Cancer metastasis therapeutic targets and drug discovery: emerging small-molecule protein kinase inhibitors

Reprogramming of astrocytes and glioma cells into neurons for central nervous system repair and glioblastoma therapy

Central nervous system (CNS) damage is usually irreversible owing to the limited regenerative capability of neurons. Following CNS injury, astrocytes are reactively activated and are the key cells involved in post-injury repair mechanisms. Consequently, research on the reprogramming of reactive astrocytes into neurons could provide new directions for the restoration of neural function after CNS injury and in the promotion of recovery in various neurodegenerative diseases. This review aims to provide an overview of the means through which reactive astrocytes around lesions can be reprogrammed into neurons, to elucidate the intrinsic connection between the two cell types from a neurogenesis perspective, and to summarize what is known about the neurotranscription factors, small-molecule compounds and MicroRNA that play major roles in astrocyte reprogramming. As the malignant proliferation of astrocytes promotes the development of glioblastoma multiforme (GBM), this review also examines the research advances on and the theoretical basis for the reprogramming of GBM cells into neurons and discusses the advantages of such approaches over traditional treatment modalities. This comprehensive review provides new insights into the field of GBM therapy and theoretical insights into the mechanisms of neurological recovery following neurological injury and in GBM treatment.

Design, Synthesis and Biological Evaluation of Novel 4-phenoxypyridine Derivatives Containing Semicarbazones Moiety as Potential c-Met Kinase Inhibitors

BACKGROUND

The Hepatocyte Growth Factor Receptor (HGFR) c-Met is over-expressed and/or mutated in various human tumor types. Dysregulation of c-Met/HGF signaling pathway affects cell proliferation, survival and motility, leading to tumor growth, angiogenesis, and metastasis. Therefore, c-Met has become an attractive target for cancer therapy.

OBJECTIVE

This study is aimed to evaluate a new series of 4-phenoxypyridine derivatives containing semicarbazones moiety for its cytotoxicity.

METHODS

A series of novel 4-phenoxypyridines containing semicarbazone moieties were synthesized and evaluated for their in vitro cytotoxic activities against MKN45 and A549 cancer cell lines and some selected compounds were further examined for their inhibitory activity against c-Met kinase. In order to evaluate the mechanism of cytotoxic activity of compound 24, cell cycle analysis, Annexin V/PI staining assay, AO/EB assay, wound-healing assay and docking analysis with c-Met were performed.

RESULTS

The results indicated that most of the compounds showed moderate to good antitumor activity. The compound 28 showed well cytotoxic activity against MKN45 and A549 cell lines with IC50 values of 0.25μM and 0.67μM, respectively. Compound 24 showed good activity on c-Met and its IC50 value was 0.093μM.

CONCLUSION

Their preliminary Structure-Activity Relationships (SARs) studies indicated that electronwithdrawing groups on the terminal phenyl rings are beneficial for improving the antitumor activity. Treatments of MKN45 cells with compound 24 resulted in cell cycle arrest in G2/M phase and induced apoptosis in a dose-dependent manner. In addition, AO/EB assays indicated 24 induced dose-dependent apoptosis of A549 and MKN45 cells. Wound-healing assay results indicated that compound 24 strongly inhibited A549 cell motility.

Phosphorylation of nucleophosmin at threonine 234/237 is associated with HCC metastasis

Hepatocellular carcinoma (HCC) is frequently complicated by the occurrence of intrahepatic and extrahepatic metastases, leading to poor prognosis. To improve the prognosis for HCC patients, there is an urgent need to understand the molecular mechanisms of metastasis in HCC. Since protein Serine/Threonine phosphorylation emerges to be an important posttranslational modification critical in signaling process associated with cell proliferation, survival and metastasis, we employed a pair of primary tumor-derived and corresponding lung-metastatic counterparts (PLC/PRF/5-PT and PLC/PRF/5-LM) and aimed to identify these changes using CelluSpot™ Serine/Threonine kinase peptide array. Upon analysis, we found phosphorylated level of nucleophosmin (NPM) at Threonine 234/237 (p-NPM-Thr^234/237) had remarkably high level in metastatic HCC cells (PLC-LM) than the corresponding primary HCC cell line (PLC-PT). Similar observation was observed in another match primary and their metastatic counterparts (MHCC-97L and MHCC-97H). By immunohistochemical staining, p-NPM-Thr^234/237 was consistently found to be preferentially expressed in metastatic HCCs when compared with primary HCC in 28 HCC cases (p < 0.0001). By overexpressing Flag-tagged NPM and its phosphorylation site mutant (Thr234/237A) into low p-NPM-Thr^234/237 expressing cells (Hep3B and Huh7) using a lentiviral based approach, we demonstrated that p-NPM-Thr^234/237 is critical in invasion and migration of HCC cells, and this effect was mediated by cyclin-dependent kinase 1 (CDK1). Wild-type NPM was found to physically interact with a metastatic gene, ROCK2, and defective in Thr234/237 phosphorylation decreased its binding affinity, resulting in decrease in ROCK2 mediated signaling pathway. Identification of CDK1/p-NPM/ROCK2 signaling pathway provides a novel target for molecular therapy against HCC metastasis.

Review of the Effects of Anti-Angiogenic Compounds on the Epiphyseal Growth Plate

The formation of new blood vessels from a pre-existing vascular bed, termed “angiogenesis,” is of critical importance for the growth and development of the animal since it is required for the growth of the skeleton during endochondral ossification, development and cycling of the corpus luteum and uterus, and for the repair of tissues during wound healing. “Vasculogenesis,” the de novo formation of blood vessels is also important for the proper function and development of the vascular system in the embryo. New blood vessel formation is a prominent feature and permissive factor in the relentless progression of many human diseases, one of the most important examples of which is neoplasia. It is for this reason that angiogenesis is considered to be one of the hallmarks of cancer. The development of new classes of drugs that inhibit the growth and proper functioning of new blood vessels in vivo is likely to provide significant therapeutic benefit in the treatment of cancer, as well as other conditions where angiogenesis is a strong driver to the disease process. During the preclinical safety testing of these drugs, it is becoming increasingly clear that their in vivo efficacy is reflected in the profile of “expected toxicity” (resulting from pharmacology) observed in laboratory animals, so much so, that this profile of “desired” toxicity may act as a signature for their anti-angiogenic effect. In this article we review the major mechanisms controlling angiogenesis and its role during endochondral ossification. We also review the effects of perturbation of endochondral ossification through four mechanisms—inhibition of vascular endothelial growth factor (VEGF), pp60 c-Src kinase and matrix metalloproteinases as well as disruption of the blood supply with vascular targeting agents. Inhibition through each of these mechanisms appears to have broadly similar effects on the epiphyseal growth plate characterised by thickening due to the retention of hypertrophic chondrocytes resulting from the inhibition of angiogenesis. In contrast, in the metaphysis there are differing effects reflecting the specific role of these targets at this site.

Small-Molecule Inhibition of Rho/MKL/SRF Transcription in Prostate Cancer Cells: Modulation of Cell Cycle, ER Stress, and Metastasis Gene Networks

Metastasis is the major cause of cancer deaths and control of gene transcription has emerged as a critical contributing factor. RhoA- and RhoC-induced gene transcription via the actin-regulated transcriptional co-activator megakaryocytic leukemia (MKL) and serum response factor (SRF) drive metastasis in breast cancer and melanoma. We recently identified a compound, CCG-1423, which blocks Rho/MKL/SRF-mediated transcription and inhibits PC-3 prostate cancer cell invasion. Here, we undertook a genome-wide expression study in PC-3 cells to explore the mechanism and function of this compound. There was significant overlap in the genes modulated by CCG-1423 and Latrunculin B (Lat B), which blocks the Rho/MKL/SRF pathway by preventing actin polymerization. In contrast, the general transcription inhibitor 5,6-dichloro-1-β-d-ribofuranosyl-1H-benzimidazole (DRB) showed a markedly different pattern. Effects of CCG-1423 and Lat B on gene expression correlated with literature studies of MKL knock-down. Gene sets involved in DNA synthesis and repair, G1/S transition, and apoptosis were modulated by CCG-1423. It also upregulated genes involved in endoplasmic reticulum stress. Targets of the known Rho target transcription factor family E2F and genes related to melanoma progression and metastasis were strongly suppressed by CCG-1423. These results confirm the ability of our compound to inhibit expression of numerous Rho/MKL-dependent genes and show effects on stress pathways as well. This suggests a novel approach to targeting aggressive cancers and metastasis.

Multistrip Western blotting: a tool for comparative quantitative analysis of multiple proteins

The qualitative and quantitative measurements of protein abundance and modification states are essential in understanding their functions in diverse cellular processes. Typical Western blotting, though sensitive, is prone to produce substantial errors and is not readily adapted to high-throughput technologies. Multistrip Western blotting is a modified immunoblotting procedure based on simultaneous electrophoretic transfer of proteins from multiple strips of polyacrylamide gels to a single membrane sheet. In comparison with the conventional technique, Multistrip Western blotting increases data output per single blotting cycle up to tenfold; allows concurrent measurement of up to nine different total and/or posttranslationally modified protein expression obtained from the same loading of the sample; and substantially improves the data accuracy by reducing immunoblotting-derived signal errors. This approach enables statistically reliable comparison of different or repeated sets of data and therefore is advantageous to apply in biomedical diagnostics, systems biology, and cell signaling research.

Folate-targeted paclitaxel-conjugated polymeric micelles inhibits pulmonary metastatic hepatoma in experimental murine H22 metastasis models

Hepatocellular carcinoma shows low response to most conventional chemotherapies; additionally, extrahepatic metastasis from hepatoma is considered refractory to conventional systemic chemotherapy. Target therapy is a promising strategy for advanced hepatoma; however, targeted accumulation and controlled release of therapeutic agents into the metastatic site is still a great challenge. Folic acid (FA) and paclitaxel (PTX) containing composite micelles (FA-M[PTX]) were prepared by coassembling the FA polymer conjugate and PTX polymer conjugate. The main purpose of this study is to investigate the inhibitory efficacy of FA-M(PTX) on the pulmonary metastasis of intravenously injected murine hepatoma 22 (H22) on BALB/c mice models. The lung metastatic burden of H22 were measured and tissues were analyzed by immunohistochemistry and histology (hematoxylin and eosin stain), followed by survival analysis. The results indicated that FA-M(PTX) prevented pulmonary metastasis of H22, and the efficacy was stronger than pure PTX and simple PTX-conjugated micelles. In particular, the formation of lung metastasis colonies in mice was evidently inhibited, which was paralleled with the downregulated expression of matrix metalloproteinase-2 and matrix metalloproteinase-9. Furthermore, the mice bearing pulmonary metastatic hepatoma in the FA-M(PTX) group gained significantly prolonged survival time when compared with others given equivalent doses of PTX of 30 mg/kg. The enhanced efficacy of FA-M(PTX) is theoretically ascribed to the target effect of FA; moreover, the extensive pulmonary capillary networks may play a role. In conclusion, FA-M(PTX) displayed great potential as a promising antimetastatic agent, and the FA-conjugated micelles is a preferential targeted delivery system when compared to micelles without FA.

Fusarisetins: Structure-function studies on a novel class of cell migration inhibitors

Herein, we report the effects of fusarisetin A on cell morphology focusing in particular on actin and microtubules dynamics. We also report the synthesis and structure-function studies of a designed library of synthetic fusarisetins in cell-based assays.

Cholesteryl butyrate solid lipid nanoparticles inhibit the adhesion and migration of colon cancer cells

BACKGROUND AND PURPOSE Cholesteryl butyrate solid lipid nanoparticles (cholbut SLN) provide a delivery system for the anti-cancer drug butyrate. These SLN inhibit the adhesion of polymorphonuclear cells to the endothelium and may act as anti-inflammatory agents. As cancer cell adhesion to endothelium is crucial for metastasis dissemination, here we have evaluated the effect of cholbut SLN on adhesion and migration of cancer cells. EXPERIMENTAL APPROACH Cholbut SLN was incubated with a number of cancer cell lines or human umbilical vein endothelial cells (HUVEC) and adhesion was quantified by a computerized micro-imaging system. Migration was detected by the scratch 'wound-healing' assay and the Boyden chamber invasion assay. Expression of ERK and p38 MAPK was analysed by Western blot. Expression of the mRNA for E-cadherin and claudin-1 was measured by RT-PCR. KEY RESULTS Cholbut SLN inhibited HUVEC adhesiveness to cancer cell lines derived from human colon-rectum, breast, prostate cancers and melanoma. The effect was concentration and time-dependent and exerted on both cancer cells and HUVEC. Moreover, these SLN inhibited migration of cancer cells and substantially down-modulated ERK and p38 phosphorylation. The anti-adhesive effect was additive to that induced by the triggering of B7h, which is another stimulus inhibiting both ERK and p38 phosphorylation, and cell adhesiveness. Furthermore, cholbut SLN induced E-cadherin and inhibited claudin-1 expression in HUVEC. CONCLUSION AND IMPLICATIONS These results suggest that cholbut SLN could act as an anti-metastastic agent and they add a new mechanism to the anti-tumour activity of this multifaceted preparation of butyrate.

Application of MM-GB/SA and WaterMap to SRC Kinase Inhibitor Potency Prediction

WaterMap and MM-GB/SA scoring methods were applied to an extensive congeneric series of small-molecule SRC inhibitors with high-quality enzyme data and well characterized binding modes to compare the performance of these scoring methods in this data set and to provide insight into the relative strengths of each method. Only minor conformational changes in SRC bound with representative DFG-in class of inhibitors were demonstrated in previous studies; thus, the protein flexibility that normally presents a challenge to pose and potency predictions was minimized in this model system. While WaterMap correctly recognized major trends in the SAR of this series, MM-GB/SA performed better in ranking the relative ligand affinities. The different scoring methods were further analyzed to determine which aspects of series SAR were more amenable to MM-GB/SA than WaterMap scoring.

Plasminogen activator inhibitor 1 RNAi suppresses gastric cancer metastasis in vivo

Cancer metastasis remains the primary cause of pain, suffering, and death in cancer patients, and even the most current therapeutic strategies have not been highly successful in preventing or inhibiting metastasis. In most patients with scirrhous gastric cancer (one of the most aggressive of diffuse-type gastric cancer), recurrence occurs even after potentially curative resection, most frequently in the form of peritoneal metastasis. Given that the occurrence of diffuse-type gastric cancers has been increasing, the development of new strategies to combat metastasis of this disease is critically important. Plasminogen activator inhibitor-1 (PAI-1) is a critical factor in cancer progression; thus, PAI-1 RNAi may be an effective therapy against cancer metastasis. In the present study, we used an RNAi technique to reduce PAI-1 expression in an in vivo model system for gastric cancer metastasis. Ex vivo plasmid transfection and adenovirus infection were tested as mechanisms to incorporate specific PAI-1 RNAi vectors into human gastric carcinoma cells. Both approaches significantly decreased peritoneal tumor growth and the formation of bloody ascites in the mouse model, suggesting that this approach may provide a new, effective strategy for inhibiting cancer metastasis.

Fusarisetin A: Scalable Total Synthesis and Related Studies

Fusarisetin A (1) is a recently isolated natural product that displays an unprecedented chemical motif and remarkable bioactivities as a potent cancer migration inhibitor. We describe here our studies leading to an efficient and scalable total synthesis of 1. Essential to the strategy was the development of a new route for the formation of a trans-decalin moiety of this compound and the application of an oxidative radical cyclization (ORC) reaction that produces fusarisetin A (1) from equisetin (2) via a bio-inspired process. TEMPO-induced and metal/O(2)-promoted ORC reactions were evaluated. Biological screening in vitro confirms the reported potency of (+)-1. Importantly, ex vivo studies show that this compound is able to inhibit different types of cell migration. Moreover, the C(5) epimer of (+)-1 was also identified as a potent cancer migration inhibitor, while (-)-1 and 2 were found to be significantly less potent. The optimized synthesis is applicable on gram scale and provides a solid platform for analogue synthesis and methodical biological study.

Metastasis-focused cell-based SELEX generates aptamers inhibiting cell migration and invasion

Metastasis, the capacity of tumour cells to disseminate and grow at distant sites, is the main factor in cancer mortality. Compounds inhibiting migration and invasion of cancer cells are promising candidates for anticancer therapy strategies. We have generated nuclease-resistant RNA ligands (aptamers) recognizing highly metastatic cells with high affinity and specificity, and inhibiting their migratory and invasive potentials. Aptamers were generated by a cell-based subtractive SELEX technology using isogenic cell lines with similar tumorigenic potentials but opposite metastatic aggressiveness. Two aptamers, E37 and E10, bound specifically to the metastatically aggressive cell line and altered the phosphorylation of several tyrosine kinases. Fluorescent microscopy showed intracellular uptake of E37, in contrast to membrane binding of E10. Both aptamers inhibited migration of tumour cells in culture (50 and 85% inhibition with respect to control pool for E10 and E37, respectively) while only E10 inhibited cell invasion (-75% with respect to control pool). This proof-of-concept study demonstrates the potential of cell-based SELEX to yield ligands that selectively recognize aggressive metastatic cells and inhibit phenotypes linked to metastatic potential.

PD 0332991, a selective cyclin D kinase 4/6 inhibitor, preferentially inhibits proliferation of luminal estrogen receptor-positive human breast cancer cell lines in vitro

INTRODUCTION

Alterations in cell cycle regulators have been implicated in human malignancies including breast cancer. PD 0332991 is an orally active, highly selective inhibitor of the cyclin D kinases (CDK)4 and CDK6 with ability to block retinoblastoma (Rb) phosphorylation in the low nanomolar range. To identify predictors of response, we determined the in vitro sensitivity to PD 0332991 across a panel of molecularly characterized human breast cancer cell lines.

METHODS

Forty-seven human breast cancer and immortalized cell lines representing the known molecular subgroups of breast cancer were treated with PD 0332991 to determine IC50 values. These data were analyzed against baseline gene expression data to identify genes associated with PD 0332991 response.

RESULTS

Cell lines representing luminal estrogen receptor-positive (ER+) subtype (including those that are HER2 amplified) were most sensitive to growth inhibition by PD 0332991 while nonluminal/basal subtypes were most resistant. Analysis of variance identified 450 differentially expressed genes between sensitive and resistant cells. pRb and cyclin D1 were elevated and CDKN2A (p16) was decreased in the most sensitive lines. Cell cycle analysis showed G0/G1 arrest in sensitive cell lines and Western blot analysis demonstrated that Rb phosphorylation is blocked in sensitive lines but not resistant lines. PD 0332991 was synergistic with tamoxifen and trastuzumab in ER+ and HER2-amplified cell lines, respectively. PD 0332991 enhanced sensitivity to tamoxifen in cell lines with conditioned resistance to ER blockade.

CONCLUSIONS

These studies suggest a role for CDK4/6 inhibition in some breast cancers and identify criteria for patient selection in clinical studies of PD 0332991

Design, synthesis and prostate cancer cell-based studies of analogs of the Rho/MKL1 transcriptional pathway inhibitor, CCG-1423

We recently identified bis(amide) CCG-1423 (1) as a novel inhibitor of RhoA/C-mediated gene transcription that is capable of inhibiting invasion of PC-3 prostate cancer cells in a Matrigel model of metastasis. An initial structure-activity relationship study focusing on bioisosteric replacement of the amides and conformational restriction identified two compounds, 4g and 8, with improved selectivity for inhibition of RhoA/C-mediated gene transcription and attenuated cytotoxicity relative to 1. Both compounds were also capable of inhibiting cell invasion with equal efficacy to 1 but with less attendant cytotoxicity.

Ezrin mediates c-Myc actions in prostate cancer cell invasion

The forced overexpression of c-Myc in mouse prostate and in normal human prostate epithelial cells results in tumor transformation with an invasive phenotype. How c-Myc regulates cell invasion is poorly understood. In this study, we have investigated the interplay of c-Myc and androgens in the regulation of prostate cancer cell invasion. We found that c-Myc induces cell invasion and anchorage-independent growth by regulating ezrin protein expression in the presence of androgens. The activity of the ezrin promoter is controlled by androgens through c-Myc, which binds to a phylogenetically conserved E-Box located in the proximal promoter region. Besides, we also show that ezrin is an important regulator of c-Myc protein levels. These effects are achieved through androgen-induced changes in ezrin phosphorylation, which results in the regulation of downstream signals. These downstream signals involve the modulation of Akt and GSK-3beta activity resulting in increased c-Myc protein synthesis and inhibition of its degradation. In summary, we have shown a key role for ezrin as a mediator of c-Myc-induced tumorigenesis in prostate cancer cells.

Prevention of pulmonary metastasis from subcutaneous tumors by binary system-based sustained delivery of catalase

Catalase delivery can be effective in inhibiting reactive oxygen species (ROS)-mediated acceleration of tumor metastasis. Our previous studies have demonstrated that increasing the plasma half-life of catalase by pegylation (PEG-catalase) significantly increases its potency of inhibiting experimental pulmonary metastasis in mice. In the present study, a biodegradable gelatin hydrogel formulation was used to further increase the circulation time of PEG-catalase. Implantation of (111)In-PEG-catalase/hydrogel into subcutaneous tissues maintained the radioactivity in plasma for more than 14 days. Then, the effect of the PEG-catalase/hydrogel on spontaneous pulmonary metastasis of tumor cells was evaluated in mice with subcutaneous tumor of B16-BL6/Luc cells, a murine melanoma cell line stably expressing luciferase. Measuring luciferase activity in the lung revealed that the PEG-catalase/hydrogel significantly (P<0.05) inhibited the pulmonary metastasis compared with PEG-catalase solution. These findings indicate that sustaining catalase activity in the blood circulation achieved by the use of pegylation and gelatin hydrogel can reduce the incidence of tumor cell metastasis.

Quantification of focal adhesion kinase activation loop phosphorylation as a biomarker of Src activity

A recently developed stable isotope dilution liquid chromatography-multiple reaction/mass spectrometry method to quantify focal adhesion kinase (FAK) activation loop phosphorylation was used to study endogenous Src kinase activity. This revealed that bis-phosphorylated pTyr(576)/Tyr(577)-FAK was a biomarker of Src activity and inactivation in vitro and in cell culture. Mouse embryonic fibroblasts (MEFs) expressing endogenous Src family kinases contained 65% unmodified Tyr(576)/Tyr(577), 33% mono-phosphorylated-pTyr(576)-FAK, and 6% bis-phosphorylated-pTyr(576)/pTyr(577)-FAK. In contrast, MEFs expressing oncogenic Y(529)FSrc contained 38% unmodified Tyr(576)/Tyr(577)-FAK, 29% mono-phosphorylated-pTyr(576)-FAK, and 19% bis-phosphorylated-pTyr(576)/pTyr(577)-FAK. This new method has made it possible to accurately determine the absolute amounts of FAK phosphorylation that occur after Src inhibition in cell culture and in vitro with increasing concentrations of the Src inhibitor N-(5-chloro-1,3-benzodioxol-4-yl)-7-[2-(4-methylpiperazin-1-yl)ethoxy]-5-(tetrahydro-2H-pyran-4-yloxy)quinazolin-4-amine (AZD0530). Phosphorylation of FAK at Tyr(576)/Tyr(577) was inhibited by AZD0530 in a dose-dependent manner both in cell culture and in vitro. However, there was a substantial difference in the ability of AZD0530 to inhibit Src that was constitutively activated in a cellular context (IC(50) = 2.12 muM) compared with the isolated enzyme (IC(50) = 0.14 muM). When normal MEFs and Y(529)FSrc-expressing MEFs were treated with pervanadate (a global phosphatase inhibitor), pTyr(576)/pTyr(577)-FAK accounted for almost 60% of the total FAK present in the cells. This suggests that activation loop phosphorylation is regulated by tyrosine phosphatases. These results confirm that FAK phosphorylation is a useful biomarker of Src inhibition in vivo. The accuracy and specificity of stable isotope dilution liquid chromatography-mass spectrometry methodology offers significant advantages over current immunochemical approaches for monitoring Src activity.

Multistrip western blotting to increase quantitative data output

The qualitative and quantitative measurements of protein abundance and modification states are essential in understanding their functions in diverse cellular processes. Typical western blotting, though sensitive, is prone to produce substantial errors and is not readily adapted to high-throughput technologies. Multistrip western blotting is a modified immunoblotting procedure based on simultaneous electrophoretic transfer of proteins from multiple strips of polyacrylamide gels to a single membrane sheet. In comparison with the conventional technique, Multistrip western blotting increases the data output per single blotting cycle up to tenfold, allows concurrent monitoring of up to nine different proteins from the same loading of the sample, and substantially improves the data accuracy by reducing immunoblotting-derived signal errors. This approach enables statistically reliable comparison of different or repeated sets of data, and therefore is beneficial to apply in biomedical diagnostics, systems biology, and cell signaling research.

Rationally designed peptide regulators of protein kinase C

Protein-protein interactions sequester enzymes close to their substrates. Protein kinase C (PKC) is one example of a ubiquitous signaling molecule with effects that are dependent upon localization. Short peptides derived from interaction sites between each PKC isozyme and its receptor for activated C kinase act as highly specific inhibitors and have become available as selective drugs in basic research and animal models of human diseases, such as myocardial infarction and hyperglycemia. Whereas the earlier inhibitory peptides are highly specific, we believe that peptides targeting additional interactions between PKC and selective substrates will generate even more selective tools that regulate different functions of individual isozymes. Here, we discuss the methodologies and applications for identifying selective regulators of PKC.

Total syntheses of (+)- and (-)-peribysin E

A convergent, stereocontrolled route to either antipode of the cell adhesion inhibitor, peribysin E, has been achieved from carvone. Highlights of the synthesis include a Diels-Alder reaction to generate a cis-decalin framework, followed by semipinacol-type ring contraction to secure the stereochemistry of the C7 quaternary center. Potential mechanistic pathways for the critical ring contraction were studied through deuterium incorporation studies. In addition, an optimized olefin isomerization/Saegusa oxidation protocol is described for the conversion of [4+2] cycloadducts of 2-(trialkylsilyloxy)-1,3-dienes to 1,6(2H,7H)-naphthalenediones, having stereochemical arrangements not accessible via conventional Robinson annulation protocols. Finally, the ability to independently prepare either enantiomer of peribysin E from the corresponding antipode of carvone led to a reassignment of the absolute configuration of peribysin E.

CCG-1423: a small-molecule inhibitor of RhoA transcriptional signaling

Lysophosphatidic acid receptors stimulate a Galpha(12/13)/RhoA-dependent gene transcription program involving the serum response factor (SRF) and its coactivator and oncogene, megakaryoblastic leukemia 1 (MKL1). Inhibitors of this pathway could serve as useful biological probes and potential cancer therapeutic agents. Through a transcription-based high-throughput serum response element-luciferase screening assay, we identified two small-molecule inhibitors of this pathway. Mechanistic studies on the more potent CCG-1423 show that it acts downstream of Rho because it blocks SRE.L-driven transcription stimulated by Galpha(12)Q231L, Galpha(13)Q226L, RhoA-G14V, and RhoC-G14V. The ability of CCG-1423 to block transcription activated by MKL1, but not that induced by SRF-VP16 or GAL4-VP16, suggests a mechanism targeting MKL/SRF-dependent transcriptional activation that does not involve alterations in DNA binding. Consistent with its role as a Rho/SRF pathway inhibitor, CCG-1423 displays activity in several in vitro cancer cell functional assays. CCG-1423 potently (<1 mumol/L) inhibits lysophosphatidic acid-induced DNA synthesis in PC-3 prostate cancer cells, and whereas it inhibits the growth of RhoC-overexpressing melanoma lines (A375M2 and SK-Mel-147) at nanomolar concentrations, it is less active on related lines (A375 and SK-Mel-28) that express lower levels of Rho. Similarly, CCG-1423 selectively stimulates apoptosis of the metastasis-prone, RhoC-overexpressing melanoma cell line (A375M2) compared with the parental cell line (A375). CCG-1423 inhibited Rho-dependent invasion by PC-3 prostate cancer cells, whereas it did not affect the Galpha(i)-dependent invasion by the SKOV-3 ovarian cancer cell line. Thus, based on its profile, CCG-1423 is a promising lead compound for the development of novel pharmacologic tools to disrupt transcriptional responses of the Rho pathway in cancer.

Non-invasive assessment of vessel morphology and function in tumors by magnetic resonance imaging

The switch to an angiogenic phenotype is an important precondition for tumor growth, invasion and spread. Since newly formed vessels are characterized by structural, functional and molecular abnormalities, they offer promising targets for tumor diagnosis and therapy. Previous studies indicate that MRI is valuable to assess vessel morphology and function. It can be used to distinguish between benign and malignant lesions and to improve delineation of proliferating areas within heterogeneous tumors. In addition, tracer kinetic analysis of contrast-enhanced image series allows the estimation of well-defined physiological parameters such as blood volume, blood flow and vessel permeability. Frequently, changes of these parameters during cytostatic, anti-angiogenic and radiation therapy precede tumor volume reduction. Moreover, target-specific MRI techniques can be used to elucidate the expression of angiogenic markers at the molecular level. This review summarizes strategies for non-invasive characterization of tumor vascularization by functional and molecular MRI, hereby introducing representative preclinical and clinical applications.

Comparing antibody and small-molecule therapies for cancer

The 'magic bullet' concept of specifically targeting cancer cells at the same time as sparing normal tissues is now proven, as several monoclonal antibodies and targeted small-molecule compounds have been approved for cancer treatment. Both antibodies and small-molecule compounds are therefore promising tools for target-protein-based cancer therapy. We discuss and compare the distinctive properties of these two therapeutic strategies so as to provide a better view for the development of new drugs and the future direction of cancer therapy.

Structural basis of Src tyrosine kinase inhibition with a new class of potent and selective trisubstituted purine-based compounds

The tyrosine kinase pp60src (Src) is the prototypical member of a family of proteins that participate in a broad array of cellular signal transduction processes, including cell growth, differentiation, survival, adhesion, and migration. Abnormal Src family kinase (SFK) signaling has been linked to several disease states, including osteoporosis and cancer metastases. Src has thus emerged as a molecular target for the discovery of small-molecule inhibitors that regulate Src kinase activity by binding to the ATP pocket within the catalytic domain. Here, we present crystal structures of the kinase domain of Src in complex with two purine-based inhibitors: AP23451, a small-molecule inhibitor designed to inhibit Src-dependent bone resorption, and AP23464, a small-molecule inhibitor designed to inhibit the Src-dependent metastatic spread of cancer. In each case, a trisubstituted purine template core was elaborated using structure-based drug design to yield a potent Src kinase inhibitor. These structures represent early examples of high affinity purine-based Src family kinase-inhibitor complexes, and they provide a detailed view of the specific protein-ligand interactions that lead to potent inhibition of Src. In particular, the 3-hydroxyphenethyl N9 substituent of AP23464 forms unique interactions with the protein that are critical to the picomolar affinity of this compound for Src. The comparison of these new structures with two relevant kinase-inhibitor complexes provides a structural basis for the observed kinase inhibitory selectivity. Further comparisons reveal a concerted induced-fit movement between the N- and C-terminal lobes of the kinase that correlates with the affinity of the ligand. Binding of the most potent inhibitor, AP23464, results in the largest induced-fit movement, which can be directly linked to interactions of the hydrophenethyl N9 substituent with a region at the interface between the two lobes. A less pronounced induced-fit movement is also observed in the Src-AP23451 complex. These new structures illustrate how the combination of structural, computational, and medicinal chemistry can be used to rationalize the process of developing high affinity, selective tyrosine kinase inhibitors as potential therapeutic agents.

AP23846, a novel and highly potent Src family kinase inhibitor, reduces vascular endothelial growth factor and interleukin-8 expression in human solid tumor cell lines and abrogates downstream angiogenic processes

c-Src is frequently activated in human malignancies, including colon, breast, and pancreatic carcinomas. Several recent studies have shown that activation of Src family kinases leads to tumor progression and metastasis by increasing cellular migration and invasion, promoting cell growth and survival, and deregulating expression of proangiogenic molecules. Therefore, selective inhibitors of Src are being developed for cancer therapy. In this study, we characterize the biological effects of the novel ATP-based Src family kinase inhibitor, AP23846, in tumor cells with high Src activity. As a lead compound, AP23846 is a potent c-Src kinase inhibitor (IC50 approximately 0.5 nmol/L in vitro, approximately 10-fold more potent than PP2, the most widely used commercially available Src family kinase inhibitor). At concentrations of 1 micromol/L, AP23846 led to complete Src inhibition for 48 hours in cells. No cytotoxicity was observed under these conditions, although proliferation rates were slower. Therefore, this was an excellent inhibitor to examine Src-regulated signaling pathways in tumor cells. AP23846 reduced cellular migration, vascular endothelial growth factor, and interleukin-8 in a dose-dependent fashion in pancreatic adenocarcinoma cells grown in vitro. Correspondingly, cell culture supernatants from L3.6pl pancreatic adenocarcinoma cells pretreated with AP23846 failed to promote migration of hepatic endothelial cells in vitro and failed to support angiogenesis into gel foams implanted s.c. in mice in vivo. These results suggest that Src inhibitors affect biological properties of tumor progression and may be useful as cancer therapeutic agents in more advanced disease.

Synthesis of a novel conformationally restricted Val-Phe dipeptidomimetic

A method for the synthesis of (3(R,S),6S,11b(R,S))-1,3,4,6,7,11b-hexahydro-4-oxo-3-phthalimidopyrido[2,1-a]isoquinoline-6-carboxylic acid 2 as a new conformationally restricted dipeptidomimetic of Val-Phe is reported. It involved cyclisation via an intramolecular electrophilic addition at the reactive bridgehead carbon. This new scaffold can be used as a building block in the preparation of libraries of peptidomimetics.

Syk activation in dendritic cells is essential for airway hyperresponsiveness and inflammation

We evaluated the role of Syk, using an inhibitor, on allergen-induced airway hyperresponsiveness (AHR) and airway inflammation in a system shown to be B cell- and mast cell-independent. Sensitization of BALB/c mice with ovalbumin (OVA) and alum after three consecutive OVA challenges resulted in AHR to inhaled methacholine and airway inflammation. The Syk inhibitor R406 (30 mg/kg, administered orally, twice daily) prevented the development of AHR, increases in eosinophils and lymphocytes and IL-13 levels in bronchoalveolar lavage (BAL) fluid, and goblet cell metaplasia when administered after sensitization and before challenge with OVA. Levels of IL-4, IL-5, and IFN-gamma in BAL fluid and allergen-specific antibody levels in serum were not affected by treatment. Because many of these responses may be influenced by dendritic cell function, we investigated the effect of R406 on bone marrow-derived dendritic cell (BMDC) function. Co-culture of BMDC with immune complexes of OVA and IgG anti-OVA together with OVA-sensitized spleen mononuclear cells resulted in increases in IL-13 production. IL-13 production was inhibited if the BMDCs were pretreated with the Syk inhibitor. Intratracheal transfer of immune complex-pulsed BMDCs (but not nonpulsed BMDCs) to naive mice before airway allergen challenge induced the development of AHR and increases in BAL eosinophils and lymphocytes. All of these responses were inhibited if the transferred BMDCs were pretreated with R406. These results demonstrate that Syk inhibition prevents allergen-induced AHR and airway inflammation after systemic sensitization and challenge, at least in part through alteration of DC function.

c-Src regulates constitutive and EGF-mediated VEGF expression in pancreatic tumor cells through activation of phosphatidyl inositol-3 kinase and p38 MAPK

OBJECTIVES

Multiple signaling proteins may be aberrantly activated and/or overexpressed in pancreatic tumors, including the nonreceptor protein tyrosine kinase Src. The goal of this study was to determine the role of Src in regulating VEGF expression and angiogenic potential in pancreatic cancer cell lines.

METHODS

Src activity was inhibited using the Src family kinase selective inhibitor PP2, and c-Src expression was down-regulated via siRNA. The activities of downstream signaling molecules phosphatidyl inositol 3'-kinase (PI3K) and p38 mitogen-activated protein kinase (MAPK) were disrupted via selective inhibitors. In vivo angiogenesis was assessed through the use of a gel-foam assay.

RESULTS

Inhibition of Src activity or expression decreases both constitutive and EGF-induced VEGF production. Both the PI3K/Akt and p38 MAPK pathways are activated in a Src family kinase-dependent fashion on EGF-R activation and are important for EGF-mediated VEGF production in pancreatic cancer cells. Additionally, media from Src-inhibited L3.6pl cells fail to promote angiogenesis into gel foams implanted subcutaneously into mice, whereas media from control cells promote a robust angiogenic response.

CONCLUSIONS

Src activity contributes to constitutive and EGF-induced VEGF expression and angiogenic potential in pancreatic cancer cells. Therefore, Src may be a viable target for antiangiogenesis therapy in pancreatic cancer.

Genetically based therapeutics for cancer: similarities and contrasts with traditional drug discovery and development

The field of molecular therapeutics is in its infancy and represents a promising and novel avenue for targeted cancer treatments. Like the small-molecule and antibody therapeutics before them, however, the genetic-based therapies will face significant research and development challenges in their maturation toward an approved cancer therapy. To facilitate this process, we outline and examine in this review the drug development process, briefly summarizing the research and development paradigms that have accompanied the recent successes of the small-molecule and antibody-based cancer therapeutics. Using this background, we compare and contrast the research and development experiences of small-molecule and antibody therapeutics with genetic-based cancer therapeutics, using oncolytic viruses as a defined example of an experimental molecular therapeutic for cancer.

Evaluation of cell penetrating peptides fused to elastin-like polypeptide for drug delivery

Translocation through the plasma membrane is a major limiting step for the cellular delivery of macromolecules. Several cell penetrating peptides (CPP) have been demonstrated to efficiently internalize various molecular cargo to targets inside eukaryotic cells. In this study, the efficiency and mechanism of cellular uptake of the CPPs penetratin, Tat, and MTS fused to elastin-like polypeptides (CPP-ELP) were evaluated. Elastin-like polypeptides are biopolymers with features that make them useful as polymeric carriers for the delivery of therapeutics. Therefore, improving efficiency of cellular uptake by fusing ELPs to CPPs and understanding the mechanism of their cellular internalization could contribute to development of new therapeutic approaches. Flow cytometry and confocal fluorescence microscopy were used to elucidate the mechanism of CPP-ELP uptake. The internalization of all CPP-ELPs was impaired dramatically at 4 degrees C, under ATP depletion conditions, and with hyperosmolar sucrose, implicating involvement of an endocytic pathway for CPP-ELP internalization. Penetratin was identified as the most effective CPP for delivering ELP. Finally, in order to demonstrate the potential of CPP-ELP for drug delivery, a fusion polypeptide was made containing penetratin, ELP, and a peptide derived from the cyclin-dependent kinase inhibitor p21. This polypeptide was shown to inhibit proliferation of SKOV-3 and HeLa cells by slowing their growth rate.

A rapid ATP affinity-based purification for the human non-receptor tyrosine kinase c-Src

The non-receptor tyrosine kinase c-Src plays a central role in a variety of cell signaling pathways that regulate cell growth, differentiation, apoptosis, and other important cellular processes. An 85-amino acid N-terminal deletion construct of c-Src (DeltaN85 c-Src) has been structurally characterized and used extensively in biochemical and biophysical studies. In this report, we have established a relatively rapid, simplified purification of DeltaN85 c-Src from recombinant baculovirus-infected insect cells. Q-Sepharose anion-exchange and aminophenyl-ATP affinity chromatography were used to isolate 5mg of >98% pure DeltaN85 c-Src from 900 mg of total soluble protein. The specific activity of DeltaN85 c-Src (20 U mg(-1)) was found to be >or = 5-fold greater than previously reported values. A lag in the autophosphorylation kinetics of DeltaN85 c-Src was observed, and the reaction occurred with observed first-order rate constants k1=0.20+/-0.01 min(-1) and k2=0.38+/-0.01 min(-1) under the experimental conditions used. Steady-state kinetic analysis of peptide phosphorylation by DeltaN85 c-Src gave Km values of 99+/-23 microM and 190+/-30 microM for the peptide and ATP substrates, respectively, and a value of k(cat)=17+/-2s(-1). Overall, we present a dramatically improved purification strategy that represents a simplified, relatively rapid protocol for the isolation of milligram quantities of DeltaN85 c-Src required for rigorous structure-function and inhibition studies that rely on a pre-steady-state kinetic approach.

Characterization of the activities of actin-affecting drugs on tumor cell migration

Metastases kill 90% of cancer patients. It is thus a major challenge in cancer therapy to inhibit the spreading of tumor cells from primary tumor sites to those particular organs where metastases are likely to occur. Whereas the actin cytoskeleton is a key component involved in cell migration, agents targeting actin dynamics have been relatively poorly investigated. Consequently, valuable in vitro pharmacological tools are needed to selectively identify this type of agent. In response to the absence of any standardized process, the present work aims to develop a multi-assay strategy for screening actin-affecting drugs with anti-migratory potentials. To validate our approach, we used two cancer cell lines (MCF7 and A549) and three actin-affecting drugs (cytochalasin D, latrunculin A, and jasplakinolide). We quantified the effects of these drugs on the kinetics of actin polymerization in tubes (by means of spectrofluorimetry) and on the dynamics of actin cytoskeletons within whole cells (by means of fluorescence microscopy). Using quantitative videomicroscopy, we investigated the actual effects of the drugs on cell motility. Finally, the combined drug effects on cell motility and cell growth were evaluated by means of a scratch-wound assay. While our results showed concordant drug-induced effects on actin polymerization occurring in vitro in test tubes and within whole cells, the whole cell assay appeared more sensitive than the tube assay. The inhibition of actin polymerization induced by cytochalasin D was paralleled by a decrease in cell motility for both cell types. In the case of jasplakinolide, which induces actin polymerization, while it significantly enhanced the locomotion of the A549 cells, it significantly inhibited that of the MCF-7 ones. All these effects were confirmed by means of the scratch-wound assay except of the jasplakinolide-induced effects on MCF-7 cell motility. These later seemed compensated by an additional effect occurring during wound recolonization (possibly acting on the cell growth features). In conclusion, the use of multi-assays with different levels of sophistication and biological relevance is recommended in the screening of new actin-affecting drugs with potentially anti-migratory effects.

Possible future issues in the treatment of glioblastomas: special emphasis on cell migration and the resistance of migrating glioblastoma cells to apoptosis

PURPOSE

The present review aims to emphasize that malignant gliomas are characterized by the diffuse invasion of distant brain tissue by a myriad of single migrating cells that exhibit decreased levels of apoptosis (programmed cell death type I), thus a resistance to cytotoxic insult.

METHODS

The present review surveys the molecular mechanisms of migration in malignant gliomas and potential issues arising from treatments, in addition to relationships between glioma cell migration and resistance to apoptosis in terms of the molecular signaling pathways.

RESULTS

Clinical and experimental data demonstrate that glioma cell migration is a complex combination of multiple molecular processes, including the alteration of tumor cell adhesion to a modified extracellular matrix, the secretion of proteases by the cells, and modifications to the actin cytoskeleton. Intracellular signaling pathways involved in the acquisition of resistance to apoptosis by migrating glioma cells concern PI3K, Akt, mTOR, NF-kappaB, and autophagy (programmed cell death type II).

CONCLUSION

A number of signaling pathways can be constitutively activated in migrating glioma cells, thus rendering these cells resistant to cytotoxic insults. However, these pathways are not all constitutively activated at the same time in any one glioma. Particular inhibitors should therefore only be chosen if the target is present in the tumor tissue, but this is only possible if individual patients are submitted to the molecular profiling of their tumors before undergoing any treatment to combat their migratory glioma cells. Specific antimigratory compounds should be added to conventional radio- and/or chemotherapy.

Identification of Src-Specific Phosphorylation Site on Focal Adhesion Kinase: Dissection of the Role of Src SH2 and Catalytic Functions and Their Consequences for Tumor Cell Behavior

Src tyrosine kinase expression and activity are elevated during colon cancer progression. How this contributes to the malignant phenotype is not fully understood. We show that in KM12C colon carcinoma cells, expression of kinase-deficient Src proteins (SrcMF and Src251) does not alter cell growth. Src kinase activity is required for turnover of cell-matrix adhesions and, in particular, the Src-dependent phosphorylation of focal adhesion kinase (FAK) is required for their disassembly. Surprisingly, we found that expression of SrcMF or Src251 resulted in increased tyrosine phosphorylation of FAK on Tyr(407), Tyr(576), Tyr(577), and Tyr(861), which are considered to be Src kinase substrates. This Src kinase-independent phosphorylation of FAK required an intact Src SH2 domain that mediates association of Src and FAK at peripheral adhesions. Use of a novel highly potent and selective Src kinase inhibitor AP23464 combined with experiments in Src/Fyn/Yes-deficient fibroblasts showed that increased phosphorylation of FAK in cells expressing SrcMF did not require Src-like kinases. However, specific phosphorylation on Tyr(925) of FAK was not evident in SrcMF- or Src251-expressing cells, and lack of Src kinase-dependent phosphorylation on this site was associated with impaired adhesion turnover. Our data show that Src kinase activity is required for adhesion turnover associated with cell migration in cancer cells and that, in addition to the catalytic activity, Src also acts as an adaptor to recruit other kinases that can phosphorylate key substrates including FAK. These studies have implications for tumor progression with respect to the use of Src kinase inhibitors.

Recombinant EWS-FLI1 oncoprotein activates transcription

The Ewing's sarcoma family of tumors (ESFT) contains a characteristic translocation the chimeric transcript of which is translated to become the EWS-FLI1 fusion protein. EWS-FLI1 regulates transcription and posttranscriptional splicing. Elimination of EWS-FLI1 protein from ESFT cells induces apoptosis and reduces xenograft tumor growth. Therefore the production of a biologically active recombinant EWS-FLI1 could lead to discoveries that would enhance our mechanistic understanding of ESFT. We have cloned, expressed, and purified a biologically active recombinant EWS-FLI1 in Escherichia coli using affinity column chromatography. A refolding procedure was required to render the recombinant EWS-FLI1 soluble in relatively native conditions. The structural alterations induced by the refolding procedure were monitored by SDS-gel electrophoresis, circular dichroism, and steady-state fluorescence spectroscopy. Recombinant EWS-FLI1 under native conditions approaches a largely unfolded conformation. Recombinant EWS-FLI1 protein under native conditions specifically binds to DNA and transcribes RNA. Our biologically active recombinant EWS-FLI1 oncoprotein will be useful to identify functional molecular partners and inhibitors.

Amplifying cancer vaccine responses by modifying pathogenic gene programs in tumor cells

Immunosuppressive factors, such as vascular endothelial growth factor, transforming growth factor-beta, prostaglandin E2, interleukin (IL)-10, and IL-6, are made frequently by cancer cells. These factors, along with others, can inhibit the development and function of tumor-reactive effector T cells and the clinical results of cancer vaccines. Production of these factors by tumor cells is associated with disease progression and may represent an active immune surveillance escape mechanism. However, a number of factors appear to be made directly in response to signaling molecules, such as RAS, AKT, and signal transducer and activator of transcription 3, which are activated as a result of genetic events that occur during oncogenesis. Methods to overcome the negative effects of immunosuppressive factors, which are "hard wired" into gene programs of cancer cells, might then improve the results of cancer vaccines. For example, specific blocking antibodies, which recognize such factors, or kinase inhibitors, which block the signaling pathways that lead to their production, could potentially be used as vaccine adjuvants. The effects of immunosuppressive factors may also be "turned off" by cytokines with tumor suppressor properties. The enhanced clinical and immunological effects of melanoma vaccines observed after the administration of high doses of interferon-alpha2b provide a "proof of principle" in human patients, that agents which counter the gene programs of cancer cells, causing them to intrinsically resist tumor-reactive T cells, may improve significantly the efficacy of cancer vaccines.