# A Novel Allosteric Inhibitor Targeting IMPDH at Y233 Overcomes Resistance to Tyrosine Kinase Inhibitors in Lymphoma

## TL;DR

A new drug, Comp-10, targets a key enzyme in cancer cell metabolism and works against cancers resistant to existing treatments.

## Contribution

A first-in-class allosteric inhibitor of IMPDH2 is developed to overcome resistance in tyrosine kinase-driven cancers.

## Key findings

- ALK and SRC phosphorylate IMPDH2 at Y233, increasing its activity in cancer cells.
- Comp-10 reduces IMPDH2 levels and inhibits growth in ALK and BTK inhibitor-resistant lymphoma cells.
- PI3P is identified as a natural inhibitor of IMPDH2, offering insight into its regulation.

## Abstract

Cancer cells often rely on altered metabolism to support their rapid growth. We discovered that two cancer-driving proteins, ALK and SRC, directly modify and activate a key metabolic enzyme called IMPDH2. This modification occurs at a specific site (Y233) and boosts the enzyme’s activity, helping cancer cells make the building blocks of DNA. We also found that a natural lipid molecule, PI3P, can bind to and inhibit IMPDH2. Based on this knowledge, we developed a new drug candidate, Comp-10, which targets the regulatory region of IMPDH2. Unlike existing drugs, Comp-10 reduces IMPDH2 protein levels, blocks its activity, and prevents the formation of harmful enzyme structures in cancer cells. Importantly, it works in cancer cells that are resistant to current treatments. These findings suggest that targeting IMPDH2 in this new way could lead to better therapies for cancers driven by ALK, SRC, or similar proteins.

Background/Objective: Oncogenic tyrosine kinases (TKs) such as ALK and SRC promote cancer progression, but their effects on metabolic enzymes are still not well understood. This study examines how TK signaling regulates inosine monophosphate dehydrogenase 2 (IMPDH2), a rate-limiting enzyme in purine biosynthesis, and assesses its potential as a therapeutic target. Methods: Phosphoproteomic screening and in vitro kinase assays were used to identify phosphorylation sites on IMPDH2. Lipid-binding assays explored the role of phosphatidylinositol 3-phosphate (PI3P) in IMPDH2 regulation. Structure-based virtual screening discovered small-molecule allosteric inhibitors, which were tested in lymphoma cell models, including ALK and BTK-inhibitor resistant lines. Results: Here, we identify Inosine monophosphate dehydrogenase-2 (IMPDH2), a rate-limiting enzyme in purine biosynthesis, as a novel substrate of ALK and SRC. We show that phosphorylation at the conserved Y233 residue within the allosteric domain enhances IMPDH2 activity, linking TK signaling to metabolic reprogramming in cancer cells. We further identify PI3P as a natural lipid inhibitor that binds IMPDH2 and suppresses its enzymatic function. Using structure-based virtual screening, we developed Comp-10, a first-in-class allosteric IMPDH inhibitor. Unlike classical active-site inhibitors such as mycophenolic acid (MPA), Comp-10 decreases IMPDH1/2 protein levels, blocks filament (rod/ring) formation, and inhibits the growth of ALK and BTK inhibitor-resistant lymphoma cells. Comp-10 acts post-transcriptionally and avoids compensatory IMPDH upregulation observed with MPA (rod/ring) formation, and inhibited growth in TKI-resistant lymphoma cells. Notably, Comp-10 avoided the compensatory IMPDH upregulation observed with MPA. Conclusion: These findings uncover a novel TK–IMPDH2 signaling axis and provide mechanistic and therapeutic insight into the allosteric regulation of IMPDH2. Comp-10 represents a promising therapeutic candidate for targeting metabolic vulnerabilities in tyrosine kinase driven cancers.