Targeting Gq pathway in uveal melanoma

Project summary:
Uveal melanoma (UM) is the most common intraocular cancer in the United States and accounts for about
5% of all kinds of melanomas. Approximate 50% of UM patients develop metastases, predominantly to the liver
with 100% mortality. UM lacks mutations in BRAF, NRAS, NF1 and KIT common to other melanoma types.
Instead, over 90% harbor somatic activating mutations in the Gaq family members GNAQ or GNA11, with the
remainder carrying mutations of genes also acting in the Gaq signaling pathway such as CYSLTR2, a Gaq-
coupled GPCR, phospholipases C b4 (PLCb4), a direct effector of Gaq. Therefore, UM is genetically defined by
activating mutations of the Gaq pathway. Despite dramatic successes in other melanoma subtypes, immune
checkpoint inhibitors and targeted therapies have failed to demonstrate clinical benefits in UM, leading to an
urgent need to develop novel and effective therapeutic regimens. The CYSLTR2->Gaq->PLCb-> protein kinase
C (PKC) module is a linear signaling cascade that drives the essential MAP-kinase (MAPK) signaling for UM cell
proliferation, making Gaq pathway the prime target for targeted therapy for this devasting disease. Although both
GNAQ/11 and PKC inhibitors are very effective to suppress UM cell proliferation/survival in vitro, targeting either
GNAQ/11 or PKC alone has shown limited efficacy in UM liver metastasis. Understanding the resistance to the
Gaq pathway inhibition is of paramount importance to develop new strategies that work in the specific signaling
context of a constitutively activated Gaq pathway. Our preliminary data show either GNAQ/11 inhibition or PKC
inhibition yields strong upregulation of the Gaq-coupled receptor EDNRB, which when encountering its ligand
EDN1 from the liver environment can lead to reactivation of MAPK, thus driving resistance to Gaq pathway
inhibition in UM. In this proposal, we will evaluate that blocking endothelin signaling will increase the therapeutic
efficacy of targeting oncogenic Gaq signaling, directly or downstream, using newly developed genetically
engineered and xenograft models of UM metastatic to the liver. While the role of endothelin signaling in
melanocyte development and melanoma progression is well documented, the nature of the feedback that
upregulates EDNRB expression/signaling is not understood. We will utilize a combination of candidate
approaches, RNAseq and phospho-proteomics to dissect the underlying mechanisms in UM cells and in
melanocytes. Our preliminary data also show that secondary mutations in GNA11 can confer resistance to the
Gaq inhibition. In this proposal, we will expand the emerging landscape of the mechanism underlying the
adaptive and acquired resistance to Gaq pathway inhibition and identify rational therapy combinations to improve
the therapeutic efficacy for metastatic UM. Using a combined genome-wide CRISPR/Cas9 synthetic lethality
screen and phospho-proteomic screen we identified a lipid synthesis pathway that is essential for the survival of
cells with Gaq mutation, which we will explore as entirely novel therapeutic target for UM.

Grant Number: 4R01CA273020-04
NIH Institute/Center: NIH
Principal Investigator: Xu Chen