AML Blasts Support a Leukemia-Permissive Microenviroment revealing the Stromal Contribution Eligible for Innovative 3D Targeting

Pediatric acute myeloid leukemia (AML) is a disease in which refinements in diagnostic approaches for patient stratification have resulted into remarkable progresses during the past decade, but chemotherapy still remains the pillar of treatment. Novel anti-leukemia agents failed during clinical validation phases, due to the inappropriateness of current preclinical models used to study drug efficacy. For this purpose, we developed a new protocol for long-term 3D-AML cultures to perform more predictable drug screenings in vitro. We used mesenchymal stromal cells derived from AML patients (AML-MSCs) documenting their support to AML cell growth. We observed that AML-MSCs did not exert anti-inflammatory activity and expressed a peculiar secretome profile. Thus, a drug targeting of AML-MSCs would be desirable, and we performed a screening of 480 compounds. This screening identified 17/480 active compounds capable of reducing AML-MSCs proliferation without toxicity over h-MSCs and AML blasts. We identified one main compound able to selectively reduce AML-MSCs proliferation, that, when combined to novel therapeutic agents for AML blasts showed a synergistic effect in 3D (CI=0.5, p<0.05). We implanted 3D scaffolds in the back of NSG mice and monitored leukemia engraftment in the scaffolds and documented this as a novel useful in vivo system to screen selected drugs in loco. In conclusion, our data support the possibility to work with long-term 3D cultures of AML in vitro to identify new drugs, and we attribute to AML-MSCs a crucial supportive role to be further considered in in vivo settings for novel combo strategies.