aphidicolin and Leukemia-P388

We have established in vivo cisplatin-resistant mouse leukemia cell lines, L-1210/DDP and P388/DDP, in order to elucidate the mechanism of acquired resistance to cisplatin. Resistance indices were 22 and 14, respectively, when the cells were exposed to cisplatin for 48 h. Uptake of cisplatin by both resistant lines was significantly reduced, compared with values for the respective parent lines (17% for L-1210/DDP and 27% for P388/DDP, at 100 microM for 1 h). While glutathione contents in the resistant cells were 1.7-1.9 times higher than those in the sensitive ones, their reduction by preincubation with buthionine sulfoximine did not influence the sensitivity of the cells to cisplatin. In addition, the resistant lines did not show lower sensitivity to CdCl2 than the respective sensitive ones, suggesting that intracellular SH groups might contribute little to the mechanism of cisplatin resistance in these cells. Postincubation with DNA repair inhibitors, caffeine and aphidicolon, did not selectively enhance the sensitivity of the resistant cells to cisplatin. These results suggested that reduced drug uptake would be a primary mechanism of cisplatin resistance in L-1210/DDP and P388/DDP. Cross-resistance patterns to platinum complexes were quite different between L-1210/DDP and P388/DDP. Colon 26/DDP, another cisplatin-resistant mouse tumor showed a different pattern from those observed with L-1210/DDP and P388/DDP. In the development of new platinum complexes we should use plural resistant lines for examining cross-resistance patterns to candidate platinum complexes.

Topics: Animals; Aphidicolin; Cadmium; Cadmium Chloride; Caffeine; Cisplatin; DNA Repair; Drug Resistance; Glutathione; Leukemia L1210; Leukemia P388; Mice

Experiments were carried out in vitro using DNA polymerase and ribonucleotide reductase inhibitors to investigate their cytotoxicity to P388 murine leukemia sensitive (P388/S) and resistant (P388/R) to adriamycin (ADR). DNA polymerase inhibitors such as cytosine arabinoside (ara-C) and aphidicolin elicited comparative inhibition of DNA biosynthesis in both parental and ADR-resistant tumor cells. However, ribonucleotide reductase inhibitors such as hydroxyurea (HU) and caracemide were collaterally more sensitive to P388/R cells. Inosine diglycolaldehyde (Inox) was ineffective in showing such a response. Pretreatment with HU significantly increased intracellular ADR levels and inhibition of RNA biosynthesis by ADR in P388/R cells while, in P388/S cells, sequential or concurrent treatment with HU did not enhance intracellular ADR levels. Mechanisms underlying such an effect, implications due to reduced intracellular ATP levels in drug-resistant cells, and the possible utility of using ribonucleotide reductase as a target in drug-resistant tumors for the therapeutic benefit are discussed.

Topics: Animals; Antimetabolites, Antineoplastic; Aphidicolin; Cytarabine; Diterpenes; DNA Polymerase II; DNA, Neoplasm; Doxorubicin; Drug Resistance; Hydroxyurea; Inosine; Leukemia P388; Leukemia, Experimental; Mice; Ribonucleotide Reductases; RNA, Neoplasm; Tumor Cells, Cultured

Derivatives of N2-(p-n-butylphenyl)guanine (BuPG) and 2-(p-n-butylanilino)adenine (BuAA) were synthesized and tested as inhibitors of mammalian DNA polymerase alpha, cell growth, and macromolecule synthesis. 2-(p-n-Butylanilino)-6-chloropurine (BuACl) served as a useful intermediate to prepare a series of 6-substituted analogues. BuACl, as its sodium salt, reacted with 2-deoxy-3,5-di-p-toluoyl-beta-D-ribofuranosyl chloride in acetonitrile to give 64% of the corresponding 9-beta nucleoside (blocked BuAdCl) and only 14% of the 7-beta isomer. Deblocking and substitution of chlorine in BuAdCl generated a series of 2-(p-n-butylanilino)-9-(2-deoxy-beta-D-ribofuranosyl)purine derivatives. Reaction of the sodium salt of BuACl with (2-acetoxyethoxy)methyl bromide also afforded, after deblocking and substitution of the 6-chloro group, a series of 2-(p-n-butylanilino)-9-[(2-hydroxyethoxy)methyl]purines. The bases synthesized were inhibitors of DNA polymerase alpha isolated from Chinese hamster ovary cells, the most potent compounds being 6-methoxy and 6-methylthio derivatives of 2-(p-n-butylanilino)purine. When tested for their ability to inhibit [3H]thymidine incorporation into DNA in HeLa cell cultures and the growth of exponentially growing HeLa cells, 9-(2-deoxy-beta-D-ribofuranosyl) derivatives had greater potency than their base counterparts, but "adenine" analogues, such as 2-(p-n-butylanilino)-2'-deoxyadenosine (BuAdA, IC50 = 1 microM), were considerably more potent than N2-(p-n-butylphenyl)-2'-deoxyguanosine (BuPdG, IC50 = 25 microM). Derivatives bearing the 9-[(2-hydroxyethoxy)methyl] group were nearly as potent inhibitors of [3H]thymidine incorporation in these experiments as the corresponding deoxyribonucleosides. Base and deoxynucleoside derivatives also inhibited cellular RNA synthesis, and several compounds, at high concentrations, inhibited protein synthesis. BuPG, BuAA, and four deoxyribonucleoside derivatives of 2-(p-n-butylanilino)purines were tested against P-388 lymphocytic leukemia in mice. None of the compounds increased the survival time of test animals, but two of them, BuAdA and its 6-desamino derivative BuAdP, were lethal at the highest concentration used (400 mg/kg).

Topics: Aniline Compounds; Animals; Antineoplastic Agents; Cell Division; Deoxyribonucleosides; DNA Polymerase II; DNA Replication; Drug Evaluation, Preclinical; HeLa Cells; Humans; Indicators and Reagents; Leukemia P388; Leukemia, Experimental; Magnetic Resonance Spectroscopy; Mice; Purines; Structure-Activity Relationship