Discovery of potent, selective, and orally bioavailable PDE5 inhibitor: Methyl-4-(3-chloro-4-methoxybenzylamino)-8-(2-hydroxyethyl)-7-methoxyquinazolin-6-ylmethylcarbamate (CKD 533).

In a continuing effort to discover novel PDE5 inhibitors, we have successfully found quinazolines with 4-benzylamino substitution as potent and selective PDE5 inhibitors. Initial lead compound (1) was found to be easily metabolized when incubated with human liver microsomes mainly through C6 amide hydrolysis. Blocking of this metabolic hot spot led to discovery of 10 (CKD533) which is highly potent, selective and orally efficacious in conscious rabbit model for erectile dysfunction and now is undergoing preclinical toxicology study.

Quinazolines as potent and highly selective PDE5 inhibitors as potential therapeutics for male erectile dysfunction.

In an effort to minimize side effects associated with low selectivity against PDE isozymes, we have successfully identified a series of 6,7,8-substituted quinzaolines as potent inhibitors of PDE5 with high level of isozyme selectivity, especially against PDE6 and PDE11. PDE5 potency and isozyme selectivity of quinazolines were greatly improved with substitutions both at 6- and 8-position. The synthesis, structure-activity relationships and in vivo efficacy of this novel series of potent PDE5 inhibitors are described.

Solid phase combinatorial synthesis of benzothiazoles and evaluation of topoisomerase II inhibitory activity.

To investigate one possible mechanism of action of the cytotoxic activity of benzothiazoles, we synthesized 2-(substituted-phenyl)benzothiazoles and evaluated their ability to inhibit topoisomerase II activities. Solid phase combinatorial method using trityl resin was employed and benzothiazole derivatives with various substitution on 2'-, 3'-, or 4'-position of phenyl group were obtained in ca. 30 mg scale (7-96% yield). Most of the compounds synthesized exhibited topoisomerase II inhibitory activity at 100 microM. 2-(3-Amino-4-methylphenyl)benzothiazole showed high activity (IC(50) = 71.7 microM), comparable to etoposide (IC(50) = 78.4 microM).

Identification of a quinoxaline derivative that is a potent telomerase inhibitor leading to cellular senescence of human cancer cells.

Telomere maintenance is essential for the continued proliferation of dividing cells, and is implicated in chromosome stability and cell immortalization. Telomerase activity allows cells to maintain their telomeric DNA and contributes to the indefinite replicative capacity of cancer cells. Telomerase is expressed in most cancer cells, but not in normal somatic cells, suggesting that telomerase is an attractive target for cancer chemotherapy. Here we screened a chemical library for inhibition of human telomerase, and identified 2,3,7-trichloro-5-nitroquinoxaline (TNQX) as a potent inhibitor. TNQX showed a potent inhibitory effect, with 50% inhibition at approximately 1.4 microM, and did not inhibit DNA and RNA polymerases, including retroviral reverse trancriptase. A series of enzyme kinetic experiments suggested that TNQX is a mixed-type non-competitive inhibitor, with an inhibitor-binding site distinct from the binding sites for the telomeric substrate (TS) primer and the dNTPs. Long-term cultivation of the MCF7 cell line with a drug concentration that did not cause acute cytotoxicity resulted in progressive telomere erosion followed by an increased incidence of chromosome abnormalities and induction of the senescence phenotype. The results presented here indicate that TNQX is a highly potent and selective anti-telomerase agent with good potential for further development as a promising anti-cancer agent.

Solid-phase combinatorial synthesis and cytotoxicity of 3-aryl-2,4-quinazolindiones.

A series of 3-aryl-2,4-quinazolinediones with various substitution on aromatic rings has been prepared by solid-phase synthesis. Several compounds showed cytotoxicity on human colon carcinoma (Col2) tested by SRB method.