Effects of photosensitive chemicals on malaria parasite cells

Synthesis of AX7593, a Quinazoline-Derived Photoaffinity Probe for EGFR

[structure: see text] The synthesis of a photoaffinity probe for EGFR is described. O-Alkylation of 4-(meta-azidoanilino)-6-methoxy-7-hydroxy-quinazoline with a protected tetraethyleneglycol linker followed by the attachment of tetramethylrhodamine yielded the fluorescent probe AX7593. Photoaffinity labeling of EGFR by AX7593 (K(b) = 280 nM) was shown to have an efficiency of 34% and to be competitive with the EGFR inhibitors PP2 and AG1478.

Analysis of micronucleated cells by flow cytometry. 1. Achieving high resolution with a malaria model

Micronucleated cells (MN cells) are present in the blood as rare events (i.e. about 2 MN cells/1000 total). Scoring MN cells by hand is both time-consuming and tedious, which is the primary reason why only 1000-2000 total cells (PCEs) are routinely scored for each sample. It is generally recognized that scoring larger numbers of cells would improve assay statistics and is desirable, but impractical with hand-scoring. In contrast, automated scoring methods can process large numbers of cells, thus improving statistical analysis. In order to accurately and quickly evaluate clastogenic activity, we have developed a flow cytometry based method of scoring micronucleated cells. One of the first steps in developing an automated assay is to demonstrate the ability of the method to resolve the cells of interest. In this case, micronucleated cells must be resolved from DNA-deficient red blood cells (RBCs). Since micronuclei are heterogeneous rare events which vary in both size and DNA content, we chose to use a more enriched and homogeneous biological model for optimizing the experimental variables of this assay, leading to high resolution of the rare cells. Experiments are described in which the murine malaria parasite, P. berghei, served as a micronucleus model and facilitated the development of an accurate flow cytometry based scoring method. This parasite resides in the red blood cell population and endows the cells with a homogeneous (genetically determined) DNA component in the micronucleus size range. The conditions developed with the malaria parasite are readily applied to the analysis of micronucleus events in blood samples.(ABSTRACT TRUNCATED AT 250 WORDS)

Arylmethanol and thiosemicarbazone influence of plasmodial macromolecular synthesis and cell stability

The influence of mefloquine and additional antimalarial drugs on (3H)adenosine uptake, macromolecular synthesis, and cell stability was determined in rodent red cells parasitized with Plasmodium berghei. High arylmethanol to cell ratios induced lysis, whereas inhibition of macromolecular synthesis occurred at lower drug/cell ratios. A 2-acetylpyridine thiosemicarbazone rapidly suppressed (3H)adenosine uptake, and also blocked macromolecular synthesis by parasitized cells.

Photoaffinity labelling of peptide hormone receptors

Photoreactive peptide derivatives for the labelling of hormone receptors are usually prepared by inserting a chemically stable aryl azide or nitroaryl azide into a specific site of the molecule, such as an alpha or omega amino or carboxyl group, or into the side-chain of an Arg, Cys, His, Trp or Tyr. With p-azidophenylalanine (Pap), a more or less isosteric replacement of Tyr or Phe can be achieved when other alterations would impair the biological activity of the hormone. Reversible attachment of photoreactive groups via S-S linkage to, e.g., SH-Trp makes it possible to release the covalently bound hormone from the receptor. This is an advantage when photolabelling is used for the isolation of receptors. Photoaffinity labelling of intact cell systems may reveal insights into dynamic aspects, such as receptor inactivation and turnover or the temporal involvement of second messengers, and may be particularly useful for the study of peptide action on target cells occurring only in small numbers. The Xenopus MSH-melanophore system which is stimulated irreversibly upon UV-irradiation of photoreactive alpha-MSH represents such an example.