The Rho kinase inhibitor fasudil inhibits tumor progression in human and rat tumor models

The ability of cancer cells to undergo invasion and migration is a prerequisite for tumor metastasis. Rho, a Ras-related small GTPase, and the Rho-associated coiled coil-containing protein kinases (Rho kinases, ROCK1 and ROCK2) are key regulators of focal adhesion, actomyosin contraction, and thus cell motility. Inhibitors of this pathway have been shown to inhibit tumor cell motility and metastasis. Here, we show that fasudil [1-(5-isoquinolinesulfonyl)-homopiperazine], an orally available inhibitor of Rho kinases, and its metabolite 1-(hydroxy-5-isoquinoline sulfonyl-homopiperazine) (fasudil-OH) modify tumor cell morphology and inhibit tumor cell migration and anchorage-independent growth. In addition, we show that fasudil inhibited tumor progression in three independent animal models. In the MM1 peritoneal dissemination model, tumor burden and ascites production were reduced by > 50% (P < 0.05). In the HT1080 experimental lung metastasis model, fasudil decreased lung nodules by approximately 40% (P < 0.05). In the orthotopic breast cancer model with MDA-MB-231, there were 3-fold more tumor-free mice in the fasudil-treated group versus saline control group (P < 0.01). Fasudil has been approved for the treatment of cerebral vasospasm and associated cerebral ischemic symptoms. In patients, fasudil is well tolerated without any serious adverse reactions. Therefore, the concept of Rho kinase inhibition as an antimetastatic therapy for cancer can now be clinically explored.

Urokinase receptors are required for alpha 5 beta 1 integrin-mediated signaling in tumor cells

Up-regulation of urokinase receptors is common during tumor progression and thought to promote invasion and metastasis. Urokinase receptors bind urokinase and a set of beta1 integrins, but it remains unclear to what degree urokinase receptor/integrin binding is important to beta1 integrin signaling. Using site-directed mutagenesis, single amino acid mutants of the urokinase receptor were identified that fail to associate with either alpha3beta1 (D262A) or alpha5beta1 (H249A) but associate normally with urokinase. To study the effects of these mutations on beta1 integrin function, endogenous urokinase receptors were first stably silenced in tumor cell lines HT1080 and H1299, and then wild type or mutant receptors were expressed. Knockdown of urokinase receptors resulted in markedly reduced fibronectin and alpha5beta1-dependent ERK activation and metalloproteinase MMP-9 expression. Re-expression of wild type or D262A mutant receptors but not the alpha5beta1 binding-deficient H249A mutant reconstituted fibronectin responses. Because urokinase receptor.alpha5beta1 complexes bind in the fibronectin heparin-binding domain (Type III 12-14) whereas alpha5beta1 primarily binds in the RGD-containing domain (Type III 7-10), signaling pathways leading to ERK and MMP-9 responses were dissected. Binding to III 7-10 led to Src/focal adhesion kinase activation, whereas binding to III 7-14 caused Rac 1 activation. Tumor cells engaging fibronectin required both Type III 7-10- and 12-14-initiated signals to activate ERK and up-regulate MMP-9. Thus urokinase receptor binding to alpha5beta1 is required for maximal responses to fibronectin and tumor cell invasion, and this operates through an enhanced Src/Rac/ERK signaling pathway.

Inhibitory effect of chitooligosaccharides on matrix metalloproteinase-9 in human fibrosarcoma cells (HT1080)

Matrix metalloproteinase-9 (MMP-9) has gelatinase activity and plays an important role in cancer invasion and metastasis. Therefore, inhibition of specific types of MMPs including MMP-9 has become an attractive target for therapeutic intervention. The aim of this study was to investigate the effect of chitooligosaccharides (COS) on activity and expression of MMP-9 in HT1080 cells. The inhibitory effect of COS with different molecular masses was examined by gelatin zymography, reverse transcriptase-polymerase chain reaction (RT-PCR), gene reporter assay, and Western blot analysis. MMP-9 inhibition in the presence of COS was clearly observed in gelatin zymography. Specifically, 1- to 3-kDa COS (COS-I) exhibited the highest inhibitory effect on MMP-9 activity in HT1080 cells among tested molecular mass fractions. It was also found that COS-I was capable of inhibiting both gene and protein expression of MMP-9 (P<0.01). These results suggest that low molecular mass COS can be considered as a potent inhibitor of MMP-9.

Tumour suppressor function of RNase L in a mouse model

RNase L is one of the key enzymes involved in the molecular mechanisms of interferon (IFN) actions. Upon binding with its activator, 5'-phosphorylated, 2'-5' oligoadenylates (2-5A), RNase L plays an important role in the antiviral and anti-proliferative functions of IFN, and exerts proapoptotic activity independent of IFN. In this study, we have found that RNase L retards proliferation in an IFN-dependent and independent fashion. To directly measure the effect of RNase L on tumour growth in the absence of other IFN-induced proteins, human RNase L cDNA was stably expressed in P-57 cells, an aggressive mouse fibrosarcoma cell line. Three clonal cell lines were isolated in which the overexpression of RNase L was 15-20-fold of the endogenous level. Groups of five nude mice were injected subcutaneously with either the human RNase L overexpressing clones (P-RL) or control cells transfected with an empty vector (P-Vec). Tumour growth by the two cell lines was monitored by measuring tumour volumes. In the P-RL group, tumour formation was significantly delayed and the tumours grew much slower compared to the control group. Morphologically, the P-RL tumour appeared to have more polygonal cells and increased single cell tumour necrosis. Interestingly, P-RL tumours eventually started to grow. Further analysis revealed, however, that these tumours no longer expressed ectopic RNase L. Our findings suggest that RNase L plays a critical role in the inhibition of fibrosarcoma growth in nude mice.

Oncolytic efficacy and enhanced safety of measles virus activated by tumor-secreted matrix metalloproteinases

Cancer cells secrete matrix metalloproteinases (MMP) that degrade the extracellular matrix and are responsible for some hallmarks of malignant cancer. Many viruses, including a few currently used in oncolytic virotherapy clinical trials, depend on intracellular proteases to process their proteins and activate their particles. We show here for measles virus (MV) that particle activation can be made dependent of proteases secreted by cancer cells. The MV depends on the intracellular protease furin to process and activate its envelope fusion (F) protein. To make F protein activation cancer cell specific, we introduced hexameric sequences recognized by an MMP and identified the mutant proteins most effective in fusing MMP-expressing human fibrosarcoma cells (HT1080). We showed that an MMP inhibitor interferes with syncytia formation elicited by mutant F proteins and confirmed MMP-dependent cleavage by Edman degradation sequence analysis. We generated recombinant MVs expressing the modified F proteins in place of furin-activated F. These viruses spread only in cells secreting MMP. In nude mice, an MMP-activated MV retarded HT1080 xenograft growth as efficiently as the furin-activated MV vaccine strain. In MV-susceptible mice, the furin-activated virus caused lethal encephalitis upon intracerebral inoculation, whereas the MMP-activated did not. Thus, MV particle activation can be made dependent of proteases secreted by cancer cells, enhancing safety. This study opens the perspective of combining targeting at the particle activation, receptor recognition, and selective replication levels to improve the therapeutic index of MV and other viruses in ongoing clinical trials of oncolysis.

Selective antitumor effect of novel protease-mediated photodynamic agent

A new approach to selective photodynamic therapy (PDT) was developed by designing chlorin e6 (Ce6)-containing macromolecules, which are sensitive to tumor-associated proteases. The agents are nontoxic in their native state but become fluorescent and produce singlet oxygen on protease conversion. Coupled with optimized delivery systems, we show that (a) the agents efficiently accumulate in tumors due to the enhanced permeability and retention effect, (b) the agents are locally activated by proteases, (c) local drug concentrations can be measured by quantitative fluorescence tomography, and (d) light-treated tumors show reduced growth. A single low dose of PDT (0.125 mg Ce6 equivalent/kg) was sufficient to suppress tumor growth by >50%. Activatable singlet oxygen generation agents provide increased efficacy with reduced toxicity, and it could become a powerful PDT.

Carboxylated chitooligosaccharides (CCOS) inhibit MMP-9 expression in human fibrosarcoma cells via down-regulation of AP-1

Matrix metalloproteinases (MMPs) play a fundamental role in invasion and metastasis of tumor and, recent advances in medicinal chemistry have approached designing of MMP inhibitors with desired structural properties, selectivity and bioavailability. In the present study, novel low-molecular-weight carboxylated chitooligosaccharides (CCOS) were evaluated for their MMP-9 inhibitory effect on human fibrosarcoma cell line (HT1080). In zymography experiments, a clear dose-dependent inhibition on MMP-9 mediated gelatinolytic activities were observed in HT1080 cells following treatment with CCOS. Further, transfection studies carried out with MMP-9 and AP-1 reporter constructs suggested that the observed reduction in MMP-9 expression was due to down-regulation of MMP-9 transcription that mediated via inhibition of AP-1. Moreover, expression of c-Fos protein levels in cytoplasm and nucleus confirmed that CCOS could inhibit AP-1 expression but not its translocation. However, in the presence of CCOS, NF-kappaB and TIMP-1 expression levels remained constant. More importantly, inhibition of MMP-9 expression clearly led to inhibit tumor invasiveness that was studied with reconstituted basement membrane matrix proteins coated synthetic membranes. Taken together, this study discusses MMP-9 inhibition potential of CCOS and their involvement to demote degradation and cellular invasion of extracellular matrix (ECM) and basement membrane. Thus, control of MMP-9 expression by CCOS has considerable significance for the regulation of tumor progression.

Interference with the complement system by tumor cell membrane type-1 matrix metalloproteinase plays a significant role in promoting metastasis in mice

Neoplasms have developed strategies to protect themselves against the complement-mediated host immunity. Invasion- and metastasis-promoting membrane type-1 (MT1) matrix metalloproteinase (MMP) is strongly associated with many metastatic cancer types. The relative importance of the individual functions of MT1-MMP in metastasis was, however, unknown. We have now determined that the expression of murine MT1-MMP in murine melanoma B16F1 cells strongly increased the number of metastatic loci in the lungs of syngeneic C57BL/6 mice. In contrast, MT1-MMP did not affect the number of metastatic loci in complement-deficient C57BL/6-C3-/- mice. Our results indicated, for the first time, that the anticomplement activity of MT1-MMP played a significant role in promoting metastasis in vivo and determined the relative importance of the anticomplement activity in the total metastatic effect of this multifunctional proteolytic enzyme. We believe that our results shed additional light on the functions of MT1-MMP in cancer and clearly make this protease a promising drug target in metastatic malignancies.

In-vivo imaging of tumor associated urokinase-type plasminogen activator activity

The ability to image tumor associated protease in vivo has biological and clinical implications. In the present study, we describe the development and validation of a urokinase-type plasminogen activator (uPA) sensitive fluorescence imaging probe. The activation of our probe is highly specific to uPA in both enzymatic and cellular-based assays. In two distinct in-vivo tumor models (human colon adenocarcinoma HT-29 and human fibrosarcoma HT-1080), the observed fluorescence changes correlate well with tumor associated uPA activity. The signal intensities of the tumors are about three-fold higher in animals with probe injections. Our results suggest a direct detection method for uPA activity in vivo and the approach can be used for monitoring tumor growth and development.

Activity-based protein profiling implicates urokinase activation as a key step in human fibrosarcoma intravasation

Entry of malignant cells into the vasculature (i.e. intravasation) requires proteolytic remodeling of the extracellular matrix so that tumor cells may pass through the local stroma and penetrate the vessel wall. The circulatory system then provides a means of transporting tumor cells to distant sites where they extravasate and establish metastatic lesions. This study utilizes activity-based protein profiling to compare the active serine hydrolase repertoire in high intravasating (HT-hi/diss) and low intravasating (HT-lo/diss) variants of the human fibrosarcoma HT-1080 cell line to determine which enzyme(s) play a role in intravasation. Activity-based protein profiling revealed multiple serine hydrolases with altered activity between HT-hi/diss and HT-lo/diss cells, with the largest difference being the activity of urokinase-type plasminogen activator (uPA). Levels of inactive uPA zymogen were similar between the two cell variants, but only HT-hi/diss conditioned medium contained active uPA, suggesting that uPA activation may contribute to the enhanced intravasation of HT-hi/diss cells. To analyze the role of uPA activity specifically in the process of intravasation, we grafted cells from the two HT-1080 variants onto the chorioallantoic membrane of chick embryos and measured levels of tumor cell intravasation in the distal chorioallantoic membrane using quantitative human-specific Alu PCR. Inhibition of uPA activity with natural (plasminogen activator inhibitor-1) or synthetic (amiloride) inhibitors diminished HT-hi/diss Matrigel invasion in vitro and intravasation and metastasis in vivo. Additionally, treatment of HT-lo/diss tumors with exogenous active uPA increased the number of intravasated cells in vivo. These results indicate that active uPA promotes tumor cell intravasation and that uPA activation appears to be a key step in tumor progression.

Focal adhesion kinase is activated in invading fibrosarcoma cells and regulates metastasis

Focal adhesion kinase (FAK) is a nonreceptor tyrosine kinase that is overexpressed in several human cancers, and induces survival, proliferation and motility of cells in culture. Phosphorylation of FAK has been studied extensively in vitro, but little is known about its regulation during tumor invasion in vivo. In the current study, green fluorescent protein (GFP) was expressed stably in an invasive murine fibrosarcoma cell line for the purpose of discrimination between tumor and normal cells. Under fluorescence microscopy, the tumor was highly fluorescent, and the margin between the tumor and normal tissue was clearly demarcated. Using this invasion model, we showed localization of pY397-FAK expression in the infiltrative edge of tumors. We reproduced local invasion in vivo using a tumor tissue culture method in a three dimensional collagen gel. Phosphorylation of FAK is also upregulated in invading fibrosarcoma cells under in vitro conditions. Expression of the FAK C-terminal domain termed FRNK (FAK-related non-kinase) in 2,472 cells decreased FAK phosphorylation without changing total FAK levels. FRNK inhibited the motility of 2,472 cells, and reduced invasion in vitro. Although FRNK did not affect cell growth, it inhibited experimental metastases in syngenic mice. These results demonstrate that the phosphorylation of FAK might be specifically upregulated in invading fibrosarcoma cells and regulate their invasion and metastasis.

Culture of Human Fibrosarcoma HT-1080 Cells in Presence of Fibronectin Activates MMP-2

The importance of tumor cell surface integrin receptors in regulation of matrix metalloproteinase (MMP) expression and function has been reported. Integrin-ECM ligand interaction leads to phosphorylation of focal adhesion kinase (FAK) and activation of mitogen activated protein kinase (MAPK) pathways. In this present study, we cultured human fibrosarcoma cells, HT-1080, in presence of fibronectin to study fibronectin-integrin mediated modulation of MMP activity.

METHODS

HT-1080 cells were cultured in serum free medium (SFCM) in presence of fibronectin, SFCM was collected, and gelatin zymography was performed. Western blot and immunocytochemistry were performed with HT-1080 cells cultured in presence of fibronectin.

RESULTS

Culture of HT-1080 cells in presence of 50 microg/1.5 ml fibronectin led to expression of pro-MMP-9 and activation of MMP-2 within 1 hr. When HT-1080 cells were treated with PI-3K inhibitor (LY294002) and grown in presence of fibronectin, MMP-2 activation was partially inhibited, but when cells were treated with ERK inhibitor (PD98059) and grown in presence of fibronectin, MMP-2 activation was almost completely inhibited. Tyrosine phosphorylation of FAK and ERK were increased in HT-1080 cells grown in presence of fibronectin. Processing of MT1-MMP was also observed in HT-1080 cells grown in presence of fibronectin. The reorganization of actin filaments in fibronectin treated HT-1080 cells was also noticeable.

CONCLUSIONS

Our findings indicate that culture of HT-1080 cells in SFCM in presence of fibronectin perhaps generates a signaling cascade that leads to expression of pro-MMP-9 and activation of MMP-2 within 1 hr. The signaling pathway activated seems to be the FAK/ERK pathway.

Src inhibits adriamycin-induced senescence and G2 checkpoint arrest by blocking the induction of p21waf1

DNA-damaging drugs stop tumor cell proliferation by inducing apoptosis, necrosis, or senescence. Cyclin-dependent kinase inhibitor p21waf1 is an important regulator of these responses, promoting senescence and preventing aberrant mitosis that leads to cell death. Because tumors expressing oncogenic tyrosine kinases are relatively resistant to DNA-damaging agents, the effects of Src on cellular responses to anticancer drug Adriamycin were investigated. Src expression increased drug survival in HT1080 fibrosarcoma cells, as measured by the colony formation assay, and strongly inhibited Adriamycin-induced senescence. Src also decreased the number of apoptotic cells while increasing the fraction of cells dying through necrosis. In addition, Src inhibited the G2 and G1 tetraploidy checkpoints of Adriamycin-treated cells, permitting these cells to proceed into mitosis and subsequently double their DNA content. Inhibition of senescence and G2-G1 checkpoints in Src-expressing cells was associated with the failure of these cells to up-regulate p21waf1 in response to Adriamycin. The failure of p21waf1 induction, despite increased expression of p53 and its binding to p21waf1 promoter, was mediated by the up-regulation of c-Myc, a negative regulator of p21waf1 transcription. Conversely, ectopic expression of p21waf1 inhibited Myc transcription in Src-expressing cells, an effect that was associated with the interaction of p21waf1 with the STAT3 transcription factor at the Myc promoter. These results reveal a complex effect of Src on cellular drug responses and provide an explanation for the effect of this oncogene on cellular drug resistance.

Unexpected effect of matrix metalloproteinase down-regulation on vascular intravasation and metastasis of human fibrosarcoma cells selected in vivo for high rates of dissemination

The human tumor/chick embryo model involving grafting of human HT-1080 fibrosarcoma cells on the chorioallantoic membrane was used in conjunction with quantitative real-time Alu PCR to select in vivo a pair of isogenic cell lines (HT-hi/diss and HT-lo/diss), dramatically differing in their ability to disseminate from the primary tumor (i.e., intravasate into the chorioallantoic membrane vasculature and metastasize to the lungs). During an immunohistochemical time course study, HT-hi/diss cells were sequentially visualized having escaped from the primary tumors, engaged with the blood vessels, and eventually observed inside the chorioallantoic membrane capillaries, thus reflecting early intravasating events. In contrast, HT-lo/diss cells seemed restricted to their primary tumor. Importantly, after i.v. inoculation, both variants arrested, extravasated, and proliferated in host tissues with similar efficiencies, highlighting that the observed earlier events at the periphery of the primary tumor could account for their differential dissemination. In a mechanistic probing of these events, we determined that HT-hi/diss intravasation was sensitive to a broad-range matrix metalloproteinase (MMP) inhibitor. To analyze the possible role of individual MMPs, membrane-bound MMP-14 and secreted MMP-9 were individually down-regulated in HT-hi/diss cells with their corresponding small interfering RNAs. Despite efficient down-regulation of MMP-14, neither intravasation nor metastasis of HT-hi/diss cells was affected significantly. However, a substantial down-regulation of MMP-9 was accompanied by a surprising 3-fold increase in intravasation and metastasis. The results emphasize a rising awareness that targeting certain MMPs might result in an enhanced malignancy, exemplified herein at the intravasation level as this step of the metastatic cascade is dissected and quantified.

Competitive disruption of the tumor-promoting function of membrane type 1 matrix metalloproteinase/matrix metalloproteinase-14 in vivo

Membrane type 1 matrix metalloproteinase (MT1-MMP) is a potent modulator of the pericellular environment and promotes tumor cell invasion and proliferation in many types of tumor. The activation of proMMP-2 and processing of collagen I by MT1-MMP have been thought to be important for its tumor-promoting function. These activities can be inhibited by mutant forms of MT1-MMP lacking the catalytic domain. However, the effect of such dominant-negative mutants has never been evaluated in vivo. Various mutants lacking the catalytic domain (dCAT) were prepared and confirmed to inhibit MT1-MMP activity in human fibrosarcoma HT1080 cells, and tumor cells expressing these mutants were implanted s.c. into nude mice to monitor tumor formation. Only the membrane-anchored form of a dCAT construct through the transmembrane domain [dCAT(1)] showed potent antitumor activity not only in HT1080 cells but also in gastric carcinoma MKN28 and MKN45 cells expressing MT1-MMP. A soluble form of dCAT lacking the transmembrane domain did not show such activity. The expression of dCAT(1) in MKN28 or MKN45 further prevented the metastatic spread of tumor cells into the peritoneal cavity; however, dCAT(1) showed no effect against TMK-1, another gastric carcinoma cell line expressing no MT1-MMP. It is of note that the tumorigenicity of TMK-1 cells enhanced by MT1-MMP overexpression was, in turn, canceled by the additional expression of dCAT(1). Thus, MT1-MMP expressed in tumor cells seems to play a pivotal role in tumor growth in mice. The results also suggest new possibilities to abrogate the tumor-promoting function of MT1-MMP other than the conventional protease inhibitor-based approach.

Inhibitory effect of DA-125, a new anthracyclin analog antitumor agent, on the invasion of human fibrosarcoma cells by down-regulating the matrix metalloproteinases

Matrix metalloproteinases (MMPs), zinc-dependent proteolytic enzymes, play a pivotal role in tumor metastasis by cleavage of extracellular matrix as well as non-matrix substrates. In this study, we examined the influence of DA-125, a new anthracyclin analog, on the gene expression of MMPs (MMP-2, MMP-9 and MT1-MMP), tissue inhibitor of metalloproteinases (TIMP-1 and TIMP-2) and in vitro invasiveness of human fibrosarcoma cells. Dose-dependent decreases of MMPs and TIMPs mRNA levels were observed in DA-125-treated HT1080 human fibrosarcoma cells detected by reverse transcriptase-polymerase chain reaction. Gelatin zymography analysis also showed a significant down-regulation of MMP-2 and MMP-9 expression in HT1080 cells treated with DA-125 compared to controls. In addition, DA-125 inhibited the invasion, motility and cell migration, and colony formation of tumor cells. These data, therefore, provide direct evidence for the role of DA-125 as a potential cancer chemotherapeutic agent, which can markedly inhibit the invasive capacity of malignant cells. Further, to clarify the transcriptional regulatory pathway, we primarily investigated the role of nuclear factor-kappaB (NF-kappaB) in the expression of MMPs by DA-125 in HT1080 cells. Electrophoretic mobility shift assay demonstrated that DA-125 modulates the binding activity of NF-kappaB. Using the luciferase reporter gene assay, a dose-dependent down-regulation of NF-kappaB-mediated luciferase expression was also observed. These results suggest that DA-125 down-regulates MMPs expression in HT1080 cells through the NF-kappaB-mediated pathway.

Focal Adhesion Kinase Regulates Syndecan-2–Mediated Tumorigenic Activity of HT1080 Fibrosarcoma Cells

Expression of syndecan-2, a transmembrane heparan sulfate proteoglycan, is crucial for the tumorigenic activity in colon carcinoma cells. However, despite the high-level expression of syndecan-2 in mesenchymal cells, few studies have addressed the function of syndecan-2 in sarcoma cells. In HT1080 fibrosarcoma cells, we found that syndecan-2 regulated migration, invasion into Matrigel, and anchorage-independent growth but not cell-extracellular matrix adhesion or proliferation, suggesting that syndecan-2 plays different functional roles in fibrosarcoma and colon carcinoma cells. Consistent with the increased cell migration/invasion of syndecan-2-overexpressing HT1080 cells, syndecan-2 overexpression increased phosphorylation and interaction of focal adhesion kinase (FAK) and phosphatidylinositol 3-kinase (PI3K), membrane localization of T-lymphoma invasion and metastasis gene-1 (Tiam-1), and activation of Rac. Syndecan-2-mediated cell migration/invasion of HT1080 cells was diminished when (a) cells were cotransfected with nonphosphorylatable mutant FAK Y397F or with other FAK mutants lacking PI3K interactions, (b) cells were treated with a specific PI3K inhibitor, or (c) levels of Tiam-1 were knocked down with small interfering RNAs. Furthermore, expression of several FAK mutants inhibited syndecan-2-mediated enhancement of anchorage-independent growth in HT1080 cells. Taken together, these data suggest that syndecan-2 regulates the tumorigenic activities of HT1080 fibrosarcoma cells and that FAK is a key regulator of syndecan-2-mediated tumorigenic activities.

Mutations of C-RAF Are Rare in Human Cancer because C-RAF Has a Low Basal Kinase Activity Compared with B-RAF

The protein kinase B-RAF is mutated in approximately 8% of human cancers. Here we show that presumptive mutants of the closely related kinase, C-RAF, were detected in only 4 of 545 (0.7%) cancer cell lines. The activity of two of the mutated proteins is not significantly different from that of wild-type C-RAF and these variants may represent rare human polymorphisms. The basal and B-RAF-stimulated kinase activities of a third variant are unaltered but its activation by RAS is significantly reduced, suggesting that it may act in a dominant-negative manner to modulate pathway signaling. The fourth variant has elevated basal kinase activity and is hypersensitive to activation by RAS but does not transform mammalian cells. Furthermore, when we introduce the equivalent of the most common cancer mutation in B-RAF (V600E) into C-RAF, it only has a weak effect on kinase activity and does not convert C-RAF into an oncogene. This lack of activation occurs because C-RAF lacks a constitutive charge within a motif in the kinase domain called the N-region. This fundamental difference in RAF isoform regulation explains why B-RAF is frequently mutated in cancer whereas C-RAF mutations are rare.

Radiation induced MMP expression from rectal cancer is short lived but contributes to in vitro invasion

AIMS

Matrix metalloproteinase (MMP) activity is increased after radiation. The aims of this study were to assess the time course of this increase and its effects on malignant cell invasion.

METHODS

Colorectal cancer (HCT 116, LoVo, C 170 HM 2, CaCO-2), fibroblast (46-BR.IGI, CCD-18 Co) and fibrosarcoma (HT1080) cell lines were irradiated at 4 gray (4 Gy) and matrix metalloproteinase gene and protein expression examined over a 96 h period by real time polymerase chain reaction and gelatin zymography. Invasion was assessed on Matrigel. Human rectal tumour MMP expression was compared before and after long course radiotherapy.

RESULTS

Radiation increased MMP gene expression of tumour cell lines, and resulted in increased MMP protein activity in the HT1080 line. HT1080 and HCT 116 in monoculture and LoVo in co-culture were more invasive after radiation at 48 h in vitro, but long course radiotherapy did not result in a consistent increase in MMP expression from human rectal tumour biopsies.

CONCLUSIONS

Radiation results in increased MMP expression for a limited time period. This results in an early increase in cell line invasion. Further clinical research is required to clarify if MMP inhibition given perioperatively following radiotherapy decreases local recurrence rates.

Early detection of tumor response to chemotherapy by 3'-deoxy-3'-[18F]fluorothymidine positron emission tomography: the effect of cisplatin on a fibrosarcoma tumor model in vivo

We have assessed the potential of [18F]fluorothymidine positron emission tomography ([18F]FLT-PET) to measure early cytostasis and cytotoxicity induced by cisplatin treatment of radiation-induced fibrosarcoma 1 (RIF-1) tumor-bearing mice. Cisplatin-mediated arrest of tumor cell growth and induction of tumor shrinkage at 24 and 48 hours, respectively, were detectable by [18F]FLT-PET. At 24 and 48 hours, the normalized uptake at 60 minutes (tumor/liver radioactivity ratio at 60 minutes after radiotracer injection; NUV60) for [18F]FLT was 0.76 +/- 0.08 (P = 0.03) and 0.51 +/- 0.08 (P = 0.03), respectively, compared with controls (1.02 +/- 0.12). The decrease in [18F]FLT uptake at 24 hours was associated with a decrease in cell proliferation assessed immunohistochemically (a decrease in proliferating cell nuclear antigen labeling index, LI(PCNA), from 14.0 +/- 2.0% to 6.2 +/- 1.0%; P = 0.001), despite the lack of a change in tumor size. There were G1-S and G2-M phase arrests after cisplatin treatment, as determined by cell cycle analysis. For the quantitative measurement of tumor cell proliferation, [18F]FLT-PET was found to be superior to [18F]fluorodeoxyglucose-PET (NUV60 versus LIPCNA: r = 0.89, P = 0.001 and r = 0.55, P = 0.06, respectively). At the biochemical level, we found that the changes in [18F]FLT and [18F]fluorodeoxyglucose uptake were due to changes in levels of thymidine kinase 1 protein, hexokinase, and ATP. This work supports the further development of [18F]FLT-PET as a generic pharmacodynamic readout for early quantitative imaging of drug-induced changes in cell proliferation in vivo.

Aloe emodin decreases the ERK-dependent anticancer activity of cisplatin

The present study describes the ability of an anthraquinone derivative aloe emodin (AE) to reduce the cytotoxic activity of the platinum(II)-based anticancer agent cisplatin toward murine L929 fibrosarcoma and C6 glioma cell lines. The protective effect of AE was demonstrated by MTT and crystal violet assays for cell viability, and involved supression of cisplatin-induced apoptosis and necrosis, as assessed by lactate dehydrogenase release and flow cytometric analysis of DNA fragmentation or phosphatidylserine exposure. Cell-based ELISA and Western blot analysis revealed that AE abolished cisplatin-triggered activation of extracellular signal-regulated kinase (ERK) in tumor cells, while activation of c-Jun N-terminal kinase was not significantly altered. A selective blockade of ERK activation with PD98059 mimicked the protective effect of AE treatment in both tumor cell lines. Moreover, AE failed to protect tumor cells against the ERK-independent toxicity of the Pt(IV)-based complex tetrachloro(O,O-dibutyl-ethylenediamine-N,N'-di-3-propanoate)platinum(IV). Taken together, these data indicate that herbal anthraquinone AE can downregulate the anticancer activity of cisplatin by blocking the activation of ERK in tumor cells.

[Preparation of anti-OPRT antibody for immunochemical detection]

Orotate phosphoribosyl transferase (OPRT, EC 2.4.2.10) is a key enzyme in the anabolism of 5-fluorouracil (5 FU), and its expression in tumor is thought to increase the efficacy of 5-FU against the tumor. To detect the OPRT protein by immunoblotting and/or immunohistochemical methods, we tried to prepare highly specific antibody against the peptide including human OPRT amino acid sequence. The anti-OPRT polyclonal antibody obtained by immunization of OPRT peptides to rabbits had high specificity for the OPRT protein in human tumor xenografts in immunoblot and immunohistochemical analysis. Furthermore, there was a positive correlation between the activity and proteins of OPRT (R2=0.632) in 12 human tumors. These results suggest that immunohistochemical detection of tumoral OPRT protein expression using our anti-OPRT antibody may provide useful methods to predict the clinical response to 5-FU-based chemotherapy.

Cytotoxic Activity of a Tumor Protease-Activated Pore-Forming Toxin

Equinatoxin II is a pore forming toxin produced by the sea anemone Actinia equina. It is able to kill very unspecifically most cell types by the membrane-perturbing action of an amphiphilic alpha-helix located at its N-terminal. A normally active N-terminal mutant, containing one single cys in the amphiphilic alpha-helix, becomes totally inactive when it is bound to avidin via a biotinylated linker. By choosing, as a linker, a peptide containing a tumor protease cleavage site, we were able to construct an enzymatically activable conjugate which should be selective for tumor cells. The introduced cleavage site was designed in order to be digested by both cathepsin B and matrix metalloproteases (MMPs). We confirmed that this conjugate could be activated in vitro by cathepsin B and MMPs. After having measured the enzymatic activity of fibrosarcoma and breast carcinoma cells, we analyzed the cytotoxic effect of the conjugate on the same lines and on human red blood cells (HRBC) as controls. We found that the conjugate was activated, at least in part, by the tumor cell lines used, whereas it was inactive on HRBC. That the activation process was dependent on the enzymatic action of cathepsin B and MMPs, was indicated by three lines of evidence: (1) binding occurred normally on all type of cells including HRBC which however were insensitive being devoid of enzymes; (2) the cytotoxic effect correlated with the amount of cathepsin B activity expressed by the cells; (3) conjugate activation was reduced by specific inhibitors of cathepsin B and MMPs. These results demonstrate the possibility of tumor cell killing by a pore-forming toxin conjugate specifically activated by tumor proteases.

Matrix metalloproteinase-2 contributes to cancer cell migration on collagen

Matrix metalloproteinases (MMP) are central to tissue penetration by cancer cells, as tumors expand and form metastases, but the mechanism by which MMP-2 contributes to cancer cell migration is not well understood. In the present experiments, both a broad-spectrum MMP inhibitor and the isolated collagen binding domain (CBD) from MMP-2 inhibited cell migration on native type I collagen. These results verified the involvement of MMPs in general and showed that MMP-2, specifically, contributes to cell migration by a mechanism involving MMP-2 interaction with collagen. To exclude potential overlapping effects of MMP-9, additional experiments showed that MMP-2 also contributed to migration of MMP-9-/- cells. To investigate whether the homologous CBD from human fibronectin also inhibited cell migration, we first showed that fragmentation of fibronectin is a feature of breast cancer tumors and that several fragments contained the CBD. However, the recombinant fibronectin domain did not alter cell migration on collagen. This lack of effect on cell migration was explored in competitive protein-protein binding assays, which showed that the affinity of MMP-2 for collagen exceeds that of fibronectin. Furthermore, whereas the isolated MMP-2 CBD inhibited the gelatinolytic activities of MMP-2 and tumor extracts, such an inhibition was not characteristic of the corresponding fibronectin domain. Together, our results provide evidence that MMP-2 is an important determinant of cancer cell behavior but is not inhibited by the collagen binding segment of fibronectin.

Radionuclide imaging of tumor xenografts in mice using a gelatinase-targeting peptide

Tumors express MMP-2 and MMP-9 gelatinases, which are involved in the formation of tumor vasculature. This suggests that a tumor and its surrounding neovasculature can be visualized by a sensitive gelatinase recognition method. We have studied tumor radioimaging using a gelatinase inhibitory peptide CTTHWGFTLC (CTT), which in a mouse model targets the tumor site following an intravenous injection. We determined a solution NMR structure of CTT and its retro-inversion peptide, and prepared 125I and 99mTc-labelled CTT peptide derivatives. Radiolabelled CTT inhibited gelatinases in vitro, and homed to a tumor xenograft in mice. In normal mice, CTT was instead rapidly cleared from the circulation mainly through the kidney and, after 24 h, no significant radioactivity was accumulated in healthy tissues. Gamma camera imaging of a primary tumor in live mice was obtained with double-labelled liposomes, which were coated with 99mTc-CTT and encapsulated with 125I albumin. CTT also targeted liposomes to the lungs of tumor-bearing mice, which may indicate the existence of non-visible lung micrometastases. Our studies suggest that selective gelatinase-targeting compounds could be useful in the early detection and imaging of primary tumors and metastases.