Background: Although standard protocols for the study of drug delivery in the upper airways using the sub-bronchial epithelial cell line Calu-3 model, particularly that of the air-liquid interface configuration, are readily available, the model remains un-validated with respect to culture conditions, barrier integrity, mucous secretion, and transporter function. With respect to the latter, the significance of functional P-glycoprotein (P-gp) activity in Calu-3 cells has recently been questioned, despite previous reports demonstrating a significant contribution by the same transporter in limiting drug uptake across the pulmonary epithelium. Therefore, the aim of this study was the standardization of this model as a tool for drug discovery. Methods: Calu-3 cells were grown using air-interfaced condition (AIC) on polyester cell culture supports. Monolayers were evaluated for transepithelial electrical resistance (TEER), permeability to the paracellular marker fluorescein sodium (flu-Na), surface P-gp expression, and functionality. Mucous secretion was also identified by alcian blue staining. Results: TEER and permeability values obtained for Calu-3 monolayers were shown to plateau between day 5 and day 21 in culture with values reaching 474 ± 44 ωcm² and 2.33 ± 0.36 × 10^–7 cm/s, respectively, irrespective of the passage number examined. 32.7 ± 1.49% of Calu-3 cells cultured under these conditions detected positive for cell surface P-gp expression from day 7 onwards. Functional cell surface expression was established by rhodamine 123 drug extrusion assays. Conclusion: This study establishes a clear dependence on culture time and passage number for optimal barrier integrity, mucous secretion, and cell-surface P-gp expression and function in Calu-3 cells. Furthermore it provides initial guidelines for the optimization of this model for high throughput screening applications.

Drug resistance is a major cause of cancer treatment failure, with multidrug resistance (MDR) being the most serious, whereby cancer cells display cross‐resistance to structurally and functionally unrelated drugs. MDR is caused by overexpression of the efflux transporters P‐glycoprotein (P‐gp) and multidrug resistance‐associated protein 1 (MRP1). These transporters act to maintain sublethal intracellular drug concentrations within the cancer cell, making the population treatment unresponsive. Recently, we discovered a novel nongenetic basis to MDR whereby microparticles (MPs) transfer P‐gp intercellularly from MDR donor cells to drug‐sensitive recipient cells. MPs isolated from MDR leukemia and breast cancer cells were cocultured with their drug‐sensitive counterparts. P‐gp transfer was assessed by direct immunolabeling, and acquired transcripts and regulatory microRNAs by quantitative real‐time PCR. We show that MDR MPs incorporate nucleic acids; MPs change recipient cells' transcriptional environment to reflect donor MDR phenotype, and distinct pathways exist among cancers of different origin that may be dependent on donor cells' ABCB1 overexpression. We demonstrate that this pathway exists for both hematological and nonhematological malignancies. By conferring MDR and “retemplating” the transcriptional landscape of recipient cells, MPs provide a novel pathway, having implications in the dissemination and acquisition of deleterious traits in clinical oncology.—Jaiswal, R., Gong, J., Sambasivam, S., Combes, V., Mathys, J.‐M., Davey, R., Grau, G. E. R., Bebawy, M. Microparticle‐associated nucleic acids mediate trait dominance in cancer. FASEB J. 26, 420–429 (2012). www.fasebj.org

Microparticles (MPs) play a vital role in cell communication by facilitating the horizontal transfer of cargo between cells. Recently, we described a novel “non-genetic” mechanism for the acquisition of multidrug resistance (MDR) in cancer cells by intercellular transfer of functional P-gp, via MPs. MDR is caused by the overexpression of the efflux transporters P-glycoprotein (P-gp) and Multidrug Resistance-Associated Protein 1 (MRP1). These transporters efflux anticancer drugs from resistant cancer cells and maintain sublethal intracellular drug concentrations. By conducting MP transfer experiments, we show that MPs derived from DX breast cancer cells selectively transfer P-gp to malignant MCF-7 breast cells only, in contrast to VLB 100 leukaemic cell-derived MPs that transfer P-gp and MRP1 to both malignant and non-malignant cells. The observed transfer selectivity is not the result of membrane restrictions for intercellular exchange, limitations in MP binding to recipient cells or the differential expression of the cytoskeletal protein, Ezrin. CD44 (isoform 10) was found to be selectively present on the breast cancer-derived MPs and not on leukaemic MPs and may contribute to the observed selective transfer of P-gp to malignant breast cells observed. Using the MCF-7 murine tumour xenograft model we demonstrated the stable transfer of P-gp by MPs in vivo , which was found to localize to the tumour core as early as 24 hours post MP exposure and to remain stable for at least 2 weeks. These findings demonstrate a remarkable capacity by MPs to disseminate a stable resistant trait in the absence of any selective pressure.

Background: Microparticles (MPs) are membrane vesicles which are released from normal and malignant cells following a process of budding and detachment from donor cells. MPs contain surface antigens, proteins and genetic material and serve as vectors of intercellular communication. MPs comprise the major source of systemic RNA including microRNA (miRNA), the aberrant expression of which appears to be associated with stage, progression and spread of many cancers. Our previous study showed that MPs carry both transcripts and miRNAs associated with the acquisition of multidrug resistance in cancer. Results: Herein, we expand on our previous finding and demonstrate that MPs carry the transcripts of the membrane vesiculation machinery (floppase and scramblase) as well as nucleic acids encoding the enzymes essential for microRNA biogenesis (Drosha, Dicer and Argonaute). We also demonstrate using microarray miRNA profiling analysis, the selective packaging of miRNAs (miR-1228*, miR-1246, miR-1308, miR-149*, miR-455-3p, miR-638 and miR-923) within the MP cargo upon release from the donor cells. Conclusions: These miRNAs are present in both haematological and non-haematological cancer cells and are involved in pathways implicated in cancer pathogenesis, membrane vesiculation and cascades regulated by ABC transporters. Our recent findings reinforce our earlier reports that MP transfer ‘re-templates’ recipient cells so as to reflect donor cell traits. We now demonstrate that this process is likely to occur via a process of selective packaging of nucleic acid species, including regulatory nucleic acids upon MP vesiculation. These findings have significant implications in understanding the cellular basis governing the intercellular acquisition and dominance of deleterious traits in cancers.