CP-225,917 and CP-263,114, novel Ras farnesylation inhibitors from an unidentified fungus. I. Taxonomy, fermentation, isolation, and biochemical properties.

During the course of our screening for squalene synthase inhibitors and Ras farnesylation inhibitors, a novel fungal culture was discovered to produce two structurally unique compounds, CP-225,917 and CP-263,114, as well as zaragozic acid A (squalestatin I). The two compounds are characterized by a bicyclo[4.3.1]dec-1,6-diene core plus two extended alkyl chains. CP-225,917 and CP-263,114 inhibit Ras farnesyl transferase from rat brain with IC50 values of 6 microM and 20 microM, respectively. CP-225,917 inhibits squalene synthase with an IC50 value of 43 microM and CP-263,114 with an IC50 of 160 microM. The producing organism, though not fully classified, exhibits the characteristics of a sterile Phoma species.

Simple spectrophotometric assay for measuring protein binding of penem antibiotics to human serum.

The binding of antibiotics to plasma (serum) proteins through hydrogen bonding can significantly influence the biological characteristics of these drugs. A rapid spectrophotometric assay has been developed that measures the level of free (unbound) penem antibiotic in serum ultrafiltrates. Whole human serum was adjusted to a standard concentration of antibiotic and then filtered by centrifugation through a Centrifree (Amicon Corp., Lexington, Mass.) filter that retained greater than 99.9% of serum protein. The degree of penem protein binding was determined spectrophotometrically by measuring the level of unbound drug in the ultrafiltrate at 322 nm. At this wavelength, no interfering absorption from residual protein was detected in the ultrafiltrate, and penem absorption was linear over a wide concentration range. The method gave protein-binding values comparable to those obtained by a high-pressure liquid chromatography assay but was more rapid, since it did not require solvent extraction and high-pressure liquid chromatography calibration procedures. The spectrophotometric assay has been used to assay over 100 penems to determine the structure-activity relationships that are involved with the high serum protein binding of these agents. As with penicillins and some cephalosporins, the nonpolar nature of the penem side chain at the C-2 position strongly influenced the degree of penem binding to serum proteins.