尼妥珠单抗对耐多西紫杉醇人肺腺癌细胞株化疗敏感性的调变作用

目的　通过体内外实验研究人源化抗表皮生长因子受体（ＥＧＦＲ）单抗尼妥珠（ｈ-Ｒ３）对耐多西紫杉醇（ＤＴＸ）人肺腺癌细胞株（ＳＰＣ-Ａ１／ＤＴＸ）化疗敏感性的调变作用。方法　免疫组化法及流式细胞仪测定人肺腺癌细胞株ＳＰＣ-Ａ１和ＳＰＣ-Ａ１／ＤＴＸ肺腺癌细胞株表面ＥＧＦＲ的表达强度,突变富集液相芯片法检测其ＥＧＦＲ、Ｋ-Ｒａｓ和ＰＩ３ＫＣＡ基因的突变情况,流式细胞仪检测ｈ-Ｒ３对细胞周期的影响以及ｈ-Ｒ３联合ＤＴＸ对细胞凋亡的影响,ＭＴＴ法检测ｈ-Ｒ３与ＤＴＸ的联合指数（ＣＩ）,裸鼠ＳＰＣ-Ａ１／ＤＴＸ移植瘤模型观察联合组及单药组对裸鼠抑制瘤模型肿瘤的增殖情况并计算瘤重抑制率（ＴＷＩ）。结果　ＳＰＣ-Ａ１细胞株ＥＧＦＲ表达强度为（＋,２１.5３％）,ＳＰＣ-Ａ１／ＤＴＸ细胞株为（＋＋＋,９２.４７％）;ＳＰＣ-Ａ１／ＤＴＸ细胞株的ＰＩ３ＫＣＡ基因外显子２０突变,ＳＰＣ-Ａ１细胞株无突变。ｈ-Ｒ３作用２４ｈ后,ＳＰＣ-Ａ１／ＤＴＸ细胞Ｇ１ 期阻滞较ＳＰＣ-Ａ１细胞更显著（Ｐ＝０.０００２）;ｈ-Ｒ３及ＤＴＸ联合用药后ＳＰＣ-Ａ１／ＤＴＸ细胞株的凋亡率为（２４.７±０.５）％,明显高于ｈ Ｒ３单药组的（１４.５±０.１）％,而单用ＤＴＸ后的凋亡率无显著升高,ＳＰＣ-Ａ１细胞株单药组及联合组凋亡率均有升高（Ｐ＜０.０５）;１００μｇ／ｍｌ及２００μｇ／ｍｌｈ Ｒ３与ＤＴＸ联合对ＳＰＣ-Ａ１或ＳＰＣ-Ａ１／ＤＴＸ细胞株的增殖抑制具有协同作用;联合组对ＳＰＣ-Ａ１／ＤＴＸ肺腺癌荷瘤裸鼠的ＴＷＩ为７１.７％,高于ＤＴＸ组的５２.６％和ｈ-Ｒ３组的３６.９％。结论　ｈ-Ｒ３能明显增加耐ＤＴＸ的人肺腺癌细胞株化疗的敏感性,其机制可能为ｈ-Ｒ３具有Ｇ１期阻滞和逆转耐药细胞凋亡抵抗的作用,并且其疗效与耐药细胞较亲本细胞的ＥＧＦＲ表达增强有关,而耐药细胞的ＰＩ３ＫＣＡ基因突变对疗效的影响不显著。     

免疫导向药物B_（159）－Dex－EPI与B_（159）－Dex－ADR抗肿瘤活性研究

作者应用氧化葡聚糖Ｔ_（１０）作为交联剂，将抗Ｂ淋巴细胞白血病单抗Ｂ_（１５９）分别与抗癌药物表阿霉素（ＥＰＩ）和阿霉素（ＡＤＲ）连接，制成免疫导向药物Ｂ_（１５９）－Ｄｅｘ－ＥＰＩ和Ｂ_（１５９）－Ｄｅｘ－ＡＤＲ，Ｂ_（１５９）与ＥＰＩ或ＡＤＲ的克分子比均为１：１２～１４。经活细胞免疫荧光法和细胞ＥＬＩＳＡ法测定，免疫导向药物保持了抗体活性。ＭＴＴ试验证实，两种免疫导向药物均具有明显的选择性杀伤作用，对非靶细胞毒性小；两种免疫导向药物对靶细胞的杀伤作用明显强于游离药物和正常鼠抗体结合物；Ｂ_（１５９）－Ｄｅｘ－ＥＰＩ的靶细胞毒性作用强于Ｂ_（１５９）－Ｄｅｘ－ＡＤＲ。     

诺维本联合氟脲嘧啶加醛氢叶酸与联合表阿霉素加氨甲喋呤治疗晚期转移性乳腺癌的临床研究

目的：临床随机性研究诺维本（ＮＡＶＥＬＢＩＮＥ）联合氟脲嘧啶（５－ＦＵ）加醛氢叶酸（ＣＦ）方案（Ａ组）与联合表阿霉素（Ｅ－ＡＤＭ）加氨甲喋呤（ＭＴＸ）方案（Ｂ组）治疗晚期转移性乳腺癌的疗效与毒副反应。方法：入组晚期转移性乳腺癌４０例,临床完全随机分为Ａ组与Ｂ组。分别予相应联合化疗,至少两个疗程,疗效及毒性判定按照ＷＨＯ标准。结果：Ａ组ＣＲ１５％,ＰＲ４５％,ＣＲ＋ＰＲ６０％;Ｂ组ＣＲ２０％,ＰＲ２     

TGFα—PE对人肺腺癌细胞生长的抑制作用

目的：探讨基因重组转化生长因子α－绿脓杆菌外毒素融合蛋白（ＴＧＦα－ＦＥ４０,简称ＴＰ４０）对人肺腺癌细胞生长的导向抑制作用。方法：用免疫组化ＬＳＡＢ法检测人肺腺癌ＳＰＣ－Ａ－１细胞表皮生长因子受体（ＥＧＦＲ）的表达,用结晶紫染色法和＾３Ｈ－亮氨酸拓入法检测ＴＰ４０地ＳＰＣ－Ａ－１细胞生长及蛋白质合成的抑制,用过量ＥＧＦ竞争拮抗ＴＰ４０的细胞毒作用。结果：ＳＰＣ－Ａ－１细胞免疫组化显示出大量棕黄色     

C－erbB－2，人表皮生长因子及其受体在大肠癌中表达的意义

用ＡＢＣ免疫组化法测定２００例大肠癌组织中Ｃ－ｅｒｂＢ－２，人表皮生长因子（ｈＥＧＦ）及其受体（ＥＧＦＲ）。结果发现：１）Ｃ－ｅｒｂＢ－２，ｈＥＧＦ，ＥＧＦＲ在２００例大肠癌中阳性表达分别为３６％、４４％、４７％，三者共同阳性为１６．５％。２）ｈＥＧＦ，ＥＧＦＲ在大肠癌ＤｕｋｅｓＣ、Ｄ期，肿瘤＞２ｃｍ、低分化腺癌，有深度浸润和淋巴结转移者阳性率显著高于其它各型（Ｐ＜０．０１）。３）Ｃ－ｅｒｂＢ－２，ｈＥＧＦ和ＥＧＦＲ阳性病例存活率明显低于这些阴性病例（Ｐ＜０．０１）。结果表明，Ｃ－ｅｒｂＢ－２，ｈＥＧＦ和ＥＧＦＲ在大肠癌的侵袭性生长中起重要作用，ｈＥＧＦ和ＥＧＦＲ可作为大肠癌患者高度恶性的生物学指标。     

半乳糖基修饰的反义硫代寡核苷酸对肝癌多药耐药细胞株MDR_1基因过度表达的抑制作用

设计合成三种互补ＭＤＲ１ｍＲＮＡ的反义硫代寡核苷酸（ＡＳＯＤＮ），分别互补ＭＤＲ１ｍＲＮＡ序列起始区、含ＡＵＧ起始密码子区及针对Ｌｏｏｐ形成位点区的序列，作用于阿霉素（ＤＯＸ）诱导的肝癌多药耐药细胞株ＢＥＬ－７４０２／ＤＯＸ。经流式细胞分析及ＲＴ－ＰＣＲ的方法检测，发现三种ＡＳＯＤＮ均能不同程度地降低ＢＥＬ－７４０２／ＤＯＸ细胞膜表面Ｐ－ＧＰ含量；同时ＭＤＲ１ｍＲＮＡ的表达也有轻度降低，其中尤以互补ＭＤＲ１ｍＲ－ＮＡＬｏｏｐ形成位点的ＡＳＯＤＮ抑制作用最强。以导向配体Ｇａｌ１０－ＰＬＬ修饰此ＡＳＯＤＮ后，作用于ＢＥＬ－７４０２／ＤＯＸ细胞，发现与相同剂量未修饰ＡＳＯＤＮ比较，Ｐ－ＧＰ含量由７６．８％降至１９．８％；对ＡＤＭ的ＩＣ５０由１．２８μｇ／ｍｌ降至０．４２μｇ／ｍｌ。实验说明，半乳糖基修饰的互补ＭＤＲ１ｍＲＮＡＬｏｏｐ形成位点的ＡＳＯＤＮ能够明显降低肝癌多药耐药细胞膜表面Ｐ－ＧＰ的含量，并较大程度地逆转多药耐药细胞ＢＥＬ－７４０２／ＤＯＸ对化疗药物的耐受性。     

半乳糖基修饰的反义硫代寡核苷酸对肝癌多药耐药细胞株MD1基因过？…

设计合成三种互补ＭＤＲ１ ｍＲＮＡ的反义硫代寡核苷酸（ＡＳＯＤＮ），分别互补ＭＤＲ１ ｍＲＮＡ序列起始区，含ＡＵＧ起始密码子区及钱对Ｌｏｏｐ形成位点区的序列，作用于阿霉素（ＤＯＸ）地的肝癌多药耐药细胞株ＢＥＬ－７４０２／ＤＯＸ。经流式细胞分析及ＲＴ－ＰＣＲ的方法检测，发现三种ＡＳＯＤＮ均能不同程度地降低ＢＥＬ－７４０２／ＤＯＳ细胞膜表面Ｐ－ＧＰ含量；同时ＭＤＲ１ ｍＲＮＡ的表达也有轻度降低，其中尤     

C—erbB—2,人表皮生长因子及其受体在大肠癌中表达的意义

用ＡＢＣ免疫组化法测定２００例大肠癌组织中Ｃ－ｅｒｂＢ－２，人表皮生和茵子及其受体，结果发现：１）Ｃ－ｅｒｂＢ－２，ｈＥＧＦ，ＥＧＦＲ在２００例大肠癌中阳性表达分别为３６％、４４％、４７％，三者共同阳性为１６．５％。２）ｈＥＧＦ，ＥＧＦＲ在大肠癌ＤｕｋｅｓＣ、Ｄ期，肿瘤＞２ｃｍ，低分化腺癌，有深度浸润和淋巴结转移者阳性率显著高于其它各型（Ｐ＜０．０１）。３）Ｃ－ｅｒｂＢ－２，ｈＥＧＦ和ＥＧＦＲ阳性     

5—氟脲嘧啶对耐顺铂人肺腺癌细胞A549^DDP的程序依赖性逆转作用

用耐顺铂（ＣＤＤＰ）人肺腺癌细胞系Ａ５４９ＤＤＰ作模型，研究了５－ＦＵ对ＣＤＤＰ耐药的程序依赖性逆转作用。５－氟脲嘧啶（５－ＦＵ）预处理Ａ５４９ＤＤＰ２４ｈ后立即给予ＣＤＤＰ，ＣＤＤＰ细胞毒性增加３．９倍；５－ＦＵ预处理Ａ５４９ＤＤＰ后间隔２４或４８ｈ再给予ＣＤＤＰ，其细胞毒性分别增加２０倍和２５０倍，甚至较亲代细胞Ａ５４９更为敏感；如先给ＣＤＤＰ后给５－ＦＵ则细胞毒性仅增加１．８倍。５－ＦＵ对亲代细胞亦有类似效应但细胞毒性增加程度明显低于耐药细胞。５－ＦＵ预处理后间隔２４，４８ｈ，细胞内ＧＳＨ含量逐渐降低，与细胞毒性逐渐增加相一致。如用ＢＳＯ耗竭Ａ５４９ＤＤＰ细胞内ＧＳＨ，ＣＤＤＰ细胞毒性增加６．４倍，仅能部分逆转ＣＤＤＰ耐药。５－ＦＵ明显抑制ＭＲＰ的表达，但对ＧＳＴπ的表达无影响。在５－ＦＵ预处理后的无药间隔时间内，给予无毒浓度的三苯氧胺则有明显的协同效应。结论：程序性给予５－ＦＵ通过降低细胞内ＧＳＨ含量和抑制ＭＲＰ的表达能完全逆转ＣＤＤＰ耐药     

铬,汞,镉,镍四种重金属化合物对FL／P4501A1细胞酶活性的影响

利用不同浓度的重金属化合物溴化汞、三氯化铬、硫酸镉、氯化镍处理人羊膜ＦＬ／Ｐ４５０１Ａ１细胞，其半数抑制浓度（ＩＣ５０，ｍｇ／ｍｌ）分别为６．０２６０，３７．５２１３，２４．５４９１和４５．３８４５。结果表明：不同的重金属化合物对ＦＬ／Ｐ４５０１Ａ１细胞的毒性相差很大，溴化汞和硫酸镉的细胞毒性较大。ＦＬ／Ｐ４５０１Ａ１细胞带有Ｐ４５０１Ａ１基因，该基因产物为乙氧基异吩恶唑Ｏ－去乙基酶（ＥＲＯＤ）。     

Cytotoxicity of a transferrin-adriamycin conjugate to anthracycline-resistant cells.

Conjugates of adriamycin coupled to transferrin by glutaraldehyde are cytotoxic to human promyelocytic (HL-60) and erythroleukemic (K562) cells. Growth inhibition of adriamycin-sensitive cells, as evaluated by thymidine incorporation and the MTT-assay, was higher for conjugates than for free adriamycin. The cytotoxicity toward adriamycin-resistant K562 and HL-60 cells was 3-fold and more than 10-fold higher, respectively, for the transferrin-adriamycin conjugate than for the free drug. The effect of the conjugate was dependent on its adriamycin content, i.e., on its conjugation number.     

In vitro cytotoxicity of the conjugate adriamycin with anti-sarcoma monoclonal antibody 19-24.

Monoclonal antibody (MoAb) 19-24, which recognizes a cell surface sarcoma-associated antigen p102, was linked via a biotin-avidin-biotin bridge to adriamycin (ADR). The molar ratios of ADR: total protein ranged from 2 to 7.5. Significant differences were not observed between the binding ability of the ADR-MoAb conjugate and of the unconjugated MoAb 19-24 to fresh sarcoma tissue membranes. The ADR-MoAb conjugate also retained the ability to compete with MoAb 19-24 for binding to sarcoma-associated antigen p102. In vitro cytotoxicity studies using human fibrosarcoma cells showed that the ADR-MoAb conjugate maintained 40% of the efficacy of free ADR. However, the conjugate was not cytotoxic to p102 antigen negative rat fibrosarcoma SP-24 cells. These data support the suggestion that MoAb-drug conjugates might be helpful in developing highly specific antisarcoma therapeutic agents.     

三唑类抗真菌药联合多柔比星逆转白血病细胞株耐药性研究

目的探讨三唑类抗真菌药伊曲康唑、氟康唑联合多柔比星逆转白血病细胞株耐药的作用。方法伊曲康唑、氟康唑或PSC833（阳性对照）分别联合多柔比星与人类慢性粒细胞白血病红白血病耐多柔比星细胞株K562／ADR共同培养,采用CCK-8法检测K562／ADR细胞增殖,流式细胞术检测K562／ADR细胞内多柔比星平均荧光强度,蛋白印迹法检测K562／ADR细胞7H2AX的表达。结果1μg／ml伊曲康唑及0．5μg／mlPSC833可将K562／ADR对多柔比星的J岛从38．30μg／ml降至8．59μg／ml和24．64μg／ml,且呈剂量依赖性。1Ng／ml伊曲康唑或0．5μg／mlPSC833联合多柔比星作用K562／ADR细胞3h和6h后,细胞内多柔比星平均荧光强度相对单加多柔比星组增加了1．54倍（3h）、1．50倍（6h）或5．97倍（3h）、5．83倍（6h）。伊曲康唑或PSC833联合多柔比星可显著增加K562／ADR细胞7H2AX的表达。结论伊曲康唑通过提高细胞内多柔比星浓度及协同增强细胞DNA的损伤,恢复K562／ADR对多柔比星的敏感性,而氟康唑则无作用。     

Indomethacin overcomes doxorubicin resistance by decreasing intracellular content of glutathione and its conjugates with decreasing expression of γ-glutamylcysteine synthetase via promoter activity in doxorubicin-resistant leukemia cells

Drug resistance continues to be a serious problem in cancer therapy. We investigated whether indomethacin, which inhibits cyclooxygenases, is able to overcome doxorubicin resistance in K562/ADR leukemia cells. Indomethacin at 10 μM increased the cytotoxicity of doxorubicin and vincristine in K562/ADR cells. Intracellular glutathione content was elevated in K562/ADR cells. Indomethacin treatment decreased glutathione content and glutathione-conjugates in K562/ADR cells. Increased expression of γ-glutamylcysteine synthetase (γ-GCS) was observed in K562/ADR cells, but this expression was decreased by indomethacin treatment. The activity of the γ-GCS promoter from K562/ADR cells decreased after indomethacin treatment in MDA231 cells. These data strongly suggest that the cyclooxygenase inhibitor indomethacin increases the cytotoxicity of doxorubicin by decreasing the intracellular contents of glutathione and its conjugates with decreasing expression of γ-GCS by inhibiting γ-GCS promoter activity.     

Indomethacin overcomes doxorubicin resistance with inhibiting multi-drug resistance protein 1 (MRP1)

Drug resistance continues to be a serious problem in cancer therapy. We investigated whether indomethacin, which inhibited cyclooxygenases, would overcome doxorubicin resistance in K562/ADR leukemia cells. Indomethacin at 10 μM increased the cytotoxicity of doxorubicin, as well as vincristine in K562/ADR. Both multi-drug resistant protein1 (MRP1) and P-glycoprotein were overexpressed in K562/ADR cells when compared with K562 parent cells (K562/P). Expression of MRP1 mRNA and protein, but not P-glycoprotein, was significantly decreased in K562/ADR cells after indomethacin treatment. Indomethacin treatment increased 5(6)-carboxyfluorescein diacetate (CFDA) efflux, as well as decreased accumulation in K562/ADR cells. The activity of the MRP1 promoter decreased after indomethacin treatment in Hela cells. These data strongly suggest that the cyclooxygenase inhibitor, indomethacin, increased the cytotoxicity of doxorubicin with decreasing expression of MRP1 through inhibition of MRP1 promoter activity.     

Dexrazoxane has no impact on sensitivity of childhood leukemic blasts to daunorubicin.

Dexrazoxane (DEX) prevents the formation of free radical, lipid peroxidation and cardiotoxicity caused by anthracyclines. Due to a concern about its possible interference with anthracyclin cytotoxicity, the in vitro effect of DEX on daunorubicin (DNR) cytotoxicity, cell cycle and induction of apoptosis by annexin-V was investigated. The sensitivity to DEX, DNR and their combination was tested by the MTT assay in human promyelocytic leukemia HL-60, the erythroid blast crisis CML K562 cell lines and in 45 children with ALL and AML. Cell cycle analysis and annexin-V expression were performed by flow cytometry. It has been observed that DEX itself weakly, but significantly caused cytotoxicity in both cell lines and in patient samples, especially in initial ALL samples. DEX sensitized K562 and HL60, but not patient samples, to cytotoxicity of DNR. The percentage of necrotic/apoptotic cells, as detected in cell cycle analysis and annexin V staining, was higher after exposure to DEX +/- DNR, when compared to respective samples not treated with DEX, in both cell lines but not in patient samples. Expression of annexin V induced by DEX in both cell lines was enlarged, regardless of the presence of DNR. This difference was not observed in patient samples, however, the number of cells expressing annexin V was higher after exposure to DEX +/- DNR in comparison to respective samples not treated with DEX. In conclusion, it seems that DEX possibly has no impact on the sensitivity of childhood leukemic blasts to DNR, however, has weak cytotoxic properties itself.     

Mechanisms involved in the development of adriamycin resistance in human leukemic cells

We have developed three adriamycin (ADR)-resistant K562 sublines with different degrees of resistance. These sublines show a decreased accumulation and an increased efflux of ADR in proportion to the degree of resistance. Two membrane proteins (mol. wt 170,000 and 230,000) reactive with monoclonal antibody against P-glycoprotein were highly expressed in both the K562/ADR200 and the K562/ADR500 subline. Less resistant K562/ADR80 cells contained only small amounts of mol. wt 230,000 protein. Thus, the level of P-glycoprotein expression was not proportionate to the degree of ADR efflux. Verapamil treatment could not completely reverse ADR resistance. No significant change of glutathione-s-transferase activity nor in the level of DNA topoisomerase II was detected in resistant sublines. In our sublines it seems that P-glycoprotein is one of the mechanisms for resistance, but additional mechanisms may be involved.     

Enhancement of adriamycin cytotoxicity in sensitive and resistant sublines of human tumor cells by calcium antagonists

The effect of the calcium antagonists cepharanthine and verapamil on adriamycin-induced cytotoxicity against sensitive (K 562 and Ov 2780) and resistant (K 562/ADM and AD 10) sublines of human tumor cells was evaluated. Nontoxic concentrations of cepharanthine moderately enhanced adriamycin cytotoxicity against sensitive sublines (2.1-2.5 fold). A significant enhancement (13-26 fold) of drug cytotoxicity was observed when resistant cells were treated with a combination of cepharanthine and adriamycin. The calcium influx blocker verapamil (used for comparison) also enhanced adriamycin cytotoxicity, although to a lesser extent. The fact that enhancement was 6-10 fold greater in resistant then in sensitive cells, as well as the loss of biphasic properties of adriamycin on dose-response curves after combined treatment, indicate that cepharanthine may play a role in overcoming drug resistance in some tumor cells.     

Modulation of doxorubicin resistance in a doxorubicin-resistant human leukaemia cell by an immunoliposome targeting transferring receptor.

Using a doxorubicin-resistant subline (K562/ADM) of human leukaemia K562 cells (Tsuruo et al, 1986), the effect of immunoliposomes that targeted a cellular transferrin receptor (TFR) was examined by neutralization of doxorubicin (DOX) resistance. OKT9-CIL, prepared by conjugation of DOX-encapsulated liposome with an anti-TFR monoclonal antibody, OKT9 (Aisenberg and Wilkes, 1980), showed similar binding to both K562 and K562/ADM. Although an 80-fold higher sensitivity to free DOX on cell growth inhibition in K562 than in K562/ADM was found, the difference was clearly diminished after OKT9-CIL treatment through the increased sensitivity of K562/ADM. The cellular DOX level 30 min after the exposure of free DOX was 45-fold lower in K562/ADM than in K562, whereas nearly equivalent DOX levels were detected in K562 and K562/ADM after OKT9-CIL treatment. In addition, DOX in K562/ADM in the free DOX treatment was efficiently excreted by 54% within 120 min of incubation, whereas almost all DOX supplied by OKT9-CIL remained uncleared. Fluorescence microscopic observation showed that OKT9-CIL was internalized into juxtanuclear vesicles in K562/ADM cells. These results suggest that OKT9-CIL has a potency to accumulate DOX, resulting in augmentation of DOX cytotoxicity in DOX-resistant tumour cells.     

Natural killer cell activity and autologous tumor killing activity in cancer patients: overlapping involvement of effector cells as determined in two-target conjugate cytotoxicity assay

The relationship between natural killer (NK) cell activity and autologous tumor killing activity was examined in patients with carcinomatous pleural effusions (PE) by means of a two-target conjugate cytotoxicity assay. Enrichment of large granular lymphocyte(s) (LGL) by discontinuous Percoll gradient centrifugation resulted in an augmentation of cytotoxicity against both K562 cells and tumor cells freshly isolated from PE of the same patients in a 4-hour 51Cr release cytotoxicity assay. At the single-cell level, the LGL-enriched fraction contained an increased number of effector cells that bound to autologous tumor cells and to K562 cells, as well as an increased frequency of cells cytotoxic to these target cells. In the two-target conjugate cytotoxicity assay, a single lymphocyte in the LGL population simultaneously bound to both a fluorescein-labeled K562 cell and a nonfluorescent autologous tumor cell. A significant number of lymphocytes in these mixed two-target conjugates lysed both autologous tumor cells and K562 cells after 6 hours' incubation, although overall lysis of K562 cells was higher than that of autologous tumor cells. These results indicate that a single LGL is involved in the lysis of both autologous tumor cells and K562 cells and thus provide direct evidence of involvement of subsets of NK cells in autologous tumor cell killing.