Water-soluble HPMA copolymer-wortmannin conjugate retains phosphoinositide 3-kinase inhibitory activity in vitro and in vivo

Preparation and characterization of (-)-Epigallocatechin-3-gallate (EGCG)-loaded nanoparticles and their inhibitory effects on Human breast cancer MCF-7 cells

We were employing nanotechnology to improve the targeting ability of (−)-Epigallocatechin-3-gallate (EGCG) towards MCF-7 cells, and two kinds of EGCG nanoparticles (FA-NPS-PEG and FA-PEG-NPS) were obtained, besides, their characteristics and effects on MCF-7 cells were studied. The results indicated that (i) both FA-NPS-PEG and FA-PEG-NPS have high stabilities; (ii) their particles sizes were 185.0 ± 13.5 nm and 142.7 ± 7.2 nm, respectively; (iii) their encapsulation efficiencies of EGCG were 90.36 ± 2.20% and 39.79 ± 7.54%, respectively. (iv) there was no cytotoxicity observed in EGCG, FA-NPS-PEG and FA-PEG-NPS toward MCF-7 cells over all concentrations (0~400 μg/mL) tested; (v) EGCG, FA-NPS-PEG and FA-PEG-NPS inhibited MCF-7 cells proliferation in dose-dependent manners, with the average IC₅₀ of 470.5 ± 33.0, 65.9 ± 0.4 and 66.6 ± 0.6 μg/mL; (vi) EGCG, FA-NPS-PEG and FA-PEG-NPS could modulated the expressions of several key regulatory proteins in PI3K-Akt pathway such as up-regulation of PTEN, p21 and Bax, and down-regulation of p-PDK1, p-AKT, CyclinD1 and Bcl-2, which gave an illustration about the mechanism by which EGCG nanoparticles inhibited MCF-7 cells proliferation. In this study, EGCG nanoparticles can significantly enhance the targeting ability and efficacy of EGCG, which is considered to an experimental foundation for further research on its activity, targeting ability and metabolism in vivo.

Advanced targeted therapies in cancer: Drug nanocarriers, the future of chemotherapy

Cancer is the second worldwide cause of death, exceeded only by cardiovascular diseases. It is characterized by uncontrolled cell proliferation and an absence of cell death that, except for hematological cancers, generates an abnormal cell mass or tumor. This primary tumor grows thanks to new vascularization and, in time, acquires metastatic potential and spreads to other body sites, which causes metastasis and finally death. Cancer is caused by damage or mutations in the genetic material of the cells due to environmental or inherited factors. While surgery and radiotherapy are the primary treatment used for local and non-metastatic cancers, anti-cancer drugs (chemotherapy, hormone and biological therapies) are the choice currently used in metastatic cancers. Chemotherapy is based on the inhibition of the division of rapidly growing cells, which is a characteristic of the cancerous cells, but unfortunately, it also affects normal cells with fast proliferation rates, such as the hair follicles, bone marrow and gastrointestinal tract cells, generating the characteristic side effects of chemotherapy. The indiscriminate destruction of normal cells, the toxicity of conventional chemotherapeutic drugs, as well as the development of multidrug resistance, support the need to find new effective targeted treatments based on the changes in the molecular biology of the tumor cells. These novel targeted therapies, of increasing interest as evidenced by FDA-approved targeted cancer drugs in recent years, block biologic transduction pathways and/or specific cancer proteins to induce the death of cancer cells by means of apoptosis and stimulation of the immune system, or specifically deliver chemotherapeutic agents to cancer cells, minimizing the undesirable side effects. Although targeted therapies can be achieved directly by altering specific cell signaling by means of monoclonal antibodies or small molecules inhibitors, this review focuses on indirect targeted approaches that mainly deliver chemotherapeutic agents to molecular targets overexpressed on the surface of tumor cells. In particular, we offer a detailed description of different cytotoxic drug carriers, such as liposomes, carbon nanotubes, dendrimers, polymeric micelles, polymeric conjugates and polymeric nanoparticles, in passive and active targeted cancer therapy, by enhancing the permeability and retention or by the functionalization of the surface of the carriers, respectively, emphasizing those that have received FDA approval or are part of the most important clinical studies up to date. These drug carriers not only transport the chemotherapeutic agents to tumors, avoiding normal tissues and reducing toxicity in the rest of the body, but also protect cytotoxic drugs from degradation, increase the half-life, payload and solubility of cytotoxic agents and reduce renal clearance. Despite the many advantages of all the anticancer drug carriers analyzed, only a few of them have reached the FDA approval, in particular, two polymer-protein conjugates, five liposomal formulations and one polymeric nanoparticle are available in the market, in contrast to the sixteen FDA approval of monoclonal antibodies. However, there are numerous clinical trials in progress of polymer-protein and polymer-drug conjugates, liposomal formulations, including immunoliposomes, polymeric micelles and polymeric nanoparticles. Regarding carbon nanotubes or dendrimers, there are no FDA approvals or clinical trials in process up to date due to their unresolved toxicity. Moreover, we analyze in detail the more promising and advanced preclinical studies of the particular case of polymeric nanoparticles as carriers of different cytotoxic agents to active and passive tumor targeting published in the last 5 years, since they have a huge potential in cancer therapy, being one of the most widely studied nano-platforms in this field in the last years. The interest that these formulations have recently achieved is stressed by the fact that 90% of the papers based on cancer therapeutics with polymeric nanoparticles have been published in the last 6 years (PubMed search).

[Effects of PI3K/AKT inhibitor wortmannin on proliferation and apoptosis of primary porcine preadipocytes]

The purpose of this study was to determine the proper concentration of wortmannin that effectively inhibits PI3K/AKT but does not affect the proliferation and apoptosis of primary porcine preadipocytes. Firstly, primary porcine preadipocytes were isolated and their abilities to be induced to differentiation into mature adipocytes were evaluated. The preadipocytes were then treated with different concentrations of wortmannin, and the proliferation of the cells was detected with methanethiosulfonate (MTS). Annexin V- FITC/PI double-staining was used to detect the level of cell apoptosis. The apoptosis-related gene expressions were also quantified by qRT-PCR. At the same time, single cell electrophoresis was used to examine the extent of cellular DNA damage. Our data demonstrated that the primary porcine preadipocytes could differ-entiate into mature adipocytes. Up to 200 nmol/L of wortmannin had no effect on the proliferation ability of primary porcine preadipocytes (P>0.05). Results from the flow cytometry Annexin V- FITC/PI double-staining showed that 200 nmol/L wortmannin significantly induced apoptosis of the primary porcine preadipocytes (P<0.05). QRT-PCR results also showed that the expressions of caspase8, TNFR1, GZMB, and Bcl-x1 were significantly upregulated, while the expression of GZMA and cFLIP were not significantly affected when treated with 200 nmol/L wortmannin. In addition, results from the single cell gel electrophoresis indicated that 100 nmol/L wortmannin did not induce DNA damage. In conclusion, our results col-lectively showed that 100 nmol/L wortmanin can be used to study the role of PI3k pathway on the preadipocytes differen-tion without affecting the cell proliferation and apoptosis.

Polymer–drug conjugates for novel molecular targets

Polymer therapeutics can be already considered as a promising field in the human healthcare context. The discovery of the enhanced permeability and retention effect by Maeda, together with the modular model for the polymer–drug conjugate proposed by Ringsdorf, directed the early steps of polymer therapeutics towards cancer therapy. Orthodox anticancer drugs were preferentially chosen in the development of the first conjugates. The fast evolution of polymer chemistry and bioconjugation techniques, and a deeper understanding of cell biology has opened up exciting new challenges and opportunities. Four main directions have to be considered to develop this ‘platform technology’ further: the control of the synthetic process, the exhaustive characterization of the conjugate architectures, the conquest of combination therapy and the disclosure of new therapeutic targets. We illustrate in this article the exciting approaches offered by polymer–drug conjugates beyond classical cancer therapy, focusing on new, more effective and selective targets in cancer and in their use as treatments for other major human diseases.

Development of HPMA copolymer-anticancer conjugates: clinical experience and lessons learnt

The concept of polymer-drug conjugates was proposed more than 30 years ago, and an N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer conjugate of doxorubicin covalently bound to the polymer backbone by a Gly-Phe-Leu-Gly peptidyl linker (FCE28068) became the first synthetic polymer-based anticancer conjugate to enter clinical trial in 1994. This conjugate arose from rational design attempting to capitalise on passive tumour targeting by the enhanced permeability and retention effect and, at the cellular level, lysosomotropic drug delivery to improve therapeutic index. Early clinical results were promising, confirming activity in chemotherapy refractory patients and the safety of HPMA as a new polymer platform. Subsequent Phase I/II trials have investigated an HPMA copolymer-based conjugate containing a doxorubicin and additionally galactose as a targeting moiety to promote liver targeting (FCE28069), and also HPMA copolymer conjugates of paclitaxel (PNU 166945), camptothecin (PNU 166148) and two platinates (AP5280 and AP5346- ProLindac). The preclinical and clinical observations made in these, and clinical studies with other polymer conjugates, should shape the development of next generation anticancer polymer therapeutics.

Role of epidermal growth factor receptor transactivation in alpha1B-adrenoceptor phosphorylation

Phosphorylation of G protein-coupled receptors is one of the earliest events that regulate their function. Current evidence indicates that homologous desensitization of these receptors mainly involves G protein-coupled receptor kinases whereas in heterologous desensitization second messenger-activated kinases play key roles. Recent data show that transactivation of EGF (epidermal growth factor) receptors may also play a role in receptor phosphorylation. The role of this process was studied for the alpha1B-adrenoceptor phosphorylation induced by agents acting through different processes using inhibitors to block the EGF receptor transactivation process at different levels. Experiments were performed using transfected rat-1 fibroblasts that express alpha1B-adrenoceptors in a stably fashion. A metalloproteinase inhibitor, an anti-heparin-binding-EGF-selective antibody, and a selective EGF-receptor kinase inhibitor blocked the alpha1B-adrenoceptor phosphorylation induced by noradrenaline or endothelin-1. Our results indicate that shedding of heparin-binding-EGF, transactivation of EGF receptors plays a more general role in alpha1B-adrenoceptor phosphorylation than previously anticipated. It is possible that other receptors/channels could be modulated through a similar pathway.

Phosphoinositide 3-kinase is required for human adipocyte differentiation in culture

OBJECTIVE

Phosphoinositide 3-kinase (PI3K) is required for murine adipocyte differentiation. However, a recent report concluded that PI3K was not involved in the differentiation of human preadipocytes into adipocytes. We have re-examined the role of PI3K in human preadipocyte differentiation, enrolling more patients and using more adipogenic indices.

METHODS

Human preadipocytes, isolated from nine patients, were induced to differentiate in the presence or absence of 100 nM wortmannin. After 12-15 days, triacylglycerol accumulation and the expression of adipogenic markers (fatty acid synthase and adiponectin) were measured.

RESULTS

A significant inhibition in triacylglycerol accumulation and in the induction of fatty acid synthase protein expression was observed, but there was no effect on adiponectin protein expression.

CONCLUSION

Inhibition of PI3K reduces the differentiation of human preadipocytes into adipocytes, suggesting a role for this enzyme in the human adipogenic process.

Wortmannin, a widely used phosphoinositide 3-kinase inhibitor, also potently inhibits mammalian polo-like kinase

Polo-like kinases (PLKs) play critical roles throughout mitosis. Here, we report that wortmannin, which was previously thought to be a highly selective inhibitor of phosphoinositide (PI) 3-kinases, is a potent inhibitor of mammalian PLK1. Observation of the wortmannin-PLK1 interaction was enabled by a tetramethylrhodamine-wortmannin conjugate (AX7503) that permits rapid detection of PLK1 activity and expression in complex proteomes. Importantly, we show that wortmannin inhibits PLK1 activity in an in vitro kinase assay with an IC(50) of 24 nM and when incubated with intact cells. Taken together, our results indicate that, at the concentrations of wortmannin commonly used to inhibit PI 3-kinases, PLK1 is also significantly inhibited.

Polyacetal−Doxorubicin Conjugates Designed for pH-Dependent Degradation

Terpolymerization of poly(ethylene glycol) (PEG), divinyl ethers, and serinol can be used to synthesize water soluble, hydrolytically labile, amino-pendent polyacetals (APEGs) suitable for drug conjugation. As these polyacetals display pH-dependent degradation (with faster rates of hydrolysis at acidic pH) and they are not inherently hepatotropic after intravenous (iv) injection, they have potential for development as biodegradable carriers to facilitate improved tumor targeting of anticancer agents. The aim of this study was to synthesize a polyacetal-doxorubicin (APEG-DOX) conjugate, determine its cytotoxicity in vitro and evaluate its potential for improved tumor targeting in vivo compared to an HPMA copolymer-DOX conjugate in clinical development. Amino-pendent polyacetals were prepared, and following succinoylation (APEG-succ), the polymeric intermediate conjugated to DOX via one of three methods using carbodiimide mediated coupling (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) in aqueous solution was the most successful). The resultant APEG-DOX conjugates had a DOX content of 3.0-8.5 wt %, contained <1.2% free DOX (relative to total DOX content) and had a M(w) = 60000-100000 g/mol and M(w)/M(n) = 1.7-2.6. In vitro cytotoxicity studies showed APEG-DOX to be 10-fold less toxic toward B16F10 cells than free DOX (IC(50) = 6 microg/mL and 0.6 microg/mL respectively), but confirmed the serinol-succinoyl-DOX liberated during main-chain degradation to be biologically active. When administered iv to C57 black mice bearing subcutaneous (sc) B16F10 melanoma, APEG-DOX of M(w) = 86000 g/mol, and 5.0 wt % DOX content exhibited significantly (p < 0.05) prolonged blood half-life and enhanced tumor accumulation compared to an HPMA copolymer-GFLG-DOX conjugate of M(w) = 30000 g/mol and 6.2 wt % DOX content. Moreover, APEG-DOX exhibited lower uptake by liver and spleen. These observations suggest that APEG anticancer conjugates warrant further development as novel polymer therapeutics for improved tumor targeting.

Activation of the PI3K/Akt pathway and chemotherapeutic resistance

The resistance of many types of cancer to conventional chemotherapies is a major factor undermining successful cancer treatment. In this review, the role of a signal transduction pathway comprised of the lipid kinase, phosphatidylinositol 3-kinase (PI3K), and the serine/threonine kinase, Akt (or PKB), in chemotherapeutic resistance will be explored. Activation of this pathway plays a pivotal role in essential cellular functions such as survival, proliferation, migration and differentiation that underlie the biology of human cancer. Akt activation also contributes to tumorigenesis and tumor metastasis, and as shown most recently, resistance to chemotherapy. Modulating Akt activity is now a commonly observed endpoint of chemotherapy administration or administration of chemopreventive agents. Studies performed in vitro and in vivo combining small molecule inhibitors of the PI3K/Akt pathway with standard chemotherapy have been successful in attenuating chemotherapeutic resistance. As a result, small molecules designed to specifically target Akt and other components of the pathway are now being developed for clinical use as single agents and in combination with chemotherapy to overcome therapeutic resistance. Specifically inhibiting Akt activity may be a valid approach to treat cancer and increase the efficacy of chemotherapy.

Water soluble polymers in tumor targeted delivery

The rationales for the use of water soluble polymers for anticancer drug delivery include: the potential to overcome some forms of multidrug resistance, preferential accumulation in solid tumors due to enhanced permeability and retention (EPR) effect, biorecognizability, and targetability. The utility of a novel paradigm for the treatment of ovarian carcinoma in an experimental animal model, which combines chemotherapy and photodynamic therapy with polymer-bound anticancer drugs is explained. Research and clinical applications as well as directions for the future development of macromolecular therapeutics are discussed.