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

描述（由申请人提供）：为了改善患有难治性疾病或在初步达到完全缓解（CR）后复发的急性髓系白血病（AML）患者目前令人沮丧的预后，克服对常见化疗方案的耐药性的策略是必要的。一种这样的新策略是下调核糖核苷酸还原酶（RNR），该酶将核苷还原为脱氧核苷以掺入新合成的DNA中，并且当在白血病细胞中过表达时，诱导对阿糖胞苷（Ara-C）的抗性，阿糖胞苷是AML中的几种前期和补救方案的核苷类似物和骨架组分。在临床前研究中，我们发现GTI-2040，一种与RNR mRNA的R2组分互补的20聚体寡核苷酸，降低了其靶点的水平，并抑制了AML细胞中的RNR功能。我们在此提出在难治性/复发性AML中测试GTI-2040与高剂量Ara-C（HiDAC）的组合。这种方法已经显示出希望（即，临床反应的证据和相对低的毒性）在类似的、强化治疗的高风险AML人群的初始I期试验中。尽管疾病缓解评估不是本试验的主要目的，但观察到靶点下调与实现CR之间存在显著相关性。目前的提议旨在明确地确定在难治性/复发性AML中对GTI-2040与HiDAC的组合的响应率，并将其与血浆药代动力学（PK）、反义的细胞内浓度和运输、R2表达水平的降低和RNR功能的抑制（即dNTP比率的消耗）相关联。我们将通过以下具体目标实现这些目标：1）开展GTI-2040联合HiDAC治疗难治性/复发性AML的II期临床试验，并确定总体缓解率（完全缓解+完全缓解伴计数不完全恢复）和1年复发率及生存率; 2）进行PK研究并确定GTI-2040的血浆和细胞内水平，并将它们与毒性、临床反应和R2表达和RNR功能的治疗后变化相关联;以及3）进行药效学（PD）相关研究，并确定连续治疗后R2 mRNA和蛋白水平以及RNR功能如何与未治疗的基线比较，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。本研究的总体目标是验证一种有效的挽救治疗方案，使复发性/难治性AML患者达到高CR/CRi率，进行同种异体干细胞移植和/或延长生存期。公共卫生相关性：急性髓性白血病（AML）是西半球最常见和最致命的白血病类型之一，通常对标准化疗具有耐药性，因此非常需要克服化疗耐药性并改善这些患者结局的新策略。在该提案中，GTI- 2040（一种降低核糖核苷酸还原酶（RNR）表达并抑制其功能的反义化合物，RNR是一种参与白血病细胞化疗耐药性的酶）与高剂量阿糖胞苷（Ara-C）组合，阿糖胞苷是AML的几种化疗方案的重要组成部分。本研究的目的是降低对阿糖胞苷的耐药性，改善难治性或复发性AML患者的临床反应。了解GTI-2040分别减少和抑制RNR的表达和功能并导致临床反应的机制的研究是该提议的关键方面。

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.