Biocompatible and bioactivable terpolymer-lipid-MnO2 Nanoparticle-based MRI contrast agent for improving tumor detection and delineation

Early and precise detection of solid tumor cancers is critical for improving therapeutic outcomes. In this regard, magnetic resonance imaging (MRI) has become a useful tool for tumor diagnosis and image-guided therapy. However, its effectiveness is limited by the shortcomings of clinically available gadolinium-based contrast agents (GBCAs), i.e. poor tumor penetration and retention, and safety concerns. Thus, we have developed a novel nanoparticulate contrast agent using a biocompatible terpolymer and lipids to encapsulate manganese dioxide nanoparticles (TPL-MDNP). The TPL-MDNP accumulated in tumor tissue and produced paramagnetic Mn2+ ions, enhancing T1-weight MRI contrast via the reaction with H2O2 rich in the acidic tumor microenvironment. Compared to the clinically used GBCA, Gadovist®1.0, TPL-MDNP generated stronger T1-weighted MR signals by over 2.0-fold at 30 % less of the recommended clinical dose with well-defined tumor delineation in preclinical orthotopic tumor models of brain, breast, prostate, and pancreas. Importantly, the MRI signals were retained for 60 min by TPL-MDNP, much longer than Gadovist®1.0. Biocompatibility of TPL-MDNP was evaluated and found to be safe up to 4-fold of the dose used for MRI. A robust large-scale manufacturing process was developed with batch-to-batch consistency. A lyophilization formulation was designed to maintain the nanostructure and storage stability of the new contrast agent.

Remodeling Tumor Immune Microenvironment by Using Polymer-Lipid-Manganese Dioxide Nanoparticles with Radiation Therapy to Boost Immune Response of Castration-Resistant Prostate Cancer

Despite substantial progress in the treatment of castration-resistant prostate cancer (CRPC), including radiation therapy and immunotherapy alone or in combination, the response to treatment remains poor due to the hypoxic and immunosuppressive nature of the tumor microenvironment. Herein, we exploited the bioreactivity of novel polymer-lipid manganese dioxide nanoparticles (PLMDs) to remodel the tumor immune microenvironment (TIME) by increasing the local oxygen levels and extracellular pH and enhancing radiation-induced immunogenic cell death. This study demonstrated that PLMD treatment sensitized hypoxic human and murine CRPC cells to radiation, significantly increasing radiation-induced DNA double-strand breaks and ultimately cell death, which enhanced the secretion of damage-associated molecular patterns, attributable to the induction of autophagy and endoplasmic reticulum stress. Reoxygenation via PLMDs also polarized hypoxic murine RAW264.7 macrophages toward the M1 phenotype, enhancing tumor necrosis factor alpha release, and thus reducing the viability of murine CRPC TRAMP-C2 cells. In a syngeneic TRAMP-C2 tumor model, intravenous injection of PLMDs suppressed, while radiation alone enhanced recruitment of regulatory T cells and myeloid-derived suppressor cells. Pretreatment with PLMDs followed by radiation down-regulated programmed death-ligand 1 and promoted the infiltration of antitumor CD8+ T cells and M1 macrophages to tumor sites. Taken together, TIME modulation by PLMDs plus radiation profoundly delayed tumor growth and prolonged median survival compared with radiation alone. These results suggest that PLMDs plus radiation is a promising treatment modality for improving therapeutic efficacy in radioresistant and immunosuppressive solid tumors.

Brain-Penetrating and Disease Site-Targeting Manganese Dioxide-Polymer-Lipid Hybrid Nanoparticles Remodel Microenvironment of Alzheimer's Disease by Regulating Multiple Pathological Pathways

Finding effective disease-modifying treatment for Alzheimer's disease remains challenging due to an array of factors contributing to the loss of neural function. The current study demonstrates a new strategy, using multitargeted bioactive nanoparticles to modify the brain microenvironment to achieve therapeutic benefits in a well-characterized mouse model of Alzheimer's disease. The application of brain-penetrating manganese dioxide nanoparticles significantly reduces hypoxia, neuroinflammation, and oxidative stress; ultimately reducing levels of amyloid β plaques within the neocortex. Analyses of molecular biomarkers and magnetic resonance imaging-based functional studies indicate that these effects improve microvessel integrity, cerebral blood flow, and cerebral lymphatic clearance of amyloid β. These changes collectively shift the brain microenvironment toward conditions more favorable to continued neural function as demonstrated by improved cognitive function following treatment. Such multimodal disease-modifying treatment may bridge critical gaps in the therapeutic treatment of neurodegenerative disease.

Advances in Nanomedicine Design: Multidisciplinary Strategies for Unmet Medical Needs

Globally, a rising burden of complex diseases takes a heavy toll on human lives and poses substantial clinical and economic challenges. This review covers nanomedicine and nanotechnology-enabled advanced drug delivery systems (DDS) designed to address various unmet medical needs. Key nanomedicine and DDSs, currently employed in the clinic to tackle some of these diseases, are discussed focusing on their versatility in diagnostics, anticancer therapy, and diabetes management. First-hand experiences from our own laboratory and the work of others are presented to provide insights into strategies to design and optimize nanomedicine- and nanotechnology-enabled DDS for enhancing therapeutic outcomes. Computational analysis is also briefly reviewed as a technology for rational design of controlled release DDS. Further explorations of DDS have illuminated the interplay of physiological barriers and their impact on DDS. It is demonstrated how such delivery systems can overcome these barriers for enhanced therapeutic efficacy and how new perspectives of next-generation DDS can be applied clinically.

Exploring the transformability of polymer-lipid hybrid nanoparticles and nanomaterial-biology interplay to facilitate tumor penetration, cellular uptake and intracellular targeting of anticancer drugs

BACKGROUND

Successful delivery of anticancer drugs to intracellular targets requires different properties of the nanocarrier to overcome multiple transport barriers. However, few nanocarrier systems, to date, possess such properties, despite knowledge about the biological fate of inorganic and polymeric nanocarriers in relation to their fixed size, shape and surface properties. Herein, a polymer-lipid hybrid nanoparticle (PLN) system is described with size and shape transformability and its mechanisms of cellular uptake and intracellular trafficking are studied.

METHODS

Pharmaceutical lipids were screened for use in transformable PLN. Mechanisms of cellular uptake and the role of fatty acid-binding proteins in intracellular trafficking of PLN were investigated in breast cancer cells. Intra-tumoral penetration and retention of doxorubicin (DOX) were evaluated by confocal microscopy.

RESULTS

The lead PLNs showed time-dependent size reduction and shape change from spherical to spiky shape. This transformability of PLNs and lipid trafficking pathways facilitated intracellular transport of DOX-loaded PLN (DOX-PLN) into mitochondria and nuclei. DOX-PLN significantly increased DOX penetration and retention over free DOX or non-transformable liposomal DOX particles at 4 h post-intravenous administration.

CONCLUSION

Transformability of PLN and lipid-biology interplay can be exploited to design new nanocarriers for effective drug delivery to tumor cells and intracellular targets.

Combining Tumor Microenvironment Modulating Nanoparticles with Doxorubicin to Enhance Chemotherapeutic Efficacy and Boost Antitumor Immunity

BACKGROUND

Tumor microenvironment (TME) and associated multiple factors are found to contribute to the failures in cancer therapies, including chemo- and immunotherapy. Here we report a new multimodal strategy that uses a bioreactive multifunctional hybrid polymer-lipid encapsulated manganese dioxide nanoparticle (PLMD NP) system to remodel the TME, suppress drug resistance factors, reverse immunosuppressive conditions, and enhance chemotherapy efficacy.

METHODS

The influence of PLMD NPs on enhancing cellular uptake in EMT6 mouse breast cancer cells and tumor penetration of doxorubicin (DOX) in EMT6 orthotopic breast tumor mouse model was evaluated using confocal microscopy (n = 3-4). Immunohistochemistry was employed to examine the effect of PLMD NPs on downregulating hypoxia-induced drug resistance proteins and anticancer activity of DOX (n = 3-4). The efficacy of the combination therapy with PLMD NPS and DOX was assessed in murine EMT6 (n = 15-23) and 4T1 (n = 7) orthotopic breast tumor mouse models. Rechallenge and splenocyte transfer were performed to validate the stimulation of adaptive tumor immunity in the surviving mice.

RESULTS

PLMD NPs enhanced intratumoral penetration and efficacy of DOX, and reduced intratumoral expression of P-glycoprotein, p53, and carbonic anhydrase IX by 74.5%, 38.0%, and 58.8% vs saline control, respectively. Combination treatment with PLMD NPs and DOX increased the number of tumor-infiltrated CD8+ T cells and resulted in up to 60.0% complete tumor regression. Of naïve mice (n = 7) that received splenocytes from the PLMD+DOX-treated surviving mice, 57.1% completely suppressed tumor growth whereas 100% of mice that received splenocytes from DOX-treated mice (n = 3) and the control group (n = 7) showed rapid tumor growth.

CONCLUSIONS

The clinically suitable PLMD NPs can effectively downregulate TME-associated drug resistance and immunosuppression. The combination therapy with PLMD NPs and DOX is a multimodal and translational treatment approach for enhancing chemotherapeutic efficacy and boosting antitumor immunity.

Multitargeted Nanoparticles Deliver Synergistic Drugs across the Blood-Brain Barrier to Brain Metastases of Triple Negative Breast Cancer Cells and Tumor-Associated Macrophages

Patients with brain metastases of triple negative breast cancer (TNBC) have a poor prognosis owing to the lack of targeted therapies, the aggressive nature of TNBC, and the presence of the blood-brain barrier (BBB) that blocks penetration of most drugs. Additionally, infiltration of tumor-associated macrophages (TAMs) promotes tumor progression. Here, a terpolymer-lipid hybrid nanoparticle (TPLN) system is designed with multiple targeting moieties to first undergo synchronized BBB crossing and then actively target TNBC cells and TAMs in microlesions of brain metastases. In vitro and in vivo studies demonstrate that covalently bound polysorbate 80 in the terpolymer enables the low-density lipoprotein receptor-mediated BBB crossing and TAM-targetability of the TPLN. Conjugation of cyclic internalizing peptide (iRGD) enhances cellular uptake, cytotoxicity, and drug delivery to brain metastases of integrin-overexpressing TNBC cells. iRGD-TPLN with coloaded doxorubicin (DOX) and mitomycin C (MMC) (iRGD-DMTPLN) exhibits higher efficacy in reducing metastatic burden and TAMs than nontargeted DMTPLN or a free DOX/MMC combination. iRGD-DMTPLN treatment reduces metastatic burden by 6-fold and 19-fold and increases host median survival by 1.3-fold and 1.6-fold compared to DMTPLN or free DOX/MMC treatments, respectively. These findings suggest that iRGD-DMTPLN is a promising multitargeted drug delivery system for the treatment of integrin-overexpressing brain metastases of TNBC.

Importance of integrating nanotechnology with pharmacology and physiology for innovative drug delivery and therapy - an illustration with firsthand examples

Nanotechnology has been applied extensively in drug delivery to improve the therapeutic outcomes of various diseases. Tremendous efforts have been focused on the development of novel nanoparticles and delineation of the physicochemical properties of nanoparticles in relation to their biological fate and functions. However, in the design and evaluation of these nanotechnology-based drug delivery systems, the pharmacology of delivered drugs and the (patho-)physiology of the host have received less attention. In this review, we discuss important pharmacological mechanisms, physiological characteristics, and pathological factors that have been integrated into the design of nanotechnology-enabled drug delivery systems and therapies. Firsthand examples are presented to illustrate the principles and advantages of such integrative design strategies for cancer treatment by exploiting 1) intracellular synergistic interactions of drug-drug and drug-nanomaterial combinations to overcome multidrug-resistant cancer, 2) the blood flow direction of the circulatory system to maximize drug delivery to the tumor neovasculature and cells overexpressing integrin receptors for lung metastases, 3) endogenous lipoproteins to decorate nanocarriers and transport them across the blood-brain barrier for brain metastases, and 4) distinct pathological factors in the tumor microenvironment to develop pH- and oxidative stress-responsive hybrid manganese dioxide nanoparticles for enhanced radiotherapy. Regarding the application in diabetes management, a nanotechnology-enabled closed-loop insulin delivery system was devised to provide dynamic insulin release at a physiologically relevant time scale and glucose levels. These examples, together with other research results, suggest that utilization of the interplay of pharmacology, (patho-)physiology and nanotechnology is a facile approach to develop innovative drug delivery systems and therapies with high efficiency and translational potential.

Sample Extraction and Simultaneous Chromatographic Quantitation of Doxorubicin and Mitomycin C Following Drug Combination Delivery in Nanoparticles to Tumor-bearing Mice

Combination chemotherapy is frequently used in the clinic for cancer treatment; however, associated adverse effects to normal tissue may limit its therapeutic benefit. Nanoparticle-based drug combination has been shown to mitigate the problems encountered by free drug combination therapy. Our previous studies have shown that the combination of two anticancer drugs, doxorubicin (DOX) and mitomycin C (MMC), produced a synergistic effect against both murine and human breast cancer cells in vitro. DOX and MMC co-loaded polymer-lipid hybrid nanoparticles (DMPLN) bypassed various efflux transporter pumps that confer multidrug resistance and demonstrated enhanced efficacy in breast tumor models. Compared to conventional solution forms, such superior efficacy of DMPLN was attributed to the synchronized pharmacokinetics of DOX and MMC and increased intracellular drug bioavailability within tumor cells enabled by the nanocarrier PLN. To evaluate the pharmacokinetics and bio-distribution of co-administered DOX and MMC in both free solution and nanoparticle forms, a simple and efficient multi-drug analysis method using reverse-phase high performance liquid chromatography (HPLC) was developed. In contrast to previously reported methods that analyzed DOX or MMC individually in the plasma, this new HPLC method is able to simultaneously quantitate DOX, MMC and a major cardio-toxic DOX metabolite, doxorubicinol (DOXol), in various biological matrices (e.g., whole blood, breast tumor, and heart). A dual fluorescent and ultraviolet absorbent probe 4-methylumbelliferone (4-MU) was used as an internal standard (I.S.) for one-step detection of multiple drug analysis with different detection wavelengths. This method was successfully applied to determine the concentrations of DOX and MMC delivered by both nanoparticle and solution approaches in whole blood and various tissues in an orthotopic breast tumor murine model. The analytical method presented is a useful tool for pre-clinical analysis of nanoparticle-based delivery of drug combinations.

Hybrid Manganese Dioxide Nanoparticles Potentiate Radiation Therapy by Modulating Tumor Hypoxia

Hypoxia in the tumor microenvironment (TME) mediates resistance to radiotherapy and contributes to poor prognosis in patients receiving radiotherapy. Here we report the design of clinically suitable formulations of hybrid manganese dioxide (MnO₂) nanoparticles (MDNP) using biocompatible materials to reoxygenate the TME by reacting with endogenous H₂O₂ MDNP containing hydrophilic terpolymer-protein-MnO₂ or hydrophobic polymer-lipid-MnO₂ provided different oxygen generation rates in the TME relevant to different clinical settings. In highly hypoxic murine or human xenograft breast tumor models, we found that administering either MDNP formulation before radiotherapy modulated tumor hypoxia and increased radiotherapy efficacy, acting to reduce tumor growth, VEGF expression, and vascular density. MDNP treatment also increased apoptosis and DNA double strand breaks, increasing median host survival 3- to 5-fold. Notably, in the murine model, approximately 40% of tumor-bearing mice were tumor-free after a single treatment with MDNPs plus radiotherapy at a 2.5-fold lower dose than required to achieve the same curative treatment without MDNPs. Overall, our findings offer a preclinical proof of concept for the use of MDNP formulations as effective radiotherapy adjuvants. Cancer Res; 76(22); 6643-56. ©2016 AACR.

Abstract 745: Hybrid bioactive nanoparticles for modulating prostate tumor microenvironment and enhancing radiation therapy

Introduction

Tumor hypoxia is a poor prognostic factor in a number of malignancies such as prostate cancer (PCa). Clinically relevant hypoxic levels are detected in 30-90% PCa with oxygen concentrations below that required for half-maximal radiosensitivity, thus making radiotherapy (RT) ineffective alone [10].

Recently our lab has created pharmaceutically acceptable bioreactive hybrid manganese dioxide nanoparticles (MDNPs) and demonstrated their ability to modulate tumor microenvironment (TME) by reacting with H2O2 and protons and producing O2 in hypoxic tumors, as well as to enhance radiation response of tumor.

Methods

Lipid encapsulated and polymer stabilizedMDNPs (LMD NPs) were prepared by dispersing MnO2 precursor particles in melted lipid and polymer and then characterized for the particle size and zeta potential. In-vitro oxygen generation of LMD NPs was examined by measuring oxygen saturation level (sO2) in the blood using photoacoustic (PA) imaging method with addition of LMD NPs and H2O2.

Biodistribution of LMD NPs in PCa tumor-bearing mice was evaluated by using a Xenogen IVIS Spectrum Imaging System following IV injection of ICG labeled NPs through the tail vein. Mice were monitored non-invasively for up to 24 hours.

To investigate the effect of combination of MDNPs and radiation therapy on tumor growth delay and survival, PCa tumor-bearing mice were treated intravenously with LMD NPs with saline as a control. Four hour post injection, 10 Gy radiation dose was given at the site of the tumor. Mice were monitored every 2 days by measuring tumor size using a caliper. Mice were sacrificed when the tumor size reached 500 mm3.

Results

PA imaging demonstrated a controlled and prolonged generation of O2 in the blood with maximum oxygen saturation (90-95%) being reached within 60 min after incubation with LMD NPs and H2O2. The biodistribution and ex-vivo images of the resected organs showed that LMD NPs accumulated in the prostate tumor sites within 1 h post i.v. injection and remained in the tumor for at least 24 h. The ex vivo optical data of excised tissue showed a significant uptake of LMD nanoparticles by prostate tumor 24 hpost particle administration. The combination of LMD NPs treatment with single dose 10 Gy RT inhibited tumor growth by 24% at 5 days post treatment, whereas the tumor size increased about 47% in mice treated with RT alone. LMD NPs plus RT also improved survival rate of the cancerous mice for up to 53 days, which was about 3.3-fold enhancement in the mean survival rate compared to saline plus RT treatment (30 days).

Conclusion

The new bioreactive MnO2 NPs exhibited desirable oxygen- generating profile and high tumor accumulation and retention after systemic administration. This work has demonstrated, in a preclinical prostate tumor model, that the combination of LMD NPs with radiation therapy is a promising treatment approach for solid tumor..

Citation Format: Mohammad Ali Amini, Azhar Z. Abbasi, Claudia R. Gordijo1, Ping Cai, Andrew M. Rauth, Robert G. Bristow, Xiao Yu Wu. Hybrid bioactive nanoparticles for modulating prostate tumor microenvironment and enhancing radiation therapy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 745.

Optimizing the design and in vitro evaluation of bioreactive glucose oxidase-microspheres for enhanced cytotoxicity against multidrug resistant breast cancer cells

Glucose oxidase (GOX) encapsulated in alginate-chitosan microspheres (GOX-MS) was shown in our previous work to produce reactive oxygen species (ROS) in situ and exhibit anticancer effects in vitro and in vivo. The purpose of present work was to optimize the design and thus enhance the efficacy of GOX-MS against multidrug resistant (MDR) cancer cells. GOX-MS with different mean diameters of 4, 20 or 140 μm were prepared using an emulsification-internal gelation-adsorption-chitosan coating method with varying compositions and conditions. The GOX loading efficiency, loading level, relative bioactivity of GOX-MS, and GOX leakage were determined and optimal chitosan concentrations in the coating solution were identified. The influence of particle size on cellular uptake, ROS generation, cytotoxicity and their underlying mechanisms was investigated. At the same GOX dose and incubation time, smaller sized GOX-MS produced larger amounts of H2O2 in cell culture medium and greater cytotoxicity toward murine breast cancer MDR (EMT6/AR1.0) and wild type (EMT6/WT) cells. Fluorescence and confocal laser scanning microscopy revealed significant uptake of small sized (4 μm) GOX-MS by both MDR and WT cells, but no cellular uptake of large (140 μm) GOX-MS. The GOX-MS were equally effective in killing both MDR cells and WT cells. The cytotoxicity of the GOX formulations was positively correlated with membrane damage and lipid peroxidation. GOX-MS induced greater membrane damage and lipid peroxidation in MDR cells than the WT cells. These results suggest that the optimized, small micron-sized GOX-MS are highly effective against MDR breast cancer cells.

A novel nanoparticle formulation overcomes multiple types of membrane efflux pumps in human breast cancer cells

Multidrug resistance (MDR) in cancer cells can involve overexpression of different types of membrane drug efflux pumps and other drug resistance mechanisms. Hence, inhibition of one resistance mechanism may not be therapeutically effective. Previously we demonstrated a new polymer lipid hybrid nanoparticle (PLN) system was able to circumvent drug resistance of P-glycoprotein (P-gp) overexpressing breast cancer cells. The objectives of the present study were 2-fold: (1) to evaluate the ability of the PLN system to overcome two other membrane efflux pumps-multidrug resistance protein 1 (MRP1+) and breast cancer resistance protein (BCRP+) overexpressed on human breast cancer cell lines MCF7 VP (MRP1+) and MCF7 MX (BCRP+); and (2) to evaluate possible synergistic effects of doxorubicin (Dox)-mitomycin C (MMC) in these cell lines. These objectives were accomplished by measuring in vitro cellular uptake, intracellular trafficking, and cytotoxicity (using a clonogenic assay and median effect analysis), of Dox, MMC, or Dox-MMC co-loaded PLN. Treatment of MDR cells with PLN encapsulating single anticancer agents significantly enhanced cell kill compared to free Dox or MMC solutions. Dox-MMC co-loaded PLN were 20-30-folds more effective in killing MDR cells than free drugs. Co-encapsulated Dox-MMC was more effective in killing MDR cells than single agent-encapsulated PLN. Microscopic images showed perinuclear localization of fluorescently labelled PLN in all cell lines. These results are consistent with our previous results for P-gp overexpressing breast cancer cells suggesting the PLN system can overcome multiple types of membrane efflux pumps increasing the cytotoxicity of Dox-MMC at significantly lower doses than free drugs.

Synergistic nanoparticulate drug combination overcomes multidrug resistance, increases efficacy, and reduces cardiotoxicity in a nonimmunocompromised breast tumor model

Anthracyclines, commonly employed for cancer chemotherapy, suffer from dose-limiting cardiotoxicity and poor efficacy due to multidrug resistance (MDR). We previously demonstrated that simultaneous delivery of the synergistic drugs doxorubicin (DOX) and mitomycin C (MMC) by polymer-lipid hybrid nanoparticles (PLN) circumvented MDR, increased efficacy, and reduced cardiotoxicity in immuncompromised mice superior to poly(ethylene glycol)-coated (PEGylated) lipososmal DOX (PLD). Herein it is shown that the DOX-MMC combination was also synergistic in MDR EMT6/AR1 murine breast cancer cells and that their nanoparticle formulations were able to overcome the MDR phenotype. In contrast PLD exhibited little or no effect on the MDR cells. For the first time, these differences in in vitro efficacy are shown to be strongly correlated with cellular uptake and intracellular distribution of DOX brought about by DOX formulations (e.g., free solution, PLN vs PLD). To take into consideration the role of an intact immune system and tumor stroma in the response of host and tumor to chemotherapy, use was made of nonimmunocomprised mouse models to study the dose tolerance, cardiotoxicity, and efficacy of DOX-MMC coloaded PLN (DMsPLN) compared to PLD. DMsPLN treatment at 50 mg/m(2) DOX and 17 mg/m(2) of MMC singly or once every 4 days for 4 cycles were well tolerated by the mice without elevated systemic toxicity blood markers or myocardial damage. In contrast, PLD was limited to a single treatment due to significant total weight loss. The DMsPLN treatment delayed tumor growth up to 312% and 28% in EMT6/WT and EMT6/AR1 models, respectively. This work supports the translational value of DMsPLN for the aggressive management of either naïve or anthracycline-resistant tumors.

Matrigel alters the pathophysiology of orthotopic human breast adenocarcinoma xenografts with implications for nanomedicine evaluation

Matrigel, a mouse sarcoma-derived basement membrane protein mixture, is frequently used to facilitate human tumor xenograft growth in rodents. Despite its known effects on tumor growth and metastasis, its impact on tumor pathophysiology and preclinical evaluation of nanomedicines in tumor xenografts has not been reported previously. Herein bilateral MDA435 tumors were established orthotopically with (Mat+) or without (Mat-) co-injection of Matrigel. Tumor perfusion, morphology and nanoparticle retention were evaluated. As compared to Mat- tumors, Mat+tumors exhibited enhanced vascular perfusion and lymphatic flow, greater blood vessel and lymphatic growth within the tumor core, and more deformation and collapse of lymphatics in tumor-associated lymph nodes. These changes were accompanied by reduced nanoparticle retention in Mat+tumors. The results suggest that Matrigel is not a passive medium for tumor growth, but rather significantly alters long-term tumor architecture. These findings have significant implications for the evaluation of therapeutic nanomedicine in xenograft mouse models.

FROM THE CLINICAL EDITOR

Matrigel is utilized in facilitating human tumor xenograft growth in rodents. The authors demonstrate that Matrigel is not a passive medium for tumor growth; instead it significantly alters long-term tumor architecture, with major implications in the evaluation of therapeutic nanomedicine in xenograft mouse models.

A novel solid lipid nanoparticle formulation for active targeting to tumor α(v) β(3) integrin receptors reveals cyclic RGD as a double-edged sword

The overexpression of α(v) β(3) integrin receptors on tumor cells and tumor vascular endothelium makes it a useful target for imaging, chemotherapy and anti-angiogenic therapy. However integrin-targeted delivery of therapeutics by nanoparticles have provided only marginal, if any, enhancement of therapeutic effect. This work was thus focused on the development of novel α(v) β(3) -targeted near infrared light-emitting solid lipid nanoparticles (SLN) through conjugation to the α(v) β(3) integrin-specific ligand cyclic Arg-Gly-Asp (cRGD), and the assessment of the effects of α(v) β(3) targeting on nanoparticle biodistribution. Since our previously developed non-targeted "stealth" SLN showed little hepatic accumulation, unlike most reported liposomes and micelles, they served as a reference for quantifying the effects of cRGD-conjugation on tumor uptake and whole animal biodistribution of SLN. Non-targeted SLN, actively targeted (RGD-SLN) and blocked RGD-SLN were prepared to contain near infrared quantum dots for live animal imaging. They were injected intravenously to nude mice bearing xenograft orthotopic human breast tumors or dorsal window chamber breast tumors. Tumor micropharmacokinetics of various SLN formulations were determined using intravital microscopy, and whole animal biodistribution was followed over time by optical imaging. The active tumor targeting with cRGD was found to be a "double-edged sword": while the specificity of RGD-SLN accumulation in tumor blood vessels and their tumor residence time increased, their distribution in the liver, spleen, and kidneys was significantly greater than the non-targeted SLN, leaving a smaller amount of nanoparticles in the tumor tissue. Nevertheless the enhanced specificity and retention of RGD-SLN in tumor neovasculature could make this novel formulation useful for tumor neovascular-specific therapies and imaging applications.

Thermally-triggered 'off-on-off' response of gadolinium-hydrogel-lipid hybrid nanoparticles defines a customizable temperature window for non-invasive magnetic resonance imaging thermometry

For effective and safe thermotherapy, real-time, accurate, three-dimensional tissue thermometry is required. Magnetic resonance imaging (MRI)-based thermometry in combination with current temperature responsive contrast agents only provides an 'off-on' signal at a certain temperature, not indicating temperature increases beyond the desired therapeutic levels. To overcome this limitation, a novel Gd-chelated hydrogel-lipid hybrid nanoparticle (HLN) formulation was developed that provides an 'off-on-off' signal defining a thermometric window for MR thermometry. Novel thermally responsive poly(N-isopropylacrylamide-co-acrylamide) (NIPAM-co-AM) hydrogel nanoparticles (<15 nm) with bisallylamidodiethylenetriaminetriacetic acid, a novel crosslinker with Gd(3+) chelation functionality, were synthesized. The Gd-hydrogel nanoparticles were encapsulated in a solid lipid nanoparticle matrix that prevented T(1)-weighted contrast signal enhancement. Melting of the matrix lipid freed the Gd-hydrogel nanoparticles into the bulk water and an 'off-on' contrast signal enhancement occurred. As the temperature was further increased to temperatures greater than, the volume phase transition temperature of the hydrogel nanoparticles, they collapsed and provided an 'on-off' signal diminution. Both the 'off-on' and the 'on-off' transition temperature could be tailored by changing the lipid matrix and altering the NIPAM/AM ratio in the hydrogel, respectively. This allowed MRI thermometry of different temperature windows using the Gd-HLN system.

The Physical State of Viral Nucleic Acid and the Sensitivity of Viruses to Ultraviolet Light

Ultraviolet light action spectra in the range 2250 to 3020 A have been determined for the plaque-forming ability of the following bacteriophage and animal viruses: T-2, varphix-174, R-17, fr, MS2, 7-S, fd, vesicular stomatitis, vaccinia, encephalomyocarditis, reovirus-3, and polyoma. Absolute quantum yields for the plaque-forming ability of MS2, fr, fd, varphix-174, and T-2 were determined over the range 2250 to 3020 A. Relative quantum yields for plaque-forming ability indicated that viruses with single-stranded nucleic acid were on the average ten times more sensitive to UV than double-stranded viruses. In addition for ten of the twelve viruses a relation existed between the shape of their action spectra and the stranded state of their nucleic acid. The ratio of the inactivation cross-section at 2650 A to that at 2250 A for these viruses was 1.0 for single-stranded viruses and 2.0 for viruses with double-stranded nucleic acid. The above relations were dependent on the stranded state of the nucleic acid not the ribose or deoxyribose form of the sugar present.

A novel doxorubicin-mitomycin C co-encapsulated nanoparticle formulation exhibits anti-cancer synergy in multidrug resistant human breast cancer cells

Anthracycline-containing treatment regimens are currently the most widely employed regimens for the management of breast cancer. These drug combinations are often designed based on non-cross resistance and minimal overlapping toxicity rather than drug synergism. Moreover, aggressive doses are normally used in chemotherapy to achieve a greater therapeutic benefit at the cost of more acute and long-term toxic effects. To increase chemotherapeutic efficacy while decreasing toxic effects, rational design of drug synergy-based regimens is needed. Our previous work showed a synergistic effect of doxorubicin (DOX) and mitomycin C (MMC) on murine breast cancer cells in vitro and improved efficacy and reduced systemic toxicity of DOX-loaded solid polymer-lipid hybrid nanoparticles (PLN) in animal models of breast cancer. Herein we have demonstrated true anticancer synergy of concurrently applied DOX and MMC, and have rationally designed PLN to effectively deliver this combination to multidrug resistant (MDR) MDA435/LCC6 human breast cancer cells. DOX-MMC co-loaded PLN were effective in killing MDR cells at 20-30-fold lower doses than the free drugs. This synergistic cell killing was correlated with enhanced induction of DNA double strand breaks that preceded apoptosis. Importantly, co-encapsulation of dual agents into a nanoparticle formulation was much more effective than concurrent application of single agent-containing PLN, demonstrating the requirement of simultaneous uptake of both drugs by the same cells to enhance the drug synergy. The rationally designed combination chemotherapeutic PLN can overcome multidrug resistance at a significantly lower dose than free drugs, exhibiting the potential to enhance chemotherapy and reduce the therapeutic limitations imposed by systemic toxicity.

On the synergistic effect of doxorubicin and mitomycin C against breast cancer cells

The combination of doxorubicin and mitomycin C has been shown previously to result in supra-additive tumor cell killing in vitro in both murine and human breast cancer cells and in vivo against murine breast cancer cells. Median effect analysis was used to determine the significance and degree of interaction. The origin of this synergy was sought by evaluating the contribution of membrane efflux pump modulation, formaldehyde production, reactive oxygen species, DNA cross-linking, and DNA double-strand breaks to this effect. The interaction of mitomycin C and doxorubicin in vitro was found to be a true synergy whose mechanism was efflux pump-independent. DNA cross-links were only found to increase additively with co-administration of the drugs; however, a supra-additive increase in DNA double-strand breaks was observed. The results suggest that poisoning of topoisomerase IIalpha by doxorubicin may interact with drug-induced DNA cross-links to enhance the formation of DNA double-strand breaks. This interaction, together with glutathione depletion and mitomycin C-derived formaldehyde, may be the underlying mechanism(s) of the synergy observed between mitomycin C and doxorubicin.

Chemotherapy with anticancer drugs encapsulated in solid lipid nanoparticles

The prospect of improved cancer chemotherapy using solid lipid nanoparticles (SLN) as a drug delivery system is promising. Several obstacles frequently encountered with anticancer compounds, such as normal tissue toxicity, poor specificity and stability and a high incidence of drug-resistant tumor cells, are at least partially overcome by delivering them using SLN. The emergence of the newer forms of SLN such as polymer-lipid hybrid nanoparticles, nanostructured lipid carriers and long-circulating SLN may further expand the role of this versatile drug carrier in cancer treatment. This review focuses on the current use of SLN for the encapsulation and delivery of cytotoxic anticancer compounds. It also discusses more recent trends in the use of SLN as vehicles for delivery of chemosensitizers and cytotoxic therapeutic molecules. It is anticipated that, in the near future, SLN will be further improved to deliver anticancer compounds in a more efficient, specific and safer manner.

Screening of Lipid Carriers and Characterization of Drug-Polymer-Lipid Interactions for the Rational Design of Polymer-Lipid Hybrid Nanoparticles (PLN)

PURPOSE

The thermodynamics and solid state properties of components and their interactions in a formulation for polymer-lipid hybrid nanoparticles (PLN) were characterized for screening lead lipid carriers and rational design of PLN.

METHODS

Verapamil HCI (VRP) was chosen as a model drug and dextran sulfate sodium (DS) as a counter-ionic polymer. Solubility parameters of VRP, VRP-DS complex, and various lipids were calculated and partition of VRP and VRP-DS in lipids was determined. Thermodynamics of VRP binding to DS was determined by isothermal titration calorimetry (ITC). The solid state properties of individual components and their interactions were characterized using differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD).

RESULTS

Dodecanoic acid (DA) was identified as the best lipid carrier among all lipids tested based on the solubility parameters and partition coefficients. VRP-DS complexation was a thermodynamically favorable process. Maximum binding capacity of DS and the highest drug loading capacity of DA were obtained at an equal ionic molar ratio of DS to VRP. In the PLN formulation, DA remained its crystal structure but had a slightly lower melting point, while VRP-DS complex was in an amorphous form.

CONCLUSIONS

Drug loading efficiency and capacity of a lipid matrix depend on the VRP-DS binding and the interactions of the complex with the lipid. A combined analysis of solubility parameters and partition coefficients is useful for screening lipid candidates for PLN preparation.

A new polymer-lipid hybrid nanoparticle system increases cytotoxicity of doxorubicin against multidrug-resistant human breast cancer cells

PURPOSE

This work is intended to develop and evaluate a new polymer-lipid hybrid nanoparticle system that can efficiently load and release water-soluble anticancer drug doxorubicin hydrochloride (Dox) and enhance Dox toxicity against multidrug-resistant (MDR) cancer cells.

METHODS

Cationic Dox was complexed with a new soybean-oil-based anionic polymer and dispersed together with a lipid in water to form Dox-loaded solid lipid nanoparticles (Dox-SLNs). Drug loading and release properties were measured spectrophotometrically. The in vitro cytotoxicity of Dox-SLN and the excipients in an MDR human breast cancer cell line (MDA435/LCC6/MDR1) and its wild-type line were evaluated by trypan blue exclusion and clonogenic assays. Cellular uptake and retention of Dox were determined with a microplate fluorometer.

RESULTS

Dox-SLNs were prepared with a drug encapsulation efficiency of 60-80% and a particle size range of 80-350 nm. About 50% of the loaded drug was released in the first few hours and an additional 10-20% in 2 weeks. Treatment of the MDR cells with Dox-SLN resulted in over 8-fold increase in cell kill when compared to Dox solution treatment at equivalent doses. The blank SLN and the excipients exhibited little cytotoxicity. The biological activity of the released Dox remained unchanged from fresh, free Dox. Cellular Dox uptake and retention by the MDR cells were both significantly enhanced (p < 0.05) when Dox was delivered in Dox-SLN form.

CONCLUSIONS

The new polymer-lipid hybrid nanoparticle system is effective for delivery of Dox and enhances its efficacy against MDR breast cancer cells.

In vitro toxicity to breast cancer cells of microsphere-delivered mitomycin C and its combination with doxorubicin

To better understand and design microsphere systems for the locoregional delivery of anticancer drug combinations to solid tumors, (1) the cytotoxicity of microsphere-delivered mitomycin C (MMC) was evaluated and (2) various schedules of MMC and doxorubicin (Dox) were tested for their toxicity in vitro towards a murine breast cancer cell-line, EMT6. To accomplish the former MMC was loaded onto oxidized sulfopropyl dextran microspheres, released in a pH 7.4 buffer solution and tested for its potency against EMT6 cells versus a standard MMC solution. For the latter EMT6 cells were exposed to MMC or Dox as single agents or together using various drug concentrations and schedules. The efficacy of the treatments was measured using a clonogenic assay. MMC released from the microspheres showed similar activity against EMT6 cells to freshly prepared MMC solutions. Greater-than-additive toxicity was observed when MMC was given either simultaneously or after Dox exposure. In contrast, administration of MMC before Dox exposure resulted in toxicity that ranged from additive to sub-additive; this reduced toxicity was mainly due to increasing cell density arising from the design of the assay. These results help explain our previous in vivo investigations using microsphere-delivered combinations of the same agents in EMT6 solid tumors.

A mechanistic study of enhanced doxorubicin uptake and retention in multidrug resistant breast cancer cells using a polymer-lipid hybrid nanoparticle system

The objectives of this study were to evaluate the potential of a polymer-lipid hybrid nanoparticle (PLN) system to enhance cellular accumulation and retention of doxorubicin (Dox), a widely used anticancer drug and an established P-glycoprotein (Pgp) substrate, in Pgp-overexpressing cancer cell lines and to explore the underlying mechanisms. Nanoparticles containing Dox complexed with a novel anionic polymer (Dox-PLN) were prepared using an ultrasound method. Two Pgp-overexpressing breast cancer cell lines (a human cell line, MDA435/LCC6/MDR1, and a mouse cell line, EMT6/AR1) were used to investigate the effect of nanoparticles on cellular uptake and retention of Dox. Endocytosis inhibition studies and fluorescence microscopic imaging were performed to elucidate the mechanisms of cellular drug uptake. Treatment of Pgp-overexpressing cell lines with Dox-PLNs resulted in significantly enhanced Dox uptake and more substantial increases in drug retention after the end of treatment compared with free Dox solutions (p < 0.05). Fluorescence microscopic images showed improved nuclear localization of Dox and uptake of lipid when the drug was delivered in the Dox-PLN form to MDA435/LCC6/MDR1 cells. Endocytosis inhibition studies revealed that phagocytosis is an important pathway in the membrane permeability of the nanoparticles. These findings suggest that some of the Dox physically associated with the nanoparticles bypass the membrane-associated Pgp when delivered as Dox-PLNs, and in this form, the drug is better retained within the Pgp-overexpressing cells than the free drug. The present study suggests a new mechanism for overcoming drug resistance in Pgp-overexpressing tumor cells using lipid-based nanoparticle formulations.

Biodegradable dextran-based microspheres for delivery of anticancer drug mitomycin C

The purpose of this work was to develop a biodegradable microsphere (MS) system for delivering mitomycin C (MMC). Various dextran-based MS systems were investigated for their loading and release characteristics, including nonionic MS, sulfopropyl dextran microspheres (SP-MS) with low or high cross-linking density, oxidized SP-MS (Ox-MS), and hydrophobically modified SP-MS. SP-MS were chemically modified by oxidation with sodium periodate or by reaction with anhydride. The chemical structure of modified SP-MS and MMC-loaded MS (MMC-MS) were examined using Fourier transform infrared (FTIR) and solid-state nuclear magnetic resonance (NMR) spectrophotometry. Drug release was conducted at 37 degrees C in aqueous solutions of 0.15 m phosphate buffer solution. The kinetics of drug absorption and release and the stability of MMC after loading and release were determined by spectrophotometry and high-performance liquid chromatography. Ionic SP-MS exhibited a higher drug-loading rate and capacity when compared to nonionic MS, while hydrophobically modified SP-MS showed an even greater loading capacity than SP-MS. These results suggest that both ionic complexation and hydrophobic interaction were important factors in MMC loading. The Ox-MS system demonstrated higher drug-loading capacity, more fractional drug release and a longer time to reach release equilibrium as compared to other investigated MS systems. Under optimized reaction and loading conditions, MMC released from Ox-MS was found to be unaltered. This work demonstrates that the Ox-MS system is a potentially useful system for the delivery of MMC.

Prediction of kinetics of doxorubicin release from sulfopropyl dextran ion-exchange microspheres using artificial neural networks

The purpose of this work was to develop artificial neural networks (ANN) models to predict in vitro release kinetics of doxorubicin (Dox) delivered by sulfopropyl dextran ion-exchange microspheres. Four ANN models for responses at different time points were developed to describe the release profiles of Dox. Model selection was performed using the Akaike information criterion (AIC). Sixteen data sets were used to train the ANN models and two data sets for the validation. Good correlations were obtained between the observed and predicted release profiles for the two randomly selected validation data sets. The difference factor (f1) and similarity factor (f2) between the ANN predicted and the observed release profiles indicated good performance of the ANN models. The established models were then applied to predict release kinetics of Dox from the microspheres of various initial loadings in media of different ionic strengths and NaCl/CaCl2 ratios. The results suggested that ANN offered a flexible and effective approach to predicting the kinetics of Dox release from the ion-exchange microspheres.

In vivo efficacy and toxicity of intratumorally delivered mitomycin C and its combination with doxorubicin using microsphere formulations

The efficacy and toxicity of intratumorally (i.t.) administered anticancer drugs mitomycin C (MMC) and doxorubicin (Dox) incorporated in polymeric microspheres were investigated. Biodegradable sulfopropyl dextran microspheres and their oxidized products were used to load Dox and MMC, respectively. EMT6 mouse mammary cancer cells were injected into the hind leg of BALB/c mice. MMC microspheres, alone or combined with Dox microspheres, were injected i.t. once tumors had reached around 0.3 g. The tumor-plus-leg diameter was measured daily and the delay in time for the tumor to grow to 1.13 g relative to control (TGD) was employed as an indication of therapeutic effect. General toxicity was determined by monitoring weight, appearance and behavior of the mice. Morphology and histology of tumor and heart tissues were also examined. An average 79% TGD was observed after i.t. injection of MMC microspheres. The i.t. co-administration of MMC and Dox microspheres resulted in a 185% TGD. The i.t. injections of the microsphere formulations did not result in visible signs of toxicity in animals. In contrast, systemic (i.e. i.p.) injections of MMC solutions caused considerable general toxicity. This study suggests that i.t. delivery of anticancer drugs by polymeric microspheres is an effective way of improving the therapeutic index for cancer chemotherapy of selected solid tumors under special conditions.

A new approach to the in vivo and in vitro investigation of drug release from locoregionally delivered microspheres

The purpose of this work was to determine the in vivo release profile of doxorubicin (Dox) delivered locoregionally by dextran-based microspheres (MS) and to develop an in vitro method for predicting in vivo drug release from MS-- in vitro-in vivo correlation (IVIVC). For the determination of in vivo Dox release, drug-loaded MS were placed into hollow fibers (HF) and implanted subcutaneously into C3H mice. Samples were retrieved at various times following implantation, MS removed from HF, and the amount of Dox remaining determined via ultraviolet/visible (UV/Vis) spectrophotometry. Various in vitro systems were designed and investigated for their ability to link in vivo and in vitro release profiles, including an open system (e.g. a column) with continuous flow of release medium at different flow rates and closed systems (e.g. a cuvette) using different release media and conditions. About 34% of loaded Dox was released from MS in vivo at 48 h. Only an incremental release was observed over the ensuing 72 h. The release kinetics of Dox from MS using three of the investigated in vitro systems, column system and HF immersed in a buffer solution or growth medium gave release profiles that were highly correlated with the in vivo release profile (r(2)>0.9). The relationships, both linear and non-linear, suggest that Level A IVIVC models can be developed for Dox release from locoregionally delivered MS using specially designed release systems.

Delivery of an anticancer drug and a chemosensitizer to murine breast sarcoma by intratumoral injection of sulfopropyl dextran microspheres

Intratumoral injection of controlled-release microsphere formulations of anticancer compounds has the potential to selectively increase tumour exposure to drugs. This work aimed to evaluate the therapeutic effect and toxicity of microsphere formulations containing the anticancer drug, doxorubicin, in a murine tumour model. The effect of co-administration of verapamil, a P-glycoprotein modulator or chemosensitizer, was investigated. Initial in-vitro studies confirmed the ability of verapamil to enhance the accumulation of both doxorubicin and [(99mTc)]sestamibi, also a P-glycoprotein substrate, in EMT6 murine breast sarcoma cells and a doxorubicin-selected multidrug-resistant variant, EMT6/AR1.0. Ex-vivo studies using confocal microscopy demonstrated release of doxorubicin from microspheres and diffusion of the drug through tissue. For in-vivo studies, EMT6 and EMT6/AR1.0 cells were grown in BALB/c mice. Following intratumoral injection of doxorubicin-loaded microspheres, alone or in combination with verapamil-loaded microspheres, the tumour diameter was measured serially as an indication of therapeutic effect, while the weight, appearance, and behaviour of the mice were monitored as an indication of general toxicity. Intratumoral injections of doxorubicin-loaded microspheres were tolerated much better than systemic administration of equivalent drug concentrations. There was a modest (up to 34%) delay of tumour growth compared with groups receiving no treatment or blank microspheres. Co-injection of verapamil microspheres with doxorubicin microspheres produced a moderate increase in toxicity but no further delay in tumour growth. Controlled-release microsphere formulations of anticancer agents administered intratumorally were an efficient way to deliver high drug doses to the tumour with little systemic toxicity.

Accumulation of technetium-99m glucarate: in vitro cell cultures and in vivo tumour models

99mTc-glucarate is an investigational radiopharmaceutical which has been shown to accumulate in acute cerebral and myocardial injuries and in some tumours. In the present work, a survey of possible factors affecting the cellular accumulation of 99mTc-glucarate was carried out in cell lines and strains in vitro and in murine tumours in vivo. Accumulation was enhanced under hypoxic conditions in 12 of the 16 human and murine cell lines and strains studied, and inhibited in the presence of nitroimidazoles. At temperatures lower than 37 degrees C, accumulation was reduced, but a hypoxic/aerobic differential was maintained. Aerobic accumulation of 99mTc-glucarate was enhanced by cyanide. In transplanted tumours in mice, 99mTc-glucarate showed high tumour/muscle and tumour/blood ratios at early times after injection. Pharmacological enhancement of the extent of hypoxia by the administration of hydralazine or nitro-L-arginine resulted in significantly increased accumulation of 99mTc-glucarate in the tumour. The in vitro and in vivo properties of 99mTc-glucarate suggest that it may be useful for tumour imaging in the clinic, although the exact mechanism(s) by which it localizes in tumours remains unknown.

Expression of the prodrug-activating enzyme DT-diaphorase via Ad5 delivery to human colon carcinoma cells in vitro

Intratumoral injection of recombinant adenoviral type 5 (Ad5) vectors that carry prodrug-activating enzymes like DT-diaphorase (DTD) could be used to selectively target tumor cells for chemotherapy. To demonstrate the feasibility of this approach, Ad5 vectors were constructed, which express human DTD minigenes for both wild-type and mutant (C-to-T change in nucleotide 609 in DTD cDNA) DTD under the control of the cytomegalovirus (CMV) promoter. HT29 human colon carcinoma cells express wild-type DTD, whereas BE human colon carcinoma cells express mutant DTD, have low to undetectable DTD activity, and are 4- to 6-fold more resistant to mitomycin C (MMC) than HT29 cells. A test of the ability of Ad5 to infect these cells (using a beta-galactosidase CMV-driven minigene) indicated that 90-100% of BE cells were infected at a multiplicity of infection (MOI) of 100, whereas only 15-40% of HT29 cells were infected at this MOI. Infection of BE cells in vitro with recombinant Ad5 carrying a minigene for wild-type DTD at MOIs of 3-100 resulted in a progressive increase in DTD activity and a maximal 8-fold increase in sensitivity to MMC as measured by a colony-forming assay. HT29 cells were sensitized 2- to 3-fold following treatment with Ad5.DTD at an MOI of 100. These results indicate that adenovirus-mediated gene transfer and expression of wild-type DTD can sensitize resistant tumor cells to MMC and that this therapeutic strategy may exert a significant bystander effect.

A study of doxorubicin loading onto and release from sulfopropyl dextran ion-exchange microspheres

The objective of this study was to investigate various factors that influence doxorubicin (Dox) loading onto and release from sulfopropyl dextran ion-exchange microspheres (MS), and to evaluate the anticancer activity of the released drug in vitro. Dox was incorporated into the MS by incubating the MS with aqueous solutions of Dox at room temperature. The drug release was carried out at 37 degrees C in aqueous solutions containing NaCl with or without CaCl2. The kinetics of drug absorption and release, the amount of Dox released, and the stability of Dox after loading, freeze-drying, and release were determined by spectrophotometry. The cytotoxicity of Dox (the original drug or that released from MS) against murine EMT6 breast cancer cells was assessed using a clonogenic assay. An increase in the MS to drug ratio resulted in a higher absorption rate and a higher fraction of the drug extracted from the solution. The release rate and the equilibrium fraction of Dox released increased with a decrease in the initial amount of Dox loaded or an increase in the salt concentration. The addition of divalent ions (Ca2+) promoted drug release compared to NaCl alone. The percent loss of colony forming ability of the cells, a measure of cytotoxicity of the released Dox, was the same as parent Dox solutions, indicating that the drug bioactivity was fully preserved after the drug loading and release cycle. This work demonstrated that various drug release rates were achieved by varying the drug loading and that the MS-delivered Dox was effective against the cancer cells in vitro.

Cellular accumulation and retention of the technetium-99m-labelled hypoxia markers BRU59-21 and butylene amine oxime

BRU59-21 and 99mTc-butylene amine oxime (BnAO, HL91) are being evaluated for imaging hypoxia in tumors. Both tracers: 1) rapidly reached a plateau in aerobic Chinese hamster ovary cells in vitro but continuously accumulated in hypoxic cells; 2) ceased to accumulate when hypoxic cells were exposed to air; 3) showed approximately 40% retention upon washing the cells; 4) showed selective hypoxic accumulation only at 37 degrees C; 5) accumulation could be modulated by addition of electron-affinic compounds; and 6) exhibited higher accumulation in cells which overexpress cytochrome P450 reductase. Both BRU59-21 and 99mTc-BnAO share properties making them suitable for hypoxia imaging.

Comparison of the accumulation and efflux kinetics of technetium-99m sestamibi and technetium-99m tetrofosmin in an MRP-expressing tumour cell line

The potential clinical use of technetium-99m labeled sestamibi (Tc-MIBI) and tetrofosmin (Tc-Tfos) to image tumours is currently being evaluated. In this study. the accumulation and efflux of Tc-MIBI and Tc-Tfos in the nasopharyngeal carcinoma cell line CNE-1 were examined in the presence or absence of various inhibitors of P-glycoprotein (PGP) and/or multidrug resistance associated protein (MRP) activity [GG918, PSC833, verapamil (Vrp), cyclosporin A (CsA) and buthionine sulfoximine (BSO)]. Reverse-transcriptase polymerase chain reaction analysis and immunodetection of the CNE-1 cells detected expression of MRP, MRPI and MRP2 but not PGP. Tc-MIBI and Tc-Tfos accumulation was increased (P < 0.0001) and efflux decreased (P < 0.05) in the presence of BSO, CsA, Vrp and PSC833 but not GG918, which is a specific inhibitor of PGP. The absolute accumulation of Tc-MIBI was approximately twofold higher than that seen with Tc-Tfos, whereas the addition of inhibitors caused a much greater suppression of Tc-Tfos transport (>2 times greater than for Tc-MIBI). However, no qualitative differences in inhibitors were seen between Tc-MIBI and Tc-Tfos. These results suggest that both Tc-MIBI and Tc-Tfos are substrates for the MRP transporter and that PSC833, Vrp, CsA and BSO but not GG918 can inhibit MRP activity. These results indicate that Tc-MIBI and Tc-Tfos may be suitable imaging agents for detecting MRP-mediated drug resistance in human cancers.

Assessment of the relationship between genotypic status of a DT-diaphorase point mutation and enzymatic activity

DT-diaphorase, a cytosolic reductase, has been implicated as an activator of chemotherapeutic prodrugs and a detoxifier of certain potentially carcinogenic xenobiotics. A common C to T nucleotide 609 substitution in DT-diaphorase cDNA has been associated with protein instability and reduced catalytic activity. The degree to which the allelic status of the substitution correlates with enzymatic activity was assessed in 45 normal human skin fibroblast strains using a PCR-RFLP assay. Included in this study was the 3437T strain, which is unique in that it is heterozygous for the polymorphism yet contains undetectable enzymatic activity. An allele-specific RT-PCR-RFLP technique attributed this phenomenon to exclusive DT-diaphorase mRNA expression from the variant allele. Overlap in activities was observed between individual strains homozygous for the wild-type allele and heterozygotes, but the former group displayed enzymatic activity that was on average 2-fold higher. Western blot analysis of the two strains in this panel that are homozygous for the variant allele revealed that they express relatively low amounts of DT-diaphorase protein, consistent with the role of the substitution in protein instability. This work confirms that genotypic status is a reliable initial estimate of DT-diaphorase activity.

A novel amine-dioxime chelator for technetium-99m: synthesis and evaluation of 2-nitroimidazole-containing analogues as markers for hypoxic cells

A novel amine-dioxime chelator for (99m)Tc has been developed. It offers the advantages of ease of synthesis and flexibility in alteration of lipophilicity. Labeling by stannous reduction of pertechnetate takes place rapidly and efficiently at room temperature and is stable for 24 h. The (99m)Tc:ligand ratio is believed to be 1:2. Seven different alkyl moieties were used to achieve a range of lipophilicities. Three series of compounds were prepared: 2-nitroimidazoles as potential hypoxia-targeting agents, 4-nitroimidazoles as a less easily reduced isomer, and untargeted anilines. In an in vitro model of cellular hypoxia, the 2-nitroimidazole compounds all showed selective accumulation whereas 4-nitroimidazoles showed variable selectivity and aniline showed no selectivity. These experiments demonstrate the potential utility of the 2-nitroimidazole derivatives of the amine-dioxime class of chelator as hypoxia-targeting agents.

Role of NADPH:cytochrome P450 reductase in the hypoxic accumulation and metabolism of BRU59-21, a technetium-99m-nitroimidazole for imaging tumor hypoxia

Nitroimidazoles labeled with technetium-99m are being investigated as non-invasive markers of tumor hypoxia. They are bioreductive compounds that require enzymatic reduction for retention in hypoxic cells, but little is known about the cellular factors affecting their accumulation in hypoxic cells. If the absolute accumulation of hypoxia markers is affected by enzyme levels, an inaccurate assessment of the hypoxic cell fraction in tumors may occur. BRU59-21, (99m)Tc-oxo[[3,3,9, 9-tetramethyl-6-[(2-nitro-1H-imidazol-1-yl)methyl]5-oxa-4, 8-diazadioximato]-(3-)-N,N',N",N"'] technetium (V), a technetium-99m-nitroimidazole that is being studied as a potential marker of tumor hypoxia, was used in the present study to evaluate the effect of NADPH:cytochrome P450 reductase (EC 1.6.2.4) levels on BRU59-21 accumulation and metabolism. Metabolism of BRU59-21 in hypoxic cellular lysates derived from Chinese hamster ovary cells overexpressing NADPH:cytochrome P450 reductase was 8-fold greater than in control cells. This effect required the presence of exogenous NADPH. The increased metabolism of BRU59-21 in lysates overexpressing NADPH:cytochrome P450 reductase was inhibited at 4 degrees and by the addition of NADPH:cytochrome P450 reductase inhibitors. The addition of inhibitors of other nitroreductase enzymes had no effect on BRU59-21 metabolism in these lysates. When the accumulation and metabolism of BRU59-21 were studied in stirred suspension cultures, it was found that cells overexpressing NADPH:cytochrome P450 reductase exhibited about a 3-fold increase in both the hypoxic metabolism and the accumulation of BRU59-21. These findings suggest that NADPH:cytochrome P450 reductase is an important enzyme in BRU59-21 metabolism in model systems of tumor hypoxia.

Targeting hypoxia in tumors using 2-nitroimidazoles with peptidic chelators for technetium-99m: effect of lipophilicity

Tumor hypoxia is an important prognostic factor for response to therapy. Radiolabeled 2-nitroimidazoles have been used for imaging hypoxia, and the octanol/water partition coefficient (P) of these compounds appears to play a crucial role in their suitability for imaging. A series of 11 2-nitroimidazoles coupled to peptidic chelators for (99m)Tc with divergent P was developed and evaluated in an in vitro system. Two classes of N(3)S chelators were used: dialkyl-Gly-Ser-Cys-linker-2-nitroimidazole (Class I) and dialkyl-Gly-Lys(2-nitroimidazole)-Cys (Class II). The chelators were prepared by automated solid-phase peptide synthesis. Xanthine oxidase was able to reduce the 2-nitroimidiazole moiety on the ligands, but the rate of reduction varied 5-fold among the different chelators. The chelators were labeled by transchelation from [(99m)Tc]gluconate at temperatures between 22 and 100 degrees C. The reaction mixtures were analyzed by HPLC and their P values determined. The accumulation of each complex in suspension cultures of Chinese hamster ovary cells incubated under aerobic or extremely hypoxic conditions was determined. Radiochemical yields ranged from 5 to 80% for the 11 compounds. HPLC showed that some of the compounds formed two complexes with (99m)Tc, possibly syn and anti conformations with respect to the Tc=O bond. In general, the Class I chelators labeled more readily than the class II chelators. The P values of the (99m)Tc complexes varied from 0.0002 to 5 and were generally in accordance with predictions based on structure. There were also differences in P as a function of pH; the free acids had a lower P at pH 7.4 than at pH 2.0 due to ionization, whereas the amides did not show this effect. Accumulation levels in aerobic cells were related to P but varied over a narrow range. Four of the 11 compounds showed selective accumulation in hypoxic cells. The peptidic class of 2-nitroimidazoles, with flexible design and convenient solid-phase synthesis, deserves further study as agents for imaging hypoxia in tumors.

BRU59-21, a second-generation 99mTc-labeled 2-nitroimidazole for imaging hypoxia in tumors

Hypoxia in tumors is believed to be an important cause of local failure of radiotherapy in certain types of cancer. BRU59-21 (BMS194796) is a second-generation 99mTc-labeled 2-nitroimidazole that has been shown to offer improved characteristics for imaging myocardial ischemia. It has now been evaluated in models of tumor hypoxia.

METHODS

Accumulation of BRU59-21 was compared with that of BMS181321 in Chinese hamster ovary cells incubated under aerobic or hypoxic conditions. The effects of competition with unlabeled nitroimidazoles and oxygen were studied. Biodistribution studies were performed in mice bearing transplanted KHT-C tumors in the leg.

RESULTS

Within 5 min, BRU59-21 partitioned into aerobic cells in vitro at a level 10 times higher than external medium with no further increase over time. In hypoxic cells this initial partitioning was followed by selective accumulation to levels 5 times higher than in aerobic cells by 4 h. Low levels of oxygen (approximately 40 ppm) inhibited the maximal accumulation rate by 50%. Unlabeled misonidazole, a 2-nitroimidazole, inhibited accumulation of radioactivity, whereas tinidazole, a 5-nitroimidazole, enhanced accumulation; similar effects had been reported with BMS181321. Biodistribution studies in mice showed rapid clearance of radioactivity from the blood, resulting in enhanced tumor-to-blood ratios compared with BMS181321. Increasing the hypoxic fraction in the tumor by injection of nitro-L-arginine resulted in increased retention of tracer in the tumor without affecting other tissues.

CONCLUSION

These results suggest that BRU59-21 warrants further investigation as an agent for imaging tumor hypoxia in the clinic.

Synthesis and evaluation of two technetium-99m-labeled peptidic 2-nitroimidazoles for imaging hypoxia

The presence of hypoxic cells in solid tumors is a marker for therapy-resistant, aggressive disease. The noninvasive detection of hypoxic cells in tumors by radiolabeled 2-nitroimidazoles is a diagnostic technique under current evaluation. Two peptidic agents, dimethylglycyl-L-seryl-L-cysteinyl-lysyl{N(epsilon)-[1-(2-nitro-1H -im idazolyl)acetamido]}glycine (RP435) and dimethylglycyl-tert-butylglycyl-L-cysteinyl-glycine-[2-(2-ni tro-1H-im idazolyl)ethyl]amide (RP535) have been synthesized. Both agents contain an N(3)S class chelator for (99m)Tc and Re and a 2-nitroimidazole group which can be enzymatically reduced and selectively trapped in cells under hypoxic conditions. Two isomers of (99m)TcO-RP435, which are assumed to be syn and anti conformations, were observed on HPLC analysis. The interconversion of the two isomers in aqueous solution was investigated. In contrast, RP535 chelated (99m)Tc to form a single isomer and no conversion to its counterpart has been observed on HPLC analysis. The tert-butyl group on the chelator may inhibit the formation and interconversion of the syn and anti isomers of (99m)TcO-RP535. Both tracers showed a significant degree of hypoxia-specific accumulation in an in vitro assay, with (99m)TcO-RP535 showing higher selectivity for hypoxic cells than (99m)TcO-RP435. These results suggest that (99m)TcO-RP535 represents a lead compound worthy of further investigation as an agent for imaging hypoxia in tumors.

Bioreductive therapies: an overview of drugs and their mechanisms of action

PURPOSE

Bioreductively activated drugs have been used as antimicrobials, chemotherapeutic agents, and radiation sensitizers. The present paper is an overview of their mechanism of action and application in the treatment of cancer.

MATERIALS AND METHODS

Drugs such as nitroimidazoles, mitomycins, and benzotriazine di-N-oxides were a focus of this research. Studies have ranged from the chemistry of the reductive process of activation to in vitro and in vivo studies in rodent and human cells, through to clinical testing. The variety of techniques and test systems brought to bear on these compounds is a strength of this field of research.

RESULTS

A detailed chemical understanding of the mechanism of action of a variety of bioreductives is now available. The enzymatic processes by which these drugs are activated and the cofactors involved in this activation are becoming well understood. Recent advances have been made in the design and use of dual-function bioreductives, bioreductive triggers of drug activation, and DNA-targeted bioreductives. Significant success has been demonstrated clinically with bioreductive drugs, used in combination with radiation and front-line chemotherapeutic agents. The areas of antibody-directed enzyme prodrug therapy (ADEPT) and gene-directed enzyme prodrug therapy (GDEPT) are identified as new directions for bioreductive therapy.

CONCLUSION

The use of bioreductively-activated drugs for the treatment of cancer has made steady progress. The success obtained clinically and the new molecular approaches currently being implemented promise significant advances in the future.

Studies of 99mTc-BnAO (HL-91): a non-nitroaromatic compound for hypoxic cell detection

PURPOSE

Solid tumours of similar type and stage can vary widely in their hypoxic cell fraction. Such cells may be prognostic for aggressive, metastatic, and radiation-resistant disease. A 99mtechnetium (99mTc)-labelled non-nitroaromatic agent, butyleneamine oxime (99mTc-BnAO) or HL-91 (Amersham International, Inc., Amersham, UK) has been evaluated both in vitro and in vivo for its possible efficacy as a noninvasive marker for the clinical detection of hypoxic cells in solid tumours.

MATERIALS AND METHODS

Suspension cultures of Chinese hamster ovary (CHO) cells under controlled levels of oxygen were used to measure the oxygen dependency of 99mTc-BnAO accumulation. V79 cells grown as multilayers on a semipermeable membrane served as an in vitro model for drug penetration through the extravascular space of the tumour. C3H mice bearing KHT-C leg tumours were the in vivo models for selective drug accumulation as a function of time after i.v. administration of 99mTc-BnAO.

RESULTS

99mTc accumulated selectively in hypoxic vs. aerobic cells, resulting in a 9 +/- 2-fold differential in radioactivity per cell at 4 h. The k(m) for this selective accumulation was 20 ppm of oxygen. The labelled drug was equally effective in penetrating the cellular multilayer under aerobic or hypoxic conditions. In vivo measurements indicated favourable labelling of solid tumours containing hypoxic cells with 1% of the total activity per g of tumour, a tumour-to-blood ratio of 1.2, and a tumour-to-muscle ratio of 4.6 at 4 to 6 h after drug administration. In contrast to more lipophilic 99mTc- labelled compounds, excretion was primarily via the urinary tract. Nitro-L-arginine selectively increased solid tumour labelling over normal tissue.

CONCLUSIONS

99mTc-BnAO or HL-91 is a promising agent for clinical studies of tumour hypoxia, although the mechanism of its selective hypoxic cell accumulation remains unexplained.

Role of a DT-diaphorase mutation in the response of anal canal carcinoma to radiation, 5-fluorouracil, and mitomycin C

PURPOSE

To determine, retrospectively, the status of the bp 609 mutation in the DT-diaphorase gene in anal canal carcinoma patients who have undergone radical radiotherapy with concurrent 5-fluorouracil (5-FU) and mitomycin C (MMC), to determine the relationship of the mutant form of the gene to treatment outcomes.

METHODS AND MATERIALS

Paraffin blocks of pretreatment tumor biopsies were obtained on 49 patients who underwent treatment with curative intent using radiation, infusional 5-FU and bolus MMC from January 1991 to December 1993. DNA was extracted and subjected to polymerase chain reaction (PCR) analysis using primers that encompassed the bp 609 C to T mutation. Restriction endonuclease cleavage with Hinf 1 and gel electrophoresis were used to determine the polymorphism status of each patient.

RESULTS

DNA of 46 patients was successfully amplified. The 46 patients were distributed as follows: 26 (56.5%) C/C-homozygous wildtype, 18 (39%) T/C-heterozygous, and 2 (4.5%) T/T-homozygous mutant. Eleven of 46 patients had suffered treatment failure. The status of the bp 609 polymorphism in this group was 5 (45.5%) C/C, 5 (45.5%) C/T, and 1 (9%) T/T.

CONCLUSION

In this series, there was not an overrepresentation of the mutant allele in patients with treatment failure, suggesting that the bp 609 alteration is not a strong determinant of treatment outcome.

Oxidative stress and 1-methyl-2-nitroimidazole cytotoxicity

The 2-nitroimidazoles have been used clinically to radiosensitize resistant hypoxic cells, but a dose-limiting peripheral neuropathy has restricted their therapeutic effectiveness. A model compound, 1-methyl-2-nitroimidazole (INO2), was used to investigate the possible role of oxidative stress in this normal tissue toxicity. Chinese hamster ovary (CHO) cells were 10-15 times more resistant to 20 mM INO2 under aerobic than hypoxic conditions. In comparison, a pair of transformed rat embryo fibroblasts (ER17-1wtp53 and ER12L5mtpP53), differing in their p53 genotype, were approximately 3- to 4-fold more sensitive than Chinese hamster ovary cells to INO2 under aerobic conditions, but had the same sensitivity as Chinese hamster ovary cells under hypoxic conditions. These results are consistent with an earlier hypothesis that the mechanism of aerobic toxicity is different from that of hypoxic toxicity (nitroreduction) and show that neither toxicity is dependent on cellular p53 status. There was an increase in the production of reactive oxygen intermediates and a decrease in the antioxidant glutathione following aerobic exposure to INO2, which correlated with cell survival in all three cell lines. No evidence of reductive adducts of the 2-nitroimidazole 2-(2-nitro-1H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl)acetam ide (EF5) was found by immunofluorescent techniques in aerobic cells. Differing activities of the antioxidant enzymes superoxide dismutase and catalase could be correlated with INO2 aerobic cytotoxicity. DNA strand breaks, as measured by the comet assay, paralleled the appearance of INO2 aerobic cytotoxicity in all three cell lines. Taken together, these results strongly support the conclusion that the aerobic toxicity of IN02 is due to active oxygen species created by futile redox cycling of the parent compound.

Transfection of COS-1 cells with DT-diaphorase cDNA: role of a base change at position 609

DT-diaphorase, a homodimeric flavoenzyme, can provide for a defence mechanism against carcinogenesis mediated by dietary or environmental quinones as well as bioactivate quinone-containing chemotherapeutic drugs. Human cell lines and strains have been identified with very low or undetectable enzymatic activity and a C to T transition at nucleotide 609 of the DT-diaphorase cDNA. This single base change is predicted to result in a proline to serine change in amino acid 187. Human cells homozygous for this base transition fail to exhibit Western blot reactivity for DT-diaphorase, suggesting that this substitution results in protein instability. To directly test whether this base change affects DT-diaphorase enzymatic activity and/or protein stability in vivo, mammalian expression vectors containing DT-diaphorase cDNA with or without the nucleotide 609 base transition were transiently transfected in COS-1 cells. Co-transfection with a human growth hormone expression vector allowed normalization for transfection efficiency. COS-1 transfectants expressing the C to T base change displayed at least a tenfold reduction in DT-diaphorase activity (P < 0.001) and a two- to threefold reduction in protein levels compared with wild-type transfectants. These results are the first to detect the presence of DT-diaphorase protein coded for by the 609 base transition in mammalian cells and confirm its predicted reduced enzymatic activity.