Developing BRAF mutant and BRAF wild-type selective strategies for radiosensitization in Anaplastic Thyroid Cancer

甲状腺间变性癌（ATC）仍然是与预后最差的实体肿瘤之一。标准治疗包括最大安全切除、外照射放射治疗（EBRT）和细胞毒性化疗。尽管如此，疾病复发率很高。ATC患者的局部/区域复发特别困难，导致气道和/或食管受损，导致死亡率和转移性播散。因此，需要新的治疗方法来改善疾病控制和延长生存期。最近，ATC的基因组分析发现了RAS-RAF-MEK-ERK通路（特别是BRAF和RAS）中的高频突变，以及其他DNA损伤和细胞周期检查点控制基因，包括TP 53。我们的临床前数据支持激活BRAFV 600 E突变通过非同源末端连接修复（NHEJ）DNA修复途径促进对EBRT和遗传毒性治疗的抗性。此外，用小分子抑制剂靶向抑制BRAFV 600 E导致BRAF突变体（BRAFm）ATC对EBRT致敏。此外，用MEK-1/2抑制剂处理BRAF突变细胞也导致放射增敏。由于BRAF野生型（BRAFwt）ATC占病例的约60-70%，因此开发BRAFwt ATC放射增敏的靶向策略也至关重要。因此，我们发现TP 53突变ATC被ATR和Wee 1激酶抑制剂有效地放射增敏，突出了这些肿瘤对G2/M细胞周期检查点的依赖性。最后，我们将探讨辐射敏化 RAS突变型ATC是ATC的另一种常见BRAFwt分子亚型。在本提案中，我们将尝试多种策略来推进BRAFm和BRAFwt ATC患者的治疗。在目标1中，我们将进行一项I期试验，以确定与EBRT同时用于BRAFm ATC的达拉非尼（BRAF抑制剂）和曲美替尼（MEK-1/2抑制剂）的最大耐受剂量，并确定应答的生物标志物和导致耐药的分子途径。在目标2中，我们将进行机制研究，以更好地了解BRAFm如何导致加速DNA修复，测试靶向DNA修复组分的新治疗策略，并开发和优化靶向DNA修复的新策略，与EBRT和其他BRAFm ATC的遗传毒性疗法相结合。在目标3中，我们将尝试通过在体外和体内测试针对TP 53和RAS缺陷或突变的ATC的不同靶向策略来开发用于治疗BRAF野生型ATC的新策略，以支持这些组合的未来临床测试。总之，这些研究将提高我们对BRAF突变如何赋予放射抗性的理解，并确定新的肿瘤选择性组合方法用于治疗BRAF突变型和BRAF野生型ATC患者。

Anaplastic thyroid cancer (ATC) remains one of the solid tumors that is associated with the poorest prognosis. Standard therapy includes maximal safe resection, external beam radiation therapy (EBRT), and cytotoxic chemotherapy. Despite this, there are high rates of disease recurrence. Local/regional recurrence is particularly difficult for patients with ATC, resulting in airway and/or esophageal compromise which contributes to mortality and metastatic dissemination. Novel therapies are thus needed to improve disease control and lengthen survival. Recently, genomic profiling of ATC has uncovered high frequency mutations in the RAS-RAF-MEK-ERK pathway (particularly BRAF and RAS), as well as other DNA damage and cell cycle checkpoint control genes, including TP53. Our preclinical data supports that an activating BRAFV600E mutation promotes resistance to EBRT and genotoxic therapies, through the non-homologous end-joining repair (NHEJ) DNA repair pathway. In addition, targeted inhibition of BRAFV600E with a small molecule inhibitor results in sensitization to EBRT in BRAF mutant (BRAFm) ATC. Furthermore, treatment of BRAF mutant cells with a MEK-1/2 inhibitor also results in radiosensitization. Since BRAF wild-type (BRAFwt) ATC accounts for ~ 60-70% of cases, developing targeted strategies for radiosensitization in BRAFwt ATC is also critical. As such, we find that TP53 mutant ATC is effectively radiosensitized by ATR and Wee1 kinase inhibitors, highlighting the dependency of these tumors on the G2/M cell cycle checkpoint. Finally, we will explore radiation sensitization approaches for RAS mutant ATC, another common BRAFwt molecular subtype of ATC. In this proposal, we will attempt multiple strategies to advance therapy for patients with BRAFm and BRAFwt ATC. In Aim 1, we will perform a phase I trial to determine the maximally-tolerated doses of dabrafenib (BRAF inhibitor) and trametinib (MEK-1/2 inhibitor) to be used concurrently with EBRT for BRAFm ATC, and identify biomarkers of response and molecular pathways leading to resistance. In Aim 2, we will perform mechanistic studies to better understand how BRAFm leads to accelerated DNA repair, test novel therapeutic strategies targeting components of DNA repair, and develop and optimize novel strategies targeting DNA repair in combination with EBRT and other genotoxic therapies for BRAFm ATC. In Aim 3, we will attempt to develop novel strategies for treating BRAF wild-type ATC, by testing different targeted strategies for TP53 and RAS deficient or mutated ATC in vitro and in vivo to support future clinical testing of these combinations. Together, these studies will improve our understanding of how BRAF mutations impart radio-resistance, and identify new tumor-selective combinatorial approaches for treating patients with BRAF mutant and BRAF wild-type ATC.