Therapeutic targeting malignant mesothelioma with a novel 6-substituted pyrrolo\[2,3-d\]pyrimidine thienoyl antifolate via its selective uptake by the proton-coupled folate transporter

Our plain-English summary of Therapeutic targeting malignant mesothelioma with a novel 6-substituted pyrrolo[2,3-d]pyrimidine thienoyl antifolate via its selective uptake by the proton-coupled folate transporter, by C. Cherian, S. Kugel Desmoulin, L. Wang, et al (Cancer Chemotherapy and Pharmacology, 2013).

The study

• Authors: C. Cherian, S. Kugel Desmoulin, L. Wang, L. Polin, K. White, J. Kushner, M. Stout, Z. Hou, A. Gangjee, L.H. Matherly
• Journal: Cancer Chemotherapy and Pharmacology
• Published: 2013;71(4):999-1011
• Cited by: 22 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Purpose: We examined whether the novel 6-substituted pyrrolo[2,3-d]pyrimidine thienoyl antifolate, compound 2, might be an effective treatment for malignant pleural mesothelioma (MPM), reflecting its selective membrane transport by the proton-coupled folate transport (PCFT) over the reduced folate carrier (RFC).

Methods: HeLa sublines expressing exclusively PCFT (R1-11-PCFT4) or RFC (R1-11-RFC6) and H2452 MPM cells were assayed for transport with [(3)H]compound 2. [(3)H]Polyglutamate metabolites of compound 2 were measured in R1-11-PCFT4 and H2452 cells. In vitro cell proliferation assays and colony formation assays were performed. Inhibition of glycinamide ribonucleotide formyltransferase (GARFTase) was assayed by nucleoside protection assays and in situ GARFTase assays with [(14)C]glycine. In vivo efficacy was established with early- and advanced-stage H2452 xenografts in severe-combined immunodeficient (SCID) mice administered intravenous compound 2.

Results: [(3)H]Compound 2 was selectively transported by PCFT and was metabolized to polyglutamates. Compound 2 selectively inhibited proliferation of R1-11-PCFT4 cells over R1-11-RFC6 cells. H2452 human MPM cells were sensitive to the antiproliferative effects of compound 2. By colony-forming assays with H2452 cells, compound 2 was cytotoxic. Compound 2 inhibited GARFTase in de novo purine biosynthesis. In vivo efficacy was confirmed toward early- and advanced-stage H2452 xenografts in SCID mice administered compound 2.

Conclusions: Our results demonstrate potent antitumor efficacy of compound 2 toward H2452 MPM cells in vitro and in vivo, reflecting its efficient membrane transport by PCFT, synthesis of polyglutamates, and inhibition of GARFTase. Selectivity for non-RFC cellular uptake processes by tumor-targeted antifolates such as compound 2 presents an exciting new opportunity for treating solid tumors.

In plain English

This was a laboratory and mouse study of an experimental drug. It did not study asbestos exposure. The authors tested 'compound 2', a new antifolate built to enter cells through the proton-coupled folate transporter (PCFT) rather than the reduced folate carrier (RFC). They used a patient-derived biphasic malignant pleural mesothelioma cell line (H2452), engineered HeLa cells, and mice carrying H2452 tumors, with 5 mice per group. It entered cells through PCFT; the authors described its transport by RFC as nominal. It was more than 35-fold more active against PCFT-expressing cells than RFC-expressing cells. In H2452 cells it reached half-maximal growth inhibition at 80 nM, similar to pemetrexed (67.3 nM), and completely stopped colony formation at 5 micromolar. In folate-deficient mice with early-stage tumors, compound 2 outperformed cisplatin. Its advantage over gemcitabine was not statistically significant, in either early-stage or advanced-stage tumors. Mice on a folate-replete diet did not respond appreciably to compound 2. The only side effect seen was reversible weight loss. The authors concluded that compound 2 showed potent antitumor efficacy against H2452 cells in the laboratory and in mice.

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 (cell-line) experiments plus an animal experiment using human mesothelioma tumors implanted in immunodeficient mice
• Who was studied: The H2452 patient-derived biphasic malignant pleural mesothelioma cell line; engineered HeLa sublines expressing only PCFT or only RFC; female SCID mice carrying H2452 tumors, 5 mice per group
• Exposure: No asbestos exposure was studied. The exposure was the experimental drug compound 2 (32 mg/kg per dose, intravenous, every 4 days for 4 doses in mice). It was compared with pemetrexed, gemcitabine (150 mg/kg) and cisplatin (2.8 mg/kg).
• Main results:
  • Compound 2 was transported into cells by PCFT. The authors described its substrate activity for RFC as nominal, whereas methotrexate and pemetrexed were transported by RFC.
  • In engineered HeLa cells, compound 2 had an IC50 of 28.2 nM in PCFT-expressing cells versus 989 nM in RFC-expressing cells, more than 35-fold more active toward the PCFT-expressing cells
  • In H2452 mesothelioma cells, the IC50 of compound 2 was 80 nM, similar to pemetrexed (67.3 nM)
  • In H2452 cells, colony formation was completely abolished at 5 micromolar compound 2
  • Compound 2 inhibited the enzyme GARFTase inside cells, with IC50s of 25.1 nM in PCFT-expressing HeLa cells and 44 nM in H2452 cells. It was slightly more potent than pemetrexed.
  • Early-stage tumors, folate-deficient mice: compound 2 gave 0% T/C, a 20-day growth delay and 2.6 logs of cell kill. Cisplatin gave 52% T/C, a 4-day delay and 0.5 logs of cell kill. The authors reported compound 2 as superior to cisplatin (p less than 0.05).
  • Early-stage tumors: gemcitabine gave 15% T/C, an 11-day growth delay and 1.4 logs of cell kill. The difference between compound 2 and gemcitabine was not statistically significant.
  • Mice on a folate-replete diet did not respond appreciably to compound 2 (78% T/C)
  • Advanced-stage tumors, folate-deficient mice: compound 2 gave 7% T/C, a 22-day growth delay and 2.9 log cell kill. Gemcitabine gave 0% T/C, a 17-day growth delay and 2.2 log cell kill. The T/C difference was not statistically significant (p = 0.25).
  • In the early-stage trial there were no drug-related deaths or adverse symptoms other than reversible weight loss. The median weight-loss low point was 8% for compound 2 and gemcitabine and 14% for cisplatin.
• The authors' conclusion: The authors concluded that compound 2 showed potent antitumor efficacy toward H2452 mesothelioma cells in the laboratory and in mice. They attributed this to its efficient transport into cells by PCFT.
• Limitations the authors state:
  • Pemetrexed showed no antitumor activity in the mice, which the authors attributed likely to elevated serum thymidine in mice. So the mouse model could not compare compound 2 with pemetrexed.
  • In H2452 cells, the PCFT protein itself could not be reliably detected; its presence was inferred from transcript and transport measurements

Topics

The National Library of Medicine indexes this study under subjects our site covers: Mesothelioma.

Medical terms in this study, explained in our Lexicon: Malignant Mesothelioma, Antifolate, Pleural Mesothelioma, De Novo.

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