Tumor-selective Accumulation Research Articles

Enhanced Bacterial Tumor Delivery by Modulating the EPR Effect and Therapeutic Potential of Lactobacillus casei

Bacteria of micrometer size could accumulate in tumor based on enhanced permeability and retention (EPR) effect. We report here Lactobacillus casei (L. casei), a nonpathogenic facultatively anaerobic bacterium, preferentially accumulated in tumor tissues after intravenously (i.v.) injection; at 24 h, live bacteria were found more in the tumor, whereas the bacteria in normal tissues including the liver and spleen were cleared rapidly. The tumor-selective accumulation and growth of L. casei is probably due to the EPR effect and the hypoxic tumor environment. Moreover, the bacterial tumor delivery was significantly increased by a nitric oxide (NO) donor nitroglycerin (NG, 10-70 times) and an angiotensin II converting enzyme inhibitor, enalapril (6-18 times). Consequently significant suppression of tumor growth was found in a colon cancer C26 model, and more remarkable antitumor effect was achieved when L. casei was combined with NG, probably by modulating the host nonspecific immune responses; tumor necrosis factor-α significantly increased in tumor after the treatment, as well as NO synthase activity and myleoperoxidase activity. These findings suggest the potential of L. casei as a candidate for targeted bacterial antitumor therapy, especially in combine with NG or other vascular mediators.

Abstract 5420: Nano-engineered mesenchymal stem cells as targeted therapeutic carriers

Abstract Poor availability of chemotherapeutics in deep-seated and metastatic cancers results in the development of drug resistance and failed therapeutic outcomes. Approaches that can specifically enhance drug delivery to the tumor tissue can potentially improve therapeutic efficacy while minimizing toxic side effects. In our current studies, we used nano-engineered mesenchymal stem cells (MSCs) as tumor-targeted therapeutic carriers. MSCs possess exquisite tumor homing capabilities. In addition, MSCs overexpress efflux transporters such as P-glycoprotein and are highly drug resistant. The inherent tumor-tropic and drug-resistant properties make MSCs ideal carriers for toxic payload. Since a majority of MSCs first accumulate in the lungs following systemic administration, this technology is particularly suitable for the delivery of anticancer therapeutics to lung tumors. The overall objective of this study was to investigate the efficacy of nano-engineered MSCs in non-small cell lung cancer. We hypothesized that incorporation of drug-loaded, polymeric nanoparticles in MSCs will allow for tumor-targeted and sustained drug delivery. Nanoparticles containing paclitaxel and imaging agent were formulated using poly (DL-lactide-co-glycolide) polymer by solvent evaporation technique and characterized for size, charge, drug loading and in vitro drug release. Nano-engineered MSCs were designed by loading MSCs with nanoparticles containing paclitaxel and an infrared (in vivo) or green fluorescent (in vitro) imaging agent and characterized for nanoparticle uptake using flow cytometry. Nano-engineered MSCs were characterized for in vitro cytotoxicity, differentiation potential and in vivo migratory potential. Human MSCs incubated with nanoparticles showed a steady increase in nanoparticle uptake, with saturation at 4 hours. Nanoparticles encapsulation did not affect the viability or the differentiation potential of MSCs. Nano-engineered MSCs resulted in dose-dependent cytotoxicity in A549 lung adenocarcinoma cells. An orthotopic lung tumor model was used to monitor the in vivo distribution of nano-engineered MSCs. Intravenous injection of A549 cells stably transfected with luciferase in mice resulted in formation of lung tumors that were monitored by bioluminescence imaging. Intravenous injection of nanoparticles alone resulted in non-specific biodistribution, with high accumulation in liver and spleen. Nano-engineered MSCs, in contrast, demonstrated selective accumulation and retention in lung tumors. These results indicate that nano-engineered MSCs can be loaded with high concentration of anticancer agents without affecting their migratory or drug resistance properties. Future studies will examine the anticancer efficacy of nano-engineered MSCs in an orthotopic mouse model of lung cancer. Citation Format: Swayam Prabha, Tanmoy Sadhukha. Nano-engineered mesenchymal stem cells as targeted therapeutic carriers. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5420. doi:10.1158/1538-7445.AM2014-5420

Synthesis and biological evaluation of new BSH-conjugated chlorin derivatives as agents for both photodynamic therapy and boron neutron capture therapy of cancer

New disodium mercaptoundecahydro-closo-dodecaborate (BSH)-conjugated chlorin derivatives 11, 12, 16 and 20 as agents for both photodynamic therapy (PDT) and boron neutron capture therapy (BNCT) of cancer were synthesized. The in vivo biodistribution and clearance of 11, 12, 16 and 20 were investigated in tumor-bearing mice. Compounds 12 and 16 showed good tumor-selective accumulation among the four derivatives. The time to maximum accumulation of compound 16 in tumor tissue was one-fourth of that of compound 12, and clearance from normal tissues of compound 16 was similar to that of compound 12. The in vivo therapeutic efficacy of PDT using 16, which has twice as many boron atoms as 12, was evaluated by measuring tumor growth rates in tumor-bearing mice with 660nm light-emitting diode irradiation at 6h after injection of 16. Tumor growth was significantly inhibited by PDT using 16. These results suggested that 16 is a good candidate for both PDT and BNCT of cancer.

Bundled assembly of helical nanostructures in polymeric micelles loaded with platinum drugs enhancing therapeutic efficiency against pancreatic tumor.

Supramolecular assemblies of amphiphilic block copolymers having polypeptide segments offer significant advantages for tailoring spatial arrangement based on secondary structures in their optically active backbones. Here, we demonstrated the critical effect of α-helix bundles in cisplatin-conjugated poly(L- (or D-)glutamate) [P(L(or D)Glu)-CDDP] segment on the packaging of poly(ethylene glycol) (PEG)-P(L(or D)Glu)-CDDP block copolymers in the core of polymeric micelles (CDDP/m) and enhanced micelle tolerability to harsh in vivo conditions for accomplishing appreciable antitumor efficacy against intractable pancreatic tumor by systemic injection. CDDP/m prepared from optically inactive PEG-poly(D,L-glutamate) (P(D,LGlu)), gradually disintegrated in the bloodstream, resulting in increased accumulation in liver and spleen and reduced antitumor efficacy. Alternatively, CDDP/m from optically active PEG-P(L(or D)Glu) maintained micelle structure during circulation, and eventually attained selective tumor accumulation while reducing nonspecific distribution to liver and spleen. Circular dichroism and small-angle X-ray scattering measurements indicated regular bundled assembly of α-helices in the core of CDDP/m from PEG-P(L(or D)Glu), which is suggested to stabilize the micelle structure against dilution in physiological condition. CDDP/m suffered corrosion by chlorides in medium, yet the optically active micelles with α-helix bundles kept the micelle structure for prolonged time, with slowly releasing unimers and dimers from the surface of the bundled core in an erosion-like process, as verified by ultracentrifugation analysis. This is in sharp contrast with the abrupt disintegration of CDDP/m from PEG-P(D,LGlu) without secondary structures. The tailored assembly in the core of the polymeric micelles through regular arrangement of constituting segments is key to overcome their undesirable disintegration in bloodstream, thereby achieving efficient delivery of loaded drugs into target tissues.

Magneto‐Plasmonic Au‐Fe Alloy Nanoparticles Designed for Multimodal SERS‐MRI‐CT Imaging

Diagnostic approaches based on multimodal imaging are needed for accurate selection of the therapeutic regimens in several diseases, although the dose of administered contrast drugs must be reduced to minimize side effects. Therefore, large efforts are deployed in the development of multimodal contrast agents (MCAs) that permit the complementary visualization of the same diseased area with different sensitivity and different spatial resolution by applying multiple diagnostic techniques. Ideally, MCAs should also allow imaging of diseased tissues with high spatial resolution during surgical interventions. Here a new system based on multifunctional Au-Fe alloy nanoparticles designed to satisfy the main requirements of an ideal MCA is reported and their biocompatibility and imaging capability are described. The MCAs show easy and versatile surface conjugation with thiolated molecules, magnetic resonance imaging (MRI) and computed X-ray tomography (CT) signals for anatomical and physiological information (i.e., diagnostic and prognostic imaging), large Raman signals amplified by surface enhanced Raman scattering (SERS) for high sensitivity and high resolution intrasurgical imaging, biocompatibility, exploitability for in vivo use and capability of selective accumulation in tumors by enhanced permeability and retention effect. Taken together, these results show that Au-Fe nanoalloys are excellent candidates as multimodal MRI-CT-SERS imaging agents.

Hybrid polymer micelles capable of cRGD targeting and pH-triggered surface charge conversion for tumor selective accumulation and promoted uptake.

This study presents both tumor-targeting ligands (cRGD) and pH-activated surface charge-conversional moiety (imidazole) decorated micelles for Dox delivery. cRGD is expected to induce preferential tumor accumulation, while imidazole switches on positive charge in a tumor acid environment, which leads to enhanced micelle uptake by tumor cells.

Enzyme-triggered supramolecular self-assembly of platinum prodrug with enhanced tumor-selective accumulation and reduced systemic toxicity.

We report the generation of a novel self-assembled platinum (Pt) prodrug from a short peptide derivative, which acted as a substrate for the phosphatase-catalyzed dephosphorylation reaction, and a Pt(iv) complex, which could undergo supramolecular self-assembly in the presence of alkaline phosphatase, and perform controlled release of the Pt(ii) drug under the reductive conditions of tumor cells. This self-assembled prodrug showed significant antitumor growth effects on a breast cancer xenograft model based on 4T1 cells in vivo, but much lower toxicity towards the kidney, liver, spleen and other major organs than the free cisplatin drug in mice. Such improved antitumor efficacy could be ascribed to the localized and sustained release of the Pt(ii) anticancer drug from the supramolecular self-assembly of the Pt(iv) prodrug, which was triggered by phosphatases in tumor sites.

Abstract B44: Mapping, targeting, and eliminating therapeutically unresponsive ovarian cancer with high content imaging and photodynamic therapy

Abstract Ovarian cancer is the 5th most common cancer among women, in which epithelial ovarian cancer (EOC) is the most common type, accounting for 90% of cases. Currently, the standard treatment for ovarian cancer is surgical debulking followed by chemotherapy. Although initially EOC patients are highly responsive to standard platinum-derived chemotherapy, the majority of cancer patients will eventually relapse and experience chemoresistance. In spite of numerous efforts to improve EOC treatment, the five-year overall survival rate is still disappointing at 30%. It is therefore necessary to examine the fundamental causes of treatment resistance and use this information to design new therapeutic strategies. Recently, the concept of tumor-initiating cells and their supporting tumor microenvironment has been proposed as potential targets for cancer treatment due to their observed chemoresistance and ability to repopulate tumors. These cells are proposed to reside deep within tumors, potentially in oxygen-deprived environments. We recently observed that a light-based treatment modality known as photodynamic therapy (PDT) may be uniquely suited to targeting and eliminating this cellular population. PDT applies a light activated drug (photosensitizer) to selectively target and kill cancer cells through generation of reactive oxygen species (ROS), making it an attractive alternative cancer treatment modality with the potential to overcome adaptive therapeutic resistance. Characteristics of PDT, including the direct destruction of cellular organelles, selective tumor accumulation, and photochemistry-driven tumor killing mechanism give PDT advantages over traditional chemotherapy and radiotherapy. We have found that a lysosome targeted photosensitizer known as EtNBS specifically localizes and accumulates into the acidic and hypoxic tumor microenvironment in 3D cultures to successfully kill otherwise unresponsive cellular populations. EtNBS-mediated PDT is thus a potential modality in treating tumor initiating cells. In addition, the quantitative and label-free optical coherence tomography (OCT) imaging modality has recently been demonstrated to provide real time information regarding tumor tissue structure and therapeutic dynamics, making it a potential tool to study tumors and their associated change during the course of tumor development and treatment. Here, we utilized a 3D in vitro metastatic ovarian cancer culture model, with an oxygen sensor and OCT imaging as a combinational platform to study tumor initiating cells and the effects of their associated tumor microenvironment on therapeutic response under standard and EtNBS-PDT treatment. By mapping tumor response with this integrated platform, this work represents a mechanism- based targeted approach that will hopefully enable the identification of cellular targets to overcome disease relapse and adaptive chemoresistance. Citation Format: Hsin-I Hung, Oliver J. Klein, Yookyung Jung, Kashmira S. Kulkarni, Bo R. Rueda, Rosemary Foster, Conor L. Evans. Mapping, targeting, and eliminating therapeutically unresponsive ovarian cancer with high content imaging and photodynamic therapy. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: From Concept to Clinic; Sep 18-21, 2013; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2013;19(19 Suppl):Abstract nr B44.

Development of Novel Tumor‐Targeted Theranostic Nanoparticles Activated by Membrane‐Type Matrix Metalloproteinases for Combined Cancer Magnetic Resonance Imaging and Therapy

A major drawback with current cancer therapy is the prevalence of unrequired dose-limiting toxicity to non-cancerous tissues and organs, which is further compounded by a limited ability to rapidly and easily monitor drug delivery, pharmacodynamics and therapeutic response. In this report, the design and characterization of novel multifunctional "theranostic" nanoparticles (TNPs) is described for enzyme-specific drug activation at tumor sites and simultaneous in vivo magnetic resonance imaging (MRI) of drug delivery. TNPs are synthesized by conjugation of FDA-approved iron oxide nanoparticles ferumoxytol to an MMP-activatable peptide conjugate of azademethylcolchicine (ICT), creating CLIO-ICTs (TNPs). Significant cell death is observed in TNP-treated MMP-14 positive MMTV-PyMT breast cancer cells in vitro, but not MMP-14 negative fibroblasts or cells treated with ferumoxytol alone. Intravenous administration of TNPs to MMTV-PyMT tumor-bearing mice and subsequent MRI demonstrates significant tumor selective accumulation of the TNP, an observation confirmed by histopathology. Treatment with CLIO-ICTs induces a significant antitumor effect and tumor necrosis, a response not observed with ferumoxytol. Furthermore, no toxicity or cell death is observed in normal tissues following treatment with CLIO-ICTs, ICT, or ferumoxytol. These findings demonstrate proof of concept for a new nanotemplate that integrates tumor specificity, drug delivery and in vivo imaging into a single TNP entity through attachment of enzyme-activated prodrugs onto magnetic nanoparticles. This novel approach holds the potential to significantly improve targeted cancer therapies, and ultimately enable personalized therapy regimens.

Systemic administration of attenuated Salmonella typhimurium in combination with interleukin-21 for cancer therapy

Attenuated Salmonella typhimurium (S. typhimurium) strain VNP20009 has been employed as a powerful anticancer agent due to its selective accumulation in tumors for targeted therapy. S. typhimurium has been demonstrated to constitute a delivery tool carrying antiangiogenic or proapoptotic genes that treat cancer. The hydrodynamic tail vein (HTV) injection of naked plasmid DNA has been developed as an effective gene delivery strategy, which has been successfully used in vivo. The aim of this study was to develop a combination therapy of S. typhimurium VNP20009 and HTV injection of interleukin-21 (IL-21) expression plasmid to evaluate the antitumor potential on an experimental melanoma model. Consistent with previous results, single VNP20009 treatment was demonstrated to possess effective activities to suppress tumor growth and prolong animal survival. Moreover, HTV injection of IL-21 plasmid promoted the antitumor activities of VNP20009. The mice that were administered combined therapy exhibited smaller tumor sizes and longer survival time compared with those administered VNP20009 or IL-21 treatment alone. IL-21 induced more infiltrating natural killer (NK) and T cells to the tumor area. These findings indicated that S. typhimurium in combination with IL-21 promotes antitumor immune responses, suggesting a novel strategy in the treatment of cancer.

Synthesis and biological evaluation of new chlorin derivatives as potential photosensitizers for photodynamic therapy

Three new water-soluble chlorin derivatives 3, 5 and 8 for potential use as photosensitizers in photodynamic therapy (PDT) for cancer were synthesized from photoprotoporphyrin IX dimethyl ester (1). The in vivo biodistribution and clearance of chlorin derivatives 3, 5 and 8 were investigated in tumor-bearing mice. Iminodiacetic acid derivative 8 showed the greatest tumor-selective accumulation among the new chlorin derivatives with maximum accumulation in tumor tissue at 3h after intravenous injection and rapid clearance from normal tissues within 24h after injection. The in vivo therapeutic efficacy of PDT using 8 was evaluated by measuring tumor growth rates in tumor-bearing mice with 660nm light-emitting diode irradiation at 3h after injection of 8. Tumor growth was significantly inhibited by PDT using 8. These results indicate that iminodiacetic acid derivative 8 is useful as a new photosensitizer to overcome the disadvantages of photosensitizers that are currently in clinical use.

Advance in Photosensitizers and Light Delivery for Photodynamic Therapy

The brief history of photodynamic therapy (PDT) research has been focused on photosensitizers (PSs) and light delivery was introduced recently. The appropriate PSs were developed from the first generation PS Photofrin (QLT) to the second (chlorins or bacteriochlorins derivatives) and third (conjugated PSs on carrier) generations PSs to overcome undesired disadvantages, and to increase selective tumor accumulation and excellent targeting. For the synthesis of new chlorin PSs chlorophyll a is isolated from natural plants or algae, and converted to methyl pheophorbide a (MPa) as an important starting material for further synthesis. MPa has various active functional groups easily modified for the preparation of different kinds of PSs, such as methyl pyropheophorbide a, purpurin-18, purpurinimide, and chlorin e6 derivatives. Combination therapy, such as chemotherapy and photothermal therapy with PDT, is shortly described here. Advanced light delivery system is shown to establish successful clinical applications of PDT. Phtodynamic efficiency of the PSs with light delivery was investigated in vitro and/or in vivo.

Micelles of zinc protoporphyrin conjugated to N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer for imaging and light-induced antitumor effects in vivo

We synthesized N-(2-hydroxypropyl)methacrylamide polymer conjugated with zinc protoporphyrin (HPMA-ZnPP) and evaluated its application for tumor detection by imaging and treatment by light exposure using in mouse sarcoma model. To characterize HPMA-ZnPP micelle, we measured its micellar size, surface charge, stability, photochemical, biochemical properties and tissue distribution. In vivo anti-tumor effect and fluorescence imaging were carried out to validate the tumor selective accumulation and therapeutic effect by inducing singlet oxygen by light exposure. HPMA-ZnPP was highly water soluble and formed micelles spontaneously having hydrophobic clustered head group of ZnPP, in aqueous solution, with a hydrodynamic diameter of 82.8±41.8nm and zeta-potential of +1.12mV. HPMA-ZnPP had a long plasma half-life and effectively and selectively accumulated in tumors. Although HPMA-ZnPP alone had no toxicity in S-180 tumor-bearing mice, light-irradiation significantly suppressed tumor growth in vivo, similar to the cytotoxicity to HeLa cells in vitro upon endoscopic light-irradiation. HPMA-ZnPP can visualize tumors by fluorescence after i.v. injection, which suggests that this micelle may be useful for both tumor imaging and therapy. Here we describe preparation of a new fluorescence nanoprobe that is useful for simultaneous tumor imaging and treatment, and application to fluorescence endoscopy is now at visible distance.

M402, a Novel Heparan Sulfate Mimetic, Targets Multiple Pathways Implicated in Tumor Progression and Metastasis

Heparan sulfate proteoglycans (HSPGs) play a key role in shaping the tumor microenvironment by presenting growth factors, cytokines, and other soluble factors that are critical for host cell recruitment and activation, as well as promoting tumor progression, metastasis, and survival. M402 is a rationally engineered, non-cytotoxic heparan sulfate (HS) mimetic, designed to inhibit multiple factors implicated in tumor-host cell interactions, including VEGF, FGF2, SDF-1α, P-selectin, and heparanase. A single s.c. dose of M402 effectively inhibited seeding of B16F10 murine melanoma cells to the lung in an experimental metastasis model. Fluorescent-labeled M402 demonstrated selective accumulation in the primary tumor. Immunohistological analyses of the primary tumor revealed a decrease in microvessel density in M402 treated animals, suggesting anti-angiogenesis to be one of the mechanisms involved in-vivo. M402 treatment also normalized circulating levels of myeloid derived suppressor cells in tumor bearing mice. Chronic administration of M402, alone or in combination with cisplatin or docetaxel, inhibited spontaneous metastasis and prolonged survival in an orthotopic 4T1 murine mammary carcinoma model. These data demonstrate that modulating HSPG biology represents a novel approach to target multiple factors involved in tumor progression and metastasis.

Multimodal silica nanoparticles are effective cancer-targeted probes in a model of human melanoma

Nanoparticle-based materials, such as drug delivery vehicles and diagnostic probes, currently under evaluation in oncology clinical trials are largely not tumor selective. To be clinically successful, the next generation of nanoparticle agents should be tumor selective, nontoxic, and exhibit favorable targeting and clearance profiles. Developing probes meeting these criteria is challenging, requiring comprehensive in vivo evaluations. Here, we describe our full characterization of an approximately 7-nm diameter multimodal silica nanoparticle, exhibiting what we believe to be a unique combination of structural, optical, and biological properties. This ultrasmall cancer-selective silica particle was recently approved for a first-in-human clinical trial. Optimized for efficient renal clearance, it concurrently achieved specific tumor targeting. Dye-encapsulating particles, surface functionalized with cyclic arginine-glycine-aspartic acid peptide ligands and radioiodine, exhibited high-affinity/avidity binding, favorable tumor-to-blood residence time ratios, and enhanced tumor-selective accumulation in αvβ3 integrin-expressing melanoma xenografts in mice. Further, the sensitive, real-time detection and imaging of lymphatic drainage patterns, particle clearance rates, nodal metastases, and differential tumor burden in a large-animal model of melanoma highlighted the distinct potential advantage of this multimodal platform for staging metastatic disease in the clinical setting.

Nucleic Acid Therapeutics: Concepts for Targeted Delivery to Solid Tumors

Solid tumors form a heterogeneous group of diseases, although common features such as hyperproliferation, overexpression of certain growth factor receptors and deregulated vessel formation including leaky vasculature give the opportunity to target macromolecular drug and nucleic acid carriers to tumor tissue. Similar to other macromolecular drugs, nucleic acid carriers have to be designed to enable tumor targeting after systemic injection. Chemical modification of nucleic acids makes them resistant towards enzymatic degradation. Cationic lipids or polycations condense nucleic acids into small, virus-like structures and the surface modification with hydrophilic polymers allows passive accumulation in tumor tissue; tumor cell binding ligands allow cellular targeting. To avoid toxic side effects, biodegradable and biocompatible carriers were designed. The design of thermoresponsive gene carriers allowed their selective tumor accumulation by locoregional hyperthermia. As a therapeutic concept, tumor-specific delivery of antitumoral RNA was realized in an orthotopic brain tumor model. The combination of gene- and radio-therapy enabled selective accumulation of radionuclides in tumors and boosted antitumoral effects. Hence, combining a smart delivery concept for nucleic acids with a suitable therapeutic strategy will allow successful treatment of otherwise incurable malignant diseases.

Abstract 2269: M402 - A novel heparan sulfate proteoglycan mimetic targeting tumor-host interactions

Abstract Heparan sulfate proteoglycans (HSPGs) play important roles in tumorigenesis by mediating tumor-stromal interactions through the presentation of growth factors, cytokines, and chemokines critical for tumor progression, survival and metastasis. M402 is a rationally engineered, non-cytotoxic HSPG mimetic, designed to disrupt tumor-host interactions. M402 binds and inhibits multiple factors including VEGF, FGF2, SDF-1α, and P-selectin. A single 20 mg/kg subcutaneous (s.c.) dose of M402 effectively reduced seeding of B16F10 murine melanoma cells to the lung in a syngeneic experimental metastasis model. Chronic administration of M402, alone or in combination with cisplatin or docetaxel, inhibited spontaneous metastasis of orthotopically implanted 4T1 murine mammary carcinoma in this model. M402 treatment also normalized circulating levels of GR1+ immature myeloid cells and platelet counts in 4T1 metastatic tumor bearing mice. Fluorescently-labeled M402 exhibited selective accumulation in the primary tumor. Immunohistological analyses of primary tumor presented a decrease in microvessel density in M402-treated animals, suggesting anti-angiogenesis may be one of the mechanisms involved in vivo. Importantly, M402, as monotherapy or in combination with chemotherapeutics, also revealed significant survival benefits in this aggressive tumor model. These data demonstrate that targeting HSPG biology may provide a useful approach to attenuate multiple pathways involved in tumor progression and metastasis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2269.

Nanomaterial standards for efficacy and toxicity assessment

Decreased toxicity via selective delivery of cancer therapeutics to tumors has become a hallmark achievement of nanotechnology. In order to be optimally efficacious, a systemically administered nanomedicine must reach cancer cells in sufficient quantities to elicit a response and assume its active form within the tumor microenvironment (e.g., be taken up by cancer cells and release a toxic component once within the cytosol or nuclei). Most nanomedicines achieve selective tumor accumulation via the enhanced permeability and retention (EPR) effect or a combination of the EPR effect and active targeting to cellular receptors. Here, we review how the fundamental physicochemical properties of a nanomedicine (its size, charge, hydrophobicity, etc.) can dramatically affect its distribution to cancerous tissue, transport across vascular walls, and retention in tumors. We also discuss how nanoparticle characteristics such as stability in the blood and tumor, cleavability of covalently bound components, cancer cell uptake, and cytotoxicity contribute to efficacy once the nanoparticle has reached the tumor's interstitial space. We elaborate on how tumor vascularization and receptor expression vary depending on cancer type, stage of disease, site of implantation, and host species, and review studies which have demonstrated that these variations affect tumor response to nanomedicines. Finally, we show how knowledge of these properties (both of the nanoparticle and the cancer/tumor under study) can be used to design meaningful in vivo tests to evaluate nanoparticle efficacy.

Transport of the Photodynamic Therapy Agent 5-Aminolevulinic Acid by Distinct H+-Coupled Nutrient Carriers Coexpressed in the Small Intestine

5-Aminolevulinic acid (ALA) is a prodrug used in photodynamic therapy, fluorescent diagnosis, and fluorescent-guided resection because it leads to accumulation of the photosensitizer protoporphyrin IX (PpIX) in tumor tissues. ALA has good oral bioavailability, but high oral doses are required to obtain selective PpIX accumulation in colonic tumors because accumulation is also observed in normal gut mucosa. Structural similarities between ALA and GABA led us to test the hypothesis that the H(+)-coupled amino acid transporter PAT1 (SLC36A1) will contribute to luminal ALA uptake. Radiolabel uptake and electrophysiological measurements identified PAT1-mediated H(+)-coupled ALA symport after heterologous expression in Xenopus oocytes. The selectivity of the nontransported inhibitors 5-hydroxytryptophan and 4-aminomethylbenzoic acid for, respectively, PAT1 and the H(+)-coupled di/tripeptide transporter PepT1 (SLC15A1) were examined. 5-Hydroxytryptophan selectively inhibited PAT1-mediated amino acid uptake across the brush-border membrane of the human intestinal (Caco-2) epithelium whereas 4-aminomethylbenzoic acid selectively inhibited PepT1-mediated dipeptide uptake. The inhibitory effects of 5-hydroxytryptophan and 4-aminomethylbenzoic acid were additive, demonstrating that both PAT1 and PepT1 contribute to intestinal transport of ALA. This is the first demonstration of overlap in substrate specificity between these distinct transporters for amino acids and dipeptides. PAT1 and PepT1 expression was monitored by reverse transcriptase-polymerase chain reaction using paired samples of normal and cancer tissue from human colon. mRNA for both transporters was detected. PepT1 mRNA was increased 2.3-fold in cancer tissues. Thus, increased PepT1 expression in colonic cancer could contribute to the increased PpIX accumulation observed. Selective inhibition of PAT1 could enhance PpIX loading in tumor tissue relative to that in normal tissue.

Mechanism of cell death by 5‐aminolevulinic acid‐based photodynamic action and its enhancement by ferrochelatase inhibitors in human histiocytic lymphoma cell line U937

Photodynamic therapy (PDT) for tumors is based on the tumor-selective accumulation of a photosensitizer, protoporphyrin IX (PpIX), followed by irradiation with visible light. However, the molecular mechanism of cell death caused by PDT has not been fully elucidated. The 5-aminolevulinic acid (ALA)-based photodynamic action (PDA) was dependent on the accumulation of PpIX, the level of which decreased rapidly by eliminating ALA from the incubation medium in human histiocytic lymphoma U937 cells. PDA induced apoptosis characterized by lipid peroxidation, increase in Bak and Bax/Bcl-xL, decrease in Bid, membrane depolarization, cytochrome c release, caspase-3 activation, phosphatidylserine (PS) externalization. PDT-induced cell death seemed to occur predominantly via apoptosis through distribution of PpIX in mitochondria. These cell death events were enhanced by ferrochelatase inhibitors. These results indicated that ALA-based-PDA induced apoptotic cell death through a mitochondrial pathway and that ferrochelatase inhibitors might enhanced the effect of PDT for tumors even at low concentrations of ALA.