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.

Characterizing the pharmacokinetics of panobinostat in a non-human primate model for the treatment of diffuse intrinsic pontine glioma.

PURPOSE: Diffuse intrinsic pontine glioma (DIPG) is one of the deadliest forms of childhood cancers. To date, no effective treatment options have been developed. Recent drug screening studies identified the HDAC inhibitor panobinostat as an active agent against DIPG cells lines and animal models. To guide in the clinical development of panobinostat, we evaluated the CNS pharmacokinetics of panobinostat using CSF as a surrogate to CNS tissue penetration in a pre-clinical nonhuman primate (NHP) model after oral administration. METHODS: Panobinostat was administered orally to NHP (n = 3) at doses 1.0, 1.8, 2.4, and 3.0 mg/kg (human equivalent dose: 20, 36, 48, 60 mg/m2, respectively). The subjects served as their own controls where possible. Serial, paired CSF and plasma samples were collected for 0-48 h. Panobinostat was quantified via a validated uHPLC-MS/MS method. Pharmacokinetic (PK) parameters were calculated using non-compartmental methods. RESULTS: CSF penetration of panobinostat after systemic delivery was low, with levels detectable in only two subjects. CONCLUSION: The CSF penetration of panobinostat was low following oral administration in this pre-clinical NHP model predictive of human PK.

Durable regression of Medulloblastoma after regional and intravenous delivery of anti-HER2 chimeric antigen receptor T cells.

BACKGROUND: Standard-of-care therapies for treating pediatric medulloblastoma have long-term side effects, even in children who are cured. One emerging modality of cancer therapy that could be equally effective without such side effects would be chimeric antigen receptor (CAR) T cells. Knowing that human epidermal growth factor receptor 2 (HER2) is overexpressed in many medulloblastomas and has been used as a CAR T target before, we sought to evaluate the efficacy of more sophisticated anti-HER2 CAR T cells, as well as the feasibility and efficacy of different routes of delivering these cells, for the treatment of pediatric medulloblastoma. METHODS: Daoy, D283 and D425 medulloblastoma cell lines were characterized by flow cytometry to evaluate HER2 expression. Anti-tumor efficacy of HER2-BBz-CAR T cells in vitro was performed using cytokine release and immune cytotoxicity assays compared to control CD19 CAR T cells. In vivo, Daoy and D283 tumor cells were orthotopically implanted in the posterior fossa of NOD.Cg-Prkdc scid Il2rg tm1Wjl /SzJ (NSG) mice and treated with regional or intravenous HER2-BBz-CAR T cells or control CD19 CAR T cells. Non-human primates (NHPs) bearing ventricular and lumbar reservoirs were treated with target autologous cells bearing extracellular HER2 followed by autologous HER2-CAR T cells intraventricularly. Cerebrospinal fluid and blood were collected serially to measure the persistence of delivered cells and cytokines. RESULTS: HER2-BBz-CAR T cells effectively clear medulloblastoma orthotopically implanted in the posterior fossa of NSG mice via both regional and intravenous delivery in xenograft models. Intravenous delivery requires a log higher dose compared to regional delivery. NHPs tolerated intraventricular delivery of autologous cells bearing extracellular HER2 followed by HER2-BBz-CAR T cells without experiencing any systemic toxicity. CONCLUSIONS: HER2-BBz-CAR T cells show excellent pre-clinical efficacy in vitro and in mouse medulloblastoma models, and their intraventricular delivery is feasible and safe in NHPs. A clinical trial of HER2-BBz-CAR T cells directly delivered into cerebrospinal fluid should be designed for patients with relapsed medulloblastoma.

Plasma and cerebrospinal fluid pharmacokinetics of select chemotherapeutic agents following intranasal delivery in a non-human primate model.

The blood-brain barrier (BBB) limits entry of most chemotherapeutic agents into the CNS, resulting in inadequate exposure within CNS tumor tissue. Intranasal administration is a proposed means of delivery that can bypass the BBB, potentially resulting in more effective chemotherapeutic exposure at the tumor site. The objective of this study was to evaluate the feasibility and pharmacokinetics (plasma and CSF) of intranasal delivery using select chemotherapeutic agents in a non-human primate (NHP) model. Three chemotherapeutic agents with known differences in CNS penetration were selected for intranasal administration in a NHP model to determine proof of principle of CNS delivery, assess tolerability and feasibility, and to evaluate whether certain drug characteristics were associated with increased CNS exposure. Intravenous (IV) temozolomide (TMZ), oral (PO) valproic acid, and PO perifosine were administered to adult male rhesus macaques. The animals received a single dose of each agent systemically and intranasally in separate experiments, with each animal acting as his own control. The dose of the agents administered systemically was the human equivalent of a clinically appropriate dose, while the intranasal dose was the maximum achievable dose based on the volume limitation of 1 mL. Multiple serial paired plasma and CSF samples were collected and quantified using a validated uHPLC/tandem mass spectrometry assay after each drug administration. Pharmacokinetic parameters were estimated using non-compartmental analysis. CSF penetration was calculated from the ratio of areas under the concentration-time curves for CSF and plasma (AUCCSF:plasma). Intranasal administration was feasible and tolerable for all agents with no significant toxicities observed. For TMZ, the degrees of CSF drug penetration after intranasal and IV administration were 36 (32-57) and 22 (20-41)%, respectively. Although maximum TMZ drug concentration in the CSF (Cmax) was lower after intranasal delivery compared to IV administration due to the lower dose administered, clinically significant exposure was achieved in the CSF after intranasal administration with the lower doses. This was associated with lower systemic exposure, suggesting increased efficiency and potentially lower toxicities of TMZ after intranasal delivery. For valproic acid and perifosine, CSF penetration after intranasal delivery was similar to systemic administration. Although this study demonstrates feasibility and safety of intranasal drug administration, further agent-specific studies are necessary to optimize agent selection and dosing to achieve clinically-relevant CSF exposures.

Minimally Invasive Lumbar Port System for the Collection of Cerebrospinal Fluid from Rhesus Macaques (Macaca mulatta).

Biomedical translational research frequently incorporates collection of CSF from NHP, because CSF drug levels are used as a surrogate for CNS tissue penetration in pharmacokinetic and dynamic studies. Surgical placement of a CNS ventricular catheter reservoir for CSF collection is an intensive model to create and maintain and thus may not be feasible or practical for short-term studies. Furthermore, previous NHP lumbar port models require laminectomy for catheter placement. The new model uses a minimally invasive technique for percutaneous placement of a lumbar catheter to create a closed, subcutaneous system for effective, repeated CSF sample collection. None of the rhesus macaques (Macaca mulatta; n = 10) implanted with our minimally invasive lumbar port (MILP) system experienced neurologic deficits, postoperative infection of the surgical site, or skin erosion around the port throughout the 21.7-mo study. Functional MILP systems were maintained in 70% of the macaques, with multiple, high-quality, 0.5- to 1.0-mL samples of CSF collected for an average of 3 mo by using aspiration or gravitational flow. Among these macaques, 57% had continuous functionality for a mean of 19.2 mo; 50% of the cohort required surgical repair for port repositioning and replacement during the study. The MILP was unsuccessful in 2 macaques, at an average of 9.5 d after surgery. Nonpatency in these animals was attributed to the position of the lumbar catheter. The MILP system is an appropriate replacement for temporary catheterization and previous models requiring laminectomy and is a short-term alternative for ventricular CSF collection systems in NHP.

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.

Quantification of Temozolomide in Nonhuman Primate Fluids by Isocratic Ultra-High Performance Liquid Chromatography-Tandem Mass Spectrometry to Study Brain Tissue Penetration Following Intranasal or Intravenous Delivery.

A sensitive and selective ultra-high performance liquid chromatography-tandem mass spectrometric method was developed for the quantification of temozolomide (TMZ) in nonhuman primate (NHP) plasma, cerebrospinal fluid (CSF), and brain extracellular fluid (ECF) following microdialysis. Ethyl acetate was used to extract the plasma and CSF samples, using theophylline as the internal standard (IS). ECF samples were diluted with acetonitrile prior to analysis. TMZ was separated on a Waters UPLC® BEH C18 column with an isocratic mobile phase of ammonium acetate (10 mM)-0.1% formic acid/acetonitrile (30:70, v/v) in a positive-ion multi pie reaction monitoring mode (m/z 195.5 →137.6 for TMZ; m/z 181.5→124.2 for IS). The retention time of TMZ and theophylline was 0.45 min with a total run time of 2.5 min. The method was validated over the range from 5-2000 ng/mL in NHP plasma, CSF, and ECF with respect to linearity, accuracy, precision, selectivity, and stability. This method was successfully applied toward the measurement of pharmacokinetic samples following various routes of drug administration.

Development of a cerebrospinal fluid lateral reservoir model in rhesus monkeys (Macaca mulatta).

Rapid, serial, and humane collection of cerebrospinal fluid (CSF) in nonhuman primates (NHP) is an essential element of numerous research studies and is currently accomplished via two different models. The CSF reservoir model (FR) combines a catheter in the 4th ventricle with a flexible silastic reservoir to permit circulating CSF flow. The CSF lateral port model (LP) consists of a lateral ventricular catheter and an IV port that provides static access to CSF and volume restrictions on sample collection. The FR model is associated with an intensive, prolonged recovery and frequent postsurgical hydrocephalus and nonpatency, whereas the LP model is associated with an easier recovery. To maximize the advantages of both systems, we developed the CSF lateral reservoir model (LR), which combines the beneficial features of the 2 previous models but avoids their limitations by using a reservoir for circulating CSF flow combined with catheter placement in the lateral ventricle. Nine adult male rhesus monkeys were utilized in this study. Pre-surgical MRI was performed to determine the coordinates of the lateral ventricle and location of choroid plexus (CP). The coordinates were determined to avoid the CP and major blood vessels. The predetermined coordinates were 100% accurate, according to MRI validation. The LR system functioned successfully in 67% of cases for 221 d, and 44% remain functional at 426 to 510 d postoperatively. Compared with established models, our LR model markedly reduced postoperative complications and recovery time. Development of the LR model was successful in rhesus macaques and is a useful alternative to the FR and LP methods of CSF collection from nonhuman primates.

Plasma and cerebrospinal fluid pharmacokinetics of the Akt inhibitor, perifosine, in a non-human primate model.

PURPOSE: Central nervous system tumors are histologically and biologically heterogeneous. Standard treatment for malignant tumors includes surgery, radiation and chemotherapy, yet surgical resection is not always an option and chemotherapeutic agents have limited benefit. Recent investigations have focused on molecularly targeted therapies aimed at critical tumorigenic pathways. Several tumor types, including high-grade gliomas and pediatric pontine gliomas, exhibit Akt activation. Perifosine, an orally bioavailable, synthetic alkylphospholipid and potent Akt inhibitor, has demonstrated activity in some preclinical models, but absent activity in a genetically engineered mouse model of pontine glioma. We evaluated the plasma and cerebrospinal fluid pharmacokinetics of orally administered perifosine in a non-human primate model to evaluate CNS penetration. METHODS: Perifosine was administered orally to three adult rhesus monkeys as a single dose of 7.0 mg/kg perifosine. Serial paired plasma and CSF samples were collected for up to 64 days. Perifosine was quantified with a validated HPLC/tandem mass spectrometry assay. Pharmacokinetic parameters were estimated using non-compartmental methods. CSF penetration was calculated from the areas under the concentration-time curves. RESULTS: Peak plasma concentrations (C max) ranged from 11.7-19.3 µM, and remained >1 µM for >28 days. Time to C max (T max) was 19 h. The median (range) AUCPl was 3148 (2502-4705) µM/h, with a median (range) terminal half-life (t 1/2) of 193 (170-221) h. Plasma clearance was 494 (329-637) mL/h/kg. Peak CSF concentrations were 4.1-10.1 nM (T max 64-235 h). CSF AUCs and t 1/2 were 6358 (2266-7568) nM/h and 277 (146-350) h, respectively. Perifosine concentrations in the CSF remained over  nM for >35 days. The mean CSF penetration was 0.16 %. CONCLUSION: CNS penetration of perifosine after systemic administration is poor. However, levels were measurable in both plasma and CSF for an extended time (>2 months) after a single oral dose.

Model for concomitant microdialysis sampling of the pons and cerebral cortex in rhesus macaques (Macaca mulatta).

Pediatric diffuse intrinsic pontine gliomas are aggressive brainstem tumors that fail to respond to treatment. We hypothesize that the protective features of the pons may hinder chemotherapeutic agents from entering pontine tissue compared with cortical brain tissue. To test this hypothesis, we developed a unique nonhuman primate model using microdialysis, a continuous in vivo extracellular sampling technique, to compare drug exposure concurrently in pontine tissue, cortical tissue, CSF, and plasma after intravenous administration of chemotherapeutic agents. The surgical coordinates and approach for microdialysis cannula-probe placement were determined in 5 adult male rhesus monkeys (Macaca mulatta) by using MRI. Microdialysis cannulas-probes were implanted stereotactically in the brain, retrodialysis was performed to measure relative recovery, and a 1-h intravenous infusion of temozolomide was administered. Continuous microdialysis samples were collected from the pons and cortex over 4 h with concurrent serial plasma and CSF samples. Postsurgical verification of microdialysis cannula-probe placement was obtained via MRI in 3 macaques and by gross pathology in all 5 animals. The MRI-determined coordinates and surgical methodologies resulted in accurate microdialysis probe placement in the pons and cortex in 4 of the 5 macaques. Histologic examination from these 4 animals revealed negligible tissue damage to the pontine and cortical tissue from microdialysis. One macaque was maintained for 8 wk and had no deficits attributed to the procedure. This animal model allows for the determination of differences in CNS penetration of chemotherapeutic agents in the pons, cortex, and CSF after systemic drug administration.

Pharmacokinetics of intrathecal gemcitabine in nonhuman primates.

PURPOSE: Gemcitabine is an excellent candidate for regional therapy. We quantified cerebrospinal fluid (CSF) and plasma concentrations of gemcitabine and its inactive metabolite, 2',2'-difluorodeoxyuridine (dFdU), in nonhuman primates given intrathecal gemcitabine. EXPERIMENTAL DESIGN: Three nonhuman primates received 5 mg of gemcitabine via lateral ventricle. CSF was sampled from the fourth ventricle in all of the animals and the lumbar space in one, and one had plasma sampled. One animal had ventricular CSF sampled after receiving 5 mg intralumbar gemcitabine. Gemcitabine and dFdU were measured by high-performance liquid chromatography. Three additional animals had 5 mg intralumbar gemcitabine administered weekly for 4 weeks and were monitored for toxicity. RESULTS: At 37 degrees C in vitro, gemcitabine was stable in CSF. Ventricular delivery of gemcitabine produced peak ventricular CSF gemcitabine concentrations of 297 +/- 105 microg/ml. After 6 h, the concentrations were <0.03 microg/ml. Intrathecal gemcitabine was rapidly and extensively converted to dFdU. CSF dFdU concentrations increased to 82 microg/ml at 1 h and then declined to very low values by 24 h. After intraventricular administration, CSF gemcitabine and dFdU area(s) under the curve (AUC) were 251 +/- 85 and 249 +/- 88 microg/ml x h. Intralumbar gemcitabine produced lower ventricular CSF gemcitabine and dFdU concentrations than did intraventricular gemcitabine. The plasma gemcitabine AUC associated with 5 mg of intraventricular gemcitabine was 2 mg/ml x h, which was >200-fold lower than the CSF gemcitabine AUC in the same animal. Transient CSF pleocytosis was the only toxicity observed. CONCLUSIONS: Our results demonstrate a large pharmacokinetic advantage of intrathecal gemcitabine and support a planned Phase I clinical trial of this dosing strategy.