EXTH-99. SYSTEMIC AND BRAIN PHARMACOKINETICS OF A GABAA RECEPTOR AGONIST, AMLAL-101, AS AN INVESTIGATIONAL THERAPEUTIC FOR THE TREATMENT OF PRIMARY AND METASTATIC BRAIN CANCERS

PURPOSE

AMLAL-101 is a novel agent which preferentially targets α3, α5 subtypes of ɣ-amino butyric acid receptors and shows anti-tumor activity against disparate cancer types. AMLAL-101 is being advanced as an ‘add-on’ to potentiate treatment of primary and metastatic brain cancers. However, AMLAL-101 must penetrate the blood-brain barrier (BBB) and show sufficient brain retention. The primary purpose of this study was to determine the plasma pharmacokinetics (PK) and quantitative estimate of the BBB permeability of AMLAL-101.

METHODS

We performed intracranial microdialysis, employing jugular vein cannulated Sprague-Dawley rats which facilitated simultaneous serial blood and brain extracellular fluid (ECF) sampling. AMLAL-101 was injected i.p. at 5 mg/kg and serial blood and brain ECF samples collected up to 10 h post-dosing. Plasma and ECF samples were analyzed by LC/MS-MS and plasma and ECF concentration vs time PK profiles determined. In vivo recovery analysis was performed using retrodialysis and rapid equilibrium dialysis employed to determine the extent of protein binding.

RESULTS

AMLAL-101 plasma protein binding was 85% and in vivo recovery from ECF was 25%. AMLAL-101 peak concentration (Cmax) in plasma and brain ECF were 15 µM and 13.8 µM, respectively. The plasma and brain ECF area under the concentration (AUC0-10) were 27.5 h.µg/mL and 24.10 h.µg/mL, respectively. The brain partitioning of unbound AMLAL-101 (Kp,uu; determined either as a ratio of brain ECF Cmax:unbound plasma Cmax or brain ECF AUC: unbound plasma AUC), were 6.13 and 4.13, respectively. The elimination half-life of AMLAL-101 was 3 h for both brain ECF and plasma.

CONCLUSIONS

These results suggest that AMLAL-101 has the requisite BBB permeability required for brain cancer therapeutics. AMLAL-101 shows significant brain retention when compared to a chemically similar agent that does not show anti-cancer activity, which may contribute to efficacy of AMLAL-101 as an anti-tumor agent for treatment of brain cancers.

HOX expression patterns identify a common signature for favorable AML

Deregulated HOX expression, by chromosomal translocations and myeloid-lymphoid leukemia (MLL) rearrangements, is causal in some types of leukemia. Using real-time reverse transcription-PCR, we examined the expression of 43 clustered HOX, polycomb, MLL and FLT3 genes in 119 newly diagnosed adult acute myeloid leukemias (AMLs) selected from all major cytogenetic groups. Downregulated HOX expression was a consistent feature of favorable AMLs and, among these cases, inv(16) cases had a distinct expression profile. Using a 17-gene predictor in 44 additional samples, we observed a 94.7% specificity for classifying favorable vs intermediate/unfavorable cytogenetic groups. Among other AMLs, HOX overexpression was associated with nucleophosmin (NPM) mutations and we also identified a phenotypically similar subset with wt-NPM. In many unfavorable and other intermediate cytogenetic AMLs, HOX levels resembled those in normal CD34+ cells, except that the homogeneity characteristic of normal samples was not present. We also observed that HOXA9 levels were significantly inversely correlated with survival and that BMI-1 was overexpressed in cases with 11q23 rearrangements, suggesting that p19(ARF) suppression may be involved in MLL-associated leukemia. These results underscore the close relationship between HOX expression patterns and certain forms of AML and emphasize the need to determine whether these differences play a role in the disease process.

Antibiotics on urethral catheter withdrawal: a hit and miss affair

Globally, millions of patients undergo urethral catheterization every year. Our objective was to study the current use of prophylactic antibiotics on urinary catheter withdrawal. A questionnaire (N = 300) was sent to healthcare professionals involved in the management of patients with urinary catheters (consultant microbiologists, infection control nurses, consultant urologists, specialist nurses in urology, continence advisers and consultants in the care of older people). The questionnaire asked about their use of prophylactic antibiotics on the withdrawal of a urethral catheter. Sixty percent of healthcare professionals advocated the use of antibiotics for either all or selected groups of patients. The remainder did not. The use of prophylactic antibiotics varied among different groups. Of the healthcare professionals who used antibiotics, the majority cited more than one reason for their use (prevent bacteraemia, avoid an infection in a prosthesis or urinary tract infection). The course and type of antibiotic used varied. Our study has shown diversity in practice that is of concern. At present, just over one-half of patients with urinary catheters are being given antibiotics, although there is no evidence to suggest that such an intervention confers any benefit. If benefits do not exist, these patients are being exposed to the harm of antibiotics and providers are incurring costs unnecessarily. A formal trial to address this issue is urgently needed.

Hox expression in AML identifies a distinct subset of patients with intermediate cytogenetics

We previously reported that favorable and poor prognostic chromosomal rearrangements in acute myeloid leukemia (AML) were associated with distinct levels of HOX expression. We have now analyzed HOX expression in 50 independent adult AML patients (median age=62 years), together with FLT3 and FLT3-ligand mRNA levels, and FLT3 mutation determination. By cluster analysis, we could divide AMLs into cases with low, intermediate and high HOX expression. Cases with high expression were uniquely restricted to a subset of AMLs with intermediate cytogenetics (P=0.0174). This subset has significantly higher levels of FLT3 expression and appears to have an increase of FLT3 mutations (44%), while CEBPalpha mutations were infrequent (6%). FLT3 mRNA levels were correlated with the expression of multiple HOX genes, whereas FLT3 mutations were correlated with HOXB3. In some cases, FLT3 was expressed at levels equivalent to GAPDH in the absence of genomic amplification. We propose that high HOX expression may be characteristically associated with a distinct biologic subset of AML. The apparent global upregulation of HOX expression could be due to growth-factor signaling or, alternatively, these patterns may reflect a particular stage of differentiation of the leukemic cells.

Analysis of 100 pregnancy outcomes in women treated systemically with tacrolimus

The aim of this paper is to provide a summary of clinical findings regarding the safety of tacrolimus in pregnancy. From 1992 to 1998 data were collected on 100 pregnancies from 84 mothers who received tacrolimus systemically; 83 cases of solid organ transplantation, and 1 case of Behçet's disease. Maternal mean age at conception was 28 years and pregnancy outcome was live birth in 68%, spontaneous abortion in 12%, induced abortion in 12%, stillbirth/perinatal death in 3%, ongoing pregnancy in 2%, and lost to follow up in 3%. Fifty-nine percent of the neonates were delivered prematurely (< 37 weeks of gestation). Birth weight was appropriate for the gestational age in 90% of the cases. Malformations occurred in 4 neonates: case 1, meningocele and urogenital defects; case 2, alcoholic embryopathy; case 3, ear defect, cleft palate and hypospadia; case 4, multicystic dysplastic kidney. There was no consistent pattern of malformations and 2 mothers subsequently delivered a healthy neonate while on tacrolimus therapy. Nearly 70% of pregnancies following systemic tacrolimus administration resulted in a favourable outcome without any significant effect on intrauterine growth. The incidence of malformations was similar to that reported with other immunosuppressants in transplant recipients.

Improved Weather and Seasonal Climate Forecasts from Multimodel Superensemble

A method for improving weather and climate forecast skill has been developed. It is called a superensemble, and it arose from a study of the statistical properties of a low-order spectral model. Multiple regression was used to determine coefficients from multimodel forecasts and observations. The coefficients were then used in the superensemble technique. The superensemble was shown to outperform all model forecasts for multiseasonal, medium-range weather and hurricane forecasts. In addition, the superensemble was shown to have higher skill than forecasts based solely on ensemble averaging.

Mibefradil, a T-type and L-type calcium channel blocker, limits infarct size through a glibenclamide-sensitive mechanism

Mibefradil is a novel calcium channel blocker with activity at both L-type and T-type calcium channels. There are data suggesting that this compound can protect the ischemic/reperfused myocardium in spite of the fact that there is a very low abundance of T-type calcium channels within ventricular tissue. The aims of this study were two-fold. First, we wished to study the protective effect of mibefradil on ischemia/reperfusion injury in the isolated rat heart using infarct size as the endpoint of injury. In this respect, we compared mibefradil with amlodipine, a well-known and potent L-type calcium channel blocker, and with ischemic preconditioning, an intervention known to reduce infarct size consistently. Secondly, we investigated the possible mechanisms through which protection was achieved. For this second purpose, we examined the effects on protection of glibenclamide (an ATP-dependent K+ channel blocker) and chelerythrine (a protein kinase C inhibitor). Isolated rat hearts were perfused in the Langendorff mode at constant pressure. Control, mibefradil-treated (0.3 microM), mibefradil plus glibenclamide (50 microM), and mibefradil plus chelerythrine (10 microM) treated hearts underwent 35 minutes regional ischemia followed by 120 minutes reperfusion. At the end of the experiments, infarct size was determined with triphenyltetrazolium chloride and was expressed as a percentage of the ischemic risk zone (I/R%). A significant reduction in infarct size with mibefradil treatment was observed (I/R 11.1 +/- 2.1% vs. 35.5 +/- 3.1% in controls). This was comparable with the infarct reduction seen with two 5-minute cycles of ischemic preconditioning (17.7 +/- 2.5%). Amlodipine 0.1 microM, a concentration that caused equivalent coronary vasodilatation as that produced by mibefradil treatment, had no significant effect on infarct size (I/R 29.7 +/- 3.5%). The protective effect of mibefradil was not significantly modified by the presence of the PKC inhibitor chelerythrine 10 microM (I/R 19.1 +/- 4.9%) but was abolished when glibenclamide 50 microM was coadministered with mibefradil prior to ischemia (I/R 28.1 +/- 4.7%). Neither chlelerythrine nor glibenclamide alone had any influence on infarct size. We conclude from these data that mibefradil, unlike amlodipine, markedly reduces infarct size in the rat isolated heart. This protection is sensitive to inhibition by glibenclamide, suggesting that KATP channel opening may be an important additional and novel mechanism of mibefradil's action.

Age dependant factors influencing digoxin pharmacokinetics in the postnatal puppy

H3-digoxin pharmacokinetics following intravenous pulse injections was studied in dogs ranging in age from 0.5--2 days (n=2), 3--10 days (n=6), 11--30 days (n=5), 31--90 days (n=3) and adult dogs (n=5). All animals in each age group exhibited a biexponential elimination of H3-digoxin from the vascular compartment and data are analyzed by use of a two compartment pharmacokinetic model. Pharmacokinetic parameters showed significant age related differences. The mean T1/2(alpha) was greater in puppies aged 0.5--2 (8.92 +/- 2.61 min), 3--10 (11.8 +/- 1.99 min) and 11--30 days (10.32 +/- 1.89 min) when compared to adult dogs (5.36 +/- 0.91 min). The mean T1/2(beta) was four times longer in 3--10 day old dogs (1342.05 min) than in adult dogs (327.0 min) and decreased with increasing age of the puppies. The beta-phase rate constants were statistically different (p less than 0.05) between 3--10 day old and adult dogs. Elimination of H3-digoxin was slower in puppies than adult dogs (Kel in 3--10 day old puppies = 0.0046 min(-1); adult dogs = 0.0197 min(-1)) and was accompanied by a lower clearance of H3-digoxin in 3--10 day old puppies (2.05 ml/min/kg) than in adult dogs (7.41 ml/min/kg) [p less than 0.0001]. Functional immaturity of the canine kidney during early development probably constitutes the physiologic basis for the differences noted in H3-digoxin kinetics. While these distinctions in elimination kinetics are age related they do not clarify why younger organisms tolerate higher digoxin levels than adults with less apparent toxicity.