氧化型低密度脂蛋白诱导主动脉和心内膜内皮细胞凋亡

目的：研究氧化型低密度脂蛋白（ｏｘ－ＬＤＬ）诱导血管和心内膜内皮细胞凋亡。方法：用超速离心法分离健康人血浆低密度脂蛋白（ＬＤＬ），以ＣｕＳＯ４１０μｍｏｌ．Ｌ＾－１氧化，观察ｏｘ－ＬＤＬ对培养新生小牛主动脉内皮细胞及心内膜细胞的损伤作用，琼脂糖凝胶电泳和Ｈｏｅｃｈｓｔ３３２５８荧光密度法定性与定量分析ＤＮＡ降解，结果：ｏｘ－ＬＤＬ诱导血管内皮细胞及以内膜细胞典型凋亡形态学改变，ＤＮＡ降解呈时间和剂     

Oxidized low-density lipoproteins induce apoptosis in aortic and endocardial endothelial cells

目的：研究氧化型低密度脂蛋白（ｏｘＬＤＬ）诱导血管和心内膜内皮细胞凋亡．方法：用超速离心法分离健康人血浆低密度脂蛋白（ＬＤＬ），以ＣｕＳＯ４１０μｍｏｌ·Ｌ－１氧化．观察ｏｘＬＤＬ对培养新生小牛主动脉内皮细胞及心内膜细胞的损伤作用．琼脂糖凝胶电泳和Ｈｏｅｃｈｓｔ３３２５８荧光密度法定性与定量分析ＤＮＡ降解．结果：ｏｘＬＤＬ诱导血管内皮细胞及心内膜细胞典型凋亡形态学改变，ＤＮＡ降解呈时间和剂量依赖性．环己米特和硫酸葡聚糖对此作用无影响．ＢＨＴ２０μｍｏｌ·Ｌ－１可取消ＤＮＡ降解．溶血性磷脂酰胆碱５０μｍｏｌ·Ｌ－１无诱导凋亡作用．ｏｘＬＤＬ诱导的ＤＮＡ降解可被依他酸取消．结论：ｏｘＬＤＬ诱导血管内皮细胞及心内膜细胞凋亡．     

Oxidized low-density lipoproteins induce apoptosis in vascular smooth muscle cells

目的：研究氧化型低密度脂蛋白（ｏｘＬＤＬ）诱导血管平滑肌细胞凋亡．方法：梯度超速离心分离血浆ＬＤＬ，以ＣｕＳＯ４１０μｍｏｌ·Ｌ－１氧化，观察ｏｘＬＤＬ对培养兔胸主动脉平滑肌细胞的损伤作用．Ｈｏｅｃｈｓｔ３３２５８荧光染色观察形态学改变，抽提细胞ＤＮＡ进行琼脂糖凝胶电泳．结果：ｏｘＬＤＬ３００ｍｇ·Ｌ－１与ＶＳＭＣ共温育２４ｈ诱导典型的凋亡形态学变化和ＤＮＡ降解，但天然低密度脂蛋白无此作用．当ｏｘＬＤＬ为４００ｍｇ·Ｌ－１或温育时间延至４８ｈ，上述变化更加明显．硫酸葡聚糖２０ｍｇ·Ｌ－１和ＢＨＴ５０μｍｏｌ·Ｌ－１对此作用无影响．ＬＰＣ１２５μｍｏｌ·Ｌ－１无诱导凋亡作用．结论：ｏｘＬＤＬ诱导血管平滑肌细胞凋亡，氧自由基和ＬＰＣ不参与这一过程．     

1-(2,6-二甲基苯氧基)-2-(3,4-二甲氧基苯乙氨基)丙烷盐酸盐对内皮素促血管平滑肌细胞增殖及癌基因表达的影响

采用内皮素－１（ＥＴ－１０．１μｍｏｌ·Ｌ－１）建立培养的血管平滑肌细胞增殖模型，用［３Ｈ］胸腺嘧啶核苷（［３Ｈ］ＴｄＲ）参入法，流式细胞术，免疫细胞化学及Ｎｏｒｔｈｅｒｎｂｌｏｔ方法，观察了１－（２，６－二甲基苯氧基）－２－（３，４－二甲氧基苯乙氨基）丙烷盐酸盐（ＤＤＰＨ０．１μｍｏｌ·Ｌ－１）对血管平滑肌细胞增殖的作用及对原癌基因及抑癌基因的影响．结果发现：ＤＤＰＨ能逆转ＥＴ－１所致［３Ｈ］ＴｄＲ参入量增多，阻止血管平滑肌细胞由静止期（Ｇ０／Ｇ１期）进入ＤＮＡ合成期（Ｓ期）和有丝分裂期（Ｇ２／Ｍ期），并能逆转ＥＴ－１引起的ｃ－ｆｏｓ，ｃ－ｍｙｃ，ｃ－ｓｉｓ原癌基因相关抗原及ｍＲＮＡ表达增强，Ｐ５３抑癌基因相关抗原及ｍＲＮＡ表达减弱．提示ＤＤＰＨ能抑制血管平滑肌细胞增殖，与癌基因调控的分子生物学机理有关．     

Bradykinin B_2receptor antagonist icatibant reduces inhibitory effect of captopril on growth of cultured neonatal rat cardiomyocytes

目的：观察内源性激肽对培养新生大鼠心肌细胞生长的影响及其机制．方法：［３Ｈ］尿嘧啶和［３Ｈ］亮氨酸参入法检测ＲＮＡ和蛋白质合成速率，Ｎｏｒｔｈｅｒｎ杂交检测ｃｍｙｃ和ｃｆｏｓｍＲＮＡ表达．结果：卡托普利１００μｍｏｌ·Ｌ－１孵育４８ｈ显著抑制［３Ｈ］尿嘧啶和［３Ｈ］亮氨酸参入，孵育２ｈ明显抑制ｃｍｙｃ和ｃｆｏｓ基因表达．ＡｎｇⅡ１μｍｏｌ·Ｌ－１处理４８ｈ刺激ＲＮＡ和蛋白质合成，１ｈ可上调ｃｍｙｃ和ｃｆｏｓ表达．Ｃａｐ１００μｍｏｌ·Ｌ－１部分抑制ＡｎｇⅡ上述作用．缓激肽Ｂ２受体拮抗剂Ｉｃａ（０１－１０μｍｏｌ·Ｌ－１）剂量依赖性阻断Ｃａｐ作用．结论：内源性激肽经ＢＫＢ２受体介导对心肌细胞的生长起负调节作用     

铅的肾细胞毒性及锌的保护作用

观察了醋酸铅１，５，１０，５０，１００μｍｏｌ／Ｌ对培养的ＬＬＣ－ＰＫ１细胞存活率、细胞内钾离子和细胞上清液中ＬＤＨ和γ－ＧＴ的影响。结果５０μｍｏｌ／Ｌ和１００μｍｏｌ／Ｌ铅作用３２小时细胞的存活率已明显减少；５μｍｏｌ／Ｌ铅处理１小时，细胞上清液中ＬＤＨ明显升高，并在１～１０μｍｏｌ／Ｌ范围内存在明显的时间－效应、剂量－效应关系；５０μｍｏｌ／Ｌ铅处理半小时，就出现细胞内钾离子明显减少；１～１００μｍｏｌ／Ｌ铅处理４小时和８小时，γ－ＧＴ已明显增加，并存在剂量－效应关系。加锌２０μｍｏｌ／Ｌ可使细胞的存活率增加，细胞内钾离子和γ－ＧＴ、ＬＤＨ的漏出明显减少。上述结果说明，醋酸铅作用于ＬＬＣ－ｐＫ１细胞，首先引起细胞膜对钾离子通透性的改变，其次为ＬＤＨ，当明显损伤细胞膜时可使膜结合酶γ－ＧＴ脱落，上述指标在一定范围内存在时间－效应和剂量－效应关系。２０μｍｏｌ／Ｌ锌在一定程度上可保护细胞膜，拮抗铅对肾小管细胞ＬＬＣ－ｐＫ１的损伤作用。     

Inhibitory effects of nifedipine on DNA and protein synthesis in cultured cardiac nonmyocytes of neonatal rats

观察硝苯地平（Ｎｉｆｅｄｉｐｉｎｅ，Ｎｉｆ）对非心肌细胞生长和增殖的抑制作用．方法：以培养乳鼠非心肌细胞作为模型，用［３Ｈ］胸腺嘧啶核苷结合及［３Ｈ］亮氨酸结合的方法．结果：在血管紧张素Ⅱ存在的情况下，Ｎｉｆ１μｍｏｌ·Ｌ－１作用细胞７２ｈ，细胞的总蛋白及细胞数目明显减少．测得血管紧张素Ⅱ１，１０，１００，１０００ｎｍｏｌ·Ｌ－１在４８ｈ内，增加ＤＮＡ合成及蛋白合成．Ｎｉｆ１－１０μｍｏｌ·Ｌ－１均能够减少１００ｎｍｏｌ·Ｌ－１血管紧张素Ⅱ诱导的细胞ＤＮＡ合成及蛋白合成．结论：Ｎｉｆ可以直接抑制非心肌细胞的生长，该种作用与其抑制心肌肥厚有关．     

c－k－ras反义寡核苷酸抑制HCe8693细胞生长及p21~（ras）表达的序列特异性

本文采用逆转录－聚合酶链式反应（ＲＴ－ＰＣＲ），并结合ＰＣＲ产物直接测序法，证明人大肠癌细胞系ＨＲ８３４８和ＨＣｅ８６９３的ｋ－ｒａｓｃＤＮＡ片段（第３～８３密码子）中存在第１２密码子ＧＧＴ→ＧＡＴ突变，未发现其它突变或ＲＮＡ剪接异常．用分别与野生型和上述突变型ｋ－ｒａｓ第９～１５密码子互补的１８聚硫代磷酸型寡核苷酸（两者仅存在一个碱基差别）及随机设计的对照寡核苷酸（终浓度为６μｍｏｌ·Ｌ－１），发现与突变型ｋ－ｒａｓ互补的寡核苷酸能抑制ＨＣｅ８６９３细胞生长并有ｐ２１ｒａｓ蛋白表达量的抑制；而与野生型ｋ－ｒａｓ互补的寡核苷酸及随机合成的对照寡核苷酸对之无明显抑制作用，说明ｃ－ｋ－ｒａｓ反义寡核苷酸对ＨＣｅ８６９３细胞生长和ｐ２１ｒａｓ蛋白合成的抑制作用存在明显的核苷酸序列特异性．     

酪氨酸相关肽的合成及抗孕酮生成活性

利用固相法合成了二十个含羟基氨基酸的小肽。其中，以０．５ｍｏｌ·Ｌ－１二甲二氯硅烷／１．５ｍｏｌ·Ｌ－１苯酚／ＤＣＭ＊为脱除Ｂｏｃ试剂，以ＴＦＭＳＡ为切除树脂试剂。经Ｃ－１８反相柱纯化后，全部产物均通过氨基酸分析要求。体外黄体细胞分泌孕酮实验表明有八个肽化物ＧｌｙＴｙｒＡｌａＬｙｓ，（ＳａｒＳｅｒ）２Ｌｙｓ及其申酯，ＴｙｒＬｙｓ，ＨｉｓＴｙｒ－ＮＨ２，ＴｈｒＰｒｏＴｙｒＬｙｓ－ＮＨ２，ＴｙｒＴｈｒＰｒｏＡｒｇＬｙｓ，ＡｓｐＨｉｓＰｒｏＴｈｒ－ＰｈｅＬｙｓ显示较强的抑制ｈＣＧ致孕酮分泌的活性，而且前三个肽还能显著抑制基础孕酮的分泌，相反，ＧｌｙＳｅｒＴｙｒ能刺激基础孕酮的分泌。目前尚未建立合理的结构一活性关系。     

放线菌素D不能抑制α-双炔失碳酯诱导的白血病K562细胞凋亡

目的：研究放线菌素Ｄ（ＡｃｔＤ）对α－双炔失碳酯（α－ａｎｏｒｄｒｉｎ，ＡＮＯ）诱导的人白血病Ｋ５６２细胞凋亡的影响。方法：用光学显微镜观察细胞形态学变化；用流式细胞仪、琼脂糖凝胶电泳分别检测ＤＮＡ含量和ＤＮＡ断裂。结果：ＡＮＯ５０μｍｏｌ·Ｌ－１处理人白血病Ｋ５６２细胞２４ｈ引起大约１０％Ｋ５６２细胞产生凋亡。同时加入ＲＮＡ合成抑制剂ＡｃｔＤ０．００５μｍｏｌ·Ｌ－１不能抑制ＡＮＯ诱导的凋亡，相反地，ＡｃｔＤ加强ＡＮＯ的这一作用，使凋亡细胞从１０％上升到２０％。ＡｃｔＤ０．５μｍｏｌ·Ｌ－１本身可诱导约３２％的Ｋ５６２细胞凋亡。Ｓ期细胞对ＡＮＯ诱导的凋亡较敏感，而ＡｃｔＤ则较易诱导Ｓ期和Ｇ２－Ｍ期细胞凋亡。结论：ＡＮＯ诱导的Ｋ５６２细胞凋亡不依赖于新的ＲＮＡ合成。     

Modulation of topoisomerase II catalytic activity by DNA minor groove binding agents distamycin, Hoechst 33258, and 4',6-diamidine-2-phenylindole

The effects of distamycin, Hoechst 33258, and 4',6-diamidine-2-phenylindole (DAPI) on the catalytic activity of topoisomerase II from L1210 cells were determined. These compounds were used as model agents capable of AT-specific binding in the minor groove of DNA while producing no profound long-range alterations to the DNA structure. Two types of reactions catalyzed by topoisomerase II were examined, relaxation of supercoiled DNA and decatenation of highly catenated DNA. Distamycin at low concentrations (0.2-2 microM) substantially stimulated relaxation of supercoiled pBR322 DNA. Higher drug levels (25-50 microM) resulted in a potent inhibition of relaxation. At the stimulatory concentrations of distamycin, only completely relaxed reaction products were observed, as in the absence of the drug. The onset of inhibition (caused by 5-10 microM distamycin) was accompanied by the appearance of partially relaxed intermediates. Similar inhibition of relaxation was observed for Hoechst 33258 and DAPI but, unlike distamycin, these agents produced only marginal stimulation of relaxation when added in low noninhibitory concentrations. Another reaction of topoisomerase II, decatenation of catenated kinetoplast DNA, was also inhibited by distamycin, Hoechst 33258, and DAPI at concentrations similar to those inhibiting the relaxation reaction. This study demonstrates that agents binding to the minor groove of DNA represent a new class of drugs interfering with topoisomerase II and provides possibilities for modulation of this important enzyme.     

Effect of minor groove binding drugs on mammalian topoisomerase I activity

Three minor groove binding drugs, distamycin A, bisbenzimide (Hoechst 33258) and 4',6-diamidino-2-phenylindole (DAPI), were examined for their abilities to modulate the activity of topoisomerase I purified from L1210 cells. At 0.5 and 1.0 microM, distamycin stimulated topoisomerase I relaxation of supercoiled DNA by 38 and 13%, respectively, while increasing the drug concentration above 2.0 microM resulted in inhibition. Inhibition was reversible. Complete relaxation could be achieved even in the presence of inhibitory concentrations of distamycin if the incubation time with topoisomerase I was increased from 7.5 to 120 min. The velocity of topoisomerase I mediated relaxation was reduced by 2 microM distamycin at DNA levels ranging from 350 to 2000 ng/reaction. Hoechst 33258 and DAPI inhibited topoisomerase I relaxation in a concentration-dependent manner. Hoechst 33258 and distamycin were equivalent in their abilities to inhibit topoisomerase I, whereas DAPI had a lesser effect (e.g. relaxation was reduced by 50% with 2.7 microM distamycin and 2.8 microM Hoechst 33258 compared to 5 microM DAPI). This study suggests that ligand binding in the minor groove can be a factor in the regulation of topoisomerase I activity.     

顺铂联合姜黄素诱导胃癌细胞凋亡的研究

目的：研究应用顺铂联合姜黄素对诱导胃癌细胞HGC27凋亡的影响及机制。方法：用CCK8法检测单独或联合使用不同剂量顺铂或/和姜黄素对胃癌细胞HGC27增殖的影响;用Hochest33258染色检测联合应用顺铂和姜黄素诱导胃癌细胞HGC27凋亡的发生率。用Western blot检测细胞凋亡相关分子PARP1蛋白剪切体和DNA损伤蛋白p-γH2AX的表达变化。结果：单用顺铂可以呈剂量依赖性地促进HGC27细胞凋亡。5μmol·L-1姜黄素对HGC27细胞增殖无明显作用,10μmol·L-1姜黄素反而轻微促进HGC27细胞增殖。20、40、80μmol·L-1姜黄素对HGC27细胞的增殖抑制率分别为10.97%、15.15%、32.93%。分析联合用药组：5μmol·L-1姜黄素联合顺铂组反而促进HGC27细胞生长;10μmol·L-1姜黄素联合不同剂量顺铂和单用顺铂组比较,组间抑制率没有统计学差异（P>0.05）。20μmol·L-1姜黄素联合4、6μmol·L-1顺铂有明显的促进细胞的凋亡作用,抑制率分别为70.68%、87.30%。 Hochest33258染色结果显示,联合用药组细胞凋亡小体和坏死细胞明显增多。 Western blot结果显示,在联合用药组HGC27细胞PARP1剪切体蛋白和p-γH2AX蛋白表达明显增加。结论：顺铂联合姜黄素可以促进胃癌细胞HGC27的凋亡,机制是姜黄素可以加重顺铂引起的细胞DNA双链损伤。     

Biphasic effect of aspirin on apoptosis of bovine vascular endothelial cells and its molecular mechanism

AIM: To investigate the effect of aspirin on the apoptosis of cultured bovine aortic endothelial cells (BAEC) and the signal pathways involved in this process. METHODS: BAEC were cultured and passaged in Dulbecco's modified Eagle's medium culture medium. Morphologic changes and quantification of apoptotic cells were determined using fluorescence microscope after staining the cells with Hoechst 33258. Cell viability was measured by 3-[4,5-dimethylthiazol-2-yl]-2,5- diphenyltetrazolium bromide (MTT) method. DNA fragmentation was visualized by agarose gel electrophoresis. Phospho-p38 mitogen-activated protein kinase (MAPK) expression was detected by Western blotting. RESULTS: Aspirin at low concentrations from 1X10( -10) mol/L to 1X10( -8) mol/L decreased the apoptosis and p38 MAPK phosphorylation induced by H2O2 in BAEC, while high doses of aspirin (1X10( -7)-1X10( -4) mol/L) induced typical apoptotic changes in BAEC and stimulated the expression of phospho-p38 MAPK in a concentration-dependent manner. SB203580, a specific p38 MAPK inhibitor, blocked such effects. CONCLUSION: Aspirin exhibits a biphasic effect on the apoptosis in BAEC, reducing apoptosis at low concentration and inducing apoptosis at high concentration. p38 MAPK may be an important signal molecule mediating the effects of aspirin.     

Synthesis, DNA binding, topoisomerase inhibition and cytotoxic properties of 2-chloroethylnitrosourea derivatives of hoechst 33258

A number of novel 2-chloroethylnitrosourea derivatives of Hoechst 33258 were synthesized and examined for cytotoxicity in breast cancer cell cultures and for inhibition of topoisomerases I and II. Evaluation of the cytotoxicity of these compounds employing a MTT assay and inhibition of [3H]thymidine incorporation into DNA in both MDA-MB-231 and MCF-7 breast cancer cells demonstrated that these compounds were more active than Hoechst 33258. The DNA-binding ability of these compounds was evaluated by an ultrafiltration method using calf thymus DNA, poly(dA-dT)2 and poly(dG-dC)2, indicated that these compounds as well as Hoechst 33258 well interact with AT base pair compared with GC pair. Binding studies indicate that these compounds bind more tightly to double-stranded DNA than the parent compound Hoechst 33258. The degree to which these compounds inhibited cell growth breast cancer cells was generally consistent with their relative DNA binding affinity. Mechanistic studies revealed that these compounds act as topoisomerase I (topo I) or topoisomerase II (topo II) inhibitors in plasmid relaxation assays.     

四嗪二甲酰胺抑制肝癌细胞株HepG2增殖并诱导细胞凋亡的研究

目的观察四嗪二甲酰胺(ZGDHu-1)体外抑制肝癌细胞株HepG2增殖并诱导细胞凋亡作用。方法将不同浓度的ZGDHu-1与HepG2细胞在体外培养,用台盼蓝染色、MTT法、5′-溴-2′脱氧尿苷(B rdu)-ELISA法观察ZGDHu-1对HepG2细胞增殖的抑制作用;用细胞形态学、DNA凝胶电泳、DNA含量及细胞周期分析、Annexin-V/PI双标记、Ho-echst33258荧光染色和ELISA法测定DNA片段等技术检测细胞凋亡。结果ZGDHu-1能抑制HepG2细胞增殖和活力,呈现作用时间和剂量的量效关系。HepG2细胞与ZG-DHu-1作用后,大部分细胞阻滞于G2-M期;出现典型的细胞形态改变,DNA片断化,亚G1峰检出并增加,Annexin V+/PI-表达升高,细胞内DNA片段含量增加,Hoechst33258荧光染色后出现凋亡细胞的特征性改变等均证实ZGDHu-1能诱导HepG2细胞凋亡。结论ZGDHu-1能抑制HepG2细胞增殖,并可诱导其细胞凋亡。     

Vasodilation Effects of RGD Containing Peptides and De rivatives

已经证实纤维蛋白分子内两个区域内的氨基酸序列可以介导纤维蛋白与ＧＰＩｂ／Ｉ┐Ｉａ受体的结合。除单克隆抗体外，用合成的含ＲＧＤ和ＡＰＬＲＶ的小分子多肽可以封闭ＧＰＩｂ／Ｉ┐Ｉａ的这种结合功能，我们的初步研究发现，ＲＧＤＳ除具有抑制血小板聚集和抗血栓形成的作用外，还显示舒血管作用。为了证实ＲＧＤＳ相关多肽的舒血管作用，研究了ＲＧＤＦ，ＡＰＬＲＶ，ＡＰＬＲＶＲＧＤＳ，ＡＰＬＲＶＲＧＤＦ，在体外用ＮＥ预处理大鼠的动脉肌条后观察了上述合成多肽的舒血管作用，检测了三种剂量（１０┐５ｍｏｌ／Ｌ，１０┐６ｍｏｌ／Ｌ，１０┐７ｍｏｌ／Ｌ）下收缩的肌条舒张的程度。     

Synthesis,DNA-binding activity and cytotoxicity of carbamate derivatives of Hoechst 33258 in breast cancer MCF-7 cells

A series of carbamate derivatives of Hoechst 33258 was prepared as potential anticancer agents. These new compounds (1-4) were readily prepared in good yields by addition of chloroethyl, bromoethyl, chloropropyl or 4-(chloromethyl)phenyl isocyanates to Hoechst 33258. Their cytotoxic activity was evaluated on human breast cancer MCF-7. Compounds 1-4 were more cytotoxic than Hoechst 33258. In particular derivative 4, the most active of the series, is up to 3 times more potent than Hoechst 33258. The DNA-binding ability of these compounds was evaluated by an ultrafiltration method using calf thymus DNA. These data show that in broad terms the cytotoxic potency of 1-4 in cultured breast cancer MCF-7 cells increases, in accord with their increases in DNA affinity, as shown by the binding constant values.     

Molecular recognition between ligands and nucleic acids: DNA binding characteristics of analogues of Hoechst 33258 designed to exhibit altered base and sequence recognition.

The DNA binding characteristics of new analogues (2-8) of Hoechst 33258 (1), containing pyridine and benzoxazole units and designed for altered base specificity, were evaluated using UV, fluorescence, and circular dichroism studies. Like Hoechst 33258 the new analogues also bind through the minor groove of B-DNA in a nonintercalative fashion. The interaction of the compounds with poly(dA-dT) is salt independent. The studies with poly(dA-dT), ct DNA, and poly(dG-dC) indicated a decrease in the relative binding strength of the new analogues to DNAs compared with the parent molecule, Hoechst 33258. Compounds 5 and 7 showed acceptance of GC bases adjacent to AT base pairs. None of the compounds studied exhibited affinity for A-DNA, double-stranded RNA, or Z-DNA. Structure-DNA binding relationships of the new analogues compared with their parent molecule, Hoechst 33258, are discussed.     

Effects of minor groove binding drugs on camptothecin-induced DNA lesions in L1210 nuclei.

Topoisomerase I inhibition detected in mammalian cells can be correlated with reduced tumor growth. Camptothecin specifically inhibits topoisomerase I by stabilization of a covalently linked DNA-enzyme complex and associated DNA single-strand breaks. Whether perturbations in nuclear DNA structure can alter camptothecin-induced DNA damage was examined using the non-intercalative DNA minor groove binders distamycin, Hoechst 33258 and DAPI (4',6-diamidino-2-phenylindole). L1210 nuclei were treated with camptothecin alone or in the presence of single minor groove binders. DNA-protein crosslinks and single-strand breaks were determined using potassium-sodium dodecyl sulfate precipitation and alkaline elution respectively. Distamycin produced a dose-dependent decrease in DNA-protein crosslinks and strand breaks. This effect was reduced if nuclei were treated with camptothecin prior to distamycin addition. Distamycin was unable to reverse lesions once induced or to prevent repair of damage upon camptothecin removal. Hoechst 33258 and DAPI also decreased camptothecin-induced DNA damage. The order of inhibitory potency was: distamycin greater than Hoechst greater than DAPI. This order corresponded to the molecular weights as well as to the size of the nucleotide binding sites of the drugs. Identifying agents which alter such DNA lesions should provide better understanding of the chemotherapeutic activity of camptothecin as well as help elucidate new leads for drug combinations of improved therapeutic benefit.