Development of flexible-heteroarotinoids for kidney cancer.

Potential chemopreventive and therapeutic value of the lead Flexible Heteroarotinoid (Flex-Het), SHetA2, was indicated by growth inhibition of multiple cancer cell lines. The objective of this study was to evaluate the SHetA2 mechanism and in vivo activity in kidney cancer. SHetA2 induced apoptosis in the Caki-1 kidney cancer cell line through reduction of Bcl-2 protein and induction of PARP-1 and caspase 3 cleavages, whereas normal kidney epithelial cells exhibited resistance. Both normal and cancerous cells underwent G(1) arrest and loss of Cyclin D1. Tubule differentiation was induced in organotypic cultures and xenograft tumors in association with increases in E-Cadherin mRNA and protein expression. SHetA2 repressed activity of nuclear factor-κB, a transcription factor that regulates apoptosis, Bcl-2, growth, Cyclin D1, differentiation, and E-Cadherin in the opposite manner as SHetA2. Glutathione binding and generation of reactive oxygen species were not required for these activities. Oral SHetA2 inhibited growth in one of two renal cancer xenograft models without causing mortality or weight loss. Structure function analysis of related Flex-Hets for potential improvement of SHetA2 pharmaceutical properties showed that compounds with increased hydrophilicity slightly reduced the growth inhibition efficacy, but retained the differential effect on cancer over normal cells. Flex-Hets and metabolites were not mutagenic in the Ames test. In conclusion, SHetA2 regulates growth, differentiation, and apoptosis in kidney cancer cells through multiple molecular events downstream of nuclear factor-κB repression. Increasing the hydrophilicity of Flex-Hets does not attenuate the differential effect on cancer cells over normal cells, thus offering alternatives for improvement of therapeutic value.