Petra Bašová ¹ Lubomir Minarik ¹ Silvia Carina Magalhaes-Novais ² Jana Balounova ² Zuzana Zemanová ³ Tatiana Aghová ³ Martin Špaček ³ Anna Jonasova ³ Kristyna Pimková ¹ Jan Prochazka ² Radislav Sedlacek ² Tomas Stopka ^1*

• ¹ First Faculty of Medicine, Charles University, Prague, Prague, Czechia
• ² Institute of Molecular Genetics (ASCR), Prague, Prague, Czechia
• ³ General University Hospital in Prague, Prague, Prague, Czechia

Progressing myelodysplastic syndrome (MDS) into acute myeloid leukemia (AML) is an indication for hypomethylating therapy (HMA, 5-Azacytidine (AZA)) and a BCL2 inhibitor (Venetoclax, VEN) for intensive chemotherapy ineligible patients. Mouse models that engraft primary AML samples may further advance VEN + AZA resistance research. We decided to create a set of patient derived xenograft (PDX) mouse models with stable engraftment of MDS/AML patient's cells who developed resistance to VEN + AZA and compare PDX leukemia with the primary sample at genetic level. Next, we validated the resistance to VEN + AZA and tested other compounds. PDX were created in NSGS mice via intraosseal injection of luciferase-encoding Lentivirus-infected MDS/AML primary cells from patient bone marrow. Transplantable PDX models for MDS/AML arise with 31 % frequency. The lower frequency of transplantable PDX models is not related to peritransplant lethality of the graft, but rather to the loss of the ability of short-term proliferation of leukemic progenitors after 10 weeks of engraftment. There exist subtle genetic and cytological changes between primary and PDX-AML samples however, the PDX models retain therapy resistance observed in patients, which allowed us to test compounds that bypass this resistance. Based on in vitro testing and in vivo validation in PDX models, Panobinostat and Dinaciclib are very promising candidate agents that overcome dual VEN + AZA resistance.