bq-123 and Astrocytoma

Endothelin ET(A) receptors on the human astrocytoma 1321N1 cell line were characterized in radioligand binding studies using the ET(A)-selective antagonist radioligand [(3)H]BQ-123. A membrane preparation of the cell line showed a high expression level of ET(A) receptors (B(max) = 128 fmol/mg protein). The K(D) value for [(3)H]BQ-123 (K(D) = 2.29 nmol/l) was comparable to that previously determined at the human neuroblastoma cell line SK-N-MC. The specific labeling of ET(A) receptors on astrocytoma 1321N1 cells by [(3)H]BQ-123 was confirmed by determining the rank order of potency of a series of agonists and antagonists. A competition assay for the screening of potential ET(A) ligands was established and a series of new disubstituted imidazo[1,2-c]pyrimidine and pyrimido[1,6-a]pyrimidine derivatives was investigated. Moderate ET(A) affinity was detected for several derivatives [30-40% inhibition of [(3)H]BQ-123 binding (3 nmol/l) at a concentration of 10 micromol/l]. Astrocytoma 1321N1 cells natively express relatively high levels of ET(A) receptors. They are useful for the screening of potential ET(A) ligands in radioligand binding assays with [(3)H]BQ-123.

Topics: Astrocytoma; Binding, Competitive; Cell Line, Tumor; Humans; In Vitro Techniques; Ligands; Peptides, Cyclic; Protein Binding; Pyrimidines; Radioligand Assay; Receptor, Endothelin A; Tritium