Targeting MET kinase with the small-molecule inhibitor amuvatinib induces cytotoxicity in primary myeloma cells and cell lines

MnO2-Mediated Oxidative Cyclization of "Formal" Schiff's Bases: Easy Access to Diverse Naphthofuro-Annulated Triazines

A different type of MnO₂-induced oxidative cyclization of dihydrotriazines has been developed. These dihydrotriazines are considered as a "formal" Schiff's base. This method provided easy access to naphthofuro-fused triazine via the C-C/C-O oxidative coupling reaction. The reaction sequence comprised the nucleophilic addition of 2-naphthol or phenol to 1,2,4-triazine, followed by oxidative cyclization. The scope and limitations of this novel coupling reaction have been investigated. Further application of the synthesized compound has been demonstrated by synthesizing carbazole-substituted benzofuro-fused triazines. The scalability of the reaction was demonstrated at a 40 mmol load. The mechanistic study strongly suggests that this reaction proceeds through the formation of an O-coordinated manganese complex.

The HGF/Met/NF-κB Pathway Regulates RANKL Expression in Osteoblasts and Bone Marrow Stromal Cells

Multiple myeloma (MM)-induced bone disease occurs through hyperactivation of osteoclasts by several factors secreted by MM cells. MM cell-secreted factors induce osteoclast differentiation and activation via direct and indirect actions including enhanced expression of receptor activator of nuclear factor κB ligand (RANKL) in osteoblasts and bone marrow stromal cells (BMSCs). Hepatocyte growth factor (HGF) is elevated in MM patients and is associated with MM-induced bone disease, although the mechanism by which HGF promotes bone disease remains unclear. In the present study, we demonstrated that HGF induces RANKL expression in osteoblasts and BMSCs, and investigated the mechanism of induction. We found that HGF and MM cell supernatants induced RANKL expression in ST2 cells, MC3T3-E1 cells, and mouse BMSCs. In addition, HGF increased phosphorylation of Met and nuclear factor κB (NF-κB) in ST2 cells, MC3T3-E1 cells, or mouse BMSCs. Moreover, Met and NF-κB inhibitors suppressed HGF-induced RANKL expression in ST2 cells, MC3T3-E1 cells, and mouse BMSCs. These results indicated that HGF promotes RANKL expression in osteoblasts and BMSCs via the Met/NF-κB signaling pathway, and Met and NF-κB inhibitors suppressed HGF-induced RANKL expression. Our findings suggest that Met and NF-κB inhibitors are potentially useful in mitigating MM-induced bone disease in patients expressing high levels of HGF.

High-quality quantum dots for multiplexed bioimaging: A critical review

Bioimaging done using two or more fluorophores possessing different emission wavelengths can be termed as a multicolor/multiplexed bioimaging technique. Traditionally, images are captured sequentially using multiple fluorophores having specific excitation and emission. For this purpose, multifunctional nanoprobes, such as organic fluorophores, metallic nanoparticles, semiconductor quantum dots, and carbon dots (CDs) are used. Among these fluorophores, quantum dots (QDs) have emerged as an ideal probe for multiplexed bioimaging due to their unique property of size tunable emission. However, the usage of quantum dots in bioimaging is limited due to their toxicity. Furthermore, the reproducibility of optical properties is cynical. These desirable properties, along with enhancement in quantum efficiency, photostability, fluorescence lifetime, etc. can be achieved by stringent control over synthesis parameters. This review summarizes the desirable properties and synthesis methods of such superior QDs followed by their application in multiplexed imaging.

Kinase inhibitors as potential agents in the treatment of multiple myeloma

Recent years have witnessed a dramatic increase in the number of therapeutic options available for the treatment of multiple myeloma (MM) - from immunomodulating agents to proteasome inhibitors to histone deacetylase (HDAC) inhibitors and, most recently, monoclonal antibodies. Used in conjunction with autologous hematopoietic stem cell transplantation, these modalities have nearly doubled the disease's five-year survival rate over the last three decades to about 50%. In spite of these advances, MM still is considered incurable as resistance and relapse are common. While small molecule protein kinase inhibitors have made inroads in the therapy of a number of cancers, to date their application to MM has been less than successful. Focusing on MM, this review examines the roles played by a number of kinases in driving the malignant state and the rationale for target development in the design of a number of kinase inhibitors that have demonstrated anti-myeloma activity in both in vitro and in vivo xenograph models, as well as those that have entered clinical trials. Among the targets and their inhibitors examined are receptor and non-receptor tyrosine kinases, cell cycle control kinases, the PI3K/AKT/mTOR pathway kinases, protein kinase C, mitogen-activated protein kinase, glycogen synthase kinase, casein kinase, integrin-linked kinase, sphingosine kinase, and kinases involved in the unfolded protein response.

Phase II study of the c-MET inhibitor tivantinib (ARQ 197) in patients with relapsed or relapsed/refractory multiple myeloma

The hepatocyte growth factor/c-MET pathway has been implicated in the pathobiology of multiple myeloma, and c-MET inhibitors induce myeloma cell apoptosis, suggesting that they could be useful clinically. We conducted a phase II study with the c-MET inhibitor tivantinib in patients with relapsed, or relapsed and refractory myeloma whose disease had progressed after one to four prior therapies. Tivantinib, 360 mg orally per dose, was administered twice daily continuously over a 4-week treatment cycle without a cap on the number of allowed cycles, barring undue toxicities or disease progression. Primary objectives were to determine the overall response rate and the toxicities of tivantinib in this patient population. Sixteen patients were enrolled in a two-stage design. Notable grade 3 and 4 hematological adverse events were limited to neutropenia in five and four patients, respectively. Nonhematological adverse events of grade 3 or higher included hypertension (in four patients); syncope, infection, and pain (two each); and fatigue, cough, and pulmonary embolism (one each). Four of 11 evaluable patients (36%) had stable disease as their best response, while the remainder showed disease progression. Overall, tivantinib as a single agent did not show promise for unselected relapsed/refractory myeloma patients. However, the ability to achieve stable disease does suggest that combination regimens incorporating targeted inhibitors in patients with c-MET pathway activation could be of interest.

Targeting the pro-survival protein MET with tivantinib (ARQ 197) inhibits growth of multiple myeloma cells

The hepatocyte growth factor (HGF)/MNNG HOS transforming gene (MET) pathway regulates cell growth, survival, and migration. MET is mutated or amplified in several malignancies. In myeloma, MET is not mutated, but patients have high plasma concentrations of HGF, high levels of MET expression, and gene copy number, which are associated with poor prognosis and advanced disease. Our previous studies demonstrated that MET is critical for myeloma cell survival and its knockdown induces apoptosis. In our current study, we tested tivantinib (ARQ 197), a small-molecule pharmacological MET inhibitor. At clinically achievable concentrations, tivantinib induced apoptosis by > 50% in all 12 human myeloma cell lines tested. This biologic response was associated with down-regulation of MET signaling and inhibition of the mitogen-activated protein kinase and phosphoinositide 3-kinase pathways, which are downstream of the HGF/MET axis. Tivantinib was equally effective in inducing apoptosis in myeloma cell lines resistant to standard chemotherapy (melphalan, dexamethasone, bortezomib, and lenalidomide) as well as in cells that were co-cultured with a protective bone marrow microenvironment or with exogenous cytokines. Tivantinib induced apoptosis in CD138 + plasma cells from patients and demonstrated efficacy in a myeloma xenograft mouse model. On the basis of these data, we initiated a clinical trial for relapsed/refractory multiple myeloma (MM). In conclusion, MET inhibitors may be an attractive target-based strategy for the treatment of MM.

Mechanism of QHF-cisplatin against hepatocellular carcinoma in a mouse model

AIM: To study the effects of QHF-cisplatin on H₂₂ hepatocellular carcinoma (HCC) and their mechanisms of action.

METHODS: Sixty BALB/c mice were randomly divided into a model group (n = 48) and a normal control group (n = 12). An HCC xenograft tumor was created by injecting H₂₂ cells directly into the liver parenchyma of the mice. The 48 BALB/c mice in the model group were randomly divided into four groups: QHF, DDP (cisplatin), QHF plus DDP, and model control. The inhibitory effects of these drugs on tumor growth were evaluated by calculating the rate of tumor growth inhibition. The mice were examined by observing their general condition, body weight and survival time. Changes in tumor tissue were observed under an optical microscope. Aspartate aminotransferase (AST), alanine aminotransferase (ALT) and α-fetoprotein (AFP) levels in serum were measured. Hepatocyte growth factor (HGF), c-mesenchymal-epithelial transition (c-Met) factor, phosphorylated (p)-c-Met, p38, p-p38, extracellular signal-regulated kinase (ERK), p-ERK and vascular endothelial growth factor (VEGF) levels were evaluated in tumor and liver tissues using western blotting.

RESULTS: Compared with the DDP group, a lower incidence of toxic reactions and a higher survival time were observed in the QHF plus DDP group. Tumor weight was significantly lower in the QHF, DDP and QHF plus DDP groups than in the model control group (0.24 ± 0.07, 0.18 ± 0.03 and 0.14 ± 0.01 g vs 0.38 ± 0.05 g, respectively), and the differences were statistically significant (P < 0.01). The rate of tumor growth inhibition in the QHF, DDP and QHF plus DDP groups was 38.7%, 52.6% and 63.5%, respectively. AST, ALT and AFP levels in serum were significantly lower in the QHF, DDP and QHF plus DDP groups compared to the model control group (P < 0.05). Similarly, HGF, p-c-Met, p-p38, p-ERK and VEGF levels in tumor tissue were significantly lower in the QHF, DDP and QHF plus DDP groups (P < 0.05).

CONCLUSION: QHF and DDP have an antiangiogenic effect on H₂₂ HCC in mice. QHF inhibits tumor growth via blocking the HGF/c-Met signaling pathway, inhibiting p38, ERK and VEGF signaling.

Targeting executioner procaspase-3 with the procaspase-activating compound B-PAC-1 induces apoptosis in multiple myeloma cells

Multiple myeloma (MM) is a plasma cell neoplasm that has a low apoptotic index. We investigated a new class of small molecules that target the terminal apoptosis pathway, called procaspase activating compounds (PACs), in myeloma cells. PAC agents (PAC-1 and B-PAC-1) convert executioner procaspases (procaspase 3, 6, and 7) to active caspases 3, 6, and 7, which cleave target substrates to induce cellular apoptosis cascade. We hypothesized that targeting this terminal step could overcome survival and drug-resistance signals in myeloma cells and induce programmed cell death. Myeloma cells expressed executioner caspases. Additionally, our studies demonstrated that B-PAC-1 is cytotoxic to chemotherapy-resistant or sensitive myeloma cell lines (n = 7) and primary patient cells (n = 11). Exogenous zinc abrogated B-PAC-1-induced cell demise. Apoptosis induced by B-PAC-1 treatment was similar in the presence or absence of growth-promoting cytokines such as interleukin 6 and hepatocyte growth factor. Presence or absence of antiapoptotic proteins such as BCL-2, BCL-XL, or MCL-1 did not impact B-PAC-1-mediated programmed cell death. Collectively, our data demonstrate the proapoptotic effect of B-PAC-1 in MM and suggest that activating terminal executioner procaspases 3, 6, and 7 bypasses survival and drug-resistance signals in myeloma cells. This novel strategy has the potential to become an effective antimyeloma therapy.

High expression of endoplasmic reticulum chaperone grp94 is a novel molecular hallmark of malignant plasma cells in multiple myeloma

BACKGROUND

Multiple myeloma (MM) is a hematologic malignancy that is characterized by the proliferation of abnormal bone marrow plasma cells (BMPC) and overproduction of immunoglobulin or light chains with evidence of end-organ damage such as bone damage, anemia, hypercalcemia, and renal dysfunction. The pathogenesis of MM is closely linked to dysregulated unfolded protein response (UPR) in the endoplasmic reticulum (ER). Constitutive activation of UPR in mice, as demonstrated by transgenic expression of a master UPR transcription factor XBP1s (a UPR-specific splice variant of X-box binding protein 1), causes myeloma. grp94 (gp96) is a key downstream chaperone in the ER that mediates the UPR as a part of the protein quality control mechanism in the secretory pathway. Our recent study has shown that the persistence of plasma cells as well as the development of myeloma in XBP1s-transgenic mice is critically dependent on grp94. However, the role of grp94 in the initiation and progression of human MM is still unknown.

METHODS

The expression level of grp94 in BMPCs was measured by flow cytometry, real-time RT-PCR, and Western blot analysis. We compared the expression levels of grp94 in BMPCs in a spectrum of patients including MM, monoclonal gammopathy of undetermined significance (MGUS), smoldering MM (SMM), as well as non-plasma cell disorders (NPC).

RESULTS

We found that grp94 was highly expressed in malignant plasma cells in patients with MM, but not in BMPCs in patients with MGUS/SMM and NPC. The expression level of grp94 correlated significantly with CD138 expression level. We also found that the grp94 expression level in BMPCs from International Staging System (ISS) stage III MM patients is higher than those in ISS stage I/II MM patients.

CONCLUSIONS

grp94 is highly expressed in BMPCs in MM, which correlates with the advanced stage of this disease. Our data demonstrated that grp94 is a novel diagnostic and prognostic biomarker. It also positioned grp94 as a promising therapeutic target for MM.

MET/HGF pathway in multiple myeloma: from diagnosis to targeted therapy?

The interaction between neoplastic cells and the microenvironment is critical in several cancers and plays a central role in multiple myeloma. Microenvironmental stimuli support plasma cell proliferation, survival, motility and can determine drug resistance. The network between plasma cells and surrounding cells is also responsible for increasing angiogenesis, unbalancing bone formation and bony lesions. The MET/HGF pathway is a key player in this interaction and has been found to be abnormally active in both malignant plasma cells and surrounding cells. Patients with abnormal MET and/or HGF levels usually have a poor outcome even when treated with novel drugs. This review addresses the role of MET/HGF in the pathogenesis of myeloma and describes the role of MET/HGF signaling as a prognostic factor. The different techniques to detect MET/HGF abnormalities are examined and a description of compounds targeting MET/HGF is also provided.

Amuvatinib has cytotoxic effects against NRAS-mutant melanoma but not BRAF-mutant melanoma

Effective targeted therapy strategies are still lacking for the 15-20% of melanoma patients whose melanomas are driven by oncogenic NRAS. Here, we report on the NRAS-specific behavior of amuvatinib, a kinase inhibitor with activity against c-KIT, Axl, PDGFRα, and Rad51. An analysis of BRAF-mutant and NRAS-mutant melanoma cell lines showed the NRAS-mutant cohort to be enriched for targets of amuvatinib, including Axl, c-KIT, and the Axl ligand Gas6. Increasing concentrations of amuvatinib selectively inhibited the growth of NRAS-mutant, but not BRAF-mutant melanoma cell lines, an effect associated with induction of S-phase and G2/M-phase cell cycle arrest and induction of apoptosis. Mechanistically, amuvatinib was noted to either inhibit Axl, AKT, and MAPK signaling or Axl and AKT signaling and to induce a DNA damage response. In three-dimensional cell culture experiments, amuvatinib was cytotoxic against NRAS-mutant melanoma cell lines. Thus, we show for the first time that amuvatinib has proapoptotic activity against melanoma cell lines, with selectivity observed for those harboring oncogenic NRAS.

The Hepatocyte Growth Factor (HGF)/Met Axis: A Neglected Target in the Treatment of Chronic Myeloproliferative Neoplasms?

Met is the receptor of hepatocyte growth factor (HGF), a cytoprotective cytokine. Disturbing the equilibrium between Met and its ligand may lead to inappropriate cell survival, accumulation of genetic abnormalities and eventually, malignancy. Abnormal activation of the HGF/Met axis is established in solid tumours and in chronic haematological malignancies, including myeloma, acute myeloid leukaemia, chronic myelogenous leukaemia (CML), and myeloproliferative neoplasms (MPNs). The molecular mechanisms potentially responsible for the abnormal activation of HGF/Met pathways are described and discussed. Importantly, inCML and in MPNs, the production of HGF is independent of Bcr-Abl and JAK2V617F, the main molecular markers of these diseases. In vitro studies showed that blocking HGF/Met function with neutralizing antibodies or Met inhibitors significantly impairs the growth of JAK2V617F-mutated cells. With personalised medicine and curative treatment in view, blocking activation of HGF/Met could be a useful addition in the treatment of CML and MPNs for those patients with high HGF/MET expression not controlled by current treatments (Bcr-Abl inhibitors in CML; phlebotomy, hydroxurea, JAK inhibitors in MPNs).

Identification of the source of elevated hepatocyte growth factor levels in multiple myeloma patients

Background

Hepatocyte growth factor (HGF) is a pleiotropic cytokine which can lead to cancer cell proliferation, migration and metastasis. In multiple myeloma (MM) patients it is an abundant component of the bone marrow. HGF levels are elevated in 50% of patients and associated with poor prognosis. Here we aim to investigate its source in myeloma.

Methods

HGF mRNA levels in bone marrow core biopsies from healthy individuals and myeloma patients were quantified by real-time PCR. HGF gene expression profiling in CD138⁺ cells isolated from bone marrow aspirates of healthy individuals and MM patients was performed by microarray analysis. HGF protein concentrations present in peripheral blood of MM patients were measured by enzyme-linked immunosorbent assay (ELISA). Cytogenetic status of CD138⁺ cells was determined by fluorescence in situ hybridization (FISH) and DNA sequencing of the HGF gene promoter. HGF secretion in co-cultures of human myeloma cell lines and bone marrow stromal cells was measured by ELISA.

Results

HGF gene expression profiling in both bone marrow core biopsies and CD138⁺ cells showed elevated HGF mRNA levels in myeloma patients. HGF mRNA levels in biopsies and in myeloma cells correlated. Quantification of HGF protein levels in serum also correlated with HGF mRNA levels in CD138⁺ cells from corresponding patients. Cytogenetic analysis showed myeloma cell clones with HGF copy numbers between 1 and 3 copies. There was no correlation between HGF copy number and HGF mRNA levels. Co-cultivation of the human myeloma cell lines ANBL-6 and JJN3 with bone marrow stromal cells or the HS-5 cell line resulted in a significant increase in secreted HGF.

Conclusions

We here show that in myeloma patients HGF is primarily produced by malignant plasma cells, and that HGF production by these cells might be supported by the bone marrow microenvironment. Considering the fact that elevated HGF serum and plasma levels predict poor prognosis, these findings are of particular importance for patients harbouring a myeloma clone which produces large amounts of HGF.