The creation of a Proximity PTM Map of PD-L1 by VistaraBio has paved the way for finding the first clues of protein traffic dysregulation and suggests rational steps in understanding the pathology of cancer cells! 

In this context, abnormal protein trafficking has long been recognized as a critical aspect of endometrioid carcinoma, playing a role in tumor growth, invasion, and treatment resistance. Endometrioid carcinoma (EC) has the second highest rate of death from gynecological cancers. 67,880 new cases were identified in the USA in 2024 and 13,250 deaths. EC is treatable with hysterectomy if diagnosed early, followed by radiation therapy. Jemperli, an FDA approved monoclonal antibody which works by blocking the interaction between the PD-1 receptor on T cells and its ligands, PD-L1 and PD-L2 on cancer cells, is used for therapy in EC.

However, the problems inherent in protein trafficking in EC cells, their relationship to PD-L1, the transport proteins involved, or the impact of mutations are poorly understood. Interestingly in VistaraBio’s map 20 proteins which help trafficking of PD-L1 in model cells have been identified. Each protein is characterized by the presence of post translational modifications which are undocumented in literature. Comparisons of the PTM information from these proteins (the amino acid modified) with mutation databases showed that every one of the 20 proteins, without exception, harbors mutations at or close to their PTM sites (as determined by VistaraBio) in EC! This suggests a strong association of the PTMs, and co-segregation with pathology in EC.

Observing PTM information at scale with PINTAC technology affords an unprecedented opportunity to unravel the underlying mechanisms in substantial molecular details than hitherto possible. First, computational analysis of the affected proteins in this study show that they can be grouped into 2 distinct classes, each class harboring a consensus protein interaction site adjacent to the PTMs. This suggests the existence of at least 2 distinct complexes during protein trafficking of PD-L1, and the existence of regulatory proteins which bind to the identified sites for modifying PD-L1 interacting proteins and/or binding to PD-L1. These proteins can be purified. Going forward, VistaraBio will validate the targets with in vitro screens and modified cells to screen for small molecules since many proteins in the set of 20 can bind to known ligands. The tools and information generated in this study raise the exciting prospect of new therapies for targeting protein trafficking defects of PD-L1 to find cures for EC which may be applicable in other types of cancer as well.

The results obtained from this study are yet another example of the power of VistaraBio’s PINTAC platform. By probing the proteome comprehensively and with exquisite selectivity, each peptide generates a wealth of data which qualifies disease candidates substantially over the state-of-the-art. The PINTAC process can be implemented as phenotypic screens in combination with candidate compounds to observe compound actions on each PTM. These studies are underway.