Evaluating TRPML1 as a novel therapeutic target for triple negative breast cancer

Tattersdill, Bethany 2025. Evaluating TRPML1 as a novel therapeutic target for triple negative breast cancer. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Triple negative breast cancer (TNBC) accounts for 15-20% of all breast cancer (BC) patients, with a 5-year survival rate of 50-60%. TNBC is defined by lack of expression of the oestrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2), usually targeted with therapeutics in receptor positive BCs. TNBC patients are largely treated irrespective of their tumour profile despite molecular heterogeneity. This has led to low treatment efficacy, high relapse rate and low survival probability, prompting research into more effective targets. Recently, TRPML1, a lysosomal Ca2+ channel, has been elucidated as a target due to its role in regulating lysosomal function, autophagy and cellular homeostasis - key processes in cancer progression and survival. This thesis evaluates whether development of novel TRPML1 inhibitors would be an effective therapeutic strategy for TNBC, across different TNBC subtypes in an aim to increase treatment effectivity and reduce relapse rates. We show across TNBC cell lines spanning basal like-1 (BL-1), immunomodulatory (IM), mesenchymal-like (M-L) and mesenchymal stem-like (MS-L) subtypes that TRPML1 expression and activity is significantly increased in comparison to ER+ BC cell line MCF-7, particularly in more invasive subtypes (M-L/ MS-L). Treatment with the TRPML1 antagonist, ML-SI1, significantly inhibits TNBC cell proliferation, migration, invasion and stemness, with cytoskeletal remodelling and cell thinning observed. Immunofluorescence analysis reveals accumulation of autolysosomes/autophagosomes and alkalinised lysosomes laden with unesterified cholesterol and Fe2+, likely contributing to cell death and reduced metastasis. Analysis of mitochondrial fitness revealed significant increases of dysfunctional mitochondria and reactive oxygen species (ROS) while morphological analysis showed cristae and network collapse. Analysis of the downstream transcriptional regulator, TFEB, reveals that parallel transcription programmes are not activated that would otherwise aid drug resistance in TNBC, as has been highlighted recently with mTORC1 inhibitors. 2 From this work we conclude that TRPML1 is a lysosome-centred vulnerability exploited in TNBC with high expression supporting malignancy, inhibition of which sensitises cells to death as a monotherapy, but with likely more potent effects as a combination therapy. We highlight that the mutational landscape must be considered, as observed with the Cal 51 cell line having a gain of function mutation in the PIK3CA gene. Recent work finds that lysosomal activity can sustain therapy resistance, therefore we propose that TRPML1 is ideally centred to reduce these effects, offering a promising first/ second line treatment option.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Biosciences
Subjects:	Q Science > Q Science (General)
Date of First Compliant Deposit:	19 May 2026
Last Modified:	19 May 2026 15:15
URI:	https://orca.cardiff.ac.uk/id/eprint/187098

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