Development and characterization of a non-natural nucleoside that displays anticancer activity against solid tumors

Nucleoside analogs are an important class of anticancer agent that historically show better efficacy against hematological cancers versus solid tumors. This report describes the development and characterization of a new class of nucleoside analog that displays anticancer effects against both hematological and adherent cancer cell lines. These new analogs lack canonical hydrogen-bonding groups yet are effective nucleotide substrates for several high-fidelity DNA polymerases. Permutations in the position of the non-hydrogen-bonding functional group greatly influence the kinetic behavior of these nucleosides. One particular analog designated 4-nitroindolyl-2'-deoxynucleoside triphosphate (4-NITP) is unique as it is incorporated opposite C and T with high catalytic efficiencies. In addition, this analog functions as a nonobligate chain terminator of DNA synthesis, since it is poorly elongated. Consistent with this mechanism, the corresponding nucleoside, 4-nitroindolyl-2'-deoxynucleoside (4-NIdR), produces antiproliferative effects against leukemia cells. 4-NIdR also produces cytostatic and cytotoxic effects against several adherent cancer cell lines, especially those that are deficient in mismatch repair and p53. Cell death in this case appears to occur via mitotic catastrophe, a specialized form of apoptosis. Mass spectroscopy experiments performed on nucleic acid isolated from cells treated with 4-NIdR validate that the non-natural nucleoside is stably incorporated into DNA. Xenograft mouse studies demonstrate that administration of 4-NIdR delays tumor growth without producing adverse side effects such as anemia and thrombocytopenia. Collectively, the results of in vitro, cell-based, and animal studies provide evidence for the development of a novel nucleoside analog that shows enhanced effectiveness against solid tumors.