Mitoxantrone Accumulation Research Articles

Potentiation of cytotoxicity of mitoxantrone toward CHO-K1 cells in vitro by dipyridamole.

Dipyridamole (DP), a clinically used vasodilator and an antiplatelet compound, augmented the activity of the anticancer drug mitoxantrone (MXN) toward chinese hamster ovary (CHO-K1) cells in culture. Clonogenic assays indicated that DP (1.0, 2.5, and 5.0 microM) decreased the survival of cells treated with MXN (5 to 25 nM) in a dose-dependent manner. Further, DP (1 and 5 microM) decreased the MXN concentration required for 50% inhibition of cell growth from 3.2 to 1.8 and from 3.0 to 0.5 nM, respectively, over a period of 3 days. DP (10 microM) increased the accumulation of MXN by 1.8-fold in exponentially growing cells exposed to MXN. The enhanced levels of MXN in CHO-K1 cells in the presence of the chemosensitizer may account for the potentiation of MXN-cytotoxicity by DP.

Mitoxantrone resistance in HL-60 leukemia cells: reduced nuclear topoisomerase II catalytic activity and drug-induced DNA cleavage in association with reduced expression of the topoisomerase II beta isoform.

Mitoxantrone-resistant variants of the human HL-60 leukemia cell line are cross-resistant to several natural product and synthetic antineoplastic agents. The resistant cells (HL-60/MX2) retain sensitivity to the Vinca alkaloids vincristine and vinblastine, drugs that are typically associated with the classical multidrug resistance phenotype. Mitoxantrone accumulation and retention are equivalent in the sensitive and resistant cell types, suggesting that mitoxantrone resistance in HL-60/MX2 cells might be associated with an alteration in the type II DNA topoisomerases. We discovered that topoisomerase II catalytic activity in 1.0 M NaCl nuclear extracts from the HL-60/MX2 variant, as measured by the decatenation of Crithidia fasciculata kinetoplast DNA, was reduced 4- to 5-fold compared to that in the parental HL-60 cells. Total cellular topoisomerase II activity in HL-60/MX2 cells was only 50% lower than that in HL-60 cells, however, because the "cytosolic fraction" of the HL-60/MX2 nuclear preparation contained high levels of decatenating activity. Antisera to calf thymus topoisomerase II defined a distinctive immunoreactive pattern of topoisomerase II proteins in crude nuclear extracts from the HL-60/MX2 cells. Both alpha (170 kDa) and beta (180 kDa) forms of topoisomerase II were detected in the HL-60 cell extracts, but only the alpha form was detected in extracts from HL-60/MX2 cells. This finding was associated with the appearance of a new 160-kDa immunoreactive species in nuclear extracts from HL-60/MX2 but not HL-60 cells. Studies were designed to minimize the proteolytic degradation of the topoisomerase II enzymes by extraction of whole cells with hot SDS.(ABSTRACT TRUNCATED AT 250 WORDS)

Protection of cultured malignant cells from mitoxantrone cytotoxicity by low extracellular pH: A possible mechanism for chemoresistance in vivo

In malignant tumors the distribution of pH values is shifted to lower values (range, pH 5.8–7.4) as compared to normal tissues (range, pH 6.9–7.4) or peripheral blood (pH 7.35–7.45). We have investigated whether the cytotoxic effect of the anthracenedione anti-cancer drug mitoxantrone (MX) on malignant cells in culture is dependent on changes of extracellular pH. The clonogenic fraction of M1R rat mammary carcinoma cells was measured after exposure to MX at an extracellular pH (pH e) of 6.5–7.4. At pH e 6.8 (approximately the average pH measured in a number of malignant tumors in vivo) the clonogenic fraction of M1R cells exposed to MX (0.1 μ g/ml) only decreased to 1 × 10 −1 as compared to 2.5 × 10 −4 at pH e 7.4, corresponding to a 400-fold inhibition of MX cytotoxicity at reduced environmental pH. The H + ion-mediated resistance of M1R cells to MX could be partially reversed by verapamil, suggesting that a reduced microenvironmental pH possibly interferes with intracellular MX accumulation. Therefore, drugs like MX may not be effective in the elimination of cells in acidic tumor areas. Moreover, investigations on anti-cancer drug activity in vitro at what is frequently referred to as ‘physiological pH’ may be irrelevant in terms of the cytotoxic effects of the respective agents at the pH values prevailing in malignant tissues in vivo.

Development of resistance and characteristics of a human colon carcinoma subline resistant to mitoxantrone in vitro.

A subline of human colon carcinoma cells (WiDr/R) resistant to the cytotoxic effects of mitoxantrone in vitro, was developed by continuous exposure to increasing concentrations of drug. After 16 culture passages in the presence of mitoxantrone, a cell population emerged which was 30-40 times more resistant to the cytolytic effect of mitoxantrone than the mitoxantrone-sensitive parent (WiDr/S) line. Resistance to mitoxantrone was retained by WiDr/R cells propagated for more than 40 cell generations in mitoxantrone-free medium. Decreased drug sensitivity was strongly associated with reduced intracellular accumulation of mitoxantrone. Moderate differences in drug retention by sensitive and resistant cells were demonstrated. However, decreased uptake due to alterations at the cell membrane which impair transport of drug into the cell, reducing interaction with DNA, appears to be the principal basis of resistance in these cells.