20(S)-PPD-HSA NPs enhance the recovery of intramedullary and extramedullary hematopoiesis in cyclophosphamide-treated mice through activation of the FGFR1/ERK pathway

Objective: Chemotherapy-induced myelosuppression (MYE) remains a major dose-limiting toxicity that severely compromises treatment efficacy and patient outcomes, while effective therapeutic agents are still lacking. This study aimed to evaluate the therapeutic effects of 20(S)-protopanaxadiol-human serum albumin nanoparticles (20(S)-PPD-HSA NPs) on cyclophosphamide-induced MYE and to elucidate the underlying mechanisms.

Methods: 20(S)-PPD-HSA NPs were characterized by electron microscopy, particle size, zeta potential, drug loading, and encapsulation efficiency. A cyclophosphamide-induced MYE mouse model was established. Hematopoietic recovery was evaluated via blood counts, ELISA for granulocyte colony-stimulating factor (G-CSF), and flow cytometry for Lin^- Sca-1⁺c-Kit⁺(LSK) cells. H&E staining, ELISA, flow cytometry, and Western blotting assessed bone marrow and spleen hematopoietic function and FGFR1/ERK pathway activation. In vitro, OP9 and mouse splenic stromal cells were treated with inhibitors to assess proliferation, Apoptosis, DNA damage, senescence, and SCF/SDF-1 expression.

Results: The 20(S)-PPD-HSA NPs exhibited a uniform nanostructure and excellent drug delivery performance. In vivo, the 20(S)-PPD-HSA NPs significantly alleviated cyclophosphamide-induced hematopoietic dysfunction, restored the structure of bone marrow and spleen tissues, and markedly increased the number of LSK cells, with their therapeutic effect being independent of elevated G-CSF levels. Further studies demonstrated that the 20(S)-PPD-HSA NPs activated the FGFR1/ERK signaling pathway, an effect that was partially blocked by FGFR1 or ERK inhibitors. In vitro, 20(S)-PPD-HSA NPs promoted the proliferation of OP9 cells and murine splenic stromal cells, inhibited Apoptosis, DNA damage, and cellular senescence, and upregulated SCF and SDF-1 expression via activation of the FGFR1/ERK pathway. Co-culture experiments further confirmed that the NPs improved the hematopoietic microenvironment and enhanced the stromal cells' hematopoietic support function.

Conclusion: 20(S)-PPD-HSA NPs effectively enhanced medullary and extramedullary hematopoietic functions in cyclophosphamide-induced MYE mice by activating the FGFR1/ERK pathway, independent of increased G-CSF levels. These findings highlight 20(S)-PPD-HSA NPs as a promising therapeutic strategy for chemotherapy-induced myelosuppression.

20(S)-PPD-HSA nanoparticles; Cyclophosphamide; FGFR1/ERK; Myelosuppression; Ras/Raf.