Diindolilmethane (DIM) selectively inhibits cancer stem cells.

Epidemiologic studies repeatedly have shown chemopreventive effects of cruciferous vegetables. Indole-3-carbinol (I3C) and its metabolite diindolylmethane (DIM) were identified in these plants as active ingredients and theirs anti-tumor activities were confirmed in multiple in vitro and in vivo experiments. Here, we demonstrate that DIM is a selective and potent inhibitor of cancer stem cells (CSCs). In several cancer cell lines, DIM inhibited tumor sphere formation at the concentrations 30-300 times lower than concentrations required for growth inhibition of parental cells cultured as adherent culture. We also found that treatment with DIM overcomes chemoresistance of CSCs to cytotoxics, such as paclitaxel, doxorubicin, and SN-38. Pre-treatment of tumor spheres with DIM before implantation to mice significantly retarded the growth of primary tumors compared to tumors formed by untreated tumor spheres. The concentrations of DIM required to suppress CSCs formation are in the close range to those achievable in human plasma after oral dosing of the compound. Therefore, DIM can potentially be used in cancer patients, either alone, or in combinations with existing drugs.

A phase 2 study of SP1049C, doxorubicin in P-glycoprotein-targeting pluronics, in patients with advanced adenocarcinoma of the esophagus and gastroesophageal junction.

PURPOSE: To evaluate the antitumor activity of SP1049C, a novel P-glycoprotein targeting micellar formulation of doxorubicin, consisting of doxorubicin and two non-ionic block copolymers (pluronics), in patients with advanced adenocarcinoma of the esophagus and gastroesophageal junction (GEJ). PATIENTS AND METHODS: Patients with metastatic or locally advanced unresectable adenocarcinoma of the esophagus or GEJ who had not previously received systemic chemotherapy and had measurable disease were treated with SP1049C 75 mg/m(2) (doxorubicin equivalents) as a brief intravenous infusion every 3 weeks until disease progression or unacceptable toxicity. The primary endpoint was the objective response rate in patients who had received a least one course of SP1049C and had undergone tumor assessment, whereas, secondary endpoints included the objective response rate, progression-free survival (PFS), overall survival, and safety in the intent-to-treat (ITT) population. A review of scans was also conducted post-hoc by a blinded panel of radiologists. RESULTS: Twenty-one patients, of which 19 were evaluable for response, were treated with at least one dose of SP1049C. Nine patients had a partial response (PR) and eight patients had either a minor response or stable disease as their best response. The objective response rate was 47% (95% CI: 24.4-71) in the evaluable patient population, whereas the objective response rate was 43% (95% CI: 21.8-65.9) in the ITT population. The post-hoc radiological review confirmed that all nine responders had a PR; seven of the nine had a PR that was confirmed by a subsequent scan, whilst two patients had unconfirmed PRs. The median overall survival and PFS were 10.0 months (95%CI: 4.8-11.2) and 6.6 months (95% CI: 4.5-7.6), respectively. Neutropenia was the principal toxicity of SP1049C. Four patients developed an absolute percentage decrement of at least 15% in their left ventricular ejection fraction, none of which decreased to below 45% nor were symptomatic. CONCLUSION: SP1049C has a notable single-agent activity in patients with adenocarcinoma of the esophagus and GEJ, as well as an acceptable safety profile. These results, in addition to the results of preclinical studies demonstrating superior antitumor activity of SP1049C compared with doxorubicin in a standard formulation, indicate that further evaluations of SP1049C alone or combined with other relevant therapeutics in this disease setting are warranted.

Effects of pluronic and doxorubicin on drug uptake, cellular metabolism, apoptosis and tumor inhibition in animal models of MDR cancers.

Cancer chemotherapy is believed to be impeded by multidrug resistance (MDR). Pluronic (triblock copolymers of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO), PEO-b-PPO-b-PEO) were previously shown to sensitize MDR tumors to antineoplastic agents. This study uses animal models of Lewis lung carcinoma (3LL-M27) and T-lymphocytic leukemia (P388/ADR and P388) derived solid tumors to delineate mechanisms of sensitization of MDR tumors by Pluronic P85 (P85) in vivo. First, non-invasive single photon emission computed tomography (SPECT) and tumor tissue radioactivity sampling demonstrate that intravenous co-administration of P85 with a Pgp substrate, 99Tc-sestamibi, greatly increases the tumor uptake of this substrate in the MDR tumors. Second, 31P magnetic resonance spectroscopy (31P-MRS) in live animals and tumor tissue sampling for ATP suggest that P85 and doxorubicin (Dox) formulations induce pronounced ATP depletion in MDR tumors. Third, these formulations are shown to increase tumor apoptosis in vivo by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay and reverse transcription polymerase chain reaction (RT-PCR) for caspases 8 and 9. Altogether, formulation of Dox with P85 results in increased inhibition of the growth solid tumors in mice and represents novel and promising strategy for therapy of drug resistant cancers.

Differential metabolic responses to pluronic in MDR and non-MDR cells: a novel pathway for chemosensitization of drug resistant cancers.

A synthetic amphiphilic block copolymer, Pluronic, is a potent chemosensitizer of multidrug resistant (MDR) cancers that has shown promise in clinical trials. It has unique activities in MDR cells, which include a decrease in ATP pools and inhibition of P-glycoprotein (Pgp) resulting in increased drug accumulation in cells. This work demonstrates that Pluronic rapidly (15min) translocates into MDR cells and co-localizes with the mitochondria. It inhibits complex I and complex IV of the mitochondria respiratory chain, decreases oxygen consumption and causes ATP depletion in MDR cells. These effects are selective and pronounced for MDR cells compared to non-MDR counterparts and demonstrated for both drug-selected and Pgp-transfected cell models. Furthermore, inhibition of Pgp functional activity also abolishes the effects of Pluronic on intracellular ATP levels in MDR cells suggesting that Pgp contributes to increased responsiveness of molecular "targets" of Pluronic in the mitochondria of MDR cells. The Pluronic-caused impairment of respiration in mitochondria of MDR cells is accompanied with a decrease in mitochondria membrane potential, production of ROS, and release of cytochrome c. Altogether these effects eventually enhance drug-induced apoptosis and contribute to potent chemosensitization of MDR tumors by Pluronic.

The effect of the nonionic block copolymer pluronic P85 on gene expression in mouse muscle and antigen-presenting cells.

DNA vaccines can be greatly improved by polymer agents that simultaneously increase transgene expression and activate immunity. We describe here Pluronic P85 (P85), a triblock copolymer of ethylene oxide (EO) and propylene oxide (PO) EO(26)-PO(40)-EO(26). Using a mouse model we demonstrate that co-administration of a bacterial plasmid DNA with P85 in a skeletal muscle greatly increases gene expression in the injection site and distant organs, especially the draining lymph nodes and spleen. The reporter expression colocalizes with the specific markers of myocytes and keratinocytes in the muscle, as well as dendritic cells (DCs) and macrophages in the muscle, lymph nodes and spleen. Furthermore, DNA/P85 and P85 alone increase the systemic expansion of CD11c+ (DC), and local expansion of CD11c+, CD14+ (macrophages) and CD49b+ (natural killer) cell populations. DNA/P85 (but not P85) also increases maturation of local DC (CD11c+ CD86+, CD11c+ CD80 +, and CD11c+ CD40+. We suggest that DNA/P85 promotes the activation and recruitment of the antigen-presenting cells, which further incorporate, express and carry the transgene to the immune system organs.

Prevention of MDR development in leukemia cells by micelle-forming polymeric surfactant.

Doxorubicin (Dox) incorporated in nanosized polymeric micelles, SP1049C, has shown promise as monotherapy in patients with advanced esophageal carcinoma. The formulation contains amphiphilic block copolymers, Pluronics, that exhibit the unique ability to chemosensitize multidrug resistant (MDR) tumors by inhibiting P-glycoprotein (Pgp) drug efflux system and enhancing pro-apoptotic signaling in cancer cells. This work evaluates whether a representative block copolymer, Pluronic P85 (P85) can also prevent development of Dox-induced MDR in leukemia cells. For in vitro studies murine lymphocytic leukemia cells (P388) were exposed to increasing concentrations of Dox with/without P85. For in vivo studies, BDF1 mice bearing P388 ascite were treated with Dox or Dox/P85. The selected P388 cell sublines and ascitic tumor-derived cells were characterized for Pgp expression and functional activity (RT-PCR, Western Blot, rhodamine 123 accumulation) as well as Dox resistance (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay). The global gene expression was determined by oligonucleotide gene microarrays. We demonstrated that P85 prevented development of MDR1 phenotype in leukemia cells in vitro and in vivo as determined by Pgp expression and functional assays of the selected cells. Cells selected with Dox in the presence of P85 in vitro and in vivo exhibited some increases in IC(50) values compared to parental cells, but these values were much less than IC(50) in respective cells selected with the drug alone. In addition to mdr1, P85 abolished alterations of genes implicated in apoptosis, drug metabolism, stress response, molecular transport and tumorigenesis. In conclusion, Pluronic formulation can prevent development of MDR in leukemia cells in vitro and in vivo.

Alteration of genomic responses to doxorubicin and prevention of MDR in breast cancer cells by a polymer excipient: pluronic P85.

Polymer therapeutics has emerged as a new clinical option for the treatment of human diseases. However, little is known about pharmacogenetic responses to drugs formulated with polymers. In this study, we demonstrate that a formulation containing the block copolymer Pluronic P85 and antineoplastic drug doxorubicin (Dox) prevents the development of multidrug resistance in the human breast carcinoma cell line, MCF7. Specifically, MCF7 cells cultured in the presence of Pluronic were unable to stably grow in concentrations of Dox that exceeded 10 ng of Dox/mL of culture medium. In sharp contrast, MCF7 cells cultured in the absence of the block copolymer resulted in the selection and stable growth of cells that tolerated a 1000 times higher concentration of the drug (10 000 ng of Dox/mL of culture medium). Detailed characterization of the isolated sublines demonstrated that those cells selected in the polymer-drug formulation did not show amplification of the MDR1 gene, likely resulting in their high sensitivity to the drug. Conversely, cells selected with Dox alone showed an elevated level in the expression of the MDR1 gene along with a corresponding increase in the expression level of the drug efflux transporter, Pgp, and likely contributing to the high resistance of the cells to Dox. Global analysis of the expression profiles of 20K genes by DNA microarray revealed that the use of Pluronic in combination with Dox drastically changed the direction and magnitude of the genetic response of the tumor cells to Dox and may potentially enhance therapeutic outcomes. Overall, this study reinforces the need for a thorough assessment of pharmacogenomic effects of polymer therapeutics.

Transcriptional activation of gene expression by pluronic block copolymers in stably and transiently transfected cells.

Amphiphilic block copolymers of poly(ethylene oxide) and poly(propylene oxide) (Pluronics) enhance gene expression, but the mechanism remains unclear. We examined the effects of Pluronics on gene expression in murine cell models (NIH3T3 fibroblasts, C2C12 myoblasts, and Cl66 mammary adenocarcinoma cells) transfected with luciferase and green fluorescent protein. Addition of Pluronics to stably or transiently transfected cells enhanced transcription of the reporter genes. mRNA levels of the heat-shock protein hsp68 were also increased, whereas a housekeeping gene, glyceraldehyde-3-phosphate dehydrogenase, was unaffected. Fibroblast and myoblast cells transfected with PathDetect cis-Reporting System constructs were used to examine the involvement of the nuclear factor-kappaB (NF-kappaB) and activating protein-1 (AP-1) in Pluronics enhancement. Pluronics enhanced reporter gene expression controlled by NF-kappaB in both cell models. They also increased expression of a gene under AP-1 in a fibroblast cell line, but not in a myoblast cell line. Activation of the inflammation signaling pathway in myoblast cells by Pluronics was shown by increased IkappaB phosphorylation. No cytotoxicity was observed at doses of Pluronics at which gene expression was increased. Overall, these results indicate that Pluronics can increase the transcription of genes, in part, through the activation of selected stress signaling pathways.

Pluronic Block Copolymers for Gene Delivery.

Amphiphilic block copolymers of poly(ethylene oxide) and poly(propylene oxide) called Pluronic or poloxamer are commercially available pharmaceutical excipients. They recently attracted considerable attention in gene delivery applications. First, they were shown to increase the transfection with adenovirus and lentivirus vectors. Second, they were shown to increase expression of genes delivered into cells using non-viral vectors. Third, the conjugates of Pluronic with polycations, were used as DNA-condensing agents to form polyplexes. Finally, it was demonstrated that they can increase regional expression of the naked DNA after its injection in the skeletal and cardiac muscles or tumor. Therefore, there is substantial evidence that Pluronic block copolymers can improve gene expression with different delivery routes and different types of vectors, including naked DNA. These results and possible mechanisms of Pluronic effects are discussed. At least in some cases, Pluronic can act as biological adjuvants by activating selected signaling pathways, such as NF-kappaB, and upregulating the transcription of the genes.

Pluronic block copolymers for gene delivery.

Amphiphilic block copolymers of poly(ethylene oxide) and poly(propylene oxide) called Pluronic or poloxamer are commercially available pharmaceutical excipients. They recently attracted considerable attention in gene delivery applications. First, they were shown to increase the transfection with adenovirus and lentivirus vectors. Second, they were shown to increase expression of genes delivered into cells using non-viral vectors. Third, the conjugates of Pluronic with polycations, were used as DNA-condensing agents to form polyplexes. Finally, it was demonstrated that they can increase regional expression of the naked DNA after its injection in the skeletal and cardiac muscles or tumor. Therefore, there is substantial evidence that Pluronic block copolymers can improve gene expression with different delivery routes and different types of vectors, including naked DNA. These results and possible mechanisms of Pluronic effects are discussed. At least in some cases, Pluronic can act as biological adjuvants by activating selected signaling pathways, such as NF-kappaB, and upregulating the transcription of the genes.

Promoter- and strain-selective enhancement of gene expression in a mouse skeletal muscle by a polymer excipient Pluronic P85.

Amphiphilic triblock copolymers of ethylene oxide and propylene oxide (Pluronic) significantly enhanced expression of plasmid DNA in the skeletal muscle. In the presence of Pluronic P85 (P85) high levels of expression of a reporter gene (luciferase) were sustained for at least 40 days and the area under the gene expression curve increased by at least 10 times compared to the DNA alone. The effect of Pluronic depended on the strain of the mouse and the type of the promoter used. Thus, P85 enhanced luciferase expression by 17 to 19-fold in immunocompetent C57Bl/6 and Balb/c mice, while no enhancement was observed with athymic Balb/c nu/nu mice. Furthermore, P85 activated the expression of luciferase gene driven by CMV promoter, NFkappaB and p53 response elements. There was much less or no effect on the gene driven by SV40 promoter or AP1 and CRE response elements. Overall, the promoter selectivity suggested that Pluronic induced transcriptional activation of gene expression by activating the p53 and NFkappaB signaling pathways. In addition Pluronic increased the number of DNA copies and thus affected initial stages of gene transfer in a promoter selective manner.

Pluronic block copolymers alter apoptotic signal transduction of doxorubicin in drug-resistant cancer cells.

Pluronic block copolymer P85 (P85) sensitizes multidrug resistant (MDR) cancer cells resulting in the increase of cytotoxic activity of antineoplastic agents. This effect is attributed to the inhibition of the most clinically relevant drug efflux transporter, P-glycoprotein (Pgp), through the combined ATP depletion and inhibition of Pgp ATPase activity. The present study elucidates effects of an anticancer agent, doxorubicin (Dox), formulated with P85 on drug-induced apoptosis in MDR cancer cells. Early and late stages of apoptosis were detected by Annexin V and TUNEL methods, respectively. In parallel experiments, the expression of genes related to apoptosis, BCL2, BCLXL, BAX, P53, APAF1, Caspase 3, and Caspase 9, was determined by RT-PCR. The obtained data suggest that Dox/P85 formulation induces apoptosis in the resistant cancer cells more efficiently than free Dox. The treatment of the cells with Dox alone simultaneously activated a proapoptotic signal and an antiapoptotic cellular defense. Therefore, the apoptosis induction by Dox was substantially limited. In contrast, the treatment of the cells with Dox/P85 formulation significantly enhanced the proapoptotic activity of the drug and prevented the activation of the antiapoptotic cellular defense. This is likely to result in the stronger cytotoxic response of the resistant cells to the Dox/P85 formulation compared to the free drug.

Biophysical characterization of complexation of DNA with block copolymers of poly(2-dimethylaminoethyl) methacrylate, poly(ethylene oxide), and poly(propylene oxide).

The interactions of DNA (salmon testes) with two new cationic block copolymers made of poly(2-dimethylaminoethyl) methacrylate and poly(ethylene oxide), PEO-pDMAEMA, or poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), L92-pDMAEMA, were studied with the aim to understand their different in vitro transfection efficiencies when used as nonviral delivery vectors. PEO-pDMAEMA does not show surface activity while L92-pDMAEMA is as surface active as its parent Pluronic L92. Surface tension, titration microcalorimetry, ethidium bromide displacement, and zeta-potential measurements were carried out in phosphate buffers at pH 5 and 7. The association of L92-pDMAEMA with DNA was strongly exothermic at both pHs; the critical aggregation concentration (CAC) corresponded to a N/P ratio of 0.3, the maximum energy evolved was reached for N/P ratios of 0.82 and 1.27 at pH 5 and pH 7, respectively, and the saturation occurred for N/P ratios close to 2. The presence of L92 in the structure of this new block copolymer apparently did not modify the thermodynamic parameters of the interaction with DNA. In contrast, the interaction with PEO-pDMAEMA was significantly less exothermic, and CAC and saturation occurred for N/Ps equal to 0.43 and 1.37, respectively. The strong affinity of L92-pDMAEMA for DNA was reflected in its capacity to displace ethidium bromide and in the jump in the values of the zeta potential when N/P is near 1. Above the N/P ratio at which electroneutral polyplexes are formed, only at pH 5 an excess of L92-pDMAEMA is incorporated in the complexes, resulting in positively charged complexes. The profile of the zeta-potential values obtained for mixtures of L92-pDMAEMA with Pluronic P123 showed a shift to a lower N/P ratio, owing to an easier interaction of L92-pDMAEMA molecules with DNA in the presence of P123. Additionally, a visual inspection of the systems indicates that P123 contributes to stabilize/solubilize the DNA/cationic polymer aggregates, by avoiding the typical phase separation near the charge neutralization point. The information obtained can be particularly useful to optimize the conditions to form efficient polyplexes for gene delivery systems.

Polycationic block copolymers of poly(ethylene oxide) and poly(propylene oxide) for cell transfection.

A facile, one-step synthesis of cationic block copolymers of poly(2-N-(dimethylaminoethyl) methacrylate) (pDMAEMA) and copolymers of poly(propylene oxide) (PPO) and poly(ethylene oxide) (PEO) has been developed. The PEO-PPO-PEO-pDMAEMA (L92-pDMAEMA) and PEO-pDMAEMA copolymers were obtained via free radical polymerization of DMAEMA initiated by polyether radicals generated by cerium(IV). Over 95% of the copolymer fraction was of molecular mass ranging from 6.9 to 7.1 kDa in size, indicating the prevalence of the polyether-monoradical initiation mechanism. The L92-pDMAEMA copolymers possess parent surfactant-like surface activity. In contrast, the PEO-pDMAEMA copolymers lack significant surface activity. Both copolymers can complex with DNA. Hydrodynamic radii of the complexes of the L92-pDMAEMA and PEO-pDMAEMA with plasmid DNA ranged in size from 60 to 400 nm, depending on the copolymer/DNA ratio. Addition of Pluronic P123 to the L92-pDMAEMA complexes with DNA masked charges and decreased the tendency of the complex to aggregate, even at stoichiometric polycation/DNA ratios. The transfection efficiency of the L92-pDMAEMA copolymer was by far greater than that of the PEO-pDMAEMA copolymer. An extra added Pluronic P123 further increased the transfecton efficacy of L92-pDMAEMA, but did not affect that of PEO-pDMAEMA.

Metastasis-associated protein S100A4 induces angiogenesis through interaction with Annexin II and accelerated plasmin formation.

Many advanced tumors overexpress and secrete the S100A4 protein that is known to promote angiogenesis and metastasis development. The mechanisms of this effect and the endothelial receptor for S100A4 are both still unknown. Here we report that extracellular S100A4 interacts with annexin II, an endothelial plasminogen co-receptor. Co-localization and direct binding of S100A4 and annexin II were demonstrated, and the binding site was identified in the N-terminal region of annexin II. S100A4 alone or in a complex with annexin II accelerated tissue plasminogen activator-mediated plasminogen activation in solution and on the endothelial cell surface through interaction of the S100A4 C-terminal lysines with the lysine-binding domains of plasminogen. A synthetic peptide corresponding to the N terminus of annexin II prevented S100A4-induced plasmin formation in the endothelial cell culture. Local plasmin formation induced by circulating S100A4 could contribute to tumor-induced angiogenesis and metastasis formation that makes this protein an attractive target for new anti-cancer and anti-angiogenic therapies.

Kinetics of swelling of polyether-modified poly(acrylic acid) microgels with permanent and degradable cross-links.

Spherical particles of 50-100 mum size composed of poly(acrylic acid) networks covalently bonded to Pluronic polyether copolymers were tested for swelling in aqueous media. The microgels were cross-linked either by permanent ethylene glycol dimethacrylate (EGDMA) cross-links alone or by EDGMA together with reversible disulfide or biodegradable azoaromatic cross-links. Optimum conditions for a rapid, diffusion-limited swelling of the pH- and temperature-sensitive microgels with nondegradable cross-links were found. The microgels cross-linked by disulfide groups and equilibrium-swollen in the buffer solution exhibited degradation-limited kinetics of swelling under physiological conditions, with a first-order reaction constant, k(1), linearly proportional to the concentration of reducing agents such as dithiotreitol and tris(2-carboxyethyl)phosphine (TCEP). A severalfold faster swelling in the presence of more powerful reducing agent, TCEP, was observed, indicating the chemical specificity of the microgel swelling. The reoxidation of the thiol groups into disulfide cross-links by sodium hypochlorite led to the restoration of the microgels' diameter measured prior to the reduction-reoxidation cycle, which confirms the shape memory of the microgels. Enzymatically degradable azoaromatic cross-links enabled slow microgel swelling due to degradation of the cross-links by azoreductases from the rat intestinal cecum. The low rate of swelling of the Pluronic-containing microgels can enable sustained drug release in colon-specific drug delivery.

Effects of pluronic P85 on GLUT1 and MCT1 transporters in the blood-brain barrier.

PURPOSE: The amphiphilic block copolymer Pluronic P85 (P85) increases the permeability of the blood-brain barrier (BBB) with respect to a broad spectrum of drugs by inhibiting the drug efflux transporter, P-glycoprotein (Pgp). In this regard, P85 serves as a promising component for CNS drug delivery systems. To assess the possible effects of P85 on other transport systems located in the brain, we examined P85 interactions with the glucose (GLUT1) and monocarboxylate (MCT1) transporters. METHODS: Polarized monolayers of primary cultured bovine brain microvessel endothelial cells (BBMEC) were used as an in vitro model of the BBB. 3H-2-deoxy-glucose and 14C-lactate were selected as GLUT1 and MCT1 substrates, respectively. The accumulation and flux of these substrates added to the luminal side of the BBMEC monolayers were determined. RESULTS: P85 has little effect on 3H-2-deoxy-glucose transport. However, a significant decrease 14C-lactate transport across BBMEC monolayers is observed. Histology, immunohistochemistry, and enzyme histochemistry studies show no evidence of P85 toxicity in liver, kidney, and brain in mice. CONCLUSIONS: This study suggests that P85 formulations do not interfere with the transport of glucose. This is, probably, due to compensatory mechanisms in the BBB. Regarding the transport of monocarboxylates, P85 formulations might slightly affect their homeostasis in the brain, however, without any significant toxic effects.

Distribution kinetics of a micelle-forming block copolymer Pluronic P85.

Pluronic block copolymers, micelle-forming polymeric surfactants, are currently being evaluated in chemotherapy clinical trials in combination with doxorubicin to treat multidrug-resistant (MDR) tumors. This study examines the pharmacokinetics and biodistribution of Pluronic P85 (P85), a potent inhibitor of P-glycoprotein (Pgp). P85 was radioactively labeled and administered intravenously (i.v.) to mice. The concentration of the copolymer was varied to examine the effects of micelle formation on the distribution kinetics. The main pharmacokinetic parameters (the area under the curve, half-life, clearance, mean residence time, and volume of distribution) were determined. The results suggest that half-life of P85 varies from 60 to 90 h, depending on its aggregation state. Formation of micelles decreased the uptake of the block copolymer in the liver. However, it had no effect on the total clearance, suggesting that the elimination of P85 was controlled by the renal elimination of P85 unimers and not by the rate of micelle disposition or disintegration. The total clearance value suggests that a significant portion of P85 is reabsorbed back into the blood, probably through the kidney's tubular membranes.

Pluronic block copolymers and Pluronic poly(acrylic acid) microgels in oral delivery of megestrol acetate.

Several Pluronic-based formulations were studied in-vitro and in a rat model with respect to the release and bioavailability of megestrol acetate (MA) after oral administration. It was demonstrated that an aqueous, micellar formulation comprising a mixture of a hydrophobic (L61) and a hydrophilic (F127) Pluronic copolymer, significantly enhanced the bioavailability of MA administered orally at relatively low doses (1-7 mg kg(-1)). Pluronic-based microgels (spherical gel particles of sub-millimetre size) were introduced as MA vehicles. The microgels comprised a cross-linked network of poly(acrylic acid) onto which the Pluronic chains were covalently attached. Microgels of Pluronic L92 and poly(acrylic acid) fabricated into tablet dosage forms exhibited dramatically lowered MA initial burst release. The MA release was pH-dependent owing to the pH sensitivity of the microgel swelling, with the drug retained by the microgel at pH 1.8 and released slowly at pH 6.8. In the rat model, a significant increase in MA bioavailability was observed when the microgel-formulated MA was administered orally at a high dose of 10 mg kg(-1), owing to the enhanced retention of the microgel. The study of the microgel passage through the gastrointestinal tract demonstrated the microgel retention characteristic of a very high molecular weight polymer and the absence of any systemic absorption of the polymer.