Abstract 5999: Therapeutic delivery of splice switching oligonucleotides to restore p53 function in liposarcoma

Abstract Introduction: Dedifferentiated liposarcoma (DDLPS) is a soft tissue sarcoma characterized by genomic amplification of proto-oncogene MDM2 alongside wildtype P53. Disease progression and poor survival rates in DDLPS are driven by MDM2 overexpression, which negatively regulates the tumor suppressor p53. While small molecules such as Nutlin and its derivatives have been employed to inhibit MDM2-p53 interaction, their significant toxicity presents a major limitation. This clinical challenge highlights the pressing need for alternative approaches to reactivate P53 through less toxic mechanisms. Alternatively spliced isoform of MDM2, MDM2-ALT1 inhibits full-length MDM2 (MDM2-FL) and stabilizes p53 expression. Additionally, MDM2-ALT1 can prevent the activity of MDMX, another negative regulator of p53, and the resulting p53 activation can sensitize tumor cells to p53-dependent chemotherapies. Thus, targeting MDM2 splicing to enhance MDM2-ALT1 production represents a promising non-toxic intervention strategy for DDLPS. Our laboratory has developed Splice Switching Oligonucleotides (SSOs) that can induce MDM2-ALT1 expression and subsequently reactivate p53 function. We hypothesize that in vivo delivery of SSOs to p53 wild-type tumor cells will induce MDM2-ALT1 expression and restore p53 activity to reverse the cancer phenotype. Results: We have synthesized a 20-mer SSO targeting the SRSF2 binding site in MDM2 exon 11, which functions as a positive regulator of MDM2 splicing. These SSOs prevent SRSF2 binding and promote MDM2-ALT1 production. To enhance both in vitro and in vivo SSO delivery, we incorporated our SSO sequence in an AAV viral vector to be expressed as an anti-sense RNA and validated its ability to induce MDM2-ALT1 splicing in vitro using RT-PCR. The SSO sequence expressed by the AAV vector successfully induced MDM2-ALT1 expression. Next, we will measure the p53 activity and perform proliferation assay to validate that SSO expressed from the AAV viral vectors can reduce cellular proliferation through the activation of p53 tumor suppressive activity. Our goal is to facilitate target specific in vivo delivery of this SSO construct using AAV viruses or extracellular vesicles in Xenograft tumor models. Conclusion: This research presents a novel therapeutic strategy by designing SSOs that reactivate p53 tumor suppressor function and developing methods for target-specific delivery. This innovative strategy could potentially revolutionize treatment for DDLPS and other cancers where p53 function is suppressed by MDM2 overexpression. Citation Format: Rafia Rahat, Akila S. Venkataramany, Matias Montes, Ravi Dhital, Kevin Cassady, Raphael E. Pollock, Dawn S. Chandler. Therapeutic delivery of splice switching oligonucleotides to restore p53 function in liposarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 5999.