Development of albumin-binding doxorubicin prodrugs that are cleaved by prostate-specific antigen

Prostate-specific antigen (PSA) is a serine protease that is overexpressed in prostate carcinoma and represents a molecular target for selectively releasing an anticancer agent from a prodrug formulation. In this work, we developed albumin-binding prodrugs with the structures MT-Ser-Ser-Tyr-Tyr- Ser-Gly-DOXO, MT-Asn-Ser-Ser-Tyr-Phe-Gln-DOXO (MT = maleimidotriethyleneglycol acid; DOXO = Doxorubicin) or EMC-Arg-Arg-Ser-Ser-Tyr-Tyr-Ser-Gly-DOXO (EMC = epsilon-maleimidocaproic acid; X = amino acid). The maleimide Doxorubicin derivatives bound rapidly to the cysteine-34 position of endogenous and exogenous albumin and were efficiently cleaved by PSA at the P(1)-P'(1) scissile bond, releasing a respective Doxorubicin dipeptide (Ser-Gly-DOXO or Phe-Gln-DOXO). The derivative containing arginine residues (EMC-Arg-Arg-Ser-Ser-Tyr-Tyr-Ser-Gly-DOXO) exhibited excellent water solubility for intravenous administration. Subsequent biological evaluation was focused on a PSA-negative xenograft model (PC 3) and a PSA-positive xenograft model (CWR22) in order to assess the selectivity of our therapeutic approach. EMC-Arg-Arg-Ser-Ser-Tyr-Tyr-Ser-Gly-DOXO showed no in vivo activity in the PSA-negative PC 3 model, but good activity in the CWR22 PSA-positive model that was comparable to Doxorubicin.