A conjugate of a D-peptide and a (R)-3-substituted fatty acid is described. The D-peptide has a sequence of SEQUENCE ID NO: 1 or is a cytotoxic variant thereof having at least 80% sequence identity with SEQUENCE ID NO: 1. The conjugate exhibits anti-proliferative activity that is greater than the peptide, exhibits improved cellular update, and exhibits selectivity for cancer cells over normal cells.