PDCD4 and lung cancer: 2006; Cho 2012; Lam et al. 2012). Jin et al. (2006) modified chitosan with urocanic acid to promote release of the nucleic acid payload into the cytosol and improve endosomal escape via the “proton sponge” effect. When complexed with the programmed cell death protein 4 (PDCD4) tumor suppressor gene and aerosolized into the lungs of model lung cancer mice, apoptosis was enhanced, the cell cycle arrested and tumor angiogenesis was suppressed.