Thymidylate synthase expression determines pemetrexed targets and resistance development in tumour cells

Our plain-English summary of Thymidylate synthase expression determines pemetrexed targets and resistance development in tumour cells, by A. Buqué, U. Aresti, B. Calvo, et al (PloS One, 2013).

The study

• Authors: A. Buqué, U. Aresti, B. Calvo, J. Sh Muhialdin, A. Muñoz, S. Carrera, E. Azkona, I. Rubio, G. López-Vivanco
• Journal: PloS One
• Published: 2013;8(5):e63338
• Cited by: 21 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Although treatment options for cancer patients are increasing every year, the drug resistance problem remains very present. It is very difficult to find a drug that acts equally on tumours of the same histology as the individual's genetic characteristics often determine the response to treatment. Furthermore, tumours that initially respond to anti-tumour therapy are able to adapt and develop resistance to the drug, while others do not. In addition, this usually implies resistance development to agents to which the cells have not been exposed, a phenomenon called cross-resistance or multidrug resistance. Given this situation, it has been suggested that the most appropriate treatment would be able to act in parallel on multiple pathways constitutively altered in tumour cells. Pemetrexed is a multitargeted antifolate that exerts its activity against folate-dependent enzymes involved in de novo pyrimidine and purine synthesis. It is currently in use in combination with cisplatin against malignant pleural mesothelioma and non-squamous non-small cell lung cancer with favourable results. By real-time RT-PCR gene expression assays and restoration viability assays we demonstrated that Pemetrexed targets folate-dependent enzymes involved in de novo biosynthesis of purines differently depending on the intrinsic genetic characteristics of the tumour. These differences did not, however, interfere either with the initial response to the drug or with the activation of apoptotic pathways. In addition, these genetic fingerprints can differentiate two groups of tumours: those capable of developing resistance to antifolate, and not capable. These results may be useful to employ targets gene expression as resistance markers, a valuable tool for identifying patients likely to receive combination therapy to prevent the development of resistance.

In plain English

This was a laboratory study of human tumour cells grown in dishes, not of people or of asbestos exposure. Mesothelioma appears only because pemetrexed (MTA), the drug tested, is used with cisplatin to treat malignant pleural mesothelioma. No mesothelioma cells were studied. The authors used four melanoma cell lines (A375, Hs294T, HT144, MeWo) and one non-small cell lung cancer line (Calu-3). Adding back the cell-building ingredients the drug blocks showed that the drug's secondary target differed between lines. Lines HT144 and Calu-3 had significantly lower levels of thymidylate synthase (TS), the drug's main target. In the melanoma lines, markers of growth signalling fell after drug exposure. After 3 months of rising doses, A375, Hs294T and MeWo became drug-resistant. HT144 and Calu-3 did not, using the method employed. In two of the resistant lines, TS levels rose. The authors concluded that sensitivity to the drug appears to follow a genetic pattern linked to TS levels. They stated that larger studies of treated patients are needed.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory (in vitro) study of human tumour cell lines
• Who was studied: Five commercially obtained human tumour cell lines: four melanoma lines (A375, Hs294T, HT144, MeWo) and one non-small cell lung cancer (lung adenocarcinoma) line (Calu-3). No patients and no mesothelioma cells were studied.
• Exposure: The anticancer drug pemetrexed (MTA), alone or with added metabolites (thymidine, hypoxanthine, AICA). Resistance was induced by repeatedly doubling the drug concentration as cells grew. There was no asbestos exposure.
• Main results:
  • In all cell lines, adding thymidine reversed the drug's growth-inhibiting effect.
  • In A375, Hs294T and MeWo, adding AICA reduced growth inhibition, pointing to GARFT as the drug's target. In HT144 and Calu-3 it did not, pointing to AICART as the target.
  • The lines in which AICART appeared to be the secondary target (HT144 and Calu-3) had significantly lower TS expression.
  • Phosphorylated Akt decreased after drug treatment. The Results text says this happened in all cell lines, but the figure summarizes results for the melanoma cell lines.
  • In the melanoma cell lines, levels of p-4EBP1, a marker of mTOR activity, fell after drug exposure.
  • Drug-resistant lines were established from A375, Hs294T and MeWo, but not from HT144 or Calu-3.
  • TS expression increased in resistant A375-M and Hs294T-M. MeWo-M showed a rise in RFC and a strong decrease in AICART, DHFR and GARFT.
• The authors' conclusion: The authors concluded that tumour cell sensitivity to pemetrexed appears to follow a genetic pattern in which high TS expression correlates with a lack of AICART inhibition. They suggested this could form the basis of a genetic approach to predicting sensitivity and the ability to become resistant.
• Limitations the authors state:
  • The authors stated that studies in a large group of patients treated with the drug are needed before a TS increase can be called a marker of resistance.
  • The failure to induce resistance in HT144 and Calu-3 applied to the method used.

Topics

Medical terms in this study, explained in our Lexicon: Pemetrexed (Alimta), Histology, Antifolate, De Novo, Cisplatin, Pleural Mesothelioma, Non-Small Cell Lung Cancer.

Related studies

• New tricks for old biomarkers: thymidylate synthase expression as a predictor of pemetrexed activity in malignant mesothelioma — P.A. Zucali, E. Giovannetti, et al. (2010)
• Thymidylate synthase and folyl-polyglutamate synthase are not clinically useful markers of response to pemetrexed in patients with malignant pleural mesothelioma — D.E. Lustgarten, C. Deshpande, et al. (2013)
• Reduced folate carrier and folylpolyglutamate synthetase, but not thymidylate synthase predict survival in pemetrexed-treated patients suffering from malignant pleural mesothelioma — F. Mairinger, C. Vollbrecht, et al. (2013)
• Molecular mechanism implicated in Pemetrexed-induced apoptosis in human melanoma cells — A. Buqué, J.S.H. Muhialdin, et al. (2012)
• Interaction and cross-resistance of cisplatin and pemetrexed in malignant pleural mesothelioma cell lines — M. Kitazono-Saitoh, Y. Takiguchi, et al. (2012)
• Putative cancer stem cells in malignant pleural mesothelioma show resistance to cisplatin and pemetrexed — L. Cortes-Dericks, G.L. Carboni, et al. (2010)

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