Combination of standard cytotoxic agents with polyamine analogues in the treatment of breast cancer cell lines.

Polyamines are essential for cell growth and differentiation. Structural polyamine analogues have been shown to have antitumor activity in experimental models including breast cancer. The ability of polyamine analogues to alter activity of cytotoxic chemotherapeutic agents in breast cancer models has not been evaluated. This study evaluates the ability of two polyamine analogues, N1-ethyl-N11-[(cyclopropyl)methyl]-4,8-diazaundecane (CPENSpm) and N1-ethyl-N11-[(cycloheptyl)methyl]-4,8-diazaundecane (CHENSpm) to synergize with cytotoxics in five human breast cancer cell lines. Antagonism, additivity, or synergy of the combinations was determined using the median effect/combination index model. The chemotherapeutic agents chosen, cis-diaminechloroplatinum(II), doxorubicin, 5-fluorouracil, fluorodeoxyuridine, 4-hydroperoxycyclophosphamide, paclitaxel, docetaxel, and vinorelbine, all have antitumor activity in breast cancer and represent a spectrum of mechanisms. Three treatment schedules of polyamine analogue and cytotoxic were tested in MCF-7 and MDA-MB-468 lines, demonstrating a schedule-dependence of synergistic growth inhibition. Cytotoxic agent alone for 24 h followed by polyamine analogue alone for 96 h resulted in the most synergistic combinations and the greatest synergy. This schedule was then tested in three additional breast cancer lines, and several synergistic combinations were again identified. Two cytotoxics, vinorelbine and the fluoropyrimidines, showed the most promise in combination with the polyamine analogues. They were able to synergize with one or both polyamine analogues in most of the breast cancer cell lines. CPENSpm was also able to synergize with virtually all of the cytotoxics in the estrogen receptor alpha-positive MCF-7 and T-47D lines. These preclinical data demonstrate a treatment schedule and combinations of polyamine analogues and cytotoxics that will be important to study mechanistically and clinically for breast cancer.

Reexamination of the effect of endotoxin on cell proliferation and transfection efficiency.

Plasmid DNA purified from bacterial cells can be contaminated with endotoxin to different extents, depending on the purification method. Earlier reports indicate that endotoxin can decrease transfection efficiency in many eukaryotic cell lines; however, the amount of endotoxin required for inhibition is unclear. We determined endotoxin effects in several cell lines and observed that endotoxin levels greater than or equal to 10,000 endotoxin units (EU) were needed to significantly affect cell proliferation and viability; levels greater than 2000 EU/mu g DNA were required to significantly inhibit transfection for all but one (Huh-7) of the cell lines tested. These endotoxin levels are significantly higher than endotoxin contamination in plasmid DNA purified by anion exchange, CsCl2 gradient and endotoxin-free purification technology, but not as high as a crude alkaline lysis preparatory method. Plasmid DNA prepared using anion exchange technology was comparable to endotoxin-free technology in terms of transfection efficiency. Even Huh-7 cells, which are markedly more sensitive to endotoxins, have comparable transfection efficiencies using plasmid DNA purified by either of these two methods. We conclude that for those cell lines commonly used for transfection studies, endotoxin-free, quality DNA is not necessary because significantly higher levels of bacterial endotoxins are required to inhibit either cell proliferation or transfection.

Transcriptional activation of estrogen receptor alpha in human breast cancer cells by histone deacetylase inhibition.

Recent findings have established a connection between DNA methylation and transcriptionally inactive chromatin characterized by deacetylated histones. Because the absence of estrogen receptor alpha (ERalpha) gene expression has been associated with aberrant methylation of its CpG island in a significant fraction of breast cancers, we tested whether histone deacetylase activity contributes to the transcriptional inactivation of the methylated ER gene in a panel of ER-negative human breast cancer cells. Treatment of these cells with trichostatin A, a specific histone deacetylase inhibitor, led to dose- and time-dependent re-expression of ER mRNA as detected by reverse transcription-PCR without alteration in ERalpha CpG island methylation. Trichostatin A-induced ER re-expression was associated with increased sensitivity to DNase I at the ER locus in MDA-MB-231 cells. These data implicate inactive chromatin mediated by histone deacetylation as a critical component of ER gene silencing in human breast cancer cells. Therefore, histone deacetylation may be a potential target for therapeutic intervention in the treatment of a subset of ER-negative breast cancers.

Mapping of ER gene CpG island methylation-specific polymerase chain reaction.

Southern analysis has shown that DNA from 25% of primary estrogen receptor (ER) alpha-negative breast tumors displays aberrant methylation at one site within the ER gene CpG island. To examine more sites and increase sensitivity, we developed a methylation-specific PCR assay to map methylation of the entire ER CpG island. The island was unmethylated in normal breast tissue and ER-positive breast cancer cell lines, but extensively methylated in all ER-negative cell lines and breast tumors examined. In addition, some of the ER-positive/progesterone receptor-negative and ER-positive/progesterone receptor-positive tumors (about 70% and 35%, respectively) displayed methylation of the ER CpG island, suggesting that this heterogeneity within tumor cell populations could potentially shed light on the etiology of ER-negative recurrent tumors arising from ER-positive tumors.