Antisense cyclin D1 induces apoptosis and tumor shrinkage in human squamous carcinomas

Cyclin D1 plays an essential regulatory role in the G(1) phase of the cell cycle The cyclin D1 gene is amplified in 20-50% of squamous cell, carcinoma s (SCCs), and the protein is overexpressed in up to 80% of SCCs, Our hypoth esis was that gene transduction of antisense (AS) cyclin D1 in human SCCs i n vivo would result in tumor reduction. A cyclin D1 cDNA was inserted into an E1/E3-deficient serotype 5 adenovirus (AS cyclin D1) in an AS orientatio n using homologous recombination. AS cyclin D1 transduction suppressed cycl in D1 protein expression in both cultured cells and tumors. AS cyclin D1 si gnificantly inhibited cell proliferation by both [H-3]thymidine incorporati on in six SCC cell lines (P = 0.01-0.001) and the conversion of tetrazolium salt to formazan in four SCC cell lines (P = 0.01-0.001). Apoptosis detect ed in >25% of cells in each cell line 48 h after AS cyclin D1 transduction paralleled the reduction in cyclin D1 protein. Preformed SCCs transduced wi th AS cyclin D1 were significantly inhibited (P = 0.002-0.005), and apoptos is aas prominent in the AS cyclin D1-treated tumors, but not in tumors trea ted with the control vector. These data extend prior in vitro a and ex vivo results and indicate that AS cyclin D1 suppresses SCC growth both in vitro and in vivo through suppression of cyclin D1 protein expression, leading t o cellular apoptosis. Our findings suggest that cyclin D1 may have a role i n cell survival and that cyclin D1 AS therapy may be useful as an adjunct t o standard treatment for SCC.