The design, chemical synthesis and
biological activities of a nuclease-resistant, nontoxic bioactive 2-5A derivative,
AA-etherA [i.e., adenylyl-(2'-5')-adenylyl-(2'-2")-9-[(2'-hydroxyethoxy)-methyl]
adenine], are described as a new approach to the inhibition of
breast cancer cell growth.
AA-etherA inhibits DNA replication and cell division of both
estrogen receptor positive (MCF-7) and
estrogen receptor negative (BT-20)
breast cancer cells in culture in a dose-dependent manner. Maximal inhibition in MCF-7 and BT-20 cells was obtained with 100 microM
AA-etherA after four days of treatment, with an GI50 of 58 and 37 microM, respectively.
AA-etherA is stable in the cytoplasm. Treated cells accumulate within the late G1/early S phase of the cell cycle and then progress only very slowly through S phase.
AA-etherA does not activate
RNase L, as do 2-5A and other 2-5A derivatives, nor does it increase
p68 kinase (PKR) content of the cells. High resolution, two-dimensional
protein gel electrophoresis reveals twofold or greater inhibition of synthesis of 92
proteins out of 682
proteins that were reproducibly detected as high quality spots with average rates of synthesis of > or = 20 p.p.m. in untreated cells. The specificity of the effects of
AA-etherA on select
proteins and its failure to activate
RNase L indicate that
AA-etherA does not act through a general effect on mRNA translation or stability, but rather inhibits cell proliferation through a block to DNA replication, with a concommitant reduction in the synthesis of specific
proteins, some of which may be required for cell cycle transit. Two likely targets to account for the
AA-etherA inhibition of DNA replication are
DNA topoisomerase I, which is inhibited by
AA-etherA in other cell lines, and
thymidine kinase, which could be inhibited in a manner similar to the effect of
acyclovir. These data indicate that 2-5A analogs, particularly bifunctional 2-5A analogs like
AA-etherA, will be useful for controlling
cancer cell growth. Further development of such 2-5A analogs may provide highly specific compounds for
chemotherapy and
chemoprevention.