Selective inhibition of the platelet-derived growth factor signal transduction pathway by a protein-tyrosine kinase inhibitor of the 2-phenylaminopyrimidine class

Tyrosine kinase inhibitors in osteosarcoma: Adapting treatment strategiesa

Osteosarcoma (OS) is an aggressive primary bone malignancy that metastasizes rapidly. The standard of care has changed little over the previous four decades, and survival rates have plateaued. In this context, tyrosine kinase inhibitors (TKIs) emerge as potential treatments. A literature search was conducted to collect data related to receptor tyrosine kinase genetic alterations and expression in OS specimens. Gene amplification and protein expression of these receptors were linked to prognosis and tumor behavior. Relevant TKIs were evaluated as monotherapies and as parts of combination therapies. Certain TKIs, such as apatinib, regorafenib, and cabozantinib, present a potential therapeutic avenue for OS patients, especially when combined with chemotherapy. Producing long-lasting responses and enhancing quality of life remain key goals in OS treatment. To this effect, optimizing the use of TKIs by identifying biomarkers predictive of response and assessing promising TKIs in larger-scale trials to validate the efficacy and safety outcomes relative to these drugs reported in phase II clinical trials. To this effect, it is necessary to identify biomarkers predictive of response to TKIs in larger-scale trials and to validate the efficacy and safety of these drugs reported in phase II clinical trials.

Compounds originating from the edible mushroom Auricularia auricula-judae inhibit tropomyosin receptor kinase B activity

Tropomyosin receptor kinase B (TrkB) serves as a pivotal factor in various cancers. To identify novel natural compounds with TrkB-inhibiting properties, a screening approach was applied using extracts from a collection of wild and cultivated mushroom fruiting bodies, and Ba/F3 cells that ectopically express TrkB (TPR-TrkB). We selected mushroom extracts that selectively inhibited proliferation of the TPR-TrkB cells. We then evaluated the ability of exogenous interleukin 3 to rescue growth inhibition by the selected TrkB-positive extracts. An ethyl acetate extract of Auricularia auricula-judae actively inhibited auto-phosphorylation of TrkB. LC-MS/MS analysis of this extract revealed substances that might be responsible for the observed activity. This screening approach demonstrates, for the first time, that extracts originating from the mushroom A. auricula-judae exhibit TrkB-inhibition properties that might hold therapeutic potential for TrkB-positive cancers.

Molecular Mechanisms of Tyrosine Kinase Inhibitor Resistance in Chronic Myeloid Leukemia

The hematopoietic neoplasm chronic myeloid leukemia (CML) is a rare disease caused by chromosomal reciprocal translocation t(9;22)(q34:q11) with subsequent formation of the BCR-ABL1 fusion gene. This fusion gene encodes a constitutively active tyrosine kinase, which results in malignant transformation of the cells. Since 2001, CML can be effectively treated using tyrosine kinase inhibitors (TKIs) such as imatinib, which prevent phosphorylation of downstream targets by blockade of the BCR-ABL kinase. Due to its tremendous success, this treatment became the role model of targeted therapy in precision oncology. Here, we review the mechanisms of TKI resistance focusing on BCR-ABL1-dependent and -independent mechanisms. These include the genomics of the BCR-ABL1, TKI metabolism and transport and alternative signaling pathways.

Ponatinib, Lestaurtinib and mTOR/PI3K inhibitors are promising repurposing candidates against Entamoeba histolytica

Dysentery caused by Entamoeba histolytica affects millions of people annually. Current treatment regimens are based on metronidazole to treat invasive parasites combined with paromomycin for luminal parasites. Issues with treatment include significant side effects, inability to easily treat breastfeeding and pregnant women, the use of two sequential agents, and concern that all therapy is based on nitroimidazole agents with no alternatives if clinical resistance emerges. Thus, the need for new drugs against amebiasis is urgent. To identify new therapeutic candidates, we screened the ReFRAME library (11,948 compounds assembled for Repurposing, Focused Rescue, and Accelerated Medchem) against E. histolytica trophozoites. We identified 159 hits in the primary screen at 10 μM and 46 compounds were confirmed in secondary assays. Overall, 26 were selected as priority molecules for further investigation including 6 FDA approved, 5 orphan designation, and 15 which are currently in clinical trials (3 phase III, 7 phase II and 5 phase I). We found that all 26 compounds are active against metronidazole resistant E. histolytica and 24 are able to block parasite recrudescence after drug removal. Additionally, 14 are able to inhibit encystation and 2 (lestaurtinib and LY-2874455) are active against mature cysts. Two classes of compounds are most interesting for further investigations: the Bcr-Abl TK inhibitors, with the ponatinib (EC₅₀ 0.39) as most potent and mTOR or PI3K inhibitors with 8 compounds in clinical development, of which 4 have nanomolar potency. Overall, these are promising candidates and represent a significant advance for drug development against E. histolytica.

Pharmacogenomics of Impaired Tyrosine Kinase Inhibitor Response: Lessons Learned From Chronic Myelogenous Leukemia

The use of small molecules became one key cornerstone of targeted anti-cancer therapy. Among them, tyrosine kinase inhibitors (TKIs) are especially important, as they were the first molecules to proof the concept of targeted anti-cancer treatment. Since 2001, TKIs can be successfully used to treat chronic myelogenous leukemia (CML). CML is a hematologic neoplasm, predominantly caused by reciprocal translocation t(9;22)(q34;q11) leading to formation of the so-called BCR-ABL1 fusion gene. By binding to the BCR-ABL1 kinase and inhibition of downstream target phosphorylation, TKIs, such as imatinib or nilotinib, can be used as single agents to treat CML patients resulting in 80 % 10-year survival rates. However, treatment failure can be observed in 20-25 % of CML patients occurring either dependent or independent from the BCR-ABL1 kinase. Here, we review approved TKIs that are indicated for the treatment of CML, their side effects and limitations. We point out mechanisms of TKI resistance focusing either on BCR-ABL1-dependent mechanisms by summarizing the clinically observed BCR-ABL1-mutations and their implications on TKI binding, as well as on BCR-ABL1-independent mechanisms of resistances. For the latter, we discuss potential mechanisms, among them cytochrome P450 implications, drug efflux transporter variants and expression, microRNA deregulation, as well as the role of alternative signaling pathways. Further, we give insights on how TKI resistance could be analyzed and what could be learned from studying TKI resistance in CML in vitro.

Chemical Intuition in Drug Design and Discovery

The medicinal chemist plays the most important role in drug design, discovery and development. The primary goal is to discover leads and optimize them to develop clinically useful drug candidates. This process requires the medicinal chemist to deal with large sets of data containing chemical descriptors, pharmacological data, pharmacokinetics parameters, and in silico predictions. The modern medicinal chemist has a large number of tools and technologies to aid him in creating strategies and supporting decision-making. Alongside with these tools, human cognition, experience and creativity are fundamental to drug research and are important for the chemical intuition of medicinal chemists. Therefore, fine-tuning of data processing and in-house experience are essential to reach clinical trials. In this article, we will provide an expert opinion on how chemical intuition contributes to the discovery of drugs, discuss where it is involved in the modern drug discovery process, and demonstrate how multidisciplinary teams can create the optimal environment for drug design, discovery, and development.

Imatinib Mesylate

Imatinib mesylate (Gleevec, Glivec [Novartis, Basel, Switzerland], formerly referred to as STI571 or CGP57148B) represents the paradigm of a new class of anticancer agents, so-called small molecules. They have a high selectivity against a specific molecular target known to be the cause for the establishment and maintenance of the malignant phenotype. Imatinib is a rationally designed oral signal transduction inhibitor that specifically targets several protein tyrosine kinases, Abl, Arg (Abl-related gene), the stem cell factor receptor (c-KIT), platelet-derived growth factor receptor (PDGF-R), and their oncogenic forms, most notably BCR-ABL. Imatinib has been shown to have remarkable clinical activity in patients with chronic myeloid leukemia (CML) and malignant gastrointestinal stroma tumors (GIST) leading to its approval for treatment of these diseases. Treatment with imatinib is generally well tolerated with a low incidence of severe side effects. The most common adverse events include mild to moderate edema, muscle cramps, diarrhea, nausea, skin rashes, and myelosuppression. Several mechanisms of resistance have been identified. Clonal evolution, amplification, or overexpression of BCR-ABL as well as mutations in the catalytic domain, P-loop, and other mutations have been demonstrated to play a role in primary and secondary resistance to imatinib, respectively. Understanding of the underlying mechanisms of resistance has led to the development of new second- and third-generation tyrosine kinase inhibitors (see chapters on dasatinib, nilotinib, bosutinib, and ponatinib).

Estrogen induces c-Kit and an aggressive phenotype in a model of invasive lobular breast cancer

Among the molecular subtypes of breast cancer are luminal (A or B) estrogen receptor positive (ER+), HER2+, and triple negative (basal-like). In addition to the molecular subtypes, there are 18 histologic breast cancer subtypes classified on appearance, including invasive lobular breast carcinoma (ILC), which are 8-15% of all breast cancers and are largely ER+ tumors. We used a new model of ER+ ILC, called BCK4. To determine the estrogen regulated genes in our ILC model, we examined BCK4 xenograft tumors from mice supplemented with or without estrogen using gene expression arrays. Approximately 3000 genes were regulated by estrogen in vivo. Hierarchical cluster analyses of the BCK4 derived tumors compared with ER+ and ER- breast cancer cell lines show the estrogen treated BCK4 tumors group with ER- breast cancers most likely due to a high proliferation score, while tumors from cellulose supplemented mice were more related to ER+ breast tumor cells. To elucidate genes regulated in vitro by estrogen in BCK4 cells, we performed expression profiling using Illumina arrays of the BCK4 cell line, treated with or without estrogen in vitro. A set of ~200 overlapping genes were regulated by estrogen in the BCK4 cell line and xenograft tumors, and pathway analysis revealed that the c-Kit pathway might be a target to reduce estrogen-induced proliferation. Subsequent studies found that inhibition of c-Kit activity using imatinib mesylate (Gleevec®) blocked estrogen mediated stimulation of BCK4 tumors and BCK4 cells in vitro as effectively as the anti-estrogen fulvestrant (Faslodex®). Decreased expression of c-Kit using shRNA also decreased baseline and estrogen induced proliferation in vitro and in vivo. These studies are the first to indicate that c-Kit inhibition is an effective approach to target c-Kit+ ILC.

Effects of crenolanib, a nonselective inhibitor of PDGFR, in a mouse model of transient middle cerebral artery occlusion

Neurogenesis in the subventricular zone (SVZ) plays a vital role in neurologic recovery after stroke. However, only a small fraction of newly generated neuroblasts from the SVZ will survive long-term. Successful migration and survival of neuroblasts requires angiogenesis, lesion-derived chemo-attractants, and appropriate local microenvironments, which are partly regulated by the platelet-derived growth factor receptor (PDGFR) signaling pathway. In this study, we investigated the effects of PDGFR inhibition in a mouse model of transient middle cerebral artery occlusion (MCAO). We blocked the pathway using a nonselective PDGFR inhibitor, crenolanib, during the acute post-MCAO phase (days 1-3) or during the sub-acute phase (days 7-9). Downregulating the PDGFR signaling pathway with crenolanib from day 1 to day 3 after MCAO significantly decreased the migration of neuroblasts from the SVZ to the peri-infarct region, decreased angiogenesis, and lowered expression of vascular endothelial growth factor, stromal cell-derived factor-1, and monocyte chemotactic protein-1. Downregulation of the PDGFR signaling pathway on days 7-9 with crenolanib significantly increased apoptosis of the neuroblasts that had migrated to the peri-infarct region, increased the number of activated microglia, and decreased the expression of brain-derived neurotrophic factor, neurotrophin-3, and interleukin-10. Crenolanib treatment increased the apoptosis of pericytes and decreased the pericyte/vascular coverage, but had no effects on apoptosis of astrocytes. We conclude that the PDGFR signaling pathway plays a vital role in the SVZ neurogenesis after stroke. It can also affect angiogenesis, lesion-derived chemo-attractants, and the local microenvironment, which are all important to stroke-induced neurogenesis.

Use of multitarget tyrosine kinase inhibitors to attenuate platelet-derived growth factor signalling in lung disease

Platelet-derived growth factors (PDGFs) and their receptors (PDGFRs) play a fundamental role in the embryonic development of the lung. Aberrant PDGF signalling has been documented convincingly in a large variety of pulmonary diseases, including idiopathic pulmonary arterial hypertension, lung cancer and lung fibrosis. Targeting PDGF signalling has been proven to be effective in these diseases. In clinical practice, the most effective way to block PDGF signalling is to inhibit the activity of the intracellular PDGFR kinases. Although the mechanism of action of such drugs is not specific for PDGF signalling, the medications have a broad therapeutic index that allows clinical use. The safety profile and therapeutic opportunities of these and future medications that target PDGFs and PDGFRs are reviewed.

An increasing role for PDGF signalling inhibitors in clinical trials for the treatment of various pulmonary diseaseshttp://ow.ly/buaI30f9HcN

Repurposing of Human Kinase Inhibitors in Neglected Protozoan Diseases

Human African trypanosomiasis (HAT), Chagas disease, and leishmaniasis belong to a group of infectious diseases known as neglected tropical diseases and are induced by infection with protozoan parasites named trypanosomatids. Drugs in current use have several limitations, and therefore new candidate drugs are required. The majority of current therapeutic trypanosomatid targets are enzymes or cell-surface receptors. Among these, eukaryotic protein kinases are a major group of protein targets whose modulation may be beneficial for the treatment of neglected tropical protozoan diseases. This review summarizes the finding of new hit compounds for neglected tropical protozoan diseases, by repurposing known human kinase inhibitors on trypanosomatids. Kinase inhibitors are grouped by human kinase family and discussed according to the screening (target-based or phenotypic) reported for these compounds on trypanosomatids. This collection aims to provide insight into repurposed human kinase inhibitors and their importance in the development of new chemical entities with potential beneficial effects on the diseases caused by trypanosomatids.

Imatinib relaxes the pulmonary venous bed of guinea pigs

Background

Recently, the IMPRES study revealed that systemic imatinib improves exercise capacity in patients with advanced pulmonary arterial hypertension. Imatinib blocks the tyrosine kinase activity of the platelet-derived growth factor (PDGF)-receptor (PDGFR), acts antiproliferative and relaxes pulmonary arteries. However so far, the relaxant effects of imatinib on pulmonary veins (PVs) and on the postcapillary resistance are unknown, although pulmonary hypertension (PH) due to left heart disease (LHD) is most common and primarily affects PVs. Next, it is unknown whether activation of PDGFR alters the pulmonary venous tone. Due to the reported adverse effects of systemic imatinib, we evaluated the effects of nebulized imatinib on the postcapillary resistance.

Methods

Precision-cut lung slices (PCLS) were prepared from guinea pigs. PVs were pre-constricted with Endothelin-1 (ET-1) and the imatinib-induced relaxation was studied by videomicroscopy; PDGF-BB-related vascular properties were evaluated as well. The effects of perfused/nebulized imatinib on the postcapillary resistance were studied in cavine isolated perfused lungs (IPL). Intracellular cAMP/cGMP was measured by ELISA in PVs.

Results

In PCLS, imatinib (100 μM) relaxed pre-constricted PVs (126%). In PVs, imatinib increased cAMP, but not cGMP and inhibition of adenyl cyclase or protein kinase A reduced the imatinib-induced relaxation. Further, inhibition of K_ATP-channels, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {\mathrm{BK}}_{\mathrm{Ca}}^{2+} $$\end{document}BKCa2+-channels or K_v-channels diminished the imatinib-induced relaxation, whereas inhibition of NO-signaling was without effect. In the IPL, perfusion or nebulization of imatinib reduced the ET-1-induced increase of the postcapillary resistance. In PCLS, PDGF-BB contracted PVs, which was blocked by imatinib and by the PDGFR-β kinase inhibitor SU6668, whereas inhibition of PDGFR-α (ponatinib) had no significant effect. Conversely, PDGFR-β kinase inhibitors (SU6668/DMPQ) relaxed PVs pre-constricted with ET-1 comparable to imatinib, whereas the PDGFR-α kinase inhibitor ponatinib did not.

Conclusions

Imatinib-induced relaxation depends on cAMP and on the activation of K⁺-channels. Perfused or nebulized imatinib significantly reduces the postcapillary resistance in the pre-constricted (ET-1) pulmonary venous bed. Hence, nebulization of imatinib is feasible and might reduce systemic side effects. Conversely, PDGF-BB contracts PVs by activation of PDGFR-β suggesting that imatinib-induced relaxation depends on PDGFR-β-antagonism. Imatinib combines short-term relaxant and long-term antiproliferative effects. Thus, imatinib might be a promising therapy for PH due to LHD.

Tyrosine Kinase Inhibitors Regulate OPG through Inhibition of PDGFRβ

Nilotinib and imatinib are tyrosine kinase inhibitors (TKIs) used in the treatment of chronic myeloid leukemia (CML) and gastrointestinal stromal tumors (GIST). In vitro, imatinib and nilotinib inhibit osteoclastogenesis, and in patients they reduce levels of bone resorption. One of the mechanisms that might underlie these effects is an increase in the production of osteoprotegerin (OPG). In the current work we report that platelet-derived growth factor receptor beta (PDGFRβ) signaling regulates OPG production in vitro. In addition, we have shown that TKIs have effects on RANKL signaling through inhibition of the PDGFRβ and other target receptors. These findings have implications for our understanding of the mechanisms by which TKIs affect osteoclastogenesis, and the role of PDGFRβ signaling in regulating osteoclastogenesis. Further studies are indicated to confirm the clinical effects of PDGFRβ-inhibitors and to elaborate the intracellular pathways that underpin these effects.

The Src kinases Hck, Fgr and Lyn activate Arg to facilitate IgG-mediated phagocytosis and Leishmania infection

Leishmaniasis is a devastating disease that disfigures or kills nearly two million people each year. Establishment and persistence of infection by the obligate intracellular parasite Leishmania requires repeated uptake by macrophages and other phagocytes. Therefore, preventing uptake could be a novel therapeutic strategy for leishmaniasis. Amastigotes, the life cycle stage found in the human host, bind Fc receptors and enter macrophages primarily through immunoglobulin-mediated phagocytosis. However, the host machinery that mediates amastigote uptake is poorly understood. We have previously shown that the Arg (also known as Abl2) non-receptor tyrosine kinase facilitates L. amazonensis amastigote uptake by macrophages. Using small-molecule inhibitors and primary macrophages lacking specific Src family kinases, we now demonstrate that the Hck, Fgr and Lyn kinases are also necessary for amastigote uptake by macrophages. Src-mediated Arg activation is required for efficient uptake. Interestingly, the dual Arg and Src kinase inhibitor bosutinib, which is approved to treat cancer, not only decreases amastigote uptake, but also significantly reduces disease severity and parasite burden in Leishmania-infected mice. Our results suggest that leishmaniasis could potentially be treated with host-cell-active agents such as kinase inhibitors.

Anti-vascular endothelial growth factor treatment induces blood flow recovery through vascular remodeling in high-fat diet induced diabetic mice

Diabetes mellitus (DM) leads to the development of microvascular diseases and is associated with impaired angiogenesis. The presence of vascular endothelial growth factor (VEGF) can block PDGF-BB dependent regulation of neovascularization and vessel normalization. We tested the hypothesis that the inhibition of VEGF improves blood flow in a mouse hindlimb ischemia model produced by femoral artery ligation. In this study, we examined the effect of bevacizumab, a humanized monoclonal antibody against VEGF-A, on blood perfusion and angiogenesis after hindlimb ischemia. We showed that bevacizumab induces functional blood flow in high fat chow (HFC)-fed diabetic mice. Treatment with bevacizumab increased the expression of platelet derived growth factor-BB (PDGF-BB) in ischemic muscle, and led to vascular normalization. It also blocked vascular leakage by improving the recruitment of pericytes associated with nascent blood vessels, but it did not affect capillary formation. Furthermore, treatment with an anti-PDGF drug significantly inhibited blood flow perfusion in diabetic mice treated with bevacizumab. These results indicate that bevacizumab improves blood flow recovery through the induction of PDGF-BB in a diabetic mouse hindlimb ischemia model, and that vessel normalization may represent a useful strategy for the prevention and treatment of diabetic peripheral arterial disease.

Knock-down of CIAPIN1 sensitizes K562 chronic myeloid leukemia cells to Imatinib by regulation of cell cycle and apoptosis-associated members via NF-κB and ERK5 signaling pathway

CIAPIN1 (cytokine-induced apoptosis inhibitor 1) was recently identified as an essential downstream effector of the Ras signaling pathway. However, its potential role in regulating myeloid leukemia cells sensitivity to Imatinib remains unclear. In this study, we found depletion of CIAPIN1 inhibited proliferation and triggered more apoptosis of K562CML (chronic myeloid leukemia) cells with or without Imatinib treatment. Meanwhile, CIAPIN1 depletion decreased ERK5 phosphorylation and NF-κB activity. Importantly, treating CIAPIN1-depleted K562 cells with ERK5 signaling pathway specific inhibitor, XMD8-92, further inhibited proliferation and promoted apoptosis with or without Imatinib treatment. Treatment with the NF-κB specific inhibitor, Bay 11-7082, induced nearly the same inhibition of proliferation and promotion of apoptosis conferred by CIAPIN1 depletion as was observed with XMD8-92 treatment. Further, XMD8-92 and Bay 11-7082 synergistically inhibited proliferation and promoted apoptosis of CIAPIN1-depleted K562 cells with or without Imatinib treatment. The nude mice transplantation model was also performed to confirm the enhanced sensitivity of CIAPIN1-depleted K562 cells to Imatinib. Thus, our results provided a potential management by which CIAPIN1 knock-down might have a crucial impact on enhancing sensitivity of K562 cells to Imatinib in the therapeutic approaches, indicating that CIAPIN1 knock-down might serve as a combination with chemotherapeutical agents in leukemia diseases therapy.

Sustained proliferation in cancer: Mechanisms and novel therapeutic targets

Proliferation is an important part of cancer development and progression. This is manifest by altered expression and/or activity of cell cycle related proteins. Constitutive activation of many signal transduction pathways also stimulates cell growth. Early steps in tumor development are associated with a fibrogenic response and the development of a hypoxic environment which favors the survival and proliferation of cancer stem cells. Part of the survival strategy of cancer stem cells may manifested by alterations in cell metabolism. Once tumors appear, growth and metastasis may be supported by overproduction of appropriate hormones (in hormonally dependent cancers), by promoting angiogenesis, by undergoing epithelial to mesenchymal transition, by triggering autophagy, and by taking cues from surrounding stromal cells. A number of natural compounds (e.g., curcumin, resveratrol, indole-3-carbinol, brassinin, sulforaphane, epigallocatechin-3-gallate, genistein, ellagitannins, lycopene and quercetin) have been found to inhibit one or more pathways that contribute to proliferation (e.g., hypoxia inducible factor 1, nuclear factor kappa B, phosphoinositide 3 kinase/Akt, insulin-like growth factor receptor 1, Wnt, cell cycle associated proteins, as well as androgen and estrogen receptor signaling). These data, in combination with bioinformatics analyses, will be very important for identifying signaling pathways and molecular targets that may provide early diagnostic markers and/or critical targets for the development of new drugs or drug combinations that block tumor formation and progression.

Targeting vascular and leukocyte communication in angiogenesis, inflammation and fibrosis

Regulation of vascular permeability, recruitment of leukocytes from blood to tissue and angiogenesis are all processes that occur at the level of the microvasculature during both physiological and pathological conditions. The interplay between microvascular cells and leukocytes during inflammation, together with the emerging roles of leukocytes in the modulation of the angiogenic process, make leukocyte-vascular interactions prime targets for therapeutics to potentially treat a wide range of diseases, including pathological and dysfunctional vessel growth, chronic inflammation and fibrosis. In this Review, we discuss how the different cell types that are present in and around microvessels interact, cooperate and instruct each other, and in this context we highlight drug targets as well as emerging druggable processes that can be exploited to restore tissue homeostasis.

Chronic myeloid leukemia: Relevance of cytogenetic and molecular assays

Chronic myeloid leukemia (CML) is the prototype cytogenetic malignancy. Even before the development of basic G- and R-banding techniques, CML was found to be associated with a persistent chromosomal abnormality, the Philadelphia (Ph) chromosome. Banding technology later showed the marker chromosome to be a translocation between the breakpoint cluster region (BCR) on chromosome 22q11.2 and the Abelson proto-oncogene (ABL) on chromosome 9q34. Further advances in cytogenetic and molecular biology have also contributed to the understanding, diagnosis, and treatment of CML. Fluorescent in situ hybridization (FISH) has revealed cryptic translocations in most cases of Ph-negative CML. Additional rare chromosomal variant translocations have been discovered as well. The understanding of cytogenetic and molecular physiopathology of CML has led to the use of tyrosine kinase inhibitors as treatment for this disease with spectacular success. Over the 40 years since being identified as the first cytogenetic disease, CML has become the greatest success in translating the basic science of oncology into the treatment of patients with cancer. In this review we will not only summarize the biology of CML, recent progress in the delineation of mechanisms and treatment strategies, but also we will discuss the laboratory tools used for diagnosing CML, for monitoring during treatment and for revealing point mutations and additional chromosomal abnormalities. In doing so, we will describe in detail our individual research on CML, identifying why and how these tests were performed to help to explain CML subgroups and clinical significance of additional chromosomal abnormalities.

OCT1 and imatinib transport in CML: is it clinically relevant?

Imatinib is a highly effective therapy for chronic phase-chronic myeloid leukaemia (CP-CML) patients; however, responses to frontline imatinib are variable. The human organic cation transporter 1 (OCT1; SLC22A1) has been reported to be the main influx transporter involved in imatinib uptake into CML cells. Furthermore, variation in the efficiency of imatinib influx via OCT1 has been demonstrated to result in the inter-patient variation observed in primary response to imatinib. Although studies have questioned the role of OCT1 in imatinib influx, these have been largely performed in non-clinical settings. Measuring both OCT1 mRNA levels and the functional activity of OCT1 in primary leukaemic cells has been demonstrated to predict molecular response and outcome in imatinib-treated CP-CML patients in several independent studies. Here, the role of OCT1 and OCT1 genetic variants in imatinib uptake and response prediction is summarised and data generated from model systems assessing the role of OCT1 in imatinib transport is discussed.

The casein kinase 2 inhibitor, CX-4945, as an anti-cancer drug in treatment of human hematological malignancies

The casein kinase 2 (CK2) protein kinase is a pro-survival kinase and therapeutic target in treatment of various human cancers. CK2 overexpression has been demonstrated in hematological malignancies, including chronic lymphocytic leukemia, chronic myeloid leukemia, acute lymphoblastic leukemia, acute myeloid leukemia, and multiple myeloma. CX-4945, also known as Silmitasertib, is an orally administered, highly specific, ATP-competitive inhibitor of CK2. CX-4945 induces cytotoxicity and apoptosis and is currently being evaluated in clinical trials for treatment of many cancer types. In the past 2 years, the focus on the therapeutic potential of CX-4945 has shifted from solid tumors to hematological malignancies. CX-4945 exerts anti-proliferative effects in hematological tumors by downregulating CK2 expression and suppressing activation of CK2-mediated PI3K/Akt/mTOR signaling pathways. Furthermore, combination of CX-4945 with other inhibitors yielded synergistic effects in cell death induction. These new findings demonstrate that CK2 overexpression contributes to blood cancer cell survival and resistance to chemotherapy. Combinatorial use of CX-4945 is a promising therapeutic tool for treatment of hematological malignancies.

Occurrence of secondary malignancies in chronic myeloid leukemia during therapy with imatinib mesylate-single institution experience

Introduction

Imatinib mesylate (IM) remains the treatment of choice for chronic myeloid leukemia (CML) showing a remarkable efficacy and offers a perspective for long disease-free survival. Due to prolonged administration of IM, the questions about the possible impact on the development of secondary malignancies (SM) are raised.

Objective

To investigate the incidence and clinical outcome of secondary malignancies during IM therapy for CML.

Material and Methods

The records of 221 CML patients treated with IM between 2003–2013 in a single institution were reviewed. The Poisson regression model was used to estimate the relative risks for SM and death in CML patients.

Results

Secondary malignancies developed in eight out of the 221 patients (3.6%) receiving IM for a median of 61 months (range, 10–137 months). Female/male ratio was 5/3. Two patients were diagnosed with their CML at accelerated phase whereas 6 had chronic phase. The median age at IM initiation was 58 years (range, 31–72 years). Five of these 8 SM patients received IM after other treatments failure: interferon α (n=5), hydroxyurea (n=4) and cytarabine (n=1). Three patients received IM as a frontline therapy. All patients were on IM at 400mg daily at SM occurrence. The therapy for SM included surgery (n=3), chemotherapy only (n=3), and chemotherapy followed by radiotherapy (n=1). One patient did not receive treatment due to disseminated disease. All CML patients were in hematologic and complete cytogenetic response (CCR) at the time of SM development. All of them also met the criteria for major molecular response (BCR-ABL^IS ≤0.1%). They continued their IM while receiving treatment for SM. Among eight patients with SM, five patients are alive and remain in CCR on IM whereas three patients died due to SM. The risks for SM development as well as death due to SM in CML patients were not statistically increased if compared to age-adjusted population.

Conclusions

The association between IM therapy for CML and SM development has not been found.

Imatinib mesylate

Imatinib mesylate (Gleevec, Glivec [Novartis, Basel, Switzerland], formerly referred to as STI571 or CGP57148B) represents the paradigm of a new class of anticancer agents, so-called small molecules. They have a high selectivity against a specific molecular target known to be the cause for the establishment and maintenance of the malignant phenotype. Imatinib is a rationally designed oral signal transduction inhibitor that specifically targets several protein tyrosine kinases, Abl, Arg (Abl-related gene), the stem cell factor receptor (c-KIT), platelet-derived growth factor receptor (PDGF-R), and their oncogenic forms, most notably BCR-ABL. Imatinib has been shown to have remarkable clinical activity in patients with chronic myeloid leukemia (CML) and malignant gastrointestinal stroma tumors (GIST) leading to its approval for treatment of these diseases. Treatment with imatinib is generally well tolerated with a low incidence of severe side effects. The most common adverse events include mild to moderate edema, muscle cramps, diarrhea, nausea, skin rashes, and myelosuppression. Several mechanisms of resistance have been identified. Clonal evolution, amplification, or overexpression of BCR-ABL as well as mutations in the catalytic domain, P-loop, and other mutations have been demonstrated to play a role in primary and secondary resistance to imatinib, respectively. Understanding of the underlying mechanisms of resistance has led to the development of new second- and third-generation tyrosine kinase inhibitors (see chapters on dasatinib, nilotinib, bosutinib, and ponatinib).

Beyond bevacizumab: investigating new angiogenesis inhibitors in ovarian cancer

INTRODUCTION

Ovarian cancer is the most lethal gynecological cancer, mainly because of the advanced stage of the disease at diagnosis, with recent research investigating novel targets and agents into the clinical practice, with the aim to improve prognosis and quality of life. Angiogenesis is a significant target for ovarian cancer therapy.

AREAS COVERED

Areas covered in this review include the most common molecular pathways of angiogenesis, which have provided novel targets for tailored therapy in ovarian cancer patients. These therapeutic strategies comprise monoclonal antibodies and tyrosine kinase inhibitors. These drugs have as molecular targets such as vascular endothelial growth factor (VEGF), VEGF receptor, platelet-derived growth factor, fibroblast growth factor, angiopoietin and Ephrin type-A receptor 2.

EXPERT OPINION

The expansion in understanding the molecular biology that characterizes cancer cells has led to the rapid development of new agents to target important pathways, but the heterogeneity of ovarian cancer biology indicates that there is no predominant defect. This review attempts to discuss progress till date in tackling a more general target applicable to ovarian cancer angiogenesis.

Cumulative clinical experience from a decade of use: imatinib as first-line treatment of chronic myeloid leukemia

Chronic myeloid leukemia (CML) is a malignant disease that originates in the bone marrow and is designated by the presence of the Philadelphia (Ph+) chromosome, a translocation between chromosomes 9 and 22. Targeted therapy against CML commenced with the development of small-molecule tyrosine kinase inhibitors (TKIs) exerting their effect against the oncogenic breakpoint cluster region (BCR)-ABL fusion protein. Imatinib emerged as the first successful example of a TKI used for the treatment of chronic-phase CML patients and resulted in significant improvements in response rate and overall survival compared with previous treatments. However, a significant portion of patients failed to respond to the therapy and developed resistance against imatinib. Second-generation TKIs nilotinib and dasatinib were to have higher efficiency in clinical trials in imatinib- resistant or intolerant CML patients compared with imatinib. Identification of novel strategies such as dose escalation, drug combination therapy, and use of novel BCR-ABL inhibitors may eventually overcome resistance against BCR-ABL TKIs. This article reviews the history of CML, including the treatment strategies used prediscovery of TKIs and the preclinical and clinical data obtained after the use of imatinib, and the second-generation TKIs developed for the treatment of CML.

Is phosphoproteomics ready for clinical research?

BACKGROUND

For many diseases such as cancer where phosphorylation-dependent signaling is the foundation of disease onset and progression, single-gene testing and genomic profiling alone are not sufficient in providing most critical information. The reason for this is that in these activated pathways the signaling changes and drug resistance are often not directly correlated with changes in protein expression levels. In order to obtain the essential information needed to evaluate pathway activation or the effects of certain drugs and therapies on the molecular level, the analysis of changes in protein phosphorylation is critical.

METHODS

Existing approaches do not differentiate clinical disease subtypes on the protein and signaling pathway level, and therefore hamper the predictive management of the disease and the selection of therapeutic targets.

CONCLUSIONS

The mini-review examines the impact of emerging systems biology tools and the possibility of applying phosphoproteomics to clinical research.

Knock-down of Kaiso induces proliferation and blocks granulocytic differentiation in blast crisis of chronic myeloid leukemia

Background

Kaiso protein has been identified as a new member of the POZ-ZF subfamily of transcription factors that are involved in development and cancer. There is consistent evidence of the role of Kaiso and its involvement in human tumorigenesis but there is no evidence about its role in hematopoietic differentiation or establishment of chronic myeloid leukemia (CML). We used, normal K562 cell line, established from a CML patient in blast crisis, and imatinib-resistant K562 cell line, to investigate the specific distribution of Kaiso and their contribution to the cell differentiation status of the blast crisis of CML (CML-BP).

Results

We found cytoplasmic expression of Kaiso, in K562 cells and patients, confirmed by immunofluorescence, immunohistochemistry and western blot of cytoplasmic protein fraction. Kaiso was weakly expressed in the imatinib-resistant K562 cell line confirmed by immunofluorescence and western blot. The cytoplasmic expression of Kaiso was not modified when the K562 cells were treated for 16 h with imatinib 0.1 and 1 μM. In our study, small interfering RNA (siRNA) was introduced to down regulate the expression of Kaiso and p120ctn in K562 cell line. Kaiso and p120ctn were down regulated individually (siRNA-Kaiso or siRNA-p120ctn) or in combination using a simultaneous co-transfection (siRNA-Kaiso/p120ctn). We next investigated whether knockdown either Kaiso or p120ctn alone or in combination affects the cell differentiation status in K562 cells. After down regulation we analyzed the expression of hematopoietic cell differentiation and proliferation genes: SCF, PU-1, c-MyB, C/EBPα, Gata-2 and maturation markers of hematopoietic cells expressed in the plasma membrane: CD15, CD11b, CD33, CD117. The levels of SCF and c-MyB were increased by 1000% and 65% respectively and PU-1, Gata-2 and C/EBPα were decreased by 66%, 50% and 80% respectively, when Kaiso levels were down regulated by siRNA. The results were similar when both Kaiso and p120ctn were down regulated by siRNA. The increased expression of SCF and decreased expression of GATA-2 could be responsible by the higher cell viability detected in K562 cells double knock-down of both Kaiso and p120ctn. Finally, we studied the effect of knock-down either Kaiso or p120ctn, alone or in combination on CD15, CD11b, CD33 and Cd117 expression. Using siRNA approach a reduction of 35%, 8% and 13% in CD15, CD33 and CD117 levels respectively, were achieved in all transfections, when compared to scrambled knock-down cells.

Conclusion

These results suggest that both Kaiso and p120ctn, contributes to maintaining the differentiated state of the K562 cells and similar to other cancers, cytoplasmic localization of Kaiso is related to a poor prognosis in CML-BP. By the broad and profound effects on the expression of genes and markers of hematopoietic differentiation produced by Kaiso knock-down, these findings reveal Kaiso as a potential target for selective therapy of CML.

Intratumoral expression profiling of genes involved in angiogenesis in colorectal cancer patients treated with chemotherapy plus the VEGFR inhibitor PTK787/ZK 222584 (vatalanib)

The phase III CONFIRM clinical trials demonstrated that metastatic colorectal cancer patients with elevated serum lactate dehydrogenase (LDH) had improved outcome when the vascular endothelial growth factor receptor (VEGFR) inhibitor PTK/ZK (Vatalanib) was added to FOLFOX4 chemotherapy. We investigated the hypothesis that high intratumoral expression of genes regulated by hypoxia-inducible factor-1 alpha (HIF1α), namely LDHA, glucose transporter-1 (GLUT-1), VEGFA, VEGFR1, and VEGFR2, were predictive of outcome in CONFIRM-1. Tumor tissue was isolated by laser-capture microdissection from 85 CONFIRM-1 tumor specimens; FOLFOX4/placebo n=42, FOLFOX4/PTK/ZK n=43. Gene expression was analyzed using quantitative RT-PCR. In univariate analyses, elevated mRNA expression of LDHA, GLUT-1, and VEGFR1 were associated with response to FOLFOX4/PTK/ZK. In univariate and multivariate analyses, elevated LDHA and VEGFR1 mRNA levels were associated with improved progression-free survival in FOLFOX4/PTK/ZK patients. Furthermore, increased HIF1α and VEGFR2 mRNA levels were associated with decreased survival in FOLFOX/placebo patients but not in patients who received FOLFOX4/PTK/ZK. These are the first data suggesting intratumoral mRNA expression of genes involved in angiogenesis/HIF pathway may predict outcome to VEGFR-inhibitors. Biomarkers that assist in directing VEGFR-inhibitors toward patients with an increased likelihood of benefit will improve the cost-effectiveness of these promising agents.

Secondary malignancy after imatinib therapy: eight cases and review of the literature

Chronic myeloid leukemia (CML) is a clonal stem cell disorder, and imatinib is a small molecule inhibitor of Bcr-Abl tyrosine kinase (TK) used in cases with CML. Immediate and short-term side effects of this tyrosine kinase inhibitor (TKI) are well known, but the long-term side effects have not yet been clearly identified. Although an increased risk of secondary cancer in cases treated by imatinib was not found in two large series, secondary malignancies have been reported in some cases using TKIs, and this issue is important in daily clinical practice for clinicians. Here we report eight cases with neoplasias that developed during imatinib therapy and review secondary malignant disorders occurring during/after imatinib treatment.

Evolution of therapies for chronic myelogenous leukemia

The clinical outcome for patients with chronic myelogenous leukemia (CML) has changed dramatically in the past 15 years. This has been due to the development of tyrosine kinase inhibitors (TKIs), compounds that inhibit the activity of the oncogenic BCR-ABL1 protein. Imatinib was the first TKI developed for CML, and it led to high rates of complete cytogenetic responses and improved survival for patients with this disease. However, approximately 35% of patients in chronic phase treated with imatinib will develop resistance or intolerance to this drug. The recognition of the problem of imatinib failure led to the design of second-generation TKI (dasatinib, nilotinib, and bosutinib). These drugs are highly active in the scenario of imatinib resistance or intolerance. More recently, both nilotinib and dasatinib were approved for frontline use in patients with chronic phase CML. Ponatinib represents the last generation of TKI, and this drug has been developed with the aim of targeting a specific BCR-ABL1 mutation (T315I), which arises in the setting of prolonged TKI therapy and leads to resistance to all commercially available TKI. Parallel to the development of specific drugs for treating CML, major advances were made in the field of disease monitoring and standardization of response criteria. In this review, we summarize how therapy with TKI for CML has evolved during the last decade.

Targeting angiogenesis in ovarian cancer

Results of standard chemotherapy in ovarian cancer are hampered by the development of drug resistance leading to disease recurrence. This prompted interest in the development of therapies targeting critical pathways responsible for tumor progression. Angiogenesis is a key process that enables ovarian cancer growth and metastasis in the peritoneal space. Its regulation relies on signaling mechanisms initiated by the vascular endothelial growth factor, the platelet-derived growth factor, the fibroblast growth factor, angiopoietins, and others. These pathways are not only important to the modulation of the tumor microenvironment and vasculature, but also control cancer cell proliferation and survival. In this review, we discuss preclinical evidence supporting the rationale for inhibiting these pathways and provide an overview for the clinical development of agents targeting them. Clinical trials evaluating such agents alone and in combination with chemotherapy are ongoing. Early clinical results position antiangiogenic therapy at the forefront of change to the standard treatment of difficult to treat ovarian cancer.

Treatment of advanced dermatofibrosarcoma protuberans with imatinib mesylate with or without surgical resection

BACKGROUND

Dermatofibrosarcoma protuberans (DFSP) is a rare soft tissue sarcoma of the skin characterized by the presence of specific COL1A1-PDGFB fusion protein, which appears as a consequence of the t(17;22) (q22;q13) translocation.

OBJECTIVE

The aim of the study was to perform an analysis of patients with advanced DFSP treated with imatinib, with or without surgery, in clinical practice outside trials.

PATIENTS AND METHODS

We analysed the data of 15 patients (6 male, 9 female; median age 56 years) with locally advanced/initially inoperable and/or metastatic DFSP treated with imatinib 400-800 mg daily between 12/2004 and 06/2009. All diagnoses were ascertained cytogenetically (fluorescent in situ hybridization). Median follow-up time was 16 months (range: 4-81).

RESULTS

Metastases were present in six cases (two lungs, two soft tissue, two lymph nodes). Fibrosarcomatous transformation (FS-DFSP) was confirmed in seven patients (47%). A 2-year progression-free survival (PFS) rate was 60%, and a 2-year overall survival (OS) rate was 78% (median time for PFS/OS was not reached). The best overall responses were: 10 partial responses (67%, including 5 FS-DFSP-1 progressed during the follow-up), 2 stable diseases (13%) and 3 progressive diseases (20%). Seven patients (47%) underwent resection of residual disease and remained free of disease.

CONCLUSIONS

We have confirmed the profound anti-tumour effect of imatinib in DFSP harbouring t(17;22) with long-term responses. Imatinib therapy may in some cases lead to tumour resectability of lesser disfiguration.

Selective inhibition of BET bromodomains

Epigenetic proteins are intently pursued targets in ligand discovery. So far, successful efforts have been limited to chromatin modifying enzymes, or so-called epigenetic 'writers' and 'erasers'. Potent inhibitors of histone binding modules have not yet been described. Here we report a cell-permeable small molecule (JQ1) that binds competitively to acetyl-lysine recognition motifs, or bromodomains. High potency and specificity towards a subset of human bromodomains is explained by co-crystal structures with bromodomain and extra-terminal (BET) family member BRD4, revealing excellent shape complementarity with the acetyl-lysine binding cavity. Recurrent translocation of BRD4 is observed in a genetically-defined, incurable subtype of human squamous carcinoma. Competitive binding by JQ1 displaces the BRD4 fusion oncoprotein from chromatin, prompting squamous differentiation and specific antiproliferative effects in BRD4-dependent cell lines and patient-derived xenograft models. These data establish proof-of-concept for targeting protein-protein interactions of epigenetic 'readers', and provide a versatile chemical scaffold for the development of chemical probes more broadly throughout the bromodomain family.

Principal long-term adverse effects of imatinib in patients with chronic myeloid leukemia in chronic phase

Imatinib mesylate (IM), an original Abl tyrosine kinase inhibitor, entered the clinics in 1998 for the treatment of patients with chronic myeloid leukemia (CML). The drug is universally considered the treatment of choice for most, if not all, patients with CML. Importantly, lessons learned from patients with CML have been applied successfully for the treatment of patients with other disorders where IM has since been found to be active by virtue of its ability to target other kinases, such as c-kit in patients with gastrointestinal stromal tumors. IM is associated with mild to moderate toxicity, mostly reversible by dose reduction or discontinuation of the drug. Most adverse effects occur within the first 2 years of starting therapy; however, late effects, many being unique, are now being recognized. In this report, we assess the toxicity associated with IM, with an emphasis on the long-term adverse effects.

Imatinib mesylate in children and adolescents with cancer

Imatinib is an inhibitor of the BCR-ABL fusion gene product that characterizes chronic myeloid leukemia (CML), and of the related tyrosine kinases c-KIT and platelet-derived growth factor (PDGF) receptor. The drug is now included as front-line therapy for CML and Philadelphia chromosome-positive acute lymphoblastic leukemia in children and adolescents, though valid concerns about serious late sequelae remain unresolved and are important issues for further study. European and North American consortia have conducted phase I and II clinical trials of imatinib in children and adolescents with brain and other solid tumors that have provided little evidence of efficacy.

A current review of targeted therapeutics for ovarian cancer

Difficult to detect, ovarian cancer typically presents at an advanced stage. Significant progress has been achieved in the treatment of ovarian cancer with therapeutics focused on DNA replication or cell division. However, despite sensitivity to induction chemotherapy the majority of patients will develop recurrent disease. Conventional agents for recurrent disease offer little in terms of long-term responses. Various targeted therapeutics have been explored in the management of ovarian cancer. These include monoclonal antibodies to epidermal growth factor receptors, small molecule tyrosine kinase inhibitors, monoclonal antibodies directed at the vascular endothelial growth factor (bevacizumab), and the small tyrosine kinase inhibitors that target the vascular endothelial growth factor receptor. Recently, several other agents have come forth as potential therapeutic agents in the management of ovarian cancer. These include monoclonal antibodies to the folate receptor, triple angiokinase inhibitors, PARP inhibitors, aurora kinase inhibitors, inhibitors of the Hedgehog pathway, folate receptor antagonists, and MTOR inhibitors.

Imatinib mesylate

IMATINIB MESYLATE (Gleevec, Glivec [Novartis, Basel, Switzerland], formerly referred to as STI571 or CGP57148B) represents the paradigm of a new class of anticancer agents, the so-called small molecules. They have a high selectivity against a specific molecular target known to be the cause for the establishment and maintenance of the malignant phenotype. Imatinib is a rationally designed oral signal transduction inhibitor that specifically targets several protein tyrosine kinases, Abl, Arg (Abl-related gene), the stem-cell factor receptor (c-KIT), platelet-derived growth factor receptor (PDGF-R), and their oncogenic forms, most notably Bcr-Abl. Imatinib has been shown to have remarkable clinical activity in patients with chronic myeloid leukemia (CML) and malignant gastrointestinal stroma tumors (GIST) leading to its approval for treatment of these diseases.Treatment with imatinib is generally well tolerated with a low incidence of severe side effects. The most common adverse events (AE) include mild to moderate edema, muscle cramps, diarrhea, nausea, skin rashes, and myelosuppression.Several mechanisms of resistance have been identified. Clonal evolution, amplification, or overexpression of Bcr-Abl as well as mutations in the catalytic domain, P-loop, and other mutations have been demonstrated to play a role in primary and secondary resistance to imatinib, respectively. Improved understanding of the underlying mechanisms of resistance has led to the development of new second-generation tyrosine kinase inhibitors (see Chaps. 7-9).

Acadesine kills chronic myelogenous leukemia (CML) cells through PKC-dependent induction of autophagic cell death

CML is an hematopoietic stem cell disease characterized by the t(9;22) (q34;q11) translocation encoding the oncoprotein p210BCR-ABL. The effect of acadesine (AICAR, 5-Aminoimidazole-4-carboxamide-1-β-D-ribofuranoside) a compound with known antileukemic effect on B cell chronic lymphoblastic leukemia (B-CLL) was investigated in different CML cell lines. Acadesine triggered loss of cell metabolism in K562, LAMA-84 and JURL-MK1 and was also effective in killing imatinib-resistant K562 cells and Ba/F3 cells carrying the T315I-BCR-ABL mutation. The anti-leukemic effect of acadesine did not involve apoptosis but required rather induction of autophagic cell death. AMPK knock-down by Sh-RNA failed to prevent the effect of acadesine, indicating an AMPK-independent mechanism. The effect of acadesine was abrogated by GF109203X and Ro-32-0432, both inhibitor of classical and new PKCs and accordingly, acadesine triggered relocation and activation of several PKC isoforms in K562 cells. In addition, this compound exhibited a potent anti-leukemic effect in clonogenic assays of CML cells in methyl cellulose and in a xenograft model of K562 cells in nude mice. In conclusion, our work identifies an original and unexpected mechanism by which acadesine triggers autophagic cell death through PKC activation. Therefore, in addition to its promising effects in B-CLL, acadesine might also be beneficial for Imatinib-resistant CML patients.

Targeted therapies: the rare cancer paradigm

This review analyzes the state of the art of targeted therapies for several tumors, starting from the paradigmatic example of Imatinib treatment in chronic myelogenous leukemia (CML). We discuss how rare tumors can be models for various mechanisms of receptor tyrosine kinase (RTK) activation, and provide the opportunity to develop new therapies also for more common cancer types. We discuss the activation of the downstream RTK effectors as further targets for therapies in colorectal cancer. Finally, we highlight how a novel multidimensional approach which adds an in silico dimension to the in vitro and in vivo approach, can predict clinical results.

Masitinib (AB1010), a potent and selective tyrosine kinase inhibitor targeting KIT

Background

The stem cell factor receptor, KIT, is a target for the treatment of cancer, mastocytosis, and inflammatory diseases. Here, we characterise the in vitro and in vivo profiles of masitinib (AB1010), a novel phenylaminothiazole-type tyrosine kinase inhibitor that targets KIT.

Methodology/Principal Findings

In vitro, masitinib had greater activity and selectivity against KIT than imatinib, inhibiting recombinant human wild-type KIT with an half inhibitory concentration (IC₅₀) of 200±40 nM and blocking stem cell factor-induced proliferation and KIT tyrosine phosphorylation with an IC₅₀ of 150±80 nM in Ba/F3 cells expressing human or mouse wild-type KIT. Masitinib also potently inhibited recombinant PDGFR and the intracellular kinase Lyn, and to a lesser extent, fibroblast growth factor receptor 3. In contrast, masitinib demonstrated weak inhibition of ABL and c-Fms and was inactive against a variety of other tyrosine and serine/threonine kinases. This highly selective nature of masitinib suggests that it will exhibit a better safety profile than other tyrosine kinase inhibitors; indeed, masitinib-induced cardiotoxicity or genotoxicity has not been observed in animal studies. Molecular modelling and kinetic analysis suggest a different mode of binding than imatinib, and masitinib more strongly inhibited degranulation, cytokine production, and bone marrow mast cell migration than imatinib. Furthermore, masitinib potently inhibited human and murine KIT with activating mutations in the juxtamembrane domain. In vivo, masitinib blocked tumour growth in mice with subcutaneous grafts of Ba/F3 cells expressing a juxtamembrane KIT mutant.

Conclusions

Masitinib is a potent and selective tyrosine kinase inhibitor targeting KIT that is active, orally bioavailable in vivo, and has low toxicity.

Does imatinib turn recurrent and/or metastasized gastrointestinal stromal tumors into a chronic disease? - single center experience

BACKGROUND

Gastrointestinal stromal tumors (GIST) are mesenchymal tumors of the gastrointestinal tract supposed to arise from the cells of Cajal because of gain-of-function mutations of the tyrosine receptor kinases c-kit or platelet-derived growth factor receptor A. Imatinib selectively inhibits the kinase activity of both receptors. Despite this breakthrough in the treatment of GIST, resistance against imatinib has been reported to be as high as 50% after the first 2 years of treatment.

AIM

Outcome of 13 consecutive patients with relapsed or metastasized GIST who were treated with imatinib was analyzed.

RESULTS

Mean duration of treatment was 53.5 months. Four patients developed progressive disease and died after a mean treatment time of 31 months in spite of increase of imatinib dosages to 800 mg daily. Two patients (23%) developed a progressive disease after 46 months or 52 months of treatment. Two patients had a stable disease and five had a partial response. The overall progression rate was 46%, the mean survival time since primary diagnosis was 85.8 months.

CONCLUSION

From our experience, frequency of resistance development to imatinib may be below that given in the literature (50% after 2 years). Individual treatment in specialized centers may improve compliance.

Gene expression profiling of imatinib and PD166326-resistant CML cell lines identifies Fyn as a gene associated with resistance to BCR-ABL inhibitors

Imatinib is used to treat chronic myelogenous leukemia (CML), but resistance develops in all phases of this disease. The purpose of the present study was to identify the mode of resistance of newly derived imatinib-resistant (IM-R) and PD166326-resistant (PD-R) CML cells. IM-R and PD-R clones exhibited an increase in viability and a decrease in caspase activation in response to various doses of imatinib and PD166326, respectively, as compared with parental K562 cells. Resistance involved neither mutations in BCR-ABL nor increased BCR-ABL, MDR1 or Lyn expression, all known modes of resistance. To gain insight into the resistance mechanisms, we used pangenomic microarrays and identified 281 genes modulated in parental versus IM-R and PD-R cells. The gene signature was similar for IM-R and PD-R cells, accordingly with the cross-sensitivity observed for both inhibitors. These genes were functionally associated with pathways linked to development, cell adhesion, cell growth, and the JAK-STAT cascade. Especially relevant were the increased expression of the tyrosine kinases AXL and Fyn as well as CD44 and HMGA2. Small interfering RNA experiments and pharmacologic approaches identified FYN as a candidate for resistance to imatinib. Our findings provide a comprehensive picture of the transcriptional events associated with imatinib and PD166326 resistance and identify Fyn as a new potential target for therapeutic intervention in CML.

Anaplastic lymphoma kinase: signalling in development and disease

RTKs (receptor tyrosine kinases) play important roles in cellular proliferation and differentiation. In addition, RTKs reveal oncogenic potential when their kinase activities are constitutively enhanced by point mutation, amplification or rearrangement of the corresponding genes. The ALK (anaplastic lymphoma kinase) RTK was originally identified as a member of the insulin receptor subfamily of RTKs that acquires transforming capability when truncated and fused to NPM (nucleophosmin) in the t(2;5) chromosomal rearrangement associated with ALCL (anaplastic large cell lymphoma). To date, many chromosomal rearrangements leading to enhanced ALK activity have been described and are implicated in a number of cancer types. Recent reports of the EML4 (echinoderm microtubule-associated protein like 4)–ALK oncoprotein in NSCLC (non-small cell lung cancer), together with the identification of activating point mutations in neuroblastoma, have highlighted ALK as a significant player and target for drug development in cancer. In the present review we address the role of ALK in development and disease and discuss implications for the future.

Abl tyrosine kinases in T-cell signaling

Stimulation of the T-cell antigen receptor (TCR) leads to the activation of signaling pathways that are essential for T-cell development and the response of mature T cells to antigens. The TCR has no intrinsic catalytic activity, but TCR engagement results in tyrosine phosphorylation of downstream targets by non-receptor tyrosine kinases. Three families of tyrosine kinases have long been recognized to play critical roles in TCR-dependent signaling. They are the Src, zeta-associated protein of 70 kDa, and Tec families of kinases. More recently, the Abelson (Abl) tyrosine kinases have been shown to be activated by TCR engagement and to be required for maximal TCR signaling. Using T-cell conditional knockout mice deficient for Abl family kinases, Abl (Abl1) and Abl-related gene (Arg) (Abl2), it was recently shown that loss of Abl kinases results in defective T-cell development and a partial block in the transition to the CD4(+)CD8(+) stage. Abl/Arg double null T cells exhibit impaired TCR-induced signaling, proliferation, and cytokine production. Moreover, conditional knockout mice lacking Abl and Arg in T cells exhibit impaired CD8(+) T-cell expansion in vivo upon Listeria monocytogenes infection. Thus, Abl kinase signaling is required for both T-cell development and mature T-cell function.