Date of Graduation
8-2014
Document Type
Dissertation (PhD)
Program Affiliation
Biomedical Sciences
Degree Name
Doctor of Philosophy (PhD)
Advisor/Committee Chair
Alexander Lazar, M.D., Ph.D.
Committee Member
Dina Chelouche-Lev, M.D.
Committee Member
David McConkey, Ph.D.
Committee Member
Elsa Flores, Ph.D.
Committee Member
Xiongbin Lu, Ph.D.
Committee Member
Rosemarie Schmandt, Ph.D.
Abstract
Dedifferentiated liposarcoma (DDLPS) is an aggressive malignancy characterized by a high rate of recurrence and dismal patient outcome. Minimal improvement in patient survival has been made in the last several decades, highlighting the crucial need for improved therapeutic strategies. A better understanding of the molecular deregulations underlying DDLPS would facilitate the discovery of improved therapeutic approaches. MDM2 is a well characterized oncoprotein and the most known negative regulator of p53. MDM2 amplification is considered the “hallmark” of DDLPS. Additionally, these tumors are known to harbor wild-type p53. We sought to take advantage of this knowledge and evaluate the role of SAR405838, a novel small molecule inhibitor of MDM2, as a potential anti-DDLPS therapeutic strategy.
To facilitate these studies, we first developed a large set of DDLPS experimental tools, specifically human cell lines and xenograft mouse models. These cell lines were further characterized, confirming the presence of MDM2 amplification and lack of p53 mutations. Other liposarcoma cell lines harboring p53 mutations, but no MDM2 amplification, were used as controls. Initial experiments demonstrated that SAR405838 was highly active in DDLPS cells but not in LPS cells that exhibit mutated p53. Cell culture based assays further demonstrated that SAR405838 selectively targeted MDM2 and led to p53 activation. In DDLPS cells, SAR405838 resulted in exemplary anti-proliferation, with EC50 values in the low nanomolar range (0.13 to 0.49 nM), as well as successfully induced cell cycle (G1 and G2 phase) arrest and apoptosis in a dose-dependent manner. The anti-DDLPS effects of SAR405838 were significantly more pronounced when compared to those of the older generation MDM2 inhibitors Nutlin-3a and MI-219. Most importantly, these cell based experiments were replicated in vivo where oral administration of SAR405838 resulted in potent anti-DDLPS effects in a dose-dependent manner (50-200 mg/kg).
Finally, to determine the mechanism of action of MDM2 inhibition in DDLPS cells, gene expression array experiments on SAR405838-treated cells and xenografts were conducted. We identified multiple pathways and genes that can further enhance our understanding of the MDM2-p53 pathway and can be studied as biomarkers of therapeutic response. Taken together, this study highlights the ability of SAR405838 to selectively inhibit a biologically relevant target, MDM2, and induce potent, anti-DDLPS effects in a pre-clinical investigation supporting further evaluation of this compound in the clinical context.
Keywords
Dedifferentiated liposarcoma, MDM2, p53, small-molecule inhibitors, SAR405838