Negative feedback-defective PRPS1 mutants drive thiopurine resistance in relapsed childhood ALL

Nat Med. 2015 Jun;21(6):563-71. doi: 10.1038/nm.3840. Epub 2015 May 11.


Relapse is the leading cause of mortality in children with acute lymphoblastic leukemia (ALL). Among chemotherapeutics, thiopurines are key drugs in ALL combination therapy. Using whole-exome sequencing, we identified relapse-specific mutations in the phosphoribosyl pyrophosphate synthetase 1 gene (PRPS1), which encodes a rate-limiting purine biosynthesis enzyme, in 24/358 (6.7%) relapsed childhood B cell ALL (B-ALL) cases. All individuals who harbored PRPS1 mutations relapsed early during treatment, and mutated ALL clones expanded exponentially before clinical relapse. Our functional analyses of PRPS1 mutants uncovered a new chemotherapy-resistance mechanism involving reduced feedback inhibition of de novo purine biosynthesis and competitive inhibition of thiopurine activation. Notably, the de novo purine synthesis inhibitor lometrexol effectively abrogated PRPS1 mutant-driven drug resistance. These results highlight the importance of constitutive activation of the de novo purine synthesis pathway in thiopurine resistance, and they offer therapeutic strategies for the treatment of relapsed and thiopurine-resistant ALL.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Child
  • Child, Preschool
  • Exome / genetics
  • Feedback, Physiological / drug effects*
  • Female
  • High-Throughput Nucleotide Sequencing
  • Humans
  • Infant
  • Leukemia, B-Cell / drug therapy
  • Leukemia, B-Cell / genetics*
  • Leukemia, B-Cell / pathology
  • Male
  • Mercaptopurine / administration & dosage
  • Mutation
  • Precursor Cell Lymphoblastic Leukemia-Lymphoma / drug therapy
  • Precursor Cell Lymphoblastic Leukemia-Lymphoma / genetics*
  • Precursor Cell Lymphoblastic Leukemia-Lymphoma / pathology
  • Purines / biosynthesis
  • Recurrence
  • Ribose-Phosphate Pyrophosphokinase / chemistry
  • Ribose-Phosphate Pyrophosphokinase / genetics*
  • Tetrahydrofolates / administration & dosage


  • Purines
  • Tetrahydrofolates
  • lometrexol
  • Mercaptopurine
  • PRPS1 protein, human
  • Ribose-Phosphate Pyrophosphokinase
  • purine