Drug delivery and transport to solid tumors

The natural frequency of nonlinear oscillation of ultrasound contrast agents in microvessels

Ultrasound contrast agents (UCAs) are under intensive investigation for their applications in physiological and molecular imaging and drug delivery. Prediction of the natural frequency of the oscillation of UCAs in microvessels has drawn increasing attention. To our knowledge, the existing models to predict the natural frequency of oscillation of UCAs in microvessels all apply the linear approximation and treat the blood vessel wall as a rigid boundary. In the potential applications of ultrasound imaging drug and gene delivery, the compliance of small vessels may play an important role in the bubble's oscillation. The goal of this work is to provide a lumped-parameter model to study the natural frequency of nonlinear oscillation of UCAs in microvessels. Three types of the blood vessel conditions have been considered: i.e., rigid vessels, normal compliable vessels and vessels with increasing stiffness that could correspond to tumor vasculature. The corresponding bubble oscillation frequencies in vessels with a radius less than 100 microm are examined in detail. When a bubble with a radius of 4 microm is confined in a compliable vessel (inner radius 5 microm and length 100 microm), the natural frequency of bubble oscillation increases by a factor of 1.7 compared with a bubble in an unbounded field. The natural frequency of oscillation of a bubble in a compliable vessel increases with decreasing vessel size while decreasing with increasing values of vessel rigidity. This model suggests that contrast agent size, blood vessel size distribution and the type of vasculature should comprehensively be considered for choosing the transmitted frequency in ultrasound contrast imaging and drug delivery.

Improving Penetration in Tumors With Nanoassemblies of Phospholipids and Doxorubicin

BACKGROUND

Drug delivery and penetration into neoplastic cells distant from tumor vessels is critical for the effectiveness of solid tumor chemotherapy. We hypothesized that 10- to 20-nm nanoassemblies of phospholipids containing doxorubicin would improve the drug's penetration, accumulation, and antitumor activity.

METHODS

Doxorubicin was incorporated into polyethylene glycol-phosphatidylethanolamine (PEG-PE) block copolymer micelles by a self-assembly procedure to form nanoassemblies of doxorubicin and PEG-PE. In vitro cytotoxicity of micelle-encapsulated doxorubicin (M-Dox) against A549 human non-small-cell lung carcinoma cells was examined using the methylthiazoletetrazolium assay, and confocal microscopy, total internal reflection fluorescence microscopy, and flow cytometry were used to examine intracellular distribution and the cellular uptake mechanism. C57Bl/6 mice (n = 10-40 per group) bearing subcutaneous or pulmonary Lewis lung carcinoma (LLC) tumors were treated with M-Dox or free doxorubicin, and tumor growth, doxorubicin pharmacokinetics, and mortality were compared. Toxicity was analyzed in tumor-free mice. All statistical tests were two-sided.

RESULTS

Encapsulation of doxorubicin in PEG-PE micelles increased its internalization by A549 cells into lysosomes and enhanced cytotoxicity. Drug-encapsulated doxorubicin was more effective in inhibiting tumor growth in the subcutaneous LLC tumor model (mean tumor volumes in mice treated with 5 mg/kg M-Dox = 1126 mm3 and in control mice = 3693 mm3, difference = 2567 mm3, 95% confidence interval [CI] = 2190 to 2943 mm3, P<.001) than free doxorubicin (mean tumor volumes in doxorubicin-treated mice = 3021 mm3 and in control mice = 3693 mm3, difference = 672 mm3, 95% CI = 296 to 1049 mm3, P = .0332, Wilcoxon signed rank test). M-Dox treatment prolonged survival in both mouse models and reduced metastases in the pulmonary model; it also reduced toxicity.

CONCLUSIONS

We have developed a novel PEG-PE-based nanocarrier of doxorubicin that increased cytotoxicity in vitro and enhanced antitumor activity in vivo with low systemic toxicity. This drug packaging technology may provide a new strategy for design of cancer therapies.

Novel thermosensitive polymeric micelles for docetaxel delivery

Targeted delivery of antitumor drugs triggered by hyperthermia has significant advantages in clinical applications, since it is easy to implement and side effects are reduced. To release drugs site-specifically upon local heating often requires the drugs to be loaded into a thermosensitive polymer matrix with a low critical solution temperature (LCST) between 37 and 42 degrees C. However, the LCSTs of most thermosensitive materials were below 37 degrees C, which limits their application in clinic because they would precipitate once injected into human body and lost thermal targeting function. Herein, we prepared a novel thermosensitive copolymer (poly(N-isopropylacrylamide-co-acrylamide)-b-poly (DL-lactide)) that exhibits no obvious physical change up to 41 degrees C when heated. Docetaxel loaded micelles made of such thermosensitive polymer were prepared by dialysis method and the maximum loading content was found to be up to 27%. The physical properties, such as structure, morphology, and size distribution of the micelles with and without docetaxel were investigated by NMR, X-ray diffraction, dynamic light scattering, atomic force microscopy, etc. The efficacy of this drug delivery system was also evaluated by examining the proliferation inhibiting activity against different cell lines in vitro. After hyperthermia, the cytotoxicity of docetaxel-loaded micelles increased prominently. Our results demonstrated that this copolymer could be an ideal candidate for thermal targeted antitumor drug delivery.

Poly(ethylene glycol)-modified thiolated gelatin nanoparticles for glutathione-responsive intracellular DNA delivery

Poly(ethylene glycol) (PEG)-modified thiolated gelatin (PEG-SHGel) anoparticles were developed as a long-circulating passively targeted delivery system that responds to intracellular glutathione concentrations to enhance DNA delivery and transfection. Reporter plasmid expressing enhanced green fluorescent protein (EGFP-N1) was encapsulated in the nanoparticles. DNA-containing gelatin (Gel) and thiolated gelatin (SHGel) nanoparticles were found to have a size range of 220 to 250 nm, whereas surface modification with PEG resulted in particles with a slightly larger size range of 310 to 350 nm. PEG modification was confirmed by electron spectroscopy for chemical analysis (ESCA), where an increase in the ether peak intensities of the C1s spectra corresponds to the surface presence of ethylene oxide residues. In addition, the PEG-SHGel nanoparticles released encapsulate plasmid DNA in response to varying concentrations of glutathione (up to 5.0 mM GSH in phosphate-buffered saline, or PBS). The stability of the encapsulated DNA was confirmed by agarose gel electrophoresis. Finally, from the qualitative and quantitative results of in vitro transfection studies in murine fibroblast cells (NIH3T3), PEG-Gel and PEG-SHGel nanoparticles afforded the highest transfection efficiency of the reporter plasmid. The results of these studies show that PEG-modified thiolated gelatin nanoparticles could serve as a very efficient nanoparticulate vector for systemic DNA delivery to solid tumors where the cells are known to have significantly higher intracellular GSH concentrations.

Tumor Priming Enhances Delivery and Efficacy of Nanomedicines

We have shown that high epithelial cell density is a major barrier to the distribution of protein-bound drugs in solid tumors, and tumor priming (expansion of interstitial space using an apoptosis-inducing pretreatment) can promote drug delivery. This study evaluated the optimal conditions of paclitaxel tumor priming (time window, particle size) and its effects on the delivery and efficacy of nanomedicines. Paclitaxel tumor priming was applied to mice bearing human xenograft tumors. The kinetics of paclitaxel-induced apoptosis was evaluated to identify the time window of tumor priming. The effects of tumor priming on the tumor delivery and interstitial dispersion of fluorescence-labeled nanoparticles of various sizes, the perfusion of tumor and normal tissues, the delivery of doxorubicin HCl liposomes to tumor and host tissues, and the antitumor activity and host toxicity were studied. Tumor priming by a single i.v. injection of paclitaxel induced apoptosis, expanded the interstitial space, vessel diameter and blood-perfused area, and promoted the delivery and interstitial dispersion of nanoparticles (100- and 200-nm diameter, administered 48 h after paclitaxel) in a tumor-selective manner. Tumor priming also enhanced the tumor delivery and antitumor activity of doxorubicin HCl liposomes (85 nm) without affecting the delivery to noncancerous host tissues or enhancing host toxicity. Tumor priming represents a potentially useful means to promote tumor-selective delivery and efficacy of nanomedicines. The current study will have significant impact on enhancing delivery and efficacy of nanomedicines and dosing regimen optimization of combination chemotherapy in the clinical setting.

Poly(ethylene glycol)-modified nanocarriers for tumor-targeted and intracellular delivery

The success of anti-cancer therapies largely depends on the ability of the therapeutics to reach their designated cellular and intracellular target sites, while minimizing accumulation and action at non-specific sites. Surface modification of nanoparticulate carriers with poly(ethylene glycol) (PEG)/poly(ethylene oxide) (PEO) has emerged as a strategy to enhance solubility of hydrophobic drugs, prolong circulation time, minimize non-specific uptake, and allow for specific tumor-targeting through the enhanced permeability and retention effect. Furthermore, PEG/PEO modification has emerged as a platform for incorporation of active targeting ligands, thereby providing the drug and gene carriers with specific tumor-targeting properties through a flexible tether. This review focuses on the recent developments surrounding such PEG/PEO-surface modification of polymeric nanocarriers to promote tumor-targeting capabilities, thereby enhancing efficacy of anti-cancer therapeutic strategies.

Antiangiogenic gene therapy with systemically administered sFlt-1 plasmid DNA in engineered gelatin-based nanovectors

This study examined the potential of engineered gelatin-based nanoparticulate vectors for systemic delivery of therapeutic genes to human solid tumor xenografts in vivo. Plasmid DNA encoding for the soluble form of the extracellular domain of vascular endothelial growth factor receptor-1 (VEGF-R1 or sFlt-1) was encapsulated in the control and poly(ethylene glycol) (PEG)-modified gelatin-based nanoparticles. When the plasmid DNA was delivered in PEG-modified thiolated gelatin nanoparticles, highest levels of sFlt-1 expression was observed in vitro in MDA-MB-435 human breast adenocarcinoma cell line. In addition, upon intravenous administration in female Nu/Nu mice bearing orthotopic MDA-MB-435 breast adenocarcinoma xenografts, efficient in vivo expression of sFlt-1 plasmid DNA was confirmed quantitatively by enzyme-linked immunosorbent assay and qualitatively by Western blot analysis. The expressed sFlt-1 was therapeutically active as shown by suppression of tumor growth and microvessel density measurements. The results of this study show that PEG-modified gelatin-based nanovectors can serve as a safe and effective systemically administered gene delivery vehicle for solid tumor.

Biodistribution and Pharmacokinetic Analysis of Long-Circulating Thiolated Gelatin Nanoparticles Following Systemic Administration in Breast Cancer-Bearing Mice

The objective of the present study was to modify thiolated gelatin nanoparticles with poly(ethylene glycol) (PEG) chains and examine their long circulating and tumor-targeting properties in vivo in an orthotopic a human breast adenocarcinoma xenograft model. The crosslinked nanoparticle systems were characterized to have a size of 150-250 nm with rapid payload release properties in a highly reducing environment. Upon PEG modification, the nanoparticle size increased to 300-350 nm in diameter. The presence of PEG chains on the surface was confirmed by characterization with electron spectroscopy for chemical analysis. The in vivo long-circulating potential, biodistribution and passive tumor targeting of the controls, and PEG-modified thiolated gelatin nanoparticles were evaluated by injecting indium-111 (111In)-labeled nanoparticles into breast tumor (MDA-MB-435)-bearing nude mice. Upon modification with PEG, the nanoparticles were found to have longer circulation times, with the plasma and tumor half-lives of 15.3 and 37.8 h, respectively. The results also showed preferential localization of thiolated nanoparticles in the tumor mass. The resulting nanoparticulate systems with long circulation properties could be used to target encapsulated drugs and genes to tumors passively by utilizing the enhanced permeability and retention effect of the tumor vasculature.

Effect of radiotherapy and hyperthermia on the tumor accumulation of HPMA copolymer-based drug delivery systems

Copolymers of N-(2-hydroxypropyl)methacrylamide (HPMA) are prototypic and well-characterized polymeric drug carriers that have been broadly implemented in the delivery of anticancer therapeutics. In an attempt to improve the tumor accumulation of HPMA copolymer-based drug delivery systems, their in vivo application was combined with radiotherapy and hyperthermia. As the effects of radiotherapy and hyperthermia were considered to depend significantly on the tumor model used, we first analyzed the accumulation of two differently sized HPMA copolymers in three different types of tumors, based on the syngeneic Dunning rat prostate carcinoma model. Subsequently, in these three models, the effects of different doses of radiotherapy and hyperthermia on the tumor accumulation of 31 kDa poly(HPMA), 65 kDa poly(HPMA) and 28 kDa poly(HPMA)-GFLG-doxorubicin were evaluated. It was found that the polymeric drug delivery systems accumulated effectively in all three tumor models. In addition, as opposed to hyperthermia, radiotherapy was found to improve the concentrations of the copolymers independent of the tumor model used. Based on these findings, we conclude that radiotherapy is an effective means for increasing the tumor accumulation of (polymeric) drug delivery systems, and we propose that the combination of carrier-based chemotherapy with radiotherapy holds significant potential for improving the treatment of advanced solid malignancies.

Antibody constructs in cancer therapy

Whereas over 85% of human cancers are solid tumors, of the 8 monoclonal antibodies (mAbs) currently approved for cancer therapy, 25% are directed at solid tumor surface antigens (Ags). This shortfall may be due to barriers to achieving adequate exposure in solid tumors. Advancements in tumor biology, protein engineering, and theoretical modeling of macromolecular transport are currently enabling identification of critical physical properties for antitumor Abs. It is now possible to structurally modify Abs or even replace full Abs with a plethora of Ab constructs. These constructs include Fab and Fab'(2) fragments, scFvs, multivalent scFvs (e.g., diabodies and tribodies), minibodies (e.g., scFv-CH3 dimers), bispecific Abs, and camel variable functional heavy chain domains. The purpose of the article is to provide investigators with a conceptual framework for exploiting the recent scientific advancements. The focus is on 2 properties that govern tumor exposure: 1) physical properties that enable penetration of and retention by tumors, and 2) favorable plasma pharmacokinetics. It is demonstrated that manipulating molecular size, charge, valence, and binding affinity can optimize these properties. These manipulations hold the key to promoting tumor exposure and to ultimately creating successful Ab therapies for solid tumors.

Examination of the distribution of the bioreductive drug AQ4N and its active metabolite AQ4 in solid tumours by imaging matrix-assisted laser desorption/ionisation mass spectrometry

AQ4N (banoxatrone) (1,4-bis-{[2-(dimethylamino-N-oxide)ethyl]amino}-5,8-dihydroxyanthracene-9,10-dione) is an example of a bioreductive prodrug in clinical development. In hypoxic cells AQ4N is reduced to the topoisomerase II inhibitor AQ4 (1,4-bis- {[2-(dimethylamino)ethyl]amino}-5,8-dihydroxyanthracene-9,10-dione). By inhibition of topoisomerase II within these hypoxic areas, AQ4N has been shown to sensitise tumours to existing chemo- and radiotherapy treatments. In this study the distribution of AQ4N and AQ4 in treated H460 human tumour xenografts has been examined by imaging matrix-assisted laser desorption/ionisation mass spectrometry. Images of the distribution of AQ4N and AQ4 have been produced that show little overlap. The distribution of ATP in the tumour xenografts was also studied as an endogenous marker of regions of hypoxia since concentrations of ATP are known to be decreased in these regions. The distribution of ATP was similar to that of AQ4N, i.e. in regions of abundant ATP there was no evidence of conversion of AQ4N into AQ4. This indicates that the cytotoxic metabolite AQ4 is confined to hypoxic regions of the tumour as intended.

Levels and distribution of BCNU in GBM tumors following intratumoral injection of DTI-015 (BCNU-ethanol)

The alkylation products formed by in vitro treatment of DNA with tritium-labeled 1,3-bis(2-chloroethyl)-1-nitrosourea ((3)H-BCNU) were identified and quantified. Twelve adducts were resolved by high-performance liquid chromatography (HPLC). The principal DNA adducts formed by BCNU treatment corresponded to N-7-(2-hydroxyethyl)guanine (N7-HOEtG) (26%), N-7-(2-chloroethyl)guanine (15%), and phosphotriesters (19%). In addition, several minor products were identified as 1,2-(diguan-7-yl)ethane, N-1-(2-hydroxyethyl)-2-deoxyguanosine, 1-(N-1-2-deoxyguanosinyl), 2-(N-3-2-deoxycytidyl)ethane cross-link, and O-6-(2-hydroxyethyl)-2-deoxyguanosine, and individually they represented 1% to 5% of the total alkylation. An HPLC-electrochemical method was applied to quantify the levels of N7-HOEtG in samples treated with BCNU. Treatment of either purified DNA or U87MG cells with various amounts of BCNU produced a linear increase in the amount of N7-HOEtG. These results demonstrated that the levels of N7-HOEtG formed by BCNU treatment could be used as a molecular dosimeter of BCNU treatment dose. We measured the levels of N7-HOEtG in DNA isolated from tumor samples taken from four patients with GBM tumors following stereotactic intratumoral injection with DTI-015 (BCNU-ethanol). The level of N7-HOEtG in these samples ranged from 14.7 to 121.9 micromol N7-HOETG/mol DNA within 1 cm of the site of injection. As the distance from the site of injection increased, the levels of N7-HOEtG in tumor DNA decreased. In two of the samples, the levels of N7-HOEtG were 0.2 to 0.3 micromol N7-HOETG/mol DNA at 3.5 to 3.9 cm from the site of injection, demonstrating significant distribution of BCNU in the tumor. The levels of N7-HOEtG in these tumor samples corresponded to BCNU treatment concentrations of 0.02 to 43.0 mM. These studies demonstrate that stereotactic intratumoral injection of DTI-015 into human GBM tumors produces high concentrations of BCNU up to 2.5 cm from the site of injection in some of the tumors. These observations suggest that intratumoral injection of DTI-015 may be of benefit in the treatment of primary and recurrent GBM tumors.

Stealth PEG-PHDCA niosomes: Effects of Chain Length of PEG and Particle Size on Niosomes Surface Properties, In Vitro Drug Release, Phagocytic Uptake, In Vivo Pharmacokinetics and Antitumor Activity

A series of novel niosomes with the amphiphilic copolymer of poly (methoxy-polyethyleneglycol cyanoacrylate-co-n-hexadecyl cyanoacrylate) (PEG-PHDCA) acted as surface modification materials were prepared and Hydroxycamptothecin (HCPT) was used as a model drug. This work concentrated on the effects of PEG chain length and particle sizes on the niosomes surface properties, in vitro drug release, phagocytic uptake, in vivo pharmacokinetics and antitumor activity. Within the range of PEG Mw from 2000 to 10000, the increasing zeta potential (from -16.08 to -5.25 mv) and thicker fixed aqueous layer (3.82 to 5.78 nm) would facilitate the niosomes' stealth effects, while the reduced PEG chain density (from 0.53 to 0.17 PEG/nm2) and the quickened speed of drug release would diminish the effects. As a result, the PEG5000-PHDCA niosomes had the least phagocytic uptake, the longest half-life of 11.46 h and the best tumor inhibition rate of 97.1%. In the groups different in particle size (PEG5000-PHDCA niosomes from 92.5 to 204.6 nm), the bigger particles could be uptaken by macrophages more quickly, regardless of the changes of other physicochemical parameters. Correspondingly, PEG5000-PHDCA niosomes with particle sizes of 92.5, 144.2, 204.6 nm could extend the half-life of HCPT to 11.46, 6.33, 4.46 h, respectively. At last, the tumor inhibition rate of PEG5000-PHDCA niosomes (92.5 nm) at a dose of 2 mg/kg was five times that of HCPT injection at 4 mg/kg. The stealth effects of the PEG-PHDCA niosomes and the enhanced stability of lactone form of HCPT were accountable for the powerful antitumor effects of niosomes.

Drug penetration in solid tumours

To be most effective anticancer drugs must penetrate tissue efficiently, reaching all the cancer cells that comprise the target population in a concentration sufficient to exert a therapeutic effect. Most research into the resistance of cancers to chemotherapy has concentrated on molecular mechanisms of resistance, whereas the role of limited drug distribution within tumours has been neglected. We summarize the evidence that indicates that the distribution of many anticancer drugs in tumour tissue is incomplete, and we suggest strategies that might be used either to improve drug penetration through tumour tissue or to select compounds based on their abilities to penetrate tissue, thereby increasing the therapeutic index.

Magnetic Targeting of Magnetoliposomes to Solid Tumors with MR Imaging Monitoring in Mice: Feasibility

PURPOSE

To establish the feasibility of magnetoliposome tumor targeting with an extracorporeal magnet.

MATERIALS AND METHODS

Animal experiments were performed in compliance with Institut National de la Santé Et de la Recherche Médicale animal protection guidelines and were approved by local government authorities. Magnetophoresis was used to measure the velocity of magnetoliposomes constituted of polyethylene glycol-lipids and anionic maghemite nanocrystals in a calibrated magnetic field in vitro. For in vivo studies, 38 male Swiss nude mice bearing a PC3 human prostate carcinoma tumor in each flank received an intravenous injection of magnetoliposomes (n = 27), saline (n = 9), or nonencapsulated superparamagnetic particles (n = 2) after a small magnet with a magnetic field of 0.3 T and a field gradient of 11 T/m was fixed to the skin above one tumor. The animals were examined at magnetic resonance (MR) imaging with eight different sequences, iron doses (13 mice), and magnet-application durations (12 mice). Their excised tumors were then stained with Perls Prussian blue and hematoxylin-eosin and were examined histologically. With use of the paired Student t test, signal intensity, tumor surface enhancement, and number of stained cells were compared between the control and magnet-exposed tumors to determine significant differences (P </= .01).

RESULTS

The mean magnetoliposome velocity ranged from 10 to 40 mum/sec when the magnetic field equaled 0.13 T and the field gradient equaled 25 T/m. At T1-weighted three-dimensional spoiled gradient-echo MR imaging in vivo, the tumor exposed to the magnet showed strong negative enhancement, -52%, compared with the -7% enhancement of the other tumor. Maximal enhancement occurred after 3 hours of magnet application. After 24 hours of magnet application, intracapillary iron particle accumulation was observed in the targeted tumors only.

CONCLUSION

Magnetic targeting of sterically stabilized magnetoliposomes after they are intravenously injected is feasible in vivo.

Multiphase imaging of gas flow in a nanoporous material using remote-detection NMR

Pore structure and connectivity determine how microstructured materials perform in applications such as catalysis, fluid storage and transport, filtering or as reactors. We report a model study on silica aerogel using a time-of-flight magnetic resonance imaging technique to characterize the flow field and explain the effects of heterogeneities in the pore structure on gas flow and dispersion with 129Xe as the gas-phase sensor. The observed chemical shift allows the separate visualization of unrestricted xenon and xenon confined in the pores of the aerogel. The asymmetrical nature of the dispersion pattern alludes to the existence of a stationary and a flow regime in the aerogel. An exchange time constant is determined to characterize the gas transfer between them. As a general methodology, this technique provides insights into the dynamics of flow in porous media where several phases or chemical species may be present.

Targeting CK2 for cancer therapy

Protein kinase CK2 is a highly ubiquitous and conserved protein serine/threonine kinase that has been found to be involved not only in cell growth and proliferation, but also in suppression of apoptosis. CK2 is capable of dynamic intracellular shuttling in response to a variety of signals. It is localized in both the nucleus and cytoplasm in normal cells, but is particularly predominant in the nuclear compartment in cancer cells. CK2 has been found to be uniformly dysregulated in all the cancers that have been examined. Downregulation of CK2 by chemical or molecular methods promotes apoptosis in cells. We have shown that antisense CK2alpha is particularly potent in inducing apoptosis in cancer cells in culture as well as in xenograft models of cancer such as prostate cancer and squamous cell carcinoma of head and neck. The antisense CK2alpha oligodeoxynucleotide (ODN) mediates tumor cell death in a dose- and time-dependent manner such that at an appropriate concentration of the antisense, a complete resolution of the xenograft tumor is observed. Interestingly, normal and benign cells (in culture as well as in vivo) demonstrate a relative resistance to the antisense CK2alpha ODN treatment, which raises the possibility of a significant therapeutic window for this therapy. Further, novel approaches such as the delivery of antisense CK2alpha ODN encapsulated in sub-50-nm tenascin nanocapsules have become available for its targeting specifically in cancer cells. Our studies minimize generally held concerns regarding suitability of CK2 as a target for cancer therapy and provide the first encouraging results for potential future application of this approach for cancer therapy.

Synergistic antitumor activity of cisplatin, paclitaxel, and gemcitabine with tumor vasculature-targeted tumor necrosis factor-alpha

PURPOSE

Subnanogram doses of NGR-tumor necrosis factor (TNF), a TNF-alpha derivative able to target tumor neovessels, can enhance the antitumor activity of doxorubicin and melphalan in murine models. We have examined the antitumor activity of NGR-TNF in combination with various chemotherapeutic drugs acting via different mechanisms, including, besides doxorubicin and melphalan, cisplatin, paclitaxel, and gemcitabine.

EXPERIMENTAL DESIGN

Chemotherapeutic drugs were tested alone and in combination with NGR-TNF (0.1 ng) in murine lymphoma, fibrosarcoma, and mammary adenocarcinoma models. Different administration schedules have been tested and the effects on tumor growth, animal weight, tumor perfusion, and cell cytotoxicity have been investigated.

RESULTS

Pretreatment with NGR-TNF enhanced the response to all these drugs although to a different extent. The increased efficacy was not accompanied by increased toxicity at least as judged from the loss of animal weight. The synergistic effect was transient, maximal synergism being observed with a 2-hour delay between NGR-TNF and drug administrations in all models and with all drugs tested. NGR-TNF did not increase the in vitro cytotoxicity of chemotherapeutic drugs against tumor cells, suggesting that the in vivo synergism depends on NGR-TNF effects on host cells rather than on tumor cells.

CONCLUSIONS

Targeted delivery of low doses of NGR-TNF to the tumor vasculature can increase the efficacy of various drugs acting via different mechanisms. Optimal administration schedule requires 2 hours of pretreatment with NGR-TNF independently from the mechanism of drug cytotoxicity. This work could provide important information for designing clinical studies with NGR-TNF in combination with chemotherapeutic drugs.

Formes galéniques nouvelles en cancérologie

Despite recent emergence of novel therapeutic agents the major progress achieved in cancer treatments results from conventional drugs used for cytotoxic or hormone therapy. Over the past 20 years, a more rational and more pharmacological-based approach to chemotherapy has led to major successes. One of the most promising avenues of research is to improve the pharmacokinetic properties of well-known anticancer drugs (bioavailability, distribution, targeting, drug carriers) by modifications of their formulations (new drug delivery systems). As an example, new pharmaceutical forms of analogs of LH-RH, (microparticles or implants) permitting sustained release of the drug for months, are now largely used in the routine chemotherapy for prostate cancers. Improvement of the oral bioavailabilty of drugs previously administered only by the parenteral route is simplifying treatment protocols. Parenteral delivery of doxorubicine entrapped in liposomes (pegylated liposomes) decreases the cardiotoxicity and increases the half-live of this drug widely used in the treatment of breast carcinomas. Molecular targeting using immunocarriers such as immunoliposomes is also a very strong field of research.

Growth inhibition, drug load, and degradation studies of gelatin/methotrexate conjugates

Macromolecular gelatin-methotrexate conjugates have potential therapeutic advantages over the free drug. Conjugates with MTX:gelatin molar ratios (MR) ranging from 1:1 to 27:1 were examined for cell growth inhibition, stability, degradation, and methotrexate (MTX) release. Conjugate growth inhibition was less than that of free MTX whose IC(50) value of 1.3 x 10(-8) M was about 10-fold less. Cell uptake of fluorescein labeled gelatin (145 kD) was observed by 24-30 h. Higher MR conjugates produced less growth inhibition, measurably greater stability at pH 7.4 based on MTX release, and had less gelatin degradation in the conjugate by the lysosomal enzyme Cathepsin B (Cat B) compared to low MR conjugates. Cat B conjugate degradation was greater at the in vitro lysosomal pH of 4.8 than the intra-tumor pH of 6.5. The presence of Cat B did not meaningfully affect MTX release, but less MTX was released at pH 4.8 than pH 6.5. The maximum MTX release was a relatively low 7% after 72 h at pH 6.5 for the low MR conjugate. Low molecular weight conjugate fragments were also produced and were also influenced by pH and MR. Reduced growth inhibition by high MR conjugates may be due to a hindered enzymatic degradation in the lysosomes. A strong peptide conjugate bond at lysosomal pH and a 24-30 h delayed gelatin uptake may contribute to reduced growth inhibition of the conjugate compared to free MTX. MTX release under these in vitro conditions occurs by aqueous hydrolysis, not by Cat B cleavage of the conjugate bond.

Engineering lipid vesicles of enhanced intratumoral transport capabilities: correlating liposome characteristics with penetration into human prostate tumor spheroids

Liposomes have been widely used delivery systems, particularly relevant to the development of cancer therapeutics. Numerous liposome-based drugs are in the clinic or in clinical trials today against multiple tumor types; however, systematic studies of liposome interactions with solid or metastatic tumor nodules are scarce. This study is describing the in vitro interaction between liposomes and avascular human prostate (LNCaP-LN3) tumor spheroids. The ability of fluorescently labelled liposomal delivery systems of varying physicochemical characteristics to penetrate within multicellular tumor spheroids has been investigated by confocal laser scanning microscopy. A variety of liposome characteristics and experimental parameters were investigated, including lipid bilayer composition, duration of liposome-spheroid interaction, mean liposome size, steric stabilization of liposomes. Electrostatic binding between cationic liposomes and spheroids was very efficient; however, it impeded any significant penetration of the vesicles within deeper layers of the tumor spheroid. Small unilamellar liposomes of neutral surface character did not bind as efficiently but exhibited enhanced penetrative transport capabilities closer to the tumor core. Polymer-coated (sterically stabilised) liposomes exhibited almost no interaction with the spheroid, indicating that their limited diffusion within avascular tissues may be a limiting step for their use against micrometastases. Multicellular tumor spheroids were used as models of solid tumor interstitium relevant to delivery systems able to extravasate from the microcapillaries or as models of prevascularized micrometastases. This study illustrates that interactions between liposomes and other drug delivery systems with multicellular tumor spheroids can offer critically important information with respect to optimizing solid or micrometastatic tumor delivery and targeting strategies.

In vivo tumor transfection mediated by polyplexes based on biodegradable poly(DMAEA)-phosphazene

In recent years, increasing interest is being paid to the design of transfectants based on non-toxic and biodegradable polymers for gene therapy purposes. We recently reported on a novel, biodegradable polymer, poly(2-dimethylamino ethylamino)phosphazene (p(DMAEA)-ppz) for use in non-viral gene delivery. In this study, the biodistribution and in vivo transfection efficiency of polyplexes composed of plasmid DNA and p(DMAEA)-ppz were investigated after intravenous administration in tumor bearing mice. Data were compared with those of polyplexes based on the non-biodegradable polyethylenimine (PEI 22kDa). Both polyplex systems were rapidly cleared from the circulation (<7% ID, at 60 min after administration) and showed considerable disposition in the liver and the lung, all in line with earlier work on cationic polyplex systems. The lung disposition is attributed to aggregates formed by interaction of the polyplexes with blood constituents. Redistribution of the polyplexes from the lung was observed for both polyplex formulations. Importantly, both polyplex systems showed a substantial tumor accumulation of 5% and 8% ID/g for p(DMAEA)-ppz and PEI22 polyplexes, respectively, at 240 min after administration. The tumor disposition of the p(DMAEA)-ppz and PEI22 polyplexes was associated with considerable expression levels of the reporter gene. In contrast to PEI22 polyplexes, p(DMAEA)-ppz polyplexes did not display substantial gene expression in the lung or other organs (organ gene expression<1/100 of tumor gene expression). The observed preferential tumor gene expression mediated by the p(DMAEA)-ppz polyplexes enables the application of this polymer to deliver therapeutic genes to tumors.

Dermatan carriers for neovascular transport targeting, deep tumor penetration and improved therapy

A new approach to functional tumor imaging and deep interstitial penetration of therapeutic agents is to target the upregulated transport activities of neovascular endothelium. Agents are formulated with the anionic glycosaminoglycan, 435-type dermatan sulfate (DS 435, 22.2 kDa), chemically enriched for oligosaccharide sequences that confer high heparin cofactor II binding and correlate with high tumor uptake. A magnetic resonance (MR) imaging agent is prepared as self-assembling, 5-nm nanoparticles of Fe(+3):deferoxamine (Fe:Df) bound by strong ion pairing to DS, which forms the outer molecular surface (Zeta potential -39 mV). On intravenous (i.v.) injection, Fe:Df-DS rapidly (<7 min) and selectively targets and transports at high capacity across the neovascular endothelium of large (2-cm) Dunning prostate R3327 AT1 rat tumors; releases from the abluminal surface, due to reversible binding of its multivalent, low-affinity (K(d) 10(-4) to 10(-5)) oligosaccharide ligands; and progressively penetrates the interstitium from its initial site of high uptake in the well-perfused outer tumor rim, into the poorly perfused central subregion. By gamma camera imaging of (67)Ga:Df-DS, the agent avoids normal site uptake and clears through the kidneys with a t(1/2) of 18 min. A therapeutic formulation of DS-doxorubicin (DS-dox) is prepared by aqueous high-pressure homogenization of the drug and DS 435, which produces 11-nm nanoparticles of doxorubicin cores coated with DS (Zeta potential -39 mV) that are stable to lyophilization. Microscopic analysis of tumor sections 3 h after i.v. injection shows much higher overall tumor fluorescence and deeper matrix penetration for DS-dox than conventional doxorubicin (dox): >75 vs. <25 microm between the nearest microvessels. DS-dox also results in enhanced tumor-cell internalization and nuclear localization of the drug. Therapeutic efficacies in established (250 +/- 15 mg) MX-1 human breast tumor xenografts at maximum tolerated doses (MTDs) are (control vehicle, dox, dox-DS) (a) median days to 7-fold tumor growth: 8.3, 25.6 (p = 0.0007), 43.2 (p = 0.0001); (b) complete 90-day tumor regressions: 0/10, 0/10, 4/10. These results demonstrate the potential to develop a novel class of carbohydrate-targeted neovascular transport agents for sensitive, high-resolution (100-microm) MR imaging and improved treatment of larger sized human tumor metastases.

Intraprostatic chemotherapy: distribution and transport mechanisms

PURPOSE

The present study evaluated the tissue distribution and targeting advantage of intraprostatic chemotherapy.

EXPERIMENTAL DESIGN

We studied the delivery and spatial distribution of a fluorescent drug, doxorubicin, in the prostate of beagle dogs, after intraprostatic or i.v. administration. Drug concentrations were measured using high-performance liquid chromatography and confocal fluorescence microscopy.

RESULTS

I.v. and intraprostatic injections yielded qualitatively and quantitatively different doxorubicin distribution in the prostate. A relatively homogeneous distribution was found after i.v. administration, whereas intraprostatic injection yielded a highly heterogeneous distribution with >10-fold higher concentrations localized in a cone-shaped glandular lobule bound by fibromuscular stroma, compared with other parts of the prostate. Compared with i.v. injection, intraprostatic injection yielded, on average, approximately 100-fold higher tissue-to-plasma concentration ratio, ranging from 963-fold near the injection site to 19-fold in the contralateral half of the prostate. The drug distribution within the prostate further suggests an important role for acinar flow in intraprostatic drug transport.

CONCLUSIONS

Intraprostatic administration represents a viable option to deliver high drug concentrations within the prostate. The results further suggest the fibromuscular stroma separating the prostatic lobules as a major barrier to drug transport and convective flow as an important drug transport mechanism in the prostate.

Formulating Paclitaxel in Nanoparticles Alters Its Disposition

PURPOSE

Paclitaxel is active and widely used to treat multiple types of solid tumors. The commercially available paclitaxel formulation uses Cremophor/ethanol (C/E) as the solubilizers. Other formulations including nanoparticles have been introduced. This study evaluated the effects of nanoparticle formulation of paclitaxel on its tissue distribution.

METHODS

We compared the plasma and tissue pharmacokinetics of paclitaxel-loaded gelatin nanoparticles and the C/E formulation. Mice were given paclitaxel-equivalent doses of 10 mg/kg by intravenous injection.

RESULTS

The nanoparticle and C/E formulations showed significant differences in paclitaxel disposition; the nanoparticles yielded 40% smaller area under the blood concentration-time curve and faster blood clearance of total paclitaxel concentrations (sum of free, protein-bound, and nanoparticle-entrapped drug). The two formulations also showed different tissue specificity. The rank order of tissue-to-blood concentration ratios was liver > small intestine > kidney >> large intestine > spleen = stomach > lung > heart for the nanoparticles, and liver > small intestine > large intestine > stomach > lung > or = kidney > spleen > heart for the C/E formulation. The nanoparticles also showed longer retention and higher accumulation in organs and tissues (average of 3.2 +/- 2.3-fold), especially in the liver, small intestine, and kidney. The most striking difference was an 8-fold greater drug accumulation and sustained retention in the kidney.

CONCLUSIONS

These data indicate that formulation of paclitaxel affects its clearance and distribution into tissues, with preferential accumulation of nanoparticles in the liver, spleen, small intestine, and kidney.

Endostatin cDNA/cationic liposome complexes as a promising therapy to prevent lung metastases in osteosarcoma: study in a human-like rat orthotopic tumor

Antiangiogenesis or destruction of tumor neovessels is an effective strategy to prevent tumor growth. Endostatin, one of the many inhibitors of angiogenesis that have been discovered, has shown conflicting results in preclinical assays. We studied the therapeutic potential of lipid/DNA complexes consisting of cationic liposomes and an endostatin-coding plasmid (Endo cDNA/CLP) in an orthotopic osteosarcoma model in rats. Empty plasmid without the endostatin gene complexed with cationic liposomes served as control. Animals were treated intravenously three times a week starting on the day tumors were detectable by (18)FDG tomoscintigraphy. During treatment, tumor progression was followed by PET scan and angioscintigraphy, and the effects of antivascular therapy on primary tumor, metastases, and tumor vascular density were confirmed by histologic analysis. Our results demonstrate that therapy using Endo cDNA/CLP is associated with pronounced delay in tumor growth. Moreover, it effectively prevented the occurrence of lung metastases, the major reason for bad prognosis and death in osteosarcoma patients. This approach could be used as an adjuvant therapy for osteosarcoma.

Advanced strategies in liposomal cancer therapy: problems and prospects of active and tumor specific drug release

Tumor specific drug delivery has become increasingly interesting in cancer therapy, as the use of chemotherapeutics is often limited due to severe side effects. Conventional drug delivery systems have shown low efficiency and a continuous search for more advanced drug delivery principles is therefore of great importance. In the first part of this review, we present current strategies in the drug delivery field, focusing on site-specific triggered drug release from liposomes in cancerous tissue. Currently marketed drug delivery systems lack the ability to actively release the carried drug and rely on passive diffusion or slow non-specific degradation of the liposomal carrier. To obtain elevated tumor-to-normal tissue drug ratios, it is important to develop drug delivery strategies where the liposomal carriers are actively degraded specifically in the tumor tissue. Many promising strategies have emerged ranging from externally triggered light- and thermosensitive liposomes to receptor targeted, pH- and enzymatically triggered liposomes relying on an endogenous trigger mechanism in the cancerous tissue. However, even though several of these strategies were introduced three decades ago, none of them have yet led to marketed drugs and are still far from achieving this goal. The most advanced and prospective technologies are probably the prodrug strategies where non-toxic drugs are carried and activated specifically in the malignant tissue by overexpressed enzymes. In the second part of this paper, we review our own work, exploiting secretory phospholipase A2 as a site-specific trigger and prodrug activator in cancer therapy. We present novel prodrug lipids together with biophysical investigations of liposome systems, constituted by these new lipids and demonstrate their degradability by secretory phospholipase A2. We furthermore give examples of the biological performance of the enzymatically degradable liposomes as advanced drug delivery systems.

Mathematical Modeling and Optimization of Drug Delivery from Intratumorally Injected Microspheres

Purpose: Paclitaxel is a highly promising phase-sensitive antitumor drug that could conceivably be improved by extended lower dosing as opposed to intermittent higher dosing. Although intratumoral delivery of paclitaxel to the whole tumor at different loads and rates has already been achieved, determining an optimal release mode of paclitaxel for tumor eradication remains difficult. This study set out to rationally design such an optimal microsphere release mode based on mathematical modeling.

Experimental Design: A computational reaction-diffusion framework was used to model drug release from intratumorally injected microspheres, drug transport and binding in tumor interstitum, and drug clearance by microvasculature and intracellular uptake and binding.

Results: Numerical simulations suggest that interstitial drug concentration is characterized by a fast spatially inhomogeneous rise phase, during which interstitial and intracellular binding sites are saturated, followed by a slow spatially homogeneous phase that is governed by the rate of drug release from microspheres. For zero-order drug release, the slow phase corresponds to a plateau drug concentration that is proportional to the ratio of the rate of blood clearance of drug to the rate of drug release from microspheres. Consequently, increasing the duration of intratumoral drug release extends the duration of cell exposure to the drug but lowers the plateau drug concentration. This tradeoff implies that intratumoral drug release can be designed to optimize tumor cell kill. Synthesizing our modeling predictions with published dose-response data, we propose an optimal protocol for the delivery of paclitaxel-loaded microspheres to small solid tumors.