Cancer and Cell Biology Division, Translational Genomics Research Institute, Phoenix, AZ, USA.
Mol Cancer. 2012 Oct 5;11:75. doi: 10.1186/1476-4598-11-75.
Melanoma is the most lethal form of skin cancer, but recent advances in molecularly targeted agents against the Ras/Raf/MAPK pathway demonstrate promise as effective therapies. Despite these advances, resistance remains an issue, as illustrated recently by the clinical experience with vemurafenib. Such acquired resistance appears to be the result of parallel pathway activation, such as PI3K, to overcome single-agent inhibition. In this report, we describe the cytotoxicity and anti-tumour activity of the novel MEK inhibitor, E6201, in a broad panel of melanoma cell lines (n = 31) of known mutational profile in vitro and in vivo. We further test the effectiveness of combining E6201 with an inhibitor of PI3K (LY294002) in overcoming resistance in these cell lines.
The majority of melanoma cell lines were either sensitive (IC50 < 500 nM, 24/31) or hypersensitive (IC50 < 100 nM, 18/31) to E6201. This sensitivity correlated with wildtype PTEN and mutant BRAF status, whereas mutant RAS and PI3K pathway activation were associated with resistance. Although MEK inhibitors predominantly exert a cytostatic effect, E6201 elicited a potent cytocidal effect on most of the sensitive lines studied, as evidenced by Annexin positivity and cell death ELISA. Conversely, E6201 did not induce cell death in the two resistant melanoma cell lines tested. E6201 inhibited xenograft tumour growth in all four melanoma cell lines studied to varying degrees, but a more pronounced anti-tumour effect was observed for cell lines that previously demonstrated a cytocidal response in vitro. In vitro combination studies of E6201 and LY294002 showed synergism in all six melanoma cell lines tested, as defined by a mean combination index < 1.
Our data demonstrate that E6201 elicits a predominantly cytocidal effect in vitro and in vivo in melanoma cells of diverse mutational background. Resistance to E6201 was associated with disruption of PTEN and activation of downstream PI3K signalling. In keeping with these data we demonstrate that co-inhibition of MAPK and PI3K is effective in overcoming resistance inherent in melanoma.
黑色素瘤是最致命的皮肤癌形式，但最近针对 Ras/Raf/MAPK 通路的分子靶向药物的进展表明它们是有效的治疗方法。尽管取得了这些进展，但耐药性仍然是一个问题，最近vemurafenib 的临床经验就说明了这一点。这种获得性耐药似乎是平行途径激活的结果，例如 PI3K，以克服单一药物抑制。在本报告中，我们描述了新型 MEK 抑制剂 E6201 在体外和体内具有已知突变特征的广泛黑色素瘤细胞系（n = 31）中的细胞毒性和抗肿瘤活性。我们进一步测试了 E6201 与 PI3K 抑制剂（LY294002）联合使用在克服这些细胞系耐药性方面的有效性。
大多数黑色素瘤细胞系对 E6201 敏感（IC50<500 nM，31/31）或超敏（IC50<100 nM，31/31）。这种敏感性与野生型 PTEN 和突变 BRAF 状态相关，而突变 RAS 和 PI3K 途径激活与耐药性相关。虽然 MEK 抑制剂主要发挥细胞抑制作用，但 E6201 在大多数研究的敏感系中引起了强烈的细胞杀伤作用，这表现在 Annexin 阳性和细胞死亡 ELISA 上。相反，E6201 不会诱导两种耐药黑色素瘤细胞系的细胞死亡。E6201 以不同程度抑制了研究的所有四种黑色素瘤细胞系的异种移植物肿瘤生长，但在体外显示细胞杀伤反应的细胞系中观察到更明显的抗肿瘤作用。E6201 和 LY294002 的体外联合研究表明，在所有测试的六种黑色素瘤细胞系中均表现出协同作用，这由平均组合指数<1 定义。
我们的数据表明，E6201 在具有不同突变背景的黑色素瘤细胞中体外和体内均引起主要的细胞杀伤作用。E6201 的耐药性与 PTEN 缺失和下游 PI3K 信号转导的激活有关。根据这些数据，我们证明了 MAPK 和 PI3K 的共同抑制可有效克服黑色素瘤固有的耐药性。
