Malignant mesothelioma is an aggressive tumor of the serosal surfaces of the lungs, heart, and abdomen. Survival rates are poor and effective treatments are not available. However, recent therapeutic regimens targeting thymidylate synthase (TS) in malignant mesothelioma patients have shown promise. We have reported the use of an antisense oligodeoxynucleotide targeting TS mRNA (antisense TS ODN 83) to inhibit growth of human tumor cells. To test the potential for antisense targeting of TS mRNA in treatment of malignant mesothelioma, we assessed and compared the effects of antisense TS ODN 83 on three human malignant mesothelioma cell lines (211H, H2052, and H28) and human nonmalignant mesothelioma cells (HT29 colorectal adenocarcinoma, HeLa cervical carcinoma, and MCF7 breast tumor cell lines). We report that ODN 83 applied as a single agent effectively reduced TS mRNA and protein in malignant mesothelioma cell lines. Furthermore, it inhibited malignant mesothelioma growth significantly more effectively than it inhibited growth of nonmalignant mesothelioma human tumor cell lines: a difference in susceptibility was not observed in response to treatment with TS proteintargeting drugs. In malignant mesothelioma cells, antisense TS both induced apoptotic cell death and reduced proliferation. In nonmalignant mesothelioma cells, only reduced proliferation was observed. Thus, antisense TSmediated induction of apoptosis may be the basis for the high malignant mesothelioma sensitivity to antisense targeting of TS. Further preclinical and clinical study of TS antisense oligodeoxynucleotides, alone and in combination with TS-targeting chemotherapy drugs, in mesothelioma is warranted.

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