A method of preparing a conditionally active polypeptide from a parent polypeptide, comprising steps of evolving a DNA encoding the parent polypeptide by increasing a net charge of the parent polypeptide using one or more techniques selected from increasing a total number of codons of charged amino acid residues in the DNA and decreasing a total number of codons of uncharged amino acid residues in the DNA to create mutant DNAs； expressing the mutant DNAs to obtain mutant polypeptides； and selecting the conditionally active polypeptide from the mutant polypeptides which exhibits a decrease in activity in a first assay at a first value of a condition compared to the same activity in a second assay at a second value of the same condition. The conditionally active polypeptide, pharmaceutical compositions containing same, nanoparticle and drug conjugates thereof and uses thereof are also provided.
