A nanocomplex, 50 to 1000 nm in size, containing a lipid-like nanoparticle formed of a cationic lipid-based compound and a modified protein formed of a protein and an anionic polymer that includes a plurality of polar groups, the lipid-like nanoparticle and the modified protein being non-covalently bonded to each other. Also disclosed are a method of preparing the above-described nanocomplex and use thereof for treating a medical condition. Further disclosed is a pharmaceutical composition containing a nanocomplex.