考布他汀A4类肿瘤血管破坏剂的研究进展

肿瘤血管破坏剂(VDA)是一类靶向肿瘤血管的抗肿瘤药物,能够快速、有选择地引发肿瘤组织内部既成血管的塌陷,阻断血液供应,从而引发肿瘤组织缺血性坏死。因此,VDA在治疗实体瘤方面具有很大的应用前景。其中,考布他汀A₄(CA4)疗效较好,但同时毒性较大。在寻找更特异性的VDA过程中,研究者合成了一系列CA4的类似物。本文分析了这些CA4类似物的结构,指出二芳基桥链的顺式构型为其特点,而且这些化合物与微管蛋白上的秋水仙碱作用位点结合,抑制微管蛋白的聚合。与传统抗肿瘤药物不同的是,CA4类VDA的抗肿瘤作用主要是通过选择性破坏肿瘤组织的血管系统实现的。同时,本文介绍了CA4类VDA的典型药物、影响CA4类VDA药效的肿瘤因素和宿主因素,以及为增强疗效和降低毒性作用而进行的联合用药情况。虽然CA4类VDA具有很大的应用前景,但目前还存在一些缺点,因而有必要继续寻找高效低毒的VDA,同时寻找可靠的生物标志物来指导VDA的临床用药也很有必要。     

联合包载Combretastatin A-4和阿霉素的长循环脂质体的体外体内初步研究

目的制备一种具有程序释药功能的联合包载抗肿瘤药物阿霉素(doxorubicin,DOX)和新生血管抑制剂(combretastatin A-4,CA-4)的新型长循环脂质体并进行体内药动学评价。方法以卵磷脂、胆固醇和聚乙二醇磷脂衍生物(1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-polyethylene gly-col,DSPE-PEG)为载体材料,采用薄膜分散法和硫酸铵梯度法分步包载CA-4和DOX制备得到脂质体。通过单因素考察,筛选最佳处方和制备工艺,并评价其体外释放情况。采用正常大鼠考察该制剂在静脉注射后的药动学行为。结果 m(卵磷脂)∶m(胆固醇)∶m(DSPE-PEG)为85∶10∶5、m(药)∶m(脂材)为1∶20、水化脂材浓度为50 mmol.L-1时,CA-4的包封率最高(>85%),DOX的包封率也在95%以上,平均粒径小于80 nm。体外释放结果表明联合包载DOX和CA-4的脂质体在pH7.4磷酸盐介质中可以快速释放CA-4,而DOX释放相对较慢。体内药动学实验结果表明,脂质体包载可明显增加CA-4的体内循环时间,但CA-4的联用并未对DOX体内药动学行为产生明显干扰。结论联合包载CA-4和DOX的脂质体可有效地实现程序释药,并延长药物体内循环时间,将可能成为肿瘤治疗的新策略。     

微管蛋白抑制剂Combretastatin A-4类似物的研究进展

微管蛋白在细胞生长、维持形态、信号传导及有丝分裂等过程中,均起着重要的作用。微管蛋白抑制剂是近年来热门的抗肿瘤药物。Combretastatin A-4(CA-4)从南非灌木柳树皮Combretum caffrum树干中提取分离得到的二苯乙烯类化合物,是目前已知微管蛋白抑制剂中活性最强的化合物之一,但是也存在着众多缺陷。近年来围绕提高CA-4水溶性、保持顺式构型等衍生物的设计研究成为了热点。本文就CA-4的结构改造及类似物设计的研究进展进行综述。     

Synthesis and antiprotozoal activity of 1,2,3,4-tetrahydro-2-thioxopyrimidine analogs of combretastatin A-4

Eighteen 1,2,3,4-tetrahydro-2-thioxopyrimidine analogs (5a?Cj, 6a?Ce, and 7a?Cc) of combretastatin A-4 were synthesized with the objective of discovering compounds capable of controlling the growth of Trypanosoma?lewisii, Leishmania?tarantole, Plasmodium?falciparum, and Giardia?lamblia. Even though the target compounds demonstrated differential cytotoxicity against mammalian cancer cells, with IC₅₀ values ranging from 0.5 to >100???M, the range of activity against Trypanosoma, Leishmania, and Plasmodium, and to a good extent for Giardia, was narrow. The IC₅₀ values of ??active?? compounds against the parasites ranged from about 10???? to slightly greater than 50???M. Specifically, compounds 5a, 5g, 5h, 6c, 7a, and 7c were not cytotoxic against mammalian cancer cells (IC₅₀?>?100???M) but showed good activity against the parasites, except Giardia (e.g., compounds 6c and 7a), suggesting that these compounds may act in a similar mechanism in parasites. Compounds 5f and 6b were previously shown to promote microtubule depolymerization in mammalian cells.     

Combretastatin A-4及其类似物构效关系研究进展

Combretastatin A-4(CA-4)是一个天然的秋水仙碱结合位点抑制剂,其突出的生物活性引起人们的高度关注,近年来,不断有结构多样的类似物被发现。这些类似物主要是针对CA-4的A环、B环和顺式双键的结构修饰,其中,以用单原子或环状结构替代顺式双键进而保持A/B环具有合适的空间距离和角度为主。本文对CA-4及其类似物构效关系的研究进行简单概述。     

In vitro and in vivo phase II metabolism of combretastatin A-4: Evidence for the formation of a sulphate conjugate metabolite

1. Combretastatin A-4 (CA-4), is a natural compound with a potent tubulin polymerization and cell growth inhibitor properties. For these reasons CA-4 is one of the most potent anti-vascular agents that shows strong cytotoxicity against a variety of human cancer cells, including multi-drug-resistant cancer cell lines. In order to complete the knowledge of metabolic fate of CA-4, the in vitro and in vivo phase II metabolism was investigated.

2. Both in incubation with rat and human liver S9 preparation in the presence of 39-phosphoadenosine-5´-phosphosulfate (PAPS) as a cofactor the formation of a previously no reported sulphate metabolite was demonstrated through liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) data and comparison with a synthetic reference sample.

3. In incubation of CA-4 using rat and human liver microsomes, the formation of CA-4 glucuronide was observed and chromatographic and mass spectral properties of the metabolite were achieved and compared with those of a synthetic reference sample.

4. Incubation of CA-4 with rat and human liver S9 preparation in the presence of uridine-5´-diphosphoglucuronic acid trisodium salt (UDPGA) and an β-nicotinamide adenine dinucleotide phosphate, reduced form (NADPH)-regenerating system as cofactors resulted in the formation of glucuronides arising from phase I CA-4 metabolites.

5. When CA-4 was administered intraperitoneally to rat at a dose of 30 mg kg^?1, both glucuronide and sulphate metabolites were observed in LC-ESI-MS-MS chromatograms and their mass spectral data were identical to those obtained from synthetic standards.

     

Potent, orally active heterocycle-based combretastatin A-4 analogues: synthesis, structure-activity relationship, pharmacokinetics, and in vivo antitumor activity evaluation

The synthesis and structure-activity relationship study of a series of compounds with heterocycles in place of the cis double bond in combretastatin A-4 (CA-4) are described. Substituted tosylmethyl isocyanides were found to be the key intermediates in construction of the heterocycles. Cytotoxicities of the heterocycle-based CA-4 analogues were evaluated against NCI-H460 and HCT-15 cancer cell lines. 3-Amino-4-methoxyphenyl and N-methyl-indol-5-yl were the best replacements for the 3-hydroxy-4-methoxyphenyl in CA-4. 4,5-Disubstituted imidazole was found to be the best for the replacement of the cis double bond in CA-4. Medicinal chemistry efforts led to the discovery of compounds 24h and 25f that were found to be 32 and 82% bioavailable, respectively, in rat. Evaluation of 24h and 25f against murine M5076 reticulum sarcoma in mice revealed that both compounds were orally efficacious with an increase in life span of 38.5 and 40.5%, respectively.     

Fluoride induces vascular contraction through activation of RhoA/Rho kinase pathway in isolated rat aortas

We hypothesized that fluoride induces vascular contraction through activation of the RhoA/Rho kinase pathway in isolated rat aortas. Rat aortic rings were mounted in organ baths and contracted with sodium fluoride (NaF). We measured the amount of GTP-RhoA as well as vascular tension. We also determined the level of phosphorylation of the myosin light chain (MLC(20)), myosin phosphatase targeting subunit 1 (MYPT1) and PKC-potentiated inhibitory protein for heterotrimeric MLCP of 17kDa (CPI17). In both physiological salt solution and Ca(2+)-free solution, NaF increased vascular tension and MLC(20) phosphorylation in dose-dependent manners. NaF increased not only phosphorylation level of MYPT1(Thr855) and CPI17(Thr38), but also the amount of GTP-RhoA. Both H1152 and Y27632, inhibitors of Rho kinase, but not Ro31-8220, an inhibitor of PKC, attenuated NaF-induced contraction and phosphorylation level of MLC(20), MYPT1(Thr855) and CPI17(Thr38). In conclusion, fluoride induces vascular contraction through activation of the RhoA/Rho kinase pathway.     

Evaluation of combretastatin A-4 prodrug in a non-Hodgkin's lymphoma xenograft model: preclinical efficacy

Combretastatin A-4 prodrug (CA4P) is a new antitubulin agent currently in phase I/II clinical trials against solid tumors. We have previously reported on the in vitro activity of CA4P against a panel of malignant human B-lymphoid cell lines. In this study, we investigated the antitumor and the antiangiogenic activity of CA4P in our diffuse large cell lymphoma WSU-DLCL2-SCID mouse model. WSU-DLCL2 cells (10(7)) were injected s.c. into 5-week-old female ICR-SCID mice. Tumor-bearing mice were treated at the CA4P maximum tolerated dose (MTD) of 800 mg/kg in different dose/schedules. CA4P showed significant antitumor activity against this lymphoma model. Best results were seen when MTD was given in two and four divided doses (400 and 200 mg/kg, respectively). CA4P given in four divided doses (4 x 200 mg/kg) showed a log10 kill of 1.01, T/C of 11.7% and T-C of 12 days. Immunohistochemical staining using anti-CD31 antibody after 6, 24, 48 and 120 h treatment revealed a significant decrease in the number of tumor blood vessels after 24 h (about 80%). Only the periphery of treated tumors revealed the presence of blood vessels. Morphological examination of the tumors after tetrachrome staining showed a necrotic center in tumors of CA4P-treated animals. New blood vessel formation was noted to emerge in tumor tissues as early as 48 h following a single dose of CA4P. The G2/M arrest observed in vitro was not detected in vivo indicating predominance of the antiangiogenic effects with regard to antitumor efficacy in vivo. We conclude that CA4P has antiangiogenic activity in this lymphoma model and the use of this agent should be explored clinically in the treatment of non-Hodgkin's lymphoma.     

The role of protein kinase C activation and the vascular complications of diabetes

Diabetes mellitus is a chronic disease caused by inherited and/or acquired deficiency in production of insulin by the pancreas, and by resistance to insulin's effects. Such a deficiency results in increased concentrations of glucose and other metabolites in the blood, which in turn damages many of the body's systems, in particular the eyes, kidneys, nerves, heart and blood vessels. There are two major types of diabetes mellitus: Type 1 diabetes (insulin-dependent diabetes, IDDM or juvenile onset diabetes) and Type 2 diabetes (non-insulin-dependent diabetes, NIDDM or adult-onset). Chronic hyperglycemia is a major initiator of diabetic micro- and cardiovascular complications, such as retinopathy, neuropathy and nephropathy. Several hyperglycemia-induced mechanisms may induce vascular dysfunctions, which include increased polyol pathway flux, altered cellular redox state, increased formation of diacylglycerol (DAG) and the subsequent activation of protein kinase C (PKC) isoforms and accelerated non-enzymatic formation of advanced glycated end products. It is likely that each of these mechanisms may contribute to the known pathophysiologic features of diabetic complications. Others and we have shown that activation of the DAG-PKC pathway is associated with many vascular abnormalities in the retinal, renal, neural and cardiovascular tissues in diabetes mellitus. DAG-PKC pathway affects cardiovascular function in many ways, such as the regulation of endothelial permeability, vasoconstriction, extracellular matrix (ECM) synthesis/turnover, cell growth, angiogenesis, cytokine activation and leucocyte adhesion, to name a few. Increased DAG levels and PKC activity, especially alpha, beta1/2 and delta isoforms in retina, aorta, heart, renal glomeruli and circulating macrophages have been reported in diabetes. Increased PKC activation have been associated with changes in blood flow, basement membrane thickening, extracellular matrix expansion, increases in vascular permeability, abnormal angiogenesis, excessive apoptosis and changes in enzymatic activity alterations such as Na(+)-K(+)-ATPase, cPLA(2), PI3Kinase and MAP kinase. Inhibition of PKC, especially the beta1/2 isoform has been reported to prevent or normalize many vascular abnormalities in the tissues described above. Clinical studies have shown that ruboxistaurin, a PKCbeta isoform selective inhibitor, normalize endothelial dysfunction, renal glomerular filtration rate and prevented loss of visual acuity in diabetic patients. Thus, PKC activation involving several isoforms is likely to be responsible for some of the pathologies in diabetic retinopathy, nephropathy and cardiovascular disease. PKC isoform selective inhibitors are likely new therapeutics, which can delay the onset or stop the progression of diabetic vascular disease with very little side effects.     

Biological potential and structure-activity relationships of most recently developed vascular disrupting agents: an overview of new derivatives of natural combretastatin a-4

Tumor blood vessels are an important emerging target for anti-cancer therapy. The antimitotic agent combretastatin A-4 (CA-4), a cis-stilbene natural product isolated from the South African tree Combretum caffrum Kuntze, is the lead compound of a new class of anti-cancer drugs that target tumor vasculature. CA-4 inhibits tubulin polymerization by interacting at the colchicine binding site on tubulin. This alters the morphology of endothelial cells and causes vascular shutdown and regression of tumor vasculature. Some tubulin-binding vascular-disrupting agents (VDAs) are currently in clinical trials for cancer therapy. As a consequence of the potential favorable applications of these compounds, several analogs projected to induce rapid and selective vascular shutdown in tumors have been synthesized during the last few years. Many of these molecules have already been tested for their effects on tubulin polymerization as well as for their antiproliferative activity and other biological properties, and possible mechanisms of action have been investigated. The aim of the present review is to offer an overview of most recently developed combretastatin derivatives, focusing on biological effects exerted by these compounds. The published data about new analogs are presented and compared, and a detailed investigation of structure-activity relationships is described.     

Thromboxane prostanoid receptor activation impairs endothelial nitric oxide-dependent vasorelaxations: The role of Rho kinase

Activation of thromboxane prostanoid (TP) receptors causes potent vasoconstriction, which contributes to increased vascular tone and blood pressure. The present study examined the hypothesis that stimulation of TP receptor impaired endothelial nitric oxide-mediated vasorelaxation via a Rho kinase-dependent mechanism. The common carotid arteries of Sprague-Dawley rats were isolated and suspended in myograph for measurement of changes in isometric tension. The production of nitric oxide in primary cultured aortic endothelial cells was assayed with an imaging technique and phosphorylated levels of endothelial NOS were determined by Western blot analysis. 9,11-dideoxy-11α,9α-epoxy-methanoprostaglandin F_2α (U46619) inhibited isoprenaline-induced relaxations in rings with or without endothelium. Treatment with Rho kinase inhibitors, Y27632 (2 μM) or HA 1077 (10 μM) prevented the effect of U46619 only in rings with endothelium while protein kinase C inhibitors were without effect. Rho kinase inhibitors did not affect isoprenaline-induced relaxations in endothelium-intact rings treated with L-NAME or 1H-[1,2,4]oxadizolo[4,3-a]quinoxalin-1-one (ODQ). Isoprenaline stimulated rises in nitric oxide (NO) production in cultured rat endothelial cells. The increased NO production was inhibited by U46619 (100 nM) and this effect was prevented by treatment with Y27632 but unaffected by the absence of extracellular calcium ions. U46619 attenuated isoprenaline-stimulated phosphorylation of eNOS, which was sensitive to inhibition by Y27632 and HA 1077. U46619-mediated effects were abolished by TP receptor antagonist, S18886 and the TP receptor was present in endothelial cells. The present results demonstrate that Rho kinase activation is likely to be the primary mechanism that underlies the U46619-stimulated TP-receptor-mediated inhibition of endothelial NO production and subsequent endothelium-dependent relaxations to isoprenaline.     

In vitro metabolism study of combretastatin A-4 in rat and human liver microsomes.

The phase I biotransformation of combretastatin A-4 (CA-4) 1, a potent tubulin polymerization inhibitor with antivascular and antitumoral properties, was studied using rat and human liver subcellular fractions. The metabolites were separated by high-performance liquid chromatography and detected with simultaneous UV and electrospray ionization (ESI) mass spectrometry. The assignment of metabolite structures was based on ESI-tandem mass spectrometry experiments, and it was confirmed by comparison with reference samples obtained by synthesis. O-Demethylation and aromatic hydroxylation are the two major phase I biotransformation pathways, the latter being regioselective for phenyl ring B of 1. Indeed, incubation with rat and human microsomal fractions led to the formation of a number of metabolites, eight of which were identified. The regioselectivity of microsomal oxidation was also demonstrated by the lack of metabolites arising from stilbenic double bond epoxidation. Alongside the oxidative metabolism, Z-E isomerization during in vitro study was also observed, contributing to the complexity of the metabolite pattern. Moreover, when 1 was incubated with a cytosolic fraction, metabolites were not observed. Aromatic hydroxylation at the C-6' of phenyl ring B and isomerization led to the formation of M1 and M2 metabolites, which were further oxidized to the corresponding para-quinone (M7 and M8) species whose role in pharmacodynamic activity is unknown. Metabolites M4 and M5, arising from O-demethylation of phenyl ring B, did not form the ortho-quinones. O-Demethylation of phenyl ring A formed the metabolite M3 with a complete isomerization of the stilbenic double bond.     

Synthesis and evaluation of 1,5-disubstituted tetrazoles as rigid analogues of combretastatin A-4 with potent antiproliferative and antitumor activity

Tubulin, the major structural component of microtubules, is a target for the development of anticancer agents. Two series of 1,5-diaryl substituted 1,2,3,4-tetrazoles were concisely synthesized, using a palladium-catalyzed cross-coupling reaction, and identified as potent antiproliferative agents and novel tubulin polymerization inhibitors that act at the colchicine site. SAR analysis indicated that compounds with a 4-ethoxyphenyl group at the N-1 or C-5 position of the 1,2,3,4-tetrazole ring exhibited maximal activity. Several of these compounds also had potent activity in inhibiting the growth of multidrug resistant cells overexpressing P-glycoprotein. Active compounds induced apoptosis through the mitochondrial pathway with activation of caspase-9 and caspase-3. Furthermore, compound 4l significantly reduced in vivo the growth of the HT-29 xenograft in a nude mouse model, suggesting that 4l is a promising new antimitotic agent with clinical potential.     

Horse chestnut extract induces contraction force generation in fibroblasts through activation of Rho/Rho kinase

Contraction forces generated by non-muscle cells such as fibroblasts play important roles in determining cell morphology, vasoconstriction, and/or wound healing. However, few factors that induce cell contraction forces are known, such as lysophosphatidic acid and thrombin. Our study analyzed various plant extracts for ingredients that induce generation of cell contraction forces in fibroblasts populating collagen gels. We found that an extract of Horse chestnut (Aesculus hippocastanum) is able to induce such contraction forces in fibroblasts. The involvement of actin polymerization and stress fiber formation in the force generation was suggested by inhibition of this effect by cytochalasin D and by Rhodamine phalloidin. Rho kinase inhibitors (Y27632 and HA1077) and a Rho inhibitor (exoenzyme C3) significantly inhibited the force generation induced by the Horse chestnut extract. H7, which inhibits Rho kinase as well as other protein kinases, also significantly inhibited induction of force generation. However, inhibitors of other protein kinases such as myosin light chain kinase (ML-9), protein kinase C (Calphostin), protein kinase A (KT5720), and tyrosine kinase (Genistein, Herbimycin A) had no effect on force generation induced by Horse chestnut extract. These results suggest that the Horse chestnut extract induces generation of contraction forces in fibroblasts through stress fiber formation followed by activation of Rho protein and Rho kinase but not myosin light chain kinase or other protein kinases.     

小分子血管阻断剂抗肿瘤研究进展

血管阻断剂 (vascular disrupting agents, VDAs) 是指一类能快速且选择性破坏恶性肿瘤新生血管从而达到治疗癌症目的的药物。作为不同的肿瘤治疗手段, VDAs的作用机制不同于血管生成抑制剂 (anti-  angiogenic drugs或angiogenesis inhibitors, AIs)。AIs能抑制肿瘤新生血管生成, 对已存在的肿瘤血管没有作用。与之相反, VDAs诱导肿瘤组织深部血管坍塌, 使其缺氧而死。所以VDAs被认为有希望治疗一些进展性肿瘤。本综述将着重介绍小分子VDAs的抗肿瘤活性、作用机制以及目前临床应用情况。     

Involvement of asymmetric dimethylarginine and Rho kinase in the vascular remodeling in monocrotaline-induced pulmonary hypertension

Recent studies have shown that the plasma level of asymmetric dimethylarginine (ADMA) was increased accompanied by the decreased dimethylarginine dimethylaminohydrolase (DDAH) activity in pulmonary hypertension (PH) and ADMA was able to regulate pulmonary endothelial cells mobility through increasing the activity of Rho kinase (ROCK). This work was conducted to explore the role of ADMA/DDAH pathway in vascular remodeling in PH and the underlying mechanisms. The rat model of PH was established by a single injection of monocrotaline (60 mg/kg, s.c.). The pulmonary arterial pressure, the remodeling of pulmonary artery, the hypertrophy of right ventricle, the plasma levels of ADMA and NO, the expression of DDAH2, ROCK1 or ROCK2 and the ROCK activity were determined. In vitro studies, the pulmonary artery smooth muscle cells (PASMCs) were isolated and cultured. The effect of ADMA on PASMCs proliferation and ROCK activation was investigated. The results showed that the injection of monocrotaline successfully induced PH characterized by the increased pulmonary arterial pressure, vascular remodeling and right ventricle hypertrophy. The plasma level of ADMA was elevated concomitantly with the increased ROCK activity and ROCK1 expression as well as the decreased DDAH2 expression in pulmonary arteries. In the cultured PASMCs, ADMA promoted cellular proliferation accompanied by the increased ROCK1 expression and ROCK activity, which was attenuated by the ROCK inhibitor or by the intracellular antioxidant. These results suggest that ADMA could promote the proliferation of PASMCs through activating ROCK pathway, which may account for, at least partially, the vascular remodeling in monocrotaline-induced PH.     

Concise synthesis and structure-activity relationships of combretastatin A-4 analogues, 1-aroylindoles and 3-aroylindoles, as novel classes of potent antitubulin agents

The synthesis and study of the structure-activity relationships of two new classes of synthetic antitubulin compounds based on 1-aroylindole and 3-aroylindole skeletons are described. Lead compounds 3, 10, and 14 displayed potent cytotoxicities with IC50 = 0.9-26 nM against human NUGC3 stomach, MKN45 stomach, MESSA uterine, A549 lung, and MCF-7 breast carcinoma cell lines. The inhibition of proliferation correlated with in vitro polymerization inhibitory activities. Structure-activity relationships revealed that 6-methoxy substitution of 3-aroylindoles and 5-methoxy substitution of 1-aroylindoles contribute to a significant extent for maximal activity by mimicking the para substitution of the methoxy group to the carbonyl group in the case of aminobenzophenones. Addition of a methyl group at the C-2 position on the indole ring exerts an increased potency. The 3,4,5-trimethoxybenzoyl moiety was necessary for better activity but not essential and can be replaced by 3,5-dimethoxybenzoyl and 3,4,5-trimethoxybenzyl moieties. We conclude that 1- and 3-aroylindoles constitute an interesting new class of antitubulin agents with the potential to be clinically developed for cancer treatment.