A number of organelles contained within mammalian cells have been implicated in the selective sequestration of chemical entities including drug molecules. Specifically, weakly basic molecules have been shown to selectively associate with either the mitochondrial compartment or lysosomes; however, the structural basis for this differentiation has not been understood. To investigate this, we have identified a series of seven weakly basic compounds, all with pK a near neutrality, which have different sequestration sites within the multidrug-resistant HL-60 human leukemic cell line. Three of the compounds were selectively sequestered into the mitochondria of the cells, whereas the remainder were predominantly localized within lysosomes. Using specific chemical inhibitors to disrupt either mitochondrial or lysosomal accumulation capacity, we demonstrated that accumulation of these compounds into respective organelles are not competitive processes. Comparison of the permeability characteristics of these compounds as a function of pH revealed striking differences that correlate with the intracellular sequestration site. Only those compounds with significantly reduced permeability in the ionized state relative to the un-ionized state had the capacity to accumulate within lysosomes. Alternatively, those compounds with relatively pH-insensitive permeability selectively accumulated into mitochondria. Using novel quantitative assays for assaying drug accumulation into subcellular organelles, we demonstrated a correlation between these permeability characteristics and the lysosomal versus mitochondrial accumulation capacity of these compounds. Together, these results suggest that the selective accumulations of weakly basic compounds in either lysosomes and mitochondria occur via exclusive pathways governed by a unique permeability parameter.

The sequestration of drugs away from cellular target sites into cytoplasmic organelles of multidrug-resistant (MDR) cancer cells has been recently shown to be a cause for ineffective drug therapy. This process is poorly understood despite the fact that it has been observed in a large number of MDR cancer cell lines. Analysis of drug sequestration in these cells has traditionally been done using fluorescent anthracycline antibiotics (i.e. daunorubicin, doxorubicin). This narrow selection of substrates has resulted in a limited understanding of sequestration mechanisms and the intracellular compartments that are involved. To better characterize this phenotype, we chose to examine the sequestration of molecules having different acid/base properties in the MDR HL-60 human leukemic cell line. Here we show that weakly basic drug daunorubicin is sequestered into lysosomes according to a pH partitioning type mechanism, whereas sulforhodamime 101, a zwitterionic molecule, is sequestered into the Golgi apparatus through a drug transporter-mediated process. Quantitative intracellular pH measurements reveal that the lysosome-tocytosol pH gradient is expanded in the MDR line. Moreover, the MDR cells overexpress the multidrug resistance-related protein (MRP1), which is localized to the Golgi apparatus. These results demonstrate, for the first time, that two distinct mechanisms for intracellular compartmentalization are operational in a single MDR cell line.The resistance of tumor cells to anticancer agents remains a major cause of treatment failure in patients with cancer. MDR 1 is a term used to describe a resistance phenotype in which cells become simultaneously resistant to different drugs with no obvious structural similarities or mechanisms of action (1). The emergence of MDR is multifactorial. Decreased drug accumulation and/or increased efflux, increased detoxification, increased DNA repair, and altered cell cycle regulation have all been implicated (2). Interestingly, many MDR cell lines have demonstrated the capacity to compartmentalize drugs away from intracellular target sites (3). In drug-sensitive cell lines, chemotherapeutic agents are localized to a significant extent within the cell nucleus. In contrast, the MDR cells compartmentalize drug within distinct cytoplasmic organelles. This sequestration serves to protect the MDR cell from the cytotoxic effects of drugs since cellular targets are often associated with the nucleus.There are at least two mechanistic explanations that can be used to rationalize the exaggerated drug sequestration capacity of subcellular compartments contained within MDR cancer cells (3). The first involves members of the ATP binding cassette superfamily of transporter proteins such as P-glycoprotein (P-gp) and the multidrug resistance-related protein 1 (MRP1). The overexpression of these transporter proteins in MDR cell lines is well known, and they are traditionally thought to participate in drug efflux at the plasma membrane (4). Recent evidence suggests that these transporters may als...

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Background:To assess the efficacy and safety of tranexamic acid (TA) in reducing blood loss and lowering transfusion needs for patients undergoing caesarean section (CS) or vaginal delivery (VD).Methods:An electronic literature search of PubMed, EMBASE, OVID, Cochrane library, Scopus, Central, and Clinical trials.gov was performed to identify studies that evaluating the usage of TA in CS or VD. The methodological quality of included trials was assessed and data extraction was performed.Results:Finally, 25 articles with 4747 participants were included. Our findings indicated TA resulted in a reduced intra-, postoperative, and total blood loss by a mean volume of 141.25 mL (95% confidence interval [CI] −186.72 to −95.79, P < 0.00001), 36.42 mL (95% CI −46.50 to −26.34, P < 0.00001), and 154.25 mL (95% CI −182.04 to −126.47, P < 0.00001) in CS. TA administration in VD was associated with a reduced intra-, postoperative, and total blood loss by a mean volume of 22.88 mL (95% CI −50.54 to 4.77, P = 0.10), 41.24 mL (95% CI −55.50 to −26.98, P < 0.00001), and 84.79 mL (95% CI −109.93 to −59.65, P < 0.00001). In addition, TA could lower the occurrence rate of postpartum hemorrhage (PPH) and severe PPH, and reduce the risk of blood transfusions. No increased risk of deep vein thrombosis (DVT) after CS or VD was associated with TA usage, while the minor side effects were more common.Conclusions:Our findings indicated that intravenous TA for patients undergoing CS was effective and safe. Although prophylactic TA administration is associated with reduced PPH, current existing data are insufficient to draw definitive recommendations about its clinical significance due to the poor to moderate quality of the included literatures. Thus, high-quality randomized controlled trials with larger samples are needed to validate our findings.