Rubitecan [Orathecin™] is a topoisomerase I inhibitor extracted from the bark and leaves of the Camptotheca acuminata tree, which is native to China. Rubitecan is an oral compound being developed for the treatment of pancreatic cancer and other solid tumours by SuperGen. Rubitecan binds to and inhibits the enzyme topoisomerase I and induces protein-linked DNA single-strand breaks, thereby blocking DNA and RNA synthesis in dividing cells; this agent also prevents repair of reversible single-strand DNA breaks.

Ethidium is a DNA intercalating agent first discovered as and used as a veterenary trypanocide. A bromide salt is commonly used as a fluorescent tag in molecular biology. The fluorescene of ethidium bromide increased 21 fold upon binding to double-stranded RNA, 25 fold upon binding double stranded DNA. Because of the binding to DNA, ethidium bromide is a powerful inhibitor of DNA polymerase.

Abexinostat (PCI-24781) is a novel, second-generation phenyl hydroxamic acid–based, orally bioavailable HDAC inhibitor that has previously been shown to have activity in vitro and in vivo against a broad array of cancers, including hematopoietic malignancies and bone and soft-tissue sarcomas. Abexinostat is a pan-HDAC inhibitor mostly targeting HDAC1 with Ki of 7 nM, modest potent to HDACs 2, 3, 6, and 10 and greater than 40-fold selectivity against HDAC8. Abexinostat exhibits potent antitumor activity against a variety of tumor cell lines with GI50 ranging from 0.15 uM to 3.09 uM. PCI-24781 also has an antiproliferative effect on HUVEC endothelial cells with GI50 of 0.43 uM. Abexinostat treatment causes dose-dependent accumulation of both acetylated histones and acetylated tubulin in HCT116 or DLD-1 cells, induces expression of p21, and leads to PARP cleavage and accumulation of the γH2AX. It has also shown good tolerability and activity in Phase I and II clinical trials against lymphoma, as well as against solid tumors in Phase-I trials. Additionally, it acts as a potent radiosensitizing agent and is synergistic with cytotoxic chemotherapy, such as doxorubicin in preclinical models.