Modulation of Stat3 Alternative Splicing in Breast Cancer

PUBLIC ABSTRACT

Alternative splicing is a fundamental step in gene expression that allows the generation of proteins with diverse functionality from the same gene. Many genes that are involved in oncogenesis can express antagonistic pro-tumorigenic and antitumorigenic isoforms. One such gene is STAT3, a transcription factor that has been shown to play a key and necessary role in the development of several cancers. In particular, 30%-60% of breast cancer samples show the improper constitutive activation of STAT3, and STAT3 has been established as a desirable target for cancer therapy. By alternative splicing, STAT3 can generate a dominant-negative variant, STAT3-beta, which not only is not tumorigenic by itself, but has the potential to block the tumorigenic activity of the active STAT3-alpha isoform. Current anti-STAT3 approaches are aimed at eliminating or blocking STAT3 activity. If the treatment is not completely effective, residual STAT3 might still show oncogenic activities, and a compensatory mechanism typically intervenes to increase transcription of knocked-down genes, thus tending to reinstate some functions, which could be deleterious. Re-direction of splicing toward a dominant negative variant presents the distinctive advantage that the oncogenic isoform is eliminated while, at the same time, an equal amount of a beneficial variant is introduced. In addition, feedback mechanisms that act by activating transcription are less likely to be activated (because there is no net loss of RNA or protein), and if they do, the anti-oncogenic variant will be prevalently induced. Because splicing re-direction acts upon pre-existing endogenous levels of RNA, it is maximally efficacious where the target oncogene is expressed at the highest levels (i.e., cancer cells), whereas it will have no effect if no or little oncogene is expressed (i.e., normal cells), thus introducing an intrinsic level of specificity for cancer cells.

We will develop antisense-based compounds to re-direct STAT3 splicing toward its dominant-negative variants and will test them in multiple in vitro and in vivo model system to assess their antioncogenic properties. Such studies will generate powerful bio-tools to study the function of different STAT3 isoforms in breast cancer development, and might identify a novel therapeutic approach for its treatment. In addition, because of the relative simplicity of their design, splicing re-direction compounds will be easily translatable to a number of other target and tumors and will potentially constitute the basis for a new class of compounds with broad potential applications.