Topoisomerase inhibition by lucanthone, an adjuvant in radiation therapy.

PURPOSE: To determine whether lucanthone can inhibit human topoisomerases in vitro. METHODS AND MATERIALS: Lucanthone was incubated with human topoisomerases II and I together with their plasmid substrates, to determine if lucanthone interfered with the catalytic activities of topoisomerases and if it enhanced the formation of DNA strand breaks, as determined by agarose gel electrophoresis of the resultant plasmid forms. RESULTS: Incubation of the enzymes with lucanthone inhibited the catalytic activity of topoisomerases II and I. With topoisomerase II, it increased the abundance of DNA double strand breaks (cleavable complexes). CONCLUSION: Lucanthone, like actinomycin D, inhibited topoisomerases II and I. It may act to enhance the yield of DNA double strand breaks in cells through a mechanism of topoisomerase II inhibition.

Protein-protein interactions between the Escherichia coli single-stranded DNA-binding protein and exonuclease I.

It was demonstrated previously that a deoxyribophosphodiesterase (dRpase) activity is associated with the DNA repair enzyme exonuclease I, and that this activity is stimulated by the addition of the E. coli single-stranded DNA-binding protein (Ssb). This activity catalyzes the release of deoxyribose-phosphate groups at apurinic/apyrimidinic (AP) sites in the DNA that have been cleared by the action of an AP endonuclease. We have now used the yeast two-hybrid system to demonstrate that a protein-protein interaction occurs between exonuclease I and Ssb. When the E. coli ssb gene was fused in frame to the DNA-activating domain of the GAL4 transcriptional activator and the exonuclease I gene was fused in frame to the DNA-binding domain, a functional GAL4 transcriptional activator was produced as determined by growth of yeast on selective medium and the measurement of beta-galactosidase activity. We have also demonstrated that Ssb can stimulate the dRpase activity of exonuclease I using double-stranded bacteriophage M13 DNA containing several strand interruptions at incised AP sites. These results suggest that Ssb may be required for efficient base-excision repair in bacteria.

A content validity analysis of neoplastic items of the National Board of Medical Examiners Part II Examination.

As part of its evaluation of the Clinical Cancer Education Program (CCEP) at the Albert Einstein College of Medicine, the Office of Educational Research and Evaluation analyzed student performance on neoplastic items of the National Board of Medical Examiners (NBME) Examination Part II. The evaluation provided a successful application of the American Association for Cancer Education (AACE) coding schema for analysis of neoplastic items. Two examinations were analyzed in order to determine the frequency with which specific disease sites, treatment modalities, and question emphasis items appeared. With reference to disease site, the greatest number of questions on both examinations dealt with gynecological issues while the fewest dealt with lung and hematologic-related disease. A breakdown of questions into various treatment modalities indicated that of items that could be categorized, most dealt with surgical treatment, while other therapeutic modalities were given little or no emphasis. Looking at question emphases, the most frequently asked questions referred to diagnostic tests and stratagems, whereas the least amount of emphasis was placed on rehabilitative and psychosocial aspects of the disease. These findings corroborate those reported by Ruckdeschel and his associates and point out several limitations to the content validity of the neoplastic items on NBME Part II.

Deficient mitogen-induced virus plaque-forming cells in patients with localized cancer.

The virus plaque assay (VPA), an assay capable of enumerating mitogen- or antigen-sensitive T-lymphocytes in a given cell population, was applied to the study of mitogen responses of peripheral blood leukocytes (PBL) in 50 patients with localized, solid cancers and in 29 normal controls. Concanavalin A (Con A)-responsive virus plaque-forming cells (V-PFC) were significantly reduced in the patients as compared with those of the controls. PBL from 20 of the patients but only 2 of the controls failed to show significant increments in V-PFC over background when cultured in the presence of Con A. This deficient response was also present in the patients when phytohemagglutinin was used as the mitogenic agent. Mitogen-stimulated uptake of [3H]thymidine (TdR) in parallel cultures failed to show a statistically significant difference between the patients and the controls, though some patients showed diminished stimulation in this assay. The VPA thus appeared to detect a defect of T-lymphocyte function not found in the [3H]TdR incorporation assay.

The effect of radial radiotherapy on delayed hypersensitivity and the inflammatory response.

Delayed hypersensitivity to DNCB and the inflammatory response to croton oil wereevaluated in 144 and 121 patients respectively, prior ro and 3 to 6 months following curative radiotherapy. Eighty-one patients had in vitri lymphocyte transformation by PHA;59 (41%) were nonreactors to DNCB and 27 (22%) to croton oil; 29 of 59 (49%) initiallyreactive became anergic. Similiar improvement of the inflammatory response was obtained. Patients who became DNCB-reactive following radiotherapy had the same favorable prognosis as those who were initially reactive. Radiotherapy did not adversely affect either delayed hypersensitivity or the inflammatory response. There was a 50% decrease in PHA stimulation and lymphocyte count after treatment. No correlation was found between DNCB reactivity and lymphocyte transfermation prior to or following radiotherapy. The evaluation of the effect of radiotherapy on cell-mediated immunity depends on the tests used.