Cancer cells continually sense and respond to mechanical cues from the extracellular matrix (ECM). Interaction with the ECM can alter intracellular signaling cascades, leading to changes in processes that promote cancer cell growth, migration, and survival. The present study used a recently developed composite hydrogel composed of a fibrin matrix and phase‐shift emulsion, termed an acoustically responsive scaffold (ARS), to investigate effects of local mechanical properties on breast cancer cell signaling. Treatment of ARSs with focused ultrasound drives acoustic droplet vaporization (ADV) in a spatiotemporally controlled manner, inducing local compaction and stiffening of the fibrin matrix adjacent to the matrix–bubble interface. Combining ARSs and live single cell imaging of triple‐negative breast cancer cells, it is discovered that both basal and growth‐factor stimulated activities of protein kinase B (also known as Akt) and extracellular signal‐regulated kinase (ERK), two major kinases driving cancer progression, negatively correlate with increasing distance from the ADV‐induced bubble both in vitro and in a mouse model. Together, these data demonstrate that local changes in ECM compaction regulate Akt and ERK signaling in breast cancer and support further applications of the novel ARS technology to analyze spatial and temporal effects of ECM mechanics on cell signaling and cancer biology.

Self-sufficiency (autonomy) in growth signaling, the earliest recognized hallmark of cancer, is fuelled by the tumor cells ability to secrete-and-sense growth factors; this translates into cell survival and proliferation that is self-sustained by auto-/paracrine secretion. Using breast cancer cells that are either endowed or impaired in growth signaling autonomy, here we reveal how autonomy impacts cancer progression. Autonomy is associated with enhanced molecular programs for stemness, immune evasiveness, proliferation, and epithelial-mesenchymal plasticity (EMP). Autonomy is both necessary and sufficient for anchorage-independent growth factor-restricted proliferation and resistance to anti-cancer drugs and is required for metastatic progression. Transcriptomic and proteomic studies show that autonomy is associated with self-sustained EGFR/ErbB signaling. A gene expression signature is derived (a.k.a., autonomy signature) which revealed that autonomy is induced in circulating tumor cells (CTCs) and particularly CTC clusters, the latter of which carry higher metastatic potential. Autonomy in CTCs tracks therapeutic response and prognosticates outcome. Autonomy is preserved during reversible (but not stable) epithelial-mesenchymal transition (EMT). These data support a role for growth signaling autonomy in multiple processes essential for the blood-borne dissemination of human breast cancer.

<div>Abstract<p>Cancer cells reprogram energy metabolism through metabolic plasticity, adapting ATP-generating pathways in response to treatment or microenvironmental changes. Such adaptations enable cancer cells to resist standard therapy. We employed a coculture model of estrogen receptor–positive (ER⁺) breast cancer and mesenchymal stem cells (MSC) to model interactions of cancer cells with stromal microenvironments. Using single-cell endogenous and engineered biosensors for cellular metabolism, coculture with MSCs increased oxidative phosphorylation, intracellular ATP, and resistance of cancer cells to standard therapies. Cocultured cancer cells had increased MCT4, a lactate transporter, and were sensitive to the MCT1/4 inhibitor syrosingopine. Combining syrosingopine with fulvestrant, a selective estrogen receptor degrading drug, overcame resistance of ER⁺ breast cancer cells in coculture with MSCs. Treatment with antiestrogenic therapy increased metabolic plasticity and maintained intracellular ATP levels, while MCT1/4 inhibition successfully limited metabolic transitions and decreased ATP levels. Furthermore, MCT1/4 inhibition decreased heterogenous metabolic treatment responses versus antiestrogenic therapy. These data establish MSCs as a mediator of cancer cell metabolic plasticity and suggest metabolic interventions as a promising strategy to treat ER⁺ breast cancer and overcome resistance to standard clinical therapies.</p>Implications:<p>This study reveals how MSCs reprogram metabolism of ER⁺ breast cancer cells and point to MCT4 as potential therapeutic target to overcome resistance to antiestrogen drugs.</p></div>

Cancer cells reprogram energy metabolism through metabolic plasticity, adapting ATP-generating pathways in response to treatment or microenvironmental changes. Such adaptations enable cancer cells to resist standard therapy. We employed a co-culture model of estrogen receptor-positive (ER+) breast cancer and mesenchymal stem cells (MSCs) to model interactions of cancer cells with stromal microenvironments. Using single-cell endogenous and engineered biosensors for cellular metabolism, co-culture with MSCs increased oxidative phosphorylation, intracellular ATP, and resistance of cancer cells to standard therapies. Co-cultured cancer cells had increased MCT4, a lactate transporter, and were sensitive to the MCT1/4 inhibitor syrosingopine. Combining syrosingopine with fulvestrant, a selective estrogen receptor degrading drug, overcame resistance of ER+ breast cancer cells in co-culture with MSCs. Treatment with antiestrogenic therapy increased metabolic plasticity and maintained intracellular ATP levels, while MCT1/4 inhibition successfully limited metabolic transitions and decreased ATP levels. Furthermore, MCT1/4 inhibition decreased heterogenous metabolic treatment responses versus antiestrogenic therapy. These data establish MSCs as a mediator of cancer cell metabolic plasticity and suggest metabolic interventions as a promising strategy to treat ER+ breast cancer and overcome resistance to standard clinical therapies. Implications: This study reveals how MSCs reprogram metabolism of ER+ breast cancer cells and point to MCT4 as potential therapeutic target to overcome resistance to anti-estrogen drugs.

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