Gold nanoparticles for the improved anticancer drug delivery of the active component of oxaliplatin

The platinum-based anticancer drugs cisplatin, carboplatin, and oxaliplatin are an important component of chemotherapy but are limited by severe dose-limiting side effects and the ability of tumors to develop resistance rapidly. These drugs can be improved through the use of drug-delivery vehicles that are able to target cancers passively or actively. In this study, we have tethered the active component of the anticancer drug oxaliplatin to a gold nanoparticle for improved drug delivery. Naked gold nanoparticles were functionalized with a thiolated poly(ethylene glycol) (PEG) monolayer capped with a carboxylate group. [Pt(1R,2R-diaminocyclohexane)(H₂O)₂]2NO₃ was added to the PEG surface to yield a supramolecular complex with 280 (±20) drug molecules per nanoparticle. The platinum-tethered nanoparticles were examined for cytotoxicity, drug uptake, and localization in the A549 lung epithelial cancer cell line and the colon cancer cell lines HCT116, HCT15, HT29, and RKO. The platinum-tethered nanoparticles demonstrated as good as, or significantly better, cytotoxicity than oxaliplatin alone in all of the cell lines and an unusual ability to penetrate the nucleus in the lung cancer cells.

Suppression of epithelial apoptosis and delayed mammary gland involution in mice with a conditional knockout of Stat3

Mammary gland involution is characterized by extensive apoptosis of the epithelial cells. At the onset of involution, Stat3 is specifically activated. To address the function of this signaling molecule in mammary epithelial apoptosis, we have generated a conditional knockout of Stat3 using the Cre-lox recombination system. Following weaning, a decrease in apoptosis and a dramatic delay of involution occurred in Stat3 null mammary tissue. Involution is normally associated with a significant increase in IGFBP-5 levels. This was observed in control glands, but not in the absence of Stat3. IGFBP-5 has been suggested to induce apoptosis by sequestering IGF-1 to casein micelles, thereby inhibiting its survival function. Our findings suggest that IGFBP-5 is a direct or indirect target for Stat3 and its upregulation is essential to normal involution. No marked differences were seen in the regulation of Stat5, Bcl-x(L), or Bax in the absence of Stat3. Precocious activation of Stat1 and increases in levels of p53 and p21 occurred and may act as compensatory mechanisms for the eventual initiation of involution observed in Stat3 null mammary glands. This is the first demonstration of the importance of a Stat factor in signaling the initiation of physiological apoptosis in vivo.

Major components of the insulin-like growth factor axis are expressed early in chicken embryogenesis, with IGF binding protein ( IGFBP) -5 expression subject to regulation by Sonic Hedgehog

Using whole-mount in situ hybridisation techniques, we have examined the expression of major components of the insulin-like growth factor (IGF) axis in early development of the chicken embryo, including both IGF-I and -II, the type 1 IGF receptor ( IGFR), and two of the IGF binding proteins, ( IGFBP) -2 and -5. We report that these genes fall into two distinct groups with respect to expression pattern, with IGFBP-2 displaying broad overlap of mRNA expression with IGFR and IGF-I during early development, whereas the expression profile of IGFBP-5 most closely resembled that of IGF-II. Comparison between different stages revealed IGFBP-2 mRNA was detected as early as stage 3, whereas IGFBP-5 was first seen at stage 4. In addition, we detected expression domains of IGFBP-5, and to a lesser extent IGFBP-2, which did not overlap with either IGFR or IGF expression patterns. This could indicate IGF independent actions of the IGFBPs during early embryonic development. A striking observation concerning the expression profiles of both IGF-II and IGFBP-5 at early stages of chick embryogenesis is that both these genes are expressed asymmetrically in a pattern similar to that of Sonic Hedgehog (Shh). Furthermore, using cyclopamine, we have demonstrated that IGFBP-5 expression in the early embryo is regulated by Shh. Taken together, these results describe an important role for the IGF system in the very early stages of the developing chicken embryo, and imply that IGFBP-2 and -5 are fundamental developmental factors, with the latter involved in Shh signalling pathways.

Insulin-like growth factor-binding protein-5 (IGFBP-5): a critical member of the IGF axis

The six members of the insulin-like growth factor-binding protein family (IGFBP-1-6) are important components of the IGF (insulin-like growth factor) axis. In this capacity, they serve to regulate the activity of both IGF-I and -II polypeptide growth factors. The IGFBPs are able to enhance or inhibit the activity of IGFs in a cell- and tissue-specific manner. One of these proteins, IGFBP-5, also has an important role in controlling cell survival, differentiation and apoptosis. In this review, we report on the structural and functional features of the protein which are important for these effects. We also examine the regulation of IGFBP-5 expression and comment on its potential role in tumour biology, with special reference to work with breast cancer cells.

Metabolism of sheep adipose tissue during pregnancy and lactation. Adaptation and regulation

1. Changes in the mean volume, the rate of fatty acid and acylglycerol glycerol synthesis, the activity of lipoprotein lipase and the numbers and affinities of insulin receptors of subcutaneous adipocytes are reported for sheep at different stages of pregnancy and lactation. In addition, the serum concentrations of insulin, progesterone, prolactin, choriomammotropin, somatotropin, glucose, acetate, L-lactate, glycerol and unesterified fatty acids are reported for these sheep. 2. A switch from lipid accumulation to net lipid mobilization accompanied by a decline in the capacity for lipid synthesis, occurred at the onset of the last third of pregnancy. Net lipid mobilization continued during lactation. 3. The changes that occurred in the serum concentrations of the various hormones listed above are discussed in relation to their possible roles in the modulation of adipose tissue metabolism in sheep during pregnancy and lactation. The observations are compared with those from previous studies on the hormonal control of adipose tissue metabolism in the rat during pregnancy and lactation.

Role of insulin receptors in the changing metabolism of adipose tissue during pregnancy and lactation in the rat

Changes in the volume, the rates of fatty acid synthesis and synthesis of the glycerol moiety of acylglycerols, the activity of lipoprotein lipase, and the number and affinity of insulin receptors of adipocytes, and concentrations of serum insulin, prolactin and progesterone were determined in virgin rats and in rats at various stages of pregnancy and lactation. Changes in the metabolic activities of adipose tissue appeared to be synchronized and primarily comprised a marked decrease in anabolic activity around parturition. In contrast, the number of insulin receptors (Kd 1.5 nM) per adipocyte doubled during pregnancy before returning to normal values around parturition. It is postulated that the increase in the number of insulin receptors is an adaptation to counteract the effects of insulin-antagonistic hormones during pregnancy and that the decrease in the number of receptors is primarily responsible for the loss of anabolic activity around parturition.

Control of milk secretion and apoptosis during mammary involution

Lactation depends on regular suckling or milking of the mammary gland. Without this stimulus, milk secretion stops and mammary involution is induced. Involution caused by abrupt cessation of milk removal is characterized by de-differentiation and apoptosis of mammary epithelial cells, the extent and time course of the latter varying between species. Apoptosis is inhibited and milk secretion is restored by re-suckling, if milk stasis is of short duration. Mammary involution and apoptosis also occur during weaning, even in concurrently-pregnant animals when the interval between lactations is restricted, suggesting that tissue remodeling is essential for subsequent lactation. Declining milk production in ruminants after peak lactation is also associated with, and probably results from, net cell loss by apoptosis. Involution and apoptosis are controlled by changes in systemic galactopoietic hormone levels, and by intra-mammary mechanisms responsive to milk removal. Milk stasis precipitated by litter removal or cessation of milking may involve intra-mammary control related to physical distension of the epithelium. Local control of apoptosis in rodents during weaning, and after peak lactation in dairy animals, may be due to the actions of milk-borne survival factors or their inhibitors, and can be manipulated by frequency of milk removal.

Thyroid surgery and voice-related outcomes

BACKGROUND

Vocal dysfunction in patients with thyroid pathology has been poorly documented, and dysfunction after thyroid surgery is generally reported in terms of recurrent laryngeal nerve or external laryngeal nerve palsy. But voice dysfunction is more complex than simply nerve integrity. The present study reports the incidence of dysphonia in patients presenting for thyroid surgery, and relates postoperative changes in vocal function to recurrent and external laryngeal nerve function, and the surgical handling of the strap muscles.

METHODS

Fifty patients were assessed by Visipitch before and after thyroidectomy. Following surgery the patients filled out a questionnaire.

RESULTS

Overall 26 of 44 patients had no subjective postoperative voice change, while 10 reported subjective deterioration and eight reported subjective improvement in voicing. Postoperative objective assessment of these patients found that 17 were the same, eight refused to come for testing because they felt their voice had not changed, 13 were better and six were worse. Following surgery two patients (4.5%) had temporary recurrent laryngeal nerve palsies (2.5% of nerves at risk), and four patients (10%) suffered external laryngeal nerve palsies. Division of strap muscles was not detrimental to voicing. Six patients were lost to follow-up. Fifteen patients (34%) presented with vocal abnormalities, six (40%) of whom improved postoperatively.

CONCLUSIONS

Patients may have voicing abnormalities before thyroid surgery is performed. Surgery may improve or worsen the voice irrespective of the pre-operative voice status.

Hormonal control of insulin-like growth factor-binding protein-5 production in the involuting mammary gland of the rat

We have demonstrated a 50-fold increase in the concentration of insulin-like growth factor-binding protein-5 (IGFBP-5) in milk after 2 days of mammary involution induced by removal of the suckling young. IGFBP-5 was identified by its immunoreactivity with an antiserum to IGFBP-5 and was shown by in situ hybridization to be synthesized by the secretory epithelial cells undergoing apoptosis. Smaller increases in IGFBP-2 and -4 messenger RNAs (mRNAs) were also evident, but neither protein could be detected on Western ligand blots of milk. Preliminary evidence failed to detect mRNAs for IGFBP-1, -3, or -6. The large increase in IGFBP-5 concentrations in milk from involuting mammary glands was inhibited by 90% if the dams received concurrent PRL injections for 2 days, but was unaffected by GH, progesterone, corticosterone, or an antiserum to insulin-like growth factor I (IGF-I). In lactating rats allowed to continue nursing their young, 17beta-estradiol failed to affect IGFBP-5 concentrations, whereas in animals that had half the teats sealed to prevent milk removal, IGFBP-5 concentrations increased 5- to 10-fold in the sealed gland compared with those in the contralateral gland where milk removal continued. The changes in IGFBP-5 concentrations in milk were accompanied by similar changes in steady state mRNA levels of IGFBP-5 in mammary tissue. We have previously shown that PRL inhibits apoptosis and involution of the mammary gland, whereas teat sealing has the opposite effect. We, therefore, propose that IGFBP-5 serves to inhibit IGF-I-mediated cell survival, but that it is normally suppressed by PRL and milk removal. Although IGFBP-5, when bound to extracellular matrix, augments the action of IGF, we believe that in the involuting mammary gland IGFBP-5 inhibits IGF action by interacting with casein micelles, which contain calcium phosphate nanoclusters, thereby preventing IGF interaction with IGF receptors. This is analogous to the interaction of IGFBP-5 with hydroxyapatite, which serves to sequester IGFs in bone. IGFBP-5 may, in fact, play a central role in inducing apoptosis, as it is also up-regulated in involuting prostate and thyroid glands as well as in atretic ovarian follicles.

Translational pharmacology of an inhaled small molecule αvβ6 integrin inhibitor for idiopathic pulmonary fibrosis

The αvβ6 integrin plays a key role in the activation of transforming growth factor-β (TGFβ), a pro-fibrotic mediator that is pivotal to the development of idiopathic pulmonary fibrosis (IPF). We identified a selective small molecule αvβ6 RGD-mimetic, GSK3008348, and profiled it in a range of disease relevant pre-clinical systems. To understand the relationship between target engagement and inhibition of fibrosis, we measured pharmacodynamic and disease-related end points. Here, we report, GSK3008348 binds to αvβ6 with high affinity in human IPF lung and reduces downstream pro-fibrotic TGFβ signaling to normal levels. In human lung epithelial cells, GSK3008348 induces rapid internalization and lysosomal degradation of the αvβ6 integrin. In the murine bleomycin-induced lung fibrosis model, GSK3008348 engages αvβ6, induces prolonged inhibition of TGFβ signaling and reduces lung collagen deposition and serum C3M, a marker of IPF disease progression. These studies highlight the potential of inhaled GSK3008348 as an anti-fibrotic therapy.

The αvβ6 integrin is key in activating the pro-fibrotic cytokine TGFβ in idiopathic pulmonary fibrosis. Here, the authors show an inhaled small molecule αvβ6 inhibitor GSK3008348 induces prolonged inhibition of TGFβ signaling pathways in human and murine models of lung fibrosis via αvβ6 degradation.

Insulin-like growth factor binding protein-5 (IGFBP-5) induces premature cell death in the mammary glands of transgenic mice

We have previously demonstrated that IGFBP-5 production by mammary epithelial cells increases dramatically during involution of the mammary gland. To demonstrate a causal relationship between IGFBP-5 and cell death we created transgenic mice expressing IGFBP-5 in the mammary gland using a mammary-specific promoter, β-lactoglobulin. DNA content in the mammary glands of transgenic mice was decreased as early as day 10 of pregnancy. Histological analysis indicated reduced numbers of alveolar end buds, with decreased ductal branching. Transgenic dams produced IGFBP-5 in their milk at concentrations similar to those achieved at the end of normal lactation. Mammary cell number and milk synthesis were both decreased by approximately 50% during the first 10 days of lactation. BrdU labelling was decreased, whereas DNA ladders were increased in transgenic animals on day 1 of lactation. On day 2 postpartum, the epithelial invasion of the mammary fat pad was clearly impaired in transgenic animals. The concentrations of the pro-apoptotic molecule caspase-3 and of plasmin were both increased in transgenic animals whilst the concentrations of 2 prosurvival molecules Bcl-2 and Bcl-xLwere both decreased. In order to examine whether IGFBP-5 acts by inhibiting the survival effect of IGF-I we examined IGF receptor phosphorylation and Akt phosphorylation and showed that both were inhibited. We attempted to “rescue” the transgenic phenotype by using growth hormone to increase endogenous IGF-I concentrations or by implanting minipumps delivering an IGF-1 analogue, R3-IGF-1, which binds weakly to IGFBP-5. Growth hormone treatment failed to affect mammary development suggesting that increased concentrations of endogenous IGF-1 are insufficient to overcome the high concentrations of IGFBP-5 produced by these transgenic animals. In contrast mammary development (gland weight and DNA content) was normalised by R3-IGF-I although milk production was only partially restored. This is the first demonstration that over-expression of IGFBP-5 can lead to; impaired mammary development, increased expression of the pro-apoptotic molecule caspase-3, increased plasmin generation and decreased expression of pro-survival molecules of the Bcl-2 family. It clearly demonstrates that IGF-I is an important developmental/survival factor for the mammary gland and, furthermore, this cell death programme may be utilised in a wide variety of tissues.

Interactions of prolactin and growth hormone (GH) in the regulation of mammary gland function and epithelial cell survival

The relative importance of GH and prolactin in mammary gland function varies between species with prolactin playing a major role in rodents and GH taking lead role in ruminants. In rodents, however, GH appears to play a vital role in maintaining a high-fat/low volume milk in the absence of prolactin and a similar finding has been demonstrated in goats where prolactin deficiency causes a more modest (15%) decrease in milk yield. Surprisingly GH-deficiency in goats induced no further decline in milk yield whereas exogenous GH or prolactin both stimulated milk output considerably. Although direct effects of prolactin on mammary epithelial cells are well-documented effects of GH are believed to be mediated indirectly via IGF-1 production from the liver. We have been unable to confirm this hypothesis in rats and believe this to be because it is too simplistic. By considering prolactin and GH to be survival factors for the mammary gland we now propose a mechanism by which they interact through the IGF system. Involution of the mammary gland involves apoptosis and, in rats, it is induced by prolactin-deficiency or milk accumulation. Coincidentally with this process mammary epithelial cells synthesize and secrete and IGF binding protein, IGFBP-5. We hypothesize that GH stimulates IGF-1 production, possibly from the mammary parenchyma. IGF-1 then acts as a survival factor for the mammary gland. Prolactin plays an essential role since it suppresses the secretion of IGFBP-5 which would otherwise inhibit IGF-1 action and lead to the induction of cell death.

Diet-induced obesity impairs mammary development and lactogenesis in murine mammary gland

We have developed a mouse model of diet-induced obesity that shows numerous abnormalities relating to mammary gland function. Animals ate approximately 40% more calories when offered a high-fat diet and gained weight at three times the rate of controls. They exhibited reduced conception rates, increased peripartum pup mortality, and impaired lactogenesis. The impairment of lactogenesis involved lipid accumulation in the secretory epithelial cells indicative of an absence of copius milk secretion. Expression of mRNAs for beta-casein, whey acid protein, and alpha-lactalbumin were all decreased immediately postpartum but recovered as lactation was established over 2-3 days. Expression of acetyl-CoA carboxylase (ACC)-alpha mRNA was also decreased at parturition as was the total enzyme activity, although there was a compensatory increase in the proportion in the active state. By day 10 of lactation, the proportion of ACC in the active state was also decreased in obese animals, indicative of suppression of de novo fatty acid synthesis resulting from the supply of preformed fatty acids in the diet. Although obese animals consumed more calories in the nonpregnant and early pregnant states, they showed a marked depression in fat intake around day 9 of pregnancy before food intake recovered in later pregnancy. Food intake increased dramatically in both lean and obese animals during lactation although total calories consumed were identical in both groups. Thus, despite access to high-energy diets, the obese animals mobilized even more adipose tissue during lactation than their lean counterparts. Obese animals also exhibited marked abnormalities in alveolar development of the mammary gland, which may partially explain the delay in differentiation evident during lactogenesis.

Insulin-like growth factor axis during embryonic development

The insulin-like growth factor (IGF) axis has been studied extensively in the developing vertebrate embryo. Knockout experiments have demonstrated that both IGF-I and -II are required for normal development in the mouse embryo, and mRNA and protein expression patterns for both growth factors, together with those for the type I IGF receptor and the six IGF-binding proteins, have been analysed in embryos from different species. Although the unique temporal and spatial expression patterns of these genes indicates important roles for the IGF axis during organ and whole animal development, the variation and complexity of expression makes these roles difficult to unravel. However, one possible mechanism unifying the IGF system in development is programmed cell death (apoptosis), which has been shown to be important in sculpting embryonic tissues, and, in particular, the developing limb bud. In addition, the very early onset of expression of various IGF family members in chicken embryos further emphasizes the fundamental importance of this system in development. This article reviews the work that has been carried out in this area in the context of current understanding of the IGF system.

The role of prolactin and growth hormone in the regulation of casein gene expression and mammary cell survival: relationships to milk synthesis and secretion

We have compared involution of the rat mammary gland, induced by litter removal, where milk accumulation occurs, with involution induced in the presence of the suckling young by combined PRL and GH deficiency. Both treatments induced involutionary processes involving apoptosis, as judged by DNA ladders and resulted in significant decreases in the DNA content of the gland. Surprisingly, the effects of hormone deprivation on protein output in milk were principally explained by the loss of secretory cells, as there were only modest decreases in casein messenger RNA (mRNA) expression and protein synthesis rates per U DNA in vitro. The association of casein mRNA with the polysome fraction was also unaffected by hormone deprivation, whereas involution induced by litter removal resulted in much greater decreases in steady state levels of casein mRNA and an increased association of the mRNAs with the monosome fraction. In PRL- and GH-deficient rats, PRL treatment could prevent all of these effects, GH was partially effective, whereas putative mediators of GH action, insulin-like growth factor I (IGF-I), IGF-II, and IGF-binding protein-3, were ineffective. This lack of effect of IGFs may be due to an inhibitory IGFBP, which we demonstrate to be present in increased amounts in the involuting mammary gland.

Role of prolactin, growth hormone and insulin-like growth factor 1 in mammary gland involution in the dairy cow

Bovine mammary involution, an important process for subsequent lactations, is characterized by loss of epithelial cells by apoptosis, but its hormonal regulation is still not well defined. Prolactin (PRL) and growth hormone (GH) play a specific role on rat mammary gland apoptosis, through insulin-like growth factor 1 (IGF-1) and the IGF binding protein (IGFBP) system. The purpose of our investigation was to determine the possible role of PRL, GH, and IGF-1 on cell survival and on IGFBP-5 expression in the bovine mammary gland. Mammary gland explants were cultured in the presence of cortisol, 17beta-estradiol, progesterone, insulin, PRL, GH, and IGF-1 and with the same treatment but without PRL, GH or IGF-1, respectively. After 24 h of culture, we determined the level of apoptosis through evaluation of DNA laddering in the oligonucleosomal fraction and examined IGFBP-5 messenger RNA (mRNA) expression. The results show a high level of DNA laddering and an increase in IGFBP-5 mRNA content in mammary explants cultured in the absence of PRL, GH, or IGF-I with respect to explants treated with all hormones. Moreover, explants cultured in presence of PRL, GH, or IGF-I show a low level of DNA laddering and IGFBP-5 expression with respect to explants cultured without any hormones. These data demonstrate a relationship between levels of apoptosis and IGFBP-5 mRNA expression in the bovine mammary gland and confirm the involvement of this binding protein programmed cell death and its relationship with the main lactogenic hormones.

The role of growth hormone, prolactin and insulin-like growth factors in the regulation of rat mammary gland and adipose tissue metabolism during lactation

Inhibition of prolactin secretion with bromocriptine and neutralization of GH action with a specific antiserum to rat GH (rGH) were used to explore the modes of action of GH and prolactin in maintaining lactation in the rat. Treatment of dams with anti-rGH caused a small reduction in litter weight gain whilst bromocriptine reduced litter weight gain by 50%. When both treatments were combined, however, milk yield ceased completely and this was accompanied by a wide variety of effects on mammary lipid metabolism including decreases in the mRNA concentrations of acetyl CoA carboxylase, fatty acid synthase, malic enzyme and lipoprotein lipase. Activities of acetyl CoA carboxylase and lipoprotein lipase were also significantly reduced. Reciprocal changes were evident in adipose tissue with increases in acetyl CoA carboxylase and lipoprotein lipase activities. In conjunction with a decreased lipolytic response to noradrenaline in adipose tissue of animals given the combined treatment of bromocriptine and anti-rGH, this represented a co-ordinated series of changes to reduce lipid synthesis in the mammary gland and enhance lipogenesis and triglyceride storage in adipose tissue as milk production ceased. All of these effects could be prevented in part by concurrent treatment with GH, but insulin-like growth factor-I (IGF-I) and IGF-II failed to affect any of the parameters measured.(ABSTRACT TRUNCATED AT 250 WORDS)

Prolactin and the regulation of adipose-tissue metabolism during lactation in rats

Removal of litters from young lactating rats for 24 or 48 h or treatment of lactating rats with bromocriptine increased the rate of fatty acid synthesis and the activities of lipoprotein lipase and fatty acid synthetase in adipose tissue, decreased the lipoprotein lipase and fatty acid synthetase activities of mammary gland and lowered the serum-prolactin concentration. Concurrent injections of prolactin prevented the effects of bromocriptine and 24 h of litter removal on most of these changes in adipose tissue, but did not prevent the effects of 48 h of litter removal. The results suggest that effects of prolactin on adipose-tissue metabolism are dependent on a functional mammary gland. Most of the responses of adipose tissue to litter removal were reduced in older rats.

Evaluation of anionic half generation 3.5-6.5 poly(amidoamine) dendrimers as delivery vehicles for the active component of the anticancer drug cisplatin

Aquated cisplatin was added to half-generation PAMAM dendrimers and the resultant complexes were purified by centrifuge. The drug-dendrimer complexes were then characterised by 1-D and diffusion (1)H NMR and ICP-AES. The amount of drug bound was found to increase in proportion with dendrimer size: G3.5, 22 cis-{Pt(NH(3))(2)} molecules per dendrimer; G4.5, 37; G5.5, 54; and G6.5, 94, which represent only a fraction of the available binding sites on each dendrimer (68, 58, 42 and 37%, respectively). Drug release studies showed that some drug remains bound to the dendrimer even after prolonged incubation with 5'-GMP at temperatures of 60°C for over a week (percentage of drug released 18, 30, 35 and 63%, respectively). Attachment of the drug was found to decrease the radius of the dendrimers. Finally, the effect of the dendrimer on drug cytotoxicity was determined using in vitro assays with the A2780, A2780cis and A2780cp ovarian cancer cell lines. The free dendrimers display no cytotoxicity whilst the drug-dendrimer complexes showed moderate activity. In vivo activity was examined using an A2780 tumour xenograft. Cisplatin, at its maximum tolerated dose of 6 mg/kg, reduced tumour size by 33% compared to an untreated control group. The G6.5 cisplatin-dendrimer complex was administered at two doses (6 and 8 mg/kg equivalent of cisplatin). Both were well tolerated by the mice. The lower dose displayed comparable activity to cisplatin with a tumour volume reduction of 32%, but the higher dose was significantly more active than free cisplatin with a tumour reduction of 45%.

Insulin-like growth factor binding protein 5 and apoptosis in mammary epithelial cells

Insulin-like growth factors (IGFs) are important survival signals that can protect a range of cell types from apoptosis. Although IGF bioavailability is modulated by high affinity interactions with IGF-binding proteins (IGFBPs), there is currently no experimental evidence that IGFBPs regulate the survival function of IGFs in the mammary gland. We have examined IGFBP expression during mammary gland development and studied the effects of IGFBPs on IGF-mediated survival and signalling in mammary epithelial cells in culture. IGFBP-5 protein was greatly increased during days 1-3 of mammary gland involution, when levels of apoptosis are dramatically elevated to remodel the gland after lactation. Primary cultures of mammary epithelial cells (MECs) expressed IGFBP-5 from their basal surface suggesting that IGFBP-5 is suitably located to inhibit IGF signalling. Addition of exogenous IGFBP-5 and IGFBP-3 to MECs suppressed IGF-I-mediated survival, resulting in threefold greater apoptosis in cells incubated with IGF-I and IGFBP-5 compared with IGF-I alone. Examination of signalling pathways involved in apoptosis revealed that phosphorylation of PKB and the forkhead transcription factor, FKHRL1, was induced by IGFs, but that phosphorylation was blocked by IGFBP-5 and IGFBP-3. This study provides evidence that IGFBP-5 plays an important role in the regulation of apoptosis in the mammary gland.

Influence of microenvironment on mammary epithelial cell survival in primary culture

Mammary epithelial cells cultured on Engelbreth-Holm-Swarm (EHS) matrix form multicellular structures termed mammospheres, in which cells and matrix become arranged around a central luminal space. In the presence of lactogenic hormones, cells within mammospheres become polarized, form tight intercellular junctions, and secrete milk proteins vectorially into the luminal space. This study examined the mechanism of lumen formation. Histological examination of developing mammospheres showed that cavitation was associated spatially and temporally with the appearance of fragmented nuclear material in apoptotic bodies, and with the presence of cells positively labeled by terminal deoxynucleotide transferase-mediated deoxyuridine nick end-labeling (TUNEL). Analysis of [(32)P]-deoxynucleotide end-labeled genomic DNA by electrophoresis and autoradiography showed DNA laddering indicative of apoptosis. A transient increase in laddering coincided with both lumen formation and the presence of TUNEL-positive cells. Lumen formation, DNA laddering, and detection of TUNEL-positive cells were all accelerated when matrix composition was altered. They were also impaired coordinately when caspase inhibitor was present during the first two days of culture. Therefore, lumen formation in mammosphere cultures is due to selective apoptosis of centrally located cells. Mammosphere cavitation was accompanied by redistribution of matrix constituents to the mammosphere periphery. Western blotting and Western ligand blotting of culture medium showed that lumen formation was also associated with a transient increase in insulin-like growth factor binding protein-5 (IGFBP5), a factor implicated in mammary apoptosis in vivo. We propose that epithelial cell survival during mammosphere development is induced selectively through stabilization by basement membrane constituents, which may act directly on the epithelial cell or confer protection against autocrine apoptotic factors.

Effects of growth hormone and prolactin on adipose tissue development and function

GH and PRL are both implicated in adipose tissue development. Whilst direct effects of GH have been clearly demonstrated, direct effects of PRL have been subject to considerable debate. Recent studies have however provided compelling evidence for PRL receptors on adipocytes and in vitro effects on leptin and lipoprotein lipase activity have been demonstrated. Quantitatively however these effects of PRL are less significant than those of GH and the most pronounced effects of PRL on adipose tissue are indirect, for example, during lactation, when prolactin drives milk synthesis which results in a homeorhetic shift towards lipid mobilization from adipose tissue to support milk production. GH also exhibits such homeorhetic effects, most notably in ruminants, but also clearly has direct, insulin-antagonistic, metabolic effects. The roles of GH and PRL on adipocyte proliferation and differentiation have also been controversial, with GH stimulating adipocyte differentiation in vitro in cell lines whilst stimulating proliferation and inhibiting differentiation of primary cell cultures. Examination of adipose tissue development in PRLRko and GHRko mice has revealed roles for both hormones. PRLRko mice show impaired development of both internal and subcutaneous adipose tissue due to decreased numbers of adipocytes. In contrast, GHRko mice exhibit major decreases in the number of internal (parametrial) adipocytes whereas subcutaneous adipocytes develop almost normally. This leads to major changes in the sites of adipose tissue accretion and bears interesting parallels with the adipose tissue redistribution which occurs in HIV-induced lipodystrophy. Such individuals exhibit a central obesity which can be partially corrected by GH treatment. However, recent studies suggest that this may be a physiological response in which adipose tissue sites containing lymphoid tissue (such as mesenteric) show preservation of adipose tissue perhaps to support augmented immune responses.

Evidence that growth hormone stimulates milk synthesis by direct action on the mammary gland and that prolactin exerts effects on milk secretion by maintenance of mammary deoxyribonucleic acid content and tight junction status

Both PRL and GH play a role in maintaining lactation in the rat, although GH can only maintain pup weight gain at around 50% of the control value, whereas PRL can maintain weight gain close to 90% in the absence of GH. In this study we examined the effects of PRL and GH deficiency (using bromocriptine and an antiserum to rat GH) on milk yield and composition in lactating rats. Treatment with bromocriptine to suppress PRL secretion for 48 h led to a 57% decrease in milk yield with a concomitant decrease in milk protein and lactose yields, but no decrease in fat output. This led to the production of milk with a lower lactose concentration but increased concentrations of protein and particularly fat (increased 100%), which suggests that GH serves an auxiliary role by maintaining an energy-rich milk for the neonate when PRL secretion is reduced. This decrease in milk synthesis was accompanied by decreases in total mammary DNA content and increased milk sodium concentrations. The latter indicates the opening of tight junctions between mammary epithelial cells, which normally occurs during dedifferentiation and involution of the mammary gland. This suggests that PRL maintains milk synthesis at least in part by inhibiting epithelial cell loss and maintaining cellular differentiation. A deficiency in GH, by contrast, caused only a small decrease (24%) in milk yield and had no effect on the major constituents of milk or on milk sodium concentrations or total mammary DNA content. When animals were made deficient in both PRL and GH, however, there was a further marked decrease (88%) in milk volume along with the yields of all major milk constituents, confirming our previous findings that PRL and GH are the major regulators of milk synthesis. Recent studies have indicated that GH exerts direct effects on mammary gland growth, but its actions on milk secretion have been proposed to be mediated indirectly via insulin-like growth factor-I (IGF-I). We, therefore, inhibited lactation by inducing PRL and GH deficiency for 48 h and then attempted to reinitiate it by administering GH either systemically or by local oil-based implants into the mammary gland. Oil-based GH implants were as effective in stimulating milk secretion in the treated (but not contralateral, control) gland as was systemic GH treatment. Thus, GH does act directly on the mammary gland to stimulate milk synthesis, although this does not rule out the possibility that GH acts by stimulating local production of IGF-I.(ABSTRACT TRUNCATED AT 400 WORDS)

Insulin-like growth factor binding proteins: IGF-dependent and -independent effects in the mammary gland

The insulin-like growth factor binding proteins (IGFBPs) are a family of proteins which bind to the IGFs with high affinity. Their expression within the mammary gland is species specific; it has thus been difficult to determine the biological roles of these binding proteins during lactation. In this article we propose a role for IGFBP-5 in the mammary gland involving the initiation of apoptosis induced by sequestration of IGF-1, an important survival factor for the mammary gland. We have shown that this binding protein retains its high affinity for IGF-1 and that it is present in extremely high concentrations compared with the growth factor. These observations make it likely that IGFBP-5 is capable of preventing interaction of IGF-1 with its receptor on the epithelial cells synthesizing milk. We have also demonstrated that IGFBP-5 interacts with alpha(s2)-casein and that this interaction implicates it in the regulation of plasminogen activation in the mammary gland. The generation of plasmin is a key initiating event in the remodeling of the extracellular matrix during mammary involution. As such, IGFBP-5 may play a key role in coordinating cell death and tissue remodeling processes. Many of the molecules involved in embryological development are also expressed in the developing and involuting mammary gland. We believe that our studies may offer mechanistic explanations for apoptotic events in a wide variety of tissues. We have recently shown that IGFBP-5 is apoptotic in the chick embryonic limb bud, adding further support to our belief that IGFBP-5 serves this function in the mammary gland. We hope to be able to explore the role of this binding protein in the mammary gland with a transgenic mouse model expressing IGFBP-5 on the beta-lactoglobulin promoter.

Control of fatty acid synthesis in lactation

Lactation results not only in an increased rate of fatty acid synthesis in the mammary gland but also in a decreased rate of fatty acid synthesis in adipose tissue and, in the rat at least, an increased rate of hepatic fatty acid synthesis. Progesterone (during pregnancy), prolactin and (in ruminants) GH are implicated in the regulation of the reciprocal changes in fatty acid synthesis in mammary gland and adipose tissue. Progesterone and prolactin, at least, appear to influence the rate of fatty acid synthesis by modulating the insulin-binding capacities of the tissues, but it is clear that steps in the mechanism of action of insulin subsequent to its binding to the receptor are also changed in adipose tissue during lactation.