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Selective killing of human malignant cell lines deficient in methylthioadenosine phosphorylase, a purine metabolic
Abstract:
Seven out of 31 (23%) human malignant tumor cell lines had no detectable methylthioadenosine phosphorylase activity (less than 0.001 nmol/min per mg of protein), assayed with 5'-chloroadenosine as substrate. The enzyme-deficient cell lines were derived from five leukemias, one melanoma, and one breast cancer. None of 16 cell lines of nonmalignant origin, derived from lymphocytes, fibroblasts, and epithelial cells, lacked the enzyme (range, 0.156-1.447 nmol/min per mg of protein). As detected by autoradiography, intact enzyme-positive cell lines normal immature bone marrow cells, and four specimens of malignant tumor cells incorporated the adenine moiety of 5'-chloroadenosine into nucleic acids; however, no enzyme-deficient cell lines used 5'-chloroadenosine. When both types of cell lines were cultured in a medium containing 0.4 microM methotrexate, 16 microM uridine, and 16 microM thymidine (or 10 microM azaserine alone), no cells grew. If methylthioadenosine was added to the same medium, only enzyme-positive cells increased in number; most enzyme-deficient cells were dead after 3 days. Thus, human malignant tumor cell lines naturally deficient in methylthioadenosine phosphorylase could be selectively killed when de novo purine synthesis was inhibited and methylthioadenosine was the only exogenous source of purines.
Insights
Certain human malignant tumor cell lines lack methylthioadenosine phosphorylase (MTAP). These MTAP-deficient cancer cells can be selectively killed by inhibiting purine synthesis and providing methylthioadenosine as the sole purine source.
Area of Science:
- Biochemistry
- Oncology
- Cell Biology
Background:
- Methylthioadenosine phosphorylase (MTAP) is a purine salvage enzyme.
- MTAP deficiency is observed in a subset of human malignant tumors.
- Understanding MTAP's role is crucial for cancer therapy development.
Purpose of the Study:
- To investigate the prevalence of MTAP deficiency in human cancer cell lines.
- To explore the potential of targeting MTAP-deficient tumors therapeutically.
- To assess the selective killing of MTAP-deficient cells under specific metabolic conditions.
Main Methods:
- Assay of methylthioadenosine phosphorylase (MTAP) activity in human malignant and non-malignant cell lines using 5'-chloroadenosine.
- Autoradiographic detection of 5'-chloroadenosine incorporation into nucleic acids.
- Cell culture experiments with methotrexate, uridine, thymidine, azaserine, and methylthioadenosine to assess cell viability.
Main Results:
- Seven out of 31 (23%) malignant tumor cell lines exhibited no detectable MTAP activity.
- Non-malignant cell lines consistently showed detectable MTAP activity.
- MTAP-deficient cell lines could not incorporate the adenine moiety of 5'-chloroadenosine.
- MTAP-deficient cells were selectively killed when de novo purine synthesis was inhibited and methylthioadenosine was the sole purine source.
Conclusions:
- Human malignant tumor cell lines can be naturally deficient in MTAP.
- MTAP deficiency presents a potential vulnerability for targeted cancer therapy.
- Selective killing of MTAP-deficient tumors is achievable by manipulating purine metabolism.
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