Pharmacology of antineoplastic agents in pregnancy.

The use of antineoplastic agents in pregnant women poses obvious risks to both the patient and the developing fetus, particularly during organogenesis. While the use of antineoplastics during pregnancy is often unavoidable, the physician may limit the risks by having a clear knowledge of the pharmacology and teratogenic potential of individual agents. Specific physiologic changes in the pregnant patient, such as enhanced renal excretion of drugs, increased or decreased hepatic function, altered gastrointestinal absorption and enterohepatic circulation, altered plasma protein binding, an increase in plasma volume (50%), and creation of a fluid filled 3rd compartment (amniotic fluid) for water soluble drugs may all significantly influence the pharmacology of antineoplastic agents. These physiological changes may effect the pregnant patients ability to absorb orally administered drugs, metabolize drugs to either active or inactive metabolites, and eliminate cytotoxically active drugs. A resulting reduction in concentration x time (C x T) for drug exposure to the maternal system may reduce the efficacy of the antineoplastic agents, while an increase in C x T may expose the patient and her fetus to undue toxicity. The timing of drug administration to gestational age is also a critical factor for some drugs. While many drugs result in adverse effects on the fetus regardless of gestational age, others appear to pose less of a threat if administered beyond the first trimester. This review addresses the pharmacology, pharmacokinetics and the teratogenic potential of individual antineoplastic agents that are commonly used in pregnant patients. The aim of this review is to help the physician select, on a patient specific basis, antineoplastic agents that avoid at least some of the fetal risk involved while maintaining efficacy in the treatment of the patient.

Prolonged tamoxifen exposure selects a breast cancer cell clone that is stable in vitro and in vivo.

The effects of long-term tamoxifen exposure on cell growth and cell cycle kinetics were compared between oestrogen receptor (ER)-positive (MCF-7) and ER-negative (MDA-MB-231) cell lines. In the MCF-7 cell line, prolonged tamoxifen exposure (0.5 mumol/l for > 100 days) blocked cells in G0-G1 of the cell cycle, and slowed the doubling time of cells from 30 to 59 h. These effects corresponded to an increase in the cellular accumulation of tamoxifen over time [mean area under concentration curve (AUC) = 77.92 mumoles/10(6)/cells/day]. In contrast, in the MDA-MB-231 cell line, long-term tamoxifen exposure had no obvious effect on the doubling time, and reduced cellular tamoxifen accumulation (mean AUC = 50.50 mumoles/10(6)/cells/day) compared to the MCF-7 cells. Flow cytometric analysis of MDA-MB-231 cells demonstrated that a new tetraploid clone emerged following 56 days of tamoxifen exposure. Inoculation of the MDA-MB-231 tetraploid clone and MDA-MB-231 wildtype cells into the opposite flanks of athymic nude mice resulted in the rapid growth of tetraploid tumours. The tetraploid tumours maintained their ploidy following tamoxifen treatment for nine consecutive serial transplantations. Histological examination of the fifth transplant generation xenografts revealed that the tetraploid tumour had a 25-30 times greater mass, area of haemorrhage and necrosis, a slightly higher mitotic index and was more anaplastic than the control neoplasm. The control wildtype MDA-MB-231 tumours maintained a stable ploidy following tamoxifen treatment until the eighth and ninth transplantation, when a tetraploid population appeared, suggesting that tamoxifen treatment may select for this clone in vivo. These studies suggest that prolonged tamoxifen exposure may select for new, stable, fast growing cell clones in vitro as well as in vivo.