Pharmacokinetic Modeling of an Induction Regimen for In Vivo Combined Testing of Novel Drugs against Pediatric Acute Lymphoblastic Leukemia Xenografts

Current regimens for induction therapy of pediatric acute lymphoblastic leukemia (ALL), or for re-induction post relapse, use a combination of vincristine (VCR), a glucocorticoid, and l-asparaginase (ASP) with or without an anthracycline. With cure rates now approximately 80%, robust pre-clinical models are necessary to prioritize active new drugs for clinical trials in relapsed/refractory patients, and the ability of these models to predict synergy/antagonism with established therapy is an essential attribute. In this study, we report optimization of an induction-type regimen by combining VCR, dexamethasone (DEX) and ASP (VXL) against ALL xenograft models established from patient biopsies in immune-deficient mice. We demonstrate that the VXL combination was synergistic in vitro against leukemia cell lines as well as in vivo against ALL xenografts. In vivo, VXL treatment caused delays in progression of individual xenografts ranging from 22 to >146 days. The median progression delay of xenografts derived from long-term surviving patients was 2-fold greater than that of xenografts derived from patients who died of their disease. Pharmacokinetic analysis revealed that systemic DEX exposure in mice increased 2-fold when administered in combination with VCR and ASP, consistent with clinical findings, which may contribute to the observed synergy between the 3 drugs. Finally, as proof-of-principle we tested the in vivo efficacy of combining VXL with either the Bcl-2/Bcl-xL/Bcl-w inhibitor, ABT-737, or arsenic trioxide to provide evidence of a robust in vivo platform to prioritize new drugs for clinical trials in children with relapsed/refractory ALL.

当前用于儿童急性淋巴细胞白血病（pediatric acute lymphoblastic leukemia, ALL）诱导治疗，或复发后再诱导治疗的标准方案，均采用长春新碱（vincristine, VCR）、糖皮质激素联合L-天冬酰胺酶（l-asparaginase, ASP）的联合用药方案，可联用或不联用蒽环类药物。目前此类方案的治愈率约为80%，因此亟需构建可靠的临床前模型，以优先筛选适用于复发/难治性患者临床试验的新型活性药物；而此类模型预测现有治疗方案协同/拮抗作用的能力，是其必备的核心属性。本研究对诱导型治疗方案进行优化，构建了由长春新碱、地塞米松（dexamethasone, DEX）与L-天冬酰胺酶联合组成的VXL方案，并将其应用于免疫缺陷小鼠体内源自患者活检组织的ALL异种移植模型。研究证实，VXL联合方案在体外对白血病细胞系、体内对ALL异种移植物均表现出协同抗肿瘤活性。体内实验结果显示，VXL治疗可使各异种移植物的肿瘤进展延迟22至146天以上不等；源自长期存活患者的异种移植物的中位进展延迟，为死于疾病患者的异种移植物的2倍。药代动力学分析显示，当与长春新碱和L-天冬酰胺酶联合给药时，小鼠体内的全身地塞米松暴露量升高至原先的2倍，这与临床研究结果一致，或可解释三种药物间观察到的协同作用机制。最后，作为原理验证性实验，本研究测试了VXL方案分别与Bcl-2/Bcl-xL/Bcl-w抑制剂ABT-737、三氧化二砷联合的体内抗肿瘤效果，为复发/难治性儿童ALL患者临床试验的新型药物优先筛选提供了可靠的体内实验平台依据。