Inhibitory effect on the establishment of hepatic metastasis by transduction of the tissue plasminogen activator gene to murine colon cancer

Diet-induced obesity and ethanol impair progression of hepatocellular carcinoma in a mouse mesenteric vein injection model

BACKGROUND

Hepatocellular carcinoma (HCC) is a rapidly increasing cancer whose known risk factors are chronic ethanol abuse, viral hepatitis infection, and aflatoxin exposure. Obesity, an emerging HCC risk factor, is reaching epidemic proportions in developed nations. This study investigated the effects of diet-induced obesity (DIO) and chronic ethanol consumption on HCC progression in mice in vivo.

METHODS

In this study, C57BL/6 DIO mice and lean litter mates were maintained on a 60% (high-fat diet [HFD]) diet or a 10% (control diet [CD]) kcal% fat diet for 7 weeks before they were weaned to 10/20% ([v/v], alternating days) ethanol in drinking water (EtOH) or maintenance on drinking water (H(2)O) alone. Hepatic tumor formation was initiated by intrahepatic Hepa1-6 cell (6 × 10(6) cells) inoculation 6 weeks later via the mesenteric vein.

RESULTS

The animals receiving the HFD showed decreased tumor incidence and area of hepatic foci versus the CD animals maintained on H(2)O alone. The action of EtOH suppressed tumor incidence further in both the CD and the HFD mice. Serologic analysis showed no significant differences in liver enzymes among the groups. Protein analysis demonstrated increased P450 2E1 (CYP2E1) in the groups maintained on EtOH, an effect exacerbated by HFD. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis demonstrated increased tumor necrosis factor-alpha (TNF-α) expression in HFD HCC mice (H(2)O and EtOH) concomitant with decreased transforming growth factor-beta (TGF-β) expression.

CONCLUSIONS

Although obesity and EtOH consumption are known risk factors for HCC initiation and development, the data in this study suggest that these factors impair progression of established tumors within the liver.

Tissue-type plasminogen activator has antiangiogenic properties without effect on tumor growth in a rat C6 glioma model

Tissue-type plasminogen activator (tPA) plays a major role in the fibrinolytic system. According to several reports, tPA may also have antiangiogenic properties, especially in combination with a free sulfhydryl donor (FSD). In the rat C6 glioma model, in vitro and in vivo tPA synthesis by glioma cells is enhanced by differentiation therapy. To address the antiangiogenic potential of tPA in this model, tPA was overexpressed in glioma tumors by ex vivo transduction of C6 cells with a lentiviral vector encoding tPA. The transduced cells were subcutaneously implanted into nude mice. Gene transfer allowed for efficient synthesis of tPA by the C6 tumors. Although the treatment of tPA+ tumor-bearing animals with the FSD captopril generated angiostatin in situ and reduced endothelial vascularization of the tumors, it had no effect on tumor growth. Alternative mechanisms could account for this lack of effect and consequently have important implications for vascular the treatment of glioblastoma.

Protease Activity of Urokinase and Tumor Progression in a Syngeneic Mammary Cancer Model

BACKGROUND

We and others have previously shown that plasminogen activators generate endogenous angiogenesis inhibitors and induce antiangiogenic activity. Here we assessed the effects of plasminogen activator overexpression on tumor progression in a syngeneic mammary cancer model.

METHODS

Genes encoding murine tissue plasminogen activator (tPA), urokinase (uPA), and vector controls were stably transfected into 4T1 murine mammary cancer cells, and cell proliferation in vitro was analyzed. Cells were also implanted into female BALB/c mice (n = 12 per group), and tumor growth, lung metastases, and survival were compared. Tumor cell proliferation and microvessel formation were analyzed by immunohistochemistry using antibodies to proliferating cell nuclear antigen and CD31, respectively. 4T1 cells transfected with proteolytically inactive uPA mutants (A and B) were assayed for proliferation in vitro and tumor growth in vivo by using the same syngeneic model (eight to 10 mice per group). All statistical tests were two-sided.

RESULTS

In vitro growth of uPA- and tPA-overexpressing and control 4T1 cells was similar. In vivo, however, inhibition of tumor growth and lung metastasis were inhibited in the mice carrying tPA- and uPA-overexpressing tumors, compared with controls (tumor weight at day 34: control, mean = 1760 mg, 95% confidence interval [CI] = 1434 to 2087 mg; tPA, mean = 921, 95% CI = 624 to 1217 mg; P < .001; uPA, mean = 395 mg, 95% CI = 161 to 629 mg; P < .001; number of lung metastases at day 34: control, mean = 117, 95% CI = 74 to 159; tPA, mean = 33, 95% CI = 13 to 52; uPA, mean = 15, 95% CI = 4 to 25; P < .001). Median survival was 42 (95% CI = 36 to 44), 55 (95% CI = 48 to 61), and 73 (95% CI = 51 to 86) days in the control, tPA, and uPA groups, respectively (P < .001). uPA- and tPA-expressing tumors had reduced angiogenesis and cell proliferation compared with controls. Tumors overexpressing uPA mutants grew faster than tumors expressing wild-type uPA (tumor volume at day 30: wild-type uPA, mean = 203, 95% CI = 121 to 285 mm3; control, mean = 534, 95% CI = 460 to 608 mm3; P < .001; mutant A, mean = 600, 95% CI = 520 to 679 mm3; P < .001; and mutant B, mean = 435, 95% CI = 358.9 to 511 mm3; P = .005).

CONCLUSIONS

In this mouse model, uPA expression delayed tumor progression and had antiangiogenic and antiproliferative effects that may be mediated by uPA's protease activity. These results challenge the current dogma of proteases being exclusively tumor promoting and provide further rationale for exploring plasminogen activators as antitumor agents.

Activation of tissue plasminogen activator gene transcription by Neovastat, a multifunctional antiangiogenic agent

We recently reported that Neovastat, an antiangiogenic drug that is currently undergoing Phase III clinical trials for the treatment of non-small cell lung cancer, may inhibit angiogenesis through an increase in tPA activity. Here, we show that Neovastat also stimulates tPA gene transcription in endothelial cells, in a TNFalpha-like manner. RT-PCR analysis and gene reporter assays using the human tPA promoter indicated that upregulation of the tPA gene transcription by both Neovastat and TNFalpha was correlated with the phosphorylation of JNK1/2 and of IkappaB and that SP600125 and BAY11-7082, inhibitors of JNK and IkappaK, respectively, inhibit the increase of tPA gene transcription induced by Neovastat and TNFalpha. These results suggest that Neovastat induces tPA gene transcription through activation of the JNK and NFkappaB signaling pathways, leading to an increase of tPA secretion by endothelial cells. This may lead to the localized destruction of the fibrin provisional matrix that is necessary for neovessel formation and thus contribute to the reported antiangiogenic properties of this compound.

In vitro and in vivo induction of antiangiogenic activity by plasminogen activators and captopril

BACKGROUND

Many antiangiogenic molecules are proteolytically cleaved from larger plasma proteins. For example, plasminogen activators cleave plasminogen into plasmin, and plasmin is converted into angiostatin in the presence of sulfhydryl donors. We thus investigated whether the antiangiogenic activity in plasma could be increased by treatment with recombinant tissue plasminogen activator (rt-PA) and the sulfhydryl donor captopril.

METHODS

Human plasma was treated with rt-PA (10 micro g/mL) and/or captopril (1 micro M). Angiogenesis was measured in vitro by human endothelial cell tube formation and endothelial cell proliferation and in vivo in mice with the Matrigel plug assay. Angiostatin was removed from treated plasma by affinity chromatography, immunoprecipitation, or ion-exchange chromatography, and the antiangiogenic activity of the depleted plasma was assessed by tube formation. Three cancer patients were treated with rt-PA and captopril, and their pretreatment and post-treatment plasmas were tested for antiangiogenic activity in vitro.

RESULTS

Angiogenesis in vitro was stimulated by untreated plasma and inhibited by plasma that had been treated with rt-PA and captopril but was not affected by treatment with rt-PA and/or captopril alone. In vivo angiogenesis in Matrigel plugs was substantially lower in mice treated with rt-PA and captopril than in untreated control mice. Antiangiogenic activity in treated plasma was largely retained after angiostatin was removed: treated plasma inhibited angiogenesis by 64.3% (95% confidence interval [CI] = 46.4% to 82.2%), relative to untreated plasma, and treated plasma depleted of angiostatin by affinity chromatography or immunoprecipitation inhibited angiogenesis by 65.1% (95% CI = 53.8% to 76.4%) or 63.7% (95% CI = 50.9% to 76.5%), respectively. Antiangiogenic activity of plasma from three cancer patients was higher after treatment with rt-PA and captopril than before such treatment.

CONCLUSION

Treatment with rt-PA and captopril induced antiangiogenic activity in vitro and in vivo that appears to be independent of angiostatin.

Molecular therapies for colorectal cancer metastatic to the liver

Colorectal cancers are the fourth most commonly diagnosed cancers and will account for over 56,000 deaths in the United States in 2002. A majority of patients with advanced colorectal cancer develop liver metastases during the course of their disease. Treatment of colorectal cancer metastatic to the liver by surgery or chemotherapy is limited and most patients succumb to their disease. Therefore, a broad spectrum of novel treatments, including innovative molecular therapies such as gene and immunotherapy or replication-competent viral therapy, is under preclinical investigation and several clinical trials are in progress. Here we review molecular therapies for colorectal cancer metastatic to the liver.