Overcoming Therapeutic Resistance in Anaplastic Thyroid Cancer

描述(由申请人提供)： 甲状腺癌是最常见的内分泌癌。大多数甲状腺癌通过手术和放射性碘(131I)治疗是成功的。然而，低分化甲状腺癌(PDTC)失去了摄取放射性碘的能力，导致疾病复发和死亡。此外，间变性甲状腺癌(ATC)患者的预后非常差，生存时间不到6个月。这些发现也适用于退伍军人；此外，退伍军人患甲状腺癌的风险可能更高，因为他们以前暴露在辐射中，而且在美国武装部队服役的个人潜在暴露于辐射的风险增加。因此，一种治疗方法可以选择性地杀死 对放射性碘治疗反应不佳的间变性甲状腺癌细胞是非常理想的。TRAIL就是这样一种潜在的治疗药物。TRAIL是一种细胞溶解药物，可以选择性地杀死 癌细胞，而不影响大多数正常细胞。然而，它在癌症治疗中的临床应用 由于TRAIL抗性因子的表达而受到限制。MAP激活死亡结构域含蛋白(MADD；又名IG20)可以抵抗TRAIL诱导的多种甲状腺和其他癌细胞的凋亡。虽然MADD在癌细胞中的敲除使它们更容易发生凋亡，但它对正常细胞没有明显的影响，这表明它可能是开发癌症治疗的理想靶点。MADD作为TRAIL抗性因子的能力依赖于它被Akt(即pMADD)的磷酸化。有趣的是，在TRAIL敏感的癌细胞中，TRAIL治疗降低了PAKT和pMADD的水平，而在TRAIL耐药细胞中它们保持不变。然而，通过抑制Akt活性降低pMADD水平可恢复TRAIL对TRAIL耐药细胞的敏感性。这是非常有趣的，因为最具侵袭性的甲状腺癌，如PDTC和ATC，由于激活RAS或Akt1的突变、PIK3CA基因扩增或PTEN的失活突变而显示出结构性的Akt激活，这可以提高肿瘤的生存和生长。PI3K/Akt信号通路是很有吸引力的治疗靶点，可以抑制这一信号通路的药物正在进行临床试验。然而，其中大多数是“细胞抑制”的，而不是“溶解细胞的”，因此允许肿瘤持续存在、产生耐药性和转移。因此，需要开发新的有效治疗方式。更清楚地了解pMADD在调节ATC细胞凋亡中的作用，可以使我们开发出有效的方法来杀死它们。我们假设TRAIL可以有效地杀死大多数间变性甲状腺癌细胞。然而，在TRAIL耐药的间变性甲状腺癌细胞中，MADD功能可以被抑制，使它们对TRAIL诱导的凋亡敏感。为了验证这一假说，在AIM-1中，我们将确定MADD的Akt磷酸化是否有助于间变性甲状腺癌细胞产生TRAIL耐药；在AIM-2中，我们将使用裸鼠原位移植瘤模型，测试下调MADD功能在间变性甲状腺癌中的体内治疗作用；在AIM-3中，我们将检测MADD和pMADD在间变性甲状腺癌中的水平，并看看它们是否与这些癌症来源的原代细胞的TRAIL耐药相关。TRAIL和MADD下调诱导的细胞凋亡主要见于癌细胞，而不是正常细胞。因此，下调间变性甲状腺癌MADD功能以增强TRAIL敏感性的新研究具有很高的临床意义，与VA任务高度相关。

DESCRIPTION (provided by applicant): Thyroid carcinoma is the most frequently occurring endocrine cancer. Most thyroid cancers are successfully treated with surgery and radioiodine (131I). However, poorly differentiated thyroid cancer (PDTC) loses its ability to take up radioiodine leading to disease recurrence and death. Additionally, patients with anaplastic thyroid cancer (ATC) show very poor prognosis and survive for less than 6 months. These findings hold true for veterans as well; moreover, veterans could be at a higher risk for developing thyroid cancer due to their previous exposure to radiation and the enhanced risk of potential exposure to radiation amongst individuals who serve in the US armed forces. Therefore, a treatment that can selectively kill tumor cells that are unresponsive to radioiodine treatment and the anaplastic thyroid cancer cells is highly desired. TRAIL is one such potential therapeutic agent. TRAIL is a cytolytic drug that can selectively kill cancer cells while sparing most normal cells. However, its clinical utility in cancer treatment has been limited due to the expression of TRAIL-resistance factors. Map kinase Activating Death Domain containing protein (MADD; a.k.a. IG20) can confer resistance to TRAIL- induced apoptosis in a variety of thyroid and other cancer cells. While knockdown of MADD in cancer cells rendered them more susceptible to apoptosis, it had no apparent effect on normal cells, suggesting that it might serve as an ideal target for developing cancer therapy. The ability of MADD to act as a TRAIL resistance factor is dependent upon it's phosphorylation by Akt (i.e. pMADD). Interestingly, in TRAIL sensitive cancer cells, TRAIL treatment reduced the levels of pAkt and pMADD, while they remained unaltered in TRAIL- resistant cells. However, reducing the pMADD levels by suppressing the Akt activity restored TRAIL sensitivity to TRAIL resistant cells. This is profoundly interesting because the most aggressive forms of thyroid cancers, such as PDTC and ATC, show constitutive activation of Akt due to activating mutations in Ras or Akt1, PIK3CA gene amplification or inactivating mutations in PTEN, which can enhance tumor survival and growth. The PI3K/Akt signalling pathways are attractive therapeutic targets and drugs that can suppress this signaling pathway are in clinical trials. However, most of these are "cytostatic" and not "cytolytic" and thus allow tumors to persist, develop resistance and metastasize. Thus there is need for developing newer modalities of effective treatment. A clearer understanding of the role of pMADD, in regulating apoptosis of ATC cells could enable us to develop effective methods to kill them. We hypothesize that "TRAIL can be used to effectively kill most anaplastic thyroid cancer cells. However, in TRAIL resistant anaplastic thyroid cancer cells, MADD function can be repressed to sensitize them to TRAIL-induced apoptosis." To test this hypothesis in Aim-1 we will determine if Akt phosphorylation of MADD contributes to TRAIL-resistance in anaplastic thyroid cancer cells; in Aim-2 we will test the in vivo therapeutic utility of down modulating MADD function in anaplastic thyroid cancer using an orthotopic xenograft athymic nude mouse model; and in Aim-3 we will determine the levels of MADD and pMADD in anaplastic thyroid cancers and see if they correlate with TRAIL-resistance of primary cells derived from those cancers. Apoptosis induced by TRAIL as well as by MADD down modulation is primarily seen in cancer cells and not normal cells. Therefore, the proposed novel studies on down modulating MADD function in anaplastic thyroid cancer to enhance TRAIL sensitivity is of high clinical significance and highly relevant to VA mission.