Specific activation of tumor suppressors repressed by oncogenes to treat cancer

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Hepatocellular carcinoma (HCC) is the most common type of malignant liver cancer representing the second most common cause of cancer-related deaths in the world. Currently, the therapeutic options for HCC patients are highly limited and the underlying mechanisms driving HCC formation are only poorly elucidated. Therefore, there is an urgent need to develop a specialized treatment with little or no side effects. The transcription factor Sal-like protein 4 (SALL4) is a promising gene target that is expressed in a significant number of solid cancers, including HCC, and not in healthy adult tissues. SALL4 binds to the retinoblastoma binding protein 4 (RBBp4) of the nucleosome remodeling and deacetylase (NuRD) complex and thereby represses various genes, including tumor suppressors, eventually leading to cancer. Recently, it was demonstrated that disruption of the SALL4-RBBp4/NuRD interaction by a synthesized peptide (FFW) results in decreased HCC growth in murine xenografts, indicating that it represents a very promising target for HCC patients. However, since RBBp4 is additionally present in other nuclear complexes, blocking RBBp4 is a nonselective therapeutic approach. To overcome this obstacle, the proposed research project aims to specifically target the SALL4-RBBp4/NuRD complex at promoters of specific repressed tumor suppressors. In the first part of the project, the most promising tumor suppressor genes that are affected by the SALL4-RBBp4/NuRD complex will be validated. Therefore, their effect on the tumorigenic properties of HCC cells, such as proliferation as well as migration, will be tested in culture. In the second part, the SALL4-RBBp4/NuRD interaction will be disrupted with the novel CRISPR/dCas9 technology at the specific promoter of a validated tumor suppressor demonstrating strong antitumor effects in part one. By designing a specific guide RNA and fusing the dCas9 protein with the FFW peptide, FFW will specifically and exclusively disrupt the SALL4-RBBp4/NuRD complex at the intended promoter and not nonspecifically at other genomic sites. Consequently, this particular tumor suppressor will become reactivated. In the third part, the antitumor effect of the activated tumor suppressor will be analyzed in HCC cells. Finally, the therapeutic potential of the dCas9-FFW construct to treat liver tumors will be investigated in vivo in a xenograft mouse model. In summary, the proposed research project will target relevant tumor suppressors downregulated in SALL4-positive HCC, providing a very novel and innovative technique to specifically reactivate repressed tumor suppressors in HCC patients. This represents a very promising strategy for personalized cancer therapy. Due to the high abundance of SALL4-positive cancers, this strategy can additionally be transferred to a variety of other cancer types.