Comparison of the in vitro activities of quassinoids with activity against Plasmodium falciparum, anisomycin and some other inhibitors of eukaryotic protein synthesis.

Using the inhibition of incorporation of [3H]hypoxanthine as an index of viability of malaria parasites, it was shown that a chloroquine-sensitive strain of Plasmodium falciparum (T9-96) and a chloroquine-resistant strain (K1) did not differ in their sensitivities to the quassinoids ailanthinone, bruceantin and chaparrin. Similarly, there were no differences between the strains in their sensitivities to the protein synthesis inhibitors anisomycin, deacetylanisomycin, cephalotaxine, homoharringtonine, cycloheximide, puromycin and puromycin aminonucleoside. The IC50 values derived for ailanthinone and bruceantin, cycloheximide, homoharringtonine and puromycin were in the nanomolar range, whereas those for the anisomycins, cephalotaxine and the aminonucleoside of puromycin were micromolar or greater. Those drugs tested which contain an ester moiety (ailanthinone, bruceantin, anisomycin, homoharringtonine) were more active than the related drugs (chaparrin, deacetylanisomycin, cephalotaxine) that do not. Cross-resistance to inhibitors of protein synthesis appeared not to accompany resistance to chloroquine.

Transcripts of the multidrug resistance genes in chloroquine-sensitive and chloroquine-resistant Plasmodium falciparum.

Homologues of the mammalian multidrug resistance gene have been identified in isolates and clones of Plasmodium falciparum and designated pfmdr1 and pfmdr2. Mutations in pfmdr1 have been associated with chloroquine resistance but confirmation could not be obtained in a genetic cross. We have examined the copy number and expression of pfmdr1 and pfmdr2 in chloroquine-sensitive and -resistant P. falciparum and have found no relationship between the copy number of either gene and chloroquine resistance. However, a marked correlation was seen between levels of mRNA transcribed for each gene and chloroquine resistance. Two transcripts of pfmdr1 were detected, and in the asexual blood cycle an 8 kb transcript appeared first, followed by the appearance of a 7 kb species.

Construction and characterization of a highly stable human: rodent monochromosomal hybrid panel for genetic complementation and genome mapping studies.

Human:rodent somatic cell hybrids carrying a single, intact, selectable human chromosome are valuable both for functional somatic cell genetic analysis and genome mapping procedures. Here, we describe the construction and detailed molecular cytogenetic characterization of a panel of 23 stable hybrids, representing all 22 human autosomes plus the X-chromosome. Individual normal human chromosomes have been tagged with a selectable fusion gene (Hytk) introduced into the chromosome in a small (4.2 kbp) retroviral vector. Use of the Hytk marker permits both positive and negative ("in-out") selection to be applied to the human chromosome in any mammalian cell background. The panel includes 18 new hybrids isolated by direct microcell transfer from normal human diploid fibroblasts into mouse A9 cells.