Investigator
Northwestern University
Novel PROTACs targeting tissue transglutaminase (TG2) suppress tumorigenicity of ovarian cancer cells
Tissue transglutaminase (TG2), a multifunctional enzyme involved in protein crosslinking through transamidation, fibronectin-integrin interactions and GTP hydrolysis, is upregulated in cancer. Due to its diverse functions, TG2 has been a challenging therapeutic target. Here, we investigate the use of PROteolysis TArgeting Chimeras (PROTACs) to degrade TG2 and inhibit its tumor-promoting functions in ovarian cancer models. We describe a novel family of VHL based PROTACs using a ligand that binds to the TG2 fibronectin interacting domain and a thiol ether PEG linker. Three structurally related PROTACs-P374, P404, and P405-induced significant proteasome dependent TG2 degradation at 24 h (p < 0.05), with stable effects at 48 h. These compounds also potently inhibited cell adhesion and migration (p < 0.005), outside-in signaling, and blocked TG2 enzymatic activity (p < 0.001). An unbiased evaluation using reverse phase protein array of P374-treated cells revealed 136 differentially expressed proteins, including protein networks related to cell adhesion and involved in extracellular matrix (ECM) interactions. P374 and P405 reduced omental colonization in vivo and P374 inhibited intraperitoneal tumor dissemination and growth. Visium HD based spatial profiling of human ovarian tumors identified TG2 as a highly enriched protein at the tumors invasive edge and the interface with the ECM. Together, our findings put forward novel TG2-targeting PROTACs which effectively degrade TG2, impair its functions, and block in-vivo tumor dissemination. These results highlight the potential development of TG2 degraders towards therapeutic targeting in ovarian cancer.
N6-Methyladenosine RNA Modifications Regulate the Response to Platinum Through Nicotinamide N-methyltransferase
Abstract Development of resistance to platinum (Pt) in ovarian cancer remains a major clinical challenge. Here we focused on identifying epitranscriptomic modifications linked to Pt resistance. Fat mass and obesity-associated protein (FTO) is a N6-methyladenosine (m6A) RNA demethylase that we recently described as a tumor suppressor in ovarian cancer. We hypothesized that FTO-induced removal of m6A marks regulates the cellular response of ovarian cancer cells to Pt and is linked to the development of resistance. To study the involvement of FTO in the cellular response to Pt, we used ovarian cancer cells in which FTO was knocked down via short hairpin RNA or overexpressed and Pt-resistant (Pt-R) models derived through repeated cycles of exposure to Pt. We found that FTO was significantly downregulated in Pt-R versus sensitive ovarian cancer cells. Forced expression of FTO, but not of mutant FTO, increased sensitivity to Pt in vitro and in vivo (P &lt; 0.05). Increased numbers of γ-H2AX foci, measuring DNA double-strand breaks, and increased apoptosis were observed after exposure to Pt in FTO-overexpressing versus control cells. Through integrated RNA sequencing and MeRIP sequencing, we identified and validated the enzyme nicotinamide N-methyltransferase (NNMT), as a new FTO target linked to Pt response. NNMT was upregulated and demethylated in FTO-overexpressing cells. Treatment with an NNMT inhibitor or NNMT knockdown restored sensitivity to Pt in FTO-overexpressing cells. Our results support a new function for FTO-dependent m6A RNA modifications in regulating the response to Pt through NNMT, a newly identified RNA methylated gene target.
