Breast Cancer (BC) initiation and progression is accompanied by extensive extracellular matrix (ECM) deposition and remodelling. Tissue fibrosis can limit drug delivery to the tumour fuelling treatment resistance, as well as enabling cancer cell invasion and metastasis. In TNBC, the predominant treatment strategy is systemic taxane-based chemotherapy; however, this approach often shows only modest efficacy and can further advance the fibrotic response. Therefore, the use of anti-fibrotic therapies has gained significant momentum for improving therapy efficacy and extending patient survival.
Our laboratory and others have shown that targeting fibrosis and the Rho-associated protein kinase 1/2 (ROCK1/2) signalling pathway in a range of cancer types can impair cancer spread and improve response to standard-of-care chemotherapy; however, poor specificity and drug toxicity of ROCK inhibitors limits successful translation into the clinic. Here, we assess efficacy of a novel, highly specific and clinically relevant ROCK2 inhibitor (ROCK2i).
Using publicly available BC patient cohorts, we show high ROCK2 expression significantly correlates with poorer patient survival. In collagen contraction and matrix production assays utilizing CAFs isolated from the PyMT mouse model and from human TNBC patients, we show that ROCK2i significantly decreases the ability of these CAFs to contract and remodel a collagen matrix and to produce a pro-tumorigenic ECM. In addition, we show that ROCK2i significantly decreases the proliferation and survival of both PyMT and MDA-MB-231 cancer cells in in vitro.
In vivo orthotopic experiments assessed the ability of ROCK2i to reduce tissue fibrosis and improve the response to standard-of-care chemotherapy. However, we were unable to show increased efficacy of chemotherapy when combined with ROCK2i in both chemo-insensitive PyMT and chemo-responsive MDA-MB-231 models.
Further investigation revealed that tumour fibrosis is increased following 3 chemotherapy cycles. We then postulated that timing ROCK2i in line with this increase in fibrosis may provide an alternate treatment strategy and show that delaying the commencement of ROCK2i in line with the accumulation of chemotherapy induced fibrosis shows slightly increased efficacy. This data indicates that ROCK2i may be valid treatment strategy to increase chemotherapy performance in TNBC but timing the addition of anti-fibrotic therapies is critical and warrants further investigation.