Deoxycytidine (dCyd) kinase is required for the phosphorylation of several deoxyribonucleosides and certain nucleoside analogs widely employed as antiviral and chemotherapeutic agents. Detailed analysis of this enzyme has been limited, however, by its low abundance and instability. Using oligonudeotides based on primary amino acid sequence derived from purified dCyd kinase, we have screened T-lymphoblast cDNA libraries and identified a cDNA sequence that encodes a 30.5-kDa protein corresponding to the subunit molecular mass of the purified protein. Expression ofthe cDNA in Escherichia coli results in a 40-fold increase in dCyd kinase activity over control levels. In dCyd kinase-deficient murine L cells, transfection with dCyd kinase cDNA in a mammalian expression vector produces a 400-fold increase over control in dCyd phosphorylating activity. The expressed enzyme has an apparent K. of 1.0 FM for dCyd and is also capable of phosphorylating dAdo and dGuo. Northern blot analysis reveals a single 2.8-kilobase mRNA expressed in T lymphoblasts at 5-to 10-fold higher levels than in B lymphoblasts, and decreased dCyd kinase mRNA levels are present in T-lymphoblast cell lines resistant to arabinofuranosylcytosine and dideoxycytidine. These rindings document that this cDNA encodes the T-lymphoblast dCyd kinase responsible for the phosphorylation of dAdo and dGuo as well as dCyd and arabinofuranosylcvtosine.Deoxycytidine (dCyd) kinase (NTP:deoxycytidine 5'-phosphotransferase; EC 2.7.1.74) is responsible for the phosphorylation of several deoxyribonucleosides and their analogs. The enzyme has been shown to have broad substrate specificity for dAdo and dGuo as well as for dCyd (1-7) and plays a physiologic role in the maintenance of normal deoxyribonucleotide pools. dCyd kinase is also a key enzyme in the phosphorylation of a variety of antineoplastic and antiviral nucleoside analogs including 1-f3-D-arabinofuranosylcytosine ("cytosine arabinoside," araC) (8,9) and dideoxycytidine (ddCyd) (10), and deficiency of dCyd kinase activity mediates resistance to these drugs. The enzyme is allosterically regulated by several deoxyribonucleotides and preferentially uses ATP as a phosphate donor for the phosphorylation of dCyd (1-7, 11). A more detailed understanding ofthe structure ofthis enzyme could therefore be ofuse in the design of new chemotherapeutic agents.In comparison with other normal and leukemic lymphoid cells, human and murine thymocytes and T lymphoblasts have relatively high levels of dCyd kinase activity (12)(13)(14), and it has been postulated that this increased enzyme activity plays a role in the sensitivity of these T cells to deoxyribonucleoside-induced cytotoxicity (15). However, it has not been determined whether the variability in activity is due to alterations at the level of gene expression. In order to define the structure and regulation of dCyd kinase, we screened a MOLT-4 T-lymphoblast cDNA library with an oligonucleotide probe coding for a 12-amino acid peptide sequence obtained from purified ...

A B S T R A C T PurposeRisedronate prevents bone loss in postmenopausal women. The purpose of this study was to determine whether risedronate prevents bone loss in premenopausal women undergoing chemotherapy for breast cancer. Patients and MethodsPremenopausal women undergoing chemotherapy for breast cancer were treated with oral calcium 600 mg and vitamin D 400 U daily and randomly assigned to receive oral risedronate 35 mg weekly or placebo, with all these therapies beginning within a month of the start of chemotherapy. Most chemotherapy regimens included anthracyclines, taxanes, or cyclophosphamide. Bone mineral density (BMD) was measured at baseline and 1 year. The primary end point was the change in lumbar spine (LS) BMD from baseline to 1 year. ResultsA total of 216 women enrolled; 170 women provided BMD data at 1 year. There was no difference in the mean change or percent change in LS BMD between groups, with a loss of 4.3% in the risedronate arm and 5.4% for placebo at 1 year (P ϭ .18). Loss of BMD at the femoral neck and total hip were also similar between treatment groups. Risedronate was well tolerated, with no significant differences in adverse events compared with placebo, except that arthralgias and chest pain were worse in those receiving the placebos. ConclusionRisedronate did not prevent bone loss in premenopausal women undergoing adjuvant chemotherapy for breast cancer.