A combat with the YAP/TAZ-TEAD oncoproteins for cancer therapy

Abstract

The transcriptional co-regulators YAP and TAZ pair primarily with the TEAD family of transcription factors to elicit a gene expression signature that plays a prominent role in cancer development, progression and metastasis. YAP and TAZ endow cells with various oncogenic traits such that they sustain proliferation, inhibit apoptosis, maintain stemness, respond to mechanical stimuli, engineer metabolism, promote angiogenesis, suppress immune response and develop resistance to therapies. Therefore, inhibiting YAP/TAZ- TEAD is an attractive and viable option for novel cancer therapy. It is exciting to know that many drugs already in the clinic restrict YAP/TAZ activities and several novel YAP/TAZ inhibitors are currently under development. We have classified YAP/TAZ-inhibiting drugs into three groups. Group I drugs act on the upstream regulators that are stimulators of YAP/TAZ activities. Many of the Group I drugs have the potential to be repurposed as YAP/TAZ indirect inhibitors to treat various solid cancers. Group II modalities act directly on YAP/TAZ or TEADs and disrupt their interaction; targeting TEADs has emerged as a novel option to inhibit YAP/TAZ, as TEADs are major mediators of their oncogenic programs. TEADs can also be leveraged on using small molecules to activate YAP/TAZ-dependent gene expression for use in regenerative medicine. Group III drugs focus on targeting one of the oncogenic downstream YAP/TAZ transcriptional target genes. With the right strategy and impetus, it is not far-fetched to expect a repurposed group I drug or a novel group II drug to combat YAP and TAZ in cancers in the near future.

Keywords: Hippo; TAZ; TEAD; YAP; cancer therapy.

Figure 1

The oncogenic milestones of the transcriptional co-regulators YAP and TAZ. Discovery of YAP/TAZ and TEAD functions predate the discovery of the Hippo pathway. Role of YAP/TAZ in the Hippo pathway and the discovery of their oncogenic abilities in cell and animal models are considered significant. The initial studies from the groups that linked YAP/TAZ to oncogenic signaling pathway, stemness, actin cytoskeleton, fusion genes, drug resistance, metabolism, angiogenesis and immune suppression are also listed.

Figure 2

Classification ofYAP/TAZ-TEAD inhibiting drugs into three groups. Group I drugs (red font) act upstream and prevent the nuclear entry of YAP and TAZ, group I drug targets for potential pharmacological exploitation in order to generate repurposed YAP/TAZ-inhibiting drugs are circled. Group II drugs (green font) disrupt the formation of the YAP/TAZ-TEAD complex and they primarily bind to the TEAD family of transcription factors. Group Ill drugs (blue font) act on the downstream transcriptional targets in order to prevent YAP/TAZ-mediated oncogenicity.

Figure 3

Disruptors, stabilizers and destabilizers/degraders. A preformed YAP/TAZ-TEAD complex prevents access to drugs that occupy either the TEADs' surface or the palmitate-binding pocket (PBP), however, unassembled TEADs are accessible to drugs. Majority of the known YAP/TEAD-binding compounds are disruptors as they prevent the formation of the YAP/TAZ-TEAD complex. Two other classes of TEAD-binding compounds are stabilizers and destabilizers/degraders. Stabilizers either stabilize TEAD expression levels or enhance the formation of the YAP/TAZ-TEAD complex. Destabilizers bind to TEADs' surface or PBP and reduce TEAD expression levels through in situ denaturation, degraders on the other hand direct TEADs for proteasomal degradation.