Discovery of Novel Small Molecules that Block Myofibroblast Formation: Implications for Capsular Contracture Treatment.

Breast cancer is the most common malignancy and a second most common cause of cancer deaths in US women, with the American Cancer Society estimating more than 266,000 new cases of invasive breast cancer diagnosis in 2018.1 The mainstay of breast cancer treatment is surgical resection, both lumpectomy and mastectomy, often followed by radiation therapy.2 Although the aforementioned treatments have helped to significantly decrease the mortality rate, many patients must face the consequences of body disfiguring surgery. Consequently, there have been a gradually increasing number of breast cancer patients who chose to undergo breast reconstructions after mastectomy. Albornoz et al.3 show that the rate of immediate breast reconstruction has steadily increased about 5% per year, resulting in a 78% increase from 1998 to 2008. The 2 main methods of breast reconstruction surgery are autologous and implant-based reconstruction, with autologous procedure being the traditionally more popular option. However, there has been a paradigm shift in recent years, as the rate of implant-based reconstruction after mastectomy surpassed that of autologous reconstruction around 2002, and continues to be the more popular procedure.3 Unfortunately, many of the patients who receive implant-based breast reconstruction, and especially those who receive adjuvant radiation therapy, suffer from a number of complications, capsular contracture being the most common long-term complication.4 Capsular contracture is a painful, debilitating condition in which excessive scar tissue encapsulates the implant, causing chronic stiffness and disfigurement.5 There are many factors that can increase the risk of capsular contracture, such as periprosthetic infection, foreign response to implant material, and location of the implant.6,7 Ionizing radiation, while effective in killing residual malignant cells, is one of the most significant factors that increases capsular contracture rate, up to 7-fold.8 Currently, it is unclear how ionizing radiation leads to the development of excessive and pathologic fibrosis. One possible mechanism is that radiation treatment leads to inflammatory cytokine cascades, which cause abnormal wound healing.9 Among those cytokines, transforming growth factor-beta (TGF-β), a prowound healing molecule, stands out as a crucial player that acts as a “master switch” to activate the fibrosis pathway.9 TGF-β is a member of a family of cellular mediators that are crucial in tissue homeostasis, cellular regulation and growth, wound healing and tissue repair, and some suggest it has a role in tumor initiation and progression.10,11 There are 3 different isoforms of TGF-β, which are TGF-β1, β2, and β3, with TGF-β1 being the most prevalent isoform associated with tissue fibrosis.10,12 In early wound healing, activation of TGF-β1 promotes endothelial cell proliferation, extracellular matrix (ECM) production, and angiogenesis.13 In later phases, TGF-β1 promotes myofibroblast differentiation, activation, and proliferation.10,14 Myofibroblast activation leads to wound contracture and closure, as these cells produce ECM and promote contracture caused by prominent alpha-smooth muscle actin (αSMA) containing stress fibers.15 Animal models show organ and tissue fibrosis following exogenous TGF-β1 injections or with genetic TGF-β1 overexpression, hence demonstrating its causative role in fibrosis.16,17 Currently, there is a major unmet need for safe, effective, and widely available treatments that can target fibrotic diseases, radiation-induced capsular contracture being one of them. Given that TGF-β is one of the most powerful players in driving fibrosis, attenuating excessive TGF-β signaling may provide an effective treatment strategy for capsular contracture, and potentially for other fibrotic diseases as well. The primary goal of this study is to identify novel small molecules with anti-TGF-β activity that can effectively prevent myofibroblast formation in human breast capsular fibroblasts. Our previous study identified salinomycin as a powerful antiscarring agent, which effectively blocked TGF-β–driven fibroblast proliferation and myofibroblast formation in vitro.18 Salinomycin is a polyether ionophore that has been approved for coccidiosis control and promotion of animal growth and feed efficiency.19 Although this previous study showed that salinomycin possesses anti-TGF-β activity and reduced myofibroblast activity in vitro, there are needs to find additional therapeutic small molecule drugs which may be easier to develop and synthesize. Salinomycin is a natural product with a high molecular weight that has potent Na+ ionophore activity, which makes it a challenging target for structure modification for optimizing desired activity. Furthermore, it is produced by fermentation, which is costly to maintain on a large scale. Alternatively, chemically synthesized small molecules may provide well-defined structures that can be modified to optimize the desired anti-TGF-β activity and can potentially prevent excessive fibrosis and scarring. Here, we report a new class of molecules that potently block TGF-β1 activity and capsular myofibroblast differentiation.