ABSTRACT

The protumorigenic insulin-like growth factor (IGF)-II is highly expressed in a significant fraction of human hepatocellular carcinomas (HCC).

Elimination of protein expression using RNA interference (RNAi) significantly improves the understanding of gene function and represents a promising technique for the treatment of diseases such as cancer and neurological disorders. Accumulating evidence suggests the so-called interferon-independent non-specific gene silencing of short interfering RNA (siRNA); however, its biological and functional cellular consequences are largely unidentified. We therefore analyzed the effects of different nonsense siRNAs on characteristic bio-parameters such as cell viability, proliferation, cell cycle distribution, apoptosis, and migration of tumor cells. All analyzed cellular aspects have been observed to be significantly affected by the presence of siRNA in an interferon-independent manner: viability, mitosis, and motility were significantly diminished and programmed cell death was significantly elevated. Moreover, all cell cycle stages (G0/G1-, G2/M-, and S-phase) were moderately shifted. Together, these results support the hypothesis that siRNA, due to sequence-specific cellular consequences, modulate bio-functionality independent of the target sequence. This phenomenon affects the design of siRNA experiments for future in vitro but also for in vivo tests as well as for potential therapeutic and preventive strategies. Moreover, monitoring interferon response after transfection of siRNAs is necessary but not sufficient to exclude potential off-target effects in non-diseased cells.

The insulin-like growth factor (IGF) system involves a complex network of ligands (IGF-I and IGF-II), receptors (IGF-1R and IGF-2R), IGF-binding proteins (IGFBP-1 to IGFBP-6), and downstream intracellular signaling elements. The IGF-axis modulates proliferation and (anti-)apoptosis in mammals, and it is therefore not surprising that dysregulation of different pathway components is involved in the development and progression of several tumor entities such as breast, prostate, lung, and liver cancer. Because IGFs, IGF-receptors, and IGFBPs play a critical role in the emergence of human neoplasias, these molecules have become the center of special interest as prime targets for potential anti-cancer therapies. In the last decade, various substances and experimental strategies, which affect the IGF-induced signal transduction, have successfully been used in treatment of neoplasias in vitro and in vivo. These approaches contain neutralizing antibodies, antagonistic peptides, selective receptor kinase inhibitors, and (antisense-)oligonucleotides.

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