Simone Matteo, Erba Eugenio, Damia Giovanna, Vikhanskaya Faina, Di Francesco Angela M, Riccardi Riccardo, Bailly Christian, Cuevas Carmen, Fernandez Sousa-Faro José Maria, D'Incalci Maurizio
Department of Oncology, Mario Negri Institute for Pharmacological Research, Via Eritrea 62, Milan, and Division of Pediatric Oncology, Catholic University A. Gemelli, Rome, Italy.
Eur J Cancer. 2005 Oct;41(15):2366-77. doi: 10.1016/j.ejca.2005.05.015. Epub 2005 Sep 21.
Variolin B (VAR-B) is a natural product isolated from the sponge Kirkpatrickia variolosa, found in Antarctica. VAR-B has been shown previously to possess potent pro-apoptotic activity. This study was undertaken to investigate the mechanism of action of chemically synthesised VAR-B and its analogue deoxy-variolin B (dVAR-B). In different human cancer cell lines both compounds inhibited colony formation, caused cell cycle perturbations and induced apoptosis at concentrations ranging from 0.1 to 2 microM. LoVo/Dx cells over-expressing Pgp were equally sensitive as the parental cell line to VAR-B and dVAR-B, indicating that variolins are not substrates of Pgp. Although variolins induced an increase in the levels of p53 with an increase in p21, their cytotoxicities did not appear to be dependent on p53 status as their potency was comparable in cells with wild-type p53, or in sub-lines with inactivated p53. Both VAR-B and dVAR-B prevent the cells from entering S phase, blocking cells in G1 and cause an accumulation of cells in G2. The apoptosis induced by VAR-B and dVAR-B occurs very rapidly in some cell lines (e.g., Jurkat leukaemia cells) and is already evident 4h after the beginning of treatment. Although intercalation of dVAR-B in DNA has been demonstrated, neither VAR-B nor dVAR-B produce detectable breaks in DNA. These results are consistent with the in vitro biochemical assays that also demonstrated that dVAR-B is not topoisomerase I or II poison. Instead, each of these variolins appears to inhibit cyclin-dependent kinases (CDKs) in the muM range. CDK1-cyclin B, CDK2-cyclin A and CDK2/cylin E complexes were inhibited in a range of concentrations lower than those required to inhibit the activity of CDK4/cyclin D or CDK7/cyclin H complexes. In conclusion, these variolins are a new class of CDK inhibitors that activate apoptosis in a p53-independent fashion and thus they may be effective against tumours with p53 mutations or deletions.
变铃菌素B（VAR - B）是从南极洲发现的海绵Kirkpatrickia variolosa中分离出的一种天然产物。先前已证明VAR - B具有强大的促凋亡活性。本研究旨在探究化学合成的VAR - B及其类似物脱氧变铃菌素B（dVAR - B）的作用机制。在不同的人类癌细胞系中，这两种化合物在0.1至2微摩尔的浓度范围内均能抑制集落形成、引起细胞周期紊乱并诱导凋亡。过表达Pgp的LoVo/Dx细胞与亲代细胞系对VAR - B和dVAR - B同样敏感，这表明变铃菌素不是Pgp的底物。尽管变铃菌素会随着p21的增加而导致p53水平升高，但其细胞毒性似乎并不依赖于p53状态，因为它们在具有野生型p53的细胞或p53失活的亚系中的效力相当。VAR - B和dVAR - B均能阻止细胞进入S期，将细胞阻滞在G1期并导致细胞在G2期积累。VAR - B和dVAR - B诱导的凋亡在某些细胞系（如Jurkat白血病细胞）中发生得非常迅速，在治疗开始后4小时就已很明显。尽管已证明dVAR - B可插入DNA，但VAR - B和dVAR - B均未在DNA中产生可检测到的断裂。这些结果与体外生化分析一致，体外生化分析也表明dVAR - B不是拓扑异构酶I或II的毒物。相反，这些变铃菌素中的每一种似乎都能在微摩尔范围内抑制细胞周期蛋白依赖性激酶（CDK）。CDK1 - 细胞周期蛋白B、CDK2 - 细胞周期蛋白A和CDK2/细胞周期蛋白E复合物在低于抑制CDK4/细胞周期蛋白D或CDK7/细胞周期蛋白H复合物活性所需浓度的范围内受到抑制。总之，这些变铃菌素是一类新型的CDK抑制剂，它们以不依赖p53的方式激活凋亡，因此可能对具有p53突变或缺失的肿瘤有效。
