Primate model for long-term study of intraventricularly or intrathecally administered drugs and intracranial pressure

Chronic Collection of Cerebrospinal Fluid from Rhesus Macaques (Macaca mulatta) with Cisterna Magna Ports: Update on Refinements

More than 20 y ago, we developed an animal model for chronic and continuous collection of cerebrospinal fluid (CSF) from conscious rhesus macaques. Since our previous publication in 2003, we have successfully implanted 168 rhesus macaquesusing this approach. Our experience enables us to provide up-to-date information regarding the model, including refinementsto our implant design, reductions in maintenance, and new procedures for dealing with contamination. The results of our experiences have reduced the number of surgeries required and helped to increase the longevity of the implant, with some functioning for more than 18 y. Building on our success in rhesus macaques, we attempted to develop similar animal models in the African green monkeys and dogs but have been unable to develop reliable chronic models for CSF collection in these species.

Flow Rate and Apparent Volume of Cerebrospinal Fluid in Rhesus Macaques (Macaca mulatta) Based on the Pharmacokinetics of Intrathecally Administered Inulin

Cerebrospinal fluid (CSF) flow rate and volume are fundamental to the design and interpretation of preclinical pharmacokinetics and pharmacodynamics studies in NHP. To determine the values of CSF flow rate and volume, we evaluated the plasma and CSF pharmacokinetics of inulin, an inert polysaccharide tracer, in 5 rhesus macaques with CSF ventricular res- ervoirs and lumbar ports; these reservoirs and ports facilitate humane intrathecal administration and serial CSF sampling in unanesthetized macaques. Inulin was administered intrathecally via the CSF ventricular reservoir (n = 3), followed by the collection of lumbar CSF via the lumbar port and plasma. The contribution of dietary inulin was evaluated by using pre- and postprandial inulin plasma concentrations (n = 2) and a feed analysis of the NHP diet. Inulin concentrations were quantified using ELISA. Pharmacokinetic parameters were calculated by using noncompartmental methods. Daily diet was analyzed for inulin by using Official Method no. 997.08 of AOAC International. In male rhesus macaques, the mean CSF flow rate, established via inulin clearance after IT administration, was 0.018 ± 0.003 mL/min; mean CSF volume, established based on apparent volume of distribution, was 10.17 ± 0.63 mL. In plasma, inulin was quantifiable in all pre-administration samples and increased over the sampling period, precluding interpretation of plasma pharmacokinetics. Evaluation of the effect of diet on plasma concentrations established quantifiable inulin levels that showed minimal variation relative to the prandial state. Analysis of the feed detected 5 inulin types ranging from 1100 to 1440 mg per100 g. The diet was the source of detectable pre-administration inulin plasma concentrations, whereas inulin was not detected in CSF before inulin administration.

Dosing, collection, and quality control issues in cerebrospinal fluid research using animal models

Cerebrospinal fluid (CSF) is a complex fluid filling the ventricular system and surrounding the brain and spinal cord. Although the bulk of CSF is created by the choroid plexus, a significant fraction derives from the interstitial fluid in the brain and spinal cord parenchyma. For this reason, CSF can often be used as a source of pharmacodynamic and prognostic biomarkers to reflect biochemical changes occurring within the brain. For instance, CSF biomarkers can be used to diagnose and track progression of disease as well as understand pharmacokinetic and pharmacodynamic relationships in clinical trials. To facilitate the use of these biomarkers in humans, studies in preclinical species are often valuable. This review summarizes methods for preclinical CSF collection for biomarkers from mice, rats, and nonhuman primates. In addition, dosing directly into CSF is increasingly being used to improve drug levels in the brain. Therefore, this review also summarizes the state of the art in CSF dosing in these preclinical species.

Plasma and cerebrospinal fluid pharmacokinetics of vincristine and vincristine sulfate liposomes injection (VSLI, marqibo®) after intravenous administration in Non-human primates

PURPOSE

Vincristine sulfate liposomes injection (VSLI, Marqibo®) is an FDA approved encapsulated preparation of standard vincristine in sphingomyelin/cholesterol liposomes. Clinical pharmacokinetics show VSLI to be a long-circulating, slow release formulation that is confined to plasma, and prior data on cerebrospinal fluid (CSF) pharmacokinetics are lacking. We report our results comparing CSF and plasma pharmacokinetic parameters of intravenous aqueous vincristine to intravenous VSLI using an established non-human primate (NHP) model.

METHODS

Three adult male rhesus monkeys (Macaca mulatta) were administered 0.1 mg/kg (1.2 mg/m(2) human-equivalent dose) of vincristine or VSLI in a crossover pharmacokinetic study. Serial paired blood and CSF samples were obtained before infusion, at the end of infusion (EOI) and at various time points thereafter.

RESULTS

In contrast to standard vincristine, which had a multi-exponential plasma disappearance curve with a median initial (EOI to 30 min post-infusion) half-life (T1/2) of 4.8 min (range, 4.4-5.0 min) and terminal T1/2 of 24.3 h, a near-monoexponential curve with a median T1/2 of 17.9 h (range, 13.9-21.5 h) hours was calculated with VSLI. The ratios Cl VCR:Cl VSLI for the individual NHP were 300, 463 and 477. Vincristine was not detected in any CSF sample after administration of either formulation.

CONCLUSIONS

In three animals, each serving as their own control, we demonstrate that the pharmacokinetic profile of VSLI shows markedly prolonged clearance (approximately 400-fold lower) of total vincristine in comparison to the standard aqueous formulation, enhancing our understanding of VSLI pharmacokinetics. Several clinical trials incorporating VSLI as substitution for standard vincristine are in progress.

An improved technique for cerebrospinal fluid collection of cisterna magna in Rhesus monkeys

BACKGROUND

Currently-used cerebellomedullary cistern puncture method for collecting cerebrospinal fluid (CSF) from monkeys is simple, inexpensive, and practical, but with high risk for brainstem injury and CSF blood contamination. An improved technique was thus developed and characterized.

METHOD

Magnetic resonance imaging was used to identify the space and position of the cisterna magna in monkeys. Accordingly, a newly defined procedure for needle punctuation was tested in comparison with the traditional method. Blood contamination in CSF samples and brainstem injury were determined to define the superior of the improved method over the transitional method.

RESULTS

The cisterna magna in monkeys was found to be a "▽" shape. The needle was punctured into the cisterna magna aiming at the wider superior gap avoided brainstem injury. The improved method showed that the rate of blood contamination in the CSF samples was reduced from 66.7% to 16.7%, the higher rate of blood contamination was associated with higher risk for brainstem injury.

COMPARISON WITH EXISTING METHODS

In traditional method, the needle is punctured aiming at the inferior gap with high density of blood vessels. In improved method, the needle is punctured aiming at the superior gap, pointing to the nose root while advancing the needle and avoiding injury to blood vessels.

CONCLUSIONS

This improved technique not only avoids blood contamination of CSF, but also prevents brainstem injury during the process of CSF collection. It is recommended for adaptation for CSF collection in monkeys.

A 4-Week Intrathecal Toxicity and Pharmacokinetic Study With Trastuzumab in Cynomolgus Monkeys

Trastuzumab is indicated for the treatment of patients with breast cancer overexpressing human epidermal growth factor 2 (HER2). Women with HER2-positive tumors have an increased risk of brain metastases. The blood-brain barrier and blood-cerebrospinal fluid (CSF) barrier may prevent trastuzumab from reaching appropriate concentrations in the brain and CSF following standard intravenous administration. To evaluate the potential of effects on the central nervous system, a 4-week toxicology study with weekly intrathecal administration of trastuzumab was performed in cynomolgus monkeys at doses of 0, 3, or 15 mg. No trastuzumab-related effects on body weight, clinical signs, neurological function, clinical pathology, or anatomic pathology were noted. The applied doses and CSF concentrations achieved in the current study exceeded those reported in patients after intrathecal administration. The results support future studies for further evaluation of intrathecal application of trastuzumab in patients with brain metastases in HER2-positive breast cancer.

Rituximab therapy for CNS lymphomas: targeting the leptomeningeal compartment

Most lymphomas that involve the central nervous system are B-cell neoplasms that express the cell surface molecule CD20. After intravenous administration, rituximab can be reproducibly measured in the cerebrospinal fluid (CSF) in patients with primary central nervous system lymphoma; however, the CSF levels of rituximab are approximately 0.1% of serum levels associated with therapeutic activity in patients with systemic non-Hodgkin lymphoma. Because lymphomatous meningitis is a frequent complication of non-Hodgkin lymphoma, we have conducted an analysis of the safety and pharmacokinetics of direct intrathecal administration of rituximab using cynomolgus monkeys. No significant acute or delayed toxicity, neurologic or otherwise, was detected. Pharmacokinetic analysis suggests that drug clearance from the CSF is biphasic, with a terminal half-life of 4.96 hours. A phase 1 study to investigate the safety and pharmacokinetics of intrathecal rituximab in patients with recurrent lymphomatous meningitis will be implemented based on these findings.

Current pharmacological treatment approaches to central nervous system leukaemia

Significant advances in the treatment and prevention of meningeal leukaemia have been made in the past 3 decades. This progress has resulted from the development of innovative approaches to treatment as well as a better understanding of the pharmacokinetics and pharmacodynamics of the commonly used antileukaemic agents. Intrathecal therapy, via the intralumbar or intraventricular route, is a form of regional therapy that results in the delivery of very high drug concentrations to the principle target tumour site (the meninges) using a relatively small drug dose, thereby minimising both systemic drug exposure and systemic toxicity. The dosage and schedules, clinical pharmacology and toxicities of the commonly used intrathecal agents, methotrexate and cytarabine (cytosine arabinoside; Ara-C) are discussed in detail. Another approach which has been used to overcome the poor penetration of antileukaemic drugs into the CNS has been the use of high-dose systemic therapy. This strategy has been successfully applied in the treatment of meningeal leukaemia using both high-dose methotrexate and high-dose cytarabine. The clinical pharmacology, toxicities, and potential limitations of this approach are outlined. Finally, new agents that are currently undergoing clinical evaluation and future directions for research are also discussed.

Penetration of SCH-39304, a new antifungal triazole, into cerebrospinal fluid of primates

We characterized the cerebrospinal fluid (CSF) penetration and pharmacokinetics of SCH-39304 in adult rhesus monkeys receiving a single oral dose of SCH-39304 (2.0 mg/kg of body weight). The mean CSF-to-plasma area under the curve ratio was 0.63 (+/- 0.18, standard error of the mean); maximum concentrations were 1.34 micrograms/ml (+/- 0.18) in CSF and 1.96 micrograms/ml (+/- 0.43) in plasma. The mean plasma half-life was 45.7 h (+/- 11), and mean CSF half-life was 38.7 h (+/- 3.5). The mean levels of SCH-39304 at 24 h were 1.48 micrograms/ml (+/- 0.3) in plasma and 0.96 microgram/ml (+/- 0.12) in CSF. We conclude that SCH-39304 effectively penetrates into CSF and achieves concentrations considered active against many opportunistic yeasts and that these concentrations are sustained in CSF for greater than or equal to 24 h.

Cerebrospinal fluid and plasma pharmacokinetics of morphine infusions in pediatric cancer patients and rhesus monkeys

The cerebrospinal fluid (CSF) and plasma pharmacokinetics of morphine administered as a continuous infusion were studied in pediatric cancer patients and in monkeys with implanted Ommaya reservoirs. In monkeys administered a constant infusion of 0.15 mg morphine sulfate/kg/h, morphine steady-state plasma and CSF concentrations were 84.4 +/- 20.0 ng/ml and 25.3 +/- 4.9 ng/ml, respectively, for a CSF:plasma ratio of 0.30 +/- 0.05. For comparison, the monkeys also received morphine as an intravenous bolus at a dose of 0.45 mg morphine sulfate/kg. The CSF:plasma area under the concentration-time curve (AUC) ratio was 0.40 +/- 0.07, similar to that seen with continuous infusion. Morphine pharmacokinetics were also studied in cancer patients administered long-term infusions of morphine sulfate over a wide dosage range (0.04-31 mg/kg/h). The steady-state plasma concentration of morphine was linearly related to the infusion rate although variability was noted. The average clearance value was 23 ml/min/kg which is at the upper end of the estimates reported for morphine clearance using bolus administration. No evidence for morphine accumulation using long-term administration was observed. A limited number of CSF samples obtained by lumbar puncture showed comparable CSF and plasma concentrations of unbound morphine assuming morphine is approximately 30% bound in human plasma.

Implantable devices for chronic access and drug delivery to the central nervous system

This is a review of implantable devices for chronic access and drug delivery to the central nervous system (CNS) via the cerebrospinal fluid, extracellular fluid, and vascular pathways. The current applications of such devices in the management of mycotic meningitis, meningeal leukemia and carcinomatosis, solid malignant tumors of the CNS, intractable cancer-associated pain, unresectable cystic tumors and in cytologic, pharmacologic, and experimental studies on the cerebrospinal fluid (CSF) are assessed. Specific attention is paid to the applications of the most commonly used device, a subcutaneous reservoir and pump (SRP), including its major uses and complications. A new system for local chemotherapy of malignant gliomas, the tumor cyst device (TCD), is also described.

Intrathecally Administered m-AMSA in the Rhesus Monkey

4'-(9-Acridinylamino)-methanesulfon-m-anisidide (m-AMSA) is an acridine compound that has been found useful in the systemic treatment of acute leukemia. This paper specifically investigates the CSF pharmacokinetics of m-AMSA following both intravenous and intraventricular administration in a subhuman primate model. Following intravenous administration, m-AMSA crossed the blood-brain barrier poorly; cerebrospinal fluid (CSF) concentrations were only 1-3% of systemic concentrations. Intraventricular administration of drug achieved high initial ventricular fluid concentrations, but the drug was rapidly cleared with a half-life of 115 min. Following 500 micrograms of intraventricular drug, CSF concentrations of m-AMSA remained above 1 microM for only 6 h. These data suggest that m-AMSA has potential as an intrathecal agent against meningeal leukemia refractory to more conventional therapy, but detailed toxicology and neurohistopathology will be required before intra-CSF m-AMSA can be considered for human use.

Pharmacokinetic study of cerebrospinal fluid penetration of cis-diamminedichloroplatinum (II)

The ability of cis-DDP and several analogs to enter the CSF was investigated in rhesus monkeys that had subcutaneously implanted Ommaya reservoirs connected to catheters in each monkey's fourth ventricle. Plasma and CSF samples were analyzed for platinum content by atomic absorption spectroscopy. Plasma platinum curves were biphasic with a very slowly declining terminal phase. CSF platinum curves rose to maximum concentrations 30-40 min after an IV bolus injection and declined mono-exponentially (T 1/2 = 60 min) without displaying a detectable slow terminal phase. cis-DDP given as an IV bolus of 1.5 mg/kg or 3.0 mg/kg produced peak CSF concentrations of 0.35 and 0.78 microM platinum. The ratio of CSF platinum:plasma platinum never exceeded 0.04. When cis-DDP at 3.0 mg/kg was given as a 2- or 7-h infusion, the peak CSF concentrations were 0.28 and 0.17 microM platinum, respectively. The total CSF exposure, measured as concentration X time, was the same for bolus and for 2- and 7-h infusions. Studies with analogs showed that neither malonato 1,2-diaminocyclohexane platinum (II) nor 4-carboxyphthalato 1,2-diaminocyclohexane platinum (II) had better CSF penetrance than cis-DDP. Sulfato 1,2-diaminocyclohexane platinum (II) could not be detected in the CSF. The ratio of CSF platinum:plasma platinum was never greater tha 0.02-0.03 for any of the analogs.

Cerebral abscesses produced by bacterial implantation and septic embolisation in primates

The degree of brain abscess encapsulation is positively related to surgical mortality and methods to enhance capsule wall formation, therefore, have therapeutic relevance. Two primate models are described which may be useful in the investigation of encapsulation of traumatic and metastatic brain abscesses. Direct intracerebral inoculation induces abscesses displaying more prominent inflammatory responses and encapsulation than does septic embolisation, despite similar abscess age and size. Cerebral ischaemia surrounding metastatic suppurative foci may retard capsule wall formation.