Abstract 6835: Inhibition of platelet activation and antibody-dependent cellular cytotoxicity by the tyrosine kinase inhibitor dasatinib in an <i>ex vivo</i> human whole blood system

Abstract Dasatinib is a second-generation tyrosine kinase inhibitor approved for therapeutic use in patients with Philadelphia-positive (Ph+) chronic myeloid leukemia. Dosing of dasatinib is limited by the potential for side effects, including pleural effusion and bleeding disorders. The propensity for bleeding problems is at least in part due to dasatinib inhibiting normal platelet functions. While dasatinib is effective in treating leukemia, the challenge in dosing is associated with a risk for emergence of the T315I mutation of BCR-ABL and potential tumor escape. Thus, the ability to combine dasatinib with other therapeutic agents is desirable and currently under investigation. We have developed an ex vivo test system using circulating fresh human whole blood, enabling direct study of the effects of various compounds on platelet aggregation and activation in a physiologically relevant environment. To see whether the clinical effects of dasatinib could be recapitulated in the test system, we incubated blood from healthy donors in the system with dasatinib prior to stimulation with Thrombin Receptor (PAR1) Activating Peptide 6 (TRAP-6). As predicted, dasatinib significantly inhibited TRAP-6-mediated platelet aggregation and activation as measured by whole blood free platelet counts, platelet expression of CD62P, and the formation of platelet-white blood cell conjugates. At the Cmax concentration, alemtuzumab (anti-CD52) results in antibody-dependent cellular cytotoxicity (ADCC) and release of large amounts of cytokines in the test system, mimicking clinical effects of the drug. We also see a drop in platelet count and platelet activation, correlating with acute effects of alemtuzumab observed in patients. Based on these observations, alemtuzumab was used in the system to investigate whether dasatinib could inhibit platelet activation by a therapeutic drug with known effects on platelets. Dasatinib significantly inhibited the drop in free platelet count and platelet activation seen in response to alemtuzumab. As dasatinib could potentially inhibit multiple signaling pathways, we also investigated whether it had effects on ADCC of CD52+ cell types (lymphocytes and monocytes) by alemtuzumab in the ex vivo system. The decreased lymphocyte and monocyte counts observed in alemtuzumab-treated samples were significantly increased by the addition of dasatinib, whereas non-CD52 expressing cells (such as neutrophils) were not affected. Taken together, the data suggest that the ex vivo test system can be used to investigate the effect of different therapeutic agents on platelet activation and that dasatinib at concentrations that inhibit platelet activation may also inhibit ADCC. Combination therapies involving dasatinib and antibodies with predicted ADCC-dependent effects may thus require further investigation prior to clinical use. Citation Format: Sakthi Srinivasan, Ali Zirakzadeh, Sofia Ramström, Erika A. Fletcher, Helena Harlin Laven. Inhibition of platelet activation and antibody-dependent cellular cytotoxicity by the tyrosine kinase inhibitor dasatinib in an ex vivo human whole blood system [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 6835.