No abstract

The P388 murine leukemia and P388/ADR, a subline expressing the multi-drug resistance (MDR) phenotype, were examined with regard to the role of MDR as a determinant of responsiveness to photodynamic therapy in vitro. Mesoporphyrin was used as a model substrate. We found no differences in porphyrin accumulation nor transport alterations associated with exposure of P388/ADR cells to the verapamil analog DMDP. There was a significant correlation between photodamage to mitochondria vs loss of cell viability in both cell lines, and LD50 sensitizer levels were not significantly different in P388 vs P388/ADR. P388/ADR cells were partly resistant to porphyrin-catalyzed photodamage to amino acid transport, but this result was not associated with differences in sensitizer localization, as indicated by fluorescence studies. Moreover, photodamage to membrane transport was not associated with loss of viability. These studies suggest that cells which express the MDR phenotype are unlikely to be cross-resistant to photodynamic therapy.

The Cbf5 protein of Saccharomyces cerevisiae was originally identified as a low-affinity centromeric DNA-binding protein, and chf5 mutants have a defect in rRNA synthesis. A closely related protein from mammals, NAP57, is a nucleolar protein that coimmunoprecipitates with the nucleolar phosphoprotein Nopp140. To study the function of this protein family in a higher eukaryote that is amenable to genetic approaches, the gene encoding a Drosophila melanogaster homolog, Nop60B, was identified. The predicted Drosophila protein shares a high degree of sequence identity over a 380-residue region with both the mammalian and yeast proteins, and shares several conserved motifs with the prokaryotic tRNA pseudouridine 55 synthases. Nop60B RNA is found at high levels in nurse cells and in the oocyte, and is present throughout development. Nop60B protein is localized primarily to the nucleolus of interphase cells, and is absent from the chromosomes during mitosis. Nop60B mutants were generated and shown to be homozygous lethal. The Drosophila gene can rescue the lethal phenotype of yeast chf5 mutations, showing that the function of this protein has been conserved from yeast to Drosophila.

Three canisters of semipermeable membrane devices (SPMDs), each containing five SPMDs, were deployed at three different locations on a transect across a small river removed from the impact of near-field point sources. Following a 62-day deployment, the masses of various polynuclear aromatic hydrocarbons (PAH) sequestered by each SPMD in each canister were determined. The compound-specific mean residues (ng/SPMD) obtained for the PAHs with pK(ow) values >4.4 showed statistically significant (alpha = 0.10) differences between the three deployment locations (canisters) ranging from approximately 10 to 160 ng/SPMD, corresponding to relative percent differences (RPDs) ranging from 10% to 54%. There were no statistically significant differences between the same three locations for the single PAH with a pK(ow) <4.4. A detailed discussion of how different (uncontrollable) environmental variables may have impacted the experimental results is provided to illustrate the uncertainties associated with interpreting the results from SPMD field deployments and highlight the need for some means of correcting for these impacts. The results from this work also illustrate the need to account for spatial variability in water column concentrations (i.e., sample heterogeneity) as part of any interpretation.