Defining the Mechanism of Action of Rigosertib in Pediatric Cancers

我们进行了几项研究，以确定rigosertib在Ras突变的神经母细胞瘤和横纹肌肉瘤中的作用机制。几条证据表明，rigosertib不是作为Ras模拟物发挥作用，而是在这些细胞类型中作为微管去稳定剂发挥作用。首先，rigosertib在具有野生型Ras的儿科癌细胞系中与在具有突变型Ras的儿科癌细胞系中同样有效。其次，rigosertib诱导M期阻滞，而Ras信号传导抑制剂通常导致G1期阻滞。我们进一步表明，治疗与rigosertib诱导有丝分裂纺锤体缺陷和减少微管蛋白乙酰化，与微管稳定性下降一致。目前的工作旨在在动物模型中验证这些结果。Rigosertib对不同组织学的儿科癌细胞系具有不同的磷酸化蛋白质组学效应。特别是，rigosertib在横纹肌肉瘤细胞中诱导ERK和AKT磷酸化，但在神经母细胞瘤细胞系中降低ERK和AKT磷酸化。我们使用nanostring分析表明，在Ras突变的横纹肌肉瘤和神经母细胞瘤中，4EBP 1在RNA和蛋白质水平的表达降低。目前的工作旨在确定这种下降的机制。除了这项临床前工作外，我们还编写了一份在儿科患者中进行rigosertib I期试验的方案。

We have conducted several studies to identify the mechanism of action of rigosertib in Ras-mutated neuroblastoma and rhabdomyosarcoma. Several lines of evidence suggest that rigosertib is not functioning as a Ras mimetic and is instead functioning as a microtubule destabilizing agent in these cell types. First, rigosertib is equally as effective in pediatric cancer cell lines with wild type Ras as it is in pediatric cancer cell lines with mutant Ras. Second, rigosertib induces an M-phase arrest, while inhibitors of Ras signaling generally cause an arrest in G1. We further show that treatment with rigosertib induces mitotic spindle defects and decreases tubulin acetylation, consistent with a decrease in microtubule stability. Current work is aimed at validating these results in animal models. Rigosertib has different phospho-proteomic effects on pediatric cancer cell lines of different histologies. In particular, rigosertib induces ERK and AKT phosphorylation in rhabdomyosarcoma cells but decreases ERK and AKT phosphorylation in neuroblastoma cell lines. We used a nanostring assay to show that in both Ras-mutated rhabdomyosarcoma and neuroblastoma, expression of 4EBP1 at the RNA and protein level is decreased. Current work is aimed at identifying the mechanism by which this decrease occurs. In addition to this preclinical work, we have written a protocol for a phase I trial of rigosertib in pediatric patients.