Human Mesenchymal Stem Cell-Derived Exosomes as Engineering Vehicles of Daunorubicin for Targeted c-Mpl+ AML Therapy

Acute myeloid leukemia (AML) is a highly heterogeneous disease with poor therapeutic outcomes and overall prognosis, particularly in c-Mpl+ AML. c-Mpl, a proto-oncogene, is expressed at significantly higher levels in AML compared to normal human tissue cells. This study aimed to develop a type of targeted exosomes (Exos) capable of delivering anticancer drugs directly to c-Mpl+ AML cells.

Human umbilical cord mesenchymal stem cells (hUCMSCs) were isolated as the source of Exos. Fusion CD63 proteins with varying numbers of thrombopoietin (TPO)-mimic peptides, designed to target c-Mpl, were bioengineered to be expressed on the membranes of hUCMSCs and their derived Exos. The targeting capability of the fusion proteins was assessed using the DUAL membrane system, fluorescence resonance energy transfer efficiency, and endocytosis assays. After encapsulating the anticancer drug daunorubicin (DNR), these targeted Exos were evaluated for their ability to eliminate c-Mpl+ AML cells. Safety and efficacy were further tested in a mouse AML model.

Our findings showed that the engineered hUCMSCs-derived Exos demonstrated excellent targeting ability to c-Mpl and a strong propensity for endocytic uptake by c-Mpl+ AML cells. Among the engineered Exos, those with the fusion protein containing three TPO-mimic peptides (CD63-mTPO₃), named as m₃Exos, exhibited the highest binding affinity for c-Mpl. When loaded with DNR, these engineered Exos (m₃Exos@DNR) effectively eliminated c-Mpl+ AML cells in both in vitro and in vivo experiments. Furthermore, safety assessments revealed that therapy-related toxicities were within acceptable limits and associated with manageable side effects.

In summary, our results suggest engineered Exos as a highly effective targeted drug delivery vehicle for eliminating c-Mpl+ AML cells while maintaining a favorable safety profile. These findings also provide valuable insights for developing therapeutic strategies for AML and other tumors characterized by specific membrane protein expression.