GTI-2040: An anti-sense strategy to reduce ribonucleotide reductase in AML

描述(由申请人提供)：克服对常用化疗方案的耐药性的策略是必要的，以改善患有难治性疾病的急性髓系白血病(AML)患者或在最初取得完全缓解(CR)后复发的患者目前令人沮丧的预后。其中一种新的策略是下调核糖核苷酸还原酶(RNR)，RNR是一种将核苷还原为脱氧核苷的酶，当在白血病细胞中过度表达时，会诱导对阿糖胞苷(Ara-C)的耐药性，阿糖胞苷是AML几种前期和挽救方案的核苷类似物和主干成分。在临床前研究中，我们发现GTI-2040，一种与RNR mRNA的R2部分互补的20聚体寡核苷酸，降低了其靶标水平，并抑制了AML细胞的RNR功能。我们建议在此测试GTI-2040与大剂量阿糖胞苷(HiDAC)联合治疗难治性/复发性AML。这种方法已经在类似的强化治疗的高危AML人群的初始阶段I试验中显示出希望(即临床反应和相对较低的毒性的证据)。虽然疾病反应的评估不是这项试验的主要目标，但观察到靶基因下调和CR的实现之间存在显著的相关性。目前的建议旨在确定联合应用GTI-2040和HiDAC治疗难治性/复发性AML的有效率，并将其与血浆药代动力学(PK)、反义核酸在细胞内的浓度和转运、R2表达水平的降低和RNR功能的抑制(即dNTP比率耗尽)相关联。我们将通过以下具体目标来实现这些目标：1)进行GTI-2040联合HiDAC治疗难治性/复发AML的II期临床试验，并测定总缓解率(完全缓解+完全缓解且计数恢复不完全)和1年复发率及生存率；2)进行PK研究，测定GTI-2040的血浆和细胞内水平，并将其与毒性、临床反应以及治疗后R2表达和RNR功能的变化相关联；3)进行药效学(PD)相关研究，确定治疗后系列R2mRNA和蛋白水平及RNR功能与未治疗基线比较，以及与GTI-2040的血浆和细胞内浓度、毒性和疾病反应的相关性。这项研究的总体目标是验证一种有效的挽救方案，使复发/难治性AML患者获得高CR/CRI率，继续进行异基因干细胞移植和/或延长生存期。公共卫生相关性：急性髓系白血病(AML)是西半球最常见和最致命的白血病类型之一，通常对标准化疗耐药，迫切需要新的策略来克服化疗耐药和改善这些患者的预后。在这项建议中，GTI-2040是一种反义化合物，可以减少核糖核苷酸还原酶(RNR)的表达并抑制其功能，核糖核苷酸还原酶(RNR)是参与白血病细胞化疗耐药的酶，GTI-2040与大剂量阿糖胞苷(Ara-C)联合使用，大剂量阿糖胞苷(Ara-C)是治疗AML的几种化疗方案的基本成分。这项研究的目标是减少对阿糖胞苷的耐药性，并改善患有难治性或复发性疾病的AML患者的临床反应。研究GTI-2040分别通过减少和抑制RNR的表达和功能并导致临床反应的机制是这一提议的关键方面。

DESCRIPTION (provided by applicant): Strategies to overcome resistance to common chemotherapy regimens are necessary to improve upon the currently dismal prognosis of acute myeloid leukemia (AML) patients with refractory disease or who have relapsed following initial achievement of complete remission (CR). One such novel strategy is to down-regulate ribonucleotide reductase (RNR), an enzyme that reduces nucleoside to deoxynucleosides for incorporation into newly synthesized DNA and, when over expressed in leukemia cells, induces resistance to cytarabine arabinoside (Ara-C), a nucleoside analog and backbone component of several up-front and salvage regimens in AML. In preclinical studies, we showed that GTI-2040, a 20-mer oligonucleotide complementary to the R2 component of RNR mRNA, decreased levels of its target and inhibited RNR function in AML cells. We propose here to test the combination of GTI-2040 with high dose Ara-C (HiDAC) in refractory/relapsed AML. This approach has already shown promise (i.e., evidence of clinical response and relatively low toxicity) in an initial phase I trial of a similarly, intensively treated high risk AML population. Although assessment of disease response was not a primary objective of this trial, a significant correlation between target down-regulation and achievement of CR was observed. The current proposal seeks to establish definitively the response rate to combination of GTI-2040 with HiDAC in refractory/relapsed AML and correlates it with plasma pharmacokinetics (PK), intracellular concentration and trafficking of the antisense, reduction in R2 expression levels and inhibition of the RNR function (i.e. depletion of dNTP ratios). We will achieve these goals through the following specific aims: 1) To conduct a Phase II clinical trial of GTI-2040 in combination with HiDAC in refractory/relapsed AML and determine the overall response rate (complete remission plus complete remission with incomplete count recovery) and the one year relapse rate and survival; 2) To conduct PK studies and determine the plasma and intracellular levels of GTI-2040 and correlate them with toxicity, clinical response, and post- treatment changes in R2 expression and RNR function; and 3) To conduct pharmacodynamic (PD) correlative studies and determine how serial post-treatment R2 mRNA and protein levels and RNR function compare with untreated baseline and correlate with plasma and intracellular concentrations of GTI-2040, toxicity and disease response. The overall goal of this study is to validate an effective salvage regimen that will allow relapsed/refractory AML patients to achieve high CR/CRi rates, proceed to allogeneic stem cell transplant and/or extend survival. PUBLIC HEALTH RELEVANCE: Acute myeloid leukemia (AML), one of the most common and lethal types of leukemia in the Western Hemisphere, is often resistant to standard chemotherapy, and novel strategies to overcome chemoresistance and improve the outcome of these patients are highly needed. In this proposal, GTI- 2040, an antisense compound that decreases expression and inhibits the function of ribonucleotide reductase (RNR), an enzyme involved in chemoresistance of leukemia cells, is combined with high dose cytarabine (Ara-C), an essential component of several chemotherapy regimens for AML. The goals of this study are to decrease chemoresistance to Ara-C and improve clinical responses in AML patients with refractory or relapsed disease. Studies to understand the mechanisms through which GTI-2040 reduces and inhibits respectively the expression and function of RNR and leads to clinical responses are critical aspects of this proposal.