Drug Accumulation In Tumors Research Articles

A free cysteine prolongs the half-life of a homing peptide and improves its tumor-penetrating activity

The accessibility of extravascular tumor tissue to drugs is critical for therapeutic efficacy. We previously described a tumor-targeting peptide (iRGD) that elicits active transport of drugs and macromolecules (covalently coupled or co-administered) across the vascular wall into tumor tissue. Short peptides (iRGD is a 9-amino acid cyclic peptide) generally have a plasma half-life measured in minutes. Since short half-life limits the window of activity obtained with a bolus injection of iRGD, we explored to extend the half-life of the peptide. We show here that addition of a cysteine residue prolongs the plasma half-life of iRGD and increases the accumulation of the peptide in tumors. This modification prolongs the activity of iRGD in inducing macromolecular extravasation and leads to greater drug accumulation in tumors than is obtained with the unmodified peptide. This effect is mediated by covalent binding of iRGD to plasma albumin through a disulfide bond. Our study provides a simple strategy to improve peptide pharmacokinetics and activity. Applied to RGD, it provides a means to increase the entry of therapeutic agents into tumors.

A Mathematical Model of the Enhanced Permeability and Retention Effect for Liposome Transport in Solid Tumors

The discovery of the enhanced permeability and retention (EPR) effect has resulted in the development of nanomedicines, including liposome-based formulations of drugs, as cancer therapies. The use of liposomes has resulted in substantial increases in accumulation of drugs in solid tumors; yet, significant improvements in therapeutic efficacy have yet to be achieved. Imaging of the tumor accumulation of liposomes has revealed that this poor or variable performance is in part due to heterogeneous inter-subject and intra-tumoral liposome accumulation, which occurs as a result of an abnormal transport microenvironment. A mathematical model that relates liposome accumulation to the underlying transport properties in solid tumors could provide insight into inter and intra-tumoral variations in the EPR effect. In this paper, we present a theoretical framework to describe liposome transport in solid tumors. The mathematical model is based on biophysical transport equations that describe pressure driven fluid flow across blood vessels and through the tumor interstitium. The model was validated by direct comparison with computed tomography measurements of tumor accumulation of liposomes in three preclinical tumor models. The mathematical model was fit to liposome accumulation curves producing predictions of transport parameters that reflect the tumor microenvironment. Notably, all fits had a high coefficient of determination and predictions of interstitial fluid pressure agreed with previously published independent measurements made in the same tumor type. Furthermore, it was demonstrated that the model attributed inter-subject heterogeneity in liposome accumulation to variations in peak interstitial fluid pressure. These findings highlight the relationship between transvascular and interstitial flow dynamics and variations in the EPR effect. In conclusion, we have presented a theoretical framework that predicts inter-subject and intra-tumoral variations in the EPR effect based on fundamental properties of the tumor microenvironment and forms the basis for transport modeling of liposome drug delivery.

Two step mechanisms of tumor selective delivery of N-(2-hydroxypropyl)methacrylamide copolymer conjugated with pirarubicin via an acid-cleavable linkage

N-(2-Hydroxypropyl)methacrylamide copolymer containing hydrazide groups (PHPMA) conjugated with pirarubicin (THP) via a hydrazone bond (PHPMA-hyd-THP) is a drug conjugate that releases THP in the acidic milieu of a tumor. PHPMA-hyd-THP has an apparent Mw of 40,000 and a hydrodynamic diameter of 8.2±1.7nm but no apparent plasma protein binding. PHPMA-hyd-THP possesses two mechanisms of selectivity toward solid tumors and has potent antitumor action. The first one is drug accumulation in tumors that depends on the enhanced permeability and retention (EPR) effect, which results in a 4–20 times higher concentration of drug in the tumor than in normal tissues such as the heart, lung, and intestine. This accumulation in tumor tissue is in great contrast to that of conventional low-Mw THP. The second one is pH-dependent release of drug from PHPMA-hyd-THP: this conjugate released free THP more efficiently at a lower pH, which exists in tumors, and exerts cytotoxic activity. Free THP is known for its much faster uptake into tumor cells compared with doxorubicin. Thus, in our in vitro study, PHPMA-hyd-THP showed a higher cytotoxicity at the lower pH of tumor tissue than at the neutral pH of normal tissue. Furthermore, much more THP was liberated from the conjugate in acidic tumor tissue than in normal tissue. The EPR effect-dependent accumulation of PHPMA-hyd-THP and tumor-selective THP release in the tumor tissues led to highly tumor-selective drug accumulation, which continued for more than 72h, whereas the lowest free drug concentration was detected in normal tissues at 24h and no longer at a later time. In conclusion, we determined in our study here that the acid-cleavable PHPMA-hyd-THP conjugate had an excellent antitumor effect without appreciable adverse effects.

Tumor perfusion imaging predicts the intra-tumoral accumulation of liposomes

Liposomes have proven to be a viable drug delivery strategy resulting in significant increases in tumor accumulation of drugs via exploitation of the enhanced permeability and retention (EPR) effect. However, significant variability has been observed in their bulk tumor accumulation and intra-tumoral distribution. The heterogeneous accumulation of liposomes in solid tumors is largely believed to result from the chaotic morphology and physiology of tumor blood vessels. Thus, tumor perfusion imaging may provide a novel method to predict the accumulation and resulting therapeutic effect of liposome formulations. In this study, dynamic contrast enhanced computed tomography (DCE-CT) was employed to quantitatively estimate the intra-tumoral distribution of perfusion and anatomical CT was used to map the spatio-temporal accumulation of a CT-liposome contrast agent. A statistically significant positive correlation was found between quantitative and semi-quantitative measures of tumor perfusion (i.e. Ktrans, vp, and AUCiox) and liposome accumulation (AUClipo and Cpeak) in two mouse xenograft models of human cervical cancer. Specifically, it was found that regions with higher Ktrans,vp, and AUCiox had greater liposome accumulation. These findings demonstrate that DCE-CT measurements of tumor perfusion may be an important technique for selecting patients that are likely to respond to liposome and potentially other nanoparticle-based therapies.

Formulation Design and Evaluation of Quantum Dot-Loaded Nanostructured Lipid Carriers for Integrating Bioimaging and Anticancer Therapy

The authors studied the bioimaging and delivery of drug-entrapped, nanostructured lipid carriers with quantum dots (QDs), called QDNLCs, for integrating imaging and therapy. Nanostructured lipid carriers consisting of QDs, including lipophilic QDs, carboxyl-function QDs or PEG QDs were prepared. Application of the nanocarriers was evaluated by cytotoxicity, cell migration, cellular uptake, in vivo real-time tumor monitoring and drug accumulation in tumors. All QDNLCs exhibited a size of 245 nm with camptothecin encapsulation of >99%. Cytotoxicity of the nanoparticles against melanoma cells was superior to that of free camptothecin. Carboxylic acid-conjugated QDNLCs (C-QDNLCs) showed the highest cell internalization and in vivo fluorescence labeling compared with the other carriers. Real-time bioimaging demonstrated that C-QDNLCs maintained signaling in tumors for at least 24 h. The camptothecin accumulation in melanomas increased by 6.4-fold after incorporation into C-QDNLCs. For the first time, nanostructured lipid carriers were coordinated with QDs and an anticancer drug to provide efficient tumor imaging and drug delivery. Original submitted 1 May 2012; Revised submitted 30 August 2012; Published online 5 February 2013.

Nanocomposite liposomes containing quantum dots and anticancer drugs for bioimaging and therapeutic delivery: a comparison of cationic, PEGylated and deformable liposomes

Multifunctional liposomes loaded with quantum dots (QDs) and anticancer drugs were prepared for simultaneous bioimaging and drug delivery. Different formulations, including cationic, PEGylated and deformable liposomes, were compared for their theranostic efficiency. We had evaluated the physicochemical characteristics of these liposomes. The developed liposomes were examined using experimental platforms of cytotoxicity, cell migration, cellular uptake, in vivo melanoma imaging and drug accumulation in tumors. The average size of various nanocomposite liposomes was found to be 92–134 nm. Transmission electron microscopy confirmed the presence of QDs within liposomal bilayers. The incorporation of polyethylene glycol (PEG) and Span 20 into the liposomes greatly increased the fluidity of the bilayers. The liposomes provided sustained release of camptothecin and irinotecan. The cytotoxicity and cell migration assay demonstrated superior activity of cationic liposomes compared with other carriers. Cationic liposomes also showed a significant fluorescence signal in melanoma cells after internalization. The liposomes were intratumorally administered to a melanoma-bearing mouse. Cationic liposomes showed the brightest fluorescence in tumors, followed by classical liposomes. This signal could last for up to 24 h for cationic nanosystems. Intratumoral accumulation of camptothecin from free control was 35 nmol g−1; it could be increased to 50 nmol g−1 after loading with cationic liposomes. However, encapsulation of irinotecan into liposomes did not further increase intratumoral drug accumulation. Cationic liposomes were preferable to other liposomes as nanocarriers in both bioimaging and therapeutic approaches.

Correlation of Tissue-Plasma Partition Coefficients Between Normal Tissues and Subcutaneous Xenografts of Human Tumor Cell Lines in Mouse as a Prediction Tool of Drug Penetration in Tumors

Understanding drug distribution and accumulation in tumors would be informative in the assessment of efficacy in targeted therapy; however, existing methods for predicting tissue drug distribution focus on normal tissues and do not incorporate tumors. The main objective of this study was to describe the relationships between tissue-plasma concentration ratios (Kp ) of normal tissues and those of subcutaneous xenograft tumors under nonsteady-state conditions, and establish regression equations that could potentially be used for the prediction of drug levels in several human tumor xenografts in mouse, based solely on a Kp value determined in a normal tissue (e.g., muscle). A dataset of 17 compounds was collected from the literature and from Genentech. Tissue and plasma concentration data in mouse were obtained following oral gavage or intraperitoneal administration. Linear regression analyses were performed between Kp values in several normal tissues (muscle, lung, liver, or brain) and those in human tumor xenografts (CL6, EBC-1, HT-29, PC3, U-87, MCF-7-neo-Her2, or BT474M1.1). The tissue-plasma ratios in normal tissues reasonably correlated with the tumor-plasma ratios in CL6, EBC-1, HT-29, U-87, BT474M1.1, and MCF-7-neo-Her2 xenografts (r(2) in the range 0.62-1) but not with the PC3 xenograft. In general, muscle and lung exhibited the strongest correlation with tumor xenografts, followed by liver. Regression coefficients from brain were low, except between brain and the glioblastoma U-87 xenograft (r(2) in the range 0.62-0.94). Furthermore, reasonably strong correlations were observed between muscle and lung and between muscle and liver (r(2) in the range 0.67-0.96). The slopes of the regressions differed depending on the class of drug (strong vs. weak base) and type of tissue (brain vs. other tissues and tumors). Overall, this study will contribute to our understanding of tissue-plasma partition coefficients for tumors and facilitate the use of physiologically based pharmacokinetics (PBPK) modeling for chemotherapy in oncology studies. © 2013 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 102:1355-1369, 2013.

Improving Drug Uptake and Penetration into Tumors: Current and Forthcoming Opportunities

Improving Drug Uptake and Penetration into Tumors: Current and Forthcoming Opportunities

Effects of ionizing radiation in combination with Erufosine on T98G glioblastoma xenograft tumours: a study in NMRI nu/nu mice

BackgroundErufosine is a promising anticancer drug that increases the efficacy of radiotherapy in glioblastoma cell lines in vitro. Moreover, treatment of nude mice with repeated intraperitoneal or subcutaneous injections of Erufosine is well tolerated and yields drug concentrations in the brain tissue that are higher than the concentrations required for cytotoxic drug effects on glioblastoma cell lines in vitro.MethodsIn the present study we aimed to evaluate the effects of a combined treatment with radiotherapy and Erufosine on growth and local control of T98G subcutaneous glioblastoma xenograft-tumours in NMRI nu/nu mice.ResultsWe show that repeated intraperitoneal injections of Erufosine resulted in a significant drug accumulation in T98G xenograft tumours on NMRI nu/nu mice. Moreover, short-term treatment with 5 intraperitoneal Erufosine injections caused a transient decrease in the growth of T98G tumours without radiotherapy. Furthermore, an increased radiation-induced growth delay of T98G xenograft tumours was observed when fractionated irradiation was combined with short-term Erufosine-treatment. However, no beneficial drug effects on fractionated radiotherapy in terms of local tumour control were observed.ConclusionsWe conclude that short-term treatment with Erufosine is not sufficient to significantly improve local control in combination with radiotherapy in T98G glioblastoma xenograft tumours. Further studies are needed to evaluate efficacy of extended drug treatment schedules.

Therapeutic nanosystems for oncology nanomedicine

Cancer is a complex disease which includes many pathologies featuring abnormal growth of healthy cells, invasion and metastization. Cellular uncontrolled growth increases the amount of abnormal cells, these cells reach the blood stream and other healthy tissues giving rise to secondary tumors. Even though great progresses have been made in understanding cancer aetiology and in the development of new anticancer drugs, cancer still remains one of the leading causes of death worldwide. Most common cancers include breast cancer, lung cancer, colorectal cancer and brain cancer. Conventional chemotherapeutics have proven to be inefficient in cancer treatment due to lack of specificity and poor drug accumulation in tumors. In addition, they cause severe side effects. Available treatments must be prolonged on time to achieve some therapeutic effect; however, this often leads to the development of multidrug resistance by tumor cells. Nanotechnology platforms are, therefore, being exploited as potential alternatives. Nanosystems have been reported to target and deliver the drug in situ to selectively kill cancer cells, decreasing toxicity on healthy organs and tissues as well as side effects. Furthermore, some nanosystems have been reported to overcome tumor resistance, at least to some extent. Over the years several nanosystems have been proposed to diagnose and treat cancers, such as dendrimers, polymeric micelles, superparamagnetic iron oxide cores, gold nanoparticles, liposomes and other lipid nanoparticles. Due to their small size and biocompatibility, they can reach the target site without being detected by the immune system and suffer cellular uptake or deliver the drug in the tumor vicinity.

Multifunctional drug delivery system for targeting tumor and its acidic microenvironment

Effective targeting drug delivery for cancer therapy still remains a formidable challenge due to the complication and heterogeneity of malignant tumors. Herein, a multifunctional targeting strategy was proposed, in which a novel pH-sensitive polymethacrylates (PMA)-grafted poly(amidoamine) (PAMAM) nano delivery system was designed to be responsive to the acidic tumor microenvironment, and thereby trigger drug release in the intra-tumoral space. In addition, folate-PEGylation was applied to modify the surface of PMA-PAMAM nanoparticles in order to enhance tumor selectivity via both active and passive targeting mechanisms: folate receptor targeting, long circulation and EPR effect. The utility and efficacy of such system was demonstrated both in vitro and in vivo. Tumor drug accumulation was significantly enhanced by folate-PEGylated PMA-PAMAM nanoparticles, and such observation corresponded to their strong inhibition of tumor growth in tumor-bearing mice, demonstrating the success of the multifunctional targeting delivery. This multifunctional targeting strategy provides a promising solution to improve targeting drug delivery for combating the complex cancer diseases.

Abstract 3972: Tumor accessiblity and composition play a major role on the efficiency of efflux transporter inhibitor - cytotoxic drug combination: Analysis with a mathematical model

Abstract Efflux transporters from the ABC family confer resistance to various anticancer drugs. Efflux transporter inhibitors were designed to reverse chemoresistance to cytotoxic drugs. Efficacy of such association is impacted by numerous factors in xenografted animals, such as tumor environment and biology. No study aims at quantifying the importance of these factors on the efficiency of association of cytotoxic-efflux transporter inhibitor. In-silico approach, through the development of mathematical models, allows testing the influence of such factors. This work aimed at evaluating the impact of tumor accessibility and composition, on efflux transporter inhibitors - cytotoxic combination with a mathematical model. Two studies (S1, S2) were carried out in mice xenografted with HEK293 cells overexpressing the ABCG2 transporter. Mice received irinotecan (CPT11) alone or combined to a new ABCG2 inhibitor, MBLI87. Tumor size was periodically measured during 4 weeks. Designs of both studies were similar but mice received a more intense dose of MBLI87 in S2 and delay of treatment onset was longer in S2. To model tumor growth, a multiscale model was developed including 4 submodels: - PK model of plasmatic drug disposition - Cellular interaction model of the cytotoxic drug accumulation in tumor in presence of inhibitor - Tumor growth model of the natural evolution of disease - Pharmacodynamic model of cytotoxic drug effect on tumor growth Cellular interaction model was based on in-vitro experiments and quantified the magnitude of CPT11 and its metabolite SN38 active efflux and the MBLI87 inhibition constant. A rate constant describing drug diffusion from plasma to tumor represented tumor accessibility. Three types of tumoral tissues were considered: proliferative, hypoxic and necrotic. Only proliferative tissues could grow and cytotoxic drugs could only affect proliferative cells. Model parameters were estimated with a non-linear mixed-effects approach using NONMEM software. Model was able to predict correctly tumor growth from our data. Addition of MBLI87 to CPT11 slowed the growth of tumors in S1 and S2. Our model showed that cytotoxic potency was equivalent in S1 and S2 but proportion of proliferative cells was smaller at treatment onset and drug active efflux was greater in S2. Equilibration between plasma and tumor was faster in S2 attesting better tumor accessibility owing to better vascularization. As a consequence, a different intensity in resistance reversion was found between S1 and S2: tumor size was 50% greater at day 40 in S2. This mathematical model quantified the role of tumor accessibility and composition on the efficiency of an efflux inhibitor - cytotoxic drug combination. It can be used as a simulation framework to optimize this type of interaction or as a template for early evaluation of other efflux transporter inhibitors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3972. doi:1538-7445.AM2012-3972

Pharmacokinetics & tissue distribution of temperature-sensitive liposomal doxorubicin in tumor-bearing mice triggered with mild hyperthermia

Drug-loaded temperature-sensitive liposomes (TSL) in combination with hyperthermia (HT) have attracted considerable attention for cancer treatment. Different TSL systems have been designed with wide variations in their temperature sensitivity and drug release profile. Low temperature-sensitive liposomes (LTSL) with the capacity for ultrafast drug release, traditional temperature-sensitive (TTSL) with intermediate drug release properties and non-temperature-sensitive liposomes (NTSL) (no drug release) were dual-labeled with 3H-cholesteryl hexadecyl ether (3H-CHE) lipid and loaded with 14C-doxorubicin (14C-Dox). Their blood profile, serum stability, tissue distribution and tumor localization (B16F10 melanoma) were studied after intravenous administration and mild HT treatment. LTSL showed higher affinity for the liver compared to TTSL and NTSL which were uptaken mainly by spleen. Under normal conditions (no HT) Dox leakage from liposomes was expected, higher for LTSL, less for TTSL and minimal for NTSL. Localized HT did not affect the overall blood circulation or organ accumulation for all TSL studied. Since LTSL showed ultrafast Dox release kinetics at 42 °C, the highest drug accumulation in tumors was observed using this system immediately after HT, however decreased significantly after 24 h. In contrast, TTSL and NTSL showed 2-3 fold increase in both liposome and Dox levels that indicated enhanced tumor extravasation of intact Dox-loaded liposomes during the 60 min HT applications. More interestingly, high levels of drug tumor accumulation were achieved 24 h post-HT. This study offers further understanding on how the mechanisms of drug release from temperature-sensitive liposomes affect their pharmacological profile under mild hyperthermia.

Synthesis, toxicity, and mouse biodistribution of 9-thiocyano-7,8-dicarba-nido-undecaborate during neutron-capture therapy

Potassium 7,8-dicarba-nido-undecaborate was thiocyanated by nondiaphragm electrolysis. The salt Me4N+[9-SCN-7,8-C2B9H11]− was isolated and converted into the trimethylammonium salt using ion-exchange. Methods for the synthesis of water-soluble sodium 7,8-dicarba-nido-undecaborate and its biphasic iodination (for 131I introduction) were developed. Thus, the synthesis and analysis of the radioactive iodine-labeled sodium salt of 11-(131I)-9-thiocyanato-7,8-dicarba-nido-undecaborate were proposed and carried out. The toxicity of the synthesized compound was evaluated. It was established that 100 and 75 mg/kg doses are 100% lethal for test animals while no significant disorders were observed at doses of 35 and 20 mg/kg. The biodistribution of the compound in organs and tissues was studied in mice with melanoma B-16. The maximum accumulation of labeled compound in tumor, skin, muscle, liver, kidneys, and spleen was observed 3 – 6 h after administration. A comparison of drug accumulation in tumor and normal tissues showed that the preparation does not possess pronounced tumor-targeting properties.

Nanobiopolymer for Direct Targeting and Inhibition of EGFR Expression in Triple Negative Breast Cancer

Treatment options for triple negative breast cancer (TNBC) are generally limited to cytotoxic chemotherapy. Recently, anti-epidermal growth factor receptor (EGFR) therapy has been introduced for TNBC patients. We engineered a novel nanobioconjugate based on a poly(β-L-malic acid) (PMLA) nanoplatform for TNBC treatment. The nanobioconjugate carries anti-tumor nucleosome-specific monoclonal antibody (mAb) 2C5 to target breast cancer cells, anti-mouse transferrin receptor (TfR) antibody for drug delivery through the host endothelial system, and Morpholino antisense oligonucleotide (AON) to inhibit EGFR synthesis. The nanobioconjugates variants were: (1) P (BioPolymer) with AON, 2C5 and anti-TfR for tumor endothelial and cancer cell targeting, and EGFR suppression (P/AON/2C5/TfR), and (2) P with AON and 2C5 (P/AON/2C5). Controls included (3) P with 2C5 but without AON (P/2C5), (4) PBS, and (5) P with PEG and leucine ester (LOEt) for endosomal escape (P/mPEG/LOEt). Drugs were injected intravenously to MDA-MB-468 TNBC bearing mice. Tissue accumulation of injected nanobioconjugates labeled with Alexa Fluor 680 was examined by Xenogen IVIS 200 (live imaging) and confocal microscopy of tissue sections. Levels of EGFR, phosphorylated and total Akt in tumor samples were detected by western blotting. In vitro western blot showed that the leading nanobioconjugate P/AON/2C5/TfR inhibited EGFR synthesis significantly better than naked AON. In vivo imaging revealed that 2C5 increased drug-tumor accumulation. Significant tumor growth inhibition was observed in mice treated with the lead nanobioconjugate (1) [P = 0.03 vs. controls; P<0.05 vs. nanobioconjugate variant (2)]. Lead nanobioconjugate (1) also showed stronger inhibition of EGFR expression and Akt phosphorylation than other treatments. Treatment of TNBC with the new nanobioconjugate results in tumor growth arrest by inhibiting EGFR and its downstream signaling intermediate, phosphorylated Akt. The nanobioconjugate represents a new generation of nanodrugs for treatment of TNBC.

Carbon monoxide, generated by heme oxygenase‐1, mediates the enhanced permeability and retention effect in solid tumors

The enhanced permeability and retention (EPR) effect is a unique pathophysiological phenomenon of solid tumors that sees biocompatible macromolecules (>40 kDa) accumulate selectively in the tumor. Various factors have been implicated in this effect. Herein, we report that heme oxygenase-1 (HO-1; also known as heat shock protein 32) significantly increases vascular permeability and thus macromolecular drug accumulation in tumors. Intradermal injection of recombinant HO-1 in mice, followed by i.v. administration of a macromolecular Evans blue-albumin complex, resulted in dose-dependent extravasation of Evans blue-albumin at the HO-1 injection site. Almost no extravasation was detected when inactivated HO-1 or a carbon monoxide (CO) scavenger was injected instead. Because HO-1 generates CO, these data imply that CO plays a key role in vascular leakage. This is supported by results obtained after intratumoral administration of a CO-releasing agent (tricarbonyldichlororuthenium(II) dimer) in the same experimental setting, specifically dose-dependent increases in vascular permeability plus augmented tumor blood flow. In addition, induction of HO-1 in tumors by the water-soluble macromolecular HO-1 inducer pegylated hemin significantly increased tumor blood flow and Evans blue-albumin accumulation in tumors. These findings suggest that HO-1 and/or CO are important mediators of the EPR effect. Thus, anticancer chemotherapy using macromolecular drugs may be improved by combination with an HO-1 inducer, such as pegylated hemin, via an enhanced EPR effect.

Tumor Specific Delivery and Therapy by Double-Targeted Nanostructured Lipid Carriers with Anti-VEGFR-2 Antibody

Vascular endothelial growth factor receptors (VEGFRs) are overexpressed on the surface of a variety of tumor cells and on tumor neovasculature in situ, which are potential targets for "double targeting" (tumor- and vascular-targeting) tumor therapy. This study aimed to develop a VEGFR-mediated drug delivery system to target chemotherapeutic agents to VEGFR-overexpressed tumor cells and tumor neovasculature endothelial cells in vitro and in vivo. An antibody modified docetaxel (DTX)-loaded targeted nanostructured lipid carrier (tNLC) was designed and prepared with DSPE-PEG-NH(2) as linker. The cellular cytotoxicity, cellular uptake, in vivo therapeutic effect and biodistribution of tNLC were investigated. The tNLC showed a particle size about 168 nm with encapsulation efficiency >95%, drug loading 5.55 ± 0.06% (w/w) and an average ligand coupling efficiency of 3.34 ± 2.63%. Cytotoxicity of tNLC against three human cell lines and one murine malignant melanoma was superior to that of Duopafei and nontargeted NLC (nNLC). The tNLC also showed better tolerance and antitumor efficacy in a murine model bearing B16 compared with Duopafei or nNLC. The studies on cellular uptake and biodistribution indicated that the better antitumor efficacy of tNLC was attributed to the increased accumulation of drug in both tumor and tumor vasculature. These findings suggested that tNLC designed to bind specifically to VEGFR-2 can be used to deliver DTX to the tumor vasculature and tumor and may inhibit tumor growth.

Abstract 1685: Nano-scale targeting of Pc 4 to improve drug delivery, accumulation, and PDT efficacy in brain tumors

Abstract Malignant gliomas are among the most lethal cancers with a median survival expectancy of only 6-12 months. Surgical resection is the mainstay of treatment. However, curative resection is often not possible due to infiltrating growth of the tumor into normal brain. Photodynamic therapy (PDT) has been suggested as an additional therapy to guide tumor resections and enhance the effect of surgery via photoreactive treatment during or at the cessation of surgical intervention. The most difficult challenge in treating malignant brain tumors may be delivering targeted therapies that preserve healthy tissue while effectively eradicating the cancer. Therefore, improving drug delivery rate and tumor selectivity of the photosensitizing agent will dramatically reduce systemic toxicity and enhance the success of PDT. EGFR amplification is the most common genetic alteration in gliomas and plays a critical role in stimulating glioma progression, making it an ideal target. Consequently, we have developed a highly efficient EGFR-targeted gold-nanoparticle (EGF-Au NP) to improve delivery of PDT cancer drugs to tumors in vivo. EGF peptides attached to PEGylated Au NPs deliver hydrophobic PDT drug, Pc 4, to brain tumors overexpressing EGFR better than either the non-targeted Au NPs or Pc 4 alone. The drug rapidly releases and penetrates deep within tumors within 1-4 hrs. In vivo small animal imaging experiments show targeted delivery of Pc 4 to tumor sites. Ex vivo imaging of the tumors confirmed as much as a 4-fold increase in the intrinsic fluorescence of Pc 4 over non-targeted conjugates after systemic administration. Moreover, in vitro experiments show a higher concentration of Pc 4 uptake per Au NP over non-targeted Au NPs per cancer cell. Histological analysis, including confocal microscopy, shows that, after targeting, the delivered Pc 4 localizes in the endosomes of the cancer cells. Transmission electron micrographs show that Au NPs cluster along the cell surface or within discrete vesicles within the cell. Localization within the endosomal pathway may be more effective for PDT and produce less off-target toxicity than free Pc 4, which preferentially accumulates in mitochondria. Further, glioma cells treated for 4 hrs with EGF-targeted Au NP-Pc 4 and then exposed to PDT show an enhanced killing effect, especially when compared to either non-targeted Au NP-Pc 4 or free Pc 4 controls. Systemic delivery of EGF-Au NP-Pc 4 to heterotopic brain tumors reveals increasing tumor necrosis after PDT. Biodistribution experiments also show that the Au NPs and Pc 4 are effectively excreted over time. This study suggests that the EGFR-targeted Au NPs improve drug delivery to tumors for PDT and are removed from the body safely after treatment. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1685. doi:10.1158/1538-7445.AM2011-1685

Materializing sequential killing of tumor vasculature and tumor cells via targeted polymeric micelle system

The purpose of this study was to develop a targeted combinatorial polymeric micelle system that can sequentially kill tumor vasculature and tumor cells and increase the anticancer efficacy. Toward this goal, αvβ3 integrin-targeting peptide (RGD) functionalized polymeric micelles (RFPMs) based on the use of poly(ethylene glycol)-b-poly(d,l-lactide) (PEG-PLA) was developed. Doxorubicin was conjugated to the biodegradable PEG-PLA micelle core, and combretastatin A4 was physically encapsulated into micelles (RFPMs-DOX-CA4). The RFPMs-DOX-CA4 has a particle size of 29.2 ± 2.5 nm with spherical shape and high encapsulation efficiency for both drugs (> 95%). The micelles exhibited sequential release kinetics for both drugs. Treatment with RFPMs-DOX-CA4 resulted in the sequential killing of endothelial cells and tumor cells in vitro. RFPMs displayed prolonged circulation time and more drug accumulation in solid tumor than unfunctionalized polymeric micelles (UFPMs). In B16-F10 tumor-bearing mice, RFPMs-DOX-CA4 showed stronger tumor growth inhibition and significantly higher survival rate compared with the other treatment groups. Treatment with RFPMs-DOX-CA4 caused a dramatic destruction of tumor vasculature and reduction of tumor cell proliferation in vivo. These results suggested that the integrated strategy can be exploited as a potential treatment modality for cancer.

ABC transporters: unvalidated therapeutic targets in cancer and the CNS.

The discovery of the multidrug transporter P-glycoprotein (Pgp) over 35 years ago in drug resistant cells prompted several decades of work attempting to overcome drug resistance by inhibition of drug efflux. Despite convincing laboratory data showing that drug transport can be inhibited in vitro, efforts to translate this discovery to the clinic have not succeeded. Since overexpression of Pgp and related transporters including ABCG2 and members of the ABCC family have been linked with poor outcome, it remains a reasonable hypothesis that this poor outcome is linked to reduction of drug exposure by efflux, and thus to drug resistance. In this review, we will discuss the question of whether ABC transporters mediate drug resistance in cancer through a reduction in drug accumulation in tumors, and whether the "Pgp inhibition hypothesis" might be wrong. The hypothesis, which holds that increased chemotherapy effectiveness can be achieved by inhibiting Pgp-mediated drug efflux has only been validated in model systems. Possible explanations for the failure to validate this clinically include the existence of other modulators of drug accumulation and uptake in tumors. Despite these difficulties, a potential role has emerged for drug transporters as therapeutic targets in the central nervous system (CNS). Both lines of investigation point to the need for imaging agents to facilitate the study of drug accumulation in human cancer. This is a critical need for targeted therapies where an important dose-response relationship is likely to exist, and where drug resistance renders many of the novel targeted agents ineffective in a subset of patients.