Overcoming Multidrug Resistance via Photodestruction of ABCG2-Rich Extracellular Vesicles Sequestering Photosensitive Chemotherapeutics

Multidrug resistance (MDR) remains a dominant impediment to curative cancer chemotherapy. Efflux transporters of the ATP-binding cassette (ABC) superfamily including ABCG2, ABCB1 and ABCC1 mediate MDR to multiple structurally and functionally distinct antitumor agents. Recently we identified a novel mechanism of MDR in which ABCG2-rich extracellular vesicles (EVs) form in between attached neighbor breast cancer cells and highly concentrate various chemotherapeutics in an ABCG2-dependent manner, thereby sequestering them away from their intracellular targets. Hence, development of novel strategies to overcome MDR modalities is a major goal of cancer research. Towards this end, we here developed a novel approach to selectively target and kill MDR cancer cells. We show that illumination of EVs that accumulated photosensitive cytotoxic drugs including imidazoacridinones (IAs) and topotecan resulted in intravesicular formation of reactive oxygen species (ROS) and severe damage to the EVs membrane that is shared by EVs-forming cells, thereby leading to tumor cell lysis and the overcoming of MDR. Furthermore, consistent with the weak base nature of IAs, MDR cells that are devoid of EVs but contained an increased number of lysosomes, highly accumulated IAs in lysosomes and upon photosensitization were efficiently killed via ROS-dependent lysosomal rupture. Combining targeted lysis of IAs-loaded EVs and lysosomes elicited a synergistic cytotoxic effect resulting in MDR reversal. In contrast, topotecan, a bona fide transport substrate of ABCG2, accumulated exclusively in EVs of MDR cells but was neither detected in lysosomes of normal breast epithelial cells nor in non-MDR breast cancer cells. This exclusive accumulation in EVs enhanced the selectivity of the cytotoxic effect exerted by photodynamic therapy to MDR cells without harming normal cells. Moreover, lysosomal alkalinization with bafilomycin A1 abrogated lysosomal accumulation of IAs, consequently preventing lysosomal photodestruction of normal breast epithelial cells. Thus, MDR modalities including ABCG2-dependent drug sequestration within EVs can be rationally converted to a pharmacologically lethal Trojan horse to selectively eradicate MDR cancer cells

Cardiovascular effects of sub-daily levels of ambient fine particles: a systematic review

<p>Abstract</p> <p>Background</p> <p>While the effects of daily fine particulate exposure (PM) have been well reviewed, the epidemiological and physiological evidence of cardiovascular effects associated to sub-daily exposures has not. We performed a theoretical model-driven systematic non-meta-analytical literature review to document the association between PM sub-daily exposures (≤6 hours) and arrhythmia, ischemia and myocardial infarction (MI) as well as the likely mechanisms by which sub-daily PM exposures might induce these acute cardiovascular effects. This review was motivated by the assessment of the risk of exposure to elevated sub-daily levels of PM during fireworks displays.</p> <p>Methods</p> <p>Medline and Elsevier's EMBase were consulted for the years 1996-2008. Search keywords covered potential cardiovascular effects, the pollutant of interest and the short duration of the exposure. Only epidemiological and experimental studies of adult humans (age > 18 yrs) published in English were reviewed. Information on design, population and PM exposure characteristics, and presence of an association with selected cardiovascular effects or physiological assessments was extracted from retrieved articles.</p> <p>Results</p> <p>Of 231 articles identified, 49 were reviewed. Of these, 17 addressed the relationship between sub-daily exposures to PM and cardiovascular effects: five assessed ST-segment depression indicating ischemia, eight assessed arrhythmia or fibrillation and five considered MI. Epidemiologic studies suggest that exposure to sub-daily levels of PM is associated with MI and ischemic events in the elderly. Epidemiological studies of sub-daily exposures suggest a plausible biological mechanism involving the autonomic nervous system while experimental studies suggest that vasomotor dysfunction may also relate to the occurrence of MI and ischemic events.</p> <p>Conclusions</p> <p>Future studies should clarify associations between cardiovascular effects of sub-daily PM exposure with PM size fraction and concurrent gaseous pollutant exposures. Experimental studies appear more promising for elucidating the physiological mechanisms, time courses and causes than epidemiological studies which employ central pollution monitors for measuring effects and for assessing their time course. Although further studies are needed to strengthen the evidence, given that exposure to sub-daily high levels of PM (for a few hours) is frequent and given the suggestive evidence that sub-daily PM exposures are associated with the occurrence of cardiovascular effects, we recommend that persons with cardiovascular diseases avoid such situations.</p

Consensus guidelines for the use and interpretation of angiogenesis assays

The formation of new blood vessels, or angiogenesis, is a complex process that plays important roles in growth and development, tissue and organ regeneration, as well as numerous pathological conditions. Angiogenesis undergoes multiple discrete steps that can be individually evaluated and quantified by a large number of bioassays. These independent assessments hold advantages but also have limitations. This article describes in vivo, ex vivo, and in vitro bioassays that are available for the evaluation of angiogenesis and highlights critical aspects that are relevant for their execution and proper interpretation. As such, this collaborative work is the first edition of consensus guidelines on angiogenesis bioassays to serve for current and future reference