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Bromodomain-containing protein 9 (BRD9), an essential component of the SWI/SNF chromatin remodeling complex termed ncBAF, has been established as a therapeutic target in a subset of sarcomas and leukemias. Here, we used novel small molecule inhibitors and degraders along with RNA interference to assess the dependency on BRD9 in the context of diverse hematological malignancies, including acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL), and multiple myeloma (MM) model systems. Following depletion of BRD9 protein, AML cells undergo terminal differentiation, whereas apoptosis was more prominent in ALL and MM. RNA-seq analysis of acute leukemia and MM cells revealed both unique and common signaling pathways affected by BRD9 degradation, with common pathways including those associated with regulation of inflammation, cell adhesion, DNA repair and cell cycle progression. Degradation of BRD9 potentiated the effects of several chemotherapeutic agents and targeted therapies against AML, ALL, and MM. Our findings support further development of therapeutic targeting of BRD9, alone or combined with other agents, as a novel strategy for acute leukemias and MM., (© 2022. The Author(s).)

KRAS is a frequent oncogenic driver in solid tumors, including non-small cell lung cancer (NSCLC). It was previously thought to be an "undruggable" target due to the lack of deep binding pockets for specific small-molecule inhibitors. A better understanding of the mechanisms that drive KRAS transformation, improved KRAS-targeted drugs, and immunological approaches that aim at yielding immune responses against KRAS neoantigens have sparked a race for approved therapies. Few treatments are available for KRAS mutant NSCLC patients, and several approaches are being tested in clinicals trials to fill this void. Here, we review promising therapeutics tested for KRAS mutant NSCLC., Competing Interests: R.S. reports speakers’ bureau participation with AstraZeneca and Merck and is an advisory board member for Janssen and Novartis. R.P., I.M., A.N., and M.S. declare no competing interests., (© 2020 The Author(s).)

The post‑translational modification of proteins by ubiquitinating enzymes plays a central role in a number of cellular functions, such as cell proteolysis, DNA repair, and cell signaling and communication. Deubiquitinating enzymes (DUBs) disassemble ubiquitin chains and remove ubiquitin moieties from proteins. Targeting DUBs in cancer models has revealed an important role for these enzymes in tumorigenesis, and they therefore have emerged as attractive therapeutic targets. In the present study, the effects of three DUB inhibitors, PR‑619, RA‑9 and LDN‑91946, on a non‑small cell lung cancer cell line (A549) and a mesothelioma cell line (H2373) were investigated. PR‑619 significantly inhibited cell adhesion and the proliferation of both cell lines. RA‑9 exerted an inhibitory effect on the adhesion and proliferation of H2373 cells, whereas it had no effect on A549 cells. Notably, however, while PR‑619 attenuated the proliferation of both cell lines, it exerted an opposite effect on cell motility; in the case of A549 cells, there was a significant increase in cell motility, while for the H2373 cells, there was a significant decrease. Furthermore, protein phosphorylation kinetic analyses revealed that the effects were cell line‑specific. In H2373 cells, the phosphorylation of only one peptide corresponding to the P85A protein was significantly affected, and while LDN‑91946 treatment increased phosphorylation, treatment with RA‑9 or PR‑619 decreased its phosphorylation compared to the DMSO control. By contrast, in the case of A549 cells, the phosphorylation of 21 peptides was significantly affected by the same compounds. In light of the potential for the negative side‑effects of DUB inhibition, such as increased cancer cell motility, the data presented herein underscore the dire need for the development of specific DUB inhibitors and to elucidate the individual role of DUB family members in cancer biology before they can be specifically pharmacologically targeted.

Mutations in two type-3 receptor tyrosine kinases (RTKs), KIT and FLT3, are common in both acute myeloid leukaemia (AML) and systemic mastocytosis (SM) and lead to hyperactivation of key signalling pathways. A large number of tyrosine kinase inhibitors (TKIs) have been developed that target either FLT3 or KIT and significant clinical benefit has been demonstrated in multiple clinical trials. Given the structural similarity of FLT3 and KIT, it is not surprising that some of these TKIs inhibit both of these receptors. This is typified by midostaurin, which has been approved by the US Food and Drug Administration for mutant FLT3-positive AML and for KIT D816V-positive SM. Here, we compare the in vitro activities of the clinically available FLT3 and KIT inhibitors with those of midostaurin against a panel of cells expressing a variety of oncogenic FLT3 or KIT receptors, including wild-type (wt) FLT3, FLT3-internal tandem duplication (ITD), FLT3 D835Y, the resistance mutant FLT3-ITD+ F691L, KIT D816V, and KIT N822K. We also examined the effects of these inhibitors in vitro and in vivo on cells expressing mutations in c-CBL found in AML that result in hypersensitization of RTKs, such as FLT3 and KIT. The results show a wide spectrum of activity of these various mutations to these clinically available TKIs., (© 2019 British Society for Haematology and John Wiley & Sons Ltd.)

Purpose: Recent studies have emphasized a key role for the anti-apoptotic Bcl-2 family member Mcl-1 in conferring tumor cell survival and drug resistance in breast cancer (BC). Mcl-1 inhibitors, such as the BH3-mimetic EU-5346, therefore represent an exciting new class of targeting agents and are a current focus of widespread cancer-drug development efforts., Methods: ONCOMINE analysis was utilized to compare expression profiles of Bcl-2 family members across all major BC subgroups. Potential toxicities of EU-5346 were evaluated using iPS-generated cardiomyocytes, blood cells and astrocytes. The anti-BC cell activity of EU-5346-based therapies was evaluated using [ 3 H]-thymidine uptake and spheroid-forming assays as well as immunoblotting and the Chou-Talalay method. Protein level-based activity of EU-5346, the specific anti-Bcl-2 inhibitor ABT-199 and the specific anti-Bcl-x L inhibitor WEHI-539 was verified in Mcl-1 Δ/null versus Mcl-1 wt/wt MEFs., Results: We previously demonstrated significant anti-tumor activity of EU-5346 in all BC subtypes. Our present results go further and suggest that EU-5346 may induce limited adverse events such as cardiotoxicity, hematotoxicity, and neurotoxicity, frequently observed with other BH3 mimetics. As demonstrated by our mathematical scoring model, the prediction of EU-5643-induced IC 50 not only relies on the protein level of Mcl-1 but also on Bak, Bim, and Noxa. Synergistic anti-BC activity of low-dose EU-5346 with the BH3 mimetics ABT-199 or WEHI-539 was observed only in those BC cells expressing Bcl-2 or Bcl-x L , respectively. Similarly, when combined with tamoxifen or trastuzumab, low-dose EU-5346 induced significant anti-BC activity in hormone receptor positive or Her2-positive BC cells, respectively. Finally, EU-5346 in combination with paclitaxel induced synergistic anti-BC activity in both paclitaxel-sensitive and paclitaxel-resistant TNBC cells., Conclusion: These data strongly support the further clinical development of EU-5346 to improve BC patient survival.

Oncogenic forms of the kinase FLT3 are important therapeutic targets in acute myeloid leukemia (AML); however, clinical responses to small-molecule kinase inhibitors are short-lived as a result of the rapid emergence of resistance due to point mutations or compensatory increases in FLT3 expression. We sought to develop a complementary pharmacological approach whereby proteasome-mediated FLT3 degradation could be promoted by inhibitors of the deubiquitinating enzymes (DUBs) responsible for cleaving ubiquitin from FLT3. Because the relevant DUBs for FLT3 are not known, we assembled a focused library of most reported small-molecule DUB inhibitors and carried out a cellular phenotypic screen to identify compounds that could induce the degradation of oncogenic FLT3. Subsequent target deconvolution efforts allowed us to identify USP10 as the critical DUB required to stabilize FLT3. Targeting of USP10 showed efficacy in preclinical models of mutant-FLT3 AML, including cell lines, primary patient specimens and mouse models of oncogenic-FLT3-driven leukemia.

The tumor suppressor p53 is a key regulator of apoptosis and functions upstream in the apoptotic cascade by both indirectly and directly regulating Bcl-2 family proteins. In cells expressing wild-type (WT) p53, the HDM2 protein binds to p53 and blocks its activity. Inhibition of HDM2:p53 interaction activates p53 and causes apoptosis or cell-cycle arrest. Here, we investigated the ability of the novel HDM2 inhibitor CGM097 to potently and selectively kill WT p53-expressing AML cells. The antileukemic effects of CGM097 were studied using cell-based proliferation assays (human AML cell lines, primary AML patient cells, and normal bone marrow samples), apoptosis, and cell-cycle assays, ELISA, immunoblotting, and an AML patient-derived in vivo mouse model. CGM097 potently and selectively inhibited the proliferation of human AML cell lines and the majority of primary AML cells expressing WT p53, but not mutant p53, in a target-specific manner. Several patient samples that harbored mutant p53 were comparatively unresponsive to CGM097. Synergy was observed when CGM097 was combined with FLT3 inhibition against oncogenic FLT3-expressing cells cultured both in the absence as well as the presence of cytoprotective stromal-secreted cytokines, as well as when combined with MEK inhibition in cells with activated MAPK signaling. Finally, CGM097 was effective in reducing leukemia burden in vivo. These data suggest that CGM097 is a promising treatment for AML characterized as harboring WT p53 as a single agent, as well as in combination with other therapies targeting oncogene-activated pathways that drive AML., (©2015 American Association for Cancer Research.)

Myeloid cell leukemia-1 (Mcl-1, HGNC: 6943), a pro-survival member of the Bcl-2 family, plays a crucial role in Multiple Myeloma (MM) pathogenesis and drug resistance, thus representing a promising therapeutic target in MM. A novel strategy to inhibit Mcl-1 activity is the induction of ubiquitin-independent Mcl-1 degradation. Our own and other previous studies have demonstrated caspase-dependent generation of a 28kDa Mcl-1 fragment, Mcl-1(128-350), which inhibits MM cell proliferation and survival. Here, we show that similar to bortezomib, the novel proteasome inhibitors carfilzomib and ixazomib, as well as staurosporine and adaphostin, induce the generation of Mcl-1(128-350) in MM cells. Next, the molecular sequelae downstream of Mcl-1(128-350), which mediate its pro-apoptotic activity, were delineated. Surprisingly, we observed nuclear accumulation of drug-induced or exogenously overexpressed Mcl-1(128-350), followed by elevated mRNA and protein levels of c-Jun, as well as enhanced AP-1 reporter activity. Moreover, drug-induced AP-1 activity was blocked after introducing a point mutation into the highly conserved Mcl-1 caspase-cleavage site Asp127, but not Asp157. Consequently, drug-triggered cell death was significantly decreased in MM cells transfected with Mcl-1 D127A, but not with Mcl-1 D157A. Consistent with these data, treatment with bortezomib triggered c-Jun upregulation followed by apoptosis in Mcl-1(wt/wt), but not Mcl-1(Δ/null) murine embryonic fibroblasts (MEFs). Transfection of a plasmid carrying Mcl-1(wt) into Mcl-1(Δ/null) MEFs restored bortezomib-induced Mcl-1 fragmentation, c-Jun upregulation and AP-1 reporter activity. Finally, our data indicate that drug-induced generation of a pro-apoptotic Mcl-1 fragment followed by c-Jun upregulation may also be a novel therapeutic approach in other tumor entities., (Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.)

Cancers of the head and neck and of the lung are associated with high morbidity and mortality rates that have remained relatively unchanged for more than 3 decades, despite advances in radiation therapies and chemotherapies over the same time. It is generally believed that the efficacy of standard therapy regimens has reached a plateau for these cancers. The discovery of specific aberrant molecular signaling pathways in solid tumors has afforded promising new directions for newer "targeted" cancer therapeutics. Among these, the epidermal growth factor receptor (EGFR) shows promise as a therapeutic target. Clinical studies have demonstrated that this targeted approach provides clinically meaningful benefit. This article reviews EGFR-targeted therapies in use and in development, with a focus on the role of EGFR in the pathophysiology of head and neck and lung cancer, and new concepts being investigated to improve outcomes with these agents.

Receptor tyrosine kinases have come to fruition as therapeutic targets in a variety of malignancies. In this group of targets, the c-Met receptor tyrosine kinase plays an important role in increased cell growth, reduced apoptosis, altered cytoskeletal function, increased metastasis, and other biologic changes. The ligand for c-Met is hepatocyte growth factor (HGF), also known as scatter factor. Met is overexpressed and mutated in a variety of malignancies, among which germline mutations are of particular interest. Most mutations of Met have been found in the juxtamembrane, the tyrosine kinase, and the semaphorin domain. Met gain-of-function mutations lead to deregulated or prolonged tyrosine kinase activity, which is instrumental to its transforming activity. This review summarizes the biologic functions regulated by Met and its structural requirements as well as related developments in targeted therapy. Treatment approaches, including antagonism of HGF binding to Met, targeting of RNA and the Met protein, and inhibition of the tyrosine kinase domain of Met, are highlighted. Targeting of the HGF/Met pathway, alone or in combination with standard therapies, is likely to improve current therapies in Met-dependent malignancies.

Imatinib mesylate (Gleevec) was developed as the first molecularly targeted therapy that specifically inhibits the BCR-ABL tyrosine kinase activity in patients with Philadelphia chromosome positive (Ph+) chronic myeloid leukemia (CML). Due to its excellent hematologic and cytogenetic responses, particularly in patients with chronic phase CML, imatinib has moved towards first-line treatment for newly diagnosed CML. Nevertheless, resistance to the drug has been frequently reported and is attributed to the fact that transformation of hematopoietic stem cells by BCR-ABL is associated with genomic instability. Point mutations within the ABL tyrosine kinase of the BCR-ABL oncoprotein are the major cause of resistance, though overexpression of the BCR-ABL protein and novel acquired cytogenetic aberrations have also been reported. A variety of strategies derived from structural studies of the ABL-imatinib complex have been developed, resulting in the design of novel ABL inhibitors, including AMN107, BMS-354825, ON012380 and others. The major goal of these efforts is to create new drugs that are more potent than imatinib and/or more effective against imatinib-resistant BCR-ABL clones. Some of these drugs have already been successfully tested in preclinical studies where they show promising results. Additional approaches are geared towards targeting the expression or stability of the BCR-ABL kinase itself or targeting signaling pathways that are chronically activated and required for transformation. In this review, we will discuss the underlying mechanisms of resistance to imatinib and novel targeted approaches to overcome imatinib resistance in CML.

We recently demonstrated that caveolae, vesicular flask-shaped invaginations of the plasma membrane, represent novel therapeutic targets in multiple myeloma. In the present study, we demonstrate that vascular endothelial growth factor (VEGF) triggers Src-dependent phosphorylation of caveolin-1, which is required for p130(Cas) phosphorylation and multiple myeloma cell migration. Conversely, depletion of caveolin-1 by antisense methodology abrogates p130(Cas) phosphorylation and VEGF-triggered multiple myeloma cell migration. The proteasome inhibitor bortezomib both inhibited VEGF-triggered caveolin-1 phosphorylation and markedly decreased caveolin-1 expression. Consequently, bortezomib inhibited VEGF-induced multiple myeloma cell migration. Bortezomib also decreased VEGF secretion in the bone marrow microenvironment and inhibited VEGF-triggered tyrosine phosphorylation of caveolin-1, migration, and survival in human umbilical vascular endothelial cells. Taken together, these studies demonstrate the requirement of caveolae for VEGF-triggered multiple myeloma cell migration and identify caveolin-1 in multiple myeloma cells and human umbilical vascular endothelial cells as a molecular target of bortezomib.

The Kit receptor tyrosine kinase is a transmembrane receptor that is expressed in a variety of different tissues and mediates pleiotropic biological effects through its ligand stem cell factor (SCF). Sporadic mutations of Kit as well as autocrine/paracrine activation mechanisms of the SCF/Kit pathway have been implicated in a variety of malignancies, where its primary contribution to metastases is in enhancing tumor growth and reducing apoptosis. For example, Kit is frequently mutated and activated in gastrointestinal stromal tumors (GISTs) and there is ligand-mediated activation of Kit in some lung cancers. Kit is a convenient target in Kit-induced tumors and inhibition of this receptor with the small molecule drug Gleevec (imatinib mesylate, STI571) in GIST has shown dramatic efficacy. Unfortunately, past experience has demonstrated that chemotherapy of cancers with a single drug often leads to resistance of the cancer. Further understanding of the molecular mechanisms underlying Kit-mediated transformation is therefore important and may lead to the identification of further novel drug targets. These Kit-specific signaling pathways may then be targeted to overcome potential drug resistance. This review will focus on our understanding of the molecular mechanisms involved in transformation by Kit. The potential mechanisms by which Kit induces cellular transformation are described. We will also discuss the role and expression of Kit in various malignancies. Ultimately, the understanding of c-Kit biology, biochemistry, and mutational analysis will lead to better therapeutics.