Intracarotid Cancer Cell Injection to Produce Mouse Models of Brain Metastasis

Metastasis, the spread and growth of malignant cells at secondary sites within a patient&#39;s body, accounts for &#62; 90% of cancer-related mortality. ...

The University of Texas MD Anderson Cancer Center

Tissue microarrays (TMAs) have emerged as a high-throughput technology for protein evaluation in large cohorts. This technique allows maximization of tissue resources by analysis of sections from 0.6-mm to 1.5-mm core "biopsies" of standard formalin-fixed, paraffin-embedded tissue blocks and by the processing of hundreds of cases arrayed on a single recipient block in an identical manner.

Quantitative evaluation of protein expression as a function of tissue microarray core diameter: is a large (1.5 mm) core better than a small (0.6 mm) core?

Bcl-2 promotes cell survival by inhibiting adapters needed for the activation and cleavage of caspases thus blocking the proteolytic cascade that ultimately dismantles the cell. Bcl-2 has been investigated as a prognostic factor in non small cell lung cancer (NSCLC) patients with conflicting results.

High expression of BCL-2 predicts favorable outcome in non-small cell lung cancer patients with non squamous histology.

Paget's "seed and soil" hypothesis stated that cancer metastasis requires permissive interactions between tumor cells and secondary organ microenvironments. Many of these "permissive interactions" are now known to be growth factor receptor and ligand interactions by which metastatic tumor cells coopt signaling pathways normally used by host organs. However, although cancer cell signaling pathways responsible for primary cancer growth have been extensively characterized, signaling pathways important in supporting tumor cell-secondary organ heterotypic interactions have been neglected. Even as targeted therapies have shown promise and efficacy in treating myriad primary tumors, metastatic cancer remains incurable. Here, we will discuss several growth factor signaling pathways known to be involved in both general and site-specific metastasis. We will address the complexity in generalizing the role of growth factor signaling in metastasis, as both pro- and antimetastatic roles for the same pathways have been demonstrated depending upon context. We will discuss the limitations of current usage of targeted therapies to pathways known to be dysregulated in metastasis. We propose that the future of cancer metastasis-targeted therapy will lie in better understanding of the interactions between tumor cells and the secondary organ microenvironments that may guide rationally designed personalized combinatorial targeted regimens. We hope to promote research to better understand the complex process of metastasis and ultimately better treatments for the abjectly underserved population of patients with metastatic cancer.

Growth factor signaling in metastasis: current understanding and future opportunities.

Despite better control of early-stage disease and improved overall survival of patients with breast cancer, the incidence of life-threatening brain metastases continues to increase in some of these patients. Unfortunately, other than palliative treatments there is no effective therapy for this condition. In this study, we reveal a critical role for Src activation in promoting brain metastasis in a preclinical model of breast cancer and we show how Src-targeting combinatorial regimens can treat HER2(+) brain metastases in this model. We found that Src was hyperactivated in brain-seeking breast cancer cells derived from human cell lines or from patients' brain metastases. Mechanistically, Src activation promoted tumor cell extravasation into the brain parenchyma via permeabilization of the blood-brain barrier. When combined with the EGFR/HER2 dual-targeting drug lapatinib, an Src-targeting combinatorial regimen prevented outgrowth of disseminated breast cancer cells through the induction of cell-cycle arrest. More importantly, this combinatorial regimen inhibited the outgrowth of established experimental brain metastases, prolonging the survival of metastases-bearing mice. Our results provide a rationale for clinical evaluation of Src-targeting regimens to treat patients with breast cancer suffering from brain metastasis.

SRC family kinases as novel therapeutic targets to treat breast cancer brain metastases.

Brain metastasis is a common cause of mortality in cancer patients, yet potential therapeutic targets remain largely unknown. The type I insulin-like growth factor receptor (IGF-IR) is known to play a role in the progression of breast cancer and is currently being investigated in the clinical setting for various types of cancer. The present study demonstrates that IGF-IR is constitutively autophosphorylated in brain-seeking breast cancer sublines. Knockdown of IGF-IR results in a decrease of phospho-AKT and phospho-p70s6k, as well as decreased migration and invasion of MDA-MB-231Br brain-seeking cells. In addition, transient ablation of IGFBP3, which is overexpressed in brain-seeking cells, blocks IGF-IR activation. Using an in vivo experimental brain metastasis model, we show that IGF-IR knockdown brain-seeking cells have reduced potential to establish brain metastases. Finally, we demonstrate that the malignancy of brain-seeking cells is attenuated by pharmacological inhibition with picropodophyllin, an IGF-IR-specific tyrosine kinase inhibitor. Together, our data suggest that the IGF-IR is an important mediator of brain metastasis and its ablation delays the onset of brain metastases in our model system.

Inhibition of type I insulin-like growth factor receptor signaling attenuates the development of breast cancer brain metastasis.

Transforming growth factor β (TGF-β) functions as a tumor suppressor in premalignant cells but as a metastasis promoter in cancer cells. The dichotomous functions of TGF-β are proposed to be dictated by different partners of its downstream effector Smads. However, the mechanism for the contextual changes of Smad partners remained undefined. Here, we demonstrate that 14-3-3ζ destabilizes p53, a Smad partner in premalignant mammary epithelial cells, by downregulating 14-3-3σ, thus turning off TGF-β's tumor suppression function. Conversely, 14-3-3ζ stabilizes Gli2 in breast cancer cells, and Gli2 partners with Smads to activate PTHrP and promote TGF-β-induced bone metastasis. The 14-3-3ζ-driven contextual changes of Smad partners from p53 to Gli2 may serve as biomarkers and therapeutic targets of TGF-β-mediated cancer progression.

14-3-3ζ turns TGF-β's function from tumor suppressor to metastasis promoter in breast cancer by contextual changes of Smad partners from p53 to Gli2.

The development of life-threatening cancer metastases at distant organs requires disseminated tumour cells' adaptation to, and co-evolution with, the drastically different microenvironments of metastatic sites. Cancer cells of common origin manifest distinct gene expression patterns after metastasizing to different organs. Clearly, the dynamic interaction between metastatic tumour cells and extrinsic signals at individual metastatic organ sites critically effects the subsequent metastatic outgrowth. Yet, it is unclear when and how disseminated tumour cells acquire the essential traits from the microenvironment of metastatic organs that prime their subsequent outgrowth. Here we show that both human and mouse tumour cells with normal expression of PTEN, an important tumour suppressor, lose PTEN expression after dissemination to the brain, but not to other organs. The PTEN level in PTEN-loss brain metastatic tumour cells is restored after leaving the brain microenvironment. This brain microenvironment-dependent, reversible PTEN messenger RNA and protein downregulation is epigenetically regulated by microRNAs from brain astrocytes. Mechanistically, astrocyte-derived exosomes mediate an intercellular transfer of PTEN-targeting microRNAs to metastatic tumour cells, while astrocyte-specific depletion of PTEN-targeting microRNAs or blockade of astrocyte exosome secretion rescues the PTEN loss and suppresses brain metastasis in vivo. Furthermore, this adaptive PTEN loss in brain metastatic tumour cells leads to an increased secretion of the chemokine CCL2, which recruits IBA1-expressing myeloid cells that reciprocally enhance the outgrowth of brain metastatic tumour cells via enhanced proliferation and reduced apoptosis. Our findings demonstrate a remarkable plasticity of PTEN expression in metastatic tumour cells in response to different organ microenvironments, underpinning an essential role of co-evolution between the metastatic cells and their microenvironment during the adaptive metastatic outgrowth. Our findings signify the dynamic and reciprocal cross-talk between tumour cells and the metastatic niche; importantly, they provide new opportunities for effective anti-metastasis therapies, especially of consequence for brain metastasis patients.

Microenvironment-induced PTEN loss by exosomal microRNA primes brain metastasis outgrowth.

The metastasis of cancer to the central nervous system (CNS) remains a devastating clinical reality, carrying an estimated survival time of less than one year in spite of recent therapeutic breakthroughs for other disease contexts. Advances in brain metastasis research are hindered by a number of factors, including its complicated nature and the difficulty of modeling metastatic cancer growth in the unique brain microenvironment. In this review, we will discuss the clinical challenge, and compare the merits and limitations of the available models for brain metastasis research. Additionally, we will specifically address current knowledge on how brain metastases take advantage of the unique brain environment to benefit their own growth. Finally, we will explore the distinctive metabolic and chemical characteristics of the brain and how these paradoxically represent barriers to establishment of brain metastasis, but also provide ample supplies for metastatic cells' growth in the brain. We envision that multi-disciplinary innovative approaches will open opportunities for the field to make breakthroughs in tackling unique challenges of brain metastasis.

Frank J. Lowery

Department of Molecular and Cellular Oncology

The University of Texas MD Anderson Cancer Center

Intracarotid Cancer Cell Injection to Produce Mouse Models of Brain Metastasis

Frank J. Lowery

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Molecular and Cellular Oncology

The University of Texas MD Anderson Cancer Center

Intracarotid Cancer Cell Injection to Produce Mouse Models of Brain Metastasis

Department of Molecular and Cellular Oncology