Tumour-stroma interactions in breast cancer progression and drug resistance.

Abstract

Triple negative breast cancer (TNBC) accounts for 10-15% of all breast cancer cases and is associated with poor prognosis due to its aggressiveness. Platinum chemotherapeutics, such as cisplatin and carboplatin are used to treat TNBC patients, however, their effects on fibroblasts and cancer-associated fibroblasts (CAFs) within the tumour microenvironment (TME) are not well studied. CAFs have important functions within the TME because they deposit and remodel the extracellular matrix (ECM). Their secretome can also impact tumour cells and mediate immune crosstalk. Through these effects CAFs can influence tumour progression and therapy resistance. In this PhD project, I investigated how both short- and long-term platinum chemotherapy treatment impacts fibroblasts and its consequences for TNBC progression and therapy resistance.

I examined phenotypical changes in carboplatin-treated fibroblasts using ECM deposition, conditioned medium and senescence assays. The influence of these changes on tumour cells was further assessed using viability, proliferation, migration and chemotaxis assays. These revealed that short-term carboplatin treatment induces a pro-tumorigenic secretome in fibroblasts which promotes tumour cell viability and chemotaxis. Long-term low-level carboplatin treatment pushes fibroblasts into senescence which is associated with an altered secretome. The secretome of these cells promotes migration, chemotaxis and reduces platinum chemotherapy responses in tumour cells. Moreover, the treated fibroblasts have an increased deposition of an anisotropic matrix. The carboplatin-induced ECM changes promote tumour cell viability, adhesion and colony formation.

Using transcriptomic analysis, GDF15 and EDIL3 were identified as potential candidates for mediating the pro-tumorigenic effects of fibroblasts after carboplatin treatment. I examine the autocrine effects of these factors on fibroblasts, as well as their paracrine effects on tumour cells. I show that GDF15, a TGFβ superfamily member, has pro-tumorigenic effects, stimulating tumour cell migration, chemotaxis and stemness. In contrast, the matrix glycoprotein EDIL3, has tumour-suppressive functions, reducing tumour cell viability and sensitising them to therapy. Further work is required to determine the expression of GDF15 and EDIL3 in breast cancer fibroblasts and tumour cells, as well as disentangle their roles in the pro-tumorigenic fibroblast phenotypes induced by carboplatin.

Together, these findings show that carboplatin induces pro-tumorigenic features in fibroblasts. There is potential that these features contribute to therapy resistance, recurrence and metastasis in TNBC patients after they receive platinum chemotherapy.

Date of Award	4 Dec 2023
Original language	English
Awarding Institution	University of Bath
Supervisor	Ute Jungwirth (Supervisor), Randy Mrsny (Supervisor) & Paul De Bank (Supervisor)