Comparative studies on bilayer systems of saturated phosphatidylcholines and phosphatidylethanolamines revealed a maximum in ionic permeability in phosphatidylcholine bilayers at the temperature of the gel to liquid-crystalline phase transition but such an increase in permeability was not detectable in bilayers of phosphatidylethanolamine. Furthermore, it was found that at the phase transition temperature the phosphatidyicholine bilayers are subject to rapid hydrolysis by pancreatic phospholipase A2 whereas phosphatidylethanolamine bilayers are not. These differences are discussed in view of detailed information on the molecular organization in the gel and liquid crystalline phases of the two phospholipid classes.

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This study has been initiated by the definite need of a rapid, in vitro and patient-specific test to examine oncolytic drug effects on tumour cells. Therefore, we applied a test in which we monitored the incorporation of labelled nucleosides in isolated tumour cells, as a measure of nucleus activity (i.e. the Volm assay). A novel technique of erythrocytes co-precipitation has been developed and this enabled us to use a small number of tumour cells per test (200,000 cells/tube). During the assay, a strict pH control and a high starting viability have been introduced. A cytotoxic control and a t-test at two levels deal with the technical errors and the imprecision. For the evaluation of a specific drug a number of 1.8 million cells proved to be sufficient. Time-course studies of the incorporation of labelled nucleosides into isolated tumour cells have shown the optimal incubation time to be 2 h. The entire assay is completed within one day. HeLa cell cultures were employed as quality control material and criteria for interpretation have been developed. Preliminary results, based upon the evaluation of 43 human breast tumours with doxorubicin, indicate the correctness of the proposed procedures. In conclusion we can state that this assay not only provides useful information but above all that the results are made available in such a short time that they can be used directly in the medical management of the individual patient.

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