Purpurin Alleviates Chemotherapy‐Induced Thrombocytopenia Through Estrogen Receptor α Dependent Phosphoinositide 3‐Kinase/Protein Kinase B Signalling

ABSTRACT Chemotherapy‐induced thrombocytopenia (CIT) increases bleeding risk and compromises chemotherapy delivery. Purpurin, a hydroxyanthraquinone found in Rubia cordifolia L., has not been examined as a regulator of megakaryopoiesis. We investigated whether purpurin restores platelet production after cyclophosphamide (CTX) exposure and examined the involvement of estrogen receptor α (ESR1)–phosphoinositide 3‐kinase (PI3K)/protein kinase B (AKT) signalling. Purpurin was evaluated in K562 and Meg‐01 megakaryocytic differentiation models, Tg(itga2b:eGFP) zebrafish, and CTX‐induced thrombocytopenic mice. Megakaryocyte (MK) differentiation, DNA ploidy, cytoskeletal remodelling, platelet recovery, and haemostatic function were assessed. Computational target prediction was used for hypothesis generation, followed by drug affinity responsive target stability analysis and pharmacological inhibition of ESR1 and PI3K. At concentrations that did not cause detectable cytotoxicity (2.5–10 μM), purpurin increased CD41 + CD42b + cells, MK ploidy, F‐actin remodelling, and expression of NF‐E2, GATA1, RUNX1, and FOSB. Purpurin increased thrombocyte abundance in zebrafish and restored platelet counts, MK maturation, and haemostatic function in CTX‐treated mice. Purpurin increased the resistance of ESR1 to proteolysis in the drug affinity responsive target stability (DARTS) assay. Pharmacological inhibition of ESR1 or PI3K attenuated purpurin‐induced differentiation and PI3K/AKT phosphorylation. These findings support the involvement of ESR1‐associated PI3K/AKT signalling through which purpurin promotes megakaryopoiesis and platelet recovery. Purpurin warrants further evaluation as a natural‐product lead for CIT, including genetic target validation, pharmacokinetic characterization, and assessment in tumour‐bearing models.