Kinetics of mammary epithelial cell proliferation in pituitary isografted BALB/c mice

Abstract

Recently, we have published that treatment of pituitary isografted BALB/c mice with a single injection of N-methyl-N-nitrosourea (MNU) leads to the rapid development of mammary tumors in over 90% of the animals (Guzman et al., Cancer Res., 52, 5732-5737). In the present study, we characterized the changes in proliferative activity and lobulo-alveolar differentiation of MECs at different time intervals after isografting animals with pituitary glands. Virgin BALB/c mice 1, 3, 5 or 8 weeks after pituitary isografting were either pulse-labeled for 2 h or continuously infused with bromodeoxyuridine (BrdU) and the percentage of BrdU-labeled MECs was assessed. The S-phase duration (TS) of MECs was evaluated by double labeling with [3H]thymidine and BrdU. The population potential doubling time (TP) was calculated from the values of BrdU-LI and TS. Three stages of proliferation and differentiation of MECs in pituitary isografted virgin BALB/c mice were observed: (i) A sharp increase in the percentage of proliferating MECs of the terminal ducts and ductal branchings in the first 1-2 weeks, (ii) Development of lobulo-alveolar structures from the terminal ductal and alveolar buds, between weeks 3 and 5 with the highest BrdU-LI in week 3 and (iii) Multiplication of the alveolar structures and decrease in the BrdU-LI between weeks 5 and 8. The BrdU-LIs of alveolar cells 5 weeks after isografting the animals were significantly higher than those of the ductal cells. The continuous administration of BrdU for 3, 5 or 7 days by using osmotic pumps revealed zones in the ducts where almost all MECs were labeled as well as zones lacking proliferate activity. When the BrdU administration was extended for 10-14 days, almost all (> 95%) ductal and lobular epithelial cells were labeled. A small percentage (< 5%), of ductal and lobulo-alveolar MECs cells, remained unlabeled even after 14 days infusion of BrdU. The TS and TP values were shorter in pituitary isografted animals than in controls, but no significant difference was found for either values between the ductal and alveolar cells in either isografted or control mice. Changes in proliferation kinetics of mouse MECs in pituitary isografted animals correlated with the circulating concentrations of prolactin, progesterone and 17 beta-estradiol, but not with corticosterone, growth hormone or thyroxin.(ABSTRACT TRUNCATED AT 400 WORDS)

Drug-induced senescence bystander proliferation in prostate cancer cells in vitro and in vivo

“…Control animals, in which only senescent cells were injected, did not develop palpable tumours through the course of these experiments. Mice were injected with 70 mg kg À1 body weight BrdU 2 h prior to tumour harvest to measure proliferation in sorted GFP ( þ ) tumour cells (Christov et al, 1993). Cells from DU145 tumours established with or without senescent cells and collected after 5 weeks contain similar fractions of proliferating cells as measured by BrdU uptake and DNA profiling (data not shown).…”

“…Tumour dimensions were measured at 3, 4 and 5 weeks after injection using a caliper. BrdU was injected into these mice interperitoneally at a concentration of 70 mg kg À1 body weight (Christov et al, 1993), harvested 2 h later and dissociated into a single-cell suspension from which GFP ( þ ) cells were isolated by fluorescence-activated cell sorting. These were fixed in ice-cold ethanol and stored at À201C.…”

Bcl-2 expression delays mammary tumor development in dimethylbenz(a)anthracene-treated transgenic mice

“…Christov et al (1993) have shown that maximal mammary proliferation (7.7 ± 10.7%) occurs at approximately three weeks post-isograft and decreases back to the baseline after 5 ± 8 weeks. If the Bcl-2 transgene is exerting an antiproliferative e ect in the transgenic mammary glands, the maximal di erence in proliferation between that and the nontransgenic gland would theoretically be seen at almost exactly the same time as the carcinogen treatments, which were performed at weeks 2 and 3 post-isograft.…”

A mammary-specific model demonstrates the role of the p53 tumor suppressor gene in tumor development

“…Treatment with DMBA is known to cause adduct formation in genomic DNA which, if improperly repaired, would result in mutations (Ross and Nesnow, 1999). In contrast, pituitary isografts provide a mitogenic stimulus similar to that encountered during midpregnancy (Christov et al, 1993), and therefore, is thought to act to expand a population of cells bearing initiating mutations. Given the role of p53 in recognizing and ensuring DNA repair, the eect attributable to DMBA was surprisingly small.…”