GLI2 inhibition abrogates human leukemia stem cell dormancy

Area of Science:

• Hematology
• Cancer Biology
• Stem Cell Biology

Background:

• Dormant leukemia stem cells (LSCs) contribute to therapeutic resistance and disease progression by activating stem cell gene expression programs.
• Deregulation of the Hedgehog (Hh) pathway, involved in stem cell self-renewal and cell cycle regulation, is hypothesized to promote dormant LSC generation.
• PF-04449913, a clinical antagonist of smoothened (SMO), is investigated for its potential to eradicate dormant human LSCs.

Purpose of the Study:

• To investigate the role of Hh pathway deregulation in dormant LSC generation.
• To evaluate the efficacy of PF-04449913 in eradicating dormant human LSCs.
• To determine the impact of SMO inhibition on LSC cell cycle and sensitivity to therapy.

Main Methods:

• Whole transcriptome RNA sequencing (RNA-seq), microarray, and qRT-PCR were employed to analyze gene expression.
• Experiments included stromal co-culture, confocal fluorescence microscopy, nanoproteomics, and serial transplantation.
• Analyses were performed on FACS-purified normal, chronic myeloid leukemia (CML) progenitors (CP and BC phases) with or without PF-04449913 treatment.

Main Results:

• RNA-seq revealed overexpression of Hh pathway and cell cycle regulatory genes correlated with leukemic progression.
• GLI2 expression promoted leukemic progenitor dormancy, while a mutant GLI2 lacking a transactivation domain did not, indicating GLI2's role in preventing cell cycle transit.
• PF-04449913 treatment reduced GLI2 protein and cell cycle gene expression, enhanced cell cycle transit, and sensitized blast crisis CML LSCs to tyrosine kinase inhibitors in vivo, sparing normal hematopoietic stem cells.

Conclusions:

• GLI2 is a key component of the Hh pathway transcriptional network driving human myeloid leukemic progression and dormant LSC generation.
• Selective SMO inhibition with PF-04449913 effectively reduces the dormant LSC burden.
• These findings provide a strong rationale for clinical trials combining SMO inhibitors with TKIs or chemotherapy to overcome therapeutic resistance, persistence, and progression in leukemia.