Intrathecal busulfan treatment of human neoplastic meningitis in athymic nude rats

A Review on the Efficacy and Safety of Intrathecal Administration of Novel Medications for Leptomeningeal Metastases in Solid Cancers

Leptomeningeal disease (LMD) is a rare and lethal manifestation that may occur in the advanced stages of solid tumors and hematological malignancies. With advances in diagnostic techniques, the detection and confirmation of the presence of LMD have increased. Although its optimal treatment remains a challenge, the use of the intrathecal route for the delivery of novel therapeutics is now considered a promising drug delivery strategy to complement radiation and systemic-based therapies. Although methotrexate, cytarabine, and thiotepa have a long history in the treatment of LMD, other medications have also been shown to be beneficial. In this article, we have reviewed the effects of novel medications administered via the intrathecal route for the treatment of solid tumors. We have searched PubMed, Scopus, and Google Scholar databases till the end of September 2021 using the following keywords: "leptomeningeal disease", "leptomeningeal carcinomatosis", "leptomeningeal metastases", "solid tumors", "solid cancers", and "intrathecal". Our literature findings have uncovered that most studies on LMD, which occurs secondary to solid cancers, are available as 'case reports', and few clinical trials have been conducted to date. Single-drug (monotherapy) or combination drug therapy, administered via the intrathecal route, especially in metastatic breast and lung cancer, has been shown to improve patients' symptoms and overall lifespan, while exhibiting a low and acceptable prevalence of side effects. However, judgments/conclusions about the effectiveness and safety of these drugs still require further clinical evaluation.

Improving the Brain Delivery of Chemotherapeutic Drugs in Childhood Brain Tumors

The central nervous system (CNS) may be considered as a sanctuary site, protected from systemic chemotherapy by the meninges, the cerebrospinal fluid (CSF) and the blood-brain barrier (BBB). Consequently, parenchymal and CSF exposure of most antineoplastic agents following intravenous (IV) administration is lower than systemic exposure. In this review, we describe the different strategies developed to improve delivery of antineoplastic agents into the brain in primary and metastatic CNS tumors. We observed that several methods, such as BBB disruption (BBBD), intra-arterial (IA) and intracavitary chemotherapy, are not routinely used because of their invasiveness and potentially serious adverse effects. Conversely, intrathecal (IT) chemotherapy has been safely and widely practiced in the treatment of pediatric primary and metastatic tumors, replacing the neurotoxic cranial irradiation for the treatment of childhood lymphoma and acute lymphoblastic leukemia (ALL). IT chemotherapy may be achieved through lumbar puncture (LP) or across the Ommaya intraventricular reservoir, which are both described in this review. Additionally, we overviewed pharmacokinetics and toxic aspects of the main IT antineoplastic drugs employed for primary or metastatic childhood CNS tumors (such as methotrexate, cytosine arabinoside, hydrocortisone), with a concise focus on new and less used IT antineoplastic agents.

Intrathecal chemotherapy for treatment of leptomeningeal dissemination of metastatic tumours

Neoplastic meningitis consists of diffuse involvement of the leptomeninges by infiltrating cancer cells, and can be caused by systemic or primary CNS tumours, such as solid cancers or lymphoproliferative malignant disease. Neoplastic meningitis is characterised by multifocal neurological signs and symptoms. Thus, careful neurological examination is needed for diagnosis of secondary diffuse involvement. Survival of patients with neoplastic meningitis is short (3-4 months), although some patients have long-lasting remission. Because most patients with neoplastic meningitis have diffuse systemic disease, treatment is typically palliative. However, more aggressive treatments are available to low-risk patients, which could increase survival. Therefore, identification of low-risk patients is important. Intrathecal chemotherapy is currently the main treatment for patients with neoplastic meningitis, but optimum anticancer chemotherapy is being studied.

Medulloblastoma in childhood: revisiting intrathecal therapy in infants and children

INTRODUCTION

Intrathecal chemotherapy is being explored in medulloblastoma in pre-school children as part of brain-sparing strategies and as an alternative to unacceptably neurotoxic cranio-spinal radiotherapy. The range of drugs suitable for this route of administration is restricted by the lack of research evidence of pharmacological suitability and efficacy of other drugs in medulloblastoma.

METHODS

Ideal clinical, biological, physicochemical and pharmaceutical properties for intrathecal administration were defined through literature review of pharmaceutical texts, Medline, Embase and consulting the manufacturers. A total of 126 chemotherapy agents were assessed against these criteria by searching the academic domain of pharmaceutical texts, computer databases and consultation with manufacturers.

RESULTS

Of the 126 candidate drugs, 99 were rejected because of documentation of their irritant nature, neurotoxicity and requirement for hepatic activation in standard pharmaceutical texts. Fifty were rejected for a single identifiable reason including, neurotoxicity (n = 24), irritant (n = 15), needs enzyme activation (n = 5), clinical evidence of intrathecal neurotoxicity (n = 4) and no evidence of tumour-specific efficacy (n = 2). Where two reasons were cited the justifications were: neurotoxic and irritant (n = 3) and needs activation and systemic administration results in equivalent concentration (n = 1). Twenty-seven drugs remained of which 12 were selected as eligible for further clinical investigation, and 15 were selected for further pre-clinical investigation.

CONCLUSIONS

The pre-determined criteria were not applicable, in their entirety, in the majority of drugs, due to lack of information in the academic domain, emphasising the importance of a more open approach for sharing basic drug information. The prioritised list of 12 candidate drugs for clinical trial and 15 for pre-clinical investigation justify that a concerted research effort in this area of practice is made.

Chemotherapy in neoplastic meningitis

Neoplastic meningitis (NM) is the result of the diffuse or multifocal localization of cancer cells in the cerebral spinal fluid (CSF). NM is more often a late complication of solid tumor or lymphoproliferative malignancies. At present, the goal of therapeutic strategies is palliative and the evaluation of high or low risk is important in identifying which patients could benefit from aggressive treatments such as radiation therapy and chemotherapy. Given that NM is a cancer complication that can spread throughout the entire subarachnoid space, chemotherapy, whether intrathecal or systemic, is currently considered the best treatment option, but optimal treatment is still controversial. This review summarizes intrathecal and systemic chemotherapeutic options in the treatment of NM and the related toxicities.

New agents for intrathecal administration

Intrathecal administration of chemotherapy, with or without radiation therapy, is the primary treatment modality for the prevention and treatment of central nervous system (CNS) metastases in patients with leukemia or lymphoma. Although this treatment strategy has been very effective for patients with hematological malignancies, currently available intrathecal agents are relatively ineffective for patients with neoplastic meningitis resulting from an underlying solid or CNS tumor effective. This article provides an overview of some of the practical considerations and limitations associated with intrathecal chemotherapy, and is followed by a comprehensive review of some of the preclinical and early phase clinical trials of novel anticancer agents and treatment strategies using the intrathecal route.

Treatment of Neoplastic Meningitis With Intrathecal 9-Nitro-camptothecin

The topoisomerase I inhibitor, 9-nitro-camptothecin (9NC), is highly tumoricidal against glioblastoma multiforme (GBM) in vitro. However, systemic administration of 9NC has not shown the expected efficacy in clinical trials. This failure may be due to the rapid hydrolysis of 9NC in plasma from the active form to the inactive and myelosuppressive form in the presence of human albumin at physiologic pH. Concurrent treatment with anticonvulsants and dexamethasone, drugs indispensable for the supportive therapy of patients with GBM, has also been shown to decrease plasma concentrations of these drugs. Intrathecal drug delivery circumvents the blood-brain barrier and minimizes systemic toxicity. Intrathecal delivery of 9NC may also have the more specific advantage of significantly reducing the hydrolysis of 9NC that occurs after systemic delivery due to the more favorable pH and reduced albumin content in cerebrospinal fluid. The present study evaluated the toxicity and efficacy of intrathecal delivery of 9NC in an athymic rat model of neoplastic meningitis. Toxicity tests showed that 0.3 micromol (5000 microM), 0.03 micromol (500 microM), 0.003 micromol (50 microM), or 0.0003 micromol (5 microM) of 9NC administered intrathecally to the athymic rats caused no evidence of clinical or histological toxicity. Intrathecal administration of 0.3 micromol (5000 microM) of 9NC twice a week for three doses to athymic rats with neoplastic meningitis induced by the GBM cell line, U87MGDeltaEGFR, resulted in a 26% increase of median survival compared to the control group (p < 0.005). These results suggest that intrathecal treatment with 9NC may be useful for patients with GBM neoplastic meningitis.

Pharmacokinetics Following Intraventricular Administration of Chemotherapy in Patients with Neoplastic Meningitis

Intraventricular administration of chemotherapy is one approach to overcoming the limited distribution of anticancer drugs and their active metabolites into the CNS. This form of regional chemotherapy has led to effective treatment of occult and overt meningeal leukaemia in humans. In contrast, the efficacy of this therapy is extremely limited in the treatment of leptomeningeal dissemination of various solid tumours. Pharmacokinetic studies of the commonly intraventricularly applied anticancer agents in humans have demonstrated that, using low drug doses, very high drug concentrations can be achieved in the cerebrospinal fluid (CSF) and relatively high concentrations in the leptomeninges but not in the brain tissue and the plasma. Therefore, this approach is not an effective treatment for bulky disease of brain tissue, and results in minimal systemic toxicity. In comparison with intralumbar administration, lower interpatient variability of CSF drug concentrations and improved clinical efficacy were observed. 'Concentration x time' schedules, i.e. frequent small drug doses over a short period, enable long-term CSF exposure to cytotoxic drug concentrations while avoiding excessively high and potentially neurotoxic drug concentrations. The technique of ventriculolumbar cerebrospinal perfusion delivers continuously high drug concentrations throughout the CSF for several hours, but its widespread use is limited by the technical complexities of this approach. In this article, the dosages, schedules and pharmacokinetic data of routinely used intraventricular agents in humans, e.g. methotrexate, cytarabine, glucocorticoids and thiotepa, are outlined in detail. In addition, pharmacokinetic data of investigational agents for intraventricular administration (diaziquone, DTC 101, mercaptopurine, mafosfamide, etoposide, topotecan, nimustine [ACNU] and bleomycin) are presented. Better understanding of the CSF pharmacology of these drugs is an essential prerequisite for safe, effective administration of these drugs. Investigational efforts are underway to verify the feasibility and efficacy of different dosages, schedules and combination therapies of these new intra-CSF agents. Current and future clinical research should also focus on methods allowing the delivery of tumoricidal drug concentrations for extended periods into the CSF and the brain tissue while minimising neurotoxicity and systemic toxicity (e.g. liposomal drug preparations, monoclonal antibodies, immunotoxins and gene therapy).

Improving the outcome of patients with leptomeningeal cancer: new clinical trials and experimental therapies

Current therapy for leptomeningeal metastases is predominantly palliative. In an effort to improve disease control and patient outcome, new strategies are being developed to target the cerebrospinal space. These include new intrathecal formulations of systemic chemotherapy as well as the development of radiolabeled immunoconjugates and antitumor antibodies. Furthermore, there is debate as to the optimal strategy of drug delivery for leptomeningeal tumor.

Nanosuspensions in drug delivery

A surprisingly large proportion of new drug candidates emerging from drug discovery programmes are water insoluble, and therefore poorly bioavailable, leading to abandoned development efforts. These so-called 'brickdust' candidates can now be rescued by formulating them into crystalline nanosuspensions. In the process of overcoming issues involving solubility, additional pharmacokinetic benefits of the drugs so formulated have come to be appreciated. As such, insolubility issues of the past have provoked a paradigm change, which now offers novel solutions for innovative drugs of the future.

Leptomeningeal metastases

LM is an increasingly common neurologic complication of cancer with variable clinical manifestations. Although there are no curative treatments, currently available therapies can preserve neurologic function and potentially improve quality of life. Further research into the mechanisms of leptomeningeal metastasis will elucidate molecular and cellular pathways that may allow identification of potential targets to interrupt this process early or to prevent this complication. Animal models are needed to further define the pathophysiology of LM and to provide an experimental system to test novel treatments [242-245]. There is an urgent need to develop new drug-based or radiation-based treatments for patients with LM. Randomized clinical trials are the appropriate study design to determine the efficacy of new treatments for LM. However, surrogate markers for response must be developed to facilitate the identification of effective regimens. Survival is not the optimal end point for such studies as most patients who develop this complication already have advanced, incurable cancer. Prevention of or delay in neurologic progression is one objective that has been utilized in recent randomized trials in patients with LM, and this end point deserves further attention. Although the development of LM represents a poor prognostic marker in patients with cancer it is important for physicians to recognize the symptoms and signs of the disease and establish the diagnosis as early in the disease course as possible. This may provide an opportunity for effective intervention that can improve quality of life, prevent further neurologic deterioration and, for a subset of patients, improve survival.

Neoplastic meningitis: a unique disease process or a 'test tube' for evaluating cancer treatments?

Improved treatment of systemic cancers has prolonged the lives of many patients but has also led to increased incidence of neoplastic meningitis. The prognosis for patients who develop neoplastic meningitis or leptomeningeal dissemination of cancer cells remains poor. This paper reviews the pathologic reasons for this poor prognosis, describes recent research in animal models that explores new therapies, and discusses the potential of these new treatment possibilities for clinical use in the context of the associated biology and pathology. The author provides an overview of the accompanying articles for the Neuro-Oncology section, which explore the mechanisms leading to neoplastic meningitis, the role of radiotherapy and chemotherapy in this disease process, and the toxicities of treatment.