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。大多数甲状腺癌可以通过手术和放射性碘（131 I）成功治疗。然而，低分化甲状腺癌（PDTC）失去了吸收放射性碘的能力，导致疾病复发和死亡。此外，患有间变性甲状腺癌（ATC）的患者显示出非常差的预后，并且存活不到6个月。这些发现也适用于退伍军人;此外，由于退伍军人以前暴露于辐射，以及在美国武装部队服役的个人中潜在暴露于辐射的风险增加，退伍军人可能患甲状腺癌的风险更高。因此，可以选择性地杀死肿瘤细胞的治疗方法， 对放射性碘治疗无反应和未分化甲状腺癌细胞的治疗是高度期望的。TRAIL就是这样一种潜在的治疗剂。 TRAIL是一种溶细胞药物， 癌细胞，同时保留大多数正常细胞。然而，其在癌症治疗中的临床效用已被证实。 由于TRAIL抗性因子的表达而受到限制。含有MAP激酶激活死亡结构域的蛋白（MADD; a.k.a. IG 20）可以在多种甲状腺和其它癌细胞中赋予对TRAIL诱导的细胞凋亡的抗性。虽然在癌细胞中敲低MADD使它们更容易凋亡，但它对正常细胞没有明显的影响，这表明它可能成为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其被Akt（即pMADD）磷酸化。有趣的是，在TRAIL敏感的癌细胞中，TRAIL处理降低了pAkt和pMADD的水平，而它们在TRAIL抗性细胞中保持不变。然而，通过抑制Akt活性降低pMADD水平恢复了TRAIL对TRAIL抗性细胞的敏感性。 这是非常有趣的，因为最具侵袭性的甲状腺癌形式，如PDTC和ATC，由于Ras或Akt 1中的激活突变，PIK 3CA基因扩增或PTEN中的失活突变而显示Akt的组成性激活，这可以增强肿瘤的存活和生长。PI 3 K/Akt信号通路是有吸引力的治疗靶点，并且可以抑制该信号通路的药物正在临床试验中。然而，大多数这些是“细胞抑制性的”而不是“细胞溶解性的”，因此允许肿瘤持续存在，产生耐药性和转移。因此，有必要开发新的有效治疗模式。 更清楚地了解pMADD在调控ATC细胞凋亡中的作用将有助于我们开发有效的方法来杀死ATC细胞。我们假设“TRAIL可用于有效杀死大多数未分化甲状腺癌细胞。然而，在TRAIL耐药的间变性甲状腺癌细胞中，MADD功能可以被抑制以使它们对TRAIL诱导的凋亡敏感。“为了在Aim-1中验证这一假设，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的TRAIL抗性;在Aim-2中，我们将使用原位异种移植无胸腺裸鼠模型测试下调MADD功能在间变性甲状腺癌中的体内治疗效用;在Aim-3中，我们将确定未分化甲状腺癌中MADD和pMADD的水平，并观察它们是否与这些癌症来源的原代细胞的TRAIL抗性相关。 由TRAIL以及MADD下调诱导的细胞凋亡主要见于癌细胞而非正常细胞。因此，所提出的下调甲状腺间变性癌中MADD功能以增强TRAIL敏感性的新研究具有高度临床意义，并且与VA使命高度相关。

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.