SRC family kinase inhibitor SU6656 enhances antiangiogenic effect of irradiation

Interfering with Tumor Hypoxia for Radiotherapy Optimization

Hypoxia in solid tumors is an important predictor of treatment resistance and poor clinical outcome. The significance of hypoxia in the development of resistance to radiotherapy has been recognized for decades and the search for hypoxia-targeting, radiosensitizing agents continues. This review summarizes the main hypoxia-related processes relevant for radiotherapy on the subcellular, cellular and tissue level and discusses the significance of hypoxia in radiation oncology, especially with regard to the current shift towards hypofractionated treatment regimens. Furthermore, we discuss the strategies to interfere with hypoxia for radiotherapy optimization, and we highlight novel insights into the molecular pathways involved in hypoxia that might be utilized to increase the efficacy of radiotherapy.

The Effect of Chemoradiotherapy with SRC Tyrosine Kinase Inhibitor, PP2 and Temozolomide on Malignant Glioma Cells In Vitro and In Vivo

PURPOSE

We investigated the effect of chemoradiotherapy with PP2 and temozolomide (TMZ) on malignant glioma cells using clonogenic assays and in vivo brain tumor model.

MATERIALS AND METHODS

The effect of PP2 on radiosensitivity of U251 and T98G cells was investigated using clonogenic assays. The expression of E-cadherin, matrix metalloproteinases 2 (MMP2), Ephrin type-A receptor 2 (EphA2), and vascular endothelial growth factor (VEGF) was measured by Western blotting and an accumulation of γH2AX foci 6 hours after radiotherapy was measured after PP2 treatment. The effect of PP2 on migration, invasion, and vasculogenic mimicry formation (VMF) of U251 cells was evaluated. In an orthotopical brain tumor model with U251 cells, PP2 was injected intraperitoneally with or without oral TMZ before, during and after whole brain radiotherapy. Bioluminescence images were taken to visualize in vivo tumors and immunohistochemical staining of VEGF, CD31, EphA2, and hypoxia-inducible factor 1a was performed.

RESULTS

PP2 increased radiosensitivity of U251 and T98G cells without decreasing survival of normal human astrocytes. Chemoradiotherapy with PP2 and TMZ resulted in increased accumulation of γH2AX foci. PP2 induced overexpression of E-cadherin and suppression of MMP2, VEGF, and EphA2. PP2 also compromised invasion, migration, and VMF of U251 cells. In brain tumors, chemoradiotherapy with PP2 and TMZ decreased tumor volume best, but not statistically significantly compared with chemoradiotherapy with TMZ. The expression of VEGF and CD31 was suppressed in PP2-treated tumors.

CONCLUSION

PP2 enhances radiosensitivity of malignant glioma cells and suppresses invasion and migration of U251 cells. Chemoradiotherapy with PP2 and TMZ resulted in non-significant tumor volume decrease.

A combined targeted/phenotypic approach for the identification of new antiangiogenics agents active on a zebrafish model: from in silico screening to cyclodextrin formulation

A combined targeted/phenotypic approach for the rapid identification of novel antiangiogenics with in vivo efficacy is herein reported. Considering the important role played by the tyrosine kinase c-Src in the regulation of tumour angiogenesis, we submitted our in-house library of c-Src inhibitors to a sequential screening approach: in silico screening on VEGFR2, in vitro screening on HUVEC cells, ADME profiling, formulation and in vivo testing on a zebrafish model. A promising antiangiogenic candidate able to interfere with the vascular growth of a zebrafish model at low micromolar concentration was thus identified.

Tyrosine kinase inhibitors as potential drugs for B-cell lymphoid malignancies and autoimmune disorders

INTRODUCTION

In the last few years, several tyrosine kinase inhibitors (TKIs) have been synthesized and become available for preclinical studies and clinical trials. This article summarizes recent achievements in the mechanism of action, pharmacological properties, and clinical activity and toxicity, as well as the emerging role of TKIs in lymphoid malignancies, allergic diseases, and autoimmune disorders.

AREAS COVERED

A literature review was conducted of the MEDLINE database PubMed for articles in English. Publications from 2000 through January 2012 were scrutinized. The search terms used were Bruton's tyrosine kinase (Btk) inhibitors, PCI-32765, GDC-0834, LFM-A13, AVL-101, AVL-292, spleen tyrosine kinase (Syk) inhibitors, R343, R406, R112, R788, fostamatinib, BAY-61-3606, C-61, piceatannol, Lyn, imatinib, nilotinib, bafetinib, dasatinib, GDC-0834, PP2, SU6656 in conjunction with lymphoid malignancy, NHL, CLL, autoimmune disease, allergic disease, asthma, and rheumatoid arthritis. Conference proceedings from the previous 5 years of the American Society of Hematology, European Hematology Association, American Society of Clinical Oncology, and ACR/ARHP Annual Scientific Meetings were searched manually. Additional relevant publications were obtained by reviewing the references from the chosen articles.

EXPERT OPINION

The use of TKIs, especially inhibitors of Btk, Syk, and Lyn, is a promising new strategy for targeted treatment of B-cell lymphoid malignancies, autoimmune disorders and allergic diseases. However, definitive data from ongoing and future clinical trials will aid in better defining the status of TKIs in the treatment of these disorders.

Differential effects on cell motility, embryonic stem cell self-renewal and senescence by diverse Src kinase family inhibitors

The Src family of non-receptor tyrosine kinases (SFKs) has been shown to play an intricate role in embryonic stem (ES) cell maintenance. In the present study we have focused on the underlying molecular mechanisms responsible for the vastly different effects induced by various commonly used SFK inhibitors. We show that several diverse cell types, including fibroblasts completely lacking SFKs, cannot undergo mitosis in response to SU6656 and that this is caused by an unselective inhibition of Aurora kinases. In contrast, PP2 and PD173952 block motility immediately upon exposure and forces cells to grow in dense colonies. The subsequent halt in proliferation of fibroblast and epithelial cells in the center of the colonies approximately 24 h post-treatment appears to be caused by cell-to-cell contact inhibition rather than a direct effect of SFK kinase inhibition. Interestingly, in addition to generating more homogenous and dense ES cell cultures, without any diverse effect on proliferation, PP2 and PD173652 also promote ES cell self-renewal by reducing the small amount of spontaneous differentiation typically observed under standard ES cell culture conditions. These effects could not be mirrored by the use of Gleevec, a potent inhibitor of c-Abl and PDGFR kinases that are also inhibited by PP2.

FAK deletion promotes p53-mediated induction of p21, DNA-damage responses and radio-resistance in advanced squamous cancer cells

Focal adhesion kinase (FAK) is a cytoplasmic tyrosine kinase that is elevated in a variety of human cancers. While FAK is implicated in many cellular processes that are perturbed in cancer, including proliferation, actin and adhesion dynamics, polarisation and invasion, there is only some limited information regarding the role of FAK in radiation survival. We have evaluated whether FAK is a general radio-sensitising target, as has been suggested by previous reports. We used a clean genetic system in which FAK was deleted from mouse squamous cell carcinoma (SCC) cells (FAK -/-), and reconstituted with exogenous FAK wild type (wt). Surprisingly, the absence of FAK was associated with increased radio-resistance in advanced SCC cells. FAK re-expression inhibited p53-mediated transcriptional up-regulation of p21, and a sub-set of other p53 target genes involved in DNA repair, after treatment with ionizing radiation. Moreover, p21 depletion promoted radio-sensitisation, implying that FAK-mediated inhibition of p21 induction is responsible for the relative radio-sensitivity of FAK-proficient SCC cells. Our work adds to a growing body of evidence that there is a close functional relationship between integrin/FAK signalling and the p53/p21 pathway, but demonstrates that FAK's role in survival after stress is context-dependent, at least in cancer cells. We suggest that there should be caution when considering inhibiting FAK in combination with radiation, as this may not always be clinically advantageous.

Enzastaurin, an inhibitor of PKCbeta, Enhances Antiangiogenic Effects and Cytotoxicity of Radiation against Endothelial Cells

PURPOSE

Angiogenesis plays an important role in pancreas cancer pathobiology. Pancreatic tumor cells secrete vascular endothelial growth factor (VEGF), activating endothelial cell protein kinase C beta (PKCbeta) that phosphorylates GSK3beta to suppress apoptosis and promote endothelial cell proliferation and microvessel formation. We used Enzastaurin (Enz) to test the hypothesis that inhibition of PKCbeta results in radiosensitization of endothelial cells in culture and in vivo.

MATERIALS/METHODS

We measured PKCbeta phosphorylation, VEGF pathway signaling, colony formation, and capillary sprout formation in primary human dermal microvessel endothelial cells (HDMECs) after Enz or radiation (RT) treatment. Microvessel density and tumor volume of human pancreatic cancer xenografts in nude mice were measured after treatment with Enz, RT, or both.

RESULTS

Enz inhibited PKCbeta and radiosensitized HDMEC with an enhancement ratio of 1.31 +/- 0.05. Enz combined with RT reduced HDMEC capillary sprouting to a greater extent than either agent alone. Enz prevented radiation-induced GSK3beta phosphorylation of serine 9 while having no direct effect on VEGFR phosphorylation. Treatment of xenografts with Enz and radiation produced greater reductions in microvessel density than either treatment alone. The reduction in microvessel density corresponded with increased tumor growth delay.

CONCLUSIONS

Enz-induced PKCbeta inhibition radiosensitizes human endothelial cells and enhances the antiangiogenic effects of RT. The combination of Enz and RT reduced microvessel density and resulted in increased growth delay in pancreatic cancer xenografts, without increase in toxicity. These results provide the rationale for combining PKCbeta inhibition with radiation and further investigating such regimens in pancreatic cancer.

Current state of knowledge regarding the use of antiangiogenic agents with radiation therapy

Angiogenesis has been a central theme of oncologic research for several years. Recently, improved understanding of its mechanisms has led to the development of several antiangiogenic agents. Some have demonstrated their effectiveness in large randomized studies; however, no antiangiogenic agent has yet been approved for treatment in combination with radiotherapy. Numerous preclinical studies and a few small clinical trials have recently reported encouraging results. The objective of this article is to review the concept of targeted antiangiogenic agents and the early clinical results of their use in combination with radiation therapy.

Targeting SRC in glioblastoma tumors and brain metastases: rationale and preclinical studies

Glioblastoma (GBM) is an extremely aggressive, infiltrative tumor with a poor prognosis. The regulatory approval of bevacizumab for recurrent GBM has confirmed that molecularly targeted agents have potential for GBM treatment. Preclinical data showing that SRC and SRC-family kinases (SFKs) mediate intracellular signaling pathways controlling key biologic/oncogenic processes provide a strong rationale for investigating SRC/SFK inhibitors, e.g., dasatinib, in GBM and clinical studies are underway. The activity of these agents against solid tumors suggests that they may also be useful in treating brain metastases. This article reviews the potential for using SRC/SFK inhibitors to treat GBM and brain metastases.

A facile, click chemistry-based approach to assembling fluorescent chemosensors for protein tyrosine kinases

A group of fluorophore-labeled peptide substrates of Src kinases have been synthesized with the aid of click chemistry. Some of the generated peptides exhibit an increase in fluorescence upon phosphorylation and are capable of detecting Src kinases with high sensitivity and specificity. Their availability permits real-time activity measurement of aberrantly activated oncogenic Src kinases in the crude lysate of chronic myelogenous leukemia cells. These new chemosensor peptides are highly useful tools that can be used for high-throughput screening to search for small molecule inhibitors of Src kinases as potential therapeutics for cancer treatment.

Mesenchymal migration as a therapeutic target in glioblastoma

Extensive infiltration of the surrounding healthy brain tissue is a cardinal feature of glioblastomas, highly lethal brain tumors. Deep infiltration by the glioblastoma cells renders complete surgical excision difficult and contemporary adjuvant therapies have had little impact on long-term survival. Thus, deep infiltration and resistance to irradiation and chemotherapy remain a major cause of patient mortality. Modern therapies specifically targeted to this unique aspect of glioblastoma cell biology hold significant promise to substantially improve survival rates for glioblastoma patients. In the present paper, we focus on the role of adhesion signaling molecules and the actin cytoskeleton in the mesenchymal mode of motility that characterizes invading glioblastoma cells. We then review current approaches to targeting these elements of the glioblastoma cell migration machinery and discuss other aspects of cell migration that may improve the treatment of infiltrating glioblastoma.

Modulation of embryonic stem cell fate and somatic cell reprogramming by small molecules

Embryonic stem cells (ESC) are pluripotent cells and have the ability to self-renew in vitro and to differentiate into cells representing all three germ layers. They provide enormous opportunities for basic research, regenerative medicine as well as drug discovery. The mechanisms that govern ESC fate are not completely understood, so a better understanding and control of ESC self-renewal and differentiation are pivotal for therapeutic applications. In contrast to growth factors and genetic manipulations, small molecules offer great advantages in modulating ESC fate. For instance, they could be conveniently identified through high-throughput screening, work across multiple signalling pathways and affect epigenetic modifications as well. This review focuses on the recent progress in the use of small molecules to regulate ESC self-renewal, differentiation and somatic cell reprogramming.

Improving the prognosis for patients with glioblastoma: the rationale for targeting Src

Glioblastoma is the most common and aggressive form of primary brain tumor. The prognosis for patients diagnosed with glioblastoma is poor, with a median survival of 12-14 months and a 5-year survival rate of <5%. The upfront standard treatment for patients with newly diagnosed glioblastoma, consisting of surgery followed by chemotherapy combined with radiotherapy, provides only short-term survival benefits. Recurrent glioblastoma is an extremely challenging therapeutic setting because of the aggressive and resistant nature of the tumor. A set of key molecular targets in oncology is the Src family of non-receptor protein kinases. Dysregulated signaling via the Src kinases has been shown to underlie glioma-related proliferation, angiogenesis, migration, and survival. Here we review the biologic role of Src in malignant glioma and discuss key preclinical studies demonstrating the potential utility of inhibiting Src in glioma. Proof of clinical benefit is forthcoming from the first clinical studies involving the newest generation of small molecule Src inhibitors currently in clinical trials for recurrent glioblastoma. Blocking Src alone will likely not translate into a significant clinical benefit; thus, strategies for combining Src inhibitors with potential synergistic therapeutic modalities will be discussed. This review will focus on dasatinib, the most advanced Src inhibitor being tested in glioblastoma, which is currently in phase I/II trials in this setting.

Cytosolic phospholipase A2 regulates viability of irradiated vascular endothelium

Radiosensitivity of various normal tissues is largely dependent on radiation-triggered signal transduction pathways. Radiation simultaneously initiates distinct signaling from both DNA damage and cell membrane. Specifically, DNA strand breaks initiate cell-cycle delay, strand-break repair or programmed cell death, whereas membrane-derived signaling through phosphatidylinositol 3-kinase/Akt and mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) enhances cell viability. Here, activation of cytosolic phospholipase A(2) (cPLA(2)) and production of the lipid second-messenger lysophosphatidylcholine were identified as initial events (within 2 min) required for radiation-induced activation of Akt and ERK1/2 in vascular endothelial cells. Inhibition of cPLA(2) significantly enhanced radiation-induced cytotoxicity due to an increased number of multinucleated giant cells and cell cycle-independent accumulation of cyclin B1 within 24-48 h of irradiation. Delayed programmed cell death was detected at 72-96 h after treatment. Endothelial functions were also affected by inhibition of cPLA(2) during irradiation resulting in attenuated cell migration and tubule formation. The role of cPLA(2) in the regulation of radiation-induced activation of Akt and ERK1/2 and cell viability was confirmed using human umbilical vein endothelial cells transfected with shRNA for cPLA(2)alpha and cultured embryonic fibroblasts from cPLA(2)alpha(-/-) mice. In summary, an immediate radiation-induced cPLA(2)-dependent signaling was identified that regulates cell viability and, therefore, represents one of the key regulators of radioresistance of vascular endothelial cells.

Hedgehog signaling in the murine melanoma microenvironment

The Hedgehog intercellular signaling pathway regulates cell proliferation and differentiation. This pathway has been implicated to play a role in the pathogenesis of cancer and in embryonic blood vessel development. In the current study, Hedgehog signaling in tumor related vasculature and microenvironment was examined using human umbilical vein endothelial cells and B16F0 (murine melanoma) tumors models. Use of exogenous Sonic hedgehog (Shh) peptide significantly increased BrdU incorporation in endothelial cells in vitro by a factor of 2 (P < 0.001). The Hedgehog pathway antagonist cyclopamine effectively reduced Shh-induced proliferation to control levels. To study Hedgehog signaling in vivo a hind limb tumor model with the B16F0 cell line was used. Treatment with 25 mg/kg cyclopamine significantly attenuated BrdU incorporation in tumor cells threefold (P < 0.001), in tumor related endothelial cells threefold (P = 0.004), and delayed tumor growth by 4 days. Immunohistochemistry revealed that the Hedgehog receptor Patched was localized to the tumor stroma and that B16F0 cells expressed Shh peptide. Furthermore, mouse embryonic fibroblasts required the presence of B16F0 cells to express Patched in a co-culture assay system. These studies indicate that Shh peptide produced by melanoma cells induces Patched expression in fibroblasts. To study tumor related angiogenesis a vascular window model was used to monitor tumor vascularity. Treatment with cyclopamine significantly attenuated vascular formation by a factor of 2.5 (P < 0.001) and altered vascular morphology. Furthermore, cyclopamine reduced tumor blood vessel permeability to FITC labeled dextran while having no effect on normal blood vessels. These studies suggest that Hedgehog signaling regulates melanoma related vascular formation and function.

HIV protease inhibitors enhance the efficacy of irradiation

Tumor vascular endothelium is rather resistant to the cytotoxic effects of radiation. The HIV protease inhibitors (HPI) amprenavir, nelfinavir, and saquinavir have previously been shown to sensitize tumor cells to the cytotoxic effects of radiation. Additionally, this class of drug has been shown to inhibit angiogenesis and tumor cell migration. Therefore, in the current study, we wanted to determine whether HPIs could enhance the effect of radiation on endothelial function. Our study shows that HPIs, particularly nelfinavir, significantly enhance radiations effect on human umbilical vein endothelial cells (HUVEC) and tumor vascular endothelium. We show that pretreatment of HUVEC with nelfinavir results in enhanced cytotoxicity, including increased apoptosis, when combined with radiation. Moreover, using several functional assays, we show that combination treatment effectively blocks endothelial cell migration and organization. These findings were accompanied by attenuation of Akt phosphorylation, a known pathway for radioresistance. Last, in vivo analysis of tumor microvasculature destruction showed a more than additive effect for nelfinavir and radiation. This study shows that HPIs can enhance the effect of ionizing radiation on vascular endothelium. Therefore, the Food and Drug Administration-approved drug, nelfinavir, may be an effective radiosensitizer in the clinic.

Human B lymphocytes and non-Hodgkin's lymphoma cells become polyploid in response to the protein kinase inhibitor SU6656

We show that prolonged exposure of non-Hodgkin's lymphoma (NHL) cell lines to low doses of the Src family protein tyrosine kinases (SFKs) inhibitor SU6656 caused proliferation abrogation as a result of the formation of cells with single multilobed nuclei and several mitotic spindle poles, features similar to polyploid megakaryocytes. The propensity of the NHL B cells tested to undergo polyploid was unrelated to the presence of p53 mutations in these cells since comparable outcomes were observed in SU6656-exposed cultures of blood B lymphocytes derived from healthy individuals. Thus, in addition to its utility for the study of megakaryocyte polyploidization, our results show that SU6656 can also induce polyploidy in cells of lymphoid origin, revealing a chemotherapeutic potential for this inhibitor to limit tumor propagation of malignant B cell lymphomas, although not without affecting normal B cells as well.

Latent Kaposi's sarcoma-associated herpesvirus infection of endothelial cells activates hypoxia-induced factors

Kaposi's sarcoma-associated herpesvirus (KSHV or HHV-8) is the etiological agent of Kaposi's sarcoma, a highly vascularized, endothelial-derived tumor. A direct role for KSHV-mediated induction of angiogenesis has been proposed based upon the nature of the neoplasia and various KSHV gene overexpression and infection model systems. We have found that KSHV infection of endothelial cells induces mRNA of hypoxia-induced factor 1alpha (HIF1alpha) and HIF2alpha, two homologous alpha subunits of the heterodimeric transcription factor HIF. HIF is a master regulator of both developmental and pathological angiogenesis, composed of an oxygen-sensitive alpha subunit and a constitutively expressed beta subunit. HIF is classically activated posttranscriptionally with hypoxia, leading to increased protein stability of HIF1alpha and/or HIF2alpha. However, we demonstrate that both alpha subunits are up-regulated at the transcript level by KSHV infection. The transcriptional activation of HIF leads to a functional increase in HIF activity under normoxic conditions, as demonstrated by both luciferase reporter assay and the increased expression of vascular endothelial growth factor receptor 1 (VEGFR1), an HIF-responsive gene. KSHV infection synergizes with hypoxia mimics and induces higher expression levels of HIF1alpha and HIF2alpha protein, and HIF1alpha is increased in a significant proportion of the latently infected endothelial cells. Src family kinases are required for the activation of HIF and the downstream gene VEGFR1 by KSHV. We also show that KS lesions, in vivo, express elevated levels of HIF1alpha and HIF2alpha proteins. Thus, KSHV stimulates the HIF pathway via transcriptional up-regulation of both HIF alphas, and this activation may play a role in KS formation, localization, and progression.