Etoposide (VP16-213) and teniposide (VM26) comparative in vitro activities in human tumors.

In order to determine if any inherent sensitivity differences may exist between VP16-213 and VM26 individual human tumors were grown in vitro and drug sensitivities were determined using the soft agar clonogenic assay method. Only nine of the 34 tumors tested so far showed a differing sensitivity to VP16-213 and VM26 as measured by a 25% or greater colony number reduction. However in none of these tumors did this added reduction result in a 70% decrease over control plate colony numbers. As yet we have been unable to demonstrate any clinically meaningful inherent in vitro sensitivity difference between VP16-213 and VM26 in any tumor type tested.

Translation of Pseudomonas aeruginosa bacteriophage PP7 RNA by a cell-free amino acid incorporating system from Escherichia coli.

We have compared the activities of the RNA genomes of Pseudomonas aeruginosa phage PP7 and coliphages Qbeta and f2 in a cell-free amino acid incorporating system derived from Escherichia coli. The rate of incorporation of [(14)C]leucine in the PP7 RNA-directed system is greater than in the systems directed by either Qbeta or f2 RNA. The response to changes in phage RNA concentrations is similar in all the systems, reaching a saturation level at 0.75 to 1.0 mg of RNA per ml of reaction mixture. Analysis of complete reaction mixtures of the PP7 RNA and of the Qbeta RNA systems by sucrose gradient centrifugation shows generally similar patterns for both RNAs. The principal differences are that in the PP7 system a slightly higher percentage of RNA forms ribosome complexes and that the polysomes are somewhat smaller. PP7 RNA is also degraded more extensively during the reaction than is Qbeta RNA. Analysis of the products of the reactions by acrylamide gel electrophoresis shows that PP7 coat protein is the only identifiable product of the PP7 RNA-directed system, suggesting that only the coat protein cistron is translated by E. coli ribosomes.

Comparison of the activities of extracts of Escherichia coli and Salmonella typhimurium in amino acid incorporation.

We have compared the amino acid incorporating activities of extracts of Escherichia coli and Salmonella typhimurium in in vitro protein-synthesizing systems directed by bacterial messenger ribonucleic acid (mRNA) of both species and by the genomes of coliphages Qbeta and f2. E. coli and S. typhimurium extracts translate both homologous and heterologous bacterial mRNAs at comparable rates. S. typhimurium extracts translate phage RNAs only 10 to 15% as fast as E. coli extracts do. The presence of glucose in the growth medium increases the activity of S. typhimurium extracts three- to fourfold in the phage RNA-directed systems. Glucose has a much more limited effect on the activities of E. coli extracts. We show that similar amounts of phage RNA-ribosome complexes are formed in both the E. coli and the S. typhimurium systems, indicating that the different activities observed may be attributed to different rates of peptide elongation or to the formation of complexes at different sites on the RNA strand.