Vascular normalization in orthotopic glioblastoma following intravenous treatment with lipid-based nanoparticulate formulations of irinotecan (Irinophore C™), doxorubicin (Caelyx®) or vincristine

Application of nanoformulations as a strategy to optimize chemotherapeutic treatment of glioblastoma: a systematic review

The aim of this review was to explore the advances of nanoformulations as a strategy to optimize glioblastoma treatment, specifically focusing on targeting and controlling drug delivery systems to the tumor. This review followed the PRISMA recommendations. The studies were selected through a literature search conducted in the electronic databases PubMed Central, Science Direct, Scopus and Web of Science, in April 2023, using the equation descriptors: (nanocapsule OR nanoformulation) AND (glioblastoma). Forty-seven investigations included were published between 2011 and 2023 to assess the application of different nanoformulations to optimize delivery of chemotherapies including temozolomide, carmustine, vincristine or cisplatin previously employed in brain tumor therapy, as well as investigating another 10 drugs. Data demonstrated the possible application of different matrices employed as nanocarriers and utilization of functionalizing agents to improve internalization of chemotherapeutics. Functionalization was developed with the application of peptides, micronutrients/vitamins, antibodies and siRNAs. Finally, this review demonstrated the practical and clinical application of nanocarriers to deliver multiple drugs in glioblastoma models. These nanomodels might ideally be developed using functionalizing ligand agents that preferably act synergistically with the drug these agents carry. The findings showed promising results, making nanoformulations one of the best prospects for innovation and improvement of glioblastoma treatment.

Local delivery of doxorubicin prodrug via lipid nanocapsule-based hydrogel for the treatment of glioblastoma

Glioblastoma (GBM) recurrences appear in most cases around the resection cavity borders and arise from residual GBM cells that cannot be removed by surgery. Here, we propose a novel treatment that combines the advantages of nanomedicine and local drug delivery to target these infiltrating GBM cells. We developed an injectable lipid nanocapsule (LNC)-based formulation loaded with lauroyl-doxorubicin prodrug (DOXC12). Firstly, we demonstrated the efficacy of intratumoral administration of DOXC12 in GL261 GBM-bearing mice, which extended mouse survival. Then, we formulated an injectable hydrogel by mixing the appropriate amount of prodrug with the lipophilic components of LNC. We optimized the hydrogel by incorporating cytidine-C16 (CytC16) to achieve a mechanical stiffness adapted for an application in the brain post-surgery (DOXC12-LNCCL). DOXC12-LNCCL exhibited high DOXC12 encapsulation efficiency (95%) and a size of approximately 60 nm with sustained drug release for over 1 month in vitro. DOXC12-LNCCL exhibited enhanced cytotoxicity compared to free DOXC12 (IC50 of 349 and 86 nM, respectively) on GL261 GBM cells and prevented the growth of GL261 spheroids cultured on organotypic brain slices. In vivo, post-surgical treatment with DOXC12-LNCCL significantly improved the survival of GL261-bearing mice. The combination of this local treatment with the systemic administration of anti-inflammatory drug ibuprofen further delayed the onset of recurrences. In conclusion, our study presents a promising therapeutic approach for the treatment of GBM. By targeting residual GBM cells and reducing the inflammation post-surgery, we present a new strategy to delay the onset of recurrences in the gap period between surgery and standard of care therapy.

Induced Vascular Normalization-Can One Force Tumors to Surrender to a Better Microenvironment?

Immunotherapy has changed the way many cancers are being treated. Researchers in the field of immunotherapy and tumor immunology are investigating similar questions: How can the positive benefits achieved with immunotherapies be enhanced? Can this be achieved through combinations with other agents and if so, which ones? In our view, there is an urgent need to improve immunotherapy to make further gains in the overall survival for those patients that should benefit from immunotherapy. While numerous different approaches are being considered, our team believes that drug delivery methods along with appropriately selected small-molecule drugs and drug candidates could help reach the goal of doubling the overall survival rate that is seen in some patients that are given immunotherapeutics. This review article is prepared to address how immunotherapies should be combined with a second treatment using an approach that could realize therapeutic gains 10 years from now. For context, an overview of immunotherapy and cancer angiogenesis is provided. The major targets in angiogenesis that have modulatory effects on the tumor microenvironment and immune cells are highlighted. A combination approach that, for us, has the greatest potential for success involves treatments that will normalize the tumor's blood vessel structure and alter the immune microenvironment to support the action of immunotherapeutics. So, this is reviewed as well. Our focus is to provide an insight into some strategies that will engender vascular normalization that may be better than previously described approaches. The potential for drug delivery systems to promote tumor blood vessel normalization is considered.

Breaking the niche: multidimensional nanotherapeutics for tumor microenvironment modulation

Most of the current antitumor therapeutics were developed targeting the cancer cells only. Unfortunately, in the majority of tumors, this single-dimensional therapy is found to be ineffective. Advanced research has shown that cancer is a multicellular disorder. The tumor microenvironment (TME), which is made by a complex network of the bulk tumor cells and other supporting cells, plays a crucial role in tumor progression. Understanding the importance of the TME in tumor growth, different treatment modalities have been developed targeting these supporting cells. Recent clinical results suggest that simultaneously targeting multiple components of the tumor ecosystem with drug combinations can be highly effective. This type of "multidimensional" therapy has a high potential for cancer treatment. However, tumor-specific delivery of such multi-drug combinations remains a challenge. Nanomedicine could be utilized for the tumor-targeted delivery of such multidimensional therapeutics. In this review, we first give a brief overview of the major components of TME. We then highlight the latest developments in nanoparticle-based combination therapies, where one drug targets cancer cells and other drug targets tumor-supporting components in the TME for a synergistic effect. We include the latest preclinical and clinical studies and discuss innovative nanoparticle-mediated targeting strategies.

Smart pH-responsive polyhydralazine/bortezomib nanoparticles for remodeling tumor microenvironment and enhancing chemotherapy

The clinical translation of nanomedicines has been impeded by the unfavorable tumor microenvironment (TME), particularly the tortuous vasculature networks, which significantly influence the transport and distribution of nanomedicines into tumors. In this work, a smart pH-responsive bortezomib (BTZ)-loaded polyhydralazine nanoparticle (PHDZ/BTZ) is presented, which has a great capacity to augment the accumulation of BTZ in tumors by dilating tumor blood vessels via specific release of vasodilator hydralazine (HDZ). The Lewis acid-base coordination effect between the boronic bond of BTZ and amino of HDZ empowered PHDZ/BTZ nanoparticles with great stability and high drug loading contents. Once triggered by the acidic tumor environment, HDZ could be released quickly to remodel TME through tumor vessel dilation, hypoxia attenuation, and lead to an increased intratumoral BTZ accumulation. Additionally, our investigation revealed that this pH-responsive nanoparticle dramatically suppressed tumor growth, inhibited the occurrence of lung metastasis with fewer side effects and induced immunogenic cell death (ICD), thereby eliciting immune activation including massive cytotoxic T lymphocytes (CTLs) infiltration in tumors and efficient serum proinflammatory cytokine secretion compared with free BTZ treatment. Thus, with efficient drug loading capacity and potent immune activation, PHDZ nanoparticles exhibit great potential in the delivery of boronic acid-containing drugs aimed at a wide range of diseases.

Metal complex-based liposomes: Applications and prospects in cancer diagnostics and therapeutics

Metal complexes are of increasing interest as pharmaceutical agents in cancer diagnostics and therapeutics, while some of them suffer from issues such as limited water solubility and severe systemic toxicity. These drawbacks severely hampered their efficacy and clinical applications. Liposomes hold promise as delivery vehicles for constructing metal complex-based liposomes to maximize the therapeutic efficacy and minimize the side effects of metal complexes. This review provides an overview on the latest advances of metal complex-based liposomal delivery systems. First, the development of metal complex-mediated liposomal encapsulation is briefly introduced. Next, applications of metal complex-based liposomes in a variety of fields are overviewed, where drug delivery, cancer imaging (single photon emission computed tomography (SPECT), positron emission tomography (PET), and magnetic resonance imaging (MRI)), and cancer therapy (chemotherapy, phototherapy, and radiotherapy) were involved. Moreover, the potential toxicity, action of toxic mechanisms, immunological effects of metal complexes as well as the advantages of metal complex-liposomes in this content are also discussed. In the end, the future expectations and challenges of metal complex-based liposomes in clinical cancer therapy are tentatively proposed.

Therapeutic Effect of IL-4 Receptor-Targeting Pro-Apoptotic Peptide (AP1-ELP-KLAK) in Glioblastoma Tumor Model

BACKGROUND

Thermal-responsive self-assembled elastin-like polypeptide (ELP)-based nanoparticles are an emerging platform for controlled delivery of therapeutic peptides, proteins and small molecular drugs. The antitumor effect of bioengineered chimeric polypeptide AP1-ELP-KLAK containing an interleukin-4 receptor (IL-4R) targeting peptide and pro-apoptotic peptide (KLAKLAK) was evaluated in glioblastoma (GBM) in vitro and in vivo.

METHODS AND RESULTS

Herein, the therapeutic effect of AP1-ELP-KLAK was tested in advanced, and less curable glioblastoma cells with higher expression of IL-4R. Glioblastoma cell lines stably expressing different reporter systems i.e., caspase-3 sensor (surrogate marker for cellular apoptosis) or effluc/enhanced firefly luciferase (cellular viability) were established to measure cell death non-invasively. Bioluminescence imaging (BLI) of D54/effluc and U97MG/effluc treated with AP1-ELP-KLAK exhibited higher cell death up to 2~3-fold than the control. Treatment with AP1-ELP-KLAK resulted in time-dependent increase of caspase-3 sensor BLI activity in D54/C cells and D54/C tumor-bearing mice. Intravenous injection of AP1-ELP-KLAK dramatically reduced tumor growth by inducing cellular apoptosis in D54/effluc tumor-bearing mice. Further, the immuno-histological examination of the excised tumor tissue confirmed the presence of apoptotic cells as well as caspase-3 activation.

CONCLUSION

Collectively, AP1-ELP-KLAK effectively induced cellular apoptosis of glioblastoma cells and non-invasive imaging provides a window for real-time monitoring of anti-tumor effect with the provision of improving therapeutic efficacy in a glioblastoma mice model.

Optical tissue clearing and machine learning can precisely characterize extravasation and blood vessel architecture in brain tumors

Precise methods for quantifying drug accumulation in brain tissue are currently very limited, challenging the development of new therapeutics for brain disorders. Transcardial perfusion is instrumental for removing the intravascular fraction of an injected compound, thereby allowing for ex vivo assessment of extravasation into the brain. However, pathological remodeling of tissue microenvironment can affect the efficiency of transcardial perfusion, which has been largely overlooked. We show that, in contrast to healthy vasculature, transcardial perfusion cannot remove an injected compound from the tumor vasculature to a sufficient extent leading to considerable overestimation of compound extravasation. We demonstrate that 3D deep imaging of optically cleared tumor samples overcomes this limitation. We developed two machine learning-based semi-automated image analysis workflows, which provide detailed quantitative characterization of compound extravasation patterns as well as tumor angioarchitecture in large three-dimensional datasets from optically cleared samples. This methodology provides a precise and comprehensive analysis of extravasation in brain tumors and allows for correlation of extravasation patterns with specific features of the heterogeneous brain tumor vasculature.

Antiangiogenic Targets for Glioblastoma Therapy from a Pre-Clinical Approach, Using Nanoformulations

Glioblastoma (GBM) is the most aggressive tumor type whose resistance to conventional treatment is mediated, in part, by the angiogenic process. New treatments involving the application of nanoformulations composed of encapsulated drugs coupled to peptide motifs that direct drugs to specific targets triggered in angiogenesis have been developed to reach and modulate different phases of this process. We performed a systematic review with the search criterion (Glioblastoma OR Glioma) AND (Therapy OR Therapeutic) AND (Nanoparticle) AND (Antiangiogenic OR Angiogenesis OR Anti-angiogenic) in Pubmed, Scopus, and Cochrane databases, in which 312 articles were identified; of these, only 27 articles were included after selection and analysis of eligibility according to the inclusion and exclusion criteria. The data of the articles were analyzed in five contexts: the characteristics of the tumor cells; the animal models used to induce GBM for antiangiogenic treatment; the composition of nanoformulations and their physical and chemical characteristics; the therapeutic anti-angiogenic process; and methods for assessing the effects on antiangiogenic markers caused by therapies. The articles included in the review were heterogeneous and varied in practically all aspects related to nanoformulations and models. However, there was slight variance in the antiangiogenic effect analysis. CD31 was extensively used as a marker, which does not provide a view of the effects on the most diverse aspects involved in angiogenesis. Therefore, the present review highlighted the need for standardization between the different approaches of antiangiogenic therapy for the GBM model that allows a more effective meta-analysis and that helps in future translational studies.

NET-02 trial protocol: a multicentre, randomised, parallel group, open-label, phase II, single-stage selection trial of liposomal irinotecan (nal-IRI) and 5-fluorouracil (5-FU)/folinic acid or docetaxel as second-line therapy in patients with progressive poorly differentiated extrapulmonary neuroendocrine carcinoma (NEC)

INTRODUCTION

Poorly differentiated (PD), extrapulmonary (EP), neuroendocrine carcinomas (NECs) are rare but aggressive neuroendocrine neoplasms. First-line treatment for advanced disease is an etoposide and platinum-based chemotherapy combination. There is no established second-line treatment for patients with PD-EP-NEC, and this is an area of unmet need.

METHODS AND ANALYSIS

NET-02 is a UK, multicentre, randomised (1:1), parallel group, open-label, phase II, single-stage selection trial of liposomal irinotecan (nal-IRI)/5-fluorouracil (5-FU)/folinic acid or docetaxel as second-line therapy in patients with progressive PD-EP-NEC. One hundred and two eligible participants will be randomised to receive either nal-IRI/5-FU/folinic acid or docetaxel. The primary objective is to determine the 6-month progression-free survival (PFS) rate. The secondary objectives of this study are to determine PFS, overall survival, objective response rate, toxicity, quality of life and whether neuron-specific enolase is predictive of treatment response. If either treatment is found to have a 6-month PFS rate of at least 25%, that treatment will be considered for a phase III trial. If both treatments meet this target, prespecified selection criteria will be applied to establish which treatment to take forward.

ETHICS AND DISSEMINATION

This study has ethical approval from the Greater Manchester Central Research Ethics Committee (reference no. 18/NW/0031) and clinical trial authorisation from the Medicine and Healthcare Products Regulatory Agency. Results will be published in peer-reviewed journals and uploaded to the European Union Clinical Trials Register.

TRIAL REGISTRATION NUMBERS

ISRCTN10996604, NCT03837977, EudraCT Number: 2017-002453-11.

Nanoparticle Delivery and Tumor Vascular Normalization: The Chicken or The Egg?

Tumor-induced angiogenesis has been a significant focus of anti-cancer therapies for several decades. The immature and "leaky" tumor vasculature leads to significant cancer cell intravasation, increasing the metastatic potential, while the disoriented and hypo-perfused tumor vessels hamper the anti-tumor efficacy of immune cells and prevent the efficient diffusion of chemotherapeutic drugs. Therefore, tumor vascular normalization has emerged as a new treatment goal, aiming to provide a mature tumor vasculature, with higher perfusion, decreased cancer cell extravasation, and higher efficacy for anti-cancer therapies. Here we propose an overview of the nanodelivery approaches that target tumor vasculature, aiming to achieve vascular normalization. At the same time, abnormal vascular architecture and leaky tumor vessels have been the cornerstone for nanodelivery approaches through the enhanced permeability and retention (EPR) effect. Vascular normalization presents new opportunities and requirements for efficient nanoparticle delivery against the tumor cells and overall improved anti-cancer therapies.

Evaluation of Elastin-Like Polypeptides for Tumor Targeted Delivery of Doxorubicin to Glioblastoma

To increase treatment efficiency for glioblastoma, we have developed a system to selectively deliver chemotherapeutic doxorubicin (Dox) to Glioblastoma (GBM) tumors. This carrier is based on elastin-like polypeptide (ELP), which is soluble at physiological temperatures but undergoes a phase transition and accumulates at tumor sites with externally applied, mild (40–41 °C) hyperthermia. The CPP-ELP-Dox conjugate consists of a cell penetrating peptide (CPP), which facilitates transcytosis through the blood brain barrier and cell entry, and a 6-maleimidocaproyl hydrazone derivative of doxorubicin at the C-terminus of ELP. The acid-sensitive hydrazone linker ensures release of Dox in the lysosomes/endosomes after cellular uptake of the drug conjugate. We have shown that CPP-ELP-Dox effectively inhibits cell proliferation in three GBM cell lines. Both the free drug and CPP-ELP-Dox conjugate exhibited similar in vitro cytotoxicity, although their subcellular localization was considerably different. The Dox conjugate was mainly dispersed in the cytoplasm, while free drug had partial nuclear accumulation in addition to cytoplasmic distribution. The intracellular Dox concentration was increased in the CPP-ELP-Dox cells compared to that in the cells treated with free Dox, which positively correlates with cytotoxic activity. In summary, our findings demonstrate that CPP-ELP-Dox effectively kills GBM cells. Development of such a drug carrier has the potential to greatly improve current therapeutic approaches for GBM by increasing the specificity and efficacy of treatment and reducing cytotoxicity in normal tissues.

Prodrugs in combination with nanocarriers as a strategy for promoting antitumoral efficiency

Prodrug entrapment into nanocarriers for tumor delivery is a strategy to achieve a valid therapy with high efficiency. The prodrug contains anticancer agents conjugating with functional moieties or ligands so that the active component is released after metabolism in the body or tumor. The advantages of nanosystems for loading prodrugs include high loading, increased prodrug stability, improved bioavailability and enhanced targeting to tumor cells. In the present article, we introduce the prodrug delivery approaches according to nanomedicine and the recent advances in prodrug-loaded nanocarriers. First, we discuss the conceptional design of combined prodrugs and nanocarriers in response to the obstruction in anticancer therapy. Then we describe the cases of prodrug-loaded nanoparticles for cancer treatment during the past 5 years.

Liposomal Formulations to Modulate the Tumour Microenvironment and Antitumour Immune Response

Tumours are complex systems of genetically diverse malignant cells that proliferate in the presence of a heterogeneous microenvironment consisting of host derived microvasculature, stromal, and immune cells. The components of the tumour microenvironment (TME) communicate with each other and with cancer cells, to regulate cellular processes that can inhibit, as well as enhance, tumour growth. Therapeutic strategies have been developed to modulate the TME and cancer-associated immune response. However, modulating compounds are often insoluble (aqueous solubility of less than 1 mg/mL) and have suboptimal pharmacokinetics that prevent therapeutically relevant drug concentrations from reaching the appropriate sites within the tumour. Nanomedicines and, in particular, liposomal formulations of relevant drug candidates, define clinically meaningful drug delivery systems that have the potential to ensure that the right drug candidate is delivered to the right area within tumours at the right time. Following encapsulation in liposomes, drug candidates often display extended plasma half-lives, higher plasma concentrations and may accumulate directly in the tumour tissue. Liposomes can normalise the tumour blood vessel structure and enhance the immunogenicity of tumour cell death; relatively unrecognised impacts associated with using liposomal formulations. This review describes liposomal formulations that affect components of the TME. A focus is placed on formulations which are approved for use in the clinic. The concept of tumour immunogenicity, and how liposomes may enhance radiation and chemotherapy-induced immunogenic cell death (ICD), is discussed. Liposomes are currently an indispensable tool in the treatment of cancer, and their contribution to cancer therapy may gain even further importance by incorporating modulators of the TME and the cancer-associated immune response.

Nanotechnology Applications for Diffuse Intrinsic Pontine Glioma

Diffuse intrinsic pontine gliomas (DIPGs) are invariably fatal tumors found in the pons of elementary school aged children. These tumors are grade II-IV gliomas, with a median survival of less than 1 year from diagnosis when treated with standard of care (SOC) therapy. Nanotechnology may offer therapeutic options for the treatment of DIPGs. Multiple nanoparticle formulations are currently being investigated for the treatment of DIPGs. Nanoparticles based upon stable elements, polymer nanoparticles, and organic nanoparticles are under development for the treatment of brain tumors, including DIPGs. Targeting of nanoparticles is now possible as delivery techniques that address the difficulty in crossing the blood brain barrier (BBB) are developed. Theranostic nanoparticles, a combination of therapeutics and diagnostic nanoparticles, improve imaging of the cancerous tissue while delivering therapy to the local region. However, additional time and attention should be directed to developing a nanoparticle delivery system for treatment of the uniformly fatal pediatric disease of DIPG.

Natural products against cancer angiogenesis

The process of angiogenesis is quite well-known nowadays. Some medicines and extracts affecting this process are already used routinely in supporting the conventional treatment of many diseases that are considered angiogenic such as cancer. However, we must be aware that the area of currently used drugs of this type is much narrower than the theoretical possibilities existing in therapeutic angiogenesis. Plant substances are a large and diverse group of compounds that are found naturally in fruits, vegetables, spices, and medicinal plants. They also have different anticancer properties. The aim of this literature review article is to present the current state of knowledge concerning the molecular targets of tumor angiogenesis and the active substances (polyphenols, alkaloids, phytohormones, carbohydrates, and terpenes) derived from natural sources, whose activity against cancer angiogenesis has been confirmed.

Advances in systemic delivery of anti-cancer agents for the treatment of metastatic cancer

INTRODUCTION

The successful treatment of metastatic cancer is refractory to strategies employed to treat confined, primary lesions, such as surgical resection and radiation therapy, and thus must be addressed by systemic delivery of anti-cancer agents. Conventional systemically administered chemotherapeutics are often ineffective and come with severe dose-limiting toxicities.

AREAS COVERED

This review focuses on the recent developments in systemic therapy for metastatic cancer. Firstly, the strategies employed to improve the efficacy of conventional chemotherapeutics by 'passively' and 'actively' targeting them to tumors are discussed. Secondly, recent advances in the use of biologics to better target cancer and to instigate anti-tumor immunity are reviewed. Under the label of 'biologics', antibody-therapies, T cell engaging therapies, oncolytic virotherapies and cell-based therapies are examined and evaluated.

EXPERT OPINION

Improving specificity of action, and engaging the immune system appear to be key goals in the development of novel or reformulated anti-cancer agents for the treatment of metastatic cancer. One of the largest areas of opportunity in this field will be the identification of robust predictive biomarkers for use in conjunction with these agents. Treatment regimens that combine an agent to elicit an immune response (such as an oncolytic virus), and an agent to potentiate/mediate that immune response (such as immune checkpoint inhibitors) are predicted to be more effective than treatment with either agent alone.

Preclinical Efficacy of the MDM2 Inhibitor RG7112 in MDM2-Amplified and TP53 Wild-type Glioblastomas

PURPOSE

p53 pathway alterations are key molecular events in glioblastoma (GBM). MDM2 inhibitors increase expression and stability of p53 and are presumed to be most efficacious in patients with TP53 wild-type and MDM2-amplified cancers. However, this biomarker hypothesis has not been tested in patients or patient-derived models for GBM.

EXPERIMENTAL DESIGN

We performed a preclinical evaluation of RG7112 MDM2 inhibitor, across a panel of 36 patient-derived GBM cell lines (PDCL), each genetically characterized according to their P53 pathway status. We then performed a pharmacokinetic (PK) profiling of RG7112 distribution in mice and evaluated the therapeutic activity of RG7112 in orthotopic and subcutaneous GBM models.

RESULTS

MDM2-amplified PDCLs were 44 times more sensitive than TP53-mutated lines that showed complete resistance at therapeutically attainable concentrations (avg. IC50 of 0.52 μmol/L vs. 21.9 μmol/L). MDM4-amplified PDCLs were highly sensitive but showed intermediate response (avg. IC50 of 1.2 μmol/L), whereas response was heterogeneous in TP53 wild-type PDCLs with normal MDM2/4 levels (avg. IC50 of 7.7 μmol/L). In MDM2-amplified lines, RG7112 restored p53 activity inducing robust p21 expression and apoptosis. PK profiling of RG7112-treated PDCL intracranial xenografts demonstrated that the compound significantly crosses the blood-brain and the blood-tumor barriers. Most importantly, treatment of MDM2-amplified/TP53 wild-type PDCL-derived model (subcutaneous and orthotopic) reduced tumor growth, was cytotoxic, and significantly increased survival.

CONCLUSIONS

These data strongly support development of MDM2 inhibitors for clinical testing in MDM2-amplified GBM patients. Moreover, significant efficacy in a subset of non-MDM2-amplified models suggests that additional markers of response to MDM2 inhibitors must be identified.

Drug delivery systems and combination therapy by using vinca alkaloids

Developing new methods for chemotherapy drug delivery has become a topic of great concern. Vinca alkaloids are among the most widely used chemotherapy reagents for tumor therapy; however, their side effects are particularly problematic for many medical doctors. To reduce the toxicity and enhance the therapeutic efficiency of vinca alkaloids, many researchers have developed strategies such as using liposome-entrapped drugs, chemical- or peptide-modified drugs, polymeric packaging drugs, and chemotherapy drug combinations. This review mainly focuses on the development of a vinca alkaloid drug delivery system and the combination therapy. Five vinca alkaloids (eg, vincristine, vinblastine, vinorelbine, vindesine, and vinflunine) are reviewed.

MM-398 (nanoliposomal irinotecan): emergence of a novel therapy for the treatment of advanced pancreatic cancer

While progress in the treatment of advanced pancreatic cancer has accelerated in recent years, this malignancy continues to have an exceedingly poor prognosis, with no standard of care options beyond front-line chemotherapy. Currently, there are a number of new therapeutic agents in varying stages of clinical development, including molecularly targeted agents, immunotherapies, and modified versions of cytotoxics. MM-398, a novel nanoliposomal formulation of irinotecan, was designed to maximize tumor exposure while minimizing systemic toxicity due to its favorable pharmacokinetic profile. Overall, across multiple clinical trials in multiple disease indications, MM-398 has been shown to have a favorable safety and tolerability profile compared with standard irinotecan. Recent results of the Phase III NAPOLI-1 trial in patients with metastatic pancreatic cancer refractory to gemcitabine-based chemotherapy have shown a significant improvement in overall survival of MM-398 when combined with 5-fluorouracil/leucovorin, compared with 5-fluorouracil/leucovorin alone. This review focuses on the development and pharmacokinetic properties of MM-398, followed by evaluation of its safety and efficacy with a primary emphasis on clinical trials in advanced pancreatic cancer.

Determination of an optimal dosing schedule for combining Irinophore C™ and temozolomide in an orthotopic model of glioblastoma

Our laboratory reported that Irinophore C™ (IrC™; a lipid-based nanoparticulate formulation of irinotecan) is effective against an orthotopic model of glioblastoma (GBM) and that treatment with IrC™ was associated with vascular normalization within the tumor. Here, the therapeutic effects of IrC™ when used in combination with temozolomide (TMZ) in concurrent and sequential treatment schedules were tested. It was anticipated that IrC™ engendered vascular normalization would increase the delivery of TMZ to the tumor and that this would be reflected by improved treatment outcomes. The approach compared equally efficacious doses of irinotecan (IRN; 50 mg/kg) and IrC™ (25 mg/kg) in order to determine if there was a unique advantage achieved when combining TMZ with IrC™. The TMZ sensitive U251MG(O) cell line (null expression of O-6-methylguanine-DNA methyltransferase (MGMT)) modified to express the fluorescent protein mKate2 was inoculated orthotopically into NOD.CB17-SCID mice and treatment was initiated 14 days later. Our results demonstrated that IrC™ and TMZ administered concurrently resulted in optimal treatment outcomes, with 50% long term survivors (>180 days) in comparison to 17% long term survivors in animals treated with IRN and TMZ or TMZ alone. Indeed, the different treatments resulted in a 353%, 222% and 280% increase in median survival time (MST) compared to untreated animals for, respectively, IrC™ combined with TMZ, IRN combined with TMZ, and TMZ alone. When TMZ was administered after completion of IRN or IrC™ dosing, an increase in median survival time of 167-174% was observed compared to untreated animals and of 67% and 74%, respectively, when IRN (50 mg/kg) and IrC™ (25mg/kg) were given as single agents. We confirmed in these studies that after completion of the Q7D×3 dosing of IrC™, but not IRN, the tumor-associated vascular was normalized as compared to untreated tumors. Specifically, reductions in the fraction of collagen IV-free CD31 staining (p<0.05) and reductions in tumor vessel diameter were observed in tumors from IrC™-treated animals when compared to tumors from untreated or IRN treated animals. Analysis by transmission electron microscopy of the ultra-structure of tumors from IrC™-treated and untreated animals revealed that tumor-associated vessels from treated animals were smaller, more organized and exhibited a morphology comparable to normal blood vessels. In conclusion, optimal treatment outcomes were achieved when IrC™ and TMZ were administered concurrently, whereas IrC™ followed by TMZ treatment given sequentially did not confer any therapeutic advantage.

Tumor-Priming Smoothened Inhibitor Enhances Deposition and Efficacy of Cytotoxic Nanoparticles in a Pancreatic Cancer Model

Most pancreatic adenocarcinoma patients present with unresectable disease and benefit little from chemotherapy. Poor tumor perfusion and vascular permeability limit drug deposition. Previous work showed that Smoothened inhibitors of hedgehog signaling (sHHI) promote neovascularization in spontaneous mouse models of pancreatic cancer (PaCA) and enhance tumor permeability to low-molecular weight compounds. Here, we tested the hypothesis that sHHI can enhance tumor deposition and efficacy of drug-containing nanoparticles consisting of 80 to 100 nm sterically-stabilized liposomes (SSL) containing doxorubicin (SSL-DXR). SCID mice bearing low-passage patient-derived PaCA xenografts (PDX) were pretreated p.o. for 10 days with 40 mg/kg/d NVP-LDE225 (erismodegib), followed by i.v. SSL-DXR. Microvessel density, permeability, perfusion, and morphology were compared with untreated controls, as was SSL deposition and therapeutic efficacy. The sHHI alone affected tumor growth minimally, but markedly increased extravasation of nanoparticles into adenocarcinoma cell-enriched regions of the tumor. Immunostaining showed that sHHI treatment decreased pericyte coverage (α-SMA(+)) of CD31(+) vascular endothelium structures, and increased the abundance of endothelium-poor (CD31(-)) basement membrane structures (collagen IV(+)), suggesting increased immature microvessels. SSL-DXR (15 mg/kg) administered after sHHI pretreatment arrested tumor volume progression and decreased tumor perfusion/permeability, suggesting an initial vascular pruning response. Compared with controls, one cycle of 10-day sHHI pretreatment followed by 6 mg/kg SSL-DXR doubled median tumor progression time. Three cycles of treatment with sHHI and SSL-DXR, with a 10-day between-cycle drug holiday, nearly tripled median tumor progression time. Based upon these data, short-term sHHI treatment sequenced with nanoparticulate drug carriers constitutes a potential strategy to enhance efficacy of pancreatic cancer therapy.

Preclinical Efficacy of the MDM2 Inhibitor RG7112 in MDM2-Amplified and TP53 Wild-type Glioblastomas

PURPOSE

p53 pathway alterations are key molecular events in glioblastoma (GBM). MDM2 inhibitors increase expression and stability of p53 and are presumed to be most efficacious in patients with TP53 wild-type and MDM2-amplified cancers. However, this biomarker hypothesis has not been tested in patients or patient-derived models for GBM.

EXPERIMENTAL DESIGN

We performed a preclinical evaluation of RG7112 MDM2 inhibitor, across a panel of 36 patient-derived GBM cell lines (PDCL), each genetically characterized according to their P53 pathway status. We then performed a pharmacokinetic (PK) profiling of RG7112 distribution in mice and evaluated the therapeutic activity of RG7112 in orthotopic and subcutaneous GBM models.

RESULTS

MDM2-amplified PDCLs were 44 times more sensitive than TP53-mutated lines that showed complete resistance at therapeutically attainable concentrations (avg. IC50 of 0.52 μmol/L vs. 21.9 μmol/L). MDM4-amplified PDCLs were highly sensitive but showed intermediate response (avg. IC50 of 1.2 μmol/L), whereas response was heterogeneous in TP53 wild-type PDCLs with normal MDM2/4 levels (avg. IC50 of 7.7 μmol/L). In MDM2-amplified lines, RG7112 restored p53 activity inducing robust p21 expression and apoptosis. PK profiling of RG7112-treated PDCL intracranial xenografts demonstrated that the compound significantly crosses the blood-brain and the blood-tumor barriers. Most importantly, treatment of MDM2-amplified/TP53 wild-type PDCL-derived model (subcutaneous and orthotopic) reduced tumor growth, was cytotoxic, and significantly increased survival.

CONCLUSIONS

These data strongly support development of MDM2 inhibitors for clinical testing in MDM2-amplified GBM patients. Moreover, significant efficacy in a subset of non-MDM2-amplified models suggests that additional markers of response to MDM2 inhibitors must be identified.

A preclinical orthotopic model for glioblastoma recapitulates key features of human tumors and demonstrates sensitivity to a combination of MEK and PI3K pathway inhibitors

Current therapies for glioblastoma multiforme (GBM), the highest grade malignant brain tumor, are mostly ineffective, and better preclinical model systems are needed to increase the successful translation of drug discovery efforts into the clinic. Previous work describes a genetically engineered mouse (GEM) model that contains perturbations in the most frequently dysregulated networks in GBM (driven by RB, KRAS and/or PI3K signaling and PTEN) that induce development of Grade IV astrocytoma with properties of the human disease. Here, we developed and characterized an orthotopic mouse model derived from the GEM that retains the features of the GEM model in an immunocompetent background; however, this model is also tractable and efficient for preclinical evaluation of candidate therapeutic regimens. Orthotopic brain tumors are highly proliferative, invasive and vascular, and express histology markers characteristic of human GBM. Primary tumor cells were examined for sensitivity to chemotherapeutics and targeted drugs. PI3K and MAPK pathway inhibitors, when used as single agents, inhibited cell proliferation but did not result in significant apoptosis. However, in combination, these inhibitors resulted in a substantial increase in cell death. Moreover, these findings translated into the in vivo orthotopic model: PI3K or MAPK inhibitor treatment regimens resulted in incomplete pathway suppression and feedback loops, whereas dual treatment delayed tumor growth through increased apoptosis and decreased tumor cell proliferation. Analysis of downstream pathway components revealed a cooperative effect on target downregulation. These concordant results, together with the morphologic similarities to the human GBM disease characteristics of the model, validate it as a new platform for the evaluation of GBM treatment.

A multifunctional polymeric nanotheranostic system delivers doxorubicin and imaging agents across the blood-brain barrier targeting brain metastases of breast cancer

Metastatic brain cancers, in particular cancers with multiple lesions, are one of the most difficult malignancies to treat owing to their location and aggressiveness. Chemotherapy for brain metastases offers some hope. However, its efficacy is severely limited as most chemotherapeutic agents are incapable of crossing the blood-brain barrier (BBB) efficiently. Thus, a multifunctional nanotheranostic system based on poly(methacrylic acid)-polysorbate 80-grafted-starch was designed herein for the delivery of BBB-impermeable imaging and therapeutic agents to brain metastases of breast cancer. In vivo magnetic resonance imaging and confocal fluorescence microscopy were used to confirm extravasation of gadolinium and dye-loaded nanoparticles from intact brain microvessels in healthy mice. The targetability of doxorubicin (Dox)-loaded nanoparticles to intracranially established brain metastases of breast cancer was evaluated using whole body and ex vivo fluorescence imaging of the brain. Coexistence of nanoparticles and Dox in brain metastatic lesions was further confirmed by histological and microscopic examination of dissected brain tissue. Immuno-histochemical staining for caspase-3 and terminal-deoxynucleotidyl transferase dUTP nick end labeling for DNA fragmentation in tumor-bearing brain sections revealed that Dox-loaded nanoparticles selectively induced cancer cell apoptosis 24 h post-injection, while sparing normal brain cells from harm. Such effects were not observed in the mice treated with free Dox. Treatment with Dox-loaded nanoparticles significantly inhibited brain tumor growth compared to free Dox at the same dose as assessed by in vivo bioluminescence imaging of the brain metastases. These findings suggest that the multifunctional nanoparticles are promising for the treatment of brain metastases.

Irinophore C™, a lipid nanoparticle formulation of irinotecan, abrogates the gastrointestinal effects of irinotecan in a rat model of clinical toxicities

Irinotecan is a water-soluble camptothecin derivative with clinical activity against colorectal and small cell lung cancers and is currently a standard of care therapeutic in the treatment of colorectal cancer in combination with 5-fluorouracil. One of the major clinical issues limiting the use of irinotecan is gastrointestinal toxicity manifested as life-threatening diarrhea which is reported in up to 45 % of treated patients. The studies summarized here tested, in a rat model of irinotecan-associated gastro-intestinal toxicity, whether a lipid nanoparticle formulation of irinotecan, Irinophore C™, mitigated early-onset or late-onset diarrhea when given at doses equivalent to unformulated irinotecan that engenders both early- and late-onset diarrhea. Specifically, rats administered intravenously on two consecutive days with unformulated irinotecan at 170 mg/kg then 160 mg/kg experienced transient early-onset diarrhea after each administration and then experienced significant late-onset diarrhea peaking 4 days after treatment. Irinophore C™ given at the identical dose and schedule did not elicit either early- or late-onset diarrhea in any animals. When Irinophore C™ was combined with 5-fluorouracil there was also no early- or late-onset diarrhea observed. Histopathological analysis of the gastro-intestinal tract confirmed that the effects associated with irinotecan treatment were absent in rats given Irinophore C™ at the identical dose. Pharmacokinetic analysis demonstrated significantly higher systemic concentrations of irinotecan in rats given the nanoparticle formulation compared to those given unformulated irinotecan. These results demonstrate that the Irinophore C™ formulation is significantly less toxic than irinotecan, used either as a single agent or in combination with 5-fluorouracil, in a rat model of irinotecan-induced gastrointestinal toxicity.

Impact of meriolins, a new class of cyclin-dependent kinase inhibitors, on malignant glioma proliferation and neo-angiogenesis

BACKGROUND

Glioblastomas are the most frequent and most aggressive primary brain tumors in adults. The median overall survival is limited to a few months despite surgery, radiotherapy, and chemotherapy. It is now clearly established that hyperactivity of cyclin-dependent kinases (CDKs) is one of the processes underlying hyperproliferation and tumoral growth. The marine natural products meridianins and variolins, characterized as CDK inhibitors, display a kinase-inhibitory activity associated with cytotoxic effects. In order to improve selectivity and efficiency of these CDK inhibitors, a series of hybrid compounds called meriolins have been synthesized.

METHODS

The potential antitumoral activity of meriolins was investigated in vitro on glioma cell lines (SW1088 and U87), native neural cells, and a human endothelial cell line (HUV-EC-C). The impact of intraperitoneal or intratumoral administrations of meriolin 15 was evaluated in vivo on 2 different nude mice-xenografted glioma models.

RESULTS

Meriolins 3, 5, and 15 exhibited antiproliferative properties with nanomolar IC50 and induced cell-cycle arrest and CDK inhibition associated with apoptotic events in human glioma cell lines. These meriolins blocked the proliferation rate of HUV-EC-C through cell cycle arrest and apoptosis. In vivo, meriolin 15 provoked a robust reduction in tumor volume in spite of toxicity for highest doses, associated with inhibition of cell division, activation of caspase 3, reduction of CD133 cells, and modifications of the vascular architecture.

CONCLUSION

Meriolins, and meriolin 15 in particular, exhibit antiproliferative and proapoptotic activities on both glioma and intratumoral endothelial cells, constituting key promising therapeutic lead compounds for the treatment of glioblastoma.

Pharmacokinetics, tumor accumulation and antitumor activity of nanoliposomal irinotecan following systemic treatment of intracranial tumors

AIM

We sought to evaluate nanoliposomal irinotecan as an intravenous treatment in an orthotopic brain tumor model.

MATERIALS & METHODS

Nanoliposomal irinotecan was administered intravenously in the intracranial U87MG brain tumor model in mice, and irinotecan and SN-38 levels were analyzed in malignant and normal tissues. Therapy studies were performed in comparison to free irinotecan and control treatments.

RESULTS

Tissue analysis demonstrated favorable properties for nanoliposomal irinotecan, including a 10.9-fold increase in tumor AUC for drug compared with free irinotecan and 35-fold selectivity for tumor versus normal tissue exposure. As a therapy for orthotopic brain tumors, nanoliposomal irinotecan showed a mean survival time of 54.2 versus 29.5 days for free irinotecan. A total of 33% of the animals receiving nanoliposomal irinotecan showed no residual tumor by study end compared with no survivors in the other groups.

CONCLUSION

Nanoliposomal irinotecan administered systemically provides significant pharmacologic advantages and may be an efficacious therapy for brain tumors.

Sequential treatment of oxaliplatin-containing PEGylated liposome together with S-1 improves intratumor distribution of subsequent doses of oxaliplatin-containing PEGylated liposome

We recently reported that combination therapy with metronomic S-1 dosing and oxaliplatin (l-OHP)-containing PEGylated liposomes improved antitumor activity in a murine colorectal tumor model. However, little is known about the mechanism underlying such improved therapeutic efficacy. Here we investigated the impact of combined treatment on biodistribution, tumor accumulation and intratumor distribution of test PEGylated liposomes and on the structure of tumor vasculature in a solid tumor. The combined treatment clearly enhanced tumor accumulation and intratumor distribution of a subsequent test dose of PEGylated liposome as a result of on the one hand prolonging blood circulation of test liposome and on the other hand the alteration in tumor microenvironment. The l-OHP-containing PEGylated liposomes contributed predominantly to the enhanced tumor accumulation and altered tumor distribution of test liposome. On the other hand, metronomic S-1 dosing contributed to the altered tumor distribution but not the tumor accumulation of test liposome. The antitumor effect of the combined treatment, reflected by the proportion of apoptotic cells in the tumor, was approximately equally accounted for by each of the two treatments, leading to a roughly additive effect. In conclusion, 1-OHP-containing PEGylated liposome together with S-1 enhanced intratumor influx, leading to improved antitumor activity of subsequently injected 1-OHP-containing PEGylated liposomes and/or S-1. This strategy we propose, which is clinically applicable, may overcome the problems related to the use of EPR effect-based nanocarrier systems.

Treatment of colorectal cancer using a combination of liposomal irinotecan (Irinophore C™) and 5-fluorouracil

Purpose

To investigate the use of liposomal irinotecan (Irinophore C™) plus or minus 5-fluorouracil (5-FU) for the treatment of colorectal cancer.

Experimental Design

The effect of irinotecan (IRI) and/or 5-FU exposure times on cytotoxicity was assessed in vitro against HT-29 or LS174T human colon carcinoma cells. The pharmacokinetics and biodistribution of Irinophore C™ (IrC™) and 5-FU, administered alone or in combination, were compared in vivo. A subcutaneous model of HT-29 human colorectal cancer in Rag2-M mice was utilized to assess the efficacy of IrC™ alone, and in combination with 5-FU.

Results

The cytotoxicity of IRI and 5-FU were strongly dependent on exposure time. Synergistic interactions were observed following prolonged exposure to IRI/5-FU combinations. Pharmacokinetics/biodistribution studies demonstrated that the 5-FU elimination rate was decreased significantly when 5-FU was co-administered intravenously with IrC™, versus alone. Significant decreases in 5-FU elimination were also observed in plasma, with an associated increase of 5-FU in some tissues when 5-FU was given by intraperitoneal injection and IrC™ was given intravenously. The elimination of IrC™ was not significantly different when administered alone or in combination with 5-FU. Therapeutic studies demonstrated that single agent IrC™ was significantly more effective than the combination of IRI/5-FU; surprisingly, IrC™/5-FU combinations were no more effective than IrC™ alone. The administration of combinations of 5-FU (16 mg/kg) and IrC™ (60 mg IRI/kg) showed increased toxicity when compared to IrC™ alone. Treatment with IrC™ alone (60 mg IRI/kg) delayed the time required for a 5-fold increase in initial tumor volume to day 49, compared to day 23 for controls. When IrC™ (40 mg IRI/kg) was used in combination with 5-FU (16 mg/kg), the time to increase tumor volume 5-fold was 43 days, which was comparable to that achieved when using IrC™ alone (40 mg IRI/kg).

Conclusions

Single agent IrC™ was well tolerated and has significant therapeutic potential. IrC™ may be a suitable replacement for IRI treatment, but its use with free 5-FU is complicated by IrC™-engendered changes in 5-FU pharmacokinetics/biodistribution which are associated with increased toxicity when using the combination.

Mechanisms of tumor vascular priming by a nanoparticulate doxorubicin formulation

PURPOSE

Tumor vascular normalization by antiangiogenic agents may increase tumor perfusion but reestablish vascular barrier properties in CNS tumors. Vascular priming via nanoparticulate carriers represents a mechanistically distinct alternative. This study investigated mechanisms by which sterically-stabilized liposomal doxorubicin (SSL-DXR) modulates tumor vascular properties.

METHODS

Functional vascular responses to SSL-DXR were investigated in orthotopic rat brain tumors using deposition of fluorescent permeability probes and dynamic contrast-enhanced magnetic resonance imaging. Microvessel density and tumor burden were quantified by immunohistochemistry (CD-31) and quantitative RT-PCR (VE-cadherin).

RESULTS

Administration of SSL-DXR (5.7 mg/kg iv) initially (3-4 days post-treatment) decreased tumor vascular permeability, k(trans) (vascular exchange constant), vascular endothelial cell content, microvessel density, and deposition of nanoparticulates. Tumor vasculature became less chaotic. Permeability and perfusion returned to control values 6-7 days post-treatment, but intratumor SSL-DXR depot continued to effect tumor vascular endothelial compartment 7-10 days post-treatment, mediating enhanced permeability.

CONCLUSIONS

SSL-DXR ultimately increased tumor vascular permeability, but initially normalized tumor vasculature and decreased tumor perfusion, permeability, and nanoparticulate deposition. These temporal changes in vascular integrity resulting from a single SSL-DXR dose have important implications for the design of combination therapies incorporating nanoparticle-based agents for tumor vascular priming.

Polo-like kinase 1 inhibition kills glioblastoma multiforme brain tumor cells in part through loss of SOX2 and delays tumor progression in mice

Glioblastoma multiforme (GBM) ranks among the deadliest types of cancer and given these new therapies are urgently needed. To identify molecular targets, we queried a microarray profiling 467 human GBMs and discovered that polo-like kinase 1 (PLK1) was highly expressed in these tumors and that it clustered with the proliferative subtype. Patients with PLK1-high tumors were more likely to die from their disease suggesting that current therapies are inactive against such tumors. This prompted us to examine its expression in brain tumor initiating cells (BTICs) given their association with treatment failure. BTICs isolated from patients expressed 110-470 times more PLK1 than normal human astrocytes. Moreover, BTICs rely on PLK1 for survival because the PLK1 inhibitor BI2536 inhibited their growth in tumorsphere cultures. PLK1 inhibition suppressed growth, caused G(2) /M arrest, induced apoptosis, and reduced the expression of SOX2, a marker of neural stem cells, in SF188 cells. Consistent with SOX2 inhibition, the loss of PLK1 activity caused the cells to differentiate based on elevated levels of glial fibrillary acidic protein and changes in cellular morphology. We then knocked glial fibrillary acidic protein (GFAP) down SOX2 with siRNA and showed that it too inhibited cell growth and induced cell death. Likewise, in U251 cells, PLK1 inhibition suppressed cell growth, downregulated SOX2, and induced cell death. Furthermore, BI2536 delayed tumor growth of U251 cells in an orthotopic brain tumor model, demonstrating that the drug is active against GBM. In conclusion, PLK1 level is elevated in GBM and its inhibition restricts the growth of brain cancer cells.

Lipid-based nanoformulation of irinotecan: dual mechanism of action allows for combination chemo/angiogenic therapy

A number of studies have outlined the antiangiogenic effects of cytotoxic agents when administered frequently at low doses. These studies suggest that the effect of the cytotoxic agent is on the vasculature within the tumor and it is assumed that there is little or negligible cytotoxicity. Liposomal drug delivery systems have the ability to provide a dual mechanism of activity where tumor accumulation can deliver high local concentrations of the drug at the site of action with concomitant slow release of the drug from carriers in the blood compartment that results in antivascular effects, similar to that achieved when dosing frequently at low levels. Although this dual mechanism of activity may be linked to other lipid nanoparticle formulations of anticancer drugs, this article summarizes the evidence supporting direct (cytotoxic) and indirect (antivascular) actions of a liposomal formulation of irinotecan.

Combination therapy with metronomic S-1 dosing and oxaliplatin-containing PEG-coated cationic liposomes in a murine colorectal tumor model: synergy or antagonism?

Combination therapy with 2 or more drugs with different mechanisms of action has been considered a promising strategy for the effective treatment of advanced and metastatic cancers. However, the rational design of combination therapy represents a potential prerequisite for its effectiveness. Recently, we showed that the combination of oral metronomic S-1 dosing with oxaliplatin (l-OHP)-containing PEG-coated "neutral" liposomes exerted excellent antitumor activity. In addition, we recently designed a PEG-coated "cationic" liposome for dual-targeting delivery of l-OHP to tumor endothelial cells and tumor cells in a solid tumor. This targeted liposomal l-OHP formulation showed efficient antitumor activity in a murine tumor model, compared with l-OHP-containing PEG-coated "neutral" liposomes. In the present study, we investigated the issue of whether metronomic S-1 dosing with l-OHP-containing PEG-coated "cationic" liposomes creates synergy. Unfortunately, metronomic S-1 dosing resulted in impaired delivery of PEG-coated "cationic" liposomes into tumor tissue, presumably by decreasing the binding sites on tumor blood vessels available for the liposomes. The anticipated cytotoxic synergistic effect of the combination treatment was not achieved. Instead, the combination treatment showed lower antitumor efficacy than l-OHP-containing PEG-coated "cationic" liposomes alone. These results suggest that the combined treatment of S-1 and l-OHP-containing PEG-coated "cationic" liposomes seems to be antagonistic rather than synergistic.

Liposomal doxorubicin improves radiotherapy response in hypoxic prostate cancer xenografts

Background

Tumor vasculature frequently fails to supply sufficient levels of oxygen to tumor tissue resulting in radioresistant hypoxic tumors. To improve therapeutic outcome radiotherapy (RT) may be combined with cytotoxic agents.

Methods

In this study we have investigated the combination of RT with the cytotoxic agent doxorubicin (DXR) encapsulated in pegylated liposomes (PL-DXR). The PL-DXR formulation Caelyx^® was administered to male mice bearing human, androgen-sensitive CWR22 prostate carcinoma xenografts in a dose of 3.5 mg DXR/kg, in combination with RT (2 Gy/day × 5 days) performed under normoxic and hypoxic conditions. Hypoxic RT was achieved by experimentally inducing tumor hypoxia by clamping the tumor-bearing leg five minutes prior to and during RT. Treatment response evaluation consisted of tumor volume measurements and dynamic contrast-enhanced magnetic resonance imaging (DCE MRI) with subsequent pharmacokinetic analysis using the Brix model. Imaging was performed pre-treatment (baseline) and 8 days later. Further, hypoxic fractions were determined by pimonidazole immunohistochemistry of excised tumor tissue.

Results

As expected, the therapeutic effect of RT was significantly less effective under hypoxic than normoxic conditions. However, concomitant administration of PL-DXR significantly improved the therapeutic outcome following RT in hypoxic tumors. Further, the pharmacokinetic DCE MRI parameters and hypoxic fractions suggest PL-DXR to induce growth-inhibitory effects without interfering with tumor vascular functions.

Conclusions

We found that DXR encapsulated in liposomes improved the therapeutic effect of RT under hypoxic conditions without affecting vascular functions. Thus, we propose that for cytotoxic agents affecting tumor vascular functions liposomes may be a promising drug delivery technology for use in chemoradiotherapy.