Evaluation of unnatural cyclic amino acids as boron delivery agents for treatment of melanomas and gliomas

Unnatural cyclic amino acids (UNAAs) are a new class of boron delivery agents that are in a pre-clinical stage of evaluation. In the present study, the biodistribution of racemic forms of the cis- and trans-isomers of the boronated UNAA 1-amino-3-boronocyclopentanecarboxylic acid (ABCPC) and 1-amino-3-boronocycloheptanecarboxylic acid (ABCHC) were evaluted in B16 melanoma bearing mice and this was compared to l-p-boronophenylalanine (BPA). Boron concentrations were determined by inductively coupled plasma-optical emission spectroscopy (ICP-OES) at 2.5h following intraperitoneal (i.p.) injection of the test agents at a concentration equivalent to 24mg/B/kg. While all compounds attained comparable tumor boron concentrations, the tumor/blood (T/Bl) boron concentration ratios were far superior for both cis-ABCPC and cis-ABCHC compared to BPA (T/Bl=16.4, and 15.1 vs. 5.4). Secondary ion mass spectrometry (SIMS) imaging revealed that the cis-ABCPC delivered boron to the nuclei, as well as the cytoplasm of B16 cells. Next, a biodistribution study of cis-ABCPC and BPA was carried out in F98 glioma bearing rats following i.p. administration. Both compounds attained comparable tumor boron concentrations but the tumor/brain (T/Br) boron ratio was superior for cis-ABCPC compared to BPA (6 vs. 3.3). Since UNAAs are water soluble and cannot be metabolized by tumor cells, they could be potentially more effective boron delivery agents than BPA. Our data suggest that further studies are warranted to evaluate these compounds prior to the initiation of clinical studies.

Transport of 14C-gamma-aminobutyric acid into brain, cerebrospinal fluid and choroid plexus in neonatal and adult rats

In general blood to brain entry of amino acids is greater in the neonatal rats compared to the adults. gamma-Aminobutyric acid (GABA), a neurotransmitter amino acid, shows limited transport across the blood-brain barrier (BBB) in the adult rat. Characteristics of GABA entry into the immature rat brain is yet to be addressed. This investigation was set to study the entry of GABA into brain of the neonatal rat compared to the adult. Using the bilateral in situ brain perfusion technique, the entry of 14C-GABA into brain, cerebrospinal fluid (CSF) and lateral ventricles choroid plexuses was studied in the adult and neonatal rats. 14C-GABA uptake into neonatal rat brain after 20 min perfusion was 0.116+/-0.014 ml g(-1), approximately twice that of the adults (P<0.01). Half saturation constant, K(m), did not change with age (P>0.05), whereas maximal transport into the brain, V(max), was reduced from 0.152 to 0.068 nmol min(-1) g(-1) showing a significant reduction with age (P<0.05). In the neonate the entry of GABA into the CSF was dominant when compared to that into the brain, this could be due to a greater diffusional component, K(d), which was detected to be high in the neonate. In conclusion, the uptake of 14C-GABA into brain of the immature rats exceeded that in the adults which is thought to be due to both greater maximal transport and greater diffusion in the neonate compared to the adult.

Cytotoxic T lymphocyte epitope analogues containing cis- or trans-4-aminocyclohexanecarboxylic acid residues

In order to improve the immunotherapeutical potential of H-Cys-Leu-Gly-Gly-Leu-Leu-Thr-Met-Val-OH (CLG) peptide, an Epstein-Barr virus (EBV) subdominant epitope derived from the membrane protein LMP2, we have synthesized and tested CLG analogues containing cis- and/or trans-4-aminocyclohexanecarboxylic acid (ACCA) replacing Gly-Gly and/or Thr-Met dipeptide units. All pseudopeptides were tested for metabolic stability and for their capacity to bind HLA-A2 molecules and to sensitize target cells to lysis. All new compounds exhibited higher enzymatic resistance compared to the original CLG and some trans-ACCA-derivatives were able to associate HLA-A2 and to efficiently stimulate CTL responses directed against the CLG natural epitope.