Abstract
Aberrant RHO guanine nucleotide exchange factor (RhoGEF) activation is chief mechanism driving abnormal activation of their GTPase targets in transformation and tumorigenesis. Consequently, a small-molecule inhibitor of RhoGEF can make an anti-cancer drug. We used cellular, mouse, and humanized models of RAC-dependent BCR-ABL1-driven and Ph-like acute lymphoblastic leukemia to identify VAV3, a tyrosine phosphorylation–dependent RacGEF, as the target of the small molecule IODVA1. We show that through binding to VAV3, IODVA1 inhibits RAC activation and signaling and increases pro-apoptotic activity in BCR-ABL1-transformed cells. Consistent with this mechanism of action, cellular and animal models of BCR-ABL1-induced leukemia in Vav3-null background do not respond to IODVA1. By durably decreasing in vivo RAC signaling, IODVA1 eradicates leukemic propagating activity of TKI-resistant BCR-ABL1(T315I) B-ALL cells after treatment withdrawal. Importantly, IODVA1 suppresses the leukemic burden in the treatment refractory pediatric Ph+ and TKI-resistant Ph+ B-ALL patient-derived xenograft models better than standard-of-care dasatinib or ponatinib and provides a more durable response after treatment withdrawal. Pediatric leukemia samples with diverse genetic lesions show high sensitivity to IODVA1 ex vivo and this sensitivity is VAV3 dependent. IODVA1 thus spearheads a novel class of drugs that inhibits a RacGEF and holds promise as an anti-tumor therapy.
Highlights
INTRODUCTION RACGTPases have been associated with pro-tumorigenic functions and development of cancer
IODVA1 targets BCR-ABL1 B-ALL cells in vitro First, we assessed whether IODVA1 is specific to oncogenetransformed cells
IODVA1 irreversibly inhibited the survival of p190- and p210-BCR-ABL1 but not of empty vector-expressing Ba/F3 cells with EC50 of 380 nM, NALM-1 cells with an EC50 of 680 nM and inhibited the colony-forming ability of BCR-ABL1-Ba/F3 cells (Supplementary Fig. S1A–D). These results indicate that IODVA1 targets proliferation and survival of BCR-ABL1transformed cells and are consistent with our previous report that IODVA1 targets transformed cells [11]
Summary
INTRODUCTION RACGTPases have been associated with pro-tumorigenic functions and development of cancer. By durably decreasing in vivo RAC signaling, IODVA1 eradicates leukemic propagating activity of TKI-resistant BCR-ABL1(T315I) B-ALL cells after treatment withdrawal. We show that by binding to VAV3, IODVA1 inhibits RAC activation and its downstream signaling and induces apoptosis in leukemic cells in vivo and in vitro.
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