The disclosed invention relates to methods of modifying peptide compositions to increase stability and delivery efficiency. Specifically, the disclosed invention relates to methods to increase the stability and delivery efficiency of protein kinase C (PKC) modulatory peptide compositions. A “therapeutic peptide composition” comprises a “carrier peptide” and a “cargo peptide.” A “carrier peptide” is a peptide or amino acid sequence within a peptide that facilitates the cellular uptake of the therapeutic peptide composition. The “cargo peptide” is a PKC modulatory peptide. Peptide modifications to either the carrier peptide, the cargo peptide, or both, which are described herein increase the stability and delivery efficiency of therapeutic peptide compositions by reducing disulfide bond exchange, physical stability, reducing proteolytic degradation, and increasing efficiency of cellular uptake.