Isodiospyrin as a novel human DNA topoisomerase I inhibitor

Isodiospyrin is a natural product from the plant Diospyros morrisiana, which consists of an asymmetrical 1,2-binaphthoquinone chromophore. Isodiospyrin exhibits cytotoxic activity to tumor cell lines but very little is known about its cellular target and mechanism of action. Unlike the prototypic human topoisomerase I (htopo I) poison camptothecin, isodiospyrin does not induce htopo I-DNA covalent complexes. However, isodiospyrin antagonizes camptothecin-induced, htopo I-mediated DNA cleavage. Binding analysis indicated that isodiospyrin binds htopo I but not DNA. These results suggest that isodiospyrin inhibits htopo I by direct binding to htopo I, which limits htopo I access to the DNA substrate. Furthermore, isodiospyrin exhibits strong inhibitory effect on the kinase activity of htopo I toward splicing factor 2/alternate splicing factor in the absence of DNA. Thus, these findings have important implications on naphthoquinone and its derivatives' cellular mode of actions, i.e. these novel DNA topoisomerase I inhibitors can prevent both DNA relaxation and kinase activities of htopo I.     

c-Myc overexpression sensitises colon cancer cells to camptothecin-induced apoptosis

The proto-oncogene c-Myc is overexpressed in 70% of colorectal tumours and can modulate proliferation and apoptosis after cytotoxic insult. Using an isogenic cell system, we demonstrate that c-Myc overexpression in colon carcinoma LoVo cells resulted in sensitisation to camptothecin-induced apoptosis, thus identifying c-Myc as a potential marker predicting response of colorectal tumour cells to camptothecin. Both camptothecin exposure and c-Myc overexpression in LoVo cells resulted in elevation of p53 protein levels, suggesting a role of p53 in the c-Myc-imposed sensitisation to the apoptotic effects of camptothecin. This was confirmed by the ability of PFT-alpha, a specific inhibitor of p53, to attenuate camptothecin-induced apoptosis. p53 can induce the expression of p21(Waf1/Cip1), an antiproliferative protein that can facilitate DNA repair and drug resistance. Importantly, although camptothecin treatment markedly increased p21(Waf1/Cip1) levels in parental LoVo cells, this effect was abrogated in c-Myc-overexpressing derivatives. Targeted inactivation of p21(Waf1/Cip1) in HCT116 colon cancer cells resulted in significantly increased levels of apoptosis following treatment with camptothecin, demonstrating the importance of p21(Waf1/Cip1) in the response to this agent. Finally, cDNA microarray analysis was used to identify genes that are modulated in expression by c-Myc upregulation that could serve as additional markers predicting response to camptothecin. Thirty-four sequences were altered in expression over four-fold in two isogenic c-Myc-overexpressing clones compared to parental LoVo cells. Moreover, the expression of 10 of these genes was confirmed to be significantly correlated with response to camptothecin in a panel of 30 colorectal cancer cell lines.     

喜树碱及其衍生物最新研究进展

喜树碱具有抗肿瘤活性,但毒副作用和水溶性差限制了它的使用,有必要对其进行结构上的修饰。该文总结了近年来喜树碱及其衍生物的合成与活性研究方面的最新进展。     

Phase I and pharmacokinetic study of Bay 38-3441, a camptothecin glycoconjugate, administered as a 30-minute infusion daily for five days every 3 weeks in patients with advanced solid malignancies

Bay 38-3441 is a camptothecin glycoconjugate which stabilizes the active lactone form of camptothecin and allows selective uptake into tumor cells. We conducted a phase I study of Bay 38-3441 administered as a 30-minute infusion daily for five consecutive days every 21 days. Thirty-one patients were enrolled at 8 dose levels. Most common nonhematologic side effects were diarrhea (29%), vomiting (19%), nausea (19%), lethargy (13%), and abdominal pain (10%). The main hematologic toxicity was prolonged neutropenia. Nine patients had a best response of stable disease with a median duration of 2.7 months (range: 2.3–20.6 months). The study was closed without reaching the maximum tolerated dose (MTD) due to excessive toxicity in a companion trial resulting in termination of development of this agent. Bay 38-3441 was well tolerated in this study with granulocytopenia as the main hematologic toxicity. This study showed that glycoconjugation is a feasible delivery technique for camptothecin.The study medication, Bay 43-9006 and a partial funding for the study were provided by Bayer Inc.     

Effects of the combination of camptothecin and doxorubicin or etoposide on rat glioma cells and camptothecin-resistant variants

From the rat C6 glioma cell line in culture, we selected camptothecin-resistant variants by growth in the presence of increasing amounts of this drug (C6(CPT10), C6(CPT50)and C6(CPT100), growing respectively with 10, 50 and 100 ng ml(-1)camptothecin). The degree of resistance to camptothecin ranged between 15-fold (C6(CPT10)) and 30-fold (C6(CPT50)and C6(CPT100)). The C6(CPT10)cell line presented a collateral sensitivity to etoposide (3.6-fold), while the C6(CPT50)and C6(CPT100)cell lines were cross-resistant to etoposide (1.8-fold) The resistant lines were characterised by a two-fold reduced content and catalytic activity of topoisomerase I, and C6(CPT50)and C6(CPT100)presented a significant increase in topoisomerase IIalpha content and catalytic activity and a marked overexpression of P-glycoprotein. We explored the cytotoxicity of combinations of a topoisomerase I inhibitor (camptothecin) and a topoisomerase II inhibitor (doxorubicin or etoposide) at several molar ratios, allowing the evaluation of their synergistic or antagonistic effects on cell survival using the median effect principle. The simultaneous combination of camptothecin and doxorubicin or etoposide was additive or antagonistic in C6 cells, slightly synergistic in the C6(CPT10)line and never more than additive in the C6(CPT50)and C6(CPT100)cell lines. The sequential combination of doxorubicin and camptothecin gave additivity in the order camptothecin --> doxorubicin and antagonism in the order doxorubicin --> camptothecin. Clinical protocols combining a topoisomerase I and a topoisomerase II inhibitor should be considered with caution because antagonistic effects have been observed with combinations of camptothecin and doxorubicin.     

从喜树叶中碱法提取喜树碱新工艺

目的探讨以喜树为原料提取喜树碱的工艺条件.方法通过均匀试验设计法.结果确定了以稀NaOH溶液为溶剂提取喜树碱的最佳工艺条件提取溶剂浓度为0.3%,提取时间为3 h,NaOH溶液用量1 6 mL/g原料·次.结论首次研究了以稀NaOH溶液为喜树碱提取溶剂,从很少被利用的喜树叶中提取喜树碱的工艺条件.结果表明喜树叶的喜树碱提取率达到0.1%以上,是一个较好的喜树碱提取原料.利用此方法提取喜树碱生产成本低、提取率高、防火等级低,是相对于乙醇提取更为优秀的喜树碱提取方法.     

喜树碱类药物传递系统的研究进展

目的对喜树碱类药物的一些特殊传递系统进行综述。方法通过文献检索,以脂质体、微球、聚合物载体等新型的传递系统为主,介绍近几年喜树碱类药物传递系统的研究进展。结果通过一些特殊的传递方法与策略,可以解决喜树碱类药物所存在的溶解度、稳定性、毒性和不良反应等问题。结论随着新的药物传递系统的不断成熟与发展,喜树碱类药物将是十分有潜力的一类抗肿瘤药物。     

5′-RS-1，5-二氧代-（5′-乙基-5′-羟基-2′H，5′H，6′1-6-氧代吡喃）-[3′，4′，f]．Δ^6（8）-四氢中氮茚的合成工艺改进

目的 改进喜树碱关键中间体5′-RS-，5-二氧代-（5′-乙基-5′-羟基-2′H，5′H，6′H-6-氧代吡喃）-[3′，4′，f]-△^6（8）-四氢中氮茚（1）的合成工艺。方法 以6-氰基-1，1-亚乙二氧基-7-（1′-乙氧羰基）丙基-5-氧代-△^6（8）-四氢中氮茚（2）为原料，经氢化和亚硝化、脱氮、混合金属催化氧化、环合及三氟乙酸脱保护反应得到目标产物。结果与结论 新工艺简化了操作、缩短了反应时间，总产率达到了72．4％。     

抑制生存传导路径可增加肿瘤细胞化疗敏感性

目的：研究抑制磷酸酰肌醇3激酶(PI3K)／Akt生存传导路径是否可增加肿瘤细胞对一些化疗药物的敏感性。方法：采用Akt亚型特异抑制剂结合多柔比星(阿霉素ADM)或喜树碱治疗各种肿瘤细胞系；检测细胞凋亡蛋白激酶3活性，来定量评估细胞凋亡程度；免疫沉淀 Werstern印迹法测定药物对磷酸化各类Akt亚型的抑制作用。结果：①各类Akt亚型抑制剂可阻断Akt1或Akt2蛋白序列上的第308位点苏氨酸(pAkt^308)和第473位点丝氨酸(pAkt^473)磷酸化，并表现出相应的Akt亚型抑制特异性；②单独抑制某一类Akt亚型并不足以增加肿瘤细胞对化疗药物的敏感性，只有同时抑制Akt1和Akt2才能增敏药物对肿瘤细胞的杀灭效应；③药物的增敏效应可能和肿瘤细胞内源性PTEN脱磷酸酶的表达有一定的关联。结论：临床应用化疗结合PI3K／Akt生存传导路径抑制剂应选择具有阻断2种Akt亚型功能的药物以达到最大的肿瘤杀灭效应。     

奥沙利铂联合羟基喜树碱和氟尿嘧啶及亚叶酸钙治疗晚期胃癌的临床研究

目的：观察以奥沙利铂（LOHP）、羟基喜树碱（HCPT）、氟尿嘧啶（5FU）及亚叶酸钙（LV）组成的HLOF方案和顺铂（DDP）、HCPT、5-FU及LV组成的HLPF方案治疗晚期胃癌的疗效与安全性。方法：61例患者随机分组，试验组32例给予HLOF方案化疗，L-OHP130mg／m^2，静脉滴入2h，d1；HCPT6mg／m^2，静脉滴入，d1～d3；5-FU500mg／m^2，静脉滴入．d1～d3；LV100mg／m^2，静脉滴入，d1～d3。对照组29例给予HLPF方案化疗，除用DDP替代L-OHP外余同对照组。DDP用法：30mg／m^2，静脉滴入，d1～d3。以上方案均每21～28d重复。每例至少完成2个周期化疗方可评价疗效。结果：试验组CR2例．PR17例，SD8例，PD5例，有效率为59．4％（19／32）；对照组PR12例．SD11例，PD6例，有效率为41．4％。两组总有效率差异无统计学意义，P〉0．05。不良反应HLOF组食欲下降、恶心、呕吐的发生率较对照纽低，P〈0．05；神经毒性发生率高于对照组。KPS评分HLOF组升高幅度高于对照，P〈0．05。两组疾病无进展时间（time to progress，TTP）及生存期比较，差异均无统计学意义，P〉0.05。结论：治疗晚期胃癌，两者均为有效、低毒的化疗方案。在改善生活质量和减轻消化道反应方面，HLOF优于HLPF方案。