細胞內DNA的拓樸狀態(topology).受topoisoerase所主宰 .
Topoisomerase 參與複製(replication)轉錄(transcription)重組(
recombination)及修復(repair)等DNA代謝中重要反應 . 喜樹精(
camptothecin)因為它能穩定topoisomerase與DNA所形成的共價化合物 ,
使DNA的缺口無法補齊 , 而造成細胞毒性(cytotoxicity), 所以被拿來作
為藉由有有效抑制topoisomerase I的抗癌藥物 . 本論文證實了兩大類有
地效topoisomerase I活性的抑制物 , 分別來自中藥波羅蜜的單離成分及
quinolone類的化學合成藥物 . 這些化和物對topoisomerase I佸性抑制
與否 , 是藉由檢測藥物是否會抑制真核細胞topoisomerase I調節DNA的
超螺旋狀態 , 這方法稱為topoisomerase I relaxation assay . 由於藥
物作用到DNA與topoisomerase 共價化何物上 , 使細胞堆積許多有缺口的
DNA與蛋白的化合物 ,這時候topoisomerase的存在反而造成細胞的毒性物
. 因DNA的斷裂 , 接著許多代謝也被迫庭止 , 最後造成細胞死亡(
apoptosis) . 已有報告指出camptothecin 會造成人類血癌細胞株HL-60
進行計畫性死亡 , 本論文篩選出的兩類藥物 , 也希望藉由一些細胞進行
有計畫性死亡的特徵 , 來觀察這些藥物對HL-60細胞株的毒性 ; 這些特
徵在本論文主要分成兩大類 , 分別是 : (1)當細胞進行有計畫性死亡時
由於活化細胞內endonuclaese , 而造成DNA小片段的斷裂 ,經藥物處理後
的細胞 , `可將萃取出來的DNA交由凝膠電泳分析出小片段的DNA .

In the cells , the topology of DNA is orchestrated by enzyme
known as topoisomerase Topoisomerases are involved in many
aspects of DNA metabolism such as replication ,transcription ,
recombination , and repair reactions . Camptothecin , which
stabolizes the covalent intermediate of topoisomerase I and DNA
is effective , by cytotoxicity , drug for cancer therapy . In
this study , two new kinds oftopoisomerase I inhibitor purified
from the Chinese herbs (Artocarpus heterophyllus ) and synthetic
quinolone derivatives have been demonstrated to be strong
topoisomerase inhibitors by using topoisomerase I relaxation
assay .Increasing the steady-state concentration of their
covalent DNA cleavage complex will convert topoisomerase into
physiological toxins that introducehigh levels of transient
protein-associated breaks in the genome of treatedcells .
Collision of DNA relication forks with cleavable complexes has
been proposed as a mechanism inducing cell death . We have known
that the topoisomerase I inhibitor camptothecin induced
apoptosis ( programmedcell death ) of cells of human
promyelogenous leukemia HL-60 cells .The two new kinds of
topoisomerase I inhibitors that we have identified in this study
, also can induce apoptosis of cell of human promyelogenous
leukemia HL-60 through the following cell features were focused
to characterize the mode cell : [a] Activation of an
endonuclease in apoptoticcells resulted in the formation of low
molecular weight DNA fragmentswhich were confirmed by agarose
gel electrophoresis . [b] Changes in cellular morphology of
apoptotic cells resulted in the early appearanceof shrunken
cells with vacuolated cytoplasma and regions of intensechromatin
staining around the nuclear periphery . By this study , we
hopeto identify the gene products which couple the stimulus of
programmed cancer cell death , and to determine intrinsic
cellular sensitivity( or resistance ) which will be important
targets for new types ofantitumor drugs .
In the cells , the topology of DNA is orchestrated by enzyme