Cinchonine, a potent efflux inhibitor to circumvent anthracycline resistance in vivo.

Circumvention of multidrug resistance is a new field of investigation in cancer chemotherapy, and safe and potent multidrug resistance inhibitors are needed for clinical use. We investigated several analogues of quinine for their ability to increase anthracycline uptake in resistant cancer cells. Cinchonine was the most potent inhibitor of anthracycline resistance in vitro, and its activity was little altered by serum proteins. Serum from rats treated with i.v. cinchonine produced greater uptake of doxorubicin in cancer cells (DHD/K12/PROb rat colon cells and K562/ADM human leukemic cells) than did serum from quinine-treated rats (ex vivo assay). Cinchonine was more effective than quinine in reducing tumor mass and increasing the survival of rats inoculated i.p. with DHD/K12/PROb cells and treated i.p. with deoxydoxorubicin. Moreover, the acute toxicity of cinchonine in rats and mice was lower than that of other quinine-related compounds. The lower toxicity and greater potentiation of in vivo anthracycline activity produced by cinchonine are favorable characteristics for its use as an anti-multidrug resistance agent in future clinical trials.

Comparative effects of quinine and cinchonine in reversing multidrug resistance on human leukemic cell line K562/ADM.

We have previously suggested that quinine and cinchonine could be good candidates for clinical circumvention of multidrug resistance (MDR) in hematological malignancies because of their tolerance and their retained efficacy in serum. In the present study, we have used the well-characterized multidrug resistant human leukemic cell line K562/ADM to compare the effect in vitro of quinine and cinchonine on doxorubicin, mitoxantrone, and vincristine uptake and cytotoxicity. In serum-free medium, quinine induced a dose-dependent increase of doxorubicin uptake reaching about 200% at 40 microM, while it had a slight and no effect on mitoxantrone and vincristine uptake respectively. In the same conditions, cinchonine induced a rapid and significant increase in the accumulation of the three drugs, reaching a plateau phase between 5 and 10 microM. Quinine and cinchonine induced both potentiation of doxorubicin, vincristine and mitoxantrone cytotoxicity in K562/ADM cells. However, quinine reached a plateau phase at 10 microM, while cinchonine had a maximal effect at 5 microM and was significantly more potent at low concentrations. When diluted in plasma, cinchonine was less bound to proteins than quinine. The free fraction of alkaloids was 37-55% for cinchonine and 20-30% for quinine. Cinchonine-induced enhancement of vincristine cellular accumulation was little modified by plasma proteins. When incubated in whole blood, the fraction of cinchonine trapped in red blood cells was rapidly and completely exchangeable with plasma. We conclude that cinchonine is a stronger inhibitor of MDR than quinine.

Confluence dependent resistance (CDR) to doxorubicin and E-cadherin expression in murine mammary cells.

Confluence dependent resistance (CDR) is one of the principal mechanisms by which solid tumor cells resist anthracyclines. CDR is thought to be mediated by cell-cell contact which increases the fraction of non-proliferating resistant cells in a post confluence monolayer culture. As E-cadherin is a major Ca2+ dependent adhesion molecule, involved in cell-cell adhesion, differentiation and polarity of normal and cancerous epithelial cells, we decided to investigate its involvement in the CDR mechanism. In order to do this, we measured the intracellular accumulation and the cytotoxicity of doxorubicin (DXR) in four subclones, derived from the same parental murine mammary cell line (NMuMG), differing in their expression of E-cadherin. A significant reduction in DXR accumulation and cytotoxicity was observed in NM-f-ras-TD-CAMx, which expresses E-cadherin, suggesting that E-cadherin could play a role in the increase of drug resistance observed in confluent cancer cells.

mdr 1 gene-expression and villin synthesis in a colon cancer cell line differentiated by sodium butyrate.

Sodium butyrate (NaBu) but not dimethylsulfoxide (DMSO) induced the synthesis of villin, a protein of the brush border microvilli cytoskeleton, in a rat colon cancer cell line. Neither NaBu nor DMSO altered mdr 1-mRNA expression or multidrug resistance (MDR)--associated cellular transport of doxorubicin. These results show that mdr 1 gene expression and activity are independent of other brush border proteins induced by differentiating agents at the apical pole of the epithelial cell.

P27KiP1 overexpression inhibits the growth and doxorubicin sensitivity of HT29 human colon cancer cells in vivo.

We have previously shown that p27KiP1 plays a role in the tumor cell resistance of HT29 confluent monolayers to cytotoxic drugs in vitro. To determine whether p27KiP1 was a resistance factor to cytotoxic drugs in vivo we tested the effect of doxorubicin on p27KiP1-overexpressing HT29 tumors in nude mice. In this study we show that ectopic overexpression of p27KiP1 in HT29 human colon cancer cells decreases their tumorigenicity in vivo in nude mice. This decreased tumor growth was associated with increased p27KiP1 protein expression, studied by Western blotting in tumor extracts. Interestingly, the overexpressing-p27KiP1 tumors were significantly more resistant to intraveneous doxorubicin treatment than the control tumors. These results indicate that p27KiP1, which delays tumor growth could also increase tumor resistance to cytotoxic drugs in vivo.

Liposomal mitoxantrone for the local treatment of peritoneal carcinomatosis induced by colon cancer cells in mice.

Since liposomes are slowly resorbed from serous cavities, they may constitute a valuable tool for the treatment of peritoneal carcinomatosis. We prepared mitoxantrone (MXN)-liposomes with various lipid compositions and checked their antitumoral activity on a peritoneal carcinomatosis induced by a colon cancer cell injection (1 x 10(5) C51 cells) in BALB/c mice. MXN entrapment in liposomes was rapid and stable due to its high lipophilicity. MXN carried in phosphatidylcholine: cholesterol (2:1; G-liposomes) displayed a reduced toxicity in mice compared to the free drug. When tested at a non-toxic dose (2 mg/kg), MXN entrapped in G-liposomes proved to be as efficient as the free drug. At a higher MXN dose (3 mg/kg), both G-liposomes and phosphatidylcholine:cholesterol:dipalmitoylphosphatidylethanolamine (7:2:1) liposomes, loaded with MXN, significantly increased the life span of mice compared to the free drug and six other liposome formulations. Increase in the MXN therapeutic index, when used in the liposomal form, could then merit further clinical investigations in regard to patients with malignancies confined to serous cavities.

Effects of cyclosporin at various concentrations on dexamethasone intracellular uptake in multidrug resistant cells.

BACKGROUND: The multidrug resistance phenomenon results from the expression of P-glycoprotein (P-gp), a drug-efflux pump. Corticosteroids are substrates for P-gp, whose function can be inhibited by cyclosporin. This study evaluates the ability of cyclosporin to modulate dexamethasone uptake in multidrug resistant cells. METHODS: The K 562 cell line, which does not express P-gp and a P-gp expressing clone, K562/ADM, were used. Cells were incubated with H3-dexamethasone in the absence or presence of cyclosporin at various concentrations. Then, cells were washed, lysed, and radioactivity was measured. RESULTS: The uptake of dexamethasone alone was higher in sensitive than in resistant cells. Addition of cyclosporin induced a dose dependent increase of dexamethasone uptake in resistant cells, whereas the drug did not influence dexamethasone uptake in parental cells. CONCLUSION: Cyclosporin, at therapeutic concentrations induces a moderate, but significant increase in dexamethasone accumulation in multidrug resistant cells. Thus, cyclosporin might increase the intestinal absorption of corticosteroids or their accumulation in mononuclear cells, or both, thereby increasing their therapeutic efficacy.

Cinchonine per os: efficient circumvention of P-glycoprotein-mediated multidrug resistance.

We have previously suggested that quinine and cinchonine could be good candidates for the clinical circumvention of multidrug resistance (MDR) in haematological malignancies because of their tolerance and their retained efficacy in serum. We have also shown that cinchonine was more efficient than quinine as an anti-MDR agent in vitro, ex vivo and in vivo after parenteral administration. Here, we report that cinchonine administered per os (po) is much more active than quinine po in circumventing MDR in rats bearing resistant colon tumours. The pharmacokinetics of cinchonine and quinine administered po in rat are shown to be very different. Cinchonine demonstrates a greater absolute bioavailability than quinine (44% versus 30%, respectively). Its serum concentration correlates with the anti-MDR activity measured ex vivo and in vivo. Cinchonine administered po does not significantly modify the pharmacokinetics of intravenous doxorubicin (DXR). However, cinchonine induces a significant increase of DXR uptake in organs which express the mdr1 gene (liver, kidney, lung). When associated with VAD (vincristine, adriamycin, dexamethasone) combined therapy in rats, cinchonine does not significantly increase the toxicity of the cytotoxic drugs. Based on these experimental data, a phase I clinical trial is currently in progress to test the tolerance of this potent MDR-reversing agent administered po.

Cellular pharmacology of azatoxins (topoisomerase-II and tubulin inhibitors) in P-glycoprotein-positive and -negative cell lines.

Azatoxin (NSC 640737), a synthetic molecule, was rationally designed as a topoisomerase-II inhibitor and was shown to be a potent cytotoxic agent that inhibits both tubulin and topoisomerase II. A structure-activity relationship study allowed to select 3 derivatives that inhibit either tubulin (methylazatoxin) only or topoisomerase II (fluoroanilinoazatoxin and nitroanilino-azatoxin) in MTT assays performed on K562 and K562/ADM cells; the latter, expressing P-glycoprotein, indicated cross-resistance of K562/ADM cells to all 4 compounds. DNA double-strand breaks induced by the 3 azatoxins that inhibit topoisomerase II in vitro were decreased in K562/ADM as compared with K562 cells. Nitroanilino-azatoxin was the only compound for which resistance and reduced DNA damage observed in K562/ADM cells was partially reversed by verapamil, suggesting that nitroanilinoazatoxin was a substrate for P-glycoprotein. These results were confirmed by testing the cytotoxic activity of azatoxins on P-glycoprotein-expressing rat colon-carcinoma DHDK12/TRb cells in the absence and the presence of verapamil. Cell-cycle and mitotic-index studies indicated that azatoxin- and methyl-azatoxin-induced M-phase arrest was less in K562/ADM than in K562 cells. The G2 block induced by fluoro- and nitroanilinoazatoxins was delayed in K562/ADM cells. Verapamil increased cell-cycle inhibition induced by nitroanilinoazatoxin in K562/ADM cells without modifying cell-cycle effects of fluoroanilinoazatoxin. These results (i) are consistent with the specific inhibition of topoisomerase II or tubulin by azatoxin derivatives in cells; (ii) indicate that the nitro group of nitroanilinoazatoxin allows recognition and efflux by the P-glycoprotein; and (iii) suggest that cross-resistance of K562/ADM cells to other azatoxin derivatives is not mediated by P-glycoprotein.