Brain intratumoural astatine-211 radiotherapy targeting syndecan-1 leads to durable glioblastoma remission and immune memory in female mice.

BACKGROUND: Glioblastoma (GB), the most aggressive brain cancer, remains a critical clinical challenge due to its resistance to conventional treatments. Here, we introduce a locoregional targeted-α-therapy (TAT) with the rat monoclonal antibody 9E7.4 targeting murine syndecan-1 (SDC1) coupled to the α-emitter radionuclide astatine-211 (211At-9E7.4). METHODS: We orthotopically transplanted 50,000 GL261 cells of murine GB into the right striatum of syngeneic female C57BL/6JRj mice using stereotaxis. After MRI validation of tumour presence at day 11, TAT was injected at the same coordinates. Biodistribution, efficacy, toxicity, local and systemic responses were assessed following application of this protocol. The 9E7.4 monoclonal antibody was labelled with iodine-125 (125I) for biodistribution and with astatine-211 (211At) for the other experiments. FINDINGS: The 211At-9E7.4 TAT demonstrated robust efficacy in reducing orthotopic tumours and achieved improved survival rates in the C57BL/6JRj model, reaching up to 70% with a minimal activity of 100 kBq. Targeting SDC1 ensured the cerebral retention of 211At over an optimal time window, enabling low-activity administration with a minimal toxicity profile. Moreover, TAT substantially reduced the occurrence of secondary tumours and provided resistance to new tumour development after contralateral rechallenge, mediated through the activation of central and effector memory T cells. INTERPRETATION: The locoregional 211At-9E7.4 TAT stands as one of the most efficient TAT across all preclinical GB models. This study validates SDC1 as a pertinent therapeutic target for GB and underscores 211At-9E7.4 TAT as a promising advancement to improve the treatment and quality of life for patients with GB. FUNDING: This work was funded by the French National Agency for Research (ANR) "France 2030 Investment Plan" Labex Iron [ANR-11-LABX-18-01], The SIRIC ILIAD [INCa-DGOS-INSERM-18011], the French program "Infrastructure d'Avenir en Biologie-Santé" (France Life Imaging) [ANR-11-INBS-0006], the PIA3 of the ANR, integrated to the "France 2030 Investment Plan" [ANR-21-RHUS-0012], and support from Inviscan SAS (Strasbourg, France). It was also related to: the ANR under the frame of EuroNanoMed III (project GLIOSILK) [ANR-19-ENM3-0003-01]; the "Région Pays-de-la-Loire" under the frame of the Target'In project; the "Ligue Nationale contre le Cancer" and the "Comité Départemental de Maine-et-Loire de la Ligue contre le Cancer" (CD49) under the frame of the FusTarG project and the "Tumour targeting, imaging and radio-therapies network" of the "Cancéropôle Grand-Ouest" (France). This work was also funded by the Institut National de la Santé et de la Recherche Médicale (INSERM), the University of Nantes, and the University of Angers.

Implantable SDF-1α-loaded silk fibroin hyaluronic acid aerogel sponges as an instructive component of the glioblastoma ecosystem: Between chemoattraction and tumor shaping into resection cavities.

In view of inevitable recurrences despite resection, glioblastoma (GB) is still an unmet clinical need. Dealing with the stromal-cell derived factor 1-alpha (SDF-1α)/CXCR4 axis as a hallmark of infiltrative GB tumors and with the resection cavity situation, the present study described the effects and relevance of a new engineered micro-nanostructured SF-HA-Hep aerogel sponges, made of silk fibroin (SF), hyaluronic acid (HA) and heparin (Hep) and loaded with SDF-1α, to interfere with the GB ecosystem and residual GB cells, attracting and confining them in a controlled area before elimination. 70 µm-pore sponges were designed as an implantable scaffold to trap GB cells. They presented shape memory and fit brain cavities. Histological results after implantation in brain immunocompetent Fischer rats revealed that SF-HA-Hep sponges are well tolerated for more than 3 months while moderately and reversibly colonized by immuno-inflammatory cells. The use of human U87MG GB cells overexpressing the CXCR4 receptor (U87MG-CXCR4+) and responding to SDF-1α allowed demonstrating directional GB cell attraction and colonization of the device in vitro and in vivo in orthotopic resection cavities in Nude rats. Not modifying global survival, aerogel sponge implantation strongly shaped U87MG-CXCR4+ tumors in cavities in contrast to random infiltrative growth in controls. Overall, those results support the interest of SF-HA-Hep sponges as modifiers of the GB ecosystem dynamics acting as "cell meeting rooms" and biocompatible niches whose properties deserve to be considered toward the development of new clinical procedures. STATEMENT OF SIGNIFICANCE: Brain tumor glioblastoma (GB) is one of the worst unmet clinical needs. To prevent the relapse in the resection cavity situation, new implantable biopolymer aerogel sponges loaded with a chemoattractant molecule were designed and preclinically tested as a prototype targeting the interaction between the initial tumor location and its attraction by the peritumoral environment. While not modifying global survival, biocompatible SDF1-loaded hyaluronic acid and silk fibroin sponges induce directional GB cell attraction and colonization in vitro and in rats in vivo. Interestingly, they strongly shaped GB tumors in contrast to random infiltrative growth in controls. These results provide original findings on application of exogenous engineered niches that shape tumors and serve as cell meeting rooms for further clinical developments.

A role for ceruloplasmin in the control of human glioblastoma cell responses to radiation.

BACKGROUND: Glioblastoma (GB) is the most common and most aggressive malignant brain tumor. In understanding its resistance to conventional treatments, iron metabolism and related pathways may represent a novel avenue. As for many cancer cells, GB cell growth is dependent on iron, which is tightly involved in red-ox reactions related to radiotherapy effectiveness. From new observations indicating an impact of RX radiations on the expression of ceruloplasmin (CP), an important regulator of iron metabolism, the aim of the present work was to study the functional effects of constitutive expression of CP within GB lines in response to beam radiation depending on the oxygen status (21% O2 versus 3% O2). METHODS AND RESULTS: After analysis of radiation responses (Hoechst staining, LDH release, Caspase 3 activation) in U251-MG and U87-MG human GB cell lines, described as radiosensitive and radioresistant respectively, the expression of 9 iron partners (TFR1, DMT1, FTH1, FTL, MFRN1, MFRN2, FXN, FPN1, CP) were tested by RTqPCR and western blots at 3 and 8 days following 4 Gy irradiation. Among those, only CP was significantly downregulated, both at transcript and protein levels in the two lines, with however, a weaker effect in the U87-MG, observable at 3% O2. To investigate specific role of CP in GB radioresistance, U251-MG and U87-MG cells were modified genetically to obtain CP depleted and overexpressing cells, respectively. Manipulation of CP expression in GB lines demonstrated impact both on cell survival and on activation of DNA repair/damage machinery (γH2AX); specifically high levels of CP led to increased production of reactive oxygen species, as shown by elevated levels of superoxide anion, SOD1 synthesis and cellular Fe2 + . CONCLUSIONS: Taken together, these in vitro results indicate for the first time that CP plays a positive role in the efficiency of radiotherapy on GB cells.

Targeting Tumor Associated Macrophages to Overcome Conventional Treatment Resistance in Glioblastoma.

Glioblastoma (GB) is the most common and devastating form of brain cancer. Despite conventional treatments, progression or recurrences are systematic. In recent years, immunotherapies have emerged as an effective treatment in a number of cancers, leaving the question of their usefulness also faced with the particular case of brain tumors. The challenge here is major not only because the brain is the seat of our consciousness but also because of its isolation by the blood-brain barrier and the presence of a unique microenvironment that constitutes the central nervous system (CNS) with very specific constituent or patrolling cells. Much of the microenvironment is made up of immune cells or inflammation. Among these, tumor-associated macrophages (TAMs) are of significant interest as they are often involved in facilitating tumor progression as well as the development of resistance to standard therapies. In this review, the ubiquity of TAMs in GB will be discussed while the specific case of microglia resident in the brain will be also emphasized. In addition, the roles of TAMs as accomplices in the progression of GB and resistance to treatment will be presented. Finally, clinical trials targeting TAMs as a means of treating cancer will be discussed.

Rapamycin-Loaded Lipid Nanocapsules Induce Selective Inhibition of the mTORC1-Signaling Pathway in Glioblastoma Cells.

Inhibition of the PI3K/Akt/mTOR signaling pathway represents a potential issue for the treatment of cancer, including glioblastoma. As such, rapamycin that inhibits the mechanistic target of rapamycin (mTOR), the downstream effector of this signaling pathway, is of great interest. However, clinical development of rapamycin has floundered due to the lack of a suitable formulation of delivery systems. In the present study, a novel method for the formulation of safe rapamycin nanocarriers is investigated. A phase inversion process was adapted to prepare lipid nanocapsules (LNCs) loaded with the lipophilic and temperature sensitive rapamycin. Rapamycin-loaded LNCs (LNC-rapa) are ~110 nm in diameter with a low polydispersity index (<0.05) and the zeta potential of about -5 mV. The encapsulation efficiency, determined by spectrophotometry conjugated with filtration/exclusion, was found to be about 69%, which represents 0.6 wt% of loading capacity. Western blot analysis showed that LNC-rapa do not act synergistically with X-ray beam radiation in U87MG glioblastoma model in vitro. Nevertheless, it demonstrated the selective inhibition of the phosphorylation of mTORC1 signaling pathway on Ser2448 at a concentration of 1 µM rapamycin in serum-free medium. Interestingly, cells cultivated in normoxia (21% O2) seem to be more sensitive to mTOR inhibition by rapamycin than those cultivated in hypoxia (0.4% O2). Finally, we also established that mTOR phosphorylation inhibition by LNC-rapa induced a negative feedback through the activation of Akt phosphorylation. This phenomenon was more noticeable after stabilization of HIF-1α in hypoxia.

Potential for Nuclear Medicine Therapy for Glioblastoma Treatment.

Glioblastoma is the most common malignant adult brain tumor and has a very poor patient prognosis. The mean survival for highly proliferative glioblastoma is only 10 to 14 months despite an aggressive current therapeutic approach known as Stupp's protocol, which consists of debulking surgery followed by radiotherapy and chemotherapy. Despite several clinical trials using anti-angiogenic targeted therapies, glioblastoma medical care remains without major progress in the last decade. Recent progress in nuclear medicine, has been mainly driven by advances in biotechnologies such as radioimmunotherapy, radiopeptide therapy, and radionanoparticles, and these bring a new promising arsenal for glioblastoma therapy. For therapeutic purposes, nuclear medicine practitioners classically use ß- particle emitters like 131I, 90Y, 186/188Re, or 177Lu. In the glioblastoma field, these radioisotopes are coupled with nanoparticles, monoclonal antibodies, or peptides. These radiopharmaceutical compounds have resulted in a stabilization and/or improvement of the neurological status with only transient side effects. In nuclear medicine, the glioblastoma-localized and targeted internal radiotherapy proof-of-concept stage has been successfully demonstrated using ß- emitting isotopes. Similarly, α particle emitters like 213Bi, 211At, or 225Ac appear to be an innovative and interesting alternative. Indeed, α particles deliver a high proportion of their energy inside or at close proximity to the targeted cells (within a few micrometers from the emission point versus several millimeters for ß- particles). This physical property is based on particle-matter interaction differences and results in α particles being highly efficient in killing tumor cells with minimal irradiation of healthy tissues and permits targeting of isolated tumor cells. The first clinical trials confirmed this idea and showed good therapeutic efficacy and less side effects, thus opening a new and promising era for glioblastoma medical care using α therapy. The objective of this literature review is focused on the developing field of nuclear medicine and aims to describe the various parameters such as targets, vectors, isotopes, or injection route (systemic and local) in relation to the clinical and preclinical results in glioblastoma pathology.

Rhenium-188 Labeled Radiopharmaceuticals: Current Clinical Applications in Oncology and Promising Perspectives.

Rhenium-188 (188Re) is a high energy beta-emitting radioisotope with a short 16.9 h physical half-life, which has been shown to be a very attractive candidate for use in therapeutic nuclear medicine. The high beta emission has an average energy of 784 keV and a maximum energy of 2.12 MeV, sufficient to penetrate and destroy targeted abnormal tissues. In addition, the low-abundant gamma emission of 155 keV (15%) is efficient for imaging and for dosimetric calculations. These key characteristics identify 188Re as an important therapeutic radioisotope for routine clinical use. Moreover, the highly reproducible on-demand availability of 188Re from the 188W/188Re generator system is an important feature and permits installation in hospital-based or central radiopharmacies for cost-effective availability of no-carrier-added (NCA) 188Re. Rhenium-188 and technetium-99 m exhibit similar chemical properties and represent a "theranostic pair." Thus, preparation and targeting of 188Re agents for therapy is similar to imaging agents prepared with 99mTc, the most commonly used diagnostic radionuclide. Over the last three decades, radiopharmaceuticals based on 188Re-labeled small molecules, including peptides, antibodies, Lipiodol and particulates have been reported. The successful application of these 188Re-labeled therapeutic radiopharmaceuticals has been reported in multiple early phase clinical trials for the management of various primary tumors, bone metastasis, rheumatoid arthritis, and endocoronary interventions. This article reviews the use of 188Re-radiopharmaceuticals which have been investigated in patients for cancer treatment, demonstrating that 188Re represents a cost effective alternative for routine clinical use in comparison to more expensive and/or less readily available therapeutic radioisotopes.

Hybrid Gd3+/cisplatin cross-linked polymer nanoparticles enhance platinum accumulation and formation of DNA adducts in glioblastoma cell lines.

Glioblastoma is the most frequent and aggressive primary malignant tumor of the central nervous system with a gloomy prognosis. Platinum derivatives and one among them, cisplatin, exhibited promising results when locally administered into the brain of glioblastoma bearing rats. Nanovectorization of anticancer agents through polymeric nanoparticles may even promote drug accumulation within cells, thus concentrating the drug efficiently at its target. Anchorage of gadolinium complexes on the corona of such smart drug delivery systems could further allow magnetic resonance imaging (MRI) monitoring of the nanoplatform biodistribution in the damaged parenchyma and its therapeutic benefit. For this purpose, a biocompatible amphiphilic triblock copolymer, made of degradable polyester and polycarbonate and bioeliminable polyethylene oxide (PEO), was synthesized by successive ring-opening polymerizations. After micellization in water, gadolinium complexes were grafted onto the PEO micelle corona and the carboxylate functions, located at the surface of the micelle's core, were able to cross-link with Pt(ii) complexes. A macromolecular prodrug was therefore recovered in which more than one third of the carboxylate functions were linked to a platinum atom. By this strategy, stable cisplatin cross-linked nanoparticles were formulated with a mean size in the range of 100.63 ± 12.04 nm consistent with biological investigations. Relaxometry measurements both in water and in plasma at 7 T, 25 °C, confirmed the intrinsic potential of these hybrid nanoparticles as alternative MRI contrast agents with a substantial increase in the r2/r1 ratio by a factor of 3.3 and 2.7, respectively, compared to the conventional low molar mass Gd-DTPA. As a result, their infusion within the striatum of glioblastoma-bearing mice resulted in a hypersignal on T2-weighted MR images that persisted over time. Ultimately, the formulated prodrug exhibited up to 50-fold increased accumulation in human glioblastoma cell lines and up to 32-fold enhanced subsequent Pt-DNA adduct formation in comparison with free cisplatin, thus supporting the potential of this innovative bimodal tool for further applications.

Locoregional Confinement and Major Clinical Benefit of 188Re-Loaded CXCR4-Targeted Nanocarriers in an Orthotopic Human to Mouse Model of Glioblastoma.

PURPOSE: Gold standard beam radiation for glioblastoma (GBM) treatment is challenged by resistance phenomena occurring in cellular populations well prepared to survive or to repair damage caused by radiation. Among signals that have been linked with radio-resistance, the SDF1/CXCR4 axis, associated with cancer stem-like cell, may be an opportune target. To avoid the problem of systemic toxicity and blood-brain barrier crossing, the relevance and efficacy of an original system of local brain internal radiation therapy combining a radiopharmaceutical with an immuno-nanoparticle was investigated. EXPERIMENT DESIGN: The nanocarrier combined lipophilic thiobenzoate complexes of rhenium-188 loaded in the core of a lipid nanocapsule (LNC188Re) with a function-blocking antibody, 12G5 directed at the CXCR4, on its surface. The efficiency of 12G5-LNC188Re was investigated in an orthotopic and xenogenic GBM model of CXCR4-positive U87MG cells implanted in the striatum of Scid mice. RESULTS: We demonstrated that 12G5-LNC188Re single infusion treatment by convection-enhanced delivery resulted in a major clinical improvement in median survival that was accompanied by locoregional effects on tumor development including hypovascularization and stimulation of the recruitment of bone marrow derived CD11b- or CD68-positive cells as confirmed by immunohistochemistry analysis. Interestingly, thorough analysis by spectral imaging in a chimeric U87MG GBM model containing CXCR4-positive/red fluorescent protein (RFP)-positive- and CXCR4-negative/RFP-negative-GBM cells revealed greater confinement of DiD-labeled 12G5-LNCs than control IgG2a-LNCs in RFP compartments. Main conclusion: These findings on locoregional impact and targeting of disseminated cancer cells in tumor margins suggest that intracerebral active targeting of nanocarriers loaded with radiopharmaceuticals may have considerable benefits in clinical applications.

Characterization of the distribution, retention, and efficacy of internal radiation of 188Re-lipid nanocapsules in an immunocompromised human glioblastoma model.

Internal radiation strategies hold great promise for glioblastoma (GB) therapy. We previously developed a nanovectorized radiotherapy that consists of lipid nanocapsules loaded with a lipophilic complex of Rhenium-188 (LNC188Re-SSS). This approach resulted in an 83 % cure rate in the 9L rat glioma model, showing great promise. The efficacy of LNC188Re-SSS treatment was optimized through the induction of a T-cell immune response in this model, as it is highly immunogenic. However, this is not representative of the human situation where T-cell suppression is usually encountered in GB patients. Thus, in this study, we investigated the efficacy of LNC188Re-SSS in a human GB model implanted in T-cell deficient nude mice. We also analyzed the distribution and tissue retention of LNC188Re-SSS. We observed that intratumoral infusion of LNCs by CED led to their complete distribution throughout the tumor and peritumoral space without leakage into the contralateral hemisphere except when large volumes were used. Seventy percent of the 188Re-SSS activity was present in the tumor region 24 h after LNC188Re-SSS injection and no toxicity was observed in the healthy brain. Double fractionated internal radiotherapy with LNC188Re-SSS triggered survival responses in the immunocompromised human GB model with a cure rate of 50 %, which was not observed with external radiotherapy. In conclusion, LNC188Re-SSS can induce long-term survival in an immunosuppressive environment, highlighting its potential for GB therapy.

68Ga and 188Re Starch-Based Microparticles as Theranostic Tool for the Hepatocellular Carcinoma: Radiolabeling and Preliminary In Vivo Rat Studies.

PURPOSE: This work aims to develop, validate and optimize the radiolabeling of Starch-Based Microparticles (SBMP) by 188Re and 68Ga in the form of ready-to-use radiolabeling kits, the ultimate goal being to obtain a unique theranostic vector for the treatment of Hepatocellular Carcinoma. METHODS: Optimal labeling conditions and composition of freeze-dried kits were defined by monitoring the radiochemical purity while varying several parameters. In vitro stability studies were carried out, as well as an in vivo biodistribution as a preliminary approach with the intra-arterial injection of 68Ga radiolabeled SBMP into the hepatic artery of DENA-induced rats followed by PET/CT imaging. RESULTS: Kits were optimized for 188Re and 68Ga with high and stable radiochemical purity (>95% and >98% respectively). The in vivo preliminary study was successful with more than 95% of activity found in the liver and mostly in the tumorous part. CONCLUSION: SBMP are a promising theranostic agent for the Selective Internal Radiation Therapy of Hepatocellular carcinoma.

Dendrimers as Innovative Radiopharmaceuticals in Cancer Radionanotherapy.

Radiotherapy is one of the most commonly used cancer treatments, with an estimate of 40% success that could be improved further if more efficient targeting and retention of radiation at the tumor site were achieved. This review focuses on the use of dendrimers in radionanotherapy, an emerging technology aimed to improve the efficiency of radiotherapy by implementing nanovectorization, an already established praxis in drug delivery and diagnosis. The labeling of dendrimers with radionuclides also aims to reduce the dose of radiolabeled materials and, hence, their toxicity and tumor resistance. Examples of radiolabeled dendrimers with alpha, beta, and Auger electron emitters are commented, along with the use of dendrimers in boron neutron capture therapy (BNCT). The conjugation of radiolabeled dendrimers to monoclonal antibodies for a more efficient targeting and the application of dendrimers in gene delivery radiotherapy are also covered.

Nanomedicine to overcome radioresistance in glioblastoma stem-like cells and surviving clones.

Radiotherapy is one of the standard treatments for glioblastoma, but its effectiveness often encounters the phenomenon of radioresistance. This resistance was recently attributed to distinct cell contingents known as glioblastoma stem-like cells (GSCs) and dominant clones. It is characterized in particular by the activation of signaling pathways and DNA repair mechanisms. Recent advances in the field of nanomedicine offer new possibilities for radiosensitizing these cell populations. Several strategies have been developed in this direction, the first consisting of encapsulating a contrast agent or synthesizing metal-based nanocarriers to concentrate the dose gradient at the level of the target tissue. In the second strategy the physicochemical properties of the vectors are used to encapsulate a wide range of pharmacological agents which act in synergy with the ionizing radiation to destroy the cancerous cells. This review reports on the various molecular anomalies present in GSCs and the predominant role of nanomedicines in the development of radiosensitization strategies.

Tumour targeting of lipid nanocapsules grafted with cRGD peptides.

Combining targeting to therapy remains a major challenge in cancer treatment. To address this subject, the surface of lipid nanocapsules (LNC) was modified by grafting cRGD peptides, which are known to be recognised by αvß3 integrins expressed by tumour endothelium and cancer cells. Applicability of this LNC-cRGD in tumour targeting was first assessed in vitro by the use of U87MG glioma cells. Biodistribution and tumour accumulation of radiolabelled LNC-cRGD in vivo were then evaluated in mice bearing the same subcutaneous xenograft. Flow cytometry and confocal microscopy results revealed that the cRGD grafting improved binding and internalisation compared to negative control LNC-cRAD and blank LNC. The peptide-grafted LNC remained in the blood circulation up to 3h with reduced capture by the RES organs. Tumour accumulation of LNC-cRGD with respect to LNC-cRAD was significantly higher at 1-3h. These results show that cRGD grafted to LNC has created a promising tumour-targetable nanocarrier that could be used in cancer treatment.

Effect of particle size on the biodistribution of lipid nanocapsules: comparison between nuclear and fluorescence imaging and counting.

In vivo biodistribution of nanoparticles depends on several physicochemical parameters such as size. After intravenous injection of 25, 50 and 100 nm lipid nanocapsules (LNC) in nude mice bearing HEK293(ß3) tumour xenografts, biodistribution was evaluated by γ-scintigraphy and by γ-counting. The small LNC 25 nm disappeared faster than the larger LNC 50 and 100 nm from the blood circulation due to faster elimination and wider tissue distribution. At 24h, biodistribution profiles of all these LNC were similar. Low LNC quantities were found in this weak EPR (enhanced permeability and retention) tumour regardless the particle size. Co-injected 50 nm fluorescent DiD-LNC and (99m)Tc-LNC allowed direct comparison of biodistribution as evaluated by the two methods. Optical imaging underestimated LNC quantity especially in dark-colored organs that were observed to capture extensive quantities of the particles by γ-counting (i.e. liver, spleen, and kidney).

Lysozyme encapsulation into nanostructured CaCO3 microparticles using a supercritical CO2 process and comparison with the normal route.

The aim of the present work was to assess the merits of supercritical CO2 (SC-CO2) as a process for protein encapsulation into calcium carbonate microparticles. Lysozyme, chosen as a model protein, was entrapped during CaCO3 precipitation in two different media: water (normal route) and SC-CO2. The particles were characterized and compared in terms of size, zeta potential, morphology by SEM, crystal polymorph and lysozyme encapsulation. Fluorescent and confocal images suggested the encapsulation and core-shell distribution of lysozyme into CaCO3 obtained by the SC-CO2 process. A high encapsulation efficiency was reached by a supercritical CO2 process (50%) as confirmed by the increased zeta potential value, lysozyme quantification by HPLC and a specific bioassay (M. lysodeikticus). Conversely, lysozyme was scarcely entrapped by the normal route (2%). Thus, supercritical CO2 appears to be an effective process for protein encapsulation within nanostructured CaCO3 particles. Moreover, this process may be used for encapsulation of a wide range of macromolecules and bioactive substances.

Nanovectorized radiotherapy: a new strategy to induce anti-tumor immunity.

Recent experimental findings show that activation of the host immune system is required for the success of chemo- and radiotherapy. However, clinically apparent tumors have already developed multiple mechanisms to escape anti-tumor immunity. The fact that tumors are able to induce a state of tolerance and immunosuppression is a major obstacle in immunotherapy. Hence, there is an overwhelming need to develop new strategies that overcome this state of immune tolerance and induce an anti-tumor immune response both at primary and metastatic sites. Nanovectorized radiotherapy that combines ionizing radiation and nanodevices, is one strategy that could boost the quality and magnitude of an immune response in a predictable and designable fashion. The potential benefits of this emerging treatment may be based on the unique combination of immunostimulatory properties of nanoparticles with the ability of ionizing radiation to induce immunogenic tumor cell death. In this review, we will discuss available data and propose that the nanovectorized radiotherapy could be a powerful new strategy to induce anti-tumor immunity required for positive patient outcome.

Tumor eradication in rat glioma and bypass of immunosuppressive barriers using internal radiation with (188)Re-lipid nanocapsules.

To date, glioblastoma treatments have only been palliative. In this context, locoregional drug delivery strategies, which allow for blood--brain barrier bypass and reduced systemic toxicity, are of major significance. Recent progress in nanotechnology has led to the development of colloidal carriers of radiopharmaceutics, such as lipid nanocapsules loaded with rhenium-188 (LNC(188)Re-SSS) that are implanted in the brain. In our study, we demonstrated that fractionated internal radiation using LNC(188)Re-SSS triggered remarkable survival responses in a rat orthotopic glioma model (cure rates of 83%). We also highlighted the importance of the radioactivity activity gradient obtained by combining a simple stereotactic injection (SI) with convection-enhanced delivery (CED).We assumed that the immune system played a role in the treatment's efficacy on account of the overproduction of peripheral cytokines, recruitment of immune cells to the tumor site, and memory response in long-term survivor animals. Hence, nanovectorized internal radiation therapy with activity gradients stimulating immune responses may represent a new and interesting alternative for the treatment of solid tumors such as glioblastomas.

Lipid nanocapsules loaded with rhenium-188 reduce tumor progression in a rat hepatocellular carcinoma model.

BACKGROUND: Due to their nanometric scale (50 nm) along with their biomimetic properties, lipid nanocapsules loaded with Rhenium-188 (LNC(188)Re-SSS) constitute a promising radiopharmaceutical carrier for hepatocellular carcinoma treatment as its size may improve tumor penetration in comparison with microspheres devices. This study was conducted to confirm the feasibility and to assess the efficacy of internal radiation with LNC(188)Re-SSS in a chemically induced hepatocellular carcinoma rat model. METHODOLOGY/PRINCIPAL FINDINGS: Animals were treated with an injection of LNC(188)Re-SSS (80 MBq or 120 MBq). The treated animals (80 MBq, n = 12; 120 MBq, n = 11) were compared with sham (n = 12), blank LNC (n = 7) and (188)Re-perrhenate (n = 4) animals. The evaluation criteria included rat survival, tumor volume assessment, and vascular endothelial growth factor quantification. Following treatment with LNC(188)Re-SSS (80 MBq) therapeutic efficiency was demonstrated by an increase in the median survival from 54 to 107% compared with control groups with up to 7 long-term survivors in the LNC(188)Re-SSS group. Decreased vascular endothelial growth factor expression in the treated rats could indicate alterations in the angiogenesis process. CONCLUSIONS/SIGNIFICANCE: Overall, these results demonstrate that internal radiation with LNC(188)Re-SSS is a promising new strategy for hepatocellular carcinoma treatment.

The importance of endo-lysosomal escape with lipid nanocapsules for drug subcellular bioavailability.

To establish the therapeutic relevance of new nanocarriers, rationalization of knowledge on their interactions with biological structures is essential. In the present study, we have investigated endocytosis and intracellular trafficking of lipid nanocapsules (LNCs) in rat glioma cells. Radiolabelled and fluorescent LNCs were synthesized by using a phase inversion process that follows the formation of an oil/water microemulsion containing triglycerides, lecithins and a non-ionic surfactant, the hydroxystearate of poly(ethylene glycol) (HS-PEG). Our data revealed that LNCs were rapidly accumulated within cells (from 2 min exposure) through active and saturating mechanisms involving endogenous cholesterol with a major contribution of clathrin/caveolae-independent pathways. Although initially present in endosomes, LNCs can bypass the endo-lysosomal compartment with only 10% of the cell-internalized fraction found in isolated lysosomes after 2 h exposure. As demonstrated by use of lysosomal probes, LNCs reverted lysosome integrity similarly to V-ATPase inhibitors and in a size-dependent fashion with best efficiency for small nanoparticles. When loaded with paclitaxel, smallest LNCs also triggered the best cell death activity. Those LNC properties are ascribed to the proportion of HS-PEG they provided to the cell. They are important to consider toward the development of nanomedicines that use drugs sensitive to lysosomal degradation or that need to reach extra endo-lysosomal targets.