ABCB1 modulation does not circumvent drug extrusion from primitive leukemic progenitor cells and may preferentially target residual normal cells in acute myelogenous leukemia.

PURPOSE: Acute myelogenous leukemia (AML) is a disease originating from normal hematopoietic CD34+ CD38- progenitor cells. Modulation of the multidrug ATP-binding cassette transporter ABCB1 has not resulted in improved outcome in AML, raising the question whether leukemic CD34+ CD38- cells are targeted by this strategy. EXPERIMENTAL DESIGN: ABCB1-mediated transport in leukemic CD34+ CD38- cells compared with their normal counterparts was assessed by quantitating the effect of specific ABCB1 modulators (verapamil and PSC-833) on mitoxantrone retention [defined as efflux index (EI), intracellular mitoxantrone fluorescence intensity in the presence/absence of inhibitor]. RESULTS: ABCB1 was the major drug transporter in CD34+ CD38- cells in normal bone marrow (n = 16), as shown by the abrogation of mitoxantrone extrusion by ABCB1 modulators (EI, 1.99 +/- 0.08). Surprisingly, ABCB1-mediated drug extrusion was invariably reduced in CD34+ CD38- cells in AML (n = 15; EI, 1.21 +/- 0.05; P < 0.001), which resulted in increased intracellular mitoxantrone retention in these cells (mitoxantrone fluorescence intensity, 4.54 +/- 0.46 versus 3.08 +/- 0.23; P = 0.004). Active drug extrusion from these cells occurred in the presence of ABCB1 modulators in the majority of samples, pointing in the direction of redundant drug extrusion mechanisms. Residual normal CD34+ CD38- cells could be identified by their conserved ABCB1-mediated extrusion capacity. CONCLUSION: ABCB1-mediated drug extrusion is reduced in leukemic CD34+ CD38- progenitor cells compared with their residual normal counterparts. Redundant drug transport mechanisms confer mitoxantrone transport from leukemic progenitors. These data argue that ABCB1 modulation is not an effective strategy to circumvent drug extrusion from primitive leukemic progenitor cells and may preferentially target residual normal progenitors in AML.

Transient protection of cultured human cells against antitumor agents by 12-O-tetradecanoylphorbol-13-acetate.

The tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) has been shown in cell cultures to enhance the frequency of resistance to methotrexate. However, we found that TPA could also partially protect human KB cells over a short time (72 h) from the cytotoxicity of several antitumor agents, including 4'-demethylepipodophyllotoxin 9-(4,6-O-ethylidene)-beta-D-glucopyranoside (VP-16), vincristine, mitoxantrone, and methotrexate, but not 1-beta-D-arabinofuranosylcytosine or 5-fluorouracil. The modes of protection were different for methotrexate and VP-16. Protection by TPA was concentration dependent up to 40 nM and could be accomplished by a 2-h incubation of cells with TPA alone prior to drug treatment. This protection disappeared after a 24-h drug-free incubation. TPA-induced protection could not be mimicked by treatment of cells with 1-oleoyl-2-acetyl-glycerol (a stimulator of protein kinase C) or phospholipase C, which increased the cellular content of diacylglycerols. Thus the action of TPA on protein kinase C may not be sufficient to exert protection. Verapamil, a calcium-channel blocker which has been found to circumvent resistance of multiple drug-resistant cells, also circumvented the protective effect of TPA when used with VP-16. The presence of TPA during a 24-h exposure to radiolabeled VP-16 reduced the cellular drug content by about 30%, whereas verapamil enhanced drug content by at least 50% in TPA-treated and untreated cultures. Since substances with some TPA-like activity have been found in foods and in human circulation, the observation of clinical resistance to some compounds may partly be due to a related mechanism.

Characterization of experimental mitoxantrone cardiotoxicity and its partial inhibition by ICRF-187 in cultured neonatal rat heart cells.

Mitoxantrone cardiotoxicity was investigated in isolated neonatal rat heart myocytes treated for 3 h in the presence or absence of the metal chelator ICRF-187. Electron microscopy studies of mitoxantrone-treated myocytes showed disorganized myofibrillar structures, swollen mitochondria, and extensive vacuolization. Cardiotoxicity, reflected as the ratio of intracellular ATP/protein and the loss of spontaneous beating, was only partially reduced by continuous ICRF-187 concentrations up to 50 micrograms/ml. ICRF-187 induced myocyte protection which was dependent on the dose and duration of exposure. ICRF-187 also reduced the cardiotoxicity of doxorubicin to a lesser extent and reduced the toxicity of a postulated cyclic mitoxantrone metabolite. However, the cardiotoxicity of ametantrone, a nonmetal-binding analogue of mitoxantrone, was unaltered with ICRF-187. The antitumor activity of mitoxantrone was unaltered by ICRF-187 in human tumor cells and in P-388-bearing mice. In addition, ICRF-187 allowed for 50% greater cumulative dosing in normal mice that, nonetheless, showed extensive histological heart damage 7 wk after dosing. These studies show that ICRF-187 provides partial protection from mitoxantrone cardiotoxicity in vitro without impairing the drug's antitumor activity in vitro or in vivo. This facilitates greater cumulative drug dosing in normal mice. The postulated mechanism of cardioprotection is metal chelation, because ICRF-187 did not alter the toxicity of a nonchelating mitoxantrone analogue.

Effects of mitoxantrone in combination with other anticancer agents on a human leukemia cell line.

To investigate the effects of mitoxantrone in combination with other anticancer agents, a human T-cell leukemia cell line, MOLT-3, was incubated for 3 days in the presence of two drugs (mitoxantrone and the combined drug) and cell growth inhibition was determined by assay with 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazonium bromide. The effects of drug combinations at doses giving 80% inhibition (ID80) were analyzed by an improved isobologram method. A supra-additive (synergistic) effect was observed for mitoxantrone in combination with amsacrine, cisplatin, or cytosine arabinoside. An additive effect was observed for its combination with bleomycin, doxorubicin, etoposide, 5-fluorouracil, mitomycin C, 6-mercaptopurine, or vincristine. A sub-additive (antagonistic) effect was observed for its combination with methotrexate. These data suggest that mitoxantrone, administered simultaneously with any one of a majority of anticancer agents we studied, is advantageous for cytokilling. Of the anticancer agents tested, amsacrine, cisplatin, and cytosine arabinoside are the most suitable for combination with mitoxantrone, and these combinations are worthy of clinical investigation. Methotrexate in our system is inappropriate for simultaneous administration with mitoxantrone. These data should provide useful information for the establishment of clinical protocols involving mitoxantrone.

Caffeine reverses the cytotoxic and cell kinetic effects of Novantrone (mitoxantrone).

Caffeine is known to potentiate the cytotoxicity of a variety of DNA damaging agents presumably by reducing the ability of the cells to repair potentially lethal lesions. However, in the present study we observe that 5 mM caffeine reverses the cell kinetic and cytotoxic effects of the intercalating drug Novantrone (mitoxantrone) on L1210, HL-60 and CHO cells. Novantrone alone, at a concentration of 20-30 ng/ml, given to cultures for 1 h, inhibits cell growth by about 50% and causes cells to accumulate in S and G2 phase and to enter a higher DNA ploidy level. Treatment of these cell lines with 5 mM caffeine alone for 1 h has a minimal effect on cell proliferation; suppression of cell growth varies from 5 to 10%. Exposure of cells to Novantrone for 1 h in the presence of caffeine results in a significant reduction of the Novantrone effects; the cell growth rate is partially restored (e.g. caffeine reduces suppression of L1210 cell growth from 48 to 83% of control) and in each of the cell lines studied, the Novantrone-induced cell accumulation in S and G2 is abolished. Combined treatment with caffeine and Novantrone also increases the clonogenicity of CHO cells 8.5 times over that seen in cultures treated with Novantrone alone. In contrast to the combined treatment with caffeine + Novantrone, pretreatment of cells with caffeine provides no protection. Likewise, post-treatment with caffeine provides little reversal of growth inhibition and G2 cell accumulation, especially if the post-treatment is delayed in time. The present data, in conjunction with evidence in the literature that caffeine protects cells against the cytotoxic effects of doxorubicin, suggest that caffeine may play a more general role in protecting cells against planar aromatic molecules such as intercalating agents.

Effects of dihydropyridines and pyridines on multidrug resistance mediated by breast cancer resistance protein: in vitro and in vivo studies.

Breast cancer resistance protein (BCRP, ABCG2) is a recently identified member of the ATP-binding cassette family of cell surface transport proteins. This study was conducted to investigate the effect of a series of newly synthesized 1,4-dihydropyridines and pyridines, designed as potent P-glycoprotein inhibitors, on BCRP-mediated drug efflux both in vitro and in vivo. The effects of 25 synthesized dihydropyridines and corresponding pyridines along with 4 commercially available dihydropyridines (niguldipine, nicardipine, nifedipine, and nitrendipine) on the intracellular accumulation of the BCRP substrate mitoxantrone were evaluated in BCRP-expressing human breast cancer MCF-7/MX100 and human non-small cell lung cancer H460/MX20 cells. At a 2.5 microM concentration, 24 of 25 newly synthesized dihydropyridines and pyridines produced a significant increase of mitoxantrone accumulation in both cell lines. The most potent compound was able to enhance mitoxantrone accumulation approximately 4.5-fold, greater than that obtained with 10 microM fumitremorgin C, which is a specific BCRP inhibitor. The results from the two cell lines showed good correlation (r(2) = 0.71, p < 0.01). Niguldipine, nicardipine, and nitrendipine also demonstrated potent BCRP inhibition, whereas nifedipine had no effect. The effects of the dihydropyridine and pyridine compounds on mitoxantrone cytotoxicity paralleled their effects on mitoxantrone accumulation. Coadministration of a selected dihydropyridine compound, I(m) [DHP-014; 3-(3-(4,4-diphenylpiperidin-1-yl)propyl) 5-methyl 4-(3,4-dimethoxyphenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate)] with topotecan, a good BCRP substrate and a moderate to poor P-glycoprotein substrate, resulted in significant increases in the systemic exposure and peak concentration of topotecan in Sprague-Dawley rats when oral topotecan (2 mg/kg) was combined with 20 mg/kg DHP-014. The observed increase of topotecan exposure provides proof-of-concept for in vivo inhibition of BCRP by these agents.

Ametantrone acetate: anthracenedione diacetate, NSC-287513

El acetato de ametantrona es el compuesto padre de una serie de antracenodionas actualmente sometidois a pruebas clínicas en los Estados Unidos. Se sintetizaron estos compuestos en un intento de eliminar la toxicidad cardíaca asociada con antibióticos antraciclínicos sin sacrificar la actividad clínica. El acetato dea meyantrona parece funcionar como un agente intercalador. En sistemas de tumores murinos, la droga produce curas en leucemias P388 y L1210, melanoma B16 y carcinoma de colon 26. En perros, los objetivos principales de la toxicidad fueron la médula ósea, el tejido linfoide, la vía gastrointestinal y los testículos. La droga no es activa por vía orla. El acetato de ametantrona muestra una curva dósis/repuesta de inclinación relativamente alta. La administración intravenosa rápida en ratones produce convulsiones instantáneas y muerte. Aunque menos frecuente y menos severa que la toxicidad producida por antraciclinas, pudo demostrarse toxicidad cardíaca en ratones, ratas, conejos y perros. El acetato de ametantrona es un compuesto de un azul intenso que imparte color azul a la orina, la materia fecal, la piel y a los órganos internos. El período de vida media plasmático de la droga es aproximadamente dos horas. Se han comenzado tres estudios clínicos Fase 1: dos utilizan un régimen de una sola dósis y uno un régimen de 5 días. Hasta la fecha se han notado muy pocas respuestas. La toxicidades más importantes han sido leucopenia, decoloración azul de la piel, alopecia e hipotensión ortostática. La dósis inicial recomendada para estudios fase 2 de una sola dósis en pacientes de alto riesgo es 140 mg/m2