastuzumab therapy occurs commonly in HER2-positive breast cancer and involves overactivation of HER2 and/or AKT1. Using the model of trastuzumab-sensitive or trastuzumab-resistant HER2-positive cells with wild-type PTEN, negative regulator of AKT1, we explore the involvement of cysteine protease calpain in mechanisms of trastuzumab resistance. Overexpression of calpain1 or activation of endogenous calpain during adhesion or trastuzumab treatment of trastuzumab-sensitive cells induces cleavage of cytoplasmic domains of HER2/phospho-HER2; cleavage occurs in HER2-positive tumors. Expression of the catalytically inactive mutant of calpain1 reduces the cleavage to enhance the activity of HER2, inactivates PTEN to enhance the activation of AKT1, induces desensitization to trastuzumab and promotes survival of trastuzumab-sensitive cells. In the model of trastuzumab resistance, constitutive overactivation of HER2 and AKT1 correlates with reduced activation of calpain. Moreover, inhibitors of the catalytic site of calpain reduce the increase in constitutive activity of AKT1 and survival of trastuzumab-resistant cells selectively. Together, by regulating the activation of HER2 and PTEN/AKT1, calpain regulates trastuzumab sensitivity and survival, and the deregulation of the activation of calpain promotes trastuzumab resistance. Trastuzumab-resistant cells activate AKT1 in a mechanism dependent on the residual calpain activity, inhibition of which restores trastuzumab sensitivity and rescues resistance. These data identify calpain as a new therapeutic target in HER2-positive breast cancer.

Proteasome inhibition potentiates antitumor effects of photodynamic therapy in mice through induction of endoplasmic reticulum stress and unfolded protein response

Photodynamic therapy (PDT) is an approved therapeutic procedure that exerts cytotoxic activity toward tumor cells by inducing production of reactive oxygen species such as singlet oxygen. PDT leads to oxidative damage of cellular macromolecules, including proteins that undergo multiple modifications such as fragmentation, cross-linking, and carbonylation that result in protein unfolding and aggregation. Because the major mechanism for elimination of carbonylated proteins is their degradation by proteasomes, we hypothesized that a combination of PDT with proteasome inhibitors might lead to accumulation of carbonylated proteins in endoplasmic reticulum (ER), aggravated ER stress, and potentiated cytotoxicity toward tumor cells. We observed that Photofrin-mediated PDT leads to robust carbonylation of cellular proteins and induction of unfolded protein response. Pretreatment of tumor cells with three different proteasome inhibitors, including bortezomib, MG132, and PSI, gave increased accumulation of carbonylated and ubiquitinated proteins in PDT-treated cells. Proteasome inhibitors effectively sensitized tumor cells of murine (EMT6 and C-26) as well as human (HeLa) origin to PDT-mediated cytotoxicity. Significant retardation of tumor growth with 60% to 100% complete responses was observed in vivo in two different murine tumor models (EMT6 and C-26) when PDT was combined with either bortezomib or PSI. Altogether, these observations indicate that combination of PDT with proteasome inhibitors leads to potentiated antitumor effects. The results of these studies are of immediate clinical application because bortezomib is a clinically approved drug that undergoes extensive clinical evaluations for the treatment of solid tumors.

Targeted inhibition of the immunoproteasome is a potent strategy against models of multiple myeloma that overcomes resistance to conventional drugs and nonspecific proteasome inhibitors

Proteasome inhibition is a validated strategy for therapy of multiple myeloma, but this disease remains challenging as relapses are common, and often associated with increasing chemoresistance. Moreover, nonspecific proteasome inhibitors such as bortezomib can induce peripheral neuropathy and other toxicities that may compromise the ability to deliver therapy at full doses, thereby decreasing efficacy. One novel approach may be to target the immunoproteasome, a proteasomal variant found predominantly in cells of hematopoietic origin that differs from the constitutive proteasome found in most other cell types. Using purified preparations of constitutive and immunoproteasomes, we screened a rationally designed series of peptidyl-aldehydes and identified several with relative specificity for the immunoproteasome. The most potent immunoproteasome-specific inhibitor, IPSI-001, preferentially targeted the beta1(i) subunit of the immunoproteasome in vitro and in cellulo in a dose-dependent manner. This agent induced accumulation of ubiquitin-protein conjugates, proapoptotic proteins, and activated caspase-mediated apoptosis. IPSI-001 potently inhibited proliferation in myeloma patient samples and other hematologic malignancies. Importantly, IPSI-001 was able to overcome conventional and novel drug resistance, including resistance to bortezomib. These findings provide a rationale for the translation of IPSIs to the clinic, where they may provide antimyeloma activity with greater specificity and less toxicity than current inhibitors.

Effect of proteasome inhibitors on proliferation and apoptosis of human cutaneous melanoma-derived cell lines

BACKGROUND

Cutaneous malignant melanoma is an aggressive type of skin cancer which causes disproportionate mortality in young and middle-aged adults. Once disseminated, melanoma can be considered an incurable disease, highly resistant to standard antineoplastic treatment, such as chemotherapy or radiation therapy. The proteasome represents a novel target for cancer therapy that can potentially be used in melanoma.

OBJECTIVES

To assess the effect of four structurally different proteasome inhibitors on human cutaneous melanoma-derived cell lines.

METHODS

Sixteen human cutaneous melanoma-derived cell lines which are original were obtained from patients who were treated by two of the authors. Cells were cultured, exposed to proteasome inhibitors (bortezomib, ALLN, MG-132 and epoxomicin) and then assayed for cell cycle and cell death analyses.

RESULTS

Proteasome inhibitors inhibited the in vitro growth of melanoma cells, and this effect was due to a reduction in cell proliferation rate and an induction of both caspase-dependent and caspase-independent cell death. Moreover, release of apoptosis-inducing factor was observed in the presence of the broad-specificity caspase inhibitor BAF (Boc-D-fmk). In addition, the four different proteasome inhibitors induced caspase 2 processing.

CONCLUSIONS

This study provides information regarding the in vitro effects of proteasome inhibitors on melanoma cell lines, and the molecular mechanisms involved. It also gives support to the future use of such inhibitors in the treatment of patients with melanoma, either administered alone or in combination with other drugs.

Interferon-gamma sensitizes hepatitis B virus-expressing hepatocarcinoma cells to 5-fluorouracil through inhibition of hepatitis B virus-mediated nuclear factor-kappaB activation

Nuclear factor (NF)-kappaB is important for immune responses and cell survival; however, abnormal activation of NF-kappaB is linked with many types of diseases, including hepatocellular carcinoma (HCC). Our previous report indicated that hepatitis B virus (HBV) induces NF-kappaB activation through NF-kappaB-inducing kinase (NIK), and this can be blocked specifically by interferon (IFN)-gamma. In the present study, we report that HBV expression in HCC cell lines induces drug resistance against 5-fluorouracil (5-FU). This drug resistance was abolished by inhibition of NF-kappaB activation through small interfering RNA-mediated NIK 'knockdown' and IFN-gamma treatment. In addition to the reduced NF-kappaB activation and drug resistance, the upregulated growth arrest- and DNA damage-inducible protein 45beta (Gadd45beta) in HBV-expressing HCC cell lines was downregulated by the small interfering RNA-mediated NIK knockdown and IFN-gamma treatment. The overexpression of Gadd45beta in HCC cell lines also induces drug resistance against 5-FU. Based on our data, we suggest that IFN-gamma treatment might be helpful for chemotherapy in HBV-integrated HCC through inhibition of the NIK-mediated NF-kappaB activation and downregulation of the NF-kappaB target gene Gadd45beta.