The harsh microenvironment of ductal carcinoma in situ (DCIS) exerts strong evolutionary selection pressures on cancer cells. We hypothesize that the poor metabolic conditions near the ductal center foment the emergence of a Warburg Effect (WE) phenotype, wherein cells rapidly ferment glucose to lactic acid, even in normoxia. To test this hypothesis, we subjected low-glycolytic breast cancer cells to different microenvironmental selection pressures using combinations of hypoxia, acidosis, low glucose, and starvation for many months and isolated single clones for metabolic and transcriptomic profiling. The two harshest conditions selected for constitutively expressed WE phenotypes. RNA sequencing analysis of WE clones identified the transcription factor KLF4 as potential inducer of the WE phenotype. In stained DCIS samples, KLF4 expression was enriched in the area with the harshest microenvironmental conditions. We simulated in vivo DCIS phenotypic evolution using a mathematical model calibrated from the in vitro results. The WE phenotype emerged in the poor metabolic conditions near the necrotic core. We propose that harsh microenvironments within DCIS select for a WE phenotype through constitutive transcriptional reprogramming, thus conferring a survival advantage and facilitating further growth and invasion.

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A combination of techniques from 3D printing, tissue engineering and biomaterials has yielded a new class of engineered biological robots that could be reliably controlled via applied signals. These machines are powered by a muscle strip composed of differentiated skeletal myofibers in a matrix of natural proteins, including fibrin, that provide physical support and cues to the cells as an engineered basement membrane. However, maintaining consistent results becomes challenging when sustaining a living system in vitro. Skeletal muscle must be preserved in a differentiated state and the system is subject to degradation by proteolytic enzymes that can break down its mechanical integrity. Here we examine the life expectancy, breakdown, and device failure of engineered skeletal muscle bio-bots as a result of degradation by three classes of proteases: plasmin, cathepsin L, and matrix metalloproteinases (MMP-2 and MMP-9). We also demonstrate the use of gelatin zymography to determine the effects of differentiation and inhibitor concentration on protease expression. With this knowledge, we are poised to design the next generation of complex biological machines with controllable function, specific life expectancy and greater consistency. These results could also prove useful for the study of disease-specific models, treatments of myopathies, and other tissue engineering applications.

Tissue-engineered skeletal muscle plays an important role not only in the field of regenerative medicine but also in emerging areas such as soft robotics, organ-on-a-chip disease models, and drug testing. However, further expansion of the applications of tissue-engineered skeletal muscle models requires a suitable method for their long-term storage and shipment. Cryopreservation has long been the standard for cell storage, but the freezing of three-dimensional tissues is accompanied by many complications due to heat and mass transfer limitations. In this study, we used a tissue-engineered skeletal muscle bioactuator as a model to characterize the effects of freezing on muscle viability, gene expression, myotube structure, and force generation. We optimized the protocol for cryopreservation by comparing outcomes when tissue was frozen undifferentiated and differentiated. Our optimized protocol, in which skeletal muscle was frozen undifferentiated, not only maintained cell viability but also led to a threefold increase in force production compared to unfrozen muscle. Furthermore, we enhanced muscle lifetime through inhibition of cysteine proteases. The reported timeline for skeletal muscle tissue fabrication, freezing, revival, and long-term culture not only promotes a more streamlined fabrication process but also enables multisite collaborative research efforts through the shipment of preformed skeletal muscle constructs.