Growth factor balance and tumor progression

Anti-Cancer Effects of Pristimerin and the Mechanisms: A Critical Review

As a quinonemethide triterpenoid extracted from species of the Celastraceae and Hippocrateaceae, pristimerin has been shown potent anti-cancer effects. Specifically, it was found that pristimerin can affect many tumor-related processes, such as apoptosis, autophagy, migration and invasion, vasculogenesis, and drug resistance. Various molecular targets or signaling pathways are also involved, such as cyclins, reactive oxygen species (ROS), microRNA, nuclear factor kappa B (NF-κB), mitogen-activated protein kinase (MAPK), and PI3K/AKT/mammalian target of rapamycin (mTOR) pathways. In this review, we will focus on the research about pristimerin-induced anti-cancer activities to achieve a deeper understanding of the targets and mechanisms, which offer evidences suggesting that pristimerin can be a potent anti-cancer drug.

ETS-1 oncogenic activity mediated by transforming growth factor alpha

Inappropriate expression of Ets-1 is observed in a variety of human cancers, and its forced expression in cultured cells results in transformation, autonomous proliferation, and tumor formation. The basis by which Ets-1 confers autonomous growth, one of the primary hallmarks of cancer cells and a critical component of persistent proliferation, has yet to be fully explained. Using a variety of cancer cell lines, we show that inhibition of Ets-1 blocks tumor formation and cell proliferation in vivo and autonomous growth in culture. A screen of multiple diffusible growth factors revealed that inhibition of Ets-1 results in the specific downregulation of transforming growth factor alpha (TGFalpha), the proximal promoter region of which contains multiple ETS family DNA binding sites that can be directly bound and regulated by Ets-1. Notably, rescuing TGFalpha expression in Ets-1-silenced cells was sufficient to restore tumor cell proliferation in vivo and autonomous growth in culture. These results reveal a previously unrecognized mechanism by which Ets-1 oncogenic activity can be explained in human cancer through its ability to regulate the important cellular mitogen TGFalpha.

Polymorphisms of pro-inflammatory genes and prostate cancer risk: a pharmacogenomic approach

In this paper, we consider the role of the genetics of inflammation in the pathophysiology of prostate cancer (PCa). This paper is not an extensive review of the literature, rather it is an expert opinion based on data from authors' laboratories on age-related diseases and inflammation. The aim is the detection of a risk profile that potentially allows both the early identification of individuals at risk for disease and the possible discovery of potential targets for medication. In fact, a major goal of clinical research is to improve early detection of age-related diseases, cancer included, by developing tools to move diagnosis backward in disease temporal course, i.e., before the clinical manifestation of the malady, where treatment might play a decisive role in preventing or significantly retarding the manifestation of the disease. The better understanding of the function and the regulation of inflammatory pathway in PCa may help to know the mechanisms of its formation and progression, as well as to identify new targets for the refinement of new treatment such as the pharmacogenomics approach.

Tumorigenicity of cortical astrocyte cell line induced by the protease ADAM17

The metalloprotease ADAM17 (a.k.a. TACE) plays a pivotal role in the cleavage and activation of membrane-anchored receptor ligands. More recently, it has been revealed that ADAM17 is a potent sheddase of the epidermal growth factor (EGF) family of ligands and regulates epidermal growth factor receptor (EGFR) activity in a variety of tumors. EGFR is a key component of autonomous growth signaling in several tumors, and correlates with the malignancy grade of astrocytoma. In this study, we tested the hypothesis that over-expression of ADAM17 in cortical astrocytes derived from normal brain would induce a progression towards a malignant phenotype. Over-expression of human ADAM17 (hADAM17) in the CTX-TNA2 cortical astrocyte cell line resulted in non-adherent growth, increased proliferation, invasiveness, production of angiogenic factors, and expression of genes associated with immature and/or neoplastic cells. hADAM17 up-regulated EGFR and AKT phosphorylation, and increased proliferation and cell invasion were significantly dependent upon EGFR activity. When implanted in the nude mouse brain, CTX-TNA2 cells induced low histological grade, benign intraventricular gliomas. In contrast, the same astrocytes with hADAM17 formed large malignant gliomas. Taken together, these findings suggest that unregulated ADAM17 activity induces functional changes in astrocytes that significantly advance the malignant phenotype.

Heterogeneity of receptor function in colon carcinoma cells determined by cross-talk between type I insulin-like growth factor receptor and epidermal growth factor receptor

This study identifies a novel cross-talk paradigm between the type I insulin-like growth factor receptor (IGF1R) and epidermal growth factor receptor (EGFR) in colon cancer cells. IGF1R activation by ligand exposure in growth factor-deprived cells induces Akt activation in the FET, CBS, and GEO colon cancer cell lines. Investigation of IGF1R-mediated signaling pathways using small interfering RNA approaches indicated that, as expected, phosphatidylinositol 3'-kinase (PI3K) was activated by IGF1R. Mitogen-activated protein kinase (MAPK) activity as reflected by phospho-extracellular signal-regulated kinase (ERK) induction was not significantly activated until later times following release of these cells from growth factor deprivation stress. The appearance of phospho-ERK was proximal to EGFR activation. Treatment of cells with the PI3K inhibitor LY294002 before release from stress resulted in a concentration-dependent loss of EGFR activation, whereas treatment with the MAPK inhibitor PD98059 did not block EGFR activation, indicating that EGFR activation was downstream of the IGF1R/PI3K pathway. PD98059 inhibition of MAPK was associated with a concentration-dependent reduction in EGFR-mediated phospho-ERK. EGFR inhibitor blocked induction of phospho-ERK, showing that MAPK activity was a consequence of EGFR-mediated signaling. On the other hand, a small-molecule IGF1R inhibitor, PQIP, blocked Akt phosphorylation. The divergent signaling functions of IGF1R and EGFR suggested the potential for synergism by a combination of therapy directed at the two receptors. Combination treatment with PQIP and EGFR inhibitor Tarceva resulted in synergistic effects as indicated by combination index analysis in all three cell lines tested.

Transforming growth factor-beta 1 gene polymorphisms and expression in the blood of prostate cancer patients

The transforming growth factor beta 1 (TGF-beta1) is a multifunctional cytokine with several regulatory activities in tumor cells affecting growth, differentiation, and function. Alterations in gene expression, secretion, and regulation of TGF-beta1 may lead to a favorable environment for tumor development by angiogenesis stimulation and immune system suppression. We evaluated the influence of the TGFB1 polymorphisms by ARMS-PCR, Leu10Pro, and Arg25Pro, on prostate cancer (PCa) and benign prostatic hyperplasia (BPH). We assessed TGFB1 polymorphisms and their relation to mRNA levels (semi-quantitative RT-PCR) in blood samples as well as the implications in disease occurrence and progression. Peripheral blood samples from 175 patients were analyzed as to 92 BPH and 83 PCa. Samples obtained from 132 healthy males were used as negative controls. PCa patients with a Gleason score greater than 7 presented a higher frequency of the C allele (Leu10Pro). This allele was associated with a higher risk of developing PCa and BPH compared to the population (2.6 and 3.6 times higher, respectively). Patients with TGFB1 transcript levels equal to or more than 70% higher than control levels presented a 5.34 and 2.14-fold higher risk of having PCa and BPH, respectively, relative to the population. No association was detected between polymorphisms and mRNA levels. The C allele of the Leu10Pro polymorphism may predispose men to a more rapid cancer progression. Additionally, higher mRNA levels in the peripheral blood of PCa patients suggest that tumor cells may be disseminated in the circulation and could be used as a biomarker for extra-capsular invasion.

Multiple Acquired Renal Carcinoma Tumor Capabilities Abolished upon Silencing of ADAM17

Malignancy is a manifestation of acquired defects in regulatory circuits that direct normal cell proliferation and homeostasis. Most of these circuits operate through cell autonomous pathways, whereas others potentially involve the neighboring microenvironment. We report that the metalloprotease ADAM17 plays a pivotal role in several acquired tumor cell capabilities by mediating the availability of soluble transforming growth factor-α, an epidermal growth factor receptor (EGFR) ligand, and thus the establishment of a key autocrine signaling pathway. Silencing of ADAM17 in human renal carcinoma cell lines corrects critical features associated with cancer cells, including growth autonomy, tumor inflammation, and tissue invasion. Highly malignant renal carcinoma cancer cells fail to form in vivo tumors in the absence of ADAM17, confirming the essential function of this molecule in tumorigenesis. These data show that ligand shedding is a crucial step in endogenous EGFR activation and endorse prospective therapeutic strategies targeting ADAM17 in human cancer. (Cancer Res 2006; 66(16): 8083-90)

Deletion of functional gastrin gene markedly increases colon carcinogenesis in response to azoxymethane in mice

BACKGROUND & AIMS

We recently reported that transgenic mice overexpressing progastrin were at a higher risk for developing colon cancers in response to azoxymethane (AOM), whereas mice overexpressing gastrin-17 were at a reduced risk. To examine further the role of gastrins in colon carcinogenesis, we generated gastrin gene knockout mice (GAS-KO).

METHODS

The height and proliferative index (PI) of colonic crypts were similar in GAS-KO and wild-type (WT) mice, suggesting that the absence of gastrins in GAS-KO mice did not significantly affect the growth of colonic mucosa. GAS-KO and WT mice were treated with AOM for 3-4 weeks; control mice received saline.

RESULTS

Colonic proliferation in response to AOM was significantly increased in GAS-KO vs. WT mice. Aberrant crypt foci (ACFs) were similarly increased significantly by approximately 2-5-fold in GAS-KO vs. WT mice after 2 weeks of AOM treatment. Female GAS-KO mice developed adenomas (Ads) and adenocarcinomas (AdCAs) at earlier times ( approximately 10 months) than the male GAS-KO mice and the male and female WT mice ( approximately 12 months). The total numbers of Ads and AdCAs were significantly higher in GAS-KO than in WT mice.

CONCLUSIONS

These results suggest the novel possibility that loss of gastrin expression (and hence amidated gastrins) significantly increases susceptibility to colon carcinogenesis in response to AOM. Previous studies with FVB/N transgenic mice similarly suggested a protective role of amidated gastrins against colon carcinogenesis, which supports the present findings of an increase in colon carcinogenesis in GAS-KO mice lacking normal physiological levels of amidated gastrins.

Activation of the TGFalpha autocrine loop is downstream of IGF-I receptor activation during mitogenesis in growth factor dependent human colon carcinoma cells

The inappropriate expression of TGFalpha in growth arrest contributes to malignant progression in human colon carcinoma cells. Early stage, non-progressed colon tumor cells show a down-regulation of TGFalpha in growth arrest and require both nutrients and growth factors for re-entry into the cell cycle. In contrast, highly progressed cells up-regulate TGFalpha during growth arrest and require only nutrients for re-entry. Given the importance of TGFalpha in malignant progression, this work addressed the regulation of TGFalpha expression in the early stage colon carcinoma cell line, FET. Growth-arrested FET cells down-regulated the expression of TGFalpha, EGFr and, in turn, EGFr activation. These quiescent cells continued to express high levels of IGF-IR protein, but IGF-IR activation was undetectable. Cell cycle re-entry required exogenous growth factor activation of the IGF-IR by insulin or IGF-I. This IGF-IR activation resulted in S phase re-entry and was accompanied by an approximate threefold induction of TGFalpha expression along with EGFr activation at 1 h following release from growth arrest. Activation of IGF-IR occurred within 5 min of cell-cycle re-entry. Previously identified DNA binding proteins which bind to a unique TGFalpha/EGF response element within the TGFalpha promoter were similarly induced following IGF-IR activation. The addition of EGFr neutralizing antibodies abolished the activated IGF-IR stimulated S phase re-entry. Moreover, disruption of the growth arrest associated down-regulation of TGFalpha in FET cells by constitutive TGFalpha expression abrogated the requirement for IGF-IR activation for cell cycle re-entry. Consequently, this study indicates, for the first time, that IGF-IR activation up-regulates components of the TGFalpha autocrine loop resulting in TGFalpha-mediated EGFr activation which was critical for IGF-IR mediated re-entry into the cell cycle from the growth-arrested state.

The physical parameters and molecular events associated with radiation-induced lung toxicity

Radiation therapy (RT) is frequently used to treat patients with tumors in and around the thorax. Clinical radiation pneumonitis is a common side effect, occurring in 5% to 20% of patients. Efforts to identify patients at risk for pneumonitis have focused on physical factors, such as dose and volume. Recently, the underlying molecular biological mechanisms behind RT-induced lung injury have come under study. Improved knowledge of the molecular events associated with RT-induced lung injury may translate into a better ability to individualized therapy. This review discusses our current understanding of the physical and molecular factors contributing to RT-induced pulmonary injury.

Progastrin expression predisposes mice to colon carcinomas and adenomas in response to a chemical carcinogen

BACKGROUND & AIMS

Processing intermediates of preprogastrin (gly-gastrin and progastrin), termed nonamidated gastrins, are mitogenic for several cell types including colonic epithelial cells. However, presently it is not known if nonamidated gastrins play a role in colon carcinogenesis and if the effects are similar to those of amidated gastrins.

METHODS

Colon carcinogenesis in response to azoxymethane (AOM) was examined in transgenic mice overexpressing either progastrin (hGAS) or amidated gastrin (INS-GAS), compared with that in wild-type (WT) mice.

RESULTS

In AOM-treated groups, the total number of tumors per colon was significantly higher in hGAS (4.8+/-0.34) than INS-GAS (3.0+/-0.16) and WT (2.7+/-0.35) mice. Total numbers of adenocarcinomas and adenomas per animal colon were also significantly higher in hGAS than INS-GAS and WT mice. The size of the tumors was greater in hGAS mice, resulting in a significantly higher tumor burden per mouse in the hGAS mice than INS-GAS and WT mice. Although >90% of the tumors were located in the distal half of the colon in INS-GAS and WT mice, a significant number (42%) were present at the proximal end of the colon in hGAS mice.

CONCLUSIONS

The results suggest that the risk for developing colon carcinomas and adenomas in response to AOM is significantly increased in mice expressing high levels of progastrin, but not amidated gastrins.

Mice overexpressing progastrin are predisposed for developing aberrant colonic crypt foci in response to AOM

Recent studies show that nonamidated gastrins (Gly-gastrin and progastrin) stimulate colonic proliferation. However, the role of nonamidated vs. amidated gastrins in colon carcinogenesis has not been defined. We measured intermediate markers of carcinogenesis in transgenic mice overexpressing either progastrin (hGAS) or amidated gastrin (INS-GAS) in response to azoxymethane (AOM). The hGAS mice showed significantly higher numbers of aberrant crypt foci (140-200% increase) compared with that in wild-type (WT) and INS-GAS mice (P < 0.05) after AOM treatment. The bromodeoxyuridine-labeling index of colonic crypts also was significantly elevated in hGAS mice vs. that in WT and INS-GAS mice. The results therefore provide evidence for a mitogenic and cocarcinogenic role of nonamidated gastrins (progastrin), which is apparently not shared by the amidated gastrins. Although nonamidated gastrins are now believed to mediate mitogenic effects via novel receptors, amidated gastrins mediate biological effects via different receptor subtypes, which may explain the difference in the cocarcinogenic potential of nonamidated vs. amidated gastrins. In conclusion, our results provide strong support for a cocarcinogenic role for nonamidated gastrins in colon carcinogenesis.

Expression of transforming growth factor-beta receptor type II and tumorigenicity in human breast adenocarcinoma MCF-7 cells

To analyze transforming growth factor-beta (TGF-beta) response during MCF-7 cell progression, early passage (MCF-7E, < 200 passage) and late passage (MCF-7L, > 500 passage) cells were compared. MCF-7E cells showed an IC50 of approximately 10 ng/ml of TGF-beta1, whereas MCF-7L cells were insensitive. MCF-7E cells contained approximately threefold higher levels of TGF-beta receptor type II (TbetaRII) mRNA than MCF-7L, but their TbetaRI levels were similar. MCF-7E parental cells showed higher TbetaRII promoter activity than MCF-7L cells, which could be attributed to changes in Sp1 nuclear protein levels. Receptor cross-linking studies indicated that the cell surface receptor levels parallel mRNA levels in both cell lines. Limiting dilution clones of MCF-7E cells were established to determine the heterogeneity of TbetaRII expression in this cell line, and they showed varying degrees of TbetaRII expression. Fibronectin was induced at higher levels in cells expressing higher TbetaRII levels. All three TGF-beta isoforms were detected in limiting dilution clones and parental cells, but TGF-beta1 was more abundant relative to TGF-beta2 or 3, and no correlation between TGF-beta isoform profile with TGF-beta sensitivity was found. MCF-7L cells were tumorigenic and formed xenografts rapidly and progressively, whereas MCF-7E parental and limiting dilution clonal cells showed transient tumor formation followed by regression. These results indicate that decreased TbetaRII transcription in breast cancer cells leads to a loss of TbetaRII expression, resulting in cellular resistance to TGF-beta which contributes to escape from negative growth regulation and tumor progression.

The relevance of transforming growth factor beta 1 in pulmonary injury after radiation therapy

The maximum dose of radiation which can be delivered to a tumor is limited by the tolerance of the surrounding normal tissues. The ability to identify patients at high or low risk of injury from radiation therapy might enable the clinician to tailor radiation doses in order to maximize efficacy and minimize risk. The cytokine transforming growth factor beta 1 (TGF beta 1) has been implicated in the development of normal tissue injury after irradiation in several organs, including the lung. Herein, the evidence supporting the role of TGF beta 1 in radiation-induced lung injury is reviewed. Using the treatment of non-small cell lung cancer as a model, we also discuss how it may be possible to identify patients at risk for this complication using measurements of plasma TGF beta 1, and how this information may be used in the future to adjust doses of radiation in the treatment of lung cancer.

Plasma transforming growth factor-beta 1 reflects disease status in patients with lung cancer after radiotherapy: a possible tumor marker

PURPOSE

To determine the frequency with which elevated plasma transforming growth factor-beta 1 (TGF beta 1) concentrations occur in lung cancer patients, to determine the kinetics of TGF beta 1 expression during and after radiotherapy and to correlate plasma TGF beta 1 levels with disease status after treatment.

MATERIALS AND METHODS

Plasma samples were obtained before, during and after radiotherapy in 54 patients with lung cancer and 20 normal controls. Plasma TGF beta 1 levels were measured using an enzyme-linked immunosorbent assay.

RESULTS

Baseline TGF beta 1 levels in lung cancer patients and normal controls were 13.0 +/- 2.5 and 4.4 +/- 0.3 ng/ml, respectively. Elevated TGF beta 1 were found in 50% (27/54) of lung cancer patients. During radiation therapy plasma TGF beta 1 levels declined, however, by the completion of treatment the mean TGF beta 1 level had not normalized in patients with lung cancer. The TGF beta 1 level at last follow-up correlated with disease status in those patients with an increased pretreatment plasma level. Three of four patients with no evidence of cancer had normal follow-up TGF beta 1 levels, compared to 2/16 patients with residual or recurrent tumor (P = 0.02).

CONCLUSIONS

Elevated plasma TGF beta 1 levels occur frequently in patients with lung cancer. In those patients with an elevated plasma TGF beta 1 level at diagnosis, monitoring this level may be useful in detecting both disease persistence and recurrence after therapy.

Mad-related genes in the human

Resistance to the growth inhibitory effects of TGF-beta is common in human cancers. However, the mechanism(s) by which tumour cells become resistant to TGF-beta are generally unknown. We have identified five novel human genes related to a Drosophila gene called Mad which is thought to transduce signals from TGF-beta family members. One of these genes was found to be somatically mutated in two of eighteen colorectal cancers, and three of the other genes were located at chromosomal positions previously suspected to harbor tumour suppressor genes. These data suggest that this gene family may prove to be important in the suppression of neoplasia, imparting the growth inhibitory effects of TGF-beta-like ligands.

Raf-1 kinase, epidermal growth factor receptors, and mutant Ras proteins in colonic carcinomas

Epidermal growth factor receptors (EGFR) and ras mutations are known to play a significant role in controlling cell growth and tumor promotion. Both of them transmit mitogenic signals to the nucleus by activation of Raf-1 kinase. In this study, the expression of EGFR and mutant Ras proteins, and, for the first time, the expression, phosphorylation and kinase activity of Raf-1 kinase have been determined in paired samples of colorectal cancer and mucosa. The tumor and mucosa samples did not differ significantly with regard to Raf-1 kinase content and activity. A major difference between tumors and mucosa was found, however, in the phosphorylation of Raf-1. Most of the mucosa samples (13/20), but only 1/20 of the cancer samples, contained hyperphosphorylated Raf-1. EGFR were significantly (p = 0.0025) decreased in the tumors. The decreased phosphorylation of Raf-1 in colonic carcinomas could be the result of activation of Raf-1 phosphatases or inactivation of kinases phosphorylating Raf-1. New forms of treatment based on EGFR overexpression do not seem to be suitable for the majority of colonic cancers.

Anti-tumor efficacy of an anti-epidermal-growth-factor-receptor monoclonal antibody and its F(ab')2 fragment against high- and low-EGFR-expressing carcinomas in nude mice

Monoclonal antibody (MAb) MINT5 specifically detects the epidermal-growth-factor receptor (EGFR). In vitro analyses of intact MINT5 (IgG1) and its F(ab')2 fragment indicated that both forms of the MAb inhibited binding of 125I-mEGF to EGFR, induced receptor internalization and blocked EGF-induced EGFR tyrosine-kinase activation in A431 cells. Both forms of the MAb also inhibited to the same extent the proliferation of the carcinoma cell lines A431 and IGROVI, despite the difference in EGFR levels on the cells. The detection of TGF alpha mRNA and the inhibition of cell growth in EGF-free conditions by anti-EGFR MAb indicated the involvement of an EGFR/TGF alpha autocrine/paracrine pathway in the in vitro growth of both cell lines. Analysis of mice xenotransplanted s.c. with A431 cells and treated with MINT5 revealed a block in A431 tumor take in 6 of 10 animals when intact MAb was administered from day 0 to day 11. On a molar basis, F(ab')2 at the same dose was ineffective, although at a 7-fold higher dose F(ab')2 reduced s.c. tumor growth by 80%. At the same dose, intact MINT5 MAb reduced s.c. growth of the EGFR-negative MeWo cell line by 5%. Survival of mice bearing IGROVI i.p. xenotransplants and treated locally with either form of MAb was significantly prolonged even when treatment was initiated on day 3. Corrected doses of intact and F(ab')2 fragment, which accounted for the difference in serum half-lives of the MAb forms, resulted in similar survival rates in the tumor-bearing mice. These pre-clinical results suggest that MINT5 MAb might be safely used for systemic therapy of EGFR-over-expressing tumors. Loco-regional therapy might be contemplated in the case of tumors with moderate/low EGFR expression.

Inactivation of the type II TGF-beta receptor in colon cancer cells with microsatellite instability

Transforming growth factor-beta (TGF-beta) is a potent inhibitor of epithelial cell growth. Human colon cancer cell lines with high rates of microsatellite instability were found to harbor mutations in the type II TGF-beta receptor (RII) gene. Eight such examples, due to three different mutations, were identified. The mutations were clustered within small repeated sequences in the RII gene, were accompanied by the absence of cell surface RII receptors, and were usually associated with small amounts of RII transcript. RII mutation, by inducing the escape of cells from TGF-beta-mediated growth control, links DNA repair defects with a specific pathway of tumor progression.