Abstract
Hemorrhage is a frequent and potentially fatal complication of acute myeloid leukemia (AML) that largely reflects disordered hematopoiesis. Central to this pathology is thrombocytopenia, which arises not only from marrow hypoplasia but also, more importantly, from quantitative and qualitative defects in megakaryocytes (MKs). Recent clinical data indicate that the overexpression of interleukin-8 (IL-8) and its receptors, particularly CXCR2, is associated with inferior outcomes in patients with AML, including increased transfusion dependence. Reparixin, a noncompetitive allosteric antagonist of CXCR1 and CXCR2, effectively dampens IL-8-mediated inflammatory signaling and has demonstrated therapeutic efficacy in diverse preclinical injury models. Therefore, this study aimed to delineate the consequences of elevated IL-8 on bone marrow MK biology and evaluate the capacity of reparixin to rectify thrombocytopenic hemorrhage in a humanized AML mouse model.
Methods Two complementary mouse models were employed. First, wild-type C57BL/6 mice received daily intraperitoneal injections of recombinant human IL-8 for 7 days. Hemograms were monitored, the tail-bleeding time was used to assess hemorrhagic diathesis, and the tibial marrow was analyzed by flow cytometry for MK progenitors and mature MKs (CD41⁺CD42b⁺). Femora underwent H&E and multiplex immunofluorescence staining to quantify MK maturation and marker expression; platelets were profiled for key molecules. Second, THP-1 cells were transduced with a GFP-lentivirus, and 1 × 10⁶ GFP-AAV-labeled cells were intravenously injected into severe combined immunodeficiency (SCID) mice to establish AML. Leukemia was validated by bi-daily complete blood count and marrow GFP⁺ blast quantification. The mice then received azacitidine+venetoclax±reparixin until chemotherapy completion and hematologic recovery, with analyses mirroring those in model 1.
Results In wild-type C57BL/6 mice, flow cytometric analysis of bone marrow-derived cells revealed that, compared with vehicle control treatment, IL-8 administration markedly reduced the number of CD41⁺ MKs (P = 0.0079). The fraction of fully mature CD41⁺CD42b⁺ MKs was even more profoundly diminished (P < 0.0001). Quantitative assessment of membrane expression showed parallel decreases in both CD41 (mean FITC fluorescence intensity, P < 0.0001) and CD41-APC (mean APC fluorescence intensity, P = 0.0285) fluorescence, while CD42b levels were similarly decreased. Consistent with these marrow findings, peripheral complete blood counts revealed a significant decrease in platelet numbers (P = 0.0509), and tail-vein bleeding times were prolonged from 2.5 min in controls to 3.36 min in IL-8-treated animals (P = 0.0405). Additionally, immunofluorescence and H&E staining of the femoral marrow revealed a marked reduction in mature polyploid MKs in the IL-8-treated group. More importantly, reparixin reversed these negative regulatory effects of IL-8 on MK biology and platelet formation.
The transfection efficiency of GFP-expressing lentivirus in THP-1 cells exceeding 85%, validating their suitability for in vivo experiments. Within two weeks, SCID mice that received intravenous injections of GFP-labeled THP-1 cells presented progressive leukocytosis that rose significantly above baseline; conversely, both erythrocyte and platelet counts declined steadily to subphysiologic levels, recapitulating the characteristic hematologic profile of acute myeloid leukemia. Flow cytometry confirmed that GFP⁺ blasts constituted a stable and elevated fraction of bone marrow-derived cells compared with those in the control groups.
At the time of hematologic recovery, mice treated with reparixin presented significantly greater proportions of MK progenitors than did those treated with standard chemotherapy alone. This increase extended to total MK counts and the fraction of terminally differentiated CD41⁺CD42b⁺ MKs, displaying a protective effect of reparixin on megakaryocytic development and highlighting its potential therapeutic value in mitigating thrombocytopenia.
Conclusions The findings suggest that systemic IL-8 suppresses megakaryocytopoiesis and platelet production, prolonging the bleeding time, similar to AML pathology. In a humanized AML model, reparixin added to azacitidine/venetoclax preserved MK maturation during hematologic recovery, indicating that CXCR1/2 blockade is a promising strategy to prevent AML-related thrombocytopenia and hemorrhage.
