Related Experiment Video

Updated: Aug 7, 2026

Chemical Inactivation of the E3 Ubiquitin Ligase Cereblon by Pomalidomide-based Homo-PROTACs
10:44

Chemical Inactivation of the E3 Ubiquitin Ligase Cereblon by Pomalidomide-based Homo-PROTACs

Published on: May 15, 2019

Molecular mechanisms underlying the enhanced sensitivity of thiopurine-resistant T-lymphoblastic cell lines to methyl

Alan Kambiz Fotoohi1, Anna Wrabel, Ali Moshfegh

  • 1Department of Oncology and Pathology, Cancer Center Karolinska (CCK), Karolinska Hospital and Institute, 171 76 Stockholm, Sweden.

Biochemical Pharmacology
|July 25, 2006
PubMed

Insights

Methylmercaptopurine riboside (meMPR) overcomes resistance to thiopurines like 6-MP and 6-TG by inhibiting purine synthesis. Resistant cells show increased sensitivity to meMPR due to altered transport and reduced purine synthesis pathways.

Area of Science:

  • Biochemistry
  • Cell Biology
  • Pharmacology

Background:

  • Thiopurines such as 6-mercaptopurine (6-MP) and 6-thioguanine (6-TG) are crucial in treating certain leukemias.
  • Resistance to thiopurines often arises from defective cellular transport mechanisms.
  • Methylmercaptopurine riboside (meMPR), a metabolite of 6-MP, is a potent inhibitor of de novo purine synthesis (DNPS).

Purpose of the Study:

  • To investigate the mechanism of enhanced sensitivity to meMPR in thiopurine-resistant T-lymphoblastic leukemia cells.
  • To elucidate the transport pathway of meMPR and its relationship to thiopurine transport.
  • To determine how meMPR affects purine synthesis and nucleotide levels in resistant cells.

Main Methods:

  • HPLC analysis to assess meMPR uptake in wild-type and resistant cell lines.
  • Inhibition studies using adenosine, dipyridamole, and nitrobenzylthioinosine to identify meMPR transporters.
  • siRNA-mediated gene silencing of equilibrative nucleoside transporter 1 (ENT1).
  • Quantitative analysis of mRNA levels for key DNPS enzymes and ribonucleoside triphosphate concentrations.

Main Results:

  • Thiopurine-resistant cells exhibited normal meMPR uptake, indicating a distinct transport mechanism from 6-MP and 6-TG.
  • meMPR uptake was significantly inhibited by adenosine, dipyridamole, and nitrobenzylthioinosine, and reduced by ENT1 knockdown.
  • Resistant cell lines showed decreased mRNA levels for key DNPS enzymes, leading to a 50% reduction in DNPS rate.
  • Lower ribonucleoside triphosphate levels were observed in resistant cells compared to parental cells.

Conclusions:

  • meMPR utilizes a transport system, likely involving ENT1, that is independent of the defective transporters for 6-MP and 6-TG.
  • Reduced de novo purine synthesis and lower ribonucleoside triphosphate pools in resistant cells contribute to their heightened sensitivity to meMPR.
  • meMPR effectively bypasses thiopurine resistance mechanisms, offering a potential therapeutic strategy for resistant leukemia.

More Related Videos

Quantitative Methods to Study Protein Arginine Methyltransferase 1-9 Activity in Cells08:11

Quantitative Methods to Study Protein Arginine Methyltransferase 1-9 Activity in Cells

Published on: August 7, 2021

Related Concept Videos

Pharmacogenetics of Drug Targets: β₂-Adrenergic Receptors, Apo E, Thymidylate Synthase01:11

Pharmacogenetics of Drug Targets: β₂-Adrenergic Receptors, Apo E, Thymidylate Synthase

Genetic polymorphisms in drug targets have emerged as critical determinants of interindividual variability in drug response and toxicity. Pharmacogenomic investigations increasingly focus on identifying these variations to personalize and optimize therapeutic interventions. A drug target may be a receptor, enzyme, or signaling protein involved in pharmacologic responses or disease-related pathways. While early pharmacogenetic studies focused primarily on drug metabolism, current research...
Abnormal Proliferation02:23

Abnormal Proliferation

Under normal conditions, most adult cells remain in a non-proliferative state unless stimulated by internal or external factors to replace lost cells. Abnormal cell proliferation is a condition in which the cell's growth exceeds and is uncoordinated with normal cells. In such situations, cell division persists in the same excessive manner even after cessation of the stimuli, leading to persistent tumors. The tumor arises from the damaged cells that replicate to pass the damage to the daughter...
Treatment Resistant Cancers02:56

Treatment Resistant Cancers

Cancer is the second leading cause of death in the United States. A cancer cell is genetically unstable and hence can mutate faster. They can also modify their microenvironment and escape immune surveillance. The difficulties in treating cancer are further compounded by the emergence of rapid resistance to anticancer drugs. The most common ways to attain resistance in cancer cells include alteration in drug transport and metabolism, modification of drug target, elevated DNA damage response, or...
Phase II Reactions: Methylation Reactions01:17

Phase II Reactions: Methylation Reactions

Methylation is a phase II biotransformation process involving the attachment of a methyl group to a substrate. Enzymes known as methyltransferases orchestrate this reaction.
The mechanism of methylation unfolds in two stages. The first stage sees a methyltransferase enzyme facilitating the transfer of a methyl group from S-adenosylmethionine (SAM) to the substrate, forming S-adenosylhomocysteine (SAH). The second stage involves further metabolism of SAH into homocysteine, which can be recycled...
Targeted Cancer Therapies02:57

Targeted Cancer Therapies

The targeted cancer therapies, also known as “molecular targeted therapies,” take advantage of the molecular and genetic differences between the cancer cells and the normal cells. It needs a thorough understanding of the cancer cells to develop drugs that can target specific molecular aspects that drive the growth, progression, and spread of cancer cells without affecting the growth and survival of other normal cells in the body.
There are several types of targeted therapies against specific...
Biosynthesis of Nucleic Acids01:28

Biosynthesis of Nucleic Acids

Nucleic acid biosynthesis is a fundamental biochemical process that produces the purine and pyrimidine nucleotides essential for DNA and RNA synthesis. This pathway maintains a balanced nucleotide pool, preventing imbalances that could jeopardize genetic integrity and cellular function. Given the crucial role of nucleotides, their synthesis is tightly regulated to ensure proper cellular homeostasis.Purine BiosynthesisThe biosynthesis of purine nucleotides begins with ribose-5-phosphate, a...