Tumor vascular permeability and the EPR effect in macromolecular therapeutics: a review

Novel fast degradable thermosensitive polymeric micelles based on PEG-block-poly(N-(2-hydroxyethyl)methacrylamide-oligolactates)

The aim of this study was to design a thermosensitive polymeric micelle system with a relatively fast degradation time of around 1 day. These micelles are of interest for the (targeted) delivery of biologically active molecules. Therefore, N-(2-hydroxyethyl)methacrylamide-oligolactates (HEMAm-Lac(n)()) were synthesized and used as building blocks for biodegradable (block co) polymers. p(HEMAm-Lac(2)) is a thermosensitive polymer with a cloud point (CP) of 22 degrees C which could be lowered by copolymerization with HEMAm-Lac(4). The block copolymer PEG-b-((80%HEMAm-Lac(2))-(20%HEMAm-Lac(4))) self-assembled into compact spherical micelles with an average size of 80 nm above the CP of the thermosensitive block (6 degrees C). Under physiological conditions (pH 7.4; 37 degrees C), the micelles started to swell after 4 h and were fully destabilized within 8 h due to hydrolysis of the lactate side chains. Rapidly degrading thermosensitive polymeric micelles based on PEG-b-((80%HEMAm-Lac(2))-(20%HEMAm-Lac(4))) have attractive features as a (targeted) drug carrier system for therapeutic applications.

ATP-loaded liposomes effectively protect the myocardium in rabbits with an acute experimental myocardial infarction

PURPOSE

We assessed whether the infusion of ATP-loaded liposomes (ATP-L) can limit the fraction of the irreversibly damaged myocardium in rabbits with an experimental myocardial infarction.

METHODS

ATP-L, empty liposomes (EL), or Krebs-Henseleit (KH) buffer were administered by intracoronary infusion, followed by 30 min of occlusion and 3 h of reperfusion. Unisperse Blue dye was used to demarcate the net size of the occlusion-induced ischemic zone (area at risk) and nitroblue tetrazolium staining was used to detect the final fraction of the irreversibly damaged myocardium within the total area at risk.

RESULTS

The total size of the area at risk in all experimental animals was approx. 20% wt. of the left ventricle. The final irreversible damage in ATP-L-treated animals was only ca. 30% of the total area at risk as compared with ca. 60% in the group treated with EL (p < 0.009) and ca. 70% in the KH buffer-treated group (p < 0.003).

CONCLUSIONS

ATP-L effectively protected the ischemic heart muscle in rabbits with an experimental myocardial infarction as evidenced by a significantly decreased fraction of the irreversibly damaged heart within the total area at risk. ATP-L may provide an effective exogenous source of the ATP in vivo to protect ischemically damaged cells.

Cisplatin-incorporating polymeric micelles (NC-6004) can reduce nephrotoxicity and neurotoxicity of cisplatin in rats

In spite of the clinical usefulness of cisplatin (CDDP), there are many occasions in which it is difficult to continue the administration of CDDP due to its nephrotoxicity and neurotoxicity. We examined the incorporation of CDDP into polymeric micelles to see if this allowed the resolution of these disadvantages. Cisplatin was incorporated into polymeric micelles through the polymer-metal complex formation between polyethylene glycol poly(glutamic acid) block copolymers and CDDP (NC-6004). The pharmacokinetics, pharmacodynamics, and toxicity studies of CDDP and NC-6004 were conducted in rats or mice. The particle size of NC-6004 was approximately 30 nm, with a narrow size distribution. In rats, the area under the curve and total body clearance values for NC-6004 were 65-fold and one-nineteenth the values for CDDP (P<0.001 and 0.01, respectively). In MKN-45-implanted mice, NC-6004 tended to show antitumour activity, which was comparable to or greater than that of CDDP. Histopathological and biochemical studies revealed that NC-6004 significantly inhibited the nephrotoxicity of CDDP. On the other hand, blood biochemistry revealed transient hepatotoxicity on day 7 after the administration of NC-6004. Furthermore, rats given CDDP showed a significant delay (P<0.05) in sensory nerve conduction velocity in their hind paws as compared with rats given NC-6004. Electron microscopy in rats given CDDP indicated the degeneration of the sciatic nerve, but these findings were not seen in rats given NC-6004. These results were presumably attributable to the significantly reduced accumulation of platinum in nerve tissue when NC-6004 was administered (P<0.05). NC-6004 preserved the antitumour activity of CDDP and reduced its nephrotoxicity and neurotoxicity, which would therefore seem to suggest that NC-6004 could allow the long-term administration of CDDP where caution against hepatic dysfunction must be exercised.

CT-2103: emerging utility and therapy for solid tumours

CT-2103 (XYOTAX, Cell Therapeutics, Inc.) is a conjugate of paclitaxel to a polyglutamate polymer. Its macromolecular nature exploits enhanced permeability and retention in tumour tissues. This compound is stable and inactive in aqueous solution and undergoes predominantly intracellular metabolism at the site where active paclitaxel is released. Because it does not require a Cremophor EL vehicle, it can be administered by short infusion into peripheral veins. In preclinical models, compared with the same dose of unconjugated paclitaxel in Cremophor EL-ethanol, CT-2103 yields >or= 12-fold increase in area under the curve in both plasma and tumour tissue. This alteration in drug pharmacokinetics and biodistribution is attributable to the ability of macromolecules to concentrate in areas of vascular leakiness, such as tumour tissue. CT-2103 is taken up by both tumour cells and normal phagocytic cells and is transported to lysosomes, where it is released by specific proteases through enzymatic action. In syngeneic and xenogeneic tumour models, at the maximally tolerated dose, CT-2103 appears to be more active than the standard doses of paclitaxel. It has also demonstrated activity in paclitaxel-resistant tumour models. Its potential enhancement of efficacy and decrease in drug-related toxicities make this agent an attractive option for therapeutic investigation. In Phase I trials it has been relatively well-tolerated, with acceptable toxicity at doses <or= 225 mg/m(2) every 3 weeks. In combination with carboplatin the maximum tolerated dose is 235 mg/m(2) and the recommended Phase II dose 210 mg/m(2). Activity has been demonstrated in both non-small cell lung carcinoma (NSCLC) and in ovarian cancer, Phase III studies are currently testing this agent versus standard paclitaxel as maintenance therapy for first-line treatment-naive ovarian cancer. In addition, CT-2103 at a dose of 210 mg/m(2) (performance status [PS] 0 - 1) or 175 mg/m(2) (PS 2) is being compared with docetaxel (75 mg/m(2)) for the second-line treatment of NSCLC. In front-line PS 2 NSCLC patients, this agent in combination with carboplatin is undergoing comparison with paclitaxel/carboplatin; in a separate effort, single-agent CT-2103 is being compared with either gemcitabine or vinorelbine. These studies will determine whether the preclinical and early clinical promise of this agent can be realised in the clinical treatment of solid tumours.

PEGylation, successful approach to drug delivery

PEGylation defines the modification of a protein, peptide or non-peptide molecule by the linking of one or more polyethylene glycol (PEG) chains. This polymer is non-toxic, non-immunogenic, non-antigenic, highly soluble in water and FDA approved. The PEG-drug conjugates have several advantages: a prolonged residence in body, a decreased degradation by metabolic enzymes and a reduction or elimination of protein immunogenicity. Thanks to these favorable properties, PEGylation now plays an important role in drug delivery, enhancing the potentials of peptides and proteins as therapeutic agents.

Mixed micelles made of poly(ethylene glycol)-phosphatidylethanolamine conjugate and d-alpha-tocopheryl polyethylene glycol 1000 succinate as pharmaceutical nanocarriers for camptothecin

Micelles from the mixture of poly(ethylene glycol)-phosphatidyl ethanolamine conjugate (PEG-PE) and d-alpha-tocopheryl polyetheyene glycol 1000 succinate (TPGS) were prepared loaded with the poorly soluble anticancer drug camptothecin (CPT). The solubilization of CPT by the mixed micelles was more efficient than with earlier described micelles made of PEG-PE alone. CPT-loaded mixed micelles were stable upon storage and dilution and firmly retained the incorporated drug. The cytotoxicity of the CPT-loaded mixed micelles against various cancer cells in vitro was remarkably higher than that of the free drug. PEG-PE/TPGS mixed micelles may serve as pharmaceutical nanocarriers with improved solubilization capacity for poorly soluble drugs.

ATP-loaded liposomes effectively protect mechanical functions of the myocardium from global ischemia in an isolated rat heart model

ATP-loaded liposomes (ATP-L) infused into Langendorff-instrumented isolated rat hearts protect the mechanical functions of the myocardium during ischemia/reperfusion. The left ventricular developed pressure (LVDP) at the end of the reperfusion in the ATP-L group recovered to 72% of the baseline (preservation of the systolic function) compared to 26%, 40%, and 51% in the groups treated with Krebs-Henseleit (KH) buffer, empty liposomes (EL), and free ATP (F-ATP), respectively. The ATP-L-treated group also showed a significantly lower left ventricular end diastolic pressure (LVEDP; better preservation of the diastolic function) after ischemia/reperfusion than controls. After incubating the F-ATP and ATP-L with ATPase, the protective effect of the F-ATP was completely eliminated because of ATP degradation, while the protective effect of the ATP-L remained unchanged. Fluorescence microscopy confirmed the accumulation of liposomes in ischemic areas, and the net ATP in the ischemic heart increased with ATP-L. Our results suggest that ATP-L can effectively protect myocardium from ischemic/reperfusion damage.

Loading of hydrophobic materials into polymer particles: implications for fluorescent nanosensors and drug delivery

A straightforward method for loading hydrophobic materials into commercially available polymer nano- or microparticles is described. PMMA and PS nano/microparticles were swelled by an organic solvent with an ionic surfactant (SDS) to stabilize the particles in aqueous solution. FITC and Ru(dpp)3Cl2 were loaded into those particles based on the principle of "like dissolves like". Further surface modification of the loaded particles was achieved via layer-by-layer (LbL) self-assembly. Culture of fibroblasts with the dye-doped, coated particles showed that the cells internalized the fluorescent particles with no apparent toxic effects. The findings suggest the facile process could be useful in a wide range of applications for fluorescent micro/nanosensors and drug delivery.

Carbon Nanohorns as Anticancer Drug Carriers

We demonstrate that oxidized single-wall carbon nanohorns (SWNHs), a type of single-wall nanotube, entrap cisplatin, an anticancer agent. We found that the cisplatin structure was maintained inside the SWNHs and that the cisplatin was slowly released from the SWNHs in aqueous environments. The released cisplatin was effective in terminating the growth of human lung-cancer cells, while the SWNHs themselves had no such effect. Cisplatin-incorporated oxidized SWNHs are thus a potential drug delivery system.

Selective targeting of antibody-conjugated nanoparticles to leukemic cells and primary T-lymphocytes

In the present study, surface-modified nanoparticles based on biodegradable material were used for antibody coupling in order to get a selective drug carrier systems. Gelatin nanoparticles were prepared by a desolvation process. Sulfhydryl groups were introduced which enabled the linkage of NeutrAvidin (NAv). Antibodies specific for the CD3 antigen on lymphocytic cells were conjugated to the nanoparticles surface. The binding of biotinylated anti-CD3 antibody was achieved by NAv-biotin-complex formation. Cellular binding and uptake were determined by flow cytometry and confocal laser scanning microscopy (CLSM). Cell-type-specific targeting of anti-CD3-conjugated nanoparticles into CD3-positive human T-cell leukemia cells and primary T-lymphocytes could be shown. Celluar uptake and effective internalization of antibody-conjugated nanoparticles into CD3 expressing cells were demonstrated. Uptake rates of about 84% into T-cell leukemia cells were observed. To confirm selectivity of T-cell targeting, competition experiments were carried out adding excessive free anti-CD3 prior to nanoparticle incubation leading to significantly reduced cellular uptake of antibody-conjugated nanoparticles. Further analysis on the mechanism of uptake confirmed a receptor-mediated endocytotic process. Protein-based nanoparticles conjugated with an antibody against a specific cellular antigen hold promise as selective drug delivery systems for specific cell types.

Enhanced intracellular delivery and improved antitumor efficacy of doxorubicin by sterically stabilized liposomes modified with a synthetic RGD mimetic

While sterically stabilized liposomes (SSL) can passively accumulate into tumor tissue due to the effect of enhanced permeability and retention (EPR), the intracellular uptake of the entrapped anticancer drugs by the tumor cells should be a determinant step for their antitumor activities. Therefore, strategies that can enhance the intracellular uptake of SSL into tumor cells could lead to an improved therapeutic efficacy for the drugs. To check this possibility, RGD-mimetic-modified SSL (RGDm-SSL) were constructed aimed to achieve tumor accumulation as well as enhanced intracellular delivery, and were loaded with doxorubicin (DOX), an anticancer drug. Flow cytometry and confocal microscopy reveal that RGDm-SSL facilitated the DOX uptake into the melanoma cells via integrin-mediated endocytosis. DOX-loaded RGDm-SSL (RGDm-SSL-DOX) displayed higher cytotoxicity on melanoma cells than DOX-loaded SSL (SSL-DOX). Tissue distribution and therapeutic experiments were examined in C57BL/6 mice carrying melanoma B16 tumors. RGDm-SSL-DOX displayed similar DOX accumulation in tumor tissue to that of SSL-DOX but showed significantly lower DOX level in blood and remarkably higher DOX level in spleen than SSL-DOX. Administration of RGDm-SSL-DOX at a dose of 5 mg DOX/kg resulted in effective retardation of tumor growth and prolonged survival times compared with SSL-DOX. These results suggest that RGDm-modified SSL may be a promising intracellular targeting carrier for efficient delivery of chemotherapeutic agents into tumor cells.

Vascular endothelial growth factor selectively targets boronated dendrimers to tumor vasculature

Tumor neovasculature is a potential but, until very recently, unexplored target for boron neutron capture therapy (BNCT) of cancer. In the present report, we describe the construction of a vascular endothelial growth factor (VEGF)-containing bioconjugate that potentially could be used to target up-regulated VEGF receptors (VEGFR), which are overexpressed on tumor neovasculature. A fifth-generation polyamidoamine dendrimer containing 128 reactive amino groups was reacted with 105 to 110 decaborate molecules to produce a macromolecule with 1,050 to 1,100 boron atoms per dendrimer. This was conjugated to thiol groups of VEGF at a 4:1 molar ratio using the heterobifunctional reagent sulfo-LC-SPDP. In addition, the boronated dendrimer was tagged with a near-IR Cy5 dye to allow for near-IR fluorescent imaging of the bioconjugate in vitro and in vivo. As would be predicted, the resulting VEGF-BD/Cy5 bioconjugate was not cytotoxic to HEK293 cells engineered to express 2.5 x 10(6) VEGFR-2 per cell. Furthermore, it showed binding and activation of VEGFR-2 comparable with that of native VEGF. Internalization of VEGF-BD/Cy5 by PAE cells expressing 2.5 x 10(5) VEGFR-2 per cell was inhibited by excess VEGF, indicating a VEGFR-2-mediated mechanism of uptake. Near-IR fluorescent imaging of 4T1 mouse breast carcinoma revealed selective accumulation of VEGF-BD/Cy5, but not BD/Cy5, particularly at the tumor periphery where angiogenesis was most active. Accumulation of VEGF-BD/Cy5 in 4T1 breast carcinoma was diminished in mice pretreated with a toxin-VEGF fusion protein that selectively killed VEGFR-2-overexpressing endothelial cells. Our data lay the groundwork for future studies using the VEGF-BD/Cy5 bioconjugate as a targeting agent for BNCT of tumor neovasculature.

Thermosensitive and biodegradable polymeric micelles for paclitaxel delivery

The preparation, release and in vitro cytotoxicity of a novel polymeric micellar formulation of paclitaxel (PTX) were investigated. The micelles consisted of an AB block copolymer of poly(N-(2-hydroxypropyl) methacrylamide lactate) and poly(ethylene glycol) (pHPMAmDL-b-PEG). Taking advantage of the thermosensitivity of pHPMAmDL-b-PEG, the loading was done by simply mixing of a small volume of a concentrated PTX solution in ethanol and an aqueous polymer solution and subsequent heating of the resulting solution above the critical micelle temperature of the polymer. PTX could be almost quantitatively loaded in the micelles up to 2 mg/mL. By dynamic light scattering and cryo-transmission electron microscopy, it was shown that PTX-loaded micelles have a mean size around 60 nm with narrow size distribution. At pH 8.8 and 37 degrees C, PTX-loaded micelles destabilized within 10 h due to the hydrolysis of the lactic acid side group of the pHPMAmDL. Because the hydrolysis of the lactic acid side groups is first order in hydroxyl ion concentration, the micelles were stable for about 200 h at physiological conditions. The presence of serum proteins did not have an adverse effect on the stability of the micelles during at least 15 h. Interestingly, the dissolution kinetics of pHPMAmDL-b-PEG micelles was retarded by incorporation of PTX, indicating a strong interaction between PTX and the pHPMAmDL block. The PTX-loaded micelles showed a release of the incorporated 70% of PTX during 20 h at 37 degrees C and at pH 7.4. PTX-loaded pHPMAmDL-b-PEG micelles showed comparable in vitro cytotoxicity against B16F10 cells compared to the Taxol standard formulation containing Cremophor EL, while pHPMAmDL-b-PEG micelles without PTX were far less toxic than the Cremophor EL vehicle. Confocal laser-scanning microscopy (CLSM) and fluorescence activated cell sorting (FACS) analysis of fluorescently labelled micelles showed that pHPMAmDL-b-PEG micelles were internalized by the B16F10 cells. The present results suggest that pHPMAmDL-b-PEG block copolymer micelles are a promising delivery system for the parenteral administration of PTX.

Modified polyvinylalcohol for encapsulation of all-trans-retinoic acid in polymeric micelles

All-trans-retinoic acid (ATRA) is now included in many antitumor therapeutic schemes for the treatment of acute promyelocytic leukaemia, Kaposi's sarcoma, head and neck squamous cell carcinoma, ovarian carcinoma, bladder cancer and neuroblastoma. Unfortunately its poor aqueous solubility hampers its parenteral formulation. To date, there is no parenteral formulation of ATRA commercially available and oral administration of ATRA is associated with progressively diminishing ATRA levels in plasma, which is related to induction of retinoic acid-binding protein and increased drug catabolism by cytochrome P-450-mediated reaction. An ATRA formulation, obtained by complexation of the drug into polymeric micelles, might be suitable for parenteral administration overcoming these unwanted effects. To this purpose we prepared an amphiphilic polymer by polyvinylalcohol (PVA) substitution with oleyl amine at 1.5% substitution degree (mol substituent per 100 mol hydroxyvinylmonomer) and evaluated its functional properties with regard to ATRA complexation. The substituted polymer displayed ability to interact with ATRA both in aqueous solution and in the solid state following spray-drying of drug-polymer hydro-alcoholic solutions. The spray-dried complexes rapidly dissolved in water providing high levels of ATRA solubilization as a function of the drug-polymer weight ratio. The complexes characterized by 1:5 drug-polymer weight ratio provided higher levels of ATRA solubilization than 1:3 and 1:10 drug-polymer weight ratios respectively. Pre-formed polymeric micelles in water equilibrated in the presence of excess solid ATRA provided the lowest levels of solubilization. The drug release from the complexes was very slow in PBS, indicating their suitability in antitumor drug targeting where a fundamental requirement is stability towards drug release for at least 24 h, corresponding to the average circulation time period of macromolecular carriers. The cytotoxicity studies against neuroblastoma cell lines outlined increased cytotoxicity of complexed ATRA with respect to free ATRA, likely due to the increased bioavailability of the hydrophobic drug from the complex. We conclude that ATRA entrapped into self-assembling polymer micelles may be a useful parenteral ATRA formulation overcoming the unwanted pharmacological mechanism that lead to acquired retinoid resistance.

Synthesis and Properties of Carborane-Functionalized Aliphatic Polyester Dendrimers

The incorporation of multiple p-carborane cages within an aliphatic polyester dendrimer was accomplished through the preparation of a bifunctional carborane synthon. A p-carborane derivative having an acid and a protected alcohol functionality was found to efficiently couple to peripheral hydroxyl groups of low-generation dendrimers under standard esterification conditions. Deprotection of carborane hydroxyl groups allowed for further dendronization through a divergent approach using the highly reactive anhydride of benzylidene-protected 2,2-bis(hydroxymethyl)propanoic acid. This approach was used to prepare fourth- and fifth-generation dendrimers that contain 4, 8, and 16 carborane cages within their interior. Upon peripheral deprotection to liberate a polyhydroxylated dendrimer exterior, these structures exhibited aqueous solubility as long as a minimum of eight hydroxyl groups per carborane were present. Several of the water-soluble structures were found to exhibit a lower critical solution temperature. Additionally, irradiation of these materials with thermal neutrons resulted in emission of gamma radiation that is indicative of boron neutron capture events occurring within the carborane-containing dendrimers.

Study of pH-sensitive copolymer/phospholipid complexes using the langmuir balance technique: effect of anchoring sequence and copolymer molecular weight

The behavior of three copolymers of N-isopropylacrylamide (NIPAM), methacrylic acid (MAA), and hydrophobic moiety was studied at phospholipid monolayer/subphase interfaces. The hydrophobic moieties, N-terminal dioctadecylamine (DODA) and random octadecylacrylate (ODA), were used as anchoring groups. The interactions between a 1,2-distearoyl-sn-glycero-3-phosphatidylcholine (DSPC) monolayer and the copolymers were studied using the Langmuir balance technique. The effect of subphase pH, distribution of anchors along the copolymer chain, and copolymer molecular weight on the nature of the interactions between the copolymer chains and the DSPC monolayer were investigated. A first-order kinetics model was used to analyze the copolymers adsorption at the DSPC monolayer/subphase interface and allowed the interaction area between the copolymer chains and the DSPC monolayer, A(x), to be determined. The interaction area appears to depend on the subphase pH and the copolymer molecular weight. On decreasing pH, the interaction area of high molecular weight copolymers increases significantly; this is consistent with the copolymer chain phase transition from an extended coil to a collapsed globule while pH is lowered. In the latter conformation, strong hydrophobic attractive interactions between the copolymer chains and the hydrophobic part of the DSPC monolayer favor the copolymer intercalation, which could eventually provoke the phospholipidic layer destabilization or rupture.

DE-310, a macromolecular prodrug of the topoisomerase-I-inhibitor exatecan (DX-8951), in patients with operable solid tumors

BACKGROUND

DE-310 is composed of the topoisomerase-I-inhibitor DX-8951 (exatecan) and a biodegradable macromolecular carrier, which are covalently linked by a peptidyl spacer. In pre-clinical studies, high levels and prolonged retention of conjugated DX-8951 (carrier-bound DX-8951) have been observed in tumor tissues following DE-310 administration. This phenomenon is explained as the enhanced permeability and retention (EPR) effect. DX-8951 and G-DX-8951 (glycyl-DX-8951) exerting anti-tumor activity in vivo are released from DE-310 by enzymatic cleavage of the spacer.

METHODS

To quantify the concentration of conjugated DX-8951, DX-8951 and G-DX-8951 in human tissues, six patients with different solid tumor types received 6.0 mg/m(2) of DE-310 (as equivalent of DX-8951) as a single three-hour infusion administered 7 days (+/-2 days) prior to scheduled tumor resection. Drug concentrations were then determined in the resected tissues. To evaluate the plasma PK of DE-310, plasma samples were taken up to 42 days post dosing.

RESULTS

There were no severe side effects of the DE-310 infusion. Concentrations of conjugated DX-8951, DX-8951 and G-DX-8951 were in general similar in tumor and relevant normal tissue samples and preferential accumulation of DE-310, DX-8951 and G-DX-8951 in human tumor tissues was not observed.

CONCLUSIONS

These data indicate that there is distribution of DE-310 into tissue and that DX-8951 and G-DX-8951 are released slowly over an extended period from DE-310 providing prolonged exposure similar to a continuous infusion. However, the similarity in the concentrations in tumor and relevant normal tissues does not support the EPR concept in the studied human cancers.

A macromolecular prodrug of doxorubicin conjugated to a biodegradable cyclotriphosphazene bearing a tetrapeptide

A new biodegradable water-soluble phosphazene trimer-doxorubicin conjugate was synthesized, in which equimolar hydrophilic methoxy-poly(ethylene glycol) with a molecular weight of 350 (MPEG350) and a tumor-specific tetrapeptide (Gly-Phe-Leu-Gly) were grafted to cyclotriphosphazene. The present conjugate exhibited cytotoxicity lower than that of free doxorubicin (IC50=0.10 microM) but a reasonably higher in vitro cytotoxicity (IC50=1.1 microM) against the leukemia L1210 cell line probably due to its enzymatically controlled release.

Distribution of gadomelitol in a human breast tumor model in mice

The study evaluates the tumor distribution of the rapid clearance blood pool agent (RCBPA) gadomelitol, in a breast tumor model. Different techniques were used : (1) tissue gadolinium concentrations measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES), (2) whole body quantitative autoradiography using radiolabeled [153Gd] gadomelitol and (3) dynamic contrast-enhanced MRI with compartmental analysis. An accumulation of gadomelitol in tumors compared to muscle was observed 30 min and 3 h post injection (p.i.). Thirty minutes p.i., the gadomelitol tumor distribution evaluated by autoradiography showed a marked difference between the rim and the center, whereas both areas showed comparable concentrations after 3 h. Using dynamic contrast-enhanced MRI, three phases could be observed during the 1 hour observation period: (1) rapid tumor uptake within the first few minutes post-injection (2) a progressive increase in tumor signal enhancement over 10 min and (3) a steady-state phase. Average +/- SD (n=5) transendothelial permeability K(PS) and the fractional blood volume fBV were 12.2+/-1.6 microl/min(-1)/g and 5.4+/-0.2% respectively. Due to its slow extravasation and high tumor residence time, gadomelitol may potentially be useful to improve characterization between benign versus malignant tumors using dynamic MRI.

Preparation and biological characterization of polymeric micelle drug carriers with intracellular pH-triggered drug release property: tumor permeability, controlled subcellular drug distribution, and enhanced in vivo antitumor efficacy

A novel intracellular pH-sensitive polymeric micelle drug carrier that controls the systemic, local, and subcellular distributions of pharmacologically active drugs has been developed in this study. The micelles were prepared from self-assembling amphiphilic block copolymers, poly(ethylene glycol)-poly(aspartate hydrazone adriamycin), in which the anticancer drug, adriamycin, was conjugated to the hydrophobic segments through acid-sensitive hydrazone linkers. By this polymer design, the micelles can stably preserve drugs under physiological conditions (pH 7.4) and selectively release them by sensing the intracellular pH decrease in endosomes and lysosomes (pH 5-6). In vitro and in vivo studies show that the micelles have the characteristic properties, such as an intracellular pH-triggered drug release capability, tumor-infiltrating permeability, and effective antitumor activity with extremely low toxicity. The acquired experimental data clearly elucidate that the optimization of both the functional and structural features of polymeric micelles provides a promising formulation not only for the development of intracellular environment-sensitive supramolecular devices for cancer therapeutic applications but also for the future treatment of intractable cancers with limited vasculature.

Polymeric micelles for delivery of poorly soluble drugs: preparation and anticancer activity in vitro of paclitaxel incorporated into mixed micelles based on poly(ethylene glycol)-lipid conjugate and positively charged lipids

Paclitaxel-loaded mixed polymeric micelles consisting of poly(ethylene glycol)-distearoyl phosphoethanolamine conjugates (PEG-PE), solid triglycerides (ST), and cationic Lipofectin lipids (LL) have been prepared. Micelles with the optimized composition (PEG-PE/ST/LL/paclitaxel = 12/12/2/1 by weight) had an average micelle size of about 100 nm, and zeta-potential of about -6 mV. Micelles were stable and did not release paclitaxel when stored at 4 degree C in the darkness (just 2.9% of paclitaxel have been lost after 4 months with the particle size remaining unchanged). The release of paclitaxel from such micelles at room temperature was also insignificant. However, at 37 degree C, approx. 16% of paclitaxel was released from PEG-PE/ST/LL/paclitaxel micelles in 72 h, probably, because of phase transition in the ST-containing micelle core. In vitro anticancer effects of PEG-PE/ST/LL/paclitaxel and control micelles were evaluated using human mammary adenocarcinoma (BT-20) and human ovarian carcinoma (A2780) cell lines. Paclitaxel in PEG-PE/ST/LL micelles demonstrated the maximum anti-cancer activity. Cellular uptake of fluorescently-labeled paclitaxel-containing micelles by BT-20 cells was investigated using a fluorescence microscopy. It seems that PEG-PE/ST/LL micelles, unlike micelles without the LL component, could escape from endosomes and enter the cytoplasm of BT-20 cancer cells thus increasing the anticancer efficiency of the micellar paclitaxel.

Nanoparticle Targeting of Anticancer Drug Improves Therapeutic Response in Animal Model of Human Epithelial Cancer

Prior studies suggested that nanoparticle drug delivery might improve the therapeutic response to anticancer drugs and allow the simultaneous monitoring of drug uptake by tumors. We employed modified PAMAM dendritic polymers <5 nm in diameter as carriers. Acetylated dendrimers were conjugated to folic acid as a targeting agent and then coupled to either methotrexate or tritium and either fluorescein or 6-carboxytetramethylrhodamine. These conjugates were injected i.v. into immunodeficient mice bearing human KB tumors that overexpress the folic acid receptor. In contrast to nontargeted polymer, folate-conjugated nanoparticles concentrated in the tumor and liver tissue over 4 days after administration. The tumor tissue localization of the folate-targeted polymer could be attenuated by prior i.v. injection of free folic acid. Confocal microscopy confirmed the internalization of the drug conjugates into the tumor cells. Targeting methotrexate increased its antitumor activity and markedly decreased its toxicity, allowing therapeutic responses not possible with a free drug.

Enzymatic Degradation of Liposome-Grafted Poly(hydroxyethyl l-glutamine)

Liposomes coated with poly(hydroxyethyl L-glutamine) (PHEG) show prolonged circulation times and biodistribution patterns comparable to PEG-coated liposomes. While PEG is a nondegradable polymer, PHEG is expected to be hydrolyzed by proteases. In this study the enzymatic degradability of PHEG both in its free form and grafted onto liposomes was investigated, using the proteases papain, pronase E, and cathepsin B. Enzymatic action was monitored with a ninhydrin assay, which quantifies amine groups formed due to hydrolysis of amide bonds, and the degradation products were characterized by MALDI-ToF mass spectrometry. PHEG, both in its free form and when grafted onto liposomes, showed degradation into low molecular weight peptides by the enzymes. Thus, we present a polymer-coated long-circulating liposome with an enzymatically degradable coating polymer, avoiding the risk of cellular accumulation.

Tumor-targeted gene delivery using poly(ethylene glycol)-modified gelatin nanoparticles: in vitro and in vivo studies

PURPOSE

To develop safe and effective systemically administered nonviral gene therapy vectors for solid tumors, DNA-containing poly(ethylene glycol)-modified (PEGylated) gelatin nanoparticles were fabricated and evaluated in vitro and in vivo.

METHODS

Reporter plasmid DNA encoding for beta-galactosidase (pCMV-beta) was encapsulated in gelatin and PEGylated gelatin nanoparticles using a water-ethanol solvent displacement method under controlled pH and temperature. Lewis lung carcinoma (LLC) cells in culture were transfected with the pCMV-beta in the control and nanoparticle formulations. Periodically, the expression of beta-galactosidase in the cells was measured quantitatively using an enzymatic assay for the conversion of o-nitrophenyl-beta-D: -galactopyranoside (ONPG) to o-nitrophenol (ONP). Qualitative expression of beta-galactosidase in LLC cells was observed by staining with 5-bromo-4-chloro-3-indolyl-beta-D: -galactopyranoside (X-gal). Additionally, the plasmid DNA-encapsulated gelatin and PEGylated gelatin nanoparticles were administered intravenously (i.v.) and intratumorally (i.t.) to LLC-bearing female C57BL/6J mice. At various time points postadministration, the animals were sacrificed and transgene expression in the tumor and liver was determined quantitatively by the ONPG to ONP enzymatic conversion assay and qualitatively by X-gal staining.

RESULTS

Almost 100% of the pCMV-beta was encapsulated in gelatin and PEGylated gelatin nanoparticles (mean diameter 200 nm) at 0.5% (w/w) concentration. PEGylated gelatin nanoparticles efficiently transfected the LLC cells and the beta-galactosidase expression, as measured by the ONPG to ONP enzymatic conversion assay at 420 nm absorbance, increased starting from 12 h until 96 h post-transfection. The efficient expression of LLC cells was also evident by the X-gal staining method that shows blue color formation. The in vivo studies showed significant expression of beta-galactosidase in the tumor following administration of DNA-containing PEGylated gelatin nanoparticles to LLC-bearing mice by both i.v. and i.t. routes. Following i.v. administration of pCMV-beta in PEGylated gelatin nanoparticles, for instance, the absorbance at 420 nm per gram of tumor increased from 0.60 after 12 h to 0.85 after 96 h of transfection. After i.t. administration, the absorbance values increased from 0.90 after 12 h to almost 1.4 after 96 h.

CONCLUSIONS

The in vitro and in vivo results of this study clearly show that a long-circulating, biocompatible and biodegradable, DNA-encapsulating nanoparticulate system would be highly desirable for systemic delivery of genetic constructs to solid tumors.

Synthesis, characterization, and tumor selectivity of a polyphosphazene–platinum(II) conjugate

A new amphiphilic poly(organophosphazene) was synthesized by stepwise nucleophilic substitutions with a hydrophilic methoxy poly(ethylene glycol) with an average molecular weight of 350 (MPEG350) and a hydrophobic glycyl-L-glutamate as side groups, and then an antitumor (dach)platinum(II) (dach: trans-(+/-)-1,2-diaminocyclohexane) moiety was conjugated to the polymer using the dipeptide as a spacer. This polymeric platinum conjugate was found to be accumulated in the tumor tissue to a remarkably greater extent than in the normal tissue (tumor/tissue ratio >4), probably due to the excellent EPR effect and the long circulating properties of the polymer conjugate (t1/2beta=6.2 h and AUC=4020 nmol h/ml) compared with carboplatin (t1/2beta=0.42 h and AUC=120 nmol h/ml). The polymer conjugate also exhibited high in vitro cytotoxicity comparable to cisplatin against several human tumor cells tested.

Liposomes targeted via two different antibodies: Assay, B-cell binding and cytotoxicity

The selective toxicity of anticancer drugs can be improved with the use of antibody-targeted liposomes. We hypothesize that liposomes targeted via antibodies against two or more receptor populations will increase the apparent receptor density on the target cells, resulting in improved therapeutic affects. A fluorescent assay was developed, using the fluorophores Alexa Fluor 350 and 532 to label monoclonal antibodies (mAb), and used to quantitate two different mAb populations coupled to the same liposome surface to within +/-10% of the values obtained with radiolabeled antibody (125I) tracers. The binding and uptake of targeted liposomes by B lymphoma (Namalwa) cells were examined for either individual populations of alphaCD19-targeted or alphaCD20-targeted liposomes, mixed populations (1:1) of alphaCD19-targeted liposomes plus alphaCD20-targeted liposomes, and dual-targeted liposomes, i.e., equal amount of both alphaCD19 and alphaCD20 on the same liposomes. At similar antibody densities, the binding and uptake of the dual-targeted liposomes were greater than that of either individually targeted liposomes alone, and showed additivity. At the same total lipid and antibody densities, 1:1 mixtures of individually targeted liposomes gave similar results to dual-targeted liposomes. Cytotoxicity was also improved, with DXR-loaded dual-targeted liposomes appearing to have higher cytotoxicity than 1:1 mixtures of individually targeted liposomes.

NK105, a paclitaxel-incorporating micellar nanoparticle formulation, can extend in vivo antitumour activity and reduce the neurotoxicity of paclitaxel

Paclitaxel (PTX) is one of the most effective anticancer agents. In clinical practice, however, high incidences of adverse reactions of the drug, for example, neurotoxicity, myelosuppression, and allergic reactions, have been reported. NK105, a micellar nanoparticle formulation, was developed to overcome these problems and to enhance the antitumour activity of PTX. Via the self-association process, PTX was incorporated into the inner core of the micelle system by physical entrapment through hydrophobic interactions between the drug and the well-designed block copolymers for PTX. NK105 was compared with free PTX with respect to their in vitro cytotoxicity, in vivo antitumour activity, pharmacokinetics, pharmacodynamics, and neurotoxicity. Consequently, the plasma area under the curve (AUC) values were approximately 90-fold higher for NK105 than for free PTX because the leakage of PTX from normal blood vessels was minimal and its capture by the reticuloendothelial system minimised. Thus, the tumour AUC value was 25-fold higher for NK105 than for free PTX. NK105 showed significantly potent antitumour activity on a human colorectal cancer cell line HT-29 xenograft as compared with PTX (P<0.001) because the enhanced accumulation of the drug in the tumour has occurred, probably followed by its effective and sustained release from micellar nanoparticles. Neurotoxicity was significantly weaker with NK105 than with free PTX. The neurotoxicity of PTX was attenuated by NK105, which was demonstrated by both histopathological (P<0.001) and physiological (P<0.05) methods for the first time. The present study suggests that NK105 warrants a clinical trial for patients with metastatic solid tumours.

RNAi-mediated gene-targeting through systemic application of polyethylenimine (PEI)-complexed siRNA in vivo

RNA interference (RNAi) represents a powerful, naturally occurring biological strategy for inhibition of gene expression. It is mediated through small interfering RNAs (siRNAs), which trigger specific mRNA degradation. In mammalian systems, however, the application of siRNAs is severely limited by the instability and poor delivery of unmodified siRNA molecules into the cells in vivo. In this study, we show that the noncovalent complexation of synthetic siRNAs with low molecular weight polyethylenimine (PEI) efficiently stabilizes siRNAs and delivers siRNAs into cells where they display full bioactivity at completely nontoxic concentrations. More importantly, in a subcutaneous mouse tumor model, the systemic (intraperitoneal, i.p.) administration of complexed, but not of naked siRNAs, leads to the delivery of the intact siRNAs into the tumors. The i.p. injection of PEI-complexed, but not of naked siRNAs targeting the c-erbB2/neu (HER-2) receptor results in a marked reduction of tumor growth through siRNA-mediated HER-2 downregulation. Hence, we establish a novel and simple system for the systemic in vivo application of siRNAs through PEI complexation as a powerful tool for future therapeutic use.

Preparation and characterisation of antibody modified gelatin nanoparticles as drug carrier system for uptake in lymphocytes

Established methods of protein chemistry can be used for the effective attachment of drug targeting ligands to the surface of protein-based nanoparticles. In the present work gelatin nanoparticles were used for the attachment of biotinylated anti-CD3 antibodies by avidin-biotin-complex formation. These antibody modified nanoparticles represent a promising carrier system for the specific drug targeting to T-lymphocytes. The objective of this work was the comprehensive quantification of every chemical reaction step during the preparation procedure of these cell specific nanoparticles. Gelatin nanoparticles were formed by a two-step desolvation process. After the first desolvation step the remaining sediment and the supernatant were analysed for molecular weight distribution by size exclusion chromatography (SEC). Nanoparticles then were formed using the high molecular gelatin fraction and subsequently were stabilised by glutaraldehyde crosslinking. A part of the detectable amino groups on the particle surface was reacted with 2-iminothiolane in order to introduce reactive sulfhydryl groups. The thiolated nanoparticles were coupled to NeutrAvidin (NAv) which previously was activated with the heterobifunctional crosslinker sulfo-MBS. All these reaction steps were quantified by photometry or gravimetry. The functionality of NAv after covalent conjugation was confirmed by a biotin-4-fluorescein assay. The NAv-modified nanoparticles then were used for the binding of biotinylated anti-CD3 antibodies by avidin-biotin-complex formation. A highly effective attachment of the ligand was ascertained by different, indirect methods: immunoblotting and fluorimetry. Therefore, a well-defined nanoparticle system with drug targeting ligand modification was established that holds promise for further effective preclinical testing.

In Vitro and in Vivo Evaluation of Hydrophilic Dendronized Linear Polymers

Rigid-rod dendronized linear polymers consisting of a poly(4-hydroxystyrene) backbone and fourth-generation polyester dendrons were evaluated in vitro and in vivo to determine their suitability as drug delivery vectors. Cytotoxicity assays indicated that the polymers were well tolerated by cells in vitro. Biodistribution studies of the polymers in both nontumored and tumored mice revealed that as for random coil linear polymers, renal clearance was a function of polymer size, with significant urinary excretion observed for a 67 kDa dendronized polymer. High accumulation in organs of the reticuloendothelial system was exhibited by a dendronized polymer with a very high molecular weight (M(n) = 1740 kDa), but was not as significant for smaller polymers with M(n) = 67 kDa and M(n) = 251 kDa. The rank order for tumor accumulation of the polymers on a percent injected dose per gram tumor basis was 251 kDa approximately 1740 kDa > 67 kDa. These data will help guide the selection of highly functionalizable rigid-rod dendronized polymers with pharmacokinetic properties appropriate for use as drug carriers.

Polymer design and incorporation methods for polymeric micelle carrier system containing water-insoluble anti-cancer agent camptothecin

A water-insoluble anti-cancer agent, camptothecin (CPT) was incorporated to a polymeric micelle carrier system forming from poly(ethylene glycol)-poly(aspartate) block copolymers. Incorporation efficiency and stability were analyzed in correlation with chemical structures of the inner core-forming hydrophobic blocks as well as with incorporation methods. Among three incorporation methods (dialysis, emulsion and evaporation methods), an evaporation method brought about much higher CPT yields with less aggregation than the other two methods. By the evaporation method, CPT was incorporated to polymeric micelles in considerably high yields and with high stability using block copolymers possessing high contents of benzyl and methylnaphtyl ester groups as hydrophobic moieties. This indicates importance of molecular design of the hydrophobic block chain to obtain targeting using polymeric micelle carriers as well as importance of the drug incorporation method.

Amphiphilic hydrogel nanoparticles. Preparation, characterization, and preliminary assessment as new colloidal drug carriers

Inverse emulsion photopolymerization of acrylated poly(ethylene glycol)-bl-poly(propylene glycol)-bl-poly(ethylene glycol) and poly(ethylene glycol) was successfully employed to prepare stable, cross-linked, amphiphilic nanoparticles. Even at low emulsifier concentrations (2%) and high water-to-hexane weight ratios (35/65), the stability of the inverse emulsion allowed for the formation of well-defined colloidal material. Inverse emulsion characteristics and polymerization conditions could be controlled to vary the size of the nanoparticles between 50 and 500 nm. The presence of hydrophobic nanodomains within these otherwise hydrophilic nanoparticles was verified by using pyrene as a microenvironmentally sensitive probe. The hydrophobic poly(propylene glycol)-rich domains appear to be suitable for incorporation of hydrophobic drugs, encapsulating Doxorubicin up to 9.8% (w/w). We believe that the complex nano-architecture of these materials makes them a potentially interesting colloidal drug delivery carrier system and that the method should be useful for a number of amphiphilic macromolecular precursors.

Future directions of liposome- and immunoliposome-based cancer therapeutics

Nanoscale drug delivery systems including liposomes, polymers, and other nanoparticles provide potential solutions for improved cancer therapeutics. Of these drug delivery systems, liposome-based agents, particularly liposomal anthracyclines, have had the greatest impact in oncology to date. Current liposomal drugs evolved from a number of design strategies for improved biodistribution over free drugs. Reticuloendothelial system-targeted formulations significantly reduce systemic exposure to high peak levels of free drug, but do not facilitate targeting to tumors. Passive or physiologic targeting of drugs to tumors is achievable using long-circulating liposomes, including pure lipid systems as well as surface-modified formulations designed to resist recognition and uptake by reticuloendothelial system cells. The latter, represented by pegylated or STEALTH liposomes, circulate for days as stable constructs and slowly extravasate in neoangiogenic vessels in tumors, providing a degree of passive targeting to tumor tissue. Future liposome therapeutics are building on these validated designs as well as on pharmacologic insights into their mechanisms of delivery. For example, camptothecin analogues, anti-angiogenesis agents, and antisense oligonucleotides each represent rational candidates for delivery in highly stabilized and long-circulating liposomes. For such agents, pegylated liposome delivery offers improved chemical stability of encapsulated drug, enhanced accumulation in tumors, and prolonged drug exposure. True molecular targeting can be achieved using liposomes linked to ligands such as monoclonal antibody fragments directed against cancer-associated antigens. Immunoliposomes combine antibody-mediated tumor recognition with liposomal delivery and, when designed for target cell internalization, provide intracellular drug release. Recent advances in immunoliposome design include rapid selection of phage antibody-derived scFv for targeting, and methods for conjugation of ligands to existing US Food and Drug Administration-approved liposomal drugs such as pegylated liposomal doxorubicin (Doxil/Caelxy [PLD]). An immunoliposome consisting of novel anti-HER2 scFv F5 conjugated to PLD, currently in development, selectively binds to and internalizes in HER2-overexpressing tumor cells. The modular organization of immunoliposome technology enables a combinatorial approach in which a repertoire of monoclonal antibody fragments can be used in conjunction with a series of liposomal drugs to yield a new generation of molecularly targeted agents.

Paclitaxel poliglumex (XYOTAX; CT-2103): an intracellularly targeted taxane

Paclitaxel poliglumex (CT-2103; XYOTAX) is an innovative macromolecular taxane designed to increase the therapeutic index of paclitaxel. This large macromolecule conjugate of paclitaxel and poly-L-glutamic acid accumulates in tumor tissues by taking advantage of the enhanced permeability of tumor vasculature and lack of lymphatic drainage. Paclitaxel poliglumex prolongs exposure to active drug and minimizes systemic exposure. Preclinical studies in animal tumor models demonstrate enhanced safety and efficacy relative to paclitaxel when administered as a single agent or in conjunction with radiation. Clinical pilot studies with paclitaxel poliglumex showed improved outcomes compared to standard taxanes and allowed a more convenient administration schedule. Human pharmacokinetic data are consistent with prolonged tumor exposure to active drug and a limited systemic exposure. Based on these results, three ongoing randomized phase III trials were initiated to test the efficacy of paclitaxel poliglumex in patients with advanced non-small cell lung carcinoma.

A Polymeric Nanoparticle Consisting of mPEG-PLA-Toco and PLMA-COONa as a Drug Carrier: Improvements in Cellular Uptake and Biodistribution

PURPOSE

To evaluate a new polymeric nanoparticulate drug delivery formulation that consists of two components: i) an amphiphilic diblock copolymer having tocopherol moiety at the end of the hydrophobic block in which the hydrophobic tocopherol moiety increases stability of hydrophobic core of the nanoparticle in aqueous medium; and ii) a biodegradable copolyester having carboxylate end group that is capable of forming ionic complex with positively charged compounds such as doxorubicin.

METHODS

A doxourubicin-loaded polymeric nanoparticle (Dox-PNP) was prepared by solvent evaporation method. The entrapment efficiency, size distribution, and in vitro release profile at various pH conditions were characterized. In vitro cellular uptake was investigated by confocal microscopy, flow cytometry, and MTT assay using drug-sensitive and drug-resistant cell lines. Pharmacokinetics and biodistribution were evaluated in rats and tumor-bearing mice.

RESULTS

Doxorubicin (Dox) was efficiently loaded into the PNP (higher than 95% of entrapment efficiency), and the diameter of Dox-PNP was in the range 20-25 nm with a narrow size distribution. In Vitro study showed that Dox-PNP exhibited higher cellular uptake into both human breast cancer cell (MCF-7) and human uterine cancer cell (MES-SA) than free doxorubicin solution (Free-Dox), especially into drug-resistant cells (MCF-7/ADR and MES-SA/Dx-5). In pharmacokinetics and tissue distribution study, the bioavailability of Dox-PNP calculated from the area under the blood concentration-time curve (AUC) was 69.8 times higher than that of Free-Dox in rats, and Dox-PNP exhibited 2 times higher bioavailability in tumor tissue of tumor-bearing mice.

CONCLUSIONS

Dox-PNP exhibited enhanced cellular uptake of the drug. In the cytotoxic activity study, this improved cellular uptake was proved to be more advantageous in drug-resistant cell. Dox-PNP exhibited much higher bioavailability in blood plasma and more drug accumulation in tumor tissue than conventional doxorubicin formulation. The results of this study suggest that the PNP system is an advantageous carrier for drug delivery.

Biological Evaluation of Polyester Dendrimer: Poly(ethylene oxide) “Bow-Tie” Hybrids with Tunable Molecular Weight and Architecture

High molecular weight (MW) polymers have shown promise in terms of improving the properties and the efficacy of low MW therapeutics. However, new systems that are highly biocompatible, are biodegradable, have well-defined MW, and have multiple functional groups for drug attachment are still needed. The biological evaluation of a library of eight polyester dendrimer-poly(ethylene oxide) (PEO) bow-tie hybrids is described here. The group of evaluated polymers was designed to include a range of MWs (from 20000 to 160000) and architectures with the number of PEO arms ranging from two to eight. In vitro experiments revealed that the polymers were nontoxic to cells and were degraded to lower MW species at pH 7.4 and pH 5.0. Biodistribution studies with (125)I-radiolabeled polymers showed that the high MW carriers (>40000) exhibited long circulation half-lives. Comparison of the renal clearances for the four-arm versus eight-arm polymers indicated that the more branched polymers were excreted more slowly into the urine, a result attributed to their decreased flexibility. Due to their essentially linear architecture that does not provide for good isolation of the iodinated phenolic moieties, the polymers with "two arms" were rapidly taken up by the liver. The biodistributions of two long-circulating high MW polymers in mice bearing subcutaneous B16F10 tumors were evaluated, and high levels of tumor accumulation were observed. These new carriers are therefore promising for applications in drug delivery and are also useful for improving our understanding of the effect of polymer architecture on pharmacokinetic properties.

Phase I and Pharmacokinetic Study of DE-310 in Patients with Advanced Solid Tumors

Purpose: To assess the maximum-tolerated dose, toxicity, and pharmacokinetics of DE-310, a macromolecular prodrug of the topoisomerase I inhibitor exatecan (DX-8951f). in patients with advanced solid tumors.

Experimental Design: Patients received DE-310 as a 3-hour infusion once every 2 weeks (dose, 1.0-2.0 mg/m2) or once every 6 weeks (dose, 6.0-9.0 mg/m2). Because pharmacokinetics revealed a drug terminal half-life exceeding the 2 weeks administration interval, the protocol was amended to a 6-week interval between administrations also based on available information from a parallel trial using an every 4 weeks schedule. Conjugated DX-8951 (the carrier-linked molecule), and the metabolites DX-8951 and glycyl-DX-8951 were assayed in various matrices up to 35 days post first and second dose.

Results: Twenty-seven patients were enrolled into the study and received a total of 86 administrations. Neutropenia and grade 3 thrombocytopenia, and grade 3 hepatotoxicity with veno-occlusive disease, were dose-limiting toxicities. Other hematologic and nonhematologic toxicities were mild to moderate and reversible. The apparent half-life of conjugated DX-8951, glycyl-DX-8951, and DX-8951 was 13 days. The area under the curve ratio for conjugated DX-8951 to DX-8951 was 600. No drug concentration was detectable in erythrocytes, skin, and saliva, although low levels of glycyl-DX-8951 and DX-8951 were detectable in tumor biopsies. One patient with metastatic adenocarcinoma of unknown primary achieved a histologically proven complete remission. One confirmed partial remission was observed in a patient with metastatic pancreatic cancer and disease stabilization was noted in 14 additional patients.

Conclusions: The recommended phase II dose of DE-310 is 7.5 mg/m2 given once every 6 weeks. The active moiety DX-8951 is released slowly from DE-310 and over an extended period, achieving the desired prolonged exposure to this topoisomerase I inhibitor.

Tumor efficacy and biodistribution of linear polyethylenimine-cholesterol/DNA complexes

Non-viral polymer/pDNA complexes were formed using linear polyethylenimine (LPEI) Mw 25 k conjugated to cholesterol in a T-shaped geometry (LPC-T) and pDNA encoding murine interleukin-12 (pmIL-12e). These complexes were subsequently injected weekly into BALB/c mice intravenously and locally for the treatment of murine renal cell adenocarcinoma (Renca) induced pulmonary metastases and subcutaneous (SC) Renca tumors, respectively. At the cessation of the pulmonary metastases study, the number of pulmonary metastases was significantly less (p < 0.001) with systemic injections of LPC-T/pmIL-12e formulations than with pmIL-12e alone or pmIL-12e complexed with LPEI, branched polyethylenimine (BPEI) Mw 25 k, or an LPEI/pEGFP control. In addition, biodistribution studies showed increased pulmonary levels of both the LPC-T carrier and pmIL-12e vector up to 3 hr after systemic injection of the LPC-T/pmIL-12e complexes into mice carrying pulmonary metastases. Furthermore, mice systemically treated with LPC-T/pmIL-12e showed a near linear profile in weight gain in the course of the pulmonary metastases study that suggests increased biocompatibility. Finally, due to favorable characteristics in vitro, LPC-T was also used for local (peritumoral) injection of SC Renca tumors. Tumor stasis and slight tumor regression were seen only with the LPC-T/pmIL-12e treated mice compared to BPEI/pmIL-12e, LPEI/pmIL-12e, and naked pmIL-12e controls. Thus, it was concluded that LPC-T is an effective carrier for passive targeting of the pulmonary tissue, treatment of Renca-induced pulmonary metastases, and local administration of Renca cell SC tumors.

Validation study of a method for assaying DE-310, a macromolecular carrier conjugate containing an anti-tumor camptothecin derivative, and the free drug in tumor tissue by high performance liquid chromatography/atmospheric pressure chemical ionization tandem mass spectrometry

DE-310 is a macromolecular carrier conjugate containing an anti-tumor camptothecin derivative, DX-8951, which is conjugated to a water-soluble polymer via a peptide spacer. Assay methods have been developed for the determination of a polymer-bonded DX-8951 conjugate, DX-8951, and Glycyl-DX-8951 concentrations in murine Meth A tumor tissue. Free DX-8951 and Glycyl-DX-8951 were extracted from tumor tissue homogenates by protein precipitation and analyzed by LC/MS/MS (method I). Conjugated DX-8951 was isolated by solid-phase extraction after digestion with a thermolysin. The productive phenylalanyl-glycyl-DX-8951 was analyzed by LC/MS/MS (method II). The lower limits of quantitation of DX-8951, Glycyl-DX-8951, and conjugated DX-8951 were 1.36, 1.34 and 73.7 ng/g (as DX-8951 equivalent). These two methods showed satisfactory sensitivity, precision and accuracy. To study the pharmacokinetics of DE-310, it would be of great help to assay the polymer-bonded DX-8951 and its released drugs in tumor tissue.

Targeting tumor angiogenic vasculature using polymer–RGD conjugates

Sites of neovascular angiogenesis are important chemotherapy targets. In this study, the synthesis, characterization, in-vivo imaging and biodistribution of a technetium-99m labeled, water-soluble, N-(2-hydroxypropyl) methacrylamide (HPMA) copolymer carrying doubly cyclized Arg-Gly-Asp motifs (HPMA copolymer-RGD4C conjugate) are reported. In vitro endothelial cell adhesion assays indicated that HPMA copolymer-RGD4C conjugates inhibited alphaVbeta3-mediated endothelial cell adhesion while HPMA copolymer Arg-Gly-Glu control conjugates (HPMA copolymer-RGE4C conjugate) and hydrolyzed HPMA copolymer precursor (HPMA copolymer) showed no activity. The scintigraphic images of prostate tumor bearing SCID mice obtained 24 h post-i.v. injection indicated greater tumor localization of HPMA copolymer-RGD4C conjugate than the control, HPMA copolymer-RGE4C conjugate. The 24-h necropsy radioactivity data showed that HPMA copolymer-RGD4C conjugate had significantly higher (p<0.001) tumor localization compared to HPMA copolymer-RGE4C conjugate and HPMA copolymer. Also, HPMA copolymer-RGD4C conjugates had sustained tumor retention over 72 h and reasonably efficient clearance from the background organs. These results suggest that specific tumor angiogenesis targeting is possible with HPMA copolymer-RGD4C conjugates. This construct provides a foundation that should support targeted delivery of radionuclides and drugs to solid tumors for diagnostic and therapeutic applications.

High-density doxorubicin-conjugated polymeric nanoparticles via ring-opening metathesis polymerization

High-density doxorubicin-conjugated polymeric nanoparticles are prepared via ring-opening metathesis polymerization and sustained release of nearly 50% of the anticancer agent is observed after 24 h in mildly acidic aqueous solution.

Phase I clinical trial and pharmacokinetic evaluation of NK911, a micelle-encapsulated doxorubicin

NK911 is a novel supramolecular nanocarrier designed for the enhanced delivery of doxorubicin (DXR) and is one of the successful polymer micelle systems to exhibit an efficient accumulation in solid tumours in mice. The purpose of this study was to define the maximum-tolerated dose (MTD) and dose-limiting toxicities (DLTs) of NK911 and to evaluate its pharmacokinetic profile in man. NK911 was given intravenously to patients with solid tumours every 3 weeks using an infusion pump at a rate of 10 mg DXR equivalent min⁻¹. The starting dose was 6 mg DXR equivalent m⁻², and the dose was escalated according to the accelerated titration method. A total of 23 patients participated in this study. Neutropenia was the predominant haematological toxicity, and grade 3 or 4 neutropenia was observed at doses of 50 and 67 mg m⁻². Common nonhaematological toxicities were mild alopecia, stomatitis, and anorexia. In the dose identification part of the study, DLTs were observed at a dose of 67 mg m⁻² (grade 4 neutropenia lasting more than 5 days). Thus, this dosage level was determined to be the MTD. Infusion-related reactions were not observed in any cases. The C_5 min and area under the concentration curve parameters of NK911 exhibited dose-dependent characteristics. Among the 23 patients, a partial response was obtained in one patient with metastatic pancreatic cancer. NK911 was well tolerated and produced only moderate nausea and vomiting at myelosuppressive dosages. The recommended phase II dose was determined to be 50 mg m⁻² every 3 weeks.