We evaluated the effect of antisense insulin-like growth factor (IGF) receptor transcripts on the proliferation and tumorigenicity in an SV40-induced, immunocompetent hamster mesothelioma model (H9A). Expression of IGF-1 and IGF-1 receptor (IGF-1R) genes was identified from H9A RNA using reverse transcription-PCR and Northern analysis. H9A cells were electroporated with inducible expression vectors (under the transcriptional control of heat shock promoter HSP70) containing a cDNA fragment corresponding to base pairs 1–309 of IGF-1R in the sense or antisense orientation to generate the respective clones A3 sense or B9 antisense. The expression vector in genomic DNA was detected with PCR analysis as a 173-bp fragment on ethidium bromide gels. The effects of the expression vectors were then evaluated in vitro under active (at 39°C) or inactive (at 34°C) conditions. At 39°C, the B9 antisense transfectants demonstrated significantly less proliferation than A3 sense transfectants (P2 < 0.02). At 34°C, cell growth of A3 sense- and B9 antisense-transfected cells was not significantly different. In vivo tumorigenicity was evaluated in hamsters inoculated with 105 A3 sense- or B9 antisense-transfected cells. The A3 sense clones resulted in greater numbers of tumors in vivo compared to the B9 antisense clone (P2 = 0.0001). When genomic DNA from tumors that developed in A3 sense and B9 antisense animals was analyzed for the expression vectors, a 173-bp fragment amplified from the expression vector was identified in the sense tumors but not in antisense B9 or wild-type H9A tumors, indicating a loss of the vector from the antisense clones that proliferated in vivo. The inhibitory effect of IGF-1R antisense transcripts on hamster mesothelioma demonstrated in this study by decreased growth and tumorigenicity in vitro and in vivo may have implications for the therapy of human mesothelioma.

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This work was partly supported by Grant 7-50386 from the DeMuth Memorial Cancer Research Fund (to M. C.), NIH Grant GM-33694 (to R. B.), Grant 06658 from Department of Health and Human Services/National Institute of Environmental Health Sciences (to C. W.), and a gift from Pfizer, Inc. (to M. C.).

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