Simultaneous determination of ribonucleoside and deoxyribonucleoside triphosphates in cells by HPLC is an analytical challenge since the concentration of dNTP present in mammalian cells is several orders of magnitude lower than the corresponding NTP. Hence, the quantitation of dNTP in cells is generally performed after selective oxidation or removal of the major NTP. The procedures reported so far are lengthy and cumbersome and do not enable the simultaneous determination of NTP. We report the development of a simple, direct HPLC method for the simultaneous determination of dNTP and NTP in colon carcinoma WiDr cell extracts using a stepwise gradient elution ion-pairing HPLC with uv detection at 260 nm and with a minimal chemical manipulation of cells. Exponentially growing WiDr cells were harvested by centrifugation, rinsed with phosphate-buffered saline, and carefully counted. The pellets were suspended in a known volume of ice-cold water and deproteinized with an equal volume of 6% trichloroacetic acid. The acid cell extracts (corresponding to 2. 5 x 10(6) cells/100 microl) were centrifuged at 13,000g for 10 min at 4 degrees C. The resulting supernatants were stored at -80 degrees C prior to analysis. Aliquots (100 microl) were neutralized with 4.3 microl saturated Na2CO3 solution prior the injection of 40 microl onto the HPLC column (injection speed 250 microl/min). Chromatographic separations were performed using two Symmetry C18 3. 5-microm (2 x 3.9 x 150 mm) columns (Waters), connected in series equipped with a Sentry guard column (3.9 x 20 mm i.d.) filled with the same packing material. The HPLC columns were kept at 30 degrees C. The mobile phase was delivered at a flow rate of 0.5 ml/min, with the following stepwise gradient elution program: % solvent A/solvent B, 100/0 at 0 min --> 100/0 at 1 min --> 36/64 at 5 min --> 31/69 at 90 min --> 31/69 at 105 min --> 0/100 at 106 min --> 0/100 at 120 min; 50/50 MeOH/solvent B from 121 to 130 min; 100% solvent A from 131 to 160 min. Solvent A contained 0.01 M KH2PO4, 0.01 M tetrabutylammonium chloride, and 0.25% MeOH and was adjusted to pH 7. 0 (550 microl 10 N NaOH for 1 liter solvent A). Solvent B consisted of 0.1 M KH2PO4, 0.028 M tetrabutylammonium chloride, and 30% MeOH and was neutralized to pH 7.0 (1.4 ml 10 N NaOH for 1 liter solvent B). Even though dNTPs are minor components of cell extracts, satisfactory regression coefficients were obtained for their calibration curves (r2 > 0.99) established with the addition-calibration methods up to 120 pmol/40-microl injection. The applicability of the method was demonstrated by in vitro studies of the modulation of NTP and dNTP pools in WiDr colon carcinoma cell lines exposed to various pharmacological concentrations of cytostatic drugs (i.e., FMdC, IUdR, gemcitabine). In conclusion, this optimized, simplified, analytical method enables the simultaneous quantitation of NTP and dNTP and may represent a valuable tool for the detection of minute alterations of cellular dNTP/NTP pools induced by anticancer/antiviral drugs and diseases.