Sir: 1-pD-Arabinofuranosylcytosine (ara-C, la) is one of the most potent drugs for the treatment of acute human leukemia.'However, ara-C has several drawbacks; its half-life is very short because of deamination to chemotherapeutically inactive 1-pD- arabinofuranosyluracil by cytidine deaminase, and it is not effective against solid tumors. In order to overcome these problems, efforts have been made to develop prodrugs3 or ...