Sadao Nakane

Efficient induction of chromosome-type aberrations by topoisomerase II inhibitors closely associated with stabilization of the cleavable complex in cultured fibroblastic cells

Eukaryotic topoisomerase II (Topo-II) inhibitors such as etoposide, adriamycin and mitoxantrone, which commonly stabilize the cleavable complex of the enzyme and DNA, have been found to efficiently induce chromosome-type aberrations (mainly breaks and exchanges) in cultured Chinese hamster lung fibroblastic cells (CHL cells). To clarify whether the induction of chromosome-type aberrations is mediated by stabilization of the cleavable complex, the present study investigated (1) the correlation between the induction of chromosome-type aberrations and the amount of cleavable complex formed; and (2) the ATP dependence of the Topo-II inhibitor-induced chromosome-type aberrations due to the ATP requirement of cleavable complex formation by Topo-II. First, in cells treated with the Topo-II inhibitors, (etoposide, adriamycin) and aclarubicin, an antagonist of the inhibitor of cleavable complex formation, the frequency of chromosome-type aberrations decreased dose-dependently with aclarubicin, in contrast to an increase of chromatid-type aberrations. The formation of the cleavable complex was further established by a proteinase K/SDS precipitation assay for cleaved double-strand DNA in a cell-free system and in CHL cells. Results from both experiments showed that aclarubicin caused a dose-dependent suppression of the accumulation of the cleavable complex induced by etoposide, which corresponded particularly well to the reduction of chromosome-type aberrations in etoposide-treated cells. In ATP-depleted cells simultaneously treated with etoposide and dinitrophenol (DNP), chromosome-type aberrations were reduced as compared with DNP-untreated cells, in contrast to an increase of chromatid exchanges in the cells. This means that etoposide-induced chromosome-type aberrations in ATP-depleted cells may be attributable to incompleteness of Topo-II activities to form DNA double-strand breaks. The present findings indicate that the stabilization of the cleavable complex on Topo-II is closely associated with the induction of chromosome-type aberrations.

Effect of several drugs on the development of stress ulcer and seepage of a pigment from the stomach of rats

本研究において，自律神経薬ほか諸種薬物の潰瘍形成と胃液分泌およびPSB漏出量におよぼす影響を検討し，以下の結果を得た．1)本実験で，phenoxybenzamineを除き，ストレス潰瘍抑制作用を示した薬物は，潰瘍抑制量で胃液分泌減少とpH上昇作用を示した．このことは，ストレス潰瘍抑制には胃液分泌の抑制が重要な要因であることを示唆するものと考えられる．2)atropineは，潰瘍抑制量において，ストレスによるPSB量減少に対し，少くとも増強作用を示さなかった．また，propranolol，DCIおよびchlorpromazineは，ストレスによるPSB量減少に対し，むしろ阻止的であった．これより，ストレスによる胃粘膜血流の阻止ないし抑制が抗潰瘍作用の一因となると考えられる．