Downregulation of PUMA underlies resistance to FGFR1 inhibitors in the stem cell leukemia/lymphoma syndrome

Yun Liu,Chang-Sheng Chang,Mingqiang Ren,Tianxiang Hu,Chesley-Anne Kemp,Yating Chong,Sumin Lu,Hualei Zhang,Baohuan Cai,John K Cowell

doi:10.1038/s41419-020-03098-1

Abstract

Resistance to molecular therapies frequently occur due to genetic changes affecting the targeted pathway. In myeloid and lymphoid leukemias/lymphomas resulting from constitutive activation of FGFR1 kinases, resistance has been shown to be due either to mutations in FGFR1 or deletions of PTEN. RNA-Seq analysis of the resistant clones demonstrates expression changes in cell death pathways centering on the p53 upregulated modulator of apoptosis (Puma) protein. Treatment with different tyrosine kinase inhibitors (TKIs) revealed that, in both FGFR1 mutation and Pten deletion-mediated resistance, sustained Akt activation in resistant cells leads to compromised Puma activation, resulting in suppression of TKI-induced apoptosis. This suppression of Puma is achieved as a result of sequestration of inactivated p-Foxo3a in the cytoplasm. CRISPR/Cas9 mediated knockout of Puma in leukemic cells led to an increased drug resistance in the knockout cells demonstrating a direct role in TKI resistance. Since Puma promotes cell death by targeting Bcl2, TKI-resistant cells showed high Bcl2 levels and targeting Bcl2 with Venetoclax (ABT199) led to increased apoptosis in these cells. In vivo treatment of mice xenografted with resistant cells using ABT199 suppressed leukemogenesis and led to prolonged survival. This in-depth survey of the underlying genetic mechanisms of resistance has identified a potential means of treating FGFR1-driven malignancies that are resistant to FGFR1 inhibitors.

Highlights

Tyrosine kinase inhibitors have proven a highly effective approach to the treatment of a wide variety of cancers[1] but, as mono therapies, resistant clones almost inevitably emerge requiring alternative approaches to treat these resistant derivatives[2]
The stem cell leukemia/lymphoma syndrome (SCLL) is an aggressive leukemia subtype that presents with myeloproliferative disease which progresses to AML and which can be accompanied by T-cell and Bcell leukemias/lymphomas[3]
Gene set enrichment analysis (GSEA) demonstrated regulation of cell death (Fig. 1B) as the most significantly altered pathway which, in particular, included downregulation of the Bbc[3] gene, which translates into the p53 upregulated modulator of apoptosis (Puma) protein

Summary

Introduction

Tyrosine kinase inhibitors have proven a highly effective approach to the treatment of a wide variety of cancers[1] but, as mono therapies, resistant clones almost inevitably emerge requiring alternative approaches to treat these resistant derivatives[2]. Liu et al Cell Death and Disease (2020)11:884 chimeric FGFR1 kinases in vitro[6] These studies, when extended to xenografts studies in vivo, support the idea that resistant cells are insensitive to these inhibitors. The mechanisms of inhibition were shown to be due, so far, to mutations in the FGFR1 domains that affect the ATPbinding sites or deletions within PTEN leading to gene inactivation[7]. Beyond these initial observations, little is known about the mechanisms of resistance, which might provide insights into alternative strategies for treatment of the resistant disease

Methods

Results

Conclusion