Potentiation of vincristine by vitamin A against drug-resistant mouse leukaemia cells

Human MDR1 and mouse mdr1a P-glycoprotein alter the cellular retention and disposition of erythromycin, but not of retinoic acid or benzo(a)pyrene

The intracellular concentration of many steroids and xenobiotics is influenced by the membrane protein P-glycoprotein (Pgp). It has been inferred that the intracellular retention of many drugs that upregulate Pgp or modulate Pgp function might also be affected by Pgp. However, the ability of Pgp to influence the translocation of these drugs needs to be established to understand Pgp's influence upon their pharmacological effect. We utilized two approaches to determine the interaction of several agents with Pgp: (a) an in vitro system, LLC-PK1 cell lines and derivative LLC cell lines stably expressing on the apical membrane either mouse mdr1a or human MDR1 Pgp grown as polarized epithelium in transwell culture to measure translocation of radiolabeled drugs; and (b) an in vivo system, mdr1a nullizygous and wild-type animals, to compare the contribution of Pgp to in vivo distribution of radiolabeled drugs. In combination these complementary approaches identified erythromycin as a drug whose intracellular retention is influenced by Pgp, while the intracellular accumulation and tissue distribution of retinoic acid and benzo(a)pyrene were unaffected by Pgp.

Combination therapy with cisplatin: modulation of activity and tumour sensitivity

Although cisplatin is applied with success in clinical oncology, this success is limited because some cancers are initially unresponsive to cisplatin or become so during treatment. In this review, some strategies to overcome this problem are discussed. Among these are combination with the differentiation inducing agent, retinoic acid, combination with radiotherapy, and the use of hyperthermia.

Cytotoxic effects of vitamin A in combination with vincristine, daunorubicin and 6-thioguanine upon cells from lymphoblastic leukemic patients

We studied whether isotretinoin potentiated the effects of vincristine (VCR), daunorubicin (DNR), and 6-thioguanine (6-TG) against cells obtained from 24 patients with acute lymphoblastic leukemia (ALL). Treatment with 5 micrograms/ml isotretinoin alone resulted in a leukemic cell survival of 82% +/- 28.1%. So isotretinoin is toxic to ALL cells. Dose-response curves were obtained for VCR, DNR and 6-TG in the presence and absence of isotretinoin Isotretinoin showed additive leukemic cell kills in combination with VCR and DNR. When corrected for cell kill by isotretinoin alone, it appeared that isotretinoin did not significantly enhance leukemic cell kills by VCR, DNR and 6-TG. No differences were found between samples from patients at initial diagnosis and at relapse with respect to cell kill by isotretinoin alone and with respect to a possible synergistic effect of isotretinoin and the cytostatic drugs. It is concluded that isotretinoin has additive antileukemic effects in combination with VCR or DNR. However, isotretinoin does not potentiate the antileukemic effects of VCR, DNR and 6-TG against leukemic cells obtained from patients with ALL.

Reversal by two dihydropyridine compounds of resistance to multiple anticancer agents in mouse P388 leukemia in vivo and in vitro

We investigated whether two representative 1,4-dihydropyridine derivatives, NK-250 and NK-252, could potentiate the antitumor activity of multiple anticancer agents including vincristine (VCR), vinblastine, vindesine and actinomycin D in drug-resistant tumor cells and their parental drug-sensitive tumor cells. NK-250 and NK-252 at 5-10 microM almost completely reversed VCR resistance in cultured VCR-resistant P388/VCR cells derived from the mouse drug-sensitive P388/S leukemia cell line and also potentiated the cytocidal activity of VCR in drug-sensitive P388/S cells. NK-250 and NK-252 at 1-10 microM inhibited the photoaffinity labeling by [3H]azidopine of the cell-surface 170,000-molecular-weight P-glycoprotein. In chemotherapeutic experiments with leukemia-bearing mice, NK-250 or NK-252 was orally administered in combination with different drugs of the MDR phenotype administered intraperitoneally. The antitumor activity of the various combinations was found to be augmented in mice bearing P388/S- and P388/VCR-leukemia. Among the combinations examined, the combination of NK-250 and VCR was the most effective. These two 1,4-dihydropyridines, NK-250 and NK-252, are unique compounds because they were effective not only in circumventing the drug resistance, but also in potentiating the action of antitumor drugs against drug-sensitive tumors.

Clinical management of the cancer patient. Principles and applications of chemotherapy

Chemotherapy is an important and effective modality of modern cancer treatment. Practitioners are encouraged to become familiar with this branch of medicine because it can be employed in the local practice setting. In the process of providing service for clientele and care for their pets, practicing clinicians will inevitably be confronted with involvement in some aspect of a chemotherapeutic protocol initiated by a veterinary oncologist. With an understanding of the principles of chemotherapy, the toxicities inherent in the use of these compounds, and the judicious handling of these agents, veterinarians will be able to provide a better standard of care for the animals presented to them.

Potentiation of some anticancer agents by dipyridamole against drug-sensitive and drug-resistant cancer cell lines

In this study, we have used two different vincristine (VCR)-resistant variants, VJ-300 and HC-7-5/VCR. VJ-300 was isolated from a human cancer KB cell line and HC-7-5/VCR from a human cancer HC-7-5 cell line. VJ-300 and HC-7-5/VCR are both multidrug-resistant (MDR) variants, showing resistance to multiple anticancer drugs such as VCR, adriamycin, actinomycin D and daunomycin. Dipyridamole, a specific inhibitor of nucleoside transport, potentiated these anticancer drugs about 2- to 10-fold against KB and VJ-300. Dipyridamole almost completely reversed drug resistance to actinomycin D in VJ-300 cells with about a 70-fold higher resistance to actinomycin D. Dipyridamole inhibited the efflux of actinomycin D and VCR from VJ-300 cells. Dipyridamole enhanced the uptake of VCR but not that of actinomycin D in VJ-300 and KB. Dipyridamole at 10-100 microM inhibited photoaffinity labeling with [3H]azidopine of the cell-surface protein P-glycoprotein in VJ-300 cells. Dipyridamole potentiated 5-fluorouracil and hexylcarbamoyl-5-fluorouracil in cultured KB and VJ-300, but it annihilated the cytotoxic action of 5-fluorouridine. Potentiation of 5-fluorouracil by dipyridamole against HC-7-5 and HC-7-5/VCR was also observed, but appeared to be less than in VJ-300 and KB cells. Dipyridamole almost completely inhibited the cellular accumulation of 5-fluorouridine, but not that of 5-fluorouracil. Thus, dipyridamole appeared to potentiate anticancer agents through pleiotropic action sites, one of which is inhibition of enhanced efflux of MDR cell lines and the other of which is inhibition of nucleoside transport. Dipyridamole might be a useful and potent agent to potentiate anticancer agents and reverse drug-resistance.

Analysis of structural features of dihydropyridine analogs needed to reverse multidrug resistance and to inhibit photoaffinity labeling of P-glycoprotein

Synthetic dihydropyridine analogs were screened to determine whether they would reverse multidrug resistance of a multidrug-resistant human KB carcinoma cell line, KB-C1. Among twenty-four dihydropyridine analogs examined, thirteen almost completely overcame drug resistance (group A), nine partially overcame resistance (group B) and two did not reverse resistance (group C). The twenty-two compounds that reversed drug-resistance (groups A and B) were hydrophobic dihydropyridine derivatives. Three compounds that reversed resistance, NK-113, NK-138 and NK-194, increased the accumulation of [3H]vincristine in the resistant KB-C1 cells, but not in the parental KB cells, nor in a revertant cell line, KB-C1-R2. NK-101 (group C), which did not reverse resistance, had no effect on drug accumulation. Enhanced efflux of vincristine from the resistant cells was inhibited completely by NK-194, but NK-194 did not affect vincristine influx. Nine of the twenty-four compounds were screened to determine whether they inhibited photoaffinity labeling of the cell surface protein gp170 (P-glycoprotein) in KB-C1 cells by N-(p-azido-[3-125I]-salicyl)-N'-beta-aminoethylvindesine [( 125I]NASV). All five compounds of group A, NK-138, NK-194, NK-200, NK-203 and NK-220, inhibited the photoaffinity labeling of gp170 at less than 10-100 microM, whereas NK-113 and NK-196 of group B inhibited the labeling at 100-200 microM. By contrast, NK-101 and NK-102 of group C did not inhibit labeling even at 2000 microM. These studies confirm the relationship among reversal of multidrug resistance, decreased efflux of vincristine, and inhibition of [125I]NASV labeling of P-glycoprotein.