Sustained Oncogenic Signaling in the Cytostatic State Enables Targeting of Nonproliferating Persistent Cancer Cells.

Many advanced therapeutics possess cytostatic properties that suppress cancer cell growth without directly inducing death. Treatment-induced cytostatic cancer cells can persist and constitute a reservoir from which recurrent growth and resistant clones can develop. Current management approaches primarily comprise maintenance and monitoring because strategies for targeting nonproliferating cancer cells have been elusive. Here, we used targeted therapy paradigms and engineered cytostatic states to explore therapeutic opportunities for depleting treatment-mediated cytostatic cancer cells. Sustained oncogenic AKT signaling was common, while nonessential, in treatment-mediated cytostatic cancer cells harboring PI3K-pathway mutations, which are associated with cancer recurrence. Engineering oncogenic signals in quiescent mammary organotypic models showed that sustained, aberrant activation of AKT sensitized cytostatic epithelial cells to proteasome inhibition. Mechanistically, sustained AKT signaling altered cytostatic state homeostasis and promoted an oxidative and proteotoxic environment, which imposed an increased proteasome dependency for maintaining cell viability. Under cytostatic conditions, inhibition of the proteasome selectively induced apoptosis in the population with aberrant AKT activation compared with normal cells. Therapeutically exploiting this AKT-driven proteasome vulnerability was effective in depleting treatment-mediated cytostatic cancer cells independent of breast cancer subtype, epithelial origin, and cytostatic agent. Moreover, transient targeting during cytostatic treatment conditions was sufficient to reduce recurrent tumor growth in spheroid and mouse models. This work identified an AKT-driven proteasome-vulnerability that enables depletion of persistent cytostatic cancer cells harboring PTEN-PI3K pathway mutations, revealing a viable strategy for targeting nonproliferating persistent cancer cell populations before drug resistance emerges. SIGNIFICANCE: This study finds that sustained oncogenic signaling in therapy-induced cytostatic cancer cells confers targetable vulnerabilities to deplete persistent cancer cell populations and reduce cancer recurrence.

A Unified Protocol to Streamline Molecular and Cellular Analysis for Three-Dimensional Cell Cultures.

Three-dimensional (3D) cell cultures based on reconstituted basement membrane materials recapitulate features of extracellular matrix (ECM) and tissue stiffness in vivo and provide a physiologically relevant platform to study complex cellular processes, such as stem cell differentiation and tissue morphogenesis, that are otherwise difficult in animal models. The form and composition of 3D matrices in culture can interfere with and pose challenges for different experimental setups and assays, which necessitate alterations to facilitate analysis. Here, we provide a unified protocol for 3D cell cultures with modular workflows that streamline procedures for compatibility with common molecular and cellular assays such as live-cell imaging, immunofluorescence , qPCR, RNAseq, western blotting, and quantitative mass spectrometry.

VivosX, a disulfide crosslinking method to capture site-specific, protein-protein interactions in yeast and human cells.

VivosX is an in vivo disulfide crosslinking approach that utilizes a pair of strategically positioned cysteines on two proteins to probe physical interactions within cells. Histone H2A.Z, which often replaces one or both copies of H2A in nucleosomes downstream of promoters, was used to validate VivosX. Disulfide crosslinks between cysteine-modified H2A.Z and/or H2A histones within nucleosomes were induced using a membrane-permeable oxidant. VivosX detected different combinations of H2A.Z and H2A within nucleosomes in yeast cells. This assay correctly reported the change in global H2A.Z occupancy previously observed when the deposition and eviction pathways of H2A.Z were perturbed. Homotypic H2A.Z/H2A.Z (ZZ) nucleosomes accumulated when assembly of the transcription preinitiation complex was blocked, revealing that the transcription machinery preferentially disassembles ZZ nucleosomes. VivosX works in human cells and distinguishes ZZ nucleosomes with one or two ubiquitin moieties, demonstrating that it can be used to detect protein-protein interactions inside cells from different species.