Several experimental models faithfully recapitulate many important facets of human metastatic disease. Here we have performed whole exome sequencing in five widely used experimental metastasis models that were independently derived through in vivo selection from heterogeneous human cancer cell lines. In addition to providing an important characterization of these model systems, our study examines the genetic evolution of metastatic phenotypes. We found that in vivo selected highly metastatic cell populations showed little genetic divergence from the corresponding parental population. However, selection of genetic variations that preexisted in parental populations, including the well-established oncogenic mutations KRASG13D and BRAFG464V, was associated with increased metastatic capability. Conversely, expression of the wild-type BRAF allele in metastatic cells inhibited metastatic outgrowth as well as tumor initiation in mice. Our findings establish that metastatic competence can arise from heterogeneous cancer cell populations without the need for acquisition of additional mutations, and that such competence can benefit from further selection of tumor-initiating mutations that seed primary tumorigenesis.

Recent efforts to sequence human cancer genomes have highlighted that point mutations in genes involved in the epigenetic setting occur in tumor cells. Small cell lung cancer (SCLC) is an aggressive tumor with poor prognosis where little is known about the genetic events related to its development. Herein, we have identified the presence of homozygous deletions of the candidate histone acetyltransferase KAT6B, and the loss of the corresponding transcript, in SCLC cell lines and primary tumors. Furthermore, we show, in vitro and in vivo, that the depletion of KAT6B expression enhances cancer growth, whilst its restoration induces tumor suppressor-like features. Most importantly, we demonstrate that KAT6B exerts its tumor inhibitory role through a newly defined type of histone H3 Lys23 acetyltransferase activity.

Future curative cancer chemotherapies have to overcome tumor cell heterogeneity and plasticity. To test the hypothesis that the tumor suppressor maspin may reduce microenvironment-dependent prostate tumor cell plasticity and thereby modulate drug sensitivity, we established a new schematic combination of 2D, 3D and suspension cultures to enrich prostate cancer cell subpopulations with distinct differentiation potentials. We report here that, depending on the level of maspin expression, tumor cells in suspension and 3D collagen I manifest the phenotypes of stem-like and dormant tumor cell populations, respectively. In suspension, the surviving maspin-expressing tumor cells lost the self-renewal capacity, underwent senescence, lost the ability to dedifferentiate in vitro and failed to generate tumors in vivo. Maspin-nonexpressing tumor cells that survived the suspension culture in compact tumorspheres, displayed a higher level of stem cell marker expression, maintained the self-renewal capacity, formed tumorspheres in 3D matrices in vitro and were tumorigenic in vivo. The drug sensitivities of the distinct cell subpopulations depend on the drug target and the differentiation state of the cells. In 2D, Docetaxel, MS275 and Salinomycin were all cytotoxic. In suspension, while MS275 and Salinomycin were toxic, Docetaxel showed no effect. Interestingly, cells adapted to 3D collagen I were only responsive to Salinomycin. Maspin expression correlated with higher sensitivity to MS275 in both 2D and suspension, and to Salinomycin in 2D and 3D collagen I. Our data suggest that maspin reduces prostate tumor cell plasticity, and enhances tumor sensitivity to Salinomycin which may hold promise in overcoming tumor cell heterogeneity and plasticity.

The aggressiveness of invasive ductal carcinoma (IDC) of the breast is associated with increased IL-17 levels. Studying the role of IL-17 in invasive breast tumor pathogenesis, we found that metastatic primary tumor-infiltrating T lymphocytes produced elevated levels of IL-17, whereas IL-17 neutralization inhibited tumor growth and prevented the migration of neutrophils and tumor cells to secondary disease sites. Tumorigenic neutrophils promote disease progression, producing CXCL1, MMP9, VEGF and TNF
, and their depletion suppressed tumor growth. IL-17A also induced IL-6 and CCL20 production in metastatic tumor cells, favoring the recruitment and differentiation of Th17. In addition, IL-17A changed the gene expression profile and the behavior of non-metastatic tumor cells, causing tumor growth in vivo, confirming the pro-tumor role of IL-17. Furthermore, high IL-17 expression was associated with lower disease-free survival (DFS) and worse prognosis in IDC patients. Thus, IL-17 blockade represents an attractive approach for the control of invasive breast tumors.

Despite successes, thus far a significant proportion of the patients treated with anti-PD1 antibodies have failed to respond. We use mouse tumor models of anti-PD1 sensitivity and resistance, and flow cytometry to assess tumor infiltrating immune cells immediately post-therapy. We demonstrate that the expression levels of T cell PD1 (PD1lo), myeloid and T cell PDL1 (PDL1hi) in the tumor microenvironment inversely correlate and dictate the efficacy of anti-PD1 mAb and function of intratumor CD8+ T cells. In sensitive tumors, we reveal a threshold for PD1 down regulation on tumor infiltrating CD8+ T cells below which the release of adaptive immune resistance is achieved. By contrast, PD1hi T cells in resistant tumors fail to be rescued by anti-PD1 therapy and remain dysfunctional unless intratumor PDL1lo immune cells are targeted. Intratumor Treg are partly responsible for the development of anti-PD1 resistant tumors and PD1hi CD8+ T cells. Our analyses provide a framework to interrogate intratumor CD8+ T cell PD1 and immune PDL1 levels and response in human cancer.