Resistance to mammary carcinogenesis in Copenhagen rats: potential roles of vascular endothelial growth factor and mast cells

Long-term hormonal promotion overcomes genetic resistance to mammary cancer

It is well known that ovarian steroids estradiol and progesterone play a vital role in the development of mammary cancer. Here, using the genetically highly resistant Copenhagen rats we demonstrate that sustained exogenous treatment with estradiol and progesterone overcomes genetic resistance to mammary cancer. It has been demonstrated that Copenhagen rats develop preneoplastic lesions upon exposure to carcinogens. However, these preneoplastic lesions fail to progress to ductal carcinomas in situ or overt mammary carcinomas. The preneoplastic lesions eventually decrease in number and are absent by 60 days post-carcinogen treatment. In the present study, we exposed 7-week-old female Copenhagen rats to N-methyl-N-nitrosourea (MNU; 50mg/kg BW). Immediately after MNU treatment the rats were divided into the following groups: (1) control; (2) 30 mg estradiol 17β; (3) 30 mg progesterone; and (4) 30 mg estradiol 17β plus 30 mg progesterone. All hormone treatments were administered via individual silastic pellets for a period of 9 months post-carcinogen treatment. The control animals displayed a low incidence of mammary cancer (10%). Hormone treatments produced significantly higher incidences of mammary cancer, with estradiol at 50%, progesterone at 65% and estradiol plus progesterone at 90%. Hormone treatment sustained the growth of the lesions induced by MNU by increasing expression of Areg, Bcl-2, Ccnd-1 and Vegf genes, while decreasing expression of Bad, Bax, Casp 3, 8, 9 and p53 genes. Furthermore, hormone treatment increased CCND-1 and PARP proteins levels. The data clearly demonstrates that hormonal environment supports mammary cancer progression by increasing cell proliferation, and angiogenesis while inhibiting apoptosis.

In vivo effect of an luteinizing hormone-releasing hormone analog on vascular endothelial growth factor and epidermal growth factor receptor expression in mammary tumors

BACKGROUND

The hypothalamic luteinizing hormone-releasing hormone (LHRH) is well known for its role in the control of pituitary gonadotropin secretion and it has demonstrated a direct antiproliferative effect on some cancer cell lines of LHRH and its synthetic analogs. The study was designed to assess whether administration of the LHRH analog (goserelin) has any effect on the expression of the vascular endothelial growth factor (VEGF) and the epidermal growth factor receptor (EGFR) in rats with N-nitroso-N-methylurea (NMU)-induced-mammary tumors " in vivo".

MATERIALS AND METHODS

The animals with tumors were assessed after acute or chronic treatment with goserelin, and in all the animals VEGF and EGFR expression was examined both in plasma and tumor homogenates by enzyme immunoassay.

RESULTS

The basal plasma values of VEGF were lower in the healthy control group than in rats with NMU-induced tumors ( P = 0.025). Following acute treatment with goserelin, VEGF expression in plasma increased above basal levels after 60 min ( P = 0.05) and dropped during chronic treatment. Likewise, in the tumor homogenate the mean VEGF expression was higher at 60 min post-goserelin administration than the basal levels, although VEGF expression then diminished at 90 min. Plasma EGFR expression was higher in rats with NMU-induced tumors than in healthy controls ( P Conclusions: The results allow us to conclude that goserelin may exert a short-term stimulatory effect on the release of VEGF, as well as a long-term inhibitory effect on VEGF but not EGFR expression.

Observation of microvasculatures in athymic nude rat transplanted tumor using synchrotron radiation microangiography system

RATIONALE AND OBJECTIVES

The diagnostic potential of tumor microvasculatures with the monochromatic synchrotron radiation microangiography (MSRA) system was examined in an experimental model using athymic nude rats.

MATERIALS AND METHODS

In the lower abdominal wall in athymic nude rats (male, 120-150 g, 6 weeks old), 1 x 10(7) cells of N-nitrosomethylurea-induced rat mammary adenocarcinoma was transplanted to prepare a lower abdominal wall tumor transplanted model. A microcatheter was inserted in the abdominal aorta in a rat under anesthesia, and microangiographic images of the normal inferior epigastric artery and vein were obtained using an MSRA system. Changes in the tumor microvasculatures were observed using an MSRA system on the day 7 (n = 3), day 14 (n = 3), day 21 (n = 3), and day 28 (n = 3) after transplant. In addition, we measured the microvessel density (MVD) with a computer using the binarization method. These results were compared among the histologic MVDs.

RESULTS

The microvasculatures of tumors measuring 20-30 microm were observable by the MSRA system in the transplanted tumor model using the inferior epigastric artery and vein as the feeding vessels. The tumor microvasculatures were observed for 7-28 days after transplantation. The tumor MVD obtained by the binarization method increased as the tumor volume increased. When histologic MVD was compared with the fixed quantitative results of angiographic MVD, a significant correlation (r = 0.933, P <.01) was observed.

CONCLUSION

These preliminary investigations indicate that MSRA proved to be suitable for quantification and appears to be a simple method for clearly imaging tumor microvasculatures.

The presence of stromal mast cells identifies a subset of invasive breast cancers with a favorable prognosis

Tissue microarrays containing 348 cases of invasive breast carcinoma were studied by immunohistochemical staining for CD-117, CD-3, CD-20, CD-68, Her2, estrogen receptor protein, and progesterone receptor protein, and results were correlated with patient outcome. Hormone receptor status (both estrogen receptor and progesterone receptor) correlated with a good outcome while Her2 overexpression was associated with a poor outcome. The presence of mast cells in the stroma, as demonstrated by positive c-kit (CD-117) staining, correlated with a good prognosis (P=0.0036). On subset analysis, this association between the presence of mast cells and favorable prognosis was present in the node-negative patients (P=0.018). The presence of mast cells showed an inverse correlation with the presence of CD-68 positive macrophages. No correlation was observed between the presence of mast cells and either B-cells (CD20-positive) or T-cells (CD3-positive). The presence of stromal mast cells was of prognostic significance independent of nodal status and tumor size (P=0.02). When the multivariate analysis was expanded to include tumor grade, estrogen receptor status and Her2 status, as well as tumor size and nodal status, the presence of stromal mast cells approached significance as an independent prognostic indicator.