Phase II studies of RMP-7 and carboplatin in the treatment of recurrent high grade glioma. RMP-7 European Study Group

Overcoming Barriers in Glioblastoma-Advances in Drug Delivery Strategies

The world of cancer treatment is evolving rapidly and has improved the prospects of many cancer patients. Yet, there are still many cancers where treatment prospects have not (or hardly) improved. Glioblastoma is the most common malignant primary brain tumor, and even though it is sensitive to many chemotherapeutics when tested under laboratory conditions, its clinical prospects are still very poor. The blood-brain barrier (BBB) is considered at least partly responsible for the high failure rate of many promising treatment strategies. We describe the workings of the BBB during healthy conditions and within the glioblastoma environment. How the BBB acts as a barrier for therapeutic options is described as well as various approaches developed and tested for passing or opening the BBB, with the ultimate aim to allow access to brain tumors and improve patient perspectives.

Biotin conjugates in targeted drug delivery: is it mediated by a biotin transporter, a yet to be identified receptor, or (an)other unknown mechanism(s)?

Conjugation of drugs with biotin is a widely studied strategy for targeted drug delivery. The structure-activity relationship (SAR) studies through H3-biotin competition experiments conclude with the presence of a free carboxylic acid being essential for its uptake via the sodium-dependent multivitamin transporter (SMVT, the major biotin transporter). However, biotin conjugation with a payload requires modification of the carboxylic acid to an amide or ester group. Then, there is the question as to how/whether the uptake of biotin conjugates goes through the SMVT. If not, then what is the mechanism? Herein, we present known uptake mechanisms of biotin and its applications reported in the literature. We also critically analyse possible uptake mechanism(s) of biotin conjugates to address the disconnect between the results from SMVT-based SAR and "biotin-facilitated" targeted drug delivery. We believe understanding the uptake mechanism of biotin conjugates is critical for their future applications and further development.

The influence of physiological and pathological perturbations on blood-brain barrier function

The blood-brain barrier (BBB) is located at the interface between the vascular system and the brain parenchyma, and is responsible for communication with systemic circulation and peripheral tissues. During life, the BBB can be subjected to a wide range of perturbations or stresses that may be endogenous or exogenous, pathological or therapeutic, or intended or unintended. The risk factors for many diseases of the brain are multifactorial and involve perturbations that may occur simultaneously (e.g., two-hit model for Alzheimer's disease) and result in different outcomes. Therefore, it is important to understand the influence of individual perturbations on BBB function in isolation. Here we review the effects of eight perturbations: mechanical forces, temperature, electromagnetic radiation, hypoxia, endogenous factors, exogenous factors, chemical factors, and pathogens. While some perturbations may result in acute or chronic BBB disruption, many are also exploited for diagnostic or therapeutic purposes. The resultant outcome on BBB function depends on the dose (or magnitude) and duration of the perturbation. Homeostasis may be restored by self-repair, for example, via processes such as proliferation of affected cells or angiogenesis to create new vasculature. Transient or sustained BBB dysfunction may result in acute or pathological symptoms, for example, microhemorrhages or hypoperfusion. In more extreme cases, perturbations may lead to cytotoxicity and cell death, for example, through exposure to cytotoxic plaques.

Peptide-Based Agents for Cancer Treatment: Current Applications and Future Directions

Peptide-based strategies have received an enormous amount of attention because of their specificity and applicability. Their specificity and tumor-targeting ability are applied to diagnosis and treatment for cancer patients. In this review, we will summarize recent advancements and future perspectives on peptide-based strategies for cancer treatment. The literature search was conducted to identify relevant articles for peptide-based strategies for cancer treatment. It was performed using PubMed for articles in English until June 2023. Information on clinical trials was also obtained from ClinicalTrial.gov. Given that peptide-based strategies have several advantages such as targeted delivery to the diseased area, personalized designs, relatively small sizes, and simple production process, bioactive peptides having anti-cancer activities (anti-cancer peptides or ACPs) have been tested in pre-clinical settings and clinical trials. The capability of peptides for tumor targeting is essentially useful for peptide-drug conjugates (PDCs), diagnosis, and image-guided surgery. Immunomodulation with peptide vaccines has been extensively tested in clinical trials. Despite such advantages, FDA-approved peptide agents for solid cancer are still limited. This review will provide a detailed overview of current approaches, design strategies, routes of administration, and new technological advancements. We will highlight the success and limitations of peptide-based therapies for cancer treatment.

Modulating the Blood-Brain Barrier: A Comprehensive Review

The highly secure blood-brain barrier (BBB) restricts drug access to the brain, limiting the molecular toolkit for treating central nervous system (CNS) diseases to small, lipophilic drugs. Development of a safe and effective BBB modulator would revolutionise the treatment of CNS diseases and future drug development in the area. Naturally, the field has garnered a great deal of attention, leading to a vast and diverse range of BBB modulators. In this review, we summarise and compare the various classes of BBB modulators developed over the last five decades-their recent advancements, advantages and disadvantages, while providing some insight into their future as BBB modulators.

Breaching the Blood-Brain Tumor Barrier for Tumor Therapy

Tumors affecting the central nervous system (CNS), either primary or secondary, are highly prevalent and represent an unmet medical need. Prognosis of these tumors remains poor, mostly due to the low intrinsic chemo/radio-sensitivity of tumor cells, a meagerly known role of the microenvironment and the poor CNS bioavailability of most used anti-cancer agents. The BBTB is the main obstacle for anticancer drugs to achieve therapeutic concentrations in the tumor tissues. During the last decades, many efforts have been devoted to the identification of modalities allowing to increase drug delivery into brain tumors. Until recently, success has been modest, as few of these approaches reached clinical testing and even less gained regulatory approval. In recent years, the scenario has changed, as various conjugates and drug delivery technologies have advanced into clinical testing, with encouraging results and without being burdened by a heavy adverse event profile. In this article, we review the different approaches aimed at increasing drug delivery to brain tumors, with particular attention to new, promising approaches that increase the permeability of the BBTB or exploit physiological transport mechanisms.

Brain Drug Delivery: Overcoming the Blood-brain Barrier to Treat Tauopathies

Tauopathies are neurodegenerative disorders characterized by the deposition of abnormal tau protein in the brain. The application of potentially effective therapeutics for their successful treatment is hampered by the presence of a naturally occurring brain protection layer called the blood-brain barrier (BBB). BBB represents one of the biggest challenges in the development of therapeutics for central nervous system (CNS) disorders, where sufficient BBB penetration is inevitable. BBB is a heavily restricting barrier regulating the movement of molecules, ions, and cells between the blood and the CNS to secure proper neuronal function and protect the CNS from dangerous substances and processes. Yet, these natural functions possessed by BBB represent a great hurdle for brain drug delivery. This review is concentrated on summarizing the available methods and approaches for effective therapeutics' delivery through the BBB to treat neurodegenerative disorders with a focus on tauopathies. It describes the traditional approaches but also new nanotechnology strategies emerging with advanced medical techniques. Their limitations and benefits are discussed.

Blood-Brain Barrier Disruption in Neuro-Oncology: Strategies, Failures, and Challenges to Overcome

The blood-brain barrier (BBB) presents a formidable challenge in the development of effective therapeutics in neuro-oncology. This has fueled several decades of efforts to develop strategies for disrupting the BBB, but progress has not been satisfactory. As such, numerous drug- and device-based methods are currently being investigated in humans. Through a focused assessment of completed, active, and pending clinical trials, our first aim in this review is to outline the scientific foundation, successes, and limitations of the BBBD strategies developed to date. Among 35 registered trials relevant to BBBD in neuro-oncology in the ClinicalTrials.gov database, mannitol was the most common drug-based method, followed by RMP-7 and regadenoson. MR-guided focused ultrasound was the most common device-based method, followed by MR-guided laser ablation, ultrasound, and transcranial magnetic stimulation. While most early-phase studies focusing on safety and tolerability have met stated objectives, advanced-phase studies focusing on survival differences and objective tumor response have been limited by heterogeneous populations and tumors, along with a lack of control arms. Based on shared challenges among all methods, our second objective is to discuss strategies for confirmation of BBBD, choice of systemic agent and drug design, alignment of BBBD method with real-world clinical workflow, and consideration of inadvertent toxicity associated with disrupting an evolutionarily-refined barrier. Finally, we conclude with a strategic proposal to approach future studies assessing BBBD.

Acoustic feedback enables safe and reliable carboplatin delivery across the blood-brain barrier with a clinical focused ultrasound system and improves survival in a rat glioma model

The blood-brain barrier (BBB) restricts delivery of most chemotherapy agents to brain tumors. Here, we investigated a clinical focused ultrasound (FUS) device to disrupt the BBB in rats and enhance carboplatin delivery to the brain using the F98 glioma model.

Methods: In each rat, 2-3 volumetric sonications (5 ms bursts at 1.1 Hz for 75s) targeted 18-27 locations in one hemisphere. Sonication was combined with Definity microbubbles (10 µl/kg) and followed by intravenous carboplatin (50 mg/kg). Closed-loop feedback control was performed based on acoustic emissions analysis.

Results: Safety and reliability were established in healthy rats after three sessions with carboplatin; BBB disruption was induced in every target without significant damage evident in MRI or histology. In tumor-bearing rats, concentrations of MRI contrast agent (Gadavist) were 1.7 and 3.3 times higher in the tumor center and margin, respectively, than non-sonicated tumors (P<0.001). Tissue-to-plasma ratios of intact carboplatin concentrations were increased by 7.3 and 2.9 times in brain and tumor respectively, at one hour after FUS and 4.2 and 2.4 times at four hours. Tumor volume doubling time in rats receiving FUS and carboplatin increased by 96% and 126% compared to rats that received carboplatin alone and non-sonicated controls, respectively (P<0.05); corresponding increases in median survival were 48% and 66% (P<0.01).

Conclusion: Overall, this work demonstrates that actively-controlled BBB disruption with a clinical device can enhance carboplatin delivery without neurotoxicity at level that reduces tumor growth and improves survival in an aggressive and infiltrative rat glioma model.

Natural Brain Penetration Enhancer-Modified Albumin Nanoparticles for Glioma Targeting Delivery

The unsatisfactory therapeutic outcome for glioma is mainly due to the poor blood-brain barrier (BBB) permeability and inefficient accumulation in the glioma area of chemotherapeutic agents. The existing drug delivery strategies can increase drug transport to the brain but are restricted by side effects and/or poor delivery efficiency. In this study, potent brain penetration enhancers were screened from the active components of aromatic resuscitation drugs used in traditional Chinese medicine. A novel glioma-targeting system based on enhancer-modified albumin nanoparticles was developed to safely and efficiently deliver drugs to the glioma regions in the brain. The nanoparticles improved the transport of nanoparticles across brain capillary endothelial cell (BCEC) monolayer by increasing endocytosis in endothelial cells and causing BBB disruption. In vivo imaging studies demonstrated that the systems could enter the brain and subsequently accumulate in glioma cells with a much higher targeting efficiency than that of transferrin-modified albumin nanoparticles. Of note, the nanoparticles could be captured and penetrate through endothelial cells fenestrae in pineal gland, which is suggestive of an effective way to deliver a nanosystem to the brain by bypassing the BBB. The nanoparticles showed good biocompatibility and negligible cytotoxicity. The results reveal an efficient and safe strategy for brain drug delivery in glioma therapy.

Progress in brain targeting drug delivery system by nasal route

The blood-brain barrier (BBB) restricts the transport of potential therapeutic moieties to the brain. Direct targeting the brain via olfactory and trigeminal neural pathways by passing the BBB has gained an important consideration for delivery of wide range of therapeutics to brain. Intranasal route of transportation directly delivers the drugs to brain without systemic absorption, thus avoiding the side effects and enhancing the efficacy of neurotherapeutics. Over the last several decades, different drug delivery systems (DDSs) have been studied for targeting the brain by the nasal route. Novel DDSs such as nanoparticles (NPs), liposomes and polymeric micelles have gained potential as useful tools for targeting the brain without toxicity in nasal mucosa and central nervous system (CNS). Complex geometry of the nasal cavity presented a big challenge to effective delivery of drugs beyond the nasal valve. Recently, pharmaceutical firms utilized latest and emerging nasal drug delivery technologies to overcome these barriers. This review aims to describe the latest development of brain targeted DDSs via nasal administration.

CHEMICAL COMPOUNDS STUDIED IN THIS ARTICLE

Carbopol 934p (PubChem CID: 6581) Carboxy methylcellulose (PubChem CID: 24748) Penetratin (PubChem CID: 101111470) Poly lactic-co-glycolic acid (PubChem CID: 23111554) Tween 80 (PubChem CID: 5284448).

Blood-brain barrier, cytotoxic chemotherapies and glioblastoma

INTRODUCTION

Glioblastomas (GBM) are the most common and aggressive primary malignant brain tumors in adults. The blood brain barrier (BBB) is a major limitation reducing efficacy of anti-cancer drugs in the treatment of GBM patients. Areas covered: Virtually all GBM recur after the first-line treatment, at least partly, due to invasive tumor cells protected from chemotherapeutic agents by the intact BBB in the brain adjacent to tumor. The passage through the BBB, taken by antitumor drugs, is poorly and heterogeneously documented in the literature. In this review, we have focused our attention on: (i) the BBB, (ii) the passage of chemotherapeutic agents across the BBB and (iii) the strategies investigated to overcome this barrier. Expert commentary: A better preclinical knowledge of the crossing of the BBB by antitumor drugs will allow optimizing their clinical development, alone or combined with BBB bypassing strategies, towards an increased success rate of clinical trials.

Evolving Drug Delivery Strategies to Overcome the Blood Brain Barrier

The blood-brain barrier (BBB) poses a unique challenge for drug delivery to the central nervous system (CNS). The BBB consists of a continuous layer of specialized endothelial cells linked together by tight junctions, pericytes, nonfenestrated basal lamina, and astrocytic foot processes. This complex barrier controls and limits the systemic delivery of therapeutics to the CNS. Several innovative strategies have been explored to enhance the transport of therapeutics across the BBB, each with individual advantages and disadvantages. Ongoing advances in delivery approaches that overcome the BBB are enabling more effective therapies for CNS diseases. In this review, we discuss: (1) the physiological properties of the BBB, (2) conventional strategies to enhance paracellular and transcellular transport through the BBB, (3) emerging concepts to overcome the BBB, and (4) alternative CNS drug delivery strategies that bypass the BBB entirely. Based on these exciting advances, we anticipate that in the near future, drug delivery research efforts will lead to more effective therapeutic interventions for diseases of the CNS.

Recent progress in tight junction modulation for improving bioavailability

INTRODUCTION

Currently, there are many novel drugs that belong to class III or IV of the Biopharmaceutics Classification System, showing low bioavailability. Tight junction (TJ) modulation offers an approach to increase bioavailability of pharmaceutical compounds. Furthermore, some diseases are accompanied by disturbed barrier function or TJ dysregulation and thus represent a second application for TJ modulators.

AREAS COVERED

This review contains a summary of three different TJ modulators: AT1002, PN159 and labradimil. Within this summary, the authors provide a description of their effects on TJs, their adverse effects and their success in clinical trials. Furthermore, the authors present the current understanding of TJ regulation and highlight opportunities to develop new TJ modulators; they also review the problems that might occur.

EXPERT OPINION

The development of new mechanism-based (MB) TJ modulators is a very promising field of research. MB approaches are expected to have the best future prospects. Further elucidation of signaling pathways and TJ regulation will be necessary for advancing MB TJ modulator research.

Modern methods for delivery of drugs across the blood-brain barrier

The blood-brain barrier (BBB) is a highly regulated and efficient barrier that provides a sanctuary to the brain. It is designed to regulate brain homeostasis and to permit selective transport of molecules that are essential for brain function. Unfortunately, drug transport to the brain is hampered by this almost impermeable, highly selective and well coordinated barrier. With progress in molecular biology, the BBB is better understood, particularly under different pathological conditions. This review will discuss the barrier issue from a biological and pathological perspective to provide a better insight to the challenges and opportunities associated with the BBB. Modern methods which can take advantage of these opportunities will be reviewed. Applications of nanotechnology in drug transport, receptor-mediated targeting and transport, and finally cell-mediated drug transport will also be covered in the review. The challenge of delivering an effective therapy to the brain is formidable; solutions will likely involve concerted multidisciplinary approaches that take into account BBB biology as well as the unique features associated with the pathological condition to be treated.

Novel and emerging strategies in drug delivery for overcoming the blood-brain barrier

Two decades of molecular research have revealed the presence of transporters and receptors expressed in the brain vascular endothelium that provide potential novel targets for the rational design of blood-brain barrier-penetrating drugs. In this review, we briefly introduce the reader to the molecular characteristics of the blood-brain barrier that make this one of the most important obstacles towards the development of efficacious CNS drugs. We highlight recent attempts to rationally target influx and bidirectional transport systems expressed on the brain endothelial cell and avoid the important obstacle presented in the form of efflux transporters. Many of these approaches are highly innovative and show promise for future human application. Some of these approaches, however, have revealed significant limitations and are critiqued in this review. Nonetheless, these combined efforts have left the field of CNS drug delivery better positioned for developing novel approaches towards the rational design of CNS-penetrating drugs.

The biology of brain metastases-translation to new therapies

Brain metastases are a serious obstacle in the treatment of patients with solid tumors and contribute to the morbidity and mortality of these cancers. It is speculated that the frequency of brain metastasis is increasing for several reasons, including improved systemic therapy and survival, and detection of metastases in asymptomatic patients. The lack of preclinical models that recapitulate the clinical setting and the exclusion of patients with brain metastases from most clinical trials have slowed progress. Molecular factors contributing to brain metastases are being elucidated, such as genes involved in cell adhesion, extravasation, metabolism, and cellular signaling. Furthermore, the role of the unique brain microenvironment is beginning to be explored. Although the presence and function of the blood-brain barrier in metastatic tumors is still poorly understood, it is likely that some tumor cells are protected from therapeutics by the blood-tumor barrier, creating a sanctuary site. This Review discusses what is known about the biology of brain metastases, what preclinical models are available to study the disease, and which novel therapeutic strategies are being studied in patients.

Modulation of brain tumor capillaries for enhanced drug delivery selectively to brain tumor

BACKGROUND

The blood-brain tumor barrier (BTB) significantly impedes delivery of most hydrophilic molecules to brain tumors. Several promising strategies, however, have been developed to overcome this problem.

METHODS

We discuss several drug delivery methods to brain tumor, including intracerebroventricular, convection enhanced delivery, BBB/BTB disruption, and BTB permeability modulation, which was developed in our laboratory.

RESULTS

Using immunolocalization, immunoblotting, and potentiometric studies, we found that brain tumor capillary endothelial cells overexpress certain unique protein markers that are absent or barely detectable in normal capillary endothelial cells. We biochemically modulated these markers to sustain and enhance drug delivery, including molecules of varying sizes, selectively to tumors in rat syngeneic and xenograft brain tumor models. We also demonstrated that the cellular mechanism for vasomodulator-mediated BTB permeability increase is due to accelerated formation of pinocytotic vesicles that transport therapeutic molecules across the BTB.

CONCLUSIONS

Other methods to deliver drugs across the BTB are effective but have severe drawbacks. Our strategy targets BTB-specific proteins to increase antineoplastic drug delivery selectively to brain tumors with few or no side effects, thus increasing the possibility of improving brain tumor treatment.

Calcium-activated potassium channels mediated blood-brain tumor barrier opening in a rat metastatic brain tumor model

Background

The blood-brain tumor barrier (BTB) impedes the delivery of therapeutic agents to brain tumors. While adequate delivery of drugs occurs in systemic tumors, the BTB limits delivery of anti-tumor agents into brain metastases.

Results

In this study, we examined the function and regulation of calcium-activated potassium (K_Ca) channels in a rat metastatic brain tumor model. We showed that intravenous infusion of NS1619, a K_Ca channel agonist, and bradykinin selectively enhanced BTB permeability in brain tumors, but not in normal brain. Iberiotoxin, a K_Ca channel antagonist, significantly attenuated NS1619-induced BTB permeability increase. We found K_Ca channels and bradykinin type 2 receptors (B2R) expressed in cultured human metastatic brain tumor cells (CRL-5904, non-small cell lung cancer, metastasized to brain), human brain microvessel endothelial cells (HBMEC) and human lung cancer brain metastasis tissues. Potentiometric assays demonstrated the activity of K_Ca channels in metastatic brain tumor cells and HBMEC. Furthermore, we detected higher expression of K_Ca channels in the metastatic brain tumor tissue and tumor capillary endothelia as compared to normal brain tissue. Co-culture of metastatic brain tumor cells and brain microvessel endothelial cells showed an upregulation of K_Ca channels, which may contribute to the overexpression of K_Ca channels in tumor microvessels and selectivity of BTB opening.

Conclusion

These findings suggest that K_Ca channels in metastatic brain tumors may serve as an effective target for biochemical modulation of BTB permeability to enhance selective delivery of chemotherapeutic drugs to metastatic brain tumors.

Bradykinin-induced blood-brain tumor barrier permeability increase is mediated by adenosine 5'-triphosphate-sensitive potassium channel

Bradykinin has been shown to selectively transiently increase the permeability of the blood-brain barrier (BBB). This study was performed to determine whether ATP-sensitive potassium (K(ATP)) channels mediate the increase in permeability of brain tumor microvessels induced by BK. Using a rat brain glioma (C6) model, we found increased expression of K(ATP) channels at tumor sites via Western blot analysis, after intracarotid infusion of bradykinin at a dose of 10 microg/kg/min for 15 min. A significant increase (73.58%) of the integrated density value (IDV) of the K(ATP) channel Kir6.2 subunit was observed in rats with glioma after 10 min of bradykinin perfusion. The over-expression of K(ATP) channels with bradykinin was significantly attenuated by the K(ATP) channel antagonist glibenclamide. Immunohistochemistry and immunolocalization experiments showed that the over-expression of K(ATP) channels was more obvious near tumor capillaries of 10 microm in diameter. I(KATP) modulation by bradykinin in cultured C6 cells was also studied using the patch-clamp technique in a whole-cell configuration. Administration of bradykinin led to a significant opening of K(ATP) channels in a time-dependent manner. This led to the conclusion that the bradykinin-mediated BBB permeability increase is due to accelerated formation of K(ATP) channels, which are thus as an important target in the biochemical regulation of this process.

Therapeutic options for recurrent high-grade glioma in adult patients: Recent advances

Despite of postoperative radiotherapy plus temozolomide for newly diagnosed glioblastoma multiforme (GBM) and improvements in the molecular characterization of high-grade glioma, these tumors continue to relapse. We reviewed all clinical studies of re-treatment published between May 2000 and September 2005. In groups of highly selected patients with re-treatment for GBM, median survival reaches 26-27 months. Re-treatment was stereotactic radiotherapy (mostly with additional chemotherapy) or re-resection plus either photodynamic treatment, radioimmunotherapy and temozolomide, or systemic and local chemotherapy. Thus, intense local treatment was always a component of more successful strategies. Additional data suggest that chemotherapy is more efficacious when minimal residual disease is present, although the recent trials have not uncovered a clear regimen of choice. Early trials of immunotherapy and toxin-delivery demonstrate the feasibility of these approaches and encouraging median survival times. Response to erlotinib was more common if tumors had epidermal growth factor receptor gene amplification, protein overexpression and low levels of phosphorylated PKB/Akt. Individual tailoring of such strategies based on molecular profiling is hoped to improve the outcome.

Chemotherapy in brain metastases

The use OF chemotherapy to treat patients with brain metastases has been viewed historically with skepticism. To date, a survival benefit has not been demonstrated with the use of systemic chemotherapy in patients with brain metastases. However, the introduction of novel agents and delivery techniques warrants a reexamination of the role of systemic chemotherapy in the management of brain metastases. Temozolomide has shown encouraging results in patients with nonsmall cell lung cancer, and implanted carmustine wafers have demonstrated excellent local tumor control rates. This review discusses clinical data from the past decade with emphasis on trial design, tumor histology, available agents, and multimodality strategies. In addition, delivery techniques that circumvent the blood-brain barrier are reviewed. Although chemotherapy is usually used as a salvage therapy, it may be considered for use in selected patients with newly diagnosed brain metastases. To better evaluate chemotherapy in brain metastases, future trials should evaluate novel agents in the preirradiation setting. Enhanced regional delivery methods warrant further investigation, and Phase III trials of current regimens stratified by histology and by prognostic factors will establish the role of specific chemotherapy regimens in the treatment of patients with brain metastases.

Phase II trial of intravenous lobradimil and carboplatin in childhood brain tumors: a report from the Children’s Oncology Group

BACKGROUND

[corrected] Lobradimil is a synthetic bradykinin analog that rapidly and transiently increases the permeability of the blood-brain barrier (BBB). The combination of lobradimil and carboplatin was studied in pediatric patients with primary brain tumors in a phase II trial, the primary endpoints of which were to estimate the response rate and time to disease progression.

PATIENTS AND METHODS

Patients were stratified by histology into five cohorts: brainstem glioma, high-grade glioma, low-grade glioma, medullobastoma/primitive neuroectodermal tumor (PNET), and ependymoma. Patients received carboplatin adaptively dosed to achieve a target AUC of 3.5 mg min/ml per day (7 mg.min/ml/cycle) intravenously over 15 min on 2 consecutive days and lobradimil 600 ng/kg ideal body weight/day on 2 consecutive days each 28 day cycle.

RESULTS

Forty-one patients, age 2-19 years, were enrolled; 38 patients, including 1 patient ultimately determined to have atypical neurocytoma, were evaluable for response. No objective responses were observed in the brainstem glioma (n=12) and high-grade glioma (n = 9) cohorts, although two patients with high-grade glioma had prolonged disease stabilization (>6 months). The study was closed for commercial reasons prior to achieving the accrual goals for the ependymoma (n = 8), medulloblastoma/PNET (n = 6) and low-grade glioma (n = 2) cohorts, although responses were observed in 1 patient with PNET and 2 patients with ependymoma.

CONCLUSION

The combination of lobradimil and carboplatin was inactive in childhood high-grade gliomas and brainstem gliomas.

A Phase I study of concurrent RMP-7 and carboplatin with radiation therapy for children with newly diagnosed brainstem gliomas

BACKGROUND

Ninety percent of children with diffuse, intrinsic brainstem tumors will die within 18 months of diagnosis. Radiotherapy is of transient benefit to these children, and a potential way to improve its efficacy is to add radiosensitizers. Carboplatin is antineoplastic and radiosensitizing; however, its delivery to the primary tumor site is problematic. RMP-7 is a bradykinin analog that causes selective permeability of the blood-brain-tumor interface. The objective of this Phase I study was to determine the toxicity and feasibility of delivering RMP-7 and carboplatin for 5 successive days during radiotherapy to children with newly diagnosed, diffuse, intrinsic brainstem gliomas.

METHODS

RMP-7 was given prior to the end of carboplatin infusion. Local radiotherapy, in dose fractions of 180 centigrays (cGy) per day (to a total dose of 5940 cGy), was given within 4 hours of completion of drug delivery. Duration of treatment was escalated in a stepwise, weekly fashion in cohorts of 3 patients, until there was treatment-limiting toxicity or until radiotherapy was completed. Thirteen patients were treated, and their median age was 7 years (age range, 3-12 yrs).

RESULTS

One child died early during treatment of progressive disease and was not assessable for toxicity. Treatment for 3 weeks, 4 weeks, and 5 weeks was tolerated well, with mild flushing, tachycardia, nausea, emesis, dizziness, and abdominal pain. One of 3 children treated at the full duration of therapy (33 doses over 7 weeks) developed dose-limiting hepatotoxicity and neutropenia. The estimated median survival was 328 days, and 1 patient remained free of disease progression for > 400 days after the initiation of treatment.

CONCLUSIONS

The results of this study confirmed the feasibility of giving RMP-7 and carboplatin daily during radiotherapy to children with brainstem tumors.

Phase 1 study of concurrent RMP-7 and carboplatin with radiotherapy for children with newly diagnosed brainstem gliomas

BACKGROUND

Ninety percent of children with diffuse intrinsic brainstem tumors will die within 18 months of diagnosis. Radiotherapy is of transient benefit, and one way to potentially improve its efficacy is to add radiosensitizers. Carboplatin is antineoplastic and radiosensitizing. However, delivery to the primary tumor site is problematic. RMP-7 is a bradykinin analog that causes selective permeability of the blood-brain-tumor interface. The goal of the current Phase I study was to determine the toxicity and feasibility of delivering RMP-7 and carboplatin for 5 successive days during radiotherapy.

METHODS

RMP-7 was given before the end of carboplatin infusion. Local radiotherapy (5940 centigrays) was given within 4 hours of completion of drug delivery. Duration of treatment was escalated in a stepwise, weekly fashion, in cohorts of 3, until there was treatment-limiting toxicity or until radiotherapy was completed. Thirteen patients were treated, whose median age was 7 years (range, 3-14 yrs).

RESULTS

One child died early in treatment of progressive disease and was not assessable for toxicity. Treatment for 3, 4, or 5 weeks was tolerated well, with mild flushing, tachycardia, nausea, emesis, dizziness, and abdominal pain. Of 3 children treated at the full duration of therapy (33 doses over 7 wks), 1 developed dose-limiting hepatotoxicity and neutropenia. The estimated median survival period was 328 days, and 1 patient remained disease progression free > 400 days from initiation of treatment.

CONCLUSIONS

The results of the current study confirmed the feasibility of giving RMP-7 and carboplatin daily during radiotherapy.

Neoadjuvant phase II multicentre study of new agents in patients with malignant glioma after minimal surgery. Report of a cohort of 187 patients treated with temozolomide

BACKGROUND

The aim of this study was to assess the efficacy of new agents in patients with malignant glioma in a neoadjuvant setting not confounded by surgery. The first study of neoadjuvant temozolomide aimed to provide a benchmark for future evaluation of new treatments.

PATIENTS AND METHODS

This was a multicentre phase II study of chemotherapy in patients with histologically verified glioblastoma multiforme (GBM) and anaplastic astrocytoma (AA) who had undergone biopsy alone. Patients were planned to receive two cycles of temozolomide at 200 mg/m(2) orally daily for 5 days at a 28-day interval prior to radiotherapy. Response was assessed by two central observers on pre- and post-chemotherapy enhanced scans using bi-dimensional criteria and as progression-free survival (PFS) at the time of second assessment prior to radiotherapy. Withdrawal from the study due to worsening clinical condition was, in the absence of second imaging, assessed as progressive disease. Survival and quality of life (QOL) were secondary endpoints.

RESULTS

Between August 1999 and June 2002, 188 patients from 15 UK and two Italian centres were entered into the study and 187 were analysed. Overall, 162 patients were assessable for response; seven had partial and 25 had minimal response. The objective response rate was 20% [95% confidence interval (CI) 14-26%] and PFS prior to commencing radiotherapy was 64% (95% CI 57-72%). The median survival was 10 months, and 1-year survival 41%. The median survival of responders was 16 months compared to 3 months in patients with progressive disease (P <0.001 on multivariate analysis).

CONCLUSION

The phase II study design of primary chemotherapy in patients with malignant glioma following biopsy alone is feasible and provides as objective a method of assessment of efficacy as is currently available. The baseline data on temozolomide provide a benchmark for assessment of efficacy of other agents and combinations.

Alkylglycerol opening of the blood-brain barrier to small and large fluorescence markers in normal and C6 glioma-bearing rats and isolated rat brain capillaries

1. The blood-brain barrier (BBB) represents the major impediment to successful delivery of therapeutic agents to target tissue within the central nervous system. Intracarotid alkylglycerols have been shown to increase the transfer of chemotherapeutics across the BBB. 2. We investigated the spatial distribution of intracarotid fluorescein sodium and intravenous lissamine-rhodamine B200 (RB 200)-albumin in the brain of normal and C6 glioma-bearing rats after intracarotid co-administration of 1-O-pentylglycerol (200 mm). To elucidate the mechanisms involved in the alkylglycerol-mediated BBB opening, intraluminal accumulation of fluorescein isothiocyanate (FITC)-dextran 40,000 was studied in freshly isolated rat brain capillaries using confocal microscopy during incubation with different alkylglycerols. Furthermore, 1-O-pentylglycerol-induced increase in delivery of methotrexate (MTX) to the brain was evaluated in nude mice. 3. Microscopic evaluation showed a marked 1-O-pentylglycerol-induced extravasation of fluorescein and RB 200-albumin in the ipsilateral normal brain. In glioma-bearing rats, increased tissue fluorescence was found in both tumor tissue and brain surrounding tumor. Confocal microscopy revealed a time- and concentration-dependent accumulation of FITC-dextran 40,000 within the lumina of isolated rat brain capillaries during incubation with 1-O-pentylglycerol and 2-O-hexyldiglycerol, indicating enhanced paracellular transfer via tight junctions. Intracarotid co-administration of MTX and 1-O-pentylglycerol (200 mm) in nude mice resulted in a significant increase in MTX concentrations in the ipsilateral brain as compared to controls without 1-O-pentylglycerol (P<0.005). 4. In conclusion, 1-O-pentylglycerol increases delivery of small and large compounds to normal brain and brain tumors and this effect is mediated at least in part by enhanced permeability of tight junctions.

Facilitation of drug entry into the CNS via transient permeation of blood brain barrier: laboratory and preliminary clinical evidence from bradykinin receptor agonist, Cereport

One novel approach of transporting drugs into the central nervous system (CNS) involves the activation of receptors on the endothelial cells comprising the blood brain barrier (BBB). Recently the selective B(2) bradykinin receptor agonist, Cereport (also called RMP-7), has been shown to transiently increase permeability of the BBB. Although initially developed to increase the permeability of the vasculature feeding glioma, recent studies have demonstrated that Cereport also increases the delivery of pharmacological agents across the normal (i.e. nontumor) BBB. In this review paper, we discuss evidence of enhanced CNS delivery of carboplatin, loperamide, and cyclosporin-A, which are accompanied by enhanced chemotherapeutic, analgesic and neuroprotective effects, respectively. These observations suggest feasibility of Cereport as an adjunct therapy to pharmacological treatments that require drug availability in the CNS to exert therapeutic efficacy. Because many potential drugs for CNS disorders normally do not cross the BBB, Cereport-induced transient permeation of BBB stands as an efficacious strategy for enhancing pharmacotherapy.

Innovations in design and delivery of chemotherapy for brain tumors

Effectiveness of chemotherapy in patients with brain tumors is hampered by the presence of the blood-brain barrier and drug resistance. In recent years, significant progress has been made in devising innovative methods of design and delivery of chemotherapy for brain tumors. This article has surveyed the issues of blood-brain barrier and drug resistance and explored some of the strategies used to circumvent problems associated with chemotherapy failure in patients with brain tumors.

Is intra-arterial chemotherapy useful in high-grade gliomas?

Low delivery of common chemotherapeutic drugs to the brain is considered to be a major obstacle for obtaining durable disease control in patients with high-grade gliomas. Intra-arterial drug injection after selective catheterization of cerebral arteries has been performed in some small clinical trials in order to achieve higher drug concentration in the tumor while minimizing systemic exposure. We reviewed the results in terms of response and toxicity from studies with intra-arterial administration of nitrosoureas and platinum derivatives, as well as the principal aspects and perspectives of the new strategy of blood-brain barrier disruption with osmotic agents or bradykinin analogs. No superiority of intra-arterial chemotherapy over its intravenous counterpart has been demonstrated so far and although the incidence of serious neurotoxicity is reduced, the risk of untoward acute complication still contraindicates internal carotid or vertebral artery catheterization for chemotherapy administration outside the setting of well-controlled clinical trials.

Strategies for increasing drug delivery to the brain: focus on brain lymphoma

The blood-brain barrier (BBB) is a gate that controls the influx and efflux of a wide variety of substances and consequently restricts the delivery of drugs into the central nervous system (CNS). Brain tumours may disrupt the function of this barrier locally and nonhomogeneously. Therefore, the delivery of drugs to brain tumours has long been a controversial subject. The current concept is that inadequate drug delivery is a major factor that explains the unsatisfactory response of chemosensitive brain tumours. Various strategies have been devised to circumvent the BBB in order to increase drug delivery to the CNS. The various approaches can be categorised as those that attempt to increase delivery of intravascularly administered drugs, and those that attempt to increase delivery by local drug administration. Strategies that increase delivery of intravascularly injected drugs can manipulate either the drugs or the capillary permeability of the various barriers (BBB or blood-tumour barrier), or may attempt to increase plasma concentration or the fraction of the drug reaching the tumour (high-dose chemotherapy, intra-arterial injection). Neurotoxicity is a major concern with increased penetration of drugs into the CNS or when local delivery is practised. Systemic toxicity remains the limiting factor for most methods that use intravascular delivery. This review evaluates the strategies used to increase drug delivery in view of current knowledge of drug pharmacokinetics and its relevance to clinical studies of chemosensitive brain tumours. The main focus is on primary CNS lymphoma, as it is a chemosensitive brain tumour and its management routinely utilises specialised strategies to enhance drug delivery to the affected CNS compartments.

Imaging response to chemotherapy with RMP-7 and carboplatin in malignant glioma: size matters but speed does not

INTRODUCTION

In recurrent malignant glioma, early imaging response to two courses of chemotherapy is generally considered to be predictive of good survival. We studied the relationships between initial tumour volume and speed of imaging response to chemotherapy in malignant glioma.

METHODS

In 43 chemotherapy naïve patients, 26 glioblastoma multiforme (GBM) + 17 anaplastic astrocytoma (AA), median age 45 years, MRI responses to intravenous cereport and carboplatin were assessed at baseline, then at 2 monthly intervals. Patients were classified as fast responders if they had reached a partial response (PR) after two courses, and slow responders if PR was achieved after three or more courses of chemotherapy.

RESULTS

PR occurred in four patients with GBM (15%) and nine patients with AA (53%). Likelihood of response was related to initial tumour enhancing volume in GBM but not in AA. PR occurred in four of five GBM patients (80%) with initial volume < 15,000 mm3 and none of the 21 cases with an initial volume > 15,000 mm3. In patients achieving a PR, there was no association between speed or duration of response and eventual survival. Fast responders with AA were significantly older than slow responders (p = 0.033).

CONCLUSIONS

Initial enhancing volume of GBMs may be an important predictor of imaging response. This has implications where response rates of phase II studies are reported and in stratification for phase III trials. Further work is necessary to confirm these findings with other types of chemotherapy and examine the relationship between proliferation markers and speed of response.

Pre-irradiation semi-intensive chemotherapy with carboplatin and cyclophosphamide in malignant glioma: a phase II study

We undertook a phase II trial in 17 patients with malignant glioma and large measurable disease to assess response rate and survival with pre-irradiation chemotherapy, using higher doses than standard, trying to improve the outcome. Patients characteristics were: male/female 10/7, age 49 (range 23-59), median Karnofsky index 90% (range 70-100), glioblastoma multiforme/anaplastic astrocytoma 14/3. Treatment consisted of 2 cycles of carboplatin 200 mg/m(2) days 1-3 (or AUC x 8, total dose) plus cyclophosphamide 1000 mg/m(2) days 1-3. One partial response (6.5%) and two stabilizations (13.5%) were observed after pre-irradiation chemotherapy. Twelve out of 15 patients (80%) progressed after chemotherapy. Median survival time was 7.6 months and the survival at 1 year was 33%. Main toxicity was hematologic in the first cycle: neutropenia grade 4 in 100%; thrombocytopenia grade 4 in 73% and grade 3 in 27%; anemia grade 3 in 7%; in the second cycle: neutropenia and thrombocytopenia grade 4 in 100% and anemia grade 3 in 50%). No toxic death was related to treatment. This regimen showed limited activity in malignant glioma with large residual disease after surgery or biopsy.

Novel chemotherapeutic approaches to brain tumors

In reviewing the numerous investigational drug trials for patients with anaplastic gliomas over the past 20 years, it would be fair to say that there have been more than a few disappointments and that the real impact of many of these therapies on patients' duration and quality of survival has been minor at best. It is also fair to state that there has been progress in developing new types of chemotherapy and other agents, in devising new treatment strategies, and in gaining a deeper understanding of the problems that must be overcome to treat patients with anaplastic gliomas successfully. The past several years have seen the realization that oligodendroglioma, primary CNS lymphoma, and medulloblastoma are sensitive to chemotherapy treatments. It is hoped that future studies will delineate better the optimal use of chemotherapy for these tumors.

The development of the bradykinin agonist labradimil as a means to increase the permeability of the blood-brain barrier: from concept to clinical evaluation

Labradimil (Cereport; also formerly referred to as RMP-7) is a 9-amino-acid peptide designed for selectivity for the bradykinin B2 receptor and a longer plasma half-life than bradykinin. It has been developed to increase the permeability of the blood-brain barrier (BBB) and is the first compound with selective bradykinin B2 receptor agonist properties to progress from concept design through to tests of efficacy in patients. In vitro studies demonstrate that labradimil has a longer half-life than bradykinin and selectively binds to bradykinin B2 receptors, initiating typical bradykinin-like second messenger systems, including increases in intracellular calcium and phosphatidylinositol turnover. Initial proof of principle studies using electron microscopy demonstrated that intravenous labradimil increases the permeability of the BBB by disengaging the tight junctions of the endothelial cells that comprise the BBB. Autoradiographic studies in rat models further demonstrated that labradimil increases the permeability of the BBB in gliomas. Intravenous or intra-arterial labradimil increases the uptake of many different radiolabelled tracers and chemotherapeutic agents into the tumour in a dose-related fashion. These effects are selective for the tumour and for the brain surrounding the tumour, and are particularly robust in tumour areas that are normally relatively impermeable. The increased chemotherapeutic concentrations are maintained for at least 90 minutes, well beyond the transient effects on the BBB. The increase in permeability with labradimil occurs rapidly but is transient, in that restoration of the BBB occurs very rapidly (2 to 5 minutes) following cessation of infusion. Even with continuous infusion of labradimil, spontaneous restoration of the barrier begins to occur within 10 to 20 minutes. Collectively, these data demonstrate that the B2 receptor system that modulates permeability of the BBB is highly sensitive and autoregulated and that careful attention to the timing of labradimil and the chemotherapeutic agent is important to achieve maximal effects. Survival studies in rodent models of both gliomas and metastatic tumours in the brain demonstrate that the enhanced uptake observed with the combination of labradimil and water-soluble chemotherapeutics enhances survival to a greater extent than achieved with chemotherapy alone. Finally, preliminary clinical trials in patients with gliomas provide confirmatory evidence that labradimil permeabilises the blood-brain tumour barrier and might, therefore, be used to increase delivery of agents such as carboplatin to tumours without the toxicity typically associated with dose escalation.

A comparison of treatment results for recurrent malignant gliomas

Retreatment of malignant gliomas may be performed with palliative intent after careful consideration of the risks and benefits, and with special regards to iatrogenic neurotoxicity and quality of life (QOL). This review compares studies of several retreatment strategies (published between 1987 and 2000) based on the quality of their evidence. Depending on both established prognostic factors and previous treatment, individually tailored retreatment strategies are possible. In all studies that included a multivariate analysis of prognostic factors, performance status was the most important. So far, predictive factors for response, which might facilitate patient selection, have not been unequivocally defined. In terms of QOL, single-agent chemotherapy (temozolomide, nitrosoureas, platinum and taxane derivatives) may offer a better therapeutic ratio than polychemotherapy. For glioblastoma multiforme, progression-free survival and QOL were more favourable after temozolomide than procarbazine (level 1 evidence). The survival of patients after various radiotherapy techniques is broadly similar. However, considerable toxicity is associated with radiosurgery or brachytherapy. Fractionated stereotactic radiotherapy plus radio-sensitizing cytostatic agents has shown promising initial results in small groups of selected patients and awaits further evaluation. Level 2 evidence derived from non-randomized studies does not suggest a substantial prolongation of survival by re-resection as compared with chemotherapy or radiotherapy alone. Level 1 evidence derived from a randomized trial suggests that application of BCNU polymers significantly improves the outcome after re-resection. However, most studies reported median survival in the range of only 25-35 weeks, thereby emphasizing the need for the development and clinical evaluation of new innovative treatment approaches.

Chemotherapy of brain tumors

This is a review of chemotherapy options for patients with brain tumors, both at the time of initial diagnosis and at recurrence. Gliomas, the most common malignant brain tumors, represent the main focus of the review; chemotherapeutic options for supratentorial, brain stem, and optic track gliomas are discussed.

Boron neutron capture therapy of brain tumors: enhanced survival and cure following blood-brain barrier disruption and intracarotid injection of sodium borocaptate and boronophenylalanine

PURPOSE

Boronophenylalanine (BPA) and sodium borocaptate (Na(2)B(12)H(11)SH or BSH) have been used clinically for boron neutron capture therapy (BNCT) of high-grade gliomas. These drugs appear to concentrate in tumors by different mechanisms and may target different subpopulations of glioma cells. The purpose of the present study was to determine if the efficacy of BNCT could be further improved in F98-glioma-bearing rats by administering both boron compounds together and by improving their delivery by means of intracarotid (i.c.) injection with or without blood-brain barrier disruption (BBB-D).

METHODS AND MATERIALS

For biodistribution studies, 10(5) F98 glioma cells were implanted stereotactically into the brains of syngeneic Fischer rats. Eleven to 13 days later animals were injected intravenously (i.v.) with BPA at doses of either 250 or 500 mg/kg body weight (b.w.) in combination with BSH at doses of either 30 or 60 mg/kg b.w. or i.c. with or without BBB-D, which was accomplished by i.c. infusion of a hyperosmotic (25%) solution of mannitol. For BNCT studies, 10(3) F98 glioma cells were implanted intracerebrally, and 14 days later animals were transported to the Brookhaven National Laboratory (BNL). They received BPA (250 mg/kg b.w.) in combination with BSH (30 mg/kg b.w. ) by i.v. or i.c. injection with or without BBB-D, and 2.5 hours later they were irradiated with a collimated beam of thermal neutrons at the BNL Medical Research Reactor.

RESULTS

The mean tumor boron concentration +/- standard deviation (SD) at 2.5 hours after i. c. injection of BPA (250 mg/kg b.w.) and BSH (30 mg/kg b.w.) was 56. 3 +/- 37.8 microgram/g with BBB-D compared to 20.8 +/- 3.9 microgram/g without BBB-D and 11.2 +/- 1.8 microgram/g after i.v. injection. Doubling the dose of BPA and BSH produced a twofold increase in tumor boron concentrations, but also concomitant increases in normal brain and blood levels, which could have adverse effects. For this reason, the lower boron dose was selected for BNCT studies. The median survival time was 25 days for untreated control rats, 29 days for irradiated controls, 42 days for rats that received BPA and BSH i.v., 53 days following i.c. injection, and 72 days following i.c. injection + BBB-D with subsets of long-term survivors and/or cured animals in the latter two groups. No histopathologic evidence of residual tumor was seen in the brains of cured animals.

CONCLUSIONS

The combination of BPA and BSH, administered i.c. with BBB-D, yielded a 25% cure rate for the heretofore incurable F98 rat glioma with minimal late radiation-induced brain damage. These results demonstrate that using a combination of boron agents and optimizing their delivery can dramatically improve the efficacy of BNCT in glioma-bearing rats.