Engineering a phosphatidylserine-targeting drug carrier based on lactadherin C2 domain fused with human serum albumin for tumor therapy.

Phosphatidylserine is a crucial component of the cell membrane, typically localized to the inner leaflet of the lipid bilayer. In neoplastic cells, phosphatidylserine is aberrantly externalized, rendering it a promising biomarker for the development of targeted oncological therapeutics. We previously elucidated the crystal structure of phosphatidylserine bound to the C2 domain of lactadherin (LAC) and revealed calcium-independent binding with nanomolar affinity (Kd = 3.3 ± 0.5 nM). Expanding upon our previous work, here we developed a novel targeted therapeutic platform by genetically fusing LAC with human serum albumin (HSA). This engineered LAC-HSA fusion protein synergistically integrates phosphatidylserine-targeting specificity with HSA's pharmacokinetic advantages, including an extended plasma half-life and drug delivery capabilities. To validate its therapeutic potential, we incorporated a potent cytotoxic agent (zinc monocarboxyphthalocyanine, CPZ) into LAC-HSA via a non-covalent strategy. In vitro, the LAC-HSA fusion protein selectively bound to phosphatidylserine-exposed tumor cells, enhancing the uptake of encoded cytotoxic agent (3-fold higher than the non-targeted control), thereby improving tumor cell-killing efficacy. In vivo, in the mouse solid tumor model, the targeted therapy group showed a 3-fold reduction in tumor volume compared to the non-targeted treatment group. These results clearly demonstrate that LAC-HSA is an effective phosphatidylserine-targeting drug carrier.