Oxynitidine Derivatives Useful as Inhibitors of Topoisomerase IB (TOP1) and Tyrosyl-DNA Phosphodiesterase 1 (TDP1) for Treating Cancer

Topoisomerase 1B (TOP1) is an enzyme that relieves the torsional strain in DNA. To relieve the torsional strain, TOP1B cleaves one strand of DNA and forms a transient complex called a TOP1-DNA covalent cleavage complex (TOP1cc). TOP1 inhibitors – such as camptothecin – stabilize the TOP1cc and prevent relegation of the broken DNA which, when encountered by replication and transcription machinery, triggers cell death. The DNA damage generated by the TOP1cc can be repaired by several pathways, including tyrosyl-DNA phosphodiesterase 1 (TDP1) pathway. 
Inhibitors of TOP1, including camptothecin (CPT), have long been recognized as anti-cancer agents; however, CPT has several known limitations like toxic side effects, chemical instability, poor solubility, and the propensity to drive drug resistance via drug efflux mechanisms. Relevantly, the activity of CPT is in direct competition with TDP1 activity which it must overcome to elicit TOP1-mediated DNA damage and cell death. Thus, much attention has been given to the discovery of non-CPT compounds that target TOP1 for treating tumors.
To this end, investigators at the National Cancer Institute (NCI) and a collaborating institution have discovered and evaluated several oxynitidine derivatives for use as non-CPT inhibitors of TOP1 and/or TDP1. These derivatives can inhibit TOP1 at nanomolar concentrations, eliciting DNA damage and cell death in cancer cell lines.  Furthermore, synergistic effects with CPT were also observed with some of the derivatives. In vivo mouse studies showed that the derivatives were generally safe and fairly well tolerated. The weight of tumors were reduced in a dose-dependent manner in mice xenografted with either human colon or breast cancer cells. Finally, the TOP1 inhibitor derivatives exhibited a greatly reduced propensity for drug efflux mediated resistance. 
Altogether, the investigators have discovered an array of new compounds targeting the diverse cancers sensitive to TOP1 and TDP1 inhibition. These oxynitidine derivatives are potentially physiologically more tolerable and may lead to better outcomes than CPT. The NCI seeks research co-development and/or potential licensees for oxynitidine derivatives as new topoisomerase IB (TOP1) and tyrosyl-DNA phosphodiesterase 1 (TDP1) inhibitors for treating cancer.