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

Abstract

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.

Variegated clonality and rapid emergence of new molecular lesions in xenografts of acute lymphoblastic leukemia are associated with drug resistance

“…Leukemia engraftment and response to drug treatment were assessed by weekly enumeration of the proportion of human CD45 + cells in the peripheral blood (%huCD45) [5]. Owing to previous experience showing that low level dissemination of xenograft cells into the peripheral blood is associated with high level infiltration of bone marrow and spleen [19], drug treatments were initiated when the %huCD45 reached 1% and continued until the %huCD45 increased through the drug treatments or until animals experienced leukemia- or drug-related morbidity. The number of emerging chemoresistant xenograft lines compared with the number of mice inoculated is depicted in Supplementary Table E1 (online only, available at www.exphem.org).…”

AKR1C3 is a biomarker of sensitivity to PR-104 in preclinical models of T-cell acute lymphoblastic leukemia

“…Development of patient-derived xenografts and assessment of in vivo drug efficacy ) and evaluated their in vivo sensitivity to PR-104 as a single agent or in combination with VXL in groups of 6-10 mice have been previously reported, 33,[35][36][37][38][39] and are described in detail in the supplemental Methods (available on the Blood Web site). PR-104 was supplied by Proacta Inc through the Cancer Therapy Evaluation Program of the National Cancer Institute, or by the Auckland Cancer Society Research Centre.…”

“…To gain a greater perspective of the efficacy of PR-104 in relation to established drugs used to treat pediatric ALL, we combined PR-104 with an induction-type VXL regimen that was previously optimized in our laboratory 35 Tables 1-2). The combination of VXL and PR-104 achieved LGDs of 34.5 to 49.5 days in the 3 xenografts, indicating that the combination was neither synergistic nor antagonistic, and also that PR-104 alone was just as effective.…”

“…In this study, we used an extensive panel of patient-derived pediatric ALL xenografts to determine whether PR-104 exhibited lineagespecific in vivo efficacy at doses that provide pharmacokinetics achievable in human cancer patients, and to compare its single-agent efficacy with an induction-type regimen consisting of the established drugs vincristine, dexamethasone, and L-asparaginase (VXL). 35 Moreover, we assessed the relationship between PR-104 in vivo efficacy or PR-104A in vitro efficacy against these xenografts and AKR1C3 messenger RNA (mRNA), protein, and activity levels. To demonstrate a causal relationship between AKR1C3 expression and sensitivity to PR-104/PR-104A, we overexpressed AKR1C3 in a resistant BCP-ALL xenograft and assessed its in vitro and in vivo responses.…”

Xenograft-directed personalized therapy for a patient with post-transplant relapse of ALL

“…Treatment of mice was commenced when the proportion of human leukemia cells in the murine peripheral blood exceeded 1%, as we have previously shown that this level of engraftment represents a considerable overall disease burden in the animals. 12 PDX responses were assessed weekly by measuring the percentage of circulating human leukemia cells in mouse peripheral blood. PDX mice treated with SAR3419 and topotecan showed clearance of ALL from the peripheral blood at the end of the 1st week of treatment, 60 days after the 2nd relapse ( Table 1).…”