The half maximal inhibitory concentration (IC50) has several limitations that make it unsuitable for examining a large number of compounds in cytotoxicity studies, particularly when multiple exposure periods are tested. This article proposes a new approach to measure drug effectiveness, which allows ranking compounds according to their toxic effects on live cells. This effectiveness measure, which combines all exposure times tested, compares the growth rates of a particular cell line in the presence of the compound with its growth rate in the presence of DMSO alone. Our approach allows measuring a wider spectrum of toxicity than the IC50 approach, and allows automatic analyses of a large number of compounds. It can be easily implemented in linear regression software, provides a comparable measure of effectiveness for each investigated compound (both toxic and non-toxic), and allows statistically testing the null hypothesis that a compound is non-toxic versus the alternative that it is toxic. Importantly, our approach allows defining an automated decision rule for deciding whether a compound is significantly toxic. As an illustration, we describe the results of a cell-based study of the cytotoxicity of 24 analogs of novobiocin, a C-terminal inhibitor of heat shock protein 90 (Hsp90); the compounds were ranked in order of cytotoxicity to a panel of 18 cancer cell lines and 1 normal cell line. Our approach may also be a good alternative to computing the half maximal effective concentration (EC50) in studies searching for compounds that promote cell growth.
Structural, optical, and electrical properties of doped hydrogenated diamond-like amorphous carbon films deposited using the dc saddle-field glow-discharge technique Fluorine ͑F͒ and boron ͑B͒ co-doped diamond-like carbon ͑FB-DLC͒ films were prepared on different substrates by the plasma immersion ion processing ͑PIIP͒ technique. A pulse glow discharge plasma was used for the PIIP deposition and was produced at a pressure of 1.33 Pa from acetylene (C 2 H 2 ), diborane (B 2 H 6 ), and hexafluoroethane (C 2 F 6 ) gas. Films of FB-DLC were deposited with different chemical compositions by varying the flow ratios of the C 2 H 2 , B 2 H 6 , and C 2 F 6 source gases. The incorporation of B 2 H 6 and C 2 F 6 into PIIP deposited DLC resulted in the formation of FuC and BuC hybridized bonding structures. The levels of the F and B concentrations effected the chemical bonding and the physical properties as was evident from the changes observed in density, hardness, stress, friction coefficient, and contact angle of water on films. Compared to B-doped or F-doped DLC films, the F and B co-doping of DLC during PIIP deposition resulted in the formation of films that possessed a reduced hydrogen concentration and stress, while maintaining a high hardness, low friction coefficient, and high wetting contact angle.
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