During cancer metastasis, tumor cells penetrate tissues through tight interstitial spaces, requiring extensive deformation of the cell and its nucleus. Here, we investigated tumor cell migration in confining microenvironments in vitro and in vivo. Nuclear deformation caused localized loss of nuclear envelope (NE) integrity, which led to the uncontrolled exchange of nucleo-cytoplasmic content, herniation of chromatin across the NE, and DNA damage. The incidence of NE rupture increased with cell confinement and with depletion of nuclear lamins, NE proteins that structurally support the nucleus. Cells restored NE integrity using components of the endosomal sorting complexes required for transport-III (ESCRT-III) machinery. Our findings indicate that cell migration incurs substantial physical stress on the NE and its content, requiring efficient NE and DNA damage repair for survival.

Solid tumors consist of genetically and phenotypically diverse subpopulations of cancer cells with unique capacities for growth, differentiation, and invasion. While the molecular and microenvironmental bases for heterogeneity are increasingly appreciated, the outcomes of such intratumor heterogeneity, particularly in the context of tumor invasion and metastasis, remain poorly understood. To study heterotypic cell-cell interactions and elucidate the biological consequences of intratumor heterogeneity, we developed a tissue-engineered multicellular spheroid (MCS) co-culture model that recapitulates the cellular diversity and fully three-dimensional cell-cell and cell-matrix interactions that characterize human carcinomas. We found that “invasion-competent” malignant cells induced the collective invasion of otherwise “invasion-incompetent” epithelial cells, and that these two cell types consistently exhibited distinct leader and follower roles during invasion. Analysis of extracellular matrix microarchitecture revealed that malignant cell invasion was accompanied by extensive extracellular matrix remodeling including matrix alignment and proteolytic track-making. Inhibition of cell contractility- and proteolysis-mediated matrix reorganization prevented leader-follower behavior and malignant cell-induced epithelial cell invasion. These results indicate that heterogeneous subpopulations within a tumor may possess specialized roles during tumor progression and suggest that complex interactions among the various subpopulations of cancer cells within a tumor may regulate critical aspects of tumor biology and affect clinical outcome.

From embryonic development to cancer metastasis, cell migration plays a central role in health and disease. It is increasingly becoming apparent that cells migrating in three-dimensional (3-D) environments exhibit some striking differences compared with their well-established 2-D counterparts. One key finding is the significant role the nucleus plays during 3-D migration: when cells move in confined spaces, the cell body and nucleus must deform to squeeze through available spaces, and the deformability of the large and relatively rigid nucleus can become rate-limiting. In this review, we highlight recent findings regarding the role of nuclear mechanics in 3-D migration, including factors that govern nuclear deformability, and emerging mechanisms by which cells apply cytoskeletal forces to the nucleus to facilitate nuclear translocation. Intriguingly, the ‘physical barrier’ imposed by the nucleus also impacts cytoplasmic dynamics that affect cell migration and signaling, and changes in nuclear structure resulting from the mechanical forces acting on the nucleus during 3-D migration could further alter cellular function. These findings have broad relevance to the migration of both normal and cancerous cells inside living tissues, and motivate further research into the molecular details by which cells move their nuclei, as well as the consequences of the mechanical stress on the nucleus.

Mammary tumor cells adopt a basal-like phenotype when invading through a dense, stiffened, 3D matrix. These cells exert higher integrin-mediated traction forces, consistent with a physical motor-clutch model, display an altered molecular organization at the nanoscale, and recruit a suite of paxillin-associated proteins implicated in metastasis.

Deregulation of the cell cycle has long been recognized as an essential driver of tumorigenesis, and agents that selectively target key cell cycle components continue to hold promise as potential therapeutics. We have developed AZD5438, a 4-(1-isopropyl-2-methylimidazol-5-yl)-2-(4-methylsulphonylanilino) pyrimidine, as a potent inhibitor of cyclin-dependent kinase (cdk) 1, 2, and 9 (IC 50 , 16, 6, and 20 nmol/L, respectively). In vitro, AZD5438 showed significant antiproliferative activity in human tumor cell lines (IC 50 range, 0.2-1.7 μmol/L), causing inhibition of the phosphorylation of cdk substrates pRb, nucleolin, protein phosphatase 1a, and RNA polymerase II COOH-terminal domain and blocking cell cycling at G 2 -M, S, and G 1 phases. In vivo, when orally administered at either 50 mg/kg twice daily or 75 mg/kg once daily, AZD5438 inhibited human tumor xenograft growth (maximum percentage tumor growth inhibition, range, 38-153; P < 0.05). In vivo, AZD5438 reduced the proportion of actively cycling cells. Further pharmacodynamic analysis of AZD5438-treated SW620 xenografts showed that efficacious doses of AZD5438 (>40% tumor growth inhibition) maintained suppression of biomarkers, such as phospho-pRbSer 249 /Thr 252 , for up to 16 hours following a single oral dose. A comparison of different schedules indicated that chronic daily oral dosing provided optimal cover to ensure antitumor efficacy. These data indicate that broad cdk inhibition may provide an effective method to impair the dysregulated cell cycle that drives tumorigenesis and AZD5438 has the pharmacologic profile that provides an ideal probe to test this premise.