Poor-Risk AML with Complex, Monosomal Karyotype: In Vivo Therapeutic Efficacy of Decitabine (DAC) in Patient-Derived Xenograft (PDX) Mouse Models
Authors: Greve Gabriele , Schüler Julia , Oswald Eva , Lübbert Michael 
Published: November 2019

Background: DNA-hypomethylating agents (HMAs) show an encouraging but not yet well-understood activity in AML/MDS patients (pts) with adverse cytogenetics, such as -7/del(7q) embedded in a complex, monosomal karyotype (MK). We have noted that MK pts with multiple monosomies responded better to DAC treatment than pts with only one monosomal autosome (Blum, Greve and Lübbert, Curr Opin Hematol. 2017). This important characteristic of HMAs differentiates them from cytarabine (AraC, lacking DNMT-inhibitory activity) as shown in randomized studies with DAC (Wierzbowska et al., Am. J. Hematology 2018) and AZA (Döhner et al., Leukemia 2018). The mechanism of action is currently under investigation and may involve preferential gene reactivation on monosomic chromosomes by DAC (Greve et al., ASH Annual Meeting 2017, #2612). In order to address this important difference between DAC and AraC, we compared their antileukemic activity in PDX models representing cytogenetically normal (CN) AML and adverse cytogenetics AML (complex, monosomal karyotypes including del(7q) and 1 or more monosomies).
Materials and Methods: PDX models were generated for 5 CN and 3 MK AML pts with a median age of 68 years (range 55-80), a median WBC of 3.0 x 103/µl (range 1.4-139.7) and a median of 42% bone marrow (BM) blasts (range 5-97). 7/8 pts were sampled at diagnosis, i.e. prior to first-line treatment (3 pts received DAC, 3 pts induction and 1 pt upfront allografting); 1/8 pt had had multiple relapses. T-cell depleted peripheral blood or bone marrow cells (3x106 cells/mouse) were injected into NSG (NOD/Shi-scid/IL-2Rγnull) mice. Leukemic cell engraftment was determined by flow cytometry (FC) in BM, peripheral blood (PB) and spleen during the course of the experiment and at the end of a study. Leukemic cells were transplanted serially at least 4-5 times to propagate and ensure full leukemic potential of the cells. Mice were treated with low-toxic concentrations of DAC (1 mg/kg/day given intraperitoneally), AraC (15 mg/kg/day given intravenously) or vehicle (PBS) for 5 consecutive days (one cycle). Drug doses were titrated to be equitoxic and as potent as possible without causing side effects. Treatment commenced upon disease onset, as evaluated by FC positivity for human CD33, increased WBC in PB and weight loss. Overall survival served as the read-out. The study was carried out in accordance with the recommendations by the Society of Laboratory Animal Science in an AAALCA accredited animal facility. The animal experiments were approved by the regional council (Regierungspräsidium Freiburg, ref. 35, permit no. G-12/86).
Results: We successfully established well-characterized PDX from pts with CN (n = 5), and with MK (n = 3) with a median of 2 autosomal monosomies (range 1-6; of chromosomes 4, 6, 7 [2x], 15, 17 [2x], 18, 21). TP53 (mutational status available for 6/8 pts) was wildtype in 4 CN pts and 1 MK pt, and mutated in 1 MK pt. All models were treated with either DAC, AraC or vehicle. Across both cytogenetic cohorts, DAC treatment significantly prolonged median survival by 36 days when compared to vehicle administration (p = 0.0002, see Fig 1A). Specifically, DAC increased median survival of CN PDX by 33 days (p = 0.0104, range 61-105 days with DAC, compared to 43-65 days with vehicle, Fig 1B), and in MK PDX by 40 days (p = 0.0197; range 72-105 days with DAC, compared to 39-50 days with vehicle, Fig 1C). Notably, disease progression in two DAC-treated PDX (one CN, one MK with 6 monosomies) was delayed to 105 days (Fig 1, marked with ⋆). AraC treatment also resulted in longer median survival across both cohorts compared to vehicle, albeit not as pronounced as with DAC, by an average of 20 days (p = 0.0066). In more detail, AraC increased median survival of CN PDX by 19 days (p = 0.0025, range 53-82 days), and, though not significantly, of MK PDX by 15 days (p = 0.2048, range 46-92 days).
Conclusion: In this PDX study recapitulating two different cytogenetic risk groups of AML, DAC showed encouraging activity also in models with complex, monosomal karyotype, even in the presence of 6 autosomal monosomies, and was superior to AraC in extending survival. These data lend further support to the treatment of such adverse genetics AML patients with HMAs.

Disclosures
No relevant conflicts of interest to declare.