20.5: Il microambiente tumorale

The Tumor Microenvironment
JoVE Core
Molecular Biology
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JoVE Core Molecular Biology
The Tumor Microenvironment

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02:17 min
April 07, 2021

Overview

Every normal cell or tissue is embedded in a complex local environment called stroma, consisting of different cell types, a basal membrane, and blood vessels. As normal cells mutate and develop into cancer cells, their local environment also changes to allow cancer progression. The tumor microenvironment (TME) consists of a complex cellular matrix of stromal cells and the developing tumor. The cross-talk between cancer cells and surrounding stromal cells is critical to disrupt normal tissue homeostasis and favor tumor progression.

Cancer-associated fibroblasts (CAFs)

Fibroblasts produce collagen and are involved in tissue repair. During the natural process of wound healing, fibroblasts are transiently present for the initial healing process. Nevertheless, in cancer, the fibroblasts remain constitutively active so that they can remodel the extracellular matrix, induce angiogenesis, recruit inflammatory cells, and stimulate cancer cell proliferation.

Angiogenesis

Tumor growth is accompanied by active blood vessel growth at the tumor site due to the release of vascular endothelial growth factor or VEGF from the cancer cells and stromal cells. VEGF is an essential growth factor for angiogenesis during tumor progression. Therefore, therapies that can target the synthesis and activity of VEGF or the VEGF receptors in the tumor microenvironment have shown significant improvement in patient survival.

Adipose cells

Hypoxia in adipose or fat tissue is highly pro-inflammatory and promotes tumor formation and maintenance. Additionally, adipose cells secrete more than 50 different cytokines and chemokines that can increase the chances of tumor initiation. Excess adipocytes in the tumor microenvironment can lead to increased blood estrogen, chronic and low-grade inflammation resulting in cancer development.

ECM and tumor microenvironment

An extracellular matrix (ECM) is a dynamic and complex structure that supports tissues and cells. The ECM contains cytokines and growth factors secreted by the tumor and stromal cells. ECM components also include collagens, laminins, fibronectins, proteoglycans, and hyaluronans. The ECM helps tumors in several ways: First, ECM components facilitate angiogenesis by providing nourishment to the stalk cells, the building blocks of new blood vessels. Second, they act as chemoattractants to immune cells to initiate inflammation at tumor sites. Inflammation facilitates rapid cell division and angiogenesis. Third, altered collagen cross-links in the ECM allow tumor cells to escape immune surveillance and metastasize to new locations in the body.

Tumor management strategies must involve effective TME management. Targeting microenvironments can help create a hostile environment for tumor cells that may lead to effective therapy and hence, increase in patient survival.

Transcript

Il microambiente tumorale comprende il tumore e il tessuto di supporto che lo circonda, noto anche come stroma. Le cellule tumorali interagiscono costantemente con lo stroma per formare un ambiente permissivo e di supporto per la loro crescita e metastasi.

Lo stroma è costituito da una matrice extracellulare che circonda il tumore e da diversi componenti cellulari.

La matrice extracellulare, o ECM, è una complessa rete di macromolecole, tra cui collagene e fibrina. Rispetto ai tessuti normali, la struttura e la composizione della MEC nel tessuto canceroso sono modificate per promuovere la progressione del tumore.

Ad esempio, nel tessuto del cancro al seno, l’aumento dell’espressione di proteasi e ossidasi degrada e linearizza la fitta rete di fibre di collagene reticolate. Ciò aumenta la rigidità del tessuto del cancro al seno, facilitando la migrazione delle cellule tumorali.

Lo stroma è costituito anche da fibroblasti associati al carcinoma, o CAF. Secernono diversi fattori di crescita per favorire la progressione del cancro. Ad esempio, con l’aumento delle dimensioni del tumore, aumenta la domanda di nutrienti e ossigeno. Le cellule tumorali più interne di un tumore solido sono soggette a una limitazione acuta dell’ossigeno; un fenomeno chiamato ipossia.

I CAF secernono fattori di crescita dell’endotelio vascolare che innescano la formazione di nuovi vasi sanguigni attorno al tumore in crescita. Questo fornisce ossigeno e sostanze nutritive alle cellule che si dividono rapidamente.

Le cellule immunitarie, come i macrofagi, i linfociti e le cellule natural killer, possono rilevare le cellule tumorali ed eliminarle. Tuttavia, a causa dell’aumento dell’instabilità genetica, le cellule tumorali acquisiscono rapidamente mutazioni per eludere la sorveglianza immunitaria.

Ad esempio, le cellule tumorali possono indurre cellule T immunosoppressori, che producono specie reattive dell’ossigeno per inibire i linfociti e impedire loro di uccidere le cellule tumorali. Le specie reattive dell’ossigeno aumentano anche il tasso di mutazioni nelle cellule tumorali, facilitando una rapida progressione del tumore.

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