Parthenolide boosts megakaryocyte maturation and restores platelet responses in Wiskott Aldrich syndrome

Wiskott-Aldrich syndrome (WAS) is an inborn error of immunity with a broad disease spectrum, classified into class I (late onset) or II (early onset) variants. Thrombocytopenia and small platelets are the most consistent findings among patients, difficult to treat and related to development of autoimmunity. To identify new treatment options for thrombocytopenia in WAS, we developed a FACS-based screening for drug repurposing. We identified parthenolide as a lead small molecule that increased WASp abundance in cells with residual WASp expression. Using the megakaryocytic MEG-01 cells, gene edited to express WAS class I and II genetic variants, parthenolide induced megakaryocyte maturation as evident by upregulation of CD61, increased cell size and complexity, increased phosphorylation of ERK1/2, and higher DNA ploidy. We generated a new mouse model harboring a WAS class I missense variant WASp-R88C, corresponding to human WASp-R86C, with reduced expression of WASp. WASp-R88C mice had lower numbers of platelets compared to WT mice. Bone marrow-derived WASp-R88C and WASp-KO megakaryocytes, differentiated in the presence of parthenolide derivative, DMAPT, showed increased ploidy and upregulation of the maturation markers CD61, CD41 and CD42d, resulting in improved platelet production in vitro. Treatment with parthenolide derivative, DMAPT, led to increased platelet numbers in vivo in WASp-R88C mice and dampened the hyperactivation of WAS patient platelets by reducing thrombin-induced CD62P exposure after activation. The identification of parthenolide offers a promising therapeutic approach for WAS patients who are unresponsive or unsuitable for definitive therapies.