# Benzoic Acid Derivatives Improve Plasma Stability of Diester Butyrophilin Ligand Prodrugs

## TL;DR

Researchers improved the plasma stability of a cancer immunotherapy compound by modifying its benzoic acid structure, leading to more potent and stable prodrugs.

## Contribution

A benzoic acid modification strategy was developed to enhance plasma stability and potency of butyrophilin ligand prodrugs.

## Key findings

- Compound 8d showed high potency for γ9δ2 T cell expansion (EC50 = 0.86 nM).
- Compound 8d exhibited strong interferon γ production (EC50 = 2.3 nM).
- Modified prodrugs displayed up to 130-fold improved plasma stability (t1/2 > 24 h).

## Abstract

The potent butyrophilin
ligand, (E)-4-hydroxy-3-methyl-but-2-enyl
diphosphate (HMBPP), is a potential cancer immunotherapy agent, but
it lacks plasma stability and membrane permeability. Aryl phosphonamidate
prodrugs of a key HMBPP analog have improved plasma stability but
poor cellular uptake, while aryl phosphonester prodrugs have improved
uptake but lack plasma stability. Here, tuning the benzoic acid substructure
of a phosphonester prodrug was explored. Twenty-one aryl phosphonester
derivatives were prepared in allylic alcohol (8a–k) and allylic acetate (9a–k) forms. Testing revealed
that this strategy can provide compounds with high potency for expansion
of γ9δ2 T cells (8d, EC50 = 0.86
nM) and interferon γ production in response to loaded K562 cells
(8d, EC50 = 2.3 nM). Importantly, these compounds
display improved plasma stability (130-fold range; 8d, t
1/2 > 24 h), showing the importance
of the benzoic acid position for plasma versus cellular metabolism.
These findings enable next-generation prodrugs with improved stability
and potency.