Experimental induction of primitive neuro-ectodermal tumours in rats: a re-appraisement of the ENU-model of neurocarcinogenesis

Mechanisms of neurotoxicity induced in the developing brain of mice and rats by DNA-damaging chemicals

It is not widely known how the developing brain responds to extrinsic damage, although the developing brain is considered to be sensitive to diverse environmental factors including DNA-damaging agents. This paper reviews the mechanisms of neurotoxicity induced in the developing brain of mice and rats by six chemicals (ethylnitrosourea, hydroxyurea, 5-azacytidine, cytosine arabinoside, 6-mercaptopurine and etoposide), which cause DNA damage in different ways, especially from the viewpoints of apoptosis and cell cycle arrest in neural progenitor cells. In addition, this paper also reviews the repair process following damage in the developing brain.

VEGF immunopositivity related to malignancy degree, proliferative activity and angiogenesis in ENU-induced gliomas

Growth of solid tumors is highly dependent on angiogenesis. During tumor development, neoplastic cells switch to an angiogenic phenotype, playing a significant role in the expression of the vascular endothelial growth factor (VEGF). Seventy-two brain gliomas were induced in Sprague Dawley rats by prenatal exposure to ethylnitrosourea (ENU). Screening and location of tumors was carried out using magnetic resonance imaging (MRI). Conventional histology and immunocytochemistry for antibodies against glial fibrillary acidic protein (GFAP), S-100, NF, oligodendrocyte Ab-2, Ki-67, and VEGF165 were performed. The proliferation index (PI) was calculated from the Ki-67 labeling index, and the concentration of VEGF165 was quantified by enzyme-linked immunosorbent assay (ELISA). In vivo identification of macro- and microtumor appears to be useful to lead morphological and biochemical studies. Histopathology allows us to identify microtumors as classic oligodendrogliomas (CO; mean PI of 6.01 +/- 2.8%) and macrotumors as anaplastic oligodendrogliomas (AO; mean PI of 14.06 +/- 5%). Classic oligodendrogliomas show scarce VEGF165 expression whereas anaplastic ones display VEGF165 protein level 100-fold increased respect to CO. Astrocytes, neoplastic, and endothelial cells show differential immunostaining patterns from the border to the core of neoplasm. Positive structures for VEGF and their distribution vary according to PI increase. Anaplastic gliomas displaying VEGF-positive intratumor capillaries correspond to the highest PI values. To identify the "angiogenic switch," we propose the glioma stage characterized by VEGF immunopositive neoplastic cells inside the tumor and positive endothelial cells surrounding it.

Central neural tumor destruction by controlled release of a synthetic glycoside dispersed in a biodegradable polymeric matrix

An octyl N-acetylglucosaminide derivative with a pentaerythritol chain at position 6 has been synthesized and evaluated as an inhibitor of neural tumor growth. The glycoside inhibited the growth of a neuroectodermic tumor implanted in rats and, when loaded on a slow-delivery polymer disk, caused the destruction of cultured human astroblastoma obtained after surgical biopsy.

Growth-inhibiting effects of intralesional docetaxel and paclitaxel on an experimental model of malignant neuroectodermal tumor

Taxoids are effective agents against a wide variety of tumors, but their effectiveness on neuroectodermal tumors is not well-known. For this reason we have carried out an experimental study on the effect of intratumoral administration of docetaxel (DC) and paclitaxel (PC) on tumor growth, using a murine model of malignant neuroectodermal tumor. The results showed a delay in tumor growth in animals treated with PC compared with controls (dose of 5 mg/kg, three times per week every other day, forming a cycle; three cycles were completed with a break of a week between each cycle). The total dose administered to each animal was 45 mg/kg. When DC was administered, the results showed distinct tumor growth inhibition and tumor regression in 80% of animals (intratumoral administration at a dose of 5 mg/kg, three times per week every other day forming a cycle; three cycles were completed with a break of a week between each cycle). The total dose administered to each animal was 20 mg/kg. These results suggest the utility of taxoids, mainly DC, by intralesional administration, on malignant tumors of the nervous system.

Antitumor effect of TNP-470 is not associated to decrease of angiogenesis in an experimental malignant neuroectodermic tumor

The hypothesis that tumor growth depends on neovascularization has been broadly used in oncology research. TNP-470 is a fumagillin synthetic analog that is isolated from Aspergillus fumigatus, and experimental studies suggested that it shows antitumor effect mediated by its strong antiangiogenic effect. Because limited experience exists about the antitumoral effect of TNP-470 in cerebral tumors, we have carried out a study in order to evaluate the effect of TNP-470 on tumor growth and the vascular area in an experimental malignant neuroectodermic tumor growing in the subcutaneous space of immunocompetent Wistar rats. Our results showed a significant tumor growth inhibition in animals treated with TNP-470 when compared to those in the control group (intratumoral injections were administered in 30 mg/kg dose, three times a week on alternate days during four consecutive weeks). Since the quantitative analysis of tumor vascular parameters--number of microvessels and total intratumor vascular area--in the experimental groups did not show significant statistical differences, we conclude that TNP-470 has a significant antitumor effect on our neuroectodermic tumor, but this effect is mediated by other antineoplastic mechanisms that are independent of its previously described angiostatic capacity.

Antitumoral effect of irinotecan (CPT-11) on an experimental model of malignant neuroectodermal tumor

Irinotecan (CPT-11) is a topoisomerase I inhibitor with antitumor activity on a wide variety of neoplasms in several preclinical studies, but it showed poor efficacy in patients with nervous system tumors. We have carried out an experimental study in order to evaluate the effect of CPT-11 on the growth of a subcutaneously implanted malignant neuroectodermal tumor, after administration by different routes. The results showed that CPT-11 administration by intraperitoneal injections (at dose 10 mg/kg, 5 days per week, for 2 weeks, followed by 7-days rest period--one course--to a total of two courses) had no significant antitumor effect. Nevertheless, continuous infusion by intraperitoneal osmotic minipump over 28 days (at an infusion rate of 4.4 microg/h) showed a significant delay in tumor growth in 4 weeks of the implantation. The best antitumor effects were observed after CPT-11 intratumoral administration (at dose of 5 mg/kg, 5 days per week, for 2 weeks, followed by 7-days rest period, to a total of three courses) reaching tumor regression in the treated animals. These results suggest the utility of CPT-11, by means of intralesional administration, on malignant tumors of the nervous system.

Magnetic resonance imaging of ethyl-nitrosourea-induced rat gliomas: a model for experimental therapeutics of low-grade gliomas

Human low-grade gliomas represent a population of brain tumors that remain a therapeutic challenge. Preclinical evaluation of agents, to test their preventive or therapeutic efficacy in these tumors, requires the use of animal models. Spontaneous gliomas develop in models of chemically induced carcinogenesis, such as in the transplacental N-ethyl-N-nitrosourea (ENU) rat model. However, without the ability to detect initial tumor formation, multiplicity or to measure growth rates, it is difficult to test compounds for their interventional or preventional capabilities. In this study Fisher-334 rats, treated transplacentally with ENU, underwent magnetic resonance imaging (MRI) examination in order to evaluate this approach for detection of tumor formation and growth. ENU-induced intracranial cerebral tumors were first observable in T2-weighted images beginning at 4 months of age and grew with a mean doubling time of 0.487 +/- 0.112 months. These tumors were found histologically to be predominately mixed gliomas. Two therapeutic interventions were evaluated using MRI, vitamin A (all-trans retinol palmitate, RP), as a chemopreventative agent and the anti-angiogenic drug SU-5416. RP was found to significantly delay the time to first tumor observation by one month (P = 0.05). No differences in rates of tumor formation or growth rates were observed between control and RP-treated groups. MRI studies of rats treated with SU-5416 resulted in reduction in tumor growth rates compared to matched controls. These results show that MRI can be used to provide novel information relating to the therapeutic efficacy of agents against the ENU-induced tumor model.

Primitive neuroectodermal tumor of cerebrum with adipose tissue

Primitive neuroectodermal tumors (PNETs) of the central nervous system are uncommon embryonal neoplasms, rarely occurring in adults. Differentiation into specific mesenchymal tissues, such as cartilage, bone, skeletal muscle, smooth muscle, or adipose tissue, is rare. We report a case of a 51-year-old woman with a PNET of cerebrum that showed extensive mature adipose tissue differentiation. This is the second case, to our knowledge, of PNET of cerebrum with adipose tissue elements that has been described.

A case of canine primitive neuroectodermal tumor (PNET)

A 2-year and 6 month-old, female, Golden Retriever showed circling behavior and seizure. By magnetic resonance imaging (MRI) examination, a mass was found on the surface of the left cerebral hemisphere, invading to the left temporal muscle. The skull bone between them was destroyed. The dog was euthanized and necropsied. Histologically, the mass contained a lot of undifferentiated anaplastic cells, forming Homer-Wright rosettes and pseudopalisading patterns. Thus, the case was diagnosed as primitive neuroectodermal tumor (PNET).

Immune-cell system provides the development of extraneural tumors in the ethyl-nitrosourea model of neurocarcinogenesis

Immunological suppression of the immune-cell system by means of cyclosporin-A was performed at a stage corresponding to microtumor development in the ethyl-nitrosourea (ENU) model of neurocarcinogenesis. The results that we have obtained suggest that this immunological manipulation is related to the appearance of extraneural undifferentiated tumors, suggesting that the immune-cell system is effective in immunocompetent rodents for providing extraneural ENU carcinogenesis.

Drug resistance and apoptosis in ENU-induced rat brain tumors treated with anti-cancer drugs

To cast light on the mechanisms of drug-resistance, experimental brain tumors were immunohistochemically evaluated for expression of glutathione S-transferase (GST)-alpha, mu, pi, p-glycoprotein and apoptosis-related factors, such as bcl-2 and p53, as well as by the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labelling (TUNEL) method. Rat brain tumors induced by means of prenatal exposure to ethylnitrosourea (ENU) were treated with 1-(4-amino-2-methyl-5-pyrimidinyl)methyl-3-(2-chloroethyl)-3-nitrosourea hydrochloride (ACNU) and/or vincristine. Tumors more than 2 mm in size were considered to be drug resistant. The expression of GST-mu was strongly positive in ACNU-treated brain tumors, while p-glycoprotein was overexpressed in vincristine-treated brain tumors. Neither p53 nor bcl-2 expression directly correlated with apoptosis identified by TUNEL method, but tumors lacking apoptotic cells always demonstrated the expression of either GST-mu or p-glycoprotein. These results indicate that tumors resistant to chemotherapy might not be susceptible to induction of apoptosis, and therefore that mechanisms of drug resistance are related to programmed cell death in brain tumors.

Gangliosides modulate the growth rate and cell phenotype of a murine primitive neuro-ectodermal tumour

Intratumoural administration of gangliosides (GSD) into a murine primitive neuro-ectodermal tumour, growing in the epicranial subcutaneous tissue of syngenic rats, results in a decrease in the tumour growth rate and causes a more differentiated phenotype of tumour cell, with immunohistochemical expression of neuronal markers. These findings suggest that the potential usefulness of intralesional administration of GSD for the control of tumours of primitive neuro-epithelial character could be considered.