Abstract

Background and Purpose Proteolytic balance is dysregulated in many diseases, with proteases playing critical roles in pathological pathways. A high level of Trypsin-3 expression has been implicated as a significant mediator of tumour progression and metastasis and this protease is associated with poor prognosis for patient in various cancers. Therefore, Trypsin-3 inhibition has emerged as a promising therapeutic target. However, no physiological or pharmacological inhibitor has yet been described that specifically target Trypsin-3. A major challenge in developing druggable inhibitor for this protease lies in achieving enough selectivity, as proteases belong to a large enzymatic family with close homologues that share similarities in their three-dimensional folding of their active conformation. Experimental Approach An advanced screening strategy of a large library of synthetic humanized nanobodies was employed to isolate highly selective recombinant antibodies targeting the active conformation of Trypsin-3. Among five hits, we combined two domains with distinct paratopes and inhibitory mechanisms to generate a macrodrug candidate capable to efficiently block the Trypsin-3 activity. Key Results This bispecific nanobody demonstrated exceptionally high selectivity and affinity towards Trypsin-3 in vitro, as well as a strong ability to inhibit cancer cell migration ex vivo on PC-3 cancer cell line. Conclusion and Implications. This study underscores the versatility and potential of synthetic nanobody engineering in the development of very selective protease inhibitors, paving the way for their consideration as drug candidates for clinical development.