RPA1 and colonic neoplasm: In addition, a previous study on colon cancer cells has shown an association between the levels of RPA1 protein and DNA synthesis rate since the reduction in the in vitro DNA replication activity resulting from tirapazamine (TPZ)-induced inhibition of DNA synthesis was associated with a decrease in the protein level of RPA1 in cytoplasmic extracts of tirapazamine-treated cells [36].