CHEUNG LAB

Research Overview

Aggressive cancers display uncontrolled growth, metastatic potential, and therapy resistance. One of the central challenges in cancer biology is understanding how these aggressive properties arise and how to thwart them. Our laboratory is studying this problem through the lens of collective tumor cell interactions. Although cancer is often depicted as the evolution of individual tumor cells, tumor cells exist as multicellular collectives. These collectives are physically coupled through cell-to-cell adhesion, biochemically coupled through signaling complexes, and composed of multiple tumor cell populations with distinct cell behaviors (Yamamoto et al. Annual Reviews 2022). In the Cheung lab, we are interested in discovering the mechanisms by which collective interactions contribute to tumor aggression.

Over 50 years ago, Isaiah Fidler and Lance Liotta first showed that tumor cell clusters form metastases more efficiently than single cells in experimental metastasis assays. Building on these results, work by us and others later showed that in different mouse models, the majority of spontaneous metastases arise from clusters (Cheung and Ewald. Science 2016). These findings establish the principle that collective interactions give rise to cellular behaviors unlike those of individual tumor cells. In the case of metastasis, collectively organized tumor cell clusters possess markedly greater survival, growth, and metastatic seeding potential. Remarkably, these behaviors are apparent even in small clusters composed of only a few cells. Yet despite the robustness of these observations in different models and tumor types, the molecular basis for this phenomenon continues to be underexplored.

Our goal: to innovate new therapies to eradicate metastatic breast cancer

On a practical level, cancers vary by tumor type and even within subtypes. Tumor biology must be interpreted within a clinically relevant pathophysiologic context. In our lab, we focus of our studies of collective interactions in breast cancer, a disease affecting 1 in 8 women worldwide. Between 20 to 30% of women diagnosed with breast cancer will eventually develop distant metastatic disease. While progress has been made in treating breast cancer through a cell-autonomous lens (with targeted therapy against estrogen and oncogenic signaling pathways being prime examples), development of approaches targeting collective tumor interactions remains limited. Importantly, work by us and others have shown that collective organization is strongly associated with metastatic potential and therapy resistance in breast cancer. In the Cheung lab, we are investigating how collective signaling interactions could reveal new avenues for (1) eradicating breast cancer, (2) preventing their progression to lethal metastasis, and (3) overriding their therapy resistance.

Tumor organoids: a platform for discovery

A core thesis of the lab is that the study of clusters – the simplest, complex biological system – can yield insight into how clustering augments the development of aggressive traits. To gain insight into the cell behaviors of metastasizing tumor cell clusters, my laboratory leverages ex-vivo ‘tumor organoid’ models, a powerful platform to directly study the metastatic process in tissue-like environments. Primary tumor specimens are dissociated into cohesive units composed of hundreds cohesive cells. These tumor organoids are then embedded within a three-dimensional extracellular matrix that models the tissue microenvironment of invasive tumors. Through time-lapse microscopy, we directly observe collective cell behaviors. Through genetic and more sophisticated approaches, we interrogate the molecular regulation of individual cells within tumor cell clusters.

Current Projects

In the Cheung lab, we have a broad interest in defining the properties, capabilities, and vulnerabilities of tumor collectives. In particular, we aim to define the biological contexts and developmental transitions where collective interactions have a major effect, to deduce the interactions- be it physical, chemical, or metabolic- that drive collective transitions in cellular states, and to disrupt these interactions as a therapeutic approach to treating cancer.

We are currently pursuing studies in three general project areas outlined below. New graduate students and postdoc candidates with interest in these areas should contact Kevin.

Project 1. Architecture and regulation of collective signaling

Collective interactions give rise to non-linearities in cell behaviors and cellular dynamics that have parallels with a range of complex systems in nature. One such non-linearity is metastatic potential where we have shown that assembly of tumor cells into small clusters augments metastatic potential over 500-fold. Molecular and cellular dissection of this process reveal induction of an intercellular signaling loop involving the EGFR ligand epigen which becomes concentrated between tumor cells in intercellular compartments (Wrenn et al. Cell 2020). Our findings suggest that these synapse-like interfaces are the business end for collective signaling. We currently have several projects on-going to dissect mechanisms regulating intercellular signaling at these interfaces. Specific questions we are trying to address include:

• How are collective signaling compartments formed (what are regulatory programs that give rise to signaling compartments?
• What defines their physical and spatial architecture?
• What therapeutic and pharmacologic strategies best suppress collective signaling interactions?

Project 2. Mechanisms for collective tumor dissemination, aka metastasis of clusters

CTC-clusters are observed in the blood of patients with breast cancer (and of patients with many other tumor types as well) and are associated with markedly greater propensity to metastasize successfully. These clinical and experimental observations have led to the incorporation of tumor cell clusters into models of metastatic dissemination. At the same time, there continue to be many questions related to how clusters gain entry into the systemic circulation, their cooperative interactions between different tumor cell types (Cheung et al. Cell 2013) and with the host microenvironment, and their differences from the behaviors of individually disseminated tumor cells. Specific questions we are trying to address include:

• How do tumor cell clusters disseminate into the systemic circulation?
• What collective interactions are most important for explaining the metastatic efficiency of tumor cell clusters?
• What factors regulate collective migratory behavior and their heterotypic phenotypic organization (leader cells)?

Project 3: Application of collective cell biology to precision medicine

Cancer genetics and tumor-host interactions are driving forces for the development of aggressive metastatic cancer. Accordingly, there has been already substantial effort toward the catalog of genome alterations and more recently single cell atlases defining each individual patient’s cancer profile. In contrast, our understanding of the collective tumor cell interactions across tumor types remains limited. In this regard, there are fertile opportunities for developing new methods for studying collective cell interactions systematically, work that is ongoing in the lab. Specific questions we are trying to address include:

• What is the parts list of signaling factors involved in collective signaling interactions?
• Do collective signaling interactions vary between tumor types, clinical contexts, and even dynamically over time?
• Which clinical contexts (e.g. metastasis development, therapy resistance, tumor evolution) depend on collective signaling? Can collective signals be targeted to therapeutically benefit breast cancer patients?