Stimulation of DNA Synthesis by Prolactin in Rabbit Mammary Tissue

Tantalum oxide nanoparticles as versatile and high-resolution X-ray contrast agent for intraductal image-guided ablative procedure in rodent models of breast cancer

There are limited options for primary prevention of breast cancer (BC). Experimental procedures to locally prevent BC have shown therapeutic efficacy in animal models. To determine the suitability of FDA-approved iodine-containing and various metal-containing (bismuth, gold, iodine, or tantalum) preclinical nanoparticle-based contrast agents for image-guided intraductal (ID) ablative treatment of BC in rodent models, we performed a prospective longitudinal study to determine the imaging performance, local retention and systemic clearance, safety profile, and compatibility with ablative solution of each contrast agent. At least six abdominal mammary glands (>3 female FVB/JN mice and/or Sprague-Dawley rats, 10-11 weeks of age) were intraductally injected with commercially available contrast agents (Omnipaque® 300, Fenestra® VC, MVivoTM Au, MVivoTM BIS) or in-house synthesized tantalum oxide (TaOx) nanoparticles. Contrast agents were administered at stock concentration or diluted in 70% ethanol (EtOH) and up to 1% ethyl cellulose (EC) as gelling agent to assess their compatibility with our image-guided ablative procedure. Mammary glands were serially imaged by microCT for up to 60 days after ID delivery. Imaging data were analyzed by radiologists and deep learning to measure in vivo signal disappearance of contrast agents. Mammary glands and major organs were ultimately collected for histopathological examination. TaOx-containing solutions provided best imaging performance for nitid visualization of ductal tree immediately after infusion, low outward diffusion (<1 day) and high homogeneity. Of all nanoparticles, TaOx had the highest local clearance rate (46% signal decay as stock and 36% as ablative solution 3 days after ID injection) and exhibited low toxicity. TaOx-containing ablative solution with 1% EC caused same percentage of epithelial cell death (88.62% ± 7.70% vs. 76.38% ± 9.99%, p value = 0.089) with similar minimal collateral damage (21.56 ± 5.28% vs. 21.50% ± 7.14%, p value = 0.98) in mouse and rat mammary glands, respectively. In conclusion, TaOx-nanoparticles are a suitable and versatile contrast agent for intraductal imaging and image-guided ablative procedures in rodent models of BC with translational potential to humans.

Systemic and Local Strategies for Primary Prevention of Breast Cancer

One in eight women will develop breast cancer in the US. For women with moderate (15-20%) to average (12.5%) risk of breast cancer, there are few options available for risk reduction. For high-risk (>20%) women, such as BRCA mutation carriers, primary prevention strategies are limited to evidence-based surgical removal of breasts and/or ovaries and anti-estrogen treatment. Despite their effectiveness in risk reduction, not many high-risk individuals opt for surgical or hormonal interventions due to severe side effects and potentially life-changing outcomes as key deterrents. Thus, better communication about the benefits of existing strategies and the development of new strategies with minimal side effects are needed to offer women adequate risk-reducing interventions. We extensively review and discuss innovative investigational strategies for primary prevention. Most of these investigational strategies are at the pre-clinical stage, but some are already being evaluated in clinical trials and others are expected to lead to first-in-human clinical trials within 5 years. Likely, these strategies would be initially tested in high-risk individuals but may be applicable to lower-risk women, if shown to decrease risk at a similar rate to existing strategies, but with minimal side effects.

Prolactin receptor expression in monolayer cultures of rabbit mammary epithelial cells: pre- and postpartum [125I]-prolactin binding activity

Expression of specific [125I]-prolactin-binding sites under culture conditions has been investigated for isolated mammary epithelial cells from virgin, pregnant, and lactating rabbits. Primary monolayer cultures were obtained by sequential enzymatic dispersion of mammary tissue followed by 48 hr incubation in a medium selective for epithelial cells. Scatchard analyses of binding data obtained from these cultures indicated a single class of receptor sites, the affinity constant of which (2.5 X 10(9) M-1) did not vary significantly during mammary development. The number of prolactin receptors, however, expressed by virgin and early pregnant epithelial cells was significantly increased over those from late pregnancy or lactation. Less differentiated cells also respond to growth in pregnant rabbit serum with an increase in specific [125I]-prolactin binding. The diminished receptor expression by cells obtained after 17 days of pregnancy coincides with the attainment of secretory capacity in the animal, and may reflect the influence of the low serum prolactin or high progesterone levels circulating during the last trimester in the rabbit, or be the cultural expression of secretory differentiation.

Prostaglandin regulation of murine mammary tumor virus production: a basis for some of the glucocorticoid and prolactin actions on mammary tumor cell cultures

Hormonal regulation of mouse mammary tumor virus (MuMTV) production has been studied in cell cultures derived from mammary carcinomas of GR mice. The purpose of this study was to define the role of prolactin in dexamethasone-induced MuMTV production and to evaluate the mechanism(s) of action of these hormones. Results of our investigations in vitro establish a central role for prostaglandins, in particular PGF2 alpha. Prolactin treatment up to 1000 ng/ml increased the MuMTV production only slightly when added alone but a maximal stimulatory response was expressed when prolactin was added simultaneously with dexamethasone 2 micrograms/ml. This prolactin-related enhancement of MuMTV production was probably mediated by PGs since it was inhibited by indomethacin, an inhibitor of prostaglandin synthesis. When higher concentrations of indomethacin were used in dexamethasone-treated cultures, MuMTV production, although inhibited, was restored in part by addition of exogeneous PGF2 alpha. PGF2 alpha added alone stimulated the MuMTV production and, in combination with dexamethasone, showed a synergistic effect on stimulation of MuMTV production. Two compounds, PGF2 alpha and TXA2 (measured as TXB2), were produced in significant concentrations by these cultures. These findings suggest that PGF2 alpha exerts a regulating role on production of MuMTV in GR cells and indicate that the actions of both dexamethasone and prolactin are mediated at least in part by prostaglandins.

Prostaglandin synthesis by murine mammary gland is modified by the state of the estrus cycle

Mammary glands were excised from female C3H mice at various stages of their estrus cycle. Homogenates incubated at 37 degrees C +/- 10(5) M indomethacin synthesized prostaglandins (PG) E and f2 alpha at rates that varied as a function of the stage at estrus. The rate of PGF2 alpha synthesis was maximal at 1330 pg per mg protein per 2 hr in early diestrus and fell to undetectable levels in early estrus. PGE synthesis exhibited a similar pattern, being maximal at 83 pg per mg protein per 2 hr in early diestrus. These observations suggest that prostaglandins play a role in the cyclic changes observed within the mammary gland.

Onset of nucleic acid synthesis during germination of Pisum sativum L

Measurments of total nucleic acid content of the embryonic axis indicated that massive net synthesis of both DNA and RNA was initiated at approximately 30 h after the onset of germination. The onset of net nucleic acid synthesis was marked by an increase in the rate of incorporation of [(3)H]thymidine into DNA, and of [(3)H]orotic acid and [(3)H]uridine into both DNA and RNA. rRNA was usually more heavily labelled than tRNA, but was not preferentially accumulated, suggesting a grater rate of turnover of rRNA than tRNA. Some incorporation of precursors occurred prior to the onset of net nucleic acid synthesis, particularly into RNA. This was taken to represent nucleic acid turnover. There was no evidence that the "scavenging" pathways for nucleotide biosynthesis were more important than the "normal" pathways in contributing precursors for net nucleic acid synthesis.

Metabolically labile DNA in aseptically grown seedlings of Pisum sativum L

Pea seedlings (Pisum sativum L.) were grown aseptically in a sterile flexible film animal isolator. Radioactivity from [Me-(3)H]thymidine, supplied to the roots of the seedlings, was specifically incorporated into pea DNA. There was no incorporation into RNA or into bacterial DNA; neither was there any non-specific binding of label to carbohydrate. Much of the radioactivity incorporated into the DNA was lost during a cold chase. The loss could not be accounted for by net DNA synthesis and cell division, and is therefore taken as strong evidence for DNA turnover. The significance of these results is discussed.