Palbociclib and Ponatinib Suppress Acute Myeloid Leukemia in Patient-Derived Xenograft

Abstract

Aims: Palbociclib, a breast cancer approved CDK4/6 inhibitor, and ponatinib, a BCR/ABL1 inhibitor with a multi-kinase activity approved for chronic myeloid and acute lymphoid leukemia, were previously shown to be effective in vitro against acute myeloid leukemia (AML). Here, we aimed to test this effect in a patient-derived xenograft model.Methods: Two newly diagnosed AMLs (AML #1: myelomonocytic AML, intermediate cytogenetic risk; AML #2: AML with myelodysplasia-related changes, poor cytogenetic risk) were xenotransplanted into NOD SCID gamma mice. Treatment was initiated at detection of approximately 5-20% hCD45+ cells in mouse peripheral blood (PB). Palbociclib, ponatinib, vehicle, and venetoclax as a comparative treatment, were administered orally for 3 weeks, 5 days per week. Chemotherapy (cytarabine+doxorubicine, AraC/Dox) 5+3 regimen served as a positive control. Azacitidine served as another comparative drug and was administered subcutaneously, five days per week in 3 cycles - 1 week on, 1 week off.Results: Significant reduction of disease burden and prolongation of overall survival (OS) were seen with palbociclib and the reference treatment venetoclax in both AMLs, and with chemotherapy in AML#1 (Fig. 1). Ponatinib prolonged OS in AML#1 but failed to provide reduction of disease burden in PB. Interestingly, azacitidine induced the longest remission (<1% hCD45+ cells in PB), for almost 10 weeks, but only in 2/4 mice for AML#2. Treatment toxicity manifested by weight decrease was only seen with chemotherapy (AML#1: 24% weight loss, p = 0.0001; AML#2: 19% loss, p = 0.04), and was also accompanied with early mouse mortality in 3/4 mice for AML#2. None of the tested treatments lead to complete AML eradication and a gradual relapse was seen in PB. The AML infiltration was higher in bone marrow than in spleen at final analysis at relapse (AML#1, 83 vs 73% of hCD45+ cells, mean, p = 0.02; AML#2, 95 vs 65%, p = 0.0001). No changes in AML phenotype were observed between treated and vehicle mice in case of AML#1, except for azacitidine which decreased monocyte (SSCdim, CD45high; 94 vs 96%, mean, p = 0.03), CD34+ (2 vs 5%, p = 0.01) and primitive CD34+CD38- cell (0.1 vs 0.3%, p = 0.005) percentages. For AML#2, blast (SSClow, CD45dim) percentage compared to vehicle (70%) was decreased by chemotherapy (24%, p = 0.01) and increased by venetoclax (80%, p = 0.03) and azacitidine (87%, p = 0.03); monocytes (6% for vehicle) were decreased by chemotherapy (1%, p = 0.004), venetoclax (3%, p = 0.01), and azacitidine (0%, p = 0.008); CD34+ cells were increased by venetoclax (59 vs 39%, p = 0.02).Summary: Palbociclib, and partially ponatinib, demonstrated AML suppression in vivo. This encourages further investigation of their efficacy in different AML subtypes and in combination with other drugs.Funding: Supported by MUNI/A/1595/2020. [Display omitted] DisclosuresMayer: AOP Orphan Pharmaceuticals: Research Funding.