INHIBITION OF HAMSTER MESOTHELIOMA TUMORIGENESIS BY AN ANTISENSE EXPRESSION PLASMID TO THE INSULIN-LIKE GROWTH-FACTOR-I RECEPTOR

We evaluated the effect of antisense insulin-like growth factor (IGF) receptor transcripts on the proliferation and tumorigenicity in an SV4 0-induced, immunocompetent hamster mesothelioma model (H9A). Expressio n of IGF-1 and IGF-1 receptor (IGP-1R) genes was identified from H9A R NA using reverse transcription-PCR and Northern analysis. H9A cells we re electroporated with inducible expression vectors (under the transcr iptional control of heat shock promoter HSP70) containing a cDNA fragm ent corresponding to base pairs 1-309 of IGF-1R in the sense or antise nse orientation to generate the respective clones A3 sense or B9 antis ense, The expression vector in genomic DNA was detected with PCR analy sis as a 173-bp fragment on ethidium bromide gels. The effects of the expression vectors were then evaluated in vitro under active (at 39 de grees C) or inactive (at 34 degrees C) conditions. At 39 degrees C, th e B9 antisense transfectants demonstrated significantly less prolifera tion than A3 sense transfectants (P-2 < 0.02), At 34 degrees C, cell g rowth of A3 sense- and B9 antisense-transfected cells was not signific antly different. In vivo tumorigenicity was evaluated in hamsters inoc ulated with 10(5) 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 (P-2 = 0.0001). When genomic DNA from tumors t hat developed in A3 sense and B9 antisense animals was analyzed for th e expression vectors, a 173-bp fragment amplified from the expression vector was identified in the sense tumors but not in antisense B9 or w ild-type H9A tumors, indicating a loss of the vector from the antisens e clones that proliferated in vivo. The inhibitory effect of IGF-1R an tisense 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.