Custom-designed Laser-based Heating Apparatus for Triggered Release of Cisplatin from Thermosensitive Liposomes with Magnetic Resonance Image Guidance

Liposomes have been employed as drug delivery systems to target solid tumors through exploitation of the enhanced permeability and retention (EPR) effect resulting in significant reductions in systemic toxicity. Nonetheless, insufficient release of encapsulated drug from liposomes has limited their clinical efficacy. Temperature-sensitive liposomes have been engineered to provide site-specific release of drug in order to overcome the problem of limited tumor drug bioavailability. Our lab has designed and developed a heat-activated thermosensitive liposome formulation of cisplatin (CDDP), known as HTLC, to provide triggered release of CDDP at solid tumors. Heat-activated delivery in vivo was achieved in murine models using a custom-built laser-based heating apparatus that provides a conformal heating pattern at the tumor site as confirmed by MR thermometry (MRT). A fiber optic temperature monitoring device was used to measure the temperature in real-time during the entire heating period with online adjustment of heat delivery by alternating the laser power. Drug delivery was optimized under magnetic resonance (MR) image guidance by co-encapsulation of an MR contrast agent (i.e., gadoteridol) along with CDDP into the thermosensitive liposomes as a means to validate the heating protocol and to assess tumor accumulation. The heating protocol consisted of a preheating period of 5 min prior to administration of HTLC and 20 min heating post-injection. This heating protocol resulted in effective release of the encapsulated agents with the highest MR signal change observed in the heated tumor in comparison to the unheated tumor and muscle. This study demonstrated the successful application of the laser-based heating apparatus for preclinical thermosensitive liposome development and the importance of MR-guided validation of the heating protocol for optimization of drug delivery.     

Development of a liposomal delivery system for temperature-triggered release of a tumor targeting agent, Ln(III)-DOTA-phenylboronate

Liposomes, capable of temperature-triggered content release at the site of interest, can be of great importance for imaging and therapy of tumors. The delivery of imaging agents or therapeutics can be improved by application of liposomes with a gel-to-liquid phase-transition temperature suitable for mild hyperthermia (41-43 °C), and by prolonging their circulation time by incorporation of lipids containing polyethyleneglycol moieties. Still, the rapid wash out of the delivered material from the tumor tissue is a major obstacle for both imaging and therapy. In this study, we developed an optimized temperature sensitive liposomal system to be used with mild hyperthermia: highly stable at physiological temperature and with a sharp transition of the bilayer at 41.5 °C, with subsequent rapid release of entrapped compounds such as calcein or tumor cell-targeting contrast agents. Intravital microscopy on calcein/rhodamine containing liposomes was applied to demonstrate the applicability of this system in vivo. The calcein loaded liposomes were injected iv into nude mice with a human BLM melanoma tumor implanted in a dorsal skin-fold window chamber. Arrival of the liposomes at the tumor site and content release after temperature increase were monitored. The results demonstrated not only accumulation of the liposomes at the tumor site, but also a massive release of calcein after increase of the temperature to 41 °C. The versatility of the thermosensitive liposomes was further demonstrated by encapsulation of a tumor cell-targeting DOTA-phenylboronate conjugate and its release at elevated temperatures. The DOTA ligand in this system is able to chelate a variety of metals suitable for both diagnostic and therapeutic applications, whereas the phenylboronate function is able to target specifically to tumor cells through a covalent binding with sialic acid moieties over-expressed on their surface upon heat-triggered release from the liposomal carrier.     

Radiolabeled liposomes for scintigraphic imaging

Liposomes have been investigated extensively as carriers for drugs in attempts to achieve selective deposition and/or reduced toxicity. Liposomes radiolabeled with gamma emitters such as (67)Ga, (111)In and (99m)Tc, can be used for imaging purposes. Liposomes as formulated in the past, are rapidly taken up by cells of the mononuclear phagocyte system (MPS), primarily those located in liver and spleen. The recent development of long-circulating liposomes (LCLs), yielded liposomes that oppose recognition by the MPS. The development of these LCLs with enhanced circulatory half-lives has broadened the potential of liposomes to scintigraphically visualize pathologic processes in vivo. Liposomes have been proposed for tumor imaging, infection imaging and blood pool imaging. Strategies have been developed that allow rapid, easy and efficient labeling of preformed liposomes with (111)In and (99m)Tc. There is now a vast body of preclinical evidence showing that LCLs can be used to image a wide variety of tumors as well as inflammatory lesions. The first studies in patients show that radiolabeled liposomes can image tumor and inflammatory lesions with good sensitivity and good specificity. Here, the present status of liposome-based radiopharmaceuticals for scintigraphic application is reviewed.     

HER2-specific affibody-conjugated thermosensitive liposomes (Affisomes) for improved delivery of anticancer agents

Thermosensitive liposomes are attractive vehicles for the delivery and release of drugs to tumors. To improvethe targeting efficacy for breast cancer treatment, an 8.3-kDa HER2-specific Affibody molecule (Z(HER2:342)-Cys) was conjugated to the surface of liposomes. The effects of this modification on physical characteristics and stability of the resulting nanoparticles denoted as "Affisomes" were investigated. Thermosensitive small unilamellar vesicle (SUV) liposomes of (80-100 nm) a diameter consisting of dipalmitoyl phosphatidylcholine (DPPC, Tm 41 degrees C) as the matrix lipid and a maleimide-conjugated pegylated phospholipid (DSPE-MaL-PEG2000) were prepared by probe sonication. Fluorescent probes were incorporated into liposomes for biophysical and/or biochemical analysis and/or triggered-release assays. Affibody was conjugated to these liposomes via its C-terminal cysteine by incubation in the presence of a reducing agent (e.g., tributylphosphine) for 16-20 hours under an argon atmosphere. Lipid-conjugated affibody molecule was visible as an 11.3-kDa band on a 4-12% Bis/Tris gel under reducing conditions. Affibody conjugation yields were approximately 70% at a protein-lipid ratio of 20 microg/mg, with an average number of 200 affibody molecules per Affisome. Affibody conjugation to thermosensitive liposomes did not have any significant effect on the hydrodynamic size distribution of the liposomes. Thermosensitivity of Affisomes was determined by monitoring the release of entrapped calcein (a water-soluble fluorescent probe, lambdaex/em 490/515 nm) as a function of temperature. Calcein was released from Affisomes (thermosensitive liposomes with affibody-Targeted SUV) as well as nontargeted SUV (thermosensitive liposomes without affibody) in a temperature-dependent manner, with optimal leakage (90-100%) at 41 degrees C. In contrast, liposomes prepared from Egg phosphatidyl choline (Egg PC, Tm approximately 0 degrees C) under similar conditions released only 5-10% calcein at 41 degrees C. Affisomes, when stored at room temperature, retained > 90% entrapped calcein up to 7 days. Moreover, incubation of liposomes in phosphate-buffered saline, supplemented with 10% heat-inactivated serum (fetal bovine serum) did not result in a destabilization of liposomes. Therefore, Affisomes present promising, novel drug-delivery candidates for breast cancer targeting.     

Nanomedicine associated with photodynamic therapy for glioblastoma treatment

Glioblastoma, also known as glioblastoma multiforme (GBM), is the most recurrent and malignant astrocytic glioma found in adults. Biologically, GBMs are highly aggressive tumors that often show diffuse infiltration of the brain parenchyma, making complete surgical resection difficult. GBM is not curable with surgery alone because tumor cells typically invade the surrounding brain, rendering complete resection unsafe. Consequently, present-day therapy for malignant glioma remains a great challenge. The location of the invasive tumor cells presents several barriers to therapeutic delivery. The blood–brain barrier regulates the trafficking of molecules to and from the brain. While high-grade brain tumors contain some “leakiness” in their neovasculature, the mechanisms of GBM onset and progression remain largely unknown. Recent advances in the understanding of the signaling pathways that underlie GBM pathogenesis have led to the development of new therapeutic approaches targeting multiple oncogenic signaling aberrations associated with the GBM. Among these, drug delivery nanosystems have been produced to target therapeutic agents and improve their biodistribution and therapeutic index in the tumor. These systems mainly include polymer or lipid-based carriers such as liposomes, metal nanoparticles, polymeric nanospheres and nanocapsules, micelles, dendrimers, nanocrystals, and nanogold. Photodynamic therapy (PDT) is a promising treatment for a variety of oncological diseases. PDT is an efficient, simple, and versatile method that is based on a combination of a photosensitive drug and light (generally laser-diode or laser); these factors are separately relatively harmless but when used together in the presence of oxygen molecules, free radicals are produced that initiate a sequence of biological events, including phototoxicity, vascular damage, and immune responses. Photodynamic pathways activate a cascade of activities, including apoptotic and necrotic cell death in both the tumor and the neovasculature, leading to a permanent lesion and destruction of GBM cells that remain in the healthy tissue. Glioblastoma tumors differ at the molecular level. For example, gene amplification epidermal growth factor receptor and its receptor are more highly expressed in primary GBM than in secondary GBM. Despite these distinguishing features, both types of tumors (primary and secondary) arise as a result dysregulation of numerous intracellular signaling pathways and have standard features, such as increased cell proliferation, survival and resistance to apoptosis, and loss of adhesion and migration, and may show a high degree of invasiveness. PDT may promote significant tumor regression and extend the lifetime of patients who experience glioma progression.     

Doxorubicin Encapsulated in Long-Circulating Thermosensitive Liposomes

Abstract

Doxorubicin (DXR) was encapsulated in long-circulating, thermosensitive liposomes (TSL, 180-200 nm in mean diameter), prepared from dipalmitoyl phosphatidyl choline (DPPC)/distearoyl phosphatidyl choline (DSPC) (9:1, m/m) and either 3 mol% of amphipathic polyethylene glycol (PEG) with 1000 in average molecular weight or 6 mol% of ganglioside GMI (GMI), with 95-98% entrapping efficiency by the pH gradient method. 57% or 45% of the entrapped DXR was released from PEG/DPPC/DSPC or G_M1/DPPC/DSPC liposomes, respectively, by incubation with 20% serum at 42°C for 5 min. Inclusion of PEG or G_M1 endowed TSL with prolonged circulation ability, resulting in increased blood levels of liposomes and decreased reticuloendothelial system (RES) uptake over 6 hours after injection. Concomitantly, high DXR level in blood was kept for long time.

Accumulation of DXR into tumor tissue of tumor-bearing mice (mouse colon carcinoma 26) by local hyperthermia after injection of DXR-long-circulating TSL was 2 times or 7 times higher than that after treatment with DXR-TSL liposomes or free DXR in combination with hyperthermia, respectively. Furthermore, the systemic treatment with DXR-long-circulating TSL and hyperthermia resulted in effective tumor growth retardation and increased survival time. These results indicate that the combination of long-circulating, thermosensitive liposomes with local hyperthermia at the tumor site could be clinically useful for delivering a wide range of chemotherapeutic agents in the treatment of solid tumors.     

HER2-Specific Affibody-Conjugated Thermosensitive Liposomes (Affisomes) for Improved Delivery of Anticancer Agents

Thermosensitive liposomes are attractive vehicles for the delivery and release of drugs to tumors. To improvethe targeting efficacy for breast cancer treatment, an 8.3-kDa HER2-specific Affibody molecule (Z_HER2:342-Cys) was conjugated to the surface of liposomes. The effects of this modification on physical characteristics and stability of the resulting nanoparticles denoted as “Affisomes” were investigated. Thermosensitive small unilamellar vesicle (SUV) liposomes of (80–100 nm) a diameter consisting of dipalmitoyl phosphatidylcholine (DPPC, Tm 41°C) as the matrix lipid and a maleimide-conjugated pegylated phospholipid (DSPE-MaL-PEG2000) were prepared by probe sonication. Fluorescent probes were incorporated into liposomes for biophysical and/or biochemical analysis and/or triggered-release assays. Affibody was conjugated to these liposomes via its C-terminal cysteine by incubation in the presence of a reducing agent (e.g., tributylphosphine) for 16–20 hours under an argon atmosphere. Lipid-conjugated affibody molecule was visible as an 11.3-kDa band on a 4–12% Bis/Tris gel under reducing conditions. Affibody conjugation yields were?～70% at a protein-lipid ratio of 20 μg/mg, with an average number of 200 affibody molecules per Affisome. Affibody conjugation to thermosensitive liposomes did not have any significant effect on the hydrodynamic size distribution of the liposomes. Thermosensitivity of Affisomes was determined by monitoring the release of entrapped calcein (a water-soluble fluorescent probe, λex/em 490/515 nm) as a function of temperature. Calcein was released from Affisomes (thermosensitive liposomes with affibody-Targeted SUV) as well as nontargeted SUV (thermosensitive liposomes without affibody) in a temperature-dependent manner, with optimal leakage (90–100%) at 41°C. In contrast, liposomes prepared from Egg phosphatidyl choline (Egg PC, Tm?～0°C) under similar conditions released only 5–10% calcein at 41°C. Affisomes, when stored at room temperature, retained?>?90% entrapped calcein up to 7 days. Moreover, incubation of liposomes in phosphate-buffered saline, supplemented with 10% heat-inactivated serum (fetal bovine serum) did not result in a destabilization of liposomes. Therefore, Affisomes present promising, novel drug-delivery candidates for breast cancer targeting.     

Epigenetic modulators for brain cancer stem cells: Implications for anticancer treatment

Primary malignant brain tumors are a major cause of morbidity and mortality in both adults and children, with a dismal prognosis despite multimodal therapeutic approaches. In the last years, a specific subpopulation of cells within the tumor bulk, named cancer stem cells(CSCs) or tumor-initiating cells, have been identified in brain tumors as responsible for cancer growth and disease progression. Stemness features of tumor cells strongly affect treatment response, leading to the escape from conventional therapeutic approaches and subsequently causing tumor relapse. Recent research efforts have focused at identifying new therapeutic strategies capable of specifically targeting CSCs in cancers by taking into consideration their complex nature. Aberrant epigenetic machinery plays a key role in the genesis and progression of brain tumors as well as inducing CSC reprogramming and preserving CSC characteristics. Thus, reverting the cancer epigenome can be considered a promising therapeutic strategy. Three main epigenetic mechanisms have been described: DNA methylation, histone modifications, and non-coding RNA, particularly micro RNAs. Each of these mechanisms has been proven to be targetable by chemical compounds, known as epigeneticbased drugs or epidrugs, that specifically target epigenetic marks. We review here recent advances in the study of epigenetic modulators promoting and sustaining brain tumor stem-like cells. We focus on their potential role in cancer therapy.     

Paramagnetic liposomes as innovative contrast agents for magnetic resonance (MR) molecular imaging applications

This article illustrates some innovative applications of liposomes loaded with paramagnetic lanthanide-based complexes in MR molecular imaging field. When a relatively high amount of a Gd(III) chelate is encapsulated in the vesicle, the nanosystem can simultaneously affect both the longitudinal (R(1)) and the transverse (R(2)) relaxation rate of the bulk H2O H-atoms, and this finding can be exploited to design improved thermosensitive liposomes whose MRI response is not longer dependent on the concentration of the probe. The observation that the liposome compartmentalization of a paramagnetic Ln(III) complex induce a significant R(2) enhancement, primarily caused by magnetic susceptibility effects, prompted us to test the potential of such agents in cell-targeting MR experiments. The results obtained indicated that these nanoprobes may have a great potential for the MR visualization of cellular targets (like the glutamine membrane transporters) overexpressing in tumor cells. Liposomes loaded with paramagnetic complexes acting as NMR shift reagents have been recently proposed as highly sensitive CEST MRI agents. The main peculiarity of CEST probes is to allow the MR visualization of different agents present in the same region of interest, and this article provides an illustrative example of the in vivo potential of liposome-based CEST agents.     

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

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

Biomaterial-based technologies for brain anti-cancer therapeutics and imaging

Treating malignant brain tumors represents one of the most formidable challenges in oncology. Contemporary treatment of brain tumors has been hampered by limited drug delivery across the blood–brain barrier (BBB) to the tumor bed. Biomaterials are playing an increasingly important role in developing more effective brain tumor treatments. In particular, polymer (nano)particles can provide prolonged drug delivery directly to the tumor following direct intracerebral injection, by making them physiochemically able to cross the BBB to the tumor, or by functionalizing the material surface with peptides and ligands allowing the drug-loaded material to be systemically administered but still specifically target the tumor endothelium or tumor cells themselves. Biomaterials can also serve as targeted delivery devices for novel therapies including gene therapy, photodynamic therapy, anti-angiogenic and thermotherapy. Nanoparticles also have the potential to play key roles in the diagnosis and imaging of brain tumors by revolutionizing both preoperative and intraoperative brain tumor detection, allowing early detection of pre-cancerous cells, and providing real-time, longitudinal, non-invasive monitoring/imaging of the effects of treatment. Additional efforts are focused on developing biomaterial systems that are uniquely capable of delivering tumor-associated antigens, immunotherapeutic agents or programming immune cells in situ to identify and facilitate immune-mediated tumor cell killing. The continued translation of current research into clinical practice will rely on solving challenges relating to the pharmacology of nanoparticles but it is envisioned that novel biomaterials will ultimately allow clinicians to target tumors and introduce multiple, pharmaceutically relevant entities for simultaneous targeting, imaging, and therapy in a unique and unprecedented manner.     

In vitro and in vivo investigation of a novel two-phase delivery system of 2-methoxyestradiol liposomes hydrogel

For improving effectiveness of conventional chemotherapy of subcutaneous tumor, we selected 2-methoxyestradiol (2-ME) as a model drug, local injectable PLGA-PEG-PLGA copolymer thermosensitive hydrogel loading 2-ME liposomes instead of free 2-ME as a novel two-phase drug delivery system was developed, which avoid rapid clearance of liposomes follwing systemic administration. This new transport system was characterized in vitro and in vivo including rheological behavior, thermo-sensitiveness, stability, released character and intratumoral delivery. The PLGA-PEG-PLGA copolymer solution exhibited still reversible thermosensitive property and better syringeability after incorporated 2-ME liposomes. The 2-ME liposomes were demonstrated stable in the hydrogel by five methods such as scanning electron microscopy (SEM), fluorescent labeling, opalescence, particle size and ultrafiltration methods. Results showed that intact liposomes could be released from the hydrogel and following zero-order model, and sustained release one–two months in vitro and in vivo. In vivo release data demonstrating that 2-ME liposomes could be transported to tumor site, improved therapeutic efficacy and bioavailability of 2-ME liposomes in subcutaneous tumor chemotherapy.     

Disc formation in cholesterol-free liposomes during phase transition

Cryogenic transmission electron microscopy (cryo-TEM) images of lysolipid-containing thermosensitive liposomes (LTSL) revealed that open liposomes and bilayer discs appeared when liposomes were cycled through the gel (Lbeta') to liquid-crystalline (Lalpha) phase transition. The amount of bilayer discs generated was dependent on the combined presence of PEG-lipid and lysolipid in the membrane. We hypothesize that micelle-forming membrane components stabilize the rim of bilayer openings and membrane discs that form when liposomes are cycled through TC.     

The complex role of eicosanoids in the brain: Implications for brain tumor development and therapeutic opportunities

Eicosanoids are a family of bioactive lipids that play diverse roles in the normal physiology of the brain, including neuronal signaling, synaptic plasticity, and regulation of cerebral blood flow. In the brain, eicosanoids are primarily derived from arachidonic acid, which is released from membrane phospholipids in response to various stimuli. Prostaglandins (PGs) and leukotrienes (LTs) are the major classes of eicosanoids produced in the brain, and they act through specific receptors to modulate various physiological and pathological processes. Dysregulation of eicosanoids has been implicated in the development and progression of brain tumors, including glioblastoma (GBM), meningioma, and medulloblastoma. Eicosanoids have been shown to promote tumor cell proliferation, migration, invasion, angiogenesis, and resistance to therapy. Particularly, PGE2 promotes GBM cell survival and resistance to chemotherapy. Understanding the role of eicosanoids in brain tumors can inform the development of diagnostic and prognostic biomarkers, as well as therapeutic strategies that target eicosanoid pathways. Cyclooxygenase (COX)-2 and 5-lipoxygenase (LOX) inhibitors have been shown to reduce the growth and invasiveness of GBM cells. Moreover, eicosanoids have immunomodulatory effects that can impact the immune response to brain tumors. Understanding the role of eicosanoids in the immune response to brain tumors can inform the development of immunotherapy approaches for these tumors. Overall, the complex role of eicosanoids in the brain underscores the importance of further research to elucidate their functions in normal physiology and disease, and highlights the potential for developing novel therapeutic approaches that target eicosanoid pathways in brain tumors.     

A brain tumor molecular imaging strategy using a new triple-modality MRI-photoacoustic-Raman nanoparticle

The difficulty in delineating brain tumor margins is a major obstacle in the path toward better outcomes for patients with brain tumors. Current imaging methods are often limited by inadequate sensitivity, specificity and spatial resolution. Here we show that a unique triple-modality magnetic resonance imaging-photoacoustic imaging-Raman imaging nanoparticle (termed here MPR nanoparticle) can accurately help delineate the margins of brain tumors in living mice both preoperatively and intraoperatively. The MPRs were detected by all three modalities with at least a picomolar sensitivity both in vitro and in living mice. Intravenous injection of MPRs into glioblastoma-bearing mice led to MPR accumulation and retention by the tumors, with no MPR accumulation in the surrounding healthy tissue, allowing for a noninvasive tumor delineation using all three modalities through the intact skull. Raman imaging allowed for guidance of intraoperative tumor resection, and a histological correlation validated that Raman imaging was accurately delineating the brain tumor margins. This new triple-modality-nanoparticle approach has promise for enabling more accurate brain tumor imaging and resection.     

The genesis of peritumoral vasogenic brain edema and tumor cysts: a hypothetical role for tumor-derived vascular permeability factor.

Cerebral edema and fluid-filled cysts are common accompaniments of brain tumors. They contribute to the mass effect imposed by the primary tumor and are often responsible for a patient''s signs and symptoms. Cerebral edema significantly increases the morbidity associated with tumor biopsy, excision, radiation therapy, and chemotherapy. Both edema and cyst formation are thought to result from a deficiency in the blood-brain barrier, with consequent extravasation of water, electrolytes, and plasma proteins from altered tumor microvessels. The resultant expansion of the cerebral interstitial space contributes to the elevated intracranial pressure observed with brain tumors. Departure from the typical blood-brain barrier microvascular architecture may only partially explain the occurrence of edema and tumor cyst formation. Biochemical mediators have also been implicated in vascular extravasation. Vascular permeability factor or vascular endothelial growth factor (VPF/VEGF) is a protein that has recently been isolated from a variety of tumors including human brain tumors. VPFb is an extraordinarily potent inducer of both microvascular extravasation (edemagenesis) and the formation of new blood vessels (angiogenesis). Its role in tumor growth and progression would therefore appear pivotal. Herein, the author presents an updated account of the investigation of VPF. Historical and clinical perspectives of the study and treatment of tumor associated edema are provided. The efficacy of high-dose dexamethasone in the treatment of neoplastic brain edema is discussed. A hypothetical role for VPF in edemagenesis is presented and discussed. It is hoped that an expanded understanding of the mechanisms responsible for the genesis of edema will ultimately facilitate therapeutic intervention.     

Exploration of Involved Key Genes and Signaling Diversity in Brain Tumors

Brain tumors are becoming a major cause of death. The classification of brain tumors has gone through restructuring with regard to some criteria such as the presence or absence of a specific genetic alteration in the 2016 central nervous system World Health Organization update. Two categories of genes with a leading role in tumorigenesis and cancer induction include tumor suppressor genes and oncogenes; tumor suppressor genes are inactivated through a variety of mechanisms that result in their loss of function. As for the oncogenes, overexpression and amplification are the most common mechanisms of alteration. Important cell cycle genes such as p53, ATM, cyclin D2, and Rb have shown altered expression patterns in different brain tumors such as meningioma and astrocytoma. Some genes in signaling pathways have a role in brain tumorigenesis. These pathways include hedgehog, EGFR, Notch, hippo, MAPK, PI3K/Akt, and WNT signaling. It has been shown that telomere length in some brain tumor samples is shortened compared to that in normal cells. As the shortening of telomere length triggers chromosome instability early in brain tumors, it could lead to initiation of cancer. On the other hand, telomerase activity was positive in some brain tumors. It is suggestive that telomere length and telomerase activity are important diagnostic markers in brain tumors. This review focuses on brain tumors with regard to the status of oncogenes, tumor suppressors, cell cycle genes, and genes in signaling pathways as well as the role of telomere length and telomerase in brain tumors.     

Temperature sensitization of liposomes using copolymers of N-isopropylacrylamide.

To obtain liposomes which release the contents in response to ambient temperature, liposomes modified with copolymers of N-isopropylacrylamide with varying lower critical solution temperatures have been designed. Poly(N-isopropylacrylamide-co-acrylamide)s with various compositions were synthesized by free-radical copolymerization. The lower critical solution temperature of the polymer increased with increasing acrylamide content in the polymer. Poly(N-isopropylacrylamide-co-acrylamide-co-N, N-didodecylacrylamide)s were also prepared via the same method as the thermosensitive polymers having anchor groups to the liposome membrane. Calcein-loaded dioleoylphosphatidylethanolamine/egg yolk phosphatidylcholine (6:4, w/w) liposomes were coated with these polymers by incubating the liposomes with aqueous solutions of the polymers. The liposomes hardly released the contents below the lower critical solution temperature of the polymer, but the release was greatly enhanced above that temperature. The liposomes were also made from a mixture of the same lipids and the polymer. The liposome revealed a more drastic release property than the liposomes prepared by the incubation with the polymer solution, because the polymer chains were bound on both surfaces of the membrane. The close relationship between lower critical solution temperatures of the polymers and temperature regions where enhancement of the release from the polymer-fixed liposomes demonstrates that the release was triggered by alteration of the polymers from a hydrophilic state to a hydrophobic state occurring at their lower critical solution temperatures.     

Pharmacokinetic Analysis of 111In-Labeled Liposomal Doxorubicin in Murine Glioblastoma after Blood-Brain Barrier Disruption by Focused Ultrasound

The goal of this study was to evaluate the pharmacokinetics of targeted and untargeted ¹¹¹In-doxorubicin liposomes after these have been intravenously administrated to tumor-bearing mice in the presence of blood-brain barrier disruption (BBB-D) induced by focused ultrasound (FUS). An intracranial brain tumor model in NOD-scid mice using human brain glioblastoma multiforme (GBM) 8401 cells was developed in this study. ¹¹¹In-labeled human atherosclerotic plaque-specific peptide-1 (AP-1)-conjugated liposomes containing doxorubicin (Lipo-Dox; AP-1 Lipo-Dox) were used as a microSPECT probe for radioactivity measurements in the GBM-bearing mice. Compared to the control tumors treated with an injection of ¹¹¹In-AP-1 Lipo-Dox or ¹¹¹In-Lipo-Dox, the animals receiving the drugs followed by FUS exhibited enhanced accumulation of the drug in the brain tumors (p<0.05). Combining sonication with drugs significantly increased the tumor-to-normal brain doxorubicin ratio of the target tumors compared to the control tumors. The tumor-to-normal brain ratio was highest after the injection of ¹¹¹In-AP-1 Lipo-Dox with sonication. The ¹¹¹In-liposomes micro-SPECT/CT should be able to provide important information about the optimum therapeutic window for the chemotherapy of brain tumors using sonication.