Dr. Zhong & Colleagues Understand Heterogeneity in Metastatic Cell Populations with Milo

Yi Zhong, M.D., Ph.D. is a Research Associate at Memorial Sloan Kettering Cancer Center in the laboratory of Christine Iacobuzio-Donahue, M.D., Ph.D. Their research focuses on the evolutionary mechanisms underlying cancer, with the goal of understanding organ-specific metastasis of pancreatic cancer. They use a variety of models and methods, including a heavy reliance on the analysis of tissue samples from pancreatic cancer patients, mouse models and experiments that track the evolutionary progress of human and mouse pancreatic cancer cells over extended periods of time.

UNDERSTANDING THE CELL BIOLOGY OF ORGAN-SPECIFIC METASTASIS

Research within the group has long focused on understanding the mechanisms that cause metastasis. To perform a search for genetic regulators of pancreatic ductal adenocarcinoma metastasis, they utilized a mouse model that exhibits disrupted TGFβ and p53 R172H mutant signaling in the epithelial precursor cell population specific to the pancreas¹. They conclude that mice with disruptions in TGFβ and mutant p53 signaling had decreased hematogenous and peritoneal metastases. Using these models, they were also able to determine the distinct signaling mechanisms that control metastases to the liver and lungs—in summary, that cell-autonomous TGFβ signaling mediates metastatic colonization of the liver and that disruption of the TGFβ signaling cascade prevents lung metastasis. The finding that different mechanisms underlie metastases to different tissues highlights the need to carefully dissect signaling pathways in these metastatic cell subpopulations. “We aim to understand these differences in greater detail with the goal of elucidating novel therapeutic vulnerabilities for metastatic pancreatic cancer,” explains Dr. Zhong.

MILO: INSIGHT INTO HETEROGENEITY OF PROTEIN EXPRESSION

To begin understanding the differences in cell signaling, Dr. Zhong completed a single-cell RNA-sequencing experiment in primary and metastatic cell samples in which he generated a list of RNA transcripts that are up- or down-regulated in metastatic cell subpopulations. Dr. Zhong explains that from there, his research aims at validating his RNA-seq findings at the protein level and gaining “a deep understanding of how cancer cells adapt in the primary versus metastatic sites, as measured through intercellular heterogeneity of protein expression.” Many of the numerous targets that they are studying may only be changed in a small subpopulation of cells and standard protein analysis techniques, such as Western blotting, which examine cellular populations by pooling thousands or millions of cells to give averaged measurements, may not detect up- or down-regulation of target proteins in these subpopulations of cells. In order to characterize protein heterogeneity at the single-cell level they needed a new approach. “Milo permits study of proteins at the single-cell level to understand the heterogeneity among metastatic cells within a population,” Dr. Zhong reports. “We expect that in turn our observations using Milo will generate new hypotheses and new areas of scientific inquiry.”