31P-NMR spectroscopy and histological studies of the response of rat mammary tumours to endocrine therapy

Abstract

Summary We have shown by 3'P-NMR spectroscopy that ovariectomy, in N-methyl-N-nitrosourea induced mammary adenocarcinomas, increases signals from phosphocreatine (PCr) relative to nucleoside triphosphate (NTP) before measurable regression (2 days) and for at least a further 13 days. The present study correlates the NMR changes with histological changes in the regressing tumour. Mammary tumours were examined by NMR before, and 2 and 14 days after, ovariectomy or sham-ovariectomy. Sections were taken from five tumours at each time point after operation for histology and for immunocytochemical staining of myoepithelial cells, luminal cells and basement membrane material. The histology showed typical cribriform papillary type mammary adenocarcinomas. The luminal cell population had a high mitotic activity and there was a prominent myoepithelial layer. At 2 days post-ovariectomy no significant change in mitotic activity was observed and no cytological characteristics attributable to ovariectomy could be seen. At 14 days postovariectomy the tumour was indistinguishable from a tubular adenoma, had significantly reduced mitotic activity, a relative increase in myoepithelial cells and basement membrane material. The changes detected by NMR must reflect early metabolic events, perhaps related to the histological changes observed at 14 days after ovariectomy. 31P-NMR spectroscopy may permit early monitoring of endocrine therapy for mammary cancer.3'P-NMR is a non-invasive technique that can be used for monitoring the energetics of tumours in situ either in animals or in patients. Among other metabolities it detects the high energy phosphate compounds, nucleoside triphosphate (NTP) and phosphocreatine (PCr) and their breakdown product, inorganic phosphate (Pi). Most therapeutic modalities, including chemotherapy (Evanochko et al., 1984; Steen et al., 1988) and irradiation (Tozer et al., 1989), perturb the energy metabolism of tumours. We have previously shown that in the untreated N-methyl-N-nitrosourea (NMU) induced mammary tumour, high energy phosphates are lost with increasing tumour size , a change that has been seen in other animal tumours (Ng et al., 1982). Ovariectomy in animals bearing NMU induced mammary adenocarcinomas caused the phosphorous metabolite ratios (PCr/ NTP, PCr/Pi and NTP/Pi) to increase . These increases may be analogous to a similar rise that has been observed after chemotherapy (Ng et al., 1982, Steen et al., 1988. The underlying mechanism of both these changes is unclear. In particular, do they reflect alterations in cell populations (infiltration by host cells, replacement of one tumour cell type by another etc.) or are they predominantly due to alterations in the metabolism of the cells that were present at the start of therapy? It seems clear that changes in cell populations must, at least in some cases, cause changes in the NMR spectrum, but these changes would probably take several days. If metabolic alterations in the original cancer cells can also change tumour high energy phosphates the...

EB1089, a synthetic analogue of vitamin D, induces apoptosis in breast cancer cells in vivo and in vitro

“…Figure 3 demonstrates the histological appearance of control tumours and tumours obtained from rats treated with 2.5 μg kg −1 EB1089 for 28 days. The majority of tumours induced by NMU are classified as adenocarcinomas, based upon cytological abnormalities and growth pattern exhibiting a papillary pattern with many mitoses (Stubbs et al , 1990; Mackay et al , 1996). In contrast, sections of tumours from animals treated with EB1089 showed marked loss of cellularity (Figure 3b).…”

Monitoring therapeutic response to tamoxifen in NMU-induced rat mammary tumours by 31P MRS

“…Alternatively, or in addition to this mechanism, the tumour blood supply might be improved either directly by tamoxifen itself or as a consequence of reduced oestrogen concentration. We have shown, in the case of ovariectomy, that the MRS changes at 48 h precede any alteration in the cell population (Stubbs et al, 1990). It is likely that this would be true for other endocrine treatments such as 4-hydroxyandrostenedione (Griffiths et al, 1987) and tamoxifen (this paper).…”

“…For instance, Vaupel et al (1987) found that small human mammary carcinoma xenografts grown in nude rats have a higher oxygen consumption than that of normal post-menopausal human breast and that both oxygen consumption and tumour blood flow decreased as the tumours increased in size. On the other hand, when a tumour responds to chemotherapy (Ng et al, 1982;Steen et al, 1988), radiotherapy (Evanochko et al, 1983;Tozer et al, 1989) or endocrine therapy (Griffiths et al, 1987;Rodrigues et al, 1988;Stubbs et al, 1990) the opposite effect is usually observed -the ratios of high energy phosphates (PCr and NTP) relative to Pi decrease, sometimes before any detectable change in the volume is recorded (Rodrigues et al, 1988) and before there are any detectable histological changes (Stubbs et al, 1990). Steen (1989) has reviewed reports of such paradoxical improvements in the ratio of high energy phosphates to Pi in experimental tumours after various forms of therapy, which he terms 'metabolic activation'.…”

“…Unfortunately decrease in tumour size, as a measure of responsiveness to endocrine therapy, tends to be slow; Powles (1984) Steen, 1989). In studies performed on oestrogen-sensitive rat mammary tumours (Rodrigues et al, 1988) we have shown that ovariectomy induced a marked change in phosphate metabolite ratios (PCr/NTP, NTP/Pi, PCr/Pi) that could be detected at 48 h, well before any measurable regression or significant histological changes (Stubbs et al, 1990) had taken place. This raised the possibility that MRS (which is non-invasive and has no known harmful effects on patients) could be used to monitor response to endocrine therapy.…”

“…Oestrogen sensitive mammary tumours were induced in female virgin Ludwig/Wistar/Olac rats with N-methyl-Nnitrosourea (NMU) as detailed in Stubbs et al (1990) …”