γ-secretase modulators( Technische Universität Darmstadt)

Clinical outcomes in cholangiocarcinoma (CC) are poor; few patients are candidates for curative resection, and palliative chemotherapy produces only modest effects on survival. With an increasing incidence, new targets are urgently needed. Notch has been identified as having potential to induce CC when transgenically overexpressed, and this study aimed to characterize how endogenous Notch might drive tumorigenesis. We identify the atypical receptor Notch3 as differentially overactivated in CCs in humans, rats, and mice, with genetic deletion significantly reducing CC growth. Notch3 sustains tumor cell survival through PI3k/Akt activation via a noncanonical mechanism independent of Recombinant Signal Binding Protein for Immunoglobulin Kappa J Region (RBPJ), presenting an opportunity to target the pathway without disrupting classical Notch and bypassing toxicities associated with γ-secretase inhibitors.

Overexpression of HER2 occurs in 25% of breast cancer. Targeting HER2 has proven to be an effective therapeutic strategy for HER2-positive breast cancer. While trastuzumab is the most commonly used HER2 targeting agent, which has significantly improved outcomes, the overall response rate is low. To develop novel therapies to boost trastuzumab efficacy, it is critical to identify the mechanisms underlying trastuzumab action and resistance. We recently showed that the inhibition of breast cancer cell growth by trastuzumab is not through the inhibition of HER2 canonical signaling. Here we report the identification of a novel non-canonical HER2 signaling pathway and its interference by trastuzumab. We showed that HER2 signaled through a non-canonical pathway, regulated intramembrane proteolysis (RIP). In this pathway, HER2 is first cleaved by metalloprotease ADAM10 to produce an extracellular domain (ECD) that is released and the p95HER2 that contains the transmembrane domain (TM) and intracellular domain (ICD). p95HER2, if further cleaved by an intramembrane protease, γ-secretase, produced a soluble ICD p75HER2 with nuclear localization signal (NLS). p75HER2 is phosphorylated and translocated to the nucleus. Nuclear p75HER2 promotes cell proliferation. Trastuzumab targets this non-canonical HER2 pathway via inhibition of the proteolytic cleavage of HER2 by both ADAM10 and γ-secretase. However, p75HER2 pathway also confers resistance to trastuzumab once aberrantly activated. Combination of trastuzumab with ADAM10 and γ-secretase inhibitors completely blocks p75HER2 production in both BT474 and SKBR3 cells. We concluded that HER2 signals through the RIP signaling pathway that promotes cell proliferation and is targeted by trastuzumab. The aberrant HER2 RIP signaling confers resistance to trastuzumab that could be overcome by the application of inhibitors to ADAM10 and γ-secretase.