The eicosasodium salt of a mixed-backbone antisense oligodeoxynucleotide with chemosensitizing properties. Custirsen inhibits testosterone-repressed prostate message-2 (TRPM-2). Administration of custirsen abrogates the anti-apoptotic effect of TRPM-2, thereby sensitizing cells to chemotherapy and resulting in tumor cell death. TRPM-2 is an anti-apoptotic clusterin that is overexpressed by prostate cancer cells and is associated with chemoresistance.