In vitro and in vivo biologic evaluation of long-circulating biodegradable drug carriers loaded with the pure antiestrogen RU 58668

The potential application of complement inhibitors-loaded nanosystem for autoimmune diseases via regulation immune balance

The complement is an important arm of the innate immune system, once activated, the complement system rapidly generates large quantities of protein fragments that are potent mediators of inflammation. Recent studies have shown that over-activated complement is the main proinflammatory system of autoimmune diseases (ADs). In addition, activated complements interact with autoantibodies, immune cells exacerbate inflammation, further worsening ADs. With the increasing threat of ADs to human health, complement-based immunotherapy has attracted wide attention. Nevertheless, efficient and targeted delivery of complement inhibitors remains a significant challenge owing to their inherent poor targeting, degradability, and low bioavailability. Nanosystems offer innovative solutions to surmount these obstacles and amplify the potency of complement inhibitors. This prime aim to present the current knowledge of complement in ADs, analyse the function of complement in the pathogenesis and treatment of ADs, we underscore the current situation of nanosystems assisting complement inhibitors in the treatment of ADs. Considering technological, physiological, and clinical validation challenges, we critically appraise the challenges for successfully translating the findings of preclinical studies of these nanosystem assisted-complement inhibitors into the clinic, and future perspectives were also summarised. (The graphical abstract is by BioRender.).

PEGylated and functionalized polylactide-based nanocapsules: An overview

Polymeric nanocapsules (NC) are versatile mixed vesicular nanocarriers, generally containing a lipid core with a polymeric wall. They have been first developed over four decades ago with outstanding applicability in the cosmetic and pharmaceutical fields. Biodegradable polyesters are frequently used in nanocapsule preparation and among them, polylactic acid (PLA) derivatives and copolymers, such as PLGA and amphiphilic block copolymers, are widely used and considered safe for different administration routes. PLA functionalization strategies have been developed to obtain more versatile polymers and to allow the conjugation with bioactive ligands for cell-targeted NC. This review intends to provide steps in the evolution of NC since its first report and the recent literature on PLA-based NC applications. PLA-based polymer synthesis and surface modifications are included, as well as the use of NC as a novel tool for combined treatment, diagnostics, and imaging in one delivery system. Furthermore, the use of NC to carry therapeutic and/or imaging agents for different diseases, mainly cancer, inflammation, and infections is presented and reviewed. Constraints that impair translation to the clinic are discussed to provide safe and reproducible PLA-based nanocapsules on the market. We reviewed the entire period in the literature where the term "nanocapsules" appears for the first time until the present day, selecting original scientific publications and the most relevant patent literature related to PLA-based NC. We presented to readers a historical overview of these Sui generis nanostructures.

Targeting steroid hormone receptors for anti-cancer therapy-A review on small molecules and nanotherapeutic approaches

The steroid hormone receptors (SHRs) among nuclear hormone receptors (NHRs) are steroid ligand-dependent transcription factors that play important roles in the regulation of transcription of genes promoted via hormone responsive elements in our genome. Aberrant expression patterns and context-specific regulation of these receptors in cancer, have been routinely reported by multiple research groups. These gave an window of opportunity to target those receptors in the context of developing novel, targeted anticancer therapeutics. Besides the development of a plethora of SHR-targeting synthetic ligands and the availability of their natural, hormonal ligands, development of many SHR-targeted, anticancer nano-delivery systems and theranostics, especially based on small molecules, have been reported. It is intriguing to realize that these cytoplasmic receptors have become a hot target for cancer selective delivery. This is in spite of the fact that these receptors do not fall in the category of conventional, targetable cell surface bound or transmembrane receptors that enjoy over-expression status. Glucocorticoid receptor (GR) is one such exciting SHR that in spite of it being expressed ubiquitously in all cells, we discovered it to behave differently in cancer cells, thus making it a truly druggable target for treating cancer. This review selectively accumulates the knowledge generated in the field of SHR-targeting as a major focus for cancer treatment with various anticancer small molecules and nanotherapeutics on progesterone receptor, mineralocorticoid receptor, and androgen receptor while selectively emphasizing on GR and estrogen receptor. This review also briefly highlights lipid-modification strategy to convert ligands into SHR-targeted cancer nanotherapeutics. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Biology-Inspired Nanomaterials > Lipid-Based Structures Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Selective Estrogen Receptor Degraders (SERDs): A Promising Strategy for Estrogen Receptor Positive Endocrine-Resistant Breast Cancer

Estrogen receptor (ER) plays important roles in gene transcription and the proliferation of ER positive breast cancers. Selective modulation of ER has been a therapeutic target for this specific type of breast cancer for more than 30 years. Selective estrogen receptor modulators (SERMs) and aromatase inhibitors (AIs) have been demonstrated to be effective therapeutic approaches for ER positive breast cancers. Unfortunately, 30-50% of ER positive tumors become resistant to SERM/AI treatment after 3-5 years. Fulvestrant, the only approved selective estrogen receptor degrader (SERD), is currently an important therapeutic approach for the treatment of endocrine-resistant breast cancers. The poor pharmacokinetic properties of fulvestrant have inspired the development of a new generation of oral SERDs to overcome drug resistance. In this review, we describe recent advances in ERα structure, functions, and mechanisms of endocrine resistance and summarize the development of oral SERDs in both academic and industrial areas.

Design and evaluation of glomerulus mesangium-targeted PEG-PLGA nanoparticles loaded with dexamethasone acetate

Mesangial proliferative glomerulonephritis (MsPGN), one of the most common glomerulonephritis pathological types, often leads to end-stage renal disease over a prolonged period. But the current treatment of MsPGN is non-specific and causes serious side effects, thus novel therapeutics and targeting strategies are urgently demanded. By combining the advantages of PEG-PLGA nanoparticles and the size selection mechanism of renal glomerulus, we designed and developed a novel PEG-PLGA nanoparticle delivery system capable of delivering dexamethasone acetate (A-DEX) into glomerular mesangium. We determined that 90 nm was the optimum size to encapsulate A-DEX for glomerular mesangium targeting based on the size-selection mechanism of glomerulus. After intravenous administration in rats, 90 nm DiD-loaded NPs were found to accumulate to a greater extent in the kidney and kidney cortex compared with the free DiD solution. The 90 nm A-DEX NPs are also more stable at room temperature and showed a sustained release pattern. In rat glomerular mesangial cells (HBZY-1) in vitro, we found that the uptake of 90 nm A-DEX NPs was both temperature-dependent and energe-dependent, and they were mostly engulfed via clathrin-dependent endocytosis pathways. In summary, we have successfully developed a glomerular mesangium-targeted PEG-PLGA NPs, which is potential for the treatment of MsPGN.

Comprehensive study of the drug delivery properties of poly(l-lactide)-poly(ethylene glycol) nanoparticles in rats and tumor-bearing mice

Nanoparticles made of polylactide-poly(ethylene glycol) block-copolymer (PLA-PEG) are promising vehicles for drug delivery due to their biodegradability and controllable payload release. However, published data on the drug delivery properties of PLA-PEG nanoparticles are heterogeneous in terms of nanoparticle characteristics and mostly refer to low injected doses (a few mg nanoparticles per kg body weight). We have performed a comprehensive study of the biodistribution of nanoparticle formulations based on PLA-PEG nanoparticles of ~100nm size at injected doses of 30 to 140mg/kg body weight in healthy rats and nude tumor-bearing mice. Nanoparticle formulations differed by surface PEG coverage and by release kinetics of the encapsulated model active pharmaceutical ingredient (API). Increase in PEG coverage prolonged nanoparticle circulation half-life up to ~20h in rats and ~10h in mice and decreased retention in liver, spleen and lungs. Circulation half-life of the encapsulated API grew monotonously as the release rate slowed down. Plasma and tissue pharmacokinetics was dose-linear for inactive nanoparticles, but markedly dose-dependent for the model therapeutic formulation, presumably because of the toxic effects of released API. A mathematical model of API distribution calibrated on the data for inactive nanoparticles and conventional API form correctly predicted the distribution of the model therapeutic formulation at the lowest investigated dose, but for higher doses the toxic action of the released API had to be explicitly modelled. Our results provide a coherent illustration of the ability of controllable-release PLA-PEG nanoparticles to serve as an effective drug delivery platform to alter API biodistribution. They also underscore the importance of physiological effects of released drug in determining the biodistribution of therapeutic drug formulations at doses approaching tolerability limits.

Periodic organosilica hollow nanospheres as anode materials for lithium ion rechargeable batteries

Polymeric micelles with core-shell-corona architecture have been found to be the efficient colloidal templates for synthesis of periodic organosilica hollow nanospheres over a broad pH range from acidic to alkaline media. In alkaline medium, poly (styrene-b-[3-(methacryloylamino)propyl] trimethylammonium chloride-b-ethylene oxide) (PS-PMAPTAC-PEO) micelles yield benzene-silica hollow nanospheres with molecular scale periodicity of benzene groups in the shell domain of hollow particles. Whereas, an acidic medium (pH 4) produces diverse hollow particles with benzene, ethylene, and a mixture of ethylene and dipropyldisulfide bridging functionalities using poly(styrene-b-2-vinyl pyridine-b-ethylene oxide) (PS-PVP-PEO) micelles. These hollow particles were thoroughly characterized by powder X-ray diffraction (XRD), dynamic light scattering (DLS), thermogravimetric analysis (TG/DTA), Fourier transformation infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), magic angle spinning-nuclear magnetic resonance ((29)Si MAS NMR and (13)CP-MAS NMR), Raman spectroscopy, and nitrogen adsorption/desorption analyses. The benzene-silica hollow nanospheres with molecular scale periodicity in the shell domain exhibit higher cycling performance of up to 300 cycles in lithium ion rechargeable batteries compared with micron-sized dense benzene-silica particles.

Brassinosteroids cause cell cycle arrest and apoptosis of human breast cancer cells

Brassinosteroids (BRs) are plant hormones that appear to be ubiquitous in both lower and higher plants. Recently, we published the first evidence that some natural BRs induce cell growth inhibitory responses in several human cancer cell lines without affecting normal non-tumor cell growth (BJ fibroblasts). The aim of the study presented here was to examine the mechanism of the antiproliferative activity of the natural BRs 28-homocastasterone (28-homoCS) and 24-epibrassinolide (24-epiBL) in human hormone-sensitive and -insensitive (MCF-7 and MDA-MB-468, respectively) breast cancer cell lines. The effects of 6, 12 and 24h treatments with 28-homoCS and 24-epiBL on cancer cells were surveyed using flow cytometry, Western blotting, TUNEL assays and immunofluorescence analyses. The studied BRs inhibited cell growth and induced blocks in the G(1) cell cycle phase. ER-α immunoreactivity was uniformly present in the nuclei of control MCF-7 cells, while cytoplasmic speckles of ER-α immunofluorescence appeared in BR-treated cells (IC(50), 24h). ER-β was relocated to the nuclei following 28-homoCS treatment and found predominantly at the periphery of the nuclei in 24-epiBL-treated cells after 24h of treatment. These changes were also accompanied by down-regulation of the ERs following BR treatment. In addition, BR application to breast cancer cells resulted in G(1) phase arrest. Furthermore, TUNEL staining and double staining with propidium iodide and acridine orange demonstrated the BR-mediated induction of apoptosis in both cell lines, although changes in the expression of apoptosis-related proteins were modulated differently by the BRs in each cell line. The studied BRs seem to exert potent growth inhibitory effects via interactions with the cell cycle machinery, and they could be highly valuable leads for agents for managing breast cancer.

Use of templates to fabricate nanoscale spherical structures for defined architectural control

Architectural design of biomaterial structures is essential to reach the full potential of the materials' chemical and biological properties. Clinically, these properties depend on the targeted applications of delivery, such as tissue regeneration, imaging, or cancer. To get an efficient material for biological applications, key properties are needed, such as degradability, low toxicity, cell specificity, relative efficiency, and capability of delivering multiple molecules. In recent years, significant progress has been made through either the design of the material itself (synthetic or natural polymers, dendrimers, crosslinking) or the fabrication technique (nozzle reactor, emulsion, and template). The combination of these materials and techniques results in a large variety of biomaterials that have varied shape and physico-chemical and biological properties. Nevertheless, these inherent properties are not sufficient and interest in discovering and developing new techniques that present these biomaterials in different light is now under focus. A useful strategy to prepare biomaterials with unique and novel architectures is through the use of templates that have defined geometrical features. This holds great promise, especially for the development of hollow structures, such as spheres. The nanoscale structural design of biomaterials via the use of templates and their potential clinical applications are discussed. In addition, the conceptual hurdles that must be overcome to produce applications that are clinically relevant are examined.

Stealth and non-stealth nanocapsules containing camptothecin: in-vitro and in-vivo activity on B16-F10 melanoma

Camptothecin (CPT) is an alkaloid that displays considerable antitumour activity, but clinical use has been limited by its poor water solubility and the instability of the lactone moiety (active form) in physiological media. We have therefore formulated the drug into nanocarrier systems in an attempt to improve its therapeutic properties. This study evaluates the effect of intraperitoneally administered stealth and non-stealth nanocapsules containing CPT on lung metastatic spread in mice inoculated with B16-F10 melanoma cells, and on the cytotoxic activity against B16-F10 melanoma cells in-vitro. Poly (d,l-lactide) PLA (non-stealth) and methoxy polyethylene glycol-(d,l-lactide) (PLA-PEG) (stealth) nanocapsules (49 and 66.6 kDa) were prepared by interfacial deposition of preformed polymer. CPT, as free drug or as drug-loaded nanocapsules, was administrated at a dose of 0.5 mg kg−1 at 3-day intervals for 17 days. Free drug and CPT-loaded nanocapsules reduced the number of metastatic nodules by 45.09–91.76% (P < 0.05 vs positive control). However, only CPT-loaded PLA-PEG 49 kD nanocapsules significantly decreased the number of lung metastases when compared with free drug (P < 0.05). The administration of CPT-loaded nanocapsules and free drug did not result in neutropenia at the administered dose. The improved effectiveness of pegylated nanocapsules was attributed to protection of the drug by nanoencapsulation and to reduced uptake of particles by macrophages located in the lymph nodes. This assumption was supported by the in-vitro study, in which both PLA and 49 kDa PLA-PEG nanocapsules containing CPT were more cytotoxic than the free drug against B16-F10 melanoma cells.

Targeted delivery with peptidomimetic conjugated self-assembled nanoparticles

Peptides produce specific nanostructures, making them useful for targeting in biological systems but they have low bioavailability, potential immunogenicity and poor metabolic stability. Peptidomimetic self-assembled NPs can possess biological recognition motifs as well as providing desired engineering properties. Inorganic NPs, coated with self-assembled macromers for stability and anti-fouling, and conjugated with target-specific ligands, are advancing imaging from the anatomy-based level to the molecular level. Ligand conjugated NPs are attractive for cell-selective tumor drug delivery, since this process has high transport capacity as well as ligand dependent cell specificity. Peptidomimetic NPs can provide stronger interaction with surface receptors on tumor cells, resulting in higher uptake and reduced drug resistance. Self-assembled NPs conjugated with peptidomimetic antigens are ideal for sustained presentation of vaccine antigens to dendritic cells and subsequent activation of T cell mediated adaptive immune response. Self-assembled NPs are a viable alternative to encapsulation for sustained delivery of proteins in tissue engineering. Cell penetrating peptides conjugated to NPs are used as intracellular delivery vectors for gene expression and as transfection agents for plasmid delivery. In this work, synthesis, characterization, properties, immunogenicity, and medical applications of peptidomimetic NPs in imaging, tumor delivery, vaccination, tissue engineering, and intracellular delivery are reviewed.

Nanoparticles loaded with ferrocenyl tamoxifen derivatives for breast cancer treatment

For the first time, two organometallic triphenylethylene compounds (Fc-diOH and DFO), with strong antiproliferative activity in breast cancer cells, but insoluble in biological fluids, were incorporated in two types of stealth nanoparticles (NP): PEG/PLA nanospheres (NS) and nanocapsules (NC). Their physicochemical parameters were measured (size, zeta potential, encapsulation and loading efficiency), and their biological activity was assessed. In vitro drug release after high dilution of loaded NPs was measured by estradiol binding competition in MELN cells. The influence of the encapsulated drugs on the cell cycle and apoptosis was studied by flow cytometry analyses. Notwithstanding potential drug adsorption at the NP surface, Fc-diOH and DFO were incorporated efficiently in NC and NS, which slowly released both compounds. They arrested the cell cycle in the S-phase and induced apoptosis, whose activity is increased by loaded NS. A decrease in their antiproliferative activity by the antioxidant alpha-tocopherol indicated that reactive oxygen species (ROS) may be involved. Therefore, nanosystems, containing for the first time a high load of anticancer organometallic triphenylethylenes, have been developed. Their small size and delayed drug release, combined with their enhanced apoptotic potential, are compatible with an increased persistence in the blood and a promising antitumour activity.

Improved anti-tumoral capacity of mixed and pure anti-oestrogens in breast cancer cell xenografts after their administration by entrapment in colloidal nanosystems

Anti-oestrogens (AEs) are currently used for treating hormone-dependent breast cancers. They specifically bind to oestrogen receptors (ERs) and inhibit their transactivation capacity. However, ERs are present in various other tissues in which AEs may have either a beneficial or detrimental action. AE administration via systems targeting breast tumours may be an important therapeutic improvement. Thus, several biodegradable drug delivery systems containing either "mixed" (4-hydroxytamoxifen - 4-HT) or "pure" (RU 58668 - RU) AEs were prepared. Liposomes and nanospheres (NS, composed of non-toxic and biodegradable lipids and poly(d,l-lactic acid) incorporated up to 1 and 0.5 mM AE, respectively. Nanocapsules (NCs) in which an oily core solubilises the AE incorporated no more than 0.02 mM of the drug. PEG-functionalised nanoparticles survived longer in plasma and had better controlled release of the drug. The small size of the vectors (100-250 nm) was compatible with their extravasation through the discontinuous endothelium of tumour vasculature, allowing their accumulation in MCF-7 cell xenografts and leading to a prolonged exposure of the tumour to AEs. In these tumours and in MCF-7/ras xenografts, RU-NS and RU-NC (6.5mg/kg/week and 0.27 mg/kg/week, respectively, doses at which free RU had a very weak effect), both inhibited tumour growth. Entrapped RU significantly induced involution of tumours and strongly induced apoptosis in tumour cells, concomitantly with inhibiting tumour angiogenesis. 4-HT-nanoparticles also arrest oestradiol-induced tumour growth, inducing apoptosis and inhibiting angiogenesis. However, unlike RU-nanoparticles, they did not promote ERalpha subtype loss in tumour cells. Subcutaneous administration of both RU- and 4-HT-NS in MCF-7 xenografts strongly arrested tumour growth for prolonged periods and RUNS decreased the number of tumour epithelial cells. Analysis of the proteins involved in cell cycle proliferation and apoptosis confirmed that RU-nanoparticles were more efficient than 4-HT-nanoparticles. Their lack of toxicity and high anti-tumour potency that affects only tumour cells in the xenograft models mean these AE-loaded colloidal systems are a breakthrough in hormone-dependent breast cancer treatment.

Improved antitumoral properties of pure antiestrogen RU 58668-loaded liposomes in multiple myeloma

In most of multiple myeloma (MM) cells, the "pure" antiestrogen (AE) RU 58668 (RU) induced either a G1-arrest (LP-1, OPM-2, NCI-H929, U266 cells) or apoptosis (RPMI 8226 cells). In RPMI 8226 cells, RU activates a caspase-dependent cell death pathway leading to the release of cytochrome c, the decrease of the essential MM survival factor Mcl-1, the cleavage of Bid and the activation of caspases-3 and -8. Incorporation of RU in pegylated cholesterol-containing liposomes allowed a controlled RU release, improving its anti-proliferative and apoptotic effects in cells. In RPMI 8226 xenografts, i.v. injected RU-liposomes but not free RU, exhibited antitumor activity. In vivo, RU-liposomes triggered the mitochondrial death pathway, concomitantly with a down-regulation of Mcl-1 and Bid cleavage. The decrease of CD34 immunoreactivity indicated a reduction of angiogenesis. The decrease of VEGF secretion in vitro supported a direct effect of RU on angiogenesis. These pro-apoptotic and antiangiogenic effects were explained by a prolonged exposure to the drug and to the endocytosis capacity of liposomes which might increase RU uptake and bypass a membrane export of free RU. Thus, these combined enhanced activities of RU-liposomes support that such a delivery of an AE may constitute a strategy of benefit for MM treatment.

Synthesis and Magnetic Properties of Biocompatible Hybrid Hollow Spheres

Magnetic hybrid hollow spheres of about 200 nm were prepared by a core-template-free route, that is, adding Fe3O4 nanoparticles stabilized by poly(vinyl alcohol) (PVA) to an aqueous solution of polymer-monomer pairs composed of a cationic polymer, chitosan (CS), and an anionic monomer, acrylic acid (AA), followed by polymerization of acrylic acid and selective cross-linking of chitosan at the end of polymerization. The obtained hybrid spheres were characterized by dynamic light scattering (DLS) in aqueous solution and observed by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM) in the solid state. Fourier transform infrared spectroscopy (FTIR) and X-ray and electron diffractions revealed that the Fe3O4 nanoparticles were incorporated into the shells of chitosan-poly(acrylic acid) (CS-AA) hollow spheres. Magnetization studies and Mössbauer spectroscopy suggested that the chains (or islands) of iron oxide nanoparticles were most likely formed in the walls of the hollow spheres. The phantom test of magnetic resonance imaging showed that the synthesized hybrid hollow spheres had a significant magnetic resonance signal enhancement in T2-weighted image.

Innovative drug delivery nanosystems improve the anti-tumor activity in vitro and in vivo of anti-estrogens in human breast cancer and multiple myeloma

Anticancer drug efficiency is governed by its bioavailability. In order to increase this parameter, we synthesized several injectable and biodegradable systems based on incorporation of anti-estrogens (AEs) in nanoparticles (NPs) and liposomes were synthesized. Both nanospheres (NS) and nanocapsules (NCs, polymers with an oily core in which AEs were solubilized) incorporated high amounts of 4-hydroxy-tamoxifen (4-HT) or RU 58668 (RU). Physico-chemical and biological parameters of these delivery systems, and coupling of polyethylene-glycol chains on the NP surface revealed to enhance the anti-tumoral activity of trapped AEs in a breast cancer MCF-7 cell xenograft model and to induce apoptosis. These features correlated with an augmentation of p21(Waf-1/Cip1) and of p27(Kip1) and a concomitant decrease of cyclin D1 and E in tumor extracts. Liposomes containing various ratios of lipids enhanced the apoptotic activity of RU in several multiple myeloma (MM) cell lines tested by flow cytometry. MM cell lines expressed both estrogen receptor alpha and beta subtypes except Karpas 620. Karpas 620 cells which did not respond to AEs became responsive following ER cDNA transfection. A new MM xenograft model was generated after s.c. injection of RPMI 8226 cells in nude mice. RU-loaded liposomes, administered i.v. in this model, at a dose of 12mgRU/kg/week, induced the arrest of tumor growth contrary to free RU or to empty liposomes. Thus, the drug delivery of anti-estrogens enhances their ability to arrest the growth of tumors which express estrogen receptors and are of particular interest for estrogen-dependent breast cancer treatment. In addition it represents a new potent therapeutic approach for multiple myeloma.

Pure antiestrogen RU 58668-loaded nanospheres: morphology, cell activity and toxicity studies

Nanospheres (NS) formulated using biodegradable and biocompatible polymers, poly(D,L-lactide-co-glycolide) (PLGA), poly(D,L-lactide) (PLA) and poly(epsilon-caprolactone) (PCL), loaded with the pure anti-estrogen RU 58668 (RU), a promising estrogen-dependent anticancer agent, have been prepared. They all possess a small size compatible with an intratumoral extravasation behavior and their pegylation reduce significantly their zeta potential. Characterization by freeze fracture electron microscopy have shown that NS are spheric particles with a size ranging between 30 and 50nm and a tendency to agglomerate which is reduced by polyethylene glycol (PEG) grafting. PEG-grafted NS are all non-toxic as revealed by cell viability assay. A specific cellular model has been used to evaluate not only the release extent of the drug but also its biological activity. All formulations tested showed that they release slowly RU as measured by the delayed ability of RU to inhibit estrogen-induced transcription in human breast cancer cells and that they possess only a small amount of surface adsorbed RU.

Drug delivery systems for oestrogenic hormones and antagonists: the need for selective targeting in estradiol-dependent cancers

The pleiotropic activity of oestrogens and their mechanism of action via their binding to the two oestrogen receptors alpha (ER alpha) and beta (ER beta) subtypes in the different tissues where oestrogens exert their action have been briefly described. The fate of these compounds trapped into different galenic forms is discussed with regard to their therapeutic applications. Firstly, the advantages and disadvantages of the different forms (pills, i.v. forms and transdermal patches) used in contraception are compared. Secondly, the therapeutic use of formulated oestrogens for the post-menopausal hormone replacement therapy (HRT) is analysed through the various results obtained in different trials. The link between HRT and the risks of breast cancer and cardiovascular disease is underlined. Finally, comparing the activity of selective oestrogen receptor modulators such as tamoxifen and pure anti-oestrogens such as RU58668 and ICI182780, we analysed the reasons leading to the need for a tumor targeting of the latters, but not of the former for the treatment of oestrogen-dependent breast cancer. Different injectable and biodegradable formulations, that lead to a remarkable anti-tumor efficiency in xenografts, have been recently developed and we believe that they may represent promising new administration ways of added therapeutic values for anti-oestrogens. Such devices could be extended to the delivery of other anti-cancer drugs with more aggressive activities than anti-oestrogens.

The use of selective estrogen receptor modulators and selective estrogen receptor down-regulators in breast cancer

Tamoxifen is one of the most effective treatments for breast cancer through its ability to antagonize estrogen-dependent growth by binding estrogen receptors (ERs) and inhibiting proliferation of breast epithelial cells. However, tamoxifen has estrogenic agonist effects in other tissues such as bone and endometrium due to liganded ER activating target genes in these different types of cell. Several novel anti-estrogen compounds have been developed which have a reduced agonist profile on breast and gynaecological tissues. These compounds offer the potential for enhanced efficacy and reduced toxicity compared with tamoxifen. In advanced breast cancer clinical data exist for two groups of agents: the selective estrogen receptor modulators (SERMs), further divided into "tamoxifen-like" (e.g. toremifene, droloxifene and idoxifene) and "fixed ring" compounds (e.g. raloxifene, arzoxifene and EM-800), and the selective estrogen receptor down-regulators (SERDs; e.g. fulvestrant (ICI 182780), SR 16234 and ZK 191703) also termed "pure anti-estrogens". In phase II trials in tamoxifen-resistant metastatic breast cancer the SERMs show low objective response rates (range 0-15%), suggesting cross resistance with tamoxifen. Randomized phase III trials for toremifene and idoxifene in over 1500 patients showed no significant difference compared with tamoxifen. Fewer clinical data exist for the "fixed ring" SERMs and it remains unclear whether any clinical advantage exists for the "fixed ring" SERMs over tamoxifen as first-line therapy. The main advantage for SERMs such as tamoxifen and raloxifene probably remains in early-stage disease (adjuvant therapy or prevention). Fulvestrant and the other SERDs have a high affinity for the estrogen receptor (ER) compared to tamoxifen, but none of its agonist activities. Of the SERDs, only fulvestrant has entered the clinic and this new agent is showing promising clinical activity in the treatment of advanced breast cancer. Recently published phase III studies have shown fulvestrant to be at least as effective as the third-generation aromatase inhibitor anastrozole in patients whose disease has relapsed or progressed on prior endocrine therapy. Surprisingly, however, in a phase III trial versus tamoxifen for the first-line therapy of advanced breast cancer fulvestrant did not attain the requirements for equivalence to tamoxifen, and in terms of time-to-treatment failure was inferior (5.9 versus 7.8 months for fulvestrant and tamoxifen, respectively; P=0.029). Future clinical studies will evaluate fulvestrant in the neoadjuvant setting together with its optimal sequencing in relation to tamoxifen and other endocrine therapies in advanced disease.