Schedule-dependent synergism of edatrexate and cisplatin in combination in the A549 lung-cancer cell line as assessed by median-effect analysis

The methotrexate analog edatrexate has been shown to have greater antitumor activity and an improved therapeutic index as compared with its parent compound in preclinical systems. These studies suggest that edatrexate may have a broad role in the treatment of solid tumors. Information regarding edatrexate in combination with other chemotherapeutic agents is limited. We evaluated the interaction of edatrexate with cisplatin in vitro as assessed by median-effect analysis in the A549 human lung-cancer cell line. The effects of dose, exposure time, and schedule dependence were assessed. Cytotoxicity was evaluated using the tetrazolium-based colorimetric (MTT) assay. The inhibitory concentration producing 50% absorbance (IC50 for edatrexate with 1 h exposure was 1.4μM. For all combination experiments, the edatrexate dose was fixed at 0.2 μM (IC10) whereas cisplatin (CDDP) concentrations were varied for 1-, 3-, and 24-h exposures either before or after edatrexate treatment. Drug interactions were assessed using the combination-index method as defined by median-effect analysis. A synergistic interaction was documented in experiments when edatrexate was applied prior to CDDP (combination index, <1). The combination studies in which edatrexate was used prior to CDDP resulted in significant reduction of all three CDDP IC50 values: 1-h IC50, from 30.0 to 3.9 μM; 3-h IC50, from 21.3 to 1.4 μM; and 24-h IC50, from 1.7 to 0.03 μM. In contrast, synergism was not observed in experiments in which edatrexate treatment occurred after cisplatin exposure. Median-effect analysis is a useful method of determining drug interactions. In the present study, the combination of edatrexate and CDDP demonstrated schedule-dependent synergism, with the synergism being observed only in the setting of edatrexate treatment before CDDP exposure. Due to the potential broad spectrum of activity of edatrexate plus CDDP, further studies are warranted to determine the mechanism responsible for the synergism and to investigate this combination in a variety of tumor models.

[1]  F. Sirotnak,et al.  Combination chemotherapy with a new folate analog: activity of 10-ethyl-10-deaza-aminopterin compared to methotrexate with 5-fluorouracil and alkylating agents against advanced metastatic disease in murine tumor models. , 1987, Cancer treatment reports.

[2]  M. Berenbaum.  What is synergy? , 1989, Pharmacological reviews.

[3]  M. Kris,et al.  Phase I trial and clinical pharmacological evaluation of 10-ethyl-10-deazaaminopterin in adult patients with advanced cancer. , 1988, Cancer research.

[4]  F. Sirotnak,et al.  New folate analogs of the 10-deaza-aminopterin series: markedly increased antitumor activity of the 10-ethyl analog compared to the parent compound and methotrexate against some human tumor xenografts in nude mice. , 1985, Cancer treatment reports.

[5]  T. Seno,et al.  Accumulation of DNA strand breaks during thymineless death in thymidylate synthase-negative mutants of mouse FM3A cells. , 1983, The Journal of biological chemistry.

[6]  F. Sirotnak,et al.  New folate analogs of the 10-deaza-aminopterin series , 2004, Cancer Chemotherapy and Pharmacology.

[7]  F. Sirotnak,et al.  Antitumor properties of a new folate analog, 10-deaza-aminopterin, in mice. , 1978, Cancer treatment reports.

[8]  F. Sirotnak.  Correlates of folate analog transport, pharmacokinetics and selective antitumor action , 1980 .

[9]  T. Chou,et al.  Quantitative analysis of dose-effect relationships: the combined effects of multiple drugs or enzyme inhibitors. , 1984, Advances in enzyme regulation.

[10]  J. Laszlo,et al.  Deoxyuridine incorporation as a useful measure of methotrexate and metoprine uptake and metabolic effectiveness. , 1979, Molecular pharmacology.

[11]  D A Scudiero,et al.  Feasibility of drug screening with panels of human tumor cell lines using a microculture tetrazolium assay. , 1988, Cancer research.

[12]  M. Kris,et al.  Edatrexate, an antifolate with antitumor activity: a review. , 1993, Cancer investigation.

[13]  M. Kris,et al.  Phase II study of 10-ethyl-10-deaza-aminopterin in patients with stage III and IV non-small-cell lung cancer. , 1988, Journal of clinical oncology : official journal of the American Society of Clinical Oncology.

[14]  E. Kaminskas,et al.  Accumulation of DNA strand breaks and methotrexate cytotoxicity. , 1984, Proceedings of the National Academy of Sciences of the United States of America.

[15]  M. Grever,et al.  New chemotherapeutic agents in non-small-cell lung cancer. , 1993, Seminars in oncology.

[16]  F. Sirotnak,et al.  New folate analogs of the 10-deaza-aminopterin series Basis for structural design and biochemical and pharmacologic properties , 2004, Cancer Chemotherapy and Pharmacology.

[17]  Berenbaum Mc.  What is synergy? , 1989, Pharmacological reviews.

[18]  O. Brown,et al.  Antifolate-induced misincorporation of deoxyuridine monophosphate into DNA: inhibition of high molecular weight DNA synthesis in human lymphoblastoid cells. , 1981, Proceedings of the National Academy of Sciences of the United States of America.

[19]  F. Sirotnak,et al.  Intracavitary therapy of murine ovarian cancer with cis-diamminedichloroplatinum(II) and 10-ethyl-10-deazaaminopterin incorporating systemic leucovorin protection. , 1989, Cancer research.

[20]  T. Chou,et al.  Quantitation of the synergistic interaction of edatrexate and cisplatin in vitro , 2004, Cancer Chemotherapy and Pharmacology.