Discovery of high-affinity ligands for prostatic acid phosphatase via DNA-encoded library screening enables targeted cancer therapy.

Improving the specificity of prostate cancer treatment requires ligands that bind selectively and with ultra-high affinity to tumour-associated targets absent from healthy tissues. Prostatic acid phosphatase has emerged as an alternative target to prostate-specific membrane antigen, as it is expressed in a broader subset of prostate cancers and is not detected in healthy organs such as the salivary glands and kidneys. Here, to discover selective binders to prostatic acid phosphatase, we constructed two DNA-encoded chemical libraries comprising over 6.7 million small molecules based on proline and phenylalanine scaffolds. Screening against the purified human prostatic acid phosphatase yielded OncoACP3, a small organic ligand with picomolar binding affinity. When radiolabelled with lutetium-177, OncoACP3 selectively accumulated in enzyme-expressing tumours with a long residence time (biological half-life greater than 72 h) and a high tumour-to-blood ratio (>148 at 2 h after administration). Lutetium-177-labelled OncoACP3 cured tumours in mice at low, well-tolerated doses. Its conjugation to the cytotoxic agent monomethyl auristatin E facilitated tumour-selective payload deposition, resulting in potent anti-tumour activity. The modular structure of OncoACP3 supports flexible payload delivery for the targeted treatment of metastatic prostate cancer.