Abstract
Targeted protein degradation by chimeric molecules has emerged as a novel therapeutic modality. The
bifunctional chimeric molecules usually have one end binding to the protein of interest (POI) and the other end
directing the ternary complex towards the degradation in proteasome or lysosome. The PROteolysis TArgeting
Chimera (PROTAC) received the most attention to date. PROTACs contain an E3 ubiquitin ligase ligand to
direct the POI for ubiquitination and route it to the proteasome for degradation. Because of this, PROTACs are
only capable of depleting intracellular proteins. About 40% of the proteome are extracellular secreted and
membrane proteins and many of them are related to cancers. To broaden the scope of targets to include
extracellular proteins, the LYsosome TArgeting Chimeras (LYTAC) were recently reported by us and others.
LYTACs are created by conjugating a ligand of a lysosome targeting receptor (LTR) on the cell surface with a
ligand that can bind to the extracellular POI. The first two LTRs employed for LYTACs are lectins or
carbohydrate binding proteins: cation-independent mannose 6-phosphate receptor (CIM6PR) and
asialoglycoprotein receptor (ASGPR). The receptor-ligand interaction triggers the internalization of the
extracellular proteins through receptor-mediated endocytosis, further inducing the degradation of the targets in
the lysosome. However, CIM6PR is ubiquitously expressed in most types of cells, while ASGPR is mainly
expressed on liver. It would be ideal to recruit a LTR that is overexpressed on cancer cells to degrade
extracellular POIs associated with cancers to achieve high efficiency and selectivity. After examining a series
of cell surface receptors that are overexpressed on cancers, we found that chimeric molecules that recruit
folate receptor (FR) could degrade extracellular POIs on cancer cells highly effectively. In this application, we
will demonstrate for the first time that the conjugation of FR ligand, folate (FA), to binders of POI on the
membrane of cancer cells can create degraders that are capable of selectively degrading the endogenous
membrane POI on cancers. We propose to exploit the potential of this strategy to develop novel FA-antibody
conjugates that can degrade check point inhibitors, such as programmed death ligand 1 (PD-L1), for the
treatment of various cancers with a focus on head neck cancers (HNC). In Aim 1, we will synthesize various
FA-antibody conjugates and test their degradation activity in cells. In Aim 2, we will evaluate the in-vivo
degradation activity and anti-tumor efficacy of the PD-L1 degrader in syngeneic and humanized mouse models
with a focus on HNC. In Aim 3, we propose to study the mechanism of the FR-mediated degradation of PD-L1
and the underlying principle for improved anti-tumor efficacy. These studies will facilitate the establishment of a
general platform for the development of efficient and tissue-selective degraders for cancer associated
extracellular POIs, which will lead to effective therapeutics for the treatment of many types of cancers.