Irregular N-methyl-D-aspartate receptor (NMDAR) function is one of the main hypotheses employed to facilitate understanding of the underlying disease state of schizophrenia. Although direct agonism of the NMDAR has not yielded promising therapeutics, advances have been made by modulating the NMDAR co-agonist site which is activated by glycine and D-serine. One approach to activate the co-agonist site is to increase synaptic D-serine levels through inhibition of D-amino acid oxidase (DAO), the major catabolic clearance pathway for this and other D-amino acids. A number of DAO inhibitors have been developed but most have not entered clinical trials. One exception to this is sodium benzoate which has demonstrated efficacy in small trials of schizophrenia and Alzheimer's disease. Herein we provide data on the effect of sodium benzoate and an optimised Takeda compound, PGM030756 on ex vivo DAO enzyme occupancy and cerebellar D-serine levels in mice. Both compounds achieve high levels of enzyme occupancy; although lower doses of PGM030756 (1, 3 and 10 mg/kg) were required to achieve this compared to sodium benzoate (300, 1000 mg/kg). Cerebellar D-serine levels were increased by both agents with a delay of approximately 6 h after dosing before the peak effect was achieved. Our data and methods may be useful in understanding the effects of sodium benzoate that have been seen in clinical trials of schizophrenia and Alzheimer's disease and to support the potential clinical assessment of other DAO inhibitors, such as PGM030756, which demonstrate good enzyme occupancy and D-serine increases following administration of low oral doses.

A series of macrocyclic calcitonin gene-related peptide (CGRP) receptor antagonists identified using structure-based design principles, exemplified by HTL0028016 (1) and HTL0028125 (2), is described. Structural characterization by X-ray crystallography of the interaction of two of the macrocycle antagonists with the CGRP receptor ectodomain is described, along with structure–activity relationships associated with point changes to the macrocyclic antagonists. The identification of non-peptidic/natural product-derived, macrocyclic ligands for a G protein coupled receptor (GPCR) is noteworthy.

AS1411 is a novel DNA aptamer that binds to the multi-functional protein nucleolin and induces cell death. AS1411 has shown activity at two different doses in combination with cytarabine in a phase II study of patients with AML. We have previously shown that AS1411 has activity against a range of solid and hematological cancer cell lines, with IC50 values between 1 and 10 μM, when cells are exposed to AS1411 continuously for more than 3 days. We have also demonstrated efficacy in vivo in both lung (A549) and renal (A498) mouse xenografts. However, it has been challenging to provide optimal continuous dosing of AS1411 in mice; use of osmotic pumps or intraperitoneal bolus injection have been associated with low drug exposure. In the current study, we optimized the continuous infusion model by using nude, athymic rats with a surgically implanted catheter in a two-cycle xenograft study. Plasma and tumor samples were collected for PK determination, allowing a correlation of PK with efficacy. The colorectal cell line HT29, which is sensitive to AS1411 in vitro, was used in this study. Cells (5×106) were implanted subcutaneously in the flank of female nude rats and tumors were allowed to grow to approximately 200 − 300 mm3 before surgical cannulation of the femoral vein. Following recovery, animals received AS1411 at 40, 80 or 180 mg/kg/day for two 7 day cycles of continuous infusion, 7 days apart. A vehicle control group received saline. Animals in the 80 and 180 mg/kg/day groups exhibited a significant (p<0.01) reduction in tumor volume compared to control animals at day 33 and at day 22 (interim analysis); this was not observed for animals in the 40mg/kg/day group (40mg kg/day in this model does not directly correlate to the clinical dose of the same name). AS1411 was well-tolerated by all animals in all dose groups. Plasma levels of AS1411 were measured at the three dose levels after one cycle of treatment. Mean AS1411 plasma concentrations were 0.7, 2.5 and 5.0 μM, for rats treated at 40, 80 and 180 mg/kg/day, respectively. The plasma concentrations in the two higher dose groups are within the range of the in vitro IC50 concentrations of a panel of cell lines. We conclude that AS1411 shows activity in vivo in the HT29 nude rat xenograft model. Doses associated with significant reductions in tumor volume were those that produced plasma concentrations close to the IC50 level for AS1411. This correlation has been used in planning further clinical development of AS1411, including a phase IIb study of patients with AML. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2614.