Chemotherapy for malignant pleural mesothelioma

New Perspectives on Diagnosis and Therapy of Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is a rare, but severe form of cancer, with an incidence that varies significantly within and among different countries around the world. It develops in about one to two persons per million of the general population, leading to thousands of deaths every year worldwide. To date, the MPM is mostly associated with occupational asbestos exposure. Asbestos represents the predominant etiological factor, with approximately 70% of cases of MPM with well-documented occupational exposure to asbestos, with the exposure time, on average greater than 40 years. Environmental exposure to asbestos is increasingly becoming recognized as a cause of mesothelioma, together with gene mutations. The possible roles of other cofactors, such as viral infection and radiation exposure, are still debated. MPM is a fatal tumor. This cancer arises during its early phase without clinical signs. Consequently, its diagnosis occurs at advanced stages. Standard clinical therapeutic approaches include surgery, chemo- and radiotherapies. Preclinical and clinical researches are making great strides in the field of this deadly disease, identifying new biomarkers and innovative therapeutic approaches. Among the newly identified markers and potential therapeutic targets, circulating microRNAs and the Notch pathway represent promising avenues that could result in the early detection of the tumor and novel therapeutic approaches.

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

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.