Development Of An Oncology VHH-ADC Candidate Via Site-Specific Non-Canonical Amino Acid Conjugation

Antibody-drug conjugate development hinges on precise, controllable conjugation chemistry, and site-specific non-canonical amino acid incorporation is emerging as a compelling path forward. This case study follows Primrose Bio's development of PET771, a VHH-ADC candidate targeting a GPCR in oncology, and the challenge of reliably introducing para-azidophenylalanine (pAzF) at defined positions without sacrificing yield or fidelity.

Starting from a screen of four substitution sites at 96-deep well scale, the team advanced three candidates to intact mass spectrometry confirmation, achieving 100% pAzF incorporation with no native amino acid misincorporation detected. A continuous pAzF feed strategy at 2L scale pushed titers to 15 g/L while maintaining incorporation quality. Flow cytometry confirmed that the resulting VHH-ADC retained binding activity against its target. Access the full case study to learn more about what a rigorous, data-driven scale-up workflow can achieve.