Platelet-derived growth factor (PDGF) and glial tumorigenesis

Platelet-derived growth factor (PDGF) has long been implicated in cancer and is known to be involved in many biological processes. In Central Nervous System (CNS) neoplasms, particularly gliomas, PDGF is often over-expressed. However, what role PDGF plays in tumor progression remains to be fully described. A wide range of work from in vitro studies to mouse models have implicated the PDGF pathway in various processes including proliferation, cellular migration, development, and angiogenesis. Being a secreted factor, PDGF not only has autocrine effects on producing cells but also has potential for paracrine effects on other tumor cells and the tumor microenvironment. The development of small molecules that inhibit the PDGF receptor and various subsequent signaling components promises to introduce new approaches to the treatment of gliomas.     

Human prostate adenocarcinomas express in-vivo messenger-rnas and protein products for platelet-derived growth factor-B and its receptor

In situ hybridization and immunocytochemistry studies have shown the in vivo expression of platelet-derived growth factor B (PDGF-B) and PDGF receptor (PDGF-R) beta mRNAs and their respective protein products in the malignant epithelial cells of eight primary human prostatic adenocarcinomas. Examination of five nonmalignant adjacent prostate tissues did not demonstrate significant expression of PDGF B and PDGF-R beta mRNAs or production of their respective protein products in nonmalignant epithelial cells. Expression of androgen receptor mRNA was shown to be present in the epithelial cells of all of the five nonmalignant adjacent prostate tissues. There was a significant reduction in the expression of androgen receptor mRNA in poorly differentiated regions, and a moderate reduction in the well differentiated regions of the malignant tissues. It appears that dedifferentiation of the tumor cells in prostatic adenocarcinomas is accompanied by a reduction in androgen receptor mRNA expression. The coexpression of PDGF and its receptor in the malignant epithelial cells of prostatic adenocarcinomas signifies an abnormal autocrine loop that may contribute to their growth and maintenance.     

Amplification and/or overexpression of platelet-derived growth factor receptors and epidermal growth factor receptor in human glial tumors.

Analysis of genomic organization and expression of platelet-derived growth factor receptors (PDGFR) and epidermal growth factor receptor (EGFR) in human malignant gliomas showed amplification and overexpression of both receptors in distinct subsets of tumors. Amplification of the alpha PDGFR was detected in 4 of 50 glioblastomas (8%). EGFR was amplified in 9 of the 50 tumors (18%). Western blot analysis showed elevated expression of alpha PDGFR and EGFR proteins in 4 (24%) and 3 (18%), respectively, of 17 tumor specimens analyzed. Increased production of alpha PDGFR as well as EGFR proteins was observed in the presence or absence of gene amplification. Three of the 4 tumors with elevated levels of alpha PDGFR also overexpressed the beta PDGFR, which was present as a single copy gene in all 50 tumors analyzed. Our findings suggest that the amplification and/or overexpression either of EGFR or of the alpha PDGFR along with the coordinate overexpression of the beta PDGFR can contribute to the malignant phenotype of distinct subsets of human glioblastoma.     

Regulatory effects of cell density on the binding of transforming growth factor beta, epidermal growth factor, platelet-derived growth factor, and fibroblast growth factor

The work described in this paper demonstrates that the cellular binding of transforming growth factor beta, epidermal growth factor, platelet-derived growth factor, and fibroblast growth factor is reduced as cell density is increased. The reduction in transforming growth factor beta binding was observed in five different cell lines. Examination of several of the cell lines, under conditions where transforming growth factor beta binding is reduced, revealed that epidermal growth factor binding, platelet-derived growth factor binding, and fibroblast growth factor binding are also reduced. In the case of NRK-49F cells, the reduction in transforming growth factor beta binding results from a decrease in the number of high-affinity receptors and not from a change in receptor affinity. Similarly, it was determined that the reduction in epidermal growth factor binding is due to a selective reduction in the high-affinity receptors for epidermal growth factor. Overall, the data suggest that the effect of cell density on growth factor binding, which we refer to as density-induced down regulation of growth factor receptors, differs both from down regulation induced by a specific growth factor and from receptor transmodulation.     

Mammary tumorigenesis in growth hormone deficient spontaneous dwarf rats; effects of hormonal treatments

This study was carried out to investigate mammary tumorigenesis in growth hormone (GH) deficient spontaneous dwarf rats (SDR). At 50–60 days of age, the rats were divided into five groups. Group 1 received bovine (b) GH (prolonged release formulation) administered at a dose of 40–50 mg/kg body wt. in 50 l weekly injections; group 2 received recombinant human insulin-like growth factor-I (IGF-I) at a dose of 1 mg/kg body wt./day administered via osmotic pumps; animals in group 3 were fitted with subcutaneous silastic capsule containing 30 g 17-estradiol (E2) plus 30 mg progesterone (P4), replaced every 2 months; group 4 received both bGH and E2 plus P4 treatments at the same doses as above, and control animals (group 5) received sham treatments (vegetable oil injection, silastic capsules containing cellulose). After 1week of treatment, all animals were injected intraperitoneally with the carcinogen N-methyl-N-nitrosourea (MNU) at a dose of 50 mg/kg body wt. Other groups of animals, receiving identical hormonal treatment to those exposed to MNU, were treated for 10 days only and then sacrificed for assessment of circulating concentrations of hormones and mammary gland characteristics at the time of carcinogen exposure. The hormonal treatments of the animals exposed to the MNU were continued for an additional 20 weeks and mammary tumor development monitored by weekly palpation and tumors collected as necessary. The rats were weighed weekly. At the end of the treatment period, all animals were sacrificed and remaining tumors were collected. Rats in all groups continued to gain weight throughout the experimental period, but the largest weight gain was see in animals receiving GH either alone or with E2 and P4. Animals treated with IGF-I also gained weight compared to controls, but this weight gain was less than that seen in GH-treated rats. GH treatment alone increased mammary tumor incidence from 4.8% in controls to 100%. Average tumor load and latency in the GH-treated rats were 7.0 ± 0.8 tumors/tumor-bearing rat (mean±SEM) and 57.3 ± 2.7 days (mean±SEM), respectively. As in intact Sprague–Dawley rats, approximately 90% of the tumors that developed in the GH-treated rats were ovarian dependent for growth. IGF-I treatment also increased mammary tumor development to 62.5%. Average tumor load and latency in the IGF-I-treated rats were 1.6 ± 0.4 tumors/tumor-bearing rat (mean±SEM) and 96.2 ± 14.5 days (mean±SEM), respectively. However E2+P4 treatments did not significantly alter tumorigenesis and, surprisingly, simultaneous treatment with E2+P4 and GH obliterated the GH-stimulated increase in tumor development. Prolactin (PRL) did not appear to influence mammary tumorigenesis in the SDRs, as untreated SDRs had significantly elevated serum concentration of PRL as compared with normal Sprague–Dawley (SD) rats, whereas GH-treated SDRs had PRL levels similar to that of normal SD rats. No obvious structural characteristics were associated with high or low susceptibility to mammary tumorigenesis, as assessed by mammary gland whole mounts from the different animal groups sacrificed at the time of carcinogen administration.Enhanced expression of the extracellular signal-regulated kinase 1/2 (ERK1/2), and activation (phosphorylation) of ERK1/2 were associated with an increase in mammary tumorigenesis. Similarly, the expression of the estrogen receptor- (ER) was significantly elevated in animal groups with the highest susceptibility to tumorigenesis, whereas the levels of cyclin D1 expression were not related to mammary tumorigenesis.     

The effects of tumor-derived platelet-derived growth factor on vascular morphology and function in vivo revealed by susceptibility MRI

Platelet-derived growth factors (PDGF) play a major role in pericyte recruitment in tumor capillaries. Pericytes are required for proper vessel development, and contribute to tumor angiogenesis by promoting stabilization and maturation of newly formed vessels. To investigate the effects of pericyte coverage on tumor vessel morphology and function in vivo, tumors derived from B16 melanoma cells transfected with either control plasmid (B16/ctr) or plasmid encoding full-length PDGF-BB (B16/PDGF), the latter previously shown to have enhanced blood vessel pericyte coverage and an increased tumor growth rate, were assessed using histopathological methods, Hoechst 33342-based perfusion analyses, and two noninvasive susceptibility magnetic resonance imaging (MRI) methods. Susceptibility-contrast MRI, incorporating the use of ultrasmall superparamagnetic iron oxide particles, revealed a significant (p < 0.05) reduction in vessel size index (R(v)) of B16/PDGF tumors, and which was validated histologically by the presence of significantly smaller (p < 0.001), more punctate blood vessels identified by fluorescence microscopy of the perfusion marker Hoechst 33342. Intrinsic-susceptibility MRI was used to measure the transverse MRI relaxation rate R(2)*, sensitive to changes in endogenous paramagnetic [deoxyhaemoglobin], and used to probe for vascular maturation and function. Hypercapnia (5% CO(2)/95% air) induced a negligible Delta R(2)* response in the B16/ctr and B16/PDGF tumors. In contrast, hyperoxia (5% CO(2)/95% O(2)) induced a significantly greater R(2)* reduction in the B16/PDGF tumors (p < 0.02). Together the susceptibility MRI-derived biomarkers reveal novel pericyte-dependent changes in the morphology and function of the perfused tumor vasculature in vivo.     

Neural precursor cell apoptosis and glial tumorigenesis following transplacental ethyl-nitrosourea exposure.

Neural precursor cells (NPCs) populate the embryonic ventricular zone and persist in the subependymal zone of the adult brain. We hypothesized that hereditary and/or acquired mutations in apoptosis-associated genes, such as p53 and caspases, may protect NPCs from DNA damage-induced death and predispose them to subsequent neoplastic transformation. To test this hypothesis, we exposed NPCs from wild-type and targeted gene-disrupted mouse embryos (p53, caspase-9, caspase-3, and bax mutants) to ethyl-nitrosourea (ENU), a known DNA mutagen and neural carcinogen, and measured NPC viability. We found that ENU produced caspase-3 activation and apoptotic NPC death 6-24 h after administration both in vivo and in vitro. This effect was critically dependent on p53 and caspase-9 expression. The long-term effect of intrauterine ENU exposure was examined in control and p53-deficient mice. High grade glial tumors were found in 60% of p53(-/-) young adult mice exposed to ENU on gestational day 12.5 but not in p53(+/-) or p53(+/+) littermates or in untreated p53-deficient mice. All the tumors were located supratentorially and possessed strong immunoreactivity for glial fibrillary acidic protein and the anti-apoptotic molecule Bcl-X(L). These results suggest that intrauterine exposure of NPCs to certain DNA damaging agents may synergistically interact with specific genetic abnormalities (e.g. p53 deficiency) to produce glial neoplasms in the adult brain.     

Effects of human platelet-derived growth factor-AB on sarcoma growth in vitro and in vivo.

Platelet-derived growth factor (PDGF) has been proposed to play an important role in the growth of tumors. In order to study the effects of PDGF-AB on tumor growth in vivo, sarcoma-bearing mice were treated with PDGF-AB. The tumors, a malignant fibrous histiocytoma and an osteosarcoma, had functional PDGF receptors in vitro, as demonstrated by stimulation of PDGF-AB using a [3H]thymidine incorporation assay. Immunohistochemistry also revealed that both sarcoma xenografts expressed PDGF receptors. The tumor-bearing mice were given human PDGF-AB for 14 days, either continuously by an intraperitoneally placed mini-osmotic pump, or by daily injections. No effects on tumor growth in vivo were observed, as measured by tumor volume, autoradiography or cell cycle distribution. The histological appearance and ploidy of the tumors remained unaltered. The results indicate that, although the tumor cells are stimulated by PDGF-AB in vitro, the in vivo milieu or tumor growth pattern may render the tumors less susceptible to exogenously administered PDGF-AB in vivo.     

Complex effects of Ras proto-oncogenes in tumorigenesis

Ras proteins have been found mutated in about one-third of human tumors. In vitro, Ras has been shown to regulate distinct and contradictory effects, such as cellular proliferation and apoptosis. Nonetheless, the effects that the wild-type protein elicits in tumorigenesis are poorly understood. Depending on the type of tissue, Ras proto-oncogenes appear to either promote or inhibit the tumor phenotype. In this report, we treated wild-type and N-ras knockout mice with 3-methylcholanthrene (MCA) to induce fibrosarcomas and found that MCA is more carcinogenic in wild-type mice than in knockout mice. After injecting different doses of a tumorigenic cell line, the wild-type mice exhibited a shorter latency of tumor development than the knockouts, indicating that there are N-ras-dependent differences in the stromal cells. Likewise, we have analyzed B-cell lymphomas induced by either N-methylnitrosourea or by the N-ras oncogene in mice that over-express the N-ras proto-oncogene and found that the over-expression of wild-type N-ras is able to increase the incidence of these lymphomas. Considered together, our results indicate that Ras proto-oncogenes can enhance or inhibit the malignant phenotype in vivo in different systems.     

Id proteins in cell growth and tumorigenesis

Since the gene encoding Id1 was cloned in 1990, Id proteins have been implicated in regulating a variety of cellular processes, including cellular growth, senescence, differentiation, apoptosis, angiogenesis, and neoplastic transformation. The development of knockout and transgenic animal models for many members of the Id gene family has been particularly useful in sorting out the biologic relevance of these genes and their expression during normal development, malignant transformation, and tumor progression. Here we review the current understanding of Id gene function, the biologic consequences of Id gene expression, and the implications for Id gene regulation of cell growth and tumorigenesis.     

Structural and functional aspects of platelet-derived growth factor.

The finding that PDGF production is common in normal as well as transformed cells indicate that PDGF has a function in autocrine and paracrine stimulation of cells in several physiological and pathological conditions. The expression of mRNA for the two chains of PDGF are independently regulated. The fact that the different dimeric forms of PDGF have different functional effects, indicate that the cellular response to PDGF may be more complex than previously thought, and may involve binding to more than one receptor. The cellular effects ascribed to PDGF, growth stimulation, ruffling and chemotaxis, seems to be mainly associated with B chain containing dimers. The function of PDGF-AA remains to be elucidated.     

Effect of platelet-derived growth factor receptor-beta inhibition with STI571 on radioimmunotherapy

Whereas radioimmunotherapy of hematologic malignancies has evolved into a viable treatment option, the responses of solid tumors to radioimmunotherapy are discouraging. The likely cause of this problem is the interstitial hypertension inherent to all solid tumors. Remarkable improvements in tumor responses to radioimmunotherapy were discovered after the inclusion of STI571 in the therapy regimen. A combination of the tumor stroma-reactive STI571, a potent platelet-derived growth factor receptor-beta (PDGFr-beta) antagonist, and the tumor-seeking radiolabeled antibody B72.3 yielded long-lasting growth arrest of the human colorectal adenocarcinoma LS174T grown as s.c. xenografts in athymic mice. The interaction of STI571 with the stromal PDGFr-beta reduced tumor interstitial fluid pressure (P(IF)) by >50% and in so doing improved the uptake of B72.3. The attenuation of P(IF) also had a positive effect on the homogeneity of antibody distribution. These effects were dose-dependent and under optimized dosing conditions allowed for a 2.45 times increase in the tumor uptake of B72.3 as determined in the biodistribution studies. Single-photon emission computed tomography imaging studies substantiated these results and indicated that the homogeneity of the radioisotope distribution was also much improved when compared with the control mice. The increased uptake of radioimmunotherapy into the tumor resulted in >400% increase in the tumor absorbed radiation doses in STI571 + radioimmunotherapy-treated mice compared with PBS + radioimmunotherapy-treated mice. The improved antibody uptake in response to the attenuation of tumor P(IF) was identified as the primary reason for the growth arrest of the STI571 + radioimmunotherapy-treated tumors. Two related causes were also identified: (a) the improved homogeneity of monoclonal antibody distribution in tumor and (b) the increased tumor radiosensitivity resulting from the improved tumor oxygenation.     

Dose-dependent hormonal effects of toremifene in postmenopausal breast cancer patients

Purpose: The purpose of the study was to compare hormonal effects of three toremifene doses, 20 mg (TOR20), 40 mg (TOR40) and 60 mg (TOR60) administered daily, in postmenopausal women with advanced breast cancer. Methods: The study was randomized and open label in three parallel groups. Biochemical variables were identified as the serum concentrations of follicle stimulating hormone (FSH), luteinizing hormone (LH) and sex hormone binding globulin (SHBG). The changes were compared with objective clinical responses and to progression-free time. Adverse reactions and liver function test (aspartate aminotransferase, ASAT) were assessed for safety. Results: A total of 260 patients were randomly grouped (90 to TOR20, 81 to TOR40 and 89 to TOR60). Of these patients 29, 29 and 22 completed at least 3 months of treatment and the results were analyzed for biochemical variables. All treatments had intrinsic estrogen agonist activity by decreasing of serum FSH and LH and by increasing of SHBG during the first 3 months (P < 0.01). Dose TOR20 showed slightly longer times to exert maximum estrogenic effects than did the two higher doses. No increases in liver function tests were seen in any of the groups. Objective response rates were 24.4, 39.5 and 32.6% (P = 0.01) and median times-to-progression were 206, 189 and 196 days in TOR20, TOR40 and TOR60, respectively (P = 0.913). Fewer responses were observed in the TOR20 group than in TOR40 (P = 0.05). Adverse events were reported in 19, 23 and 30 patients in the treatment groups (P = 0.20). The most frequently reported events were hot flushes and nausea. These were mostly mild or moderate, and only 1.5% of treatments was discontinued due to toxicity. Conclusions: Toremifene doses of 40 and 60 mg daily were effective and safe treatments of breast cancer in postmenopausal women, and no differences in their biochemical or clinical effects were seen. Toremifene at 20 mg/day had similar but slightly less potent antiestrogenic and estrogenic effects than the two higher doses. Received: 5 August 1999 / Accepted: 28 October 1999     

The role of platelet-derived growth factor on human pluripotent progenitor (CFU-GEMM) growth in vitro

The effect of serum on the proliferation of human bone marrow pluripotent progenitor cells (CFU-GEMM), was compared to that of fresh frozen plasma (FFP). Serum significantly increased the number of mixed erythroid-granulocytic-megakaryocytic colonies (CFU-GEMM) and erythrocytic bursts (BFU-E) in this assay system (p less than 0.01 and 0.02, respectively). Two possible explanations for this finding were considered: first the presence of citrate-phosphate-dextrose (CPD) in plasma but not in serum, and second the presence of platelet-derived growth factor (PDGF) in serum but not in plasma. CPD was indeed found to have an inhibitory effect on growth of colonies of all types when added to serum-stimulated cultures. Nevertheless, when heparinized plasma was compared to serum from the same donors, growth of CFU-GEMM and BFU-E was higher in the serum-stimulated cultures (p less than 0.001 and p less than 0.05, respectively). PDGF at concentrations of 120-240 pM was found to enhance the formation of CFU-GEMM and BFU-E by three- and four-fold respectively when added to cultures containing FFP but not when added to cultures containing serum derived from whole blood (WBS). Purified PDGF added at the same concentrations, to cultures containing platelet-poor derived serum (PDS), promoted similar increases in growth of CFU-GEMM and BFU-E but not of granulocytic-macrophage or megakaryocytic colonies. Whether PDGF has a direct action on CFU-GEMM or its growth promoting activity is via an interacting cell population is currently being studied.     

Dose-dependent benefits of quercetin on tumorigenesis in the C3(1)/SV40Tag transgenic mouse model of breast cancer

Breast cancer is the leading cause of cancer related death in women. Quercetin is a flavonol shown to have anti-carcinogenic actions. However, few studies have investigated the dose-dependent effects of quercetin on tumorigenesis and none have used the C3(1)/SV40 Tag breast cancer mouse model. At 4 weeks of age female C3(1)/SV40 Tag mice were randomized to one of four dietary treatments (n = 15–16/group): control (no quercetin), low-dose quercetin (0.02% diet), moderate-dose quercetin (0.2% diet), or high-dose quercetin (2% diet). Tumor number and volume was assessed twice a week and at sacrifice (20 wks). Results showed an inverted ‘U’ dose-dependent effect of dietary quercetin on tumor number and volume; at sacrifice the moderate dose was most efficacious and reduced tumor number 20% and tumor volume 78% compared to control mice (C3-Con: 9.0 ± 0.9; C3-0.2%: 7.3 ± 0.9) and (C3-Con: 2061.8 ± 977.0 mm³; and C3-0.2%: 462.9 ± 75.9 mm³). Tumor volume at sacrifice was also reduced by the moderate dose compared to the high and low doses (C3-2%: 1163.2 ± 305.9 mm³; C3-0.02%: 1401.5 ± 555.6 mm³), as was tumor number (C3-2%: 10.7 ± 1.3 mm³; C3-0.02%: 8.1 ± 1.1 mm³). Gene expression microarray analysis performed on mammary glands from C3-Con and C3-0.2% mice determined that 31 genes were down-regulated and 9 genes were up-regulated more than 2-fold (P < 0.05) by quercetin treatment. We report the novel finding that there is a distinct dose-dependent effect of quercetin on tumor number and volume in a transgenic mouse model of human breast cancer, which is associated with a specific gene expression signature related to quercetin treatment.     

Inhibitory effects of BCG on adenovirus tumorigenesis: dependence on administration schedule

The cumulative incidence of tumours was registered in CBA mice inoculated with adenovirus type 12 when newborn and treated with BCG in different ways during the latency period. A single subcutaneous dose of BCG at 3–4 weeks of age had a preventive effect, while no prevention could be recorded after a single BCG dose at 9 weeks of age or eight BCG injections at intervals of 1 week. Sera obtained during the latency period were tested for capacity to block lymph-node cell-mediated tumour immunity. Blocking activity was detectable in pooled serum of the mice which had been infected with BCG at 9 weeks of age, already at 10 weeks, i.e. 1 to 2 weeks before the appearance of palpable tumours. Blocking activity could not be demonstrated in a serum pool from control mice until 14 weeks after virus inoculation, at which time sera from mice inoculated with BCG at the age of 3 weeks were still negative. The results indicate that the effect of BCG upon tumour development is dependent upon the point of time of BCG treatment and further suggest that BCG treatment initiated at a stage when serum blocking activity is already present can further stimulate the production of blocking factors and tentatively promote tumour development.     

胞葬作用对肿瘤发生发展影响的研究进展

胞葬作用是吞噬细胞清除凋亡细胞的过程,具有抗炎和促瘤作用。胞葬作用作为在肿瘤微环境（TME）中发生频率最高的事件之一,能对肿瘤细胞的增殖、凋亡、转移和侵袭,以及抗肿瘤免疫等生物学特征产生重要影响。胞葬作用过程中的复杂代谢状态可以通过“找我（find me）”、“吃我（eat me）”信号和释放降解产物影响肿瘤的发生与发展。此外,胞葬作用可促进肿瘤相关巨噬细胞（TAM）极化为M2表型、调节抗炎因子和促炎细胞因子分泌以及调节T细胞、NK细胞等免疫细胞的激活和成熟,产生一系列的抗炎和免疫抑制信号,影响TME,从而促进肿瘤细胞逃避免疫监视机制,导致肿瘤进展。从胞葬作用角度出发探讨肿瘤治疗的潜在靶点,为抗肿瘤药物的研发提供新的思路。