Pan-PPAR Agonists as Potential Treatments for Type 2 Diabetes, and the Effect of Adipocyte-derived Fatty Acids in Breast Cancer Therapy

Abstract

The prevalence of Type 2 diabetes (T2DM) has been increased dramatically, and it is a challenging disease to treat effectively in the long term and usually associated with other metabolic syndrome. The development of a single agent with an ability to target T2DM, dyslipidaemia and other associated metabolic syndrome is thus of great importance. On the other hand, breast cancer is the most frequently occurring malignancy, and obesity is linked with increased breast cancer growth, progression and decreased efficacy of anti-cancer drugs. However, the underlying mechanisms for this link are still not clear. Therefore, the need for a better understanding, and the development of pharmacological interventions is of utmost importance. To develop new agents for treating T2DM and its associated metabolic syndrome, we focused on Peroxisome Proliferator-Activated Receptors (PPARs). There are three PPARs subtypes have been identified: PPARα, PPARγ and PPARδ. A single compound which can simultaneously activate all three PPAR subtypes, i.e. a pan-PPAR agonist, has emerged as a possible treatment for both T2DM and other features of the metabolic syndrome, and it is also believed that it can ameliorate the side effects associated with selective PPARα and PPARγ agonists. For this purpose, we present our extended study on an active dual PPARα/γ agonist i.e. N-{4-(diethylamino)phenyl}-2-{2-(indolin-1-yl)-2-oxoethoxy}benzamide (Compound 1), and found 11 derivatives (i.e. compounds 2 - 12) using fragment-based and shape-based screening approaches. Compared to established PPAR agonists, all these 12 compounds showed comparable docking scores towards PPARα, -γ and -δ receptors. Cell-based studies confirmed most of these compounds demonstrated a comparable cytotoxicity profile to the commercially available PPAR agonists. Based on the results of the transactivation assays, compounds 1, 2, 4, 7, and 12 were identified as the most efficacious potential pan-PPAR agonists and selected for further biological assays. In support of their potential as pan-PPAR agonists, these 5 compounds were first demonstrated to have a trend towards small increase in some of the cholesterol transporter expressions, including ABCA1, ABCG1 and SR-B1, indicating their potential in regulating cholesterol export. Further, treatment with compounds 1, 2 and 12 displayed a trend for an increase in CPT1A protein level, which was comparable to the activity of bezafibrate and fenofibrate, suggesting they will likely promote fatty acid oxidation. It was noteworthy that compounds 2 and 7 significantly stimulated triacylglycerol (TAG) accumulation in mature 3T3-L1 adipocytes. On the other hand, our group has recently shown that fatty acids (FAs) release from adipocytes promote breast cancer cell proliferation and migration using both co-culture and conditioned media (CM) approaches. Based on this observation, we hypothesised that adipocytes-derived FAs could compromise anti-cancer treatments. Indeed, we found that estrogen receptor (ER)-positive MCF-7 breast cancer cells cultured in adipocyte CM resulted in decreased efficacy of several anti-cancer therapies including cyclophosphamide, docetaxel, doxorubicin and paclitaxel. We demonstrated that an increase in drug efflux may, at least in part, play a role in this reduced ability of anti-cancer agents. Surprisingly, CM-derived from adipocytes treated with metformin had a lower non-esterified (free) fatty acids (NEFA) level, and significantly restored the efficacy of both doxorubicin and paclitaxel, indicating the benefit of metformin as adjunct therapy in treating breast cancer. We also demonstrated that these anti-cancer agents could affect MCF-7 FA metabolism, however, adipocyte CM-induced reduction in the efficacy of anti-cancer therapies was not associated with changes in fatty acid metabolism. Overall, the studies in this thesis demonstrate that compounds 1, 2, 4, 7 and 12 may have some potential as pan-PPAR agonists to be studied further for treating T2DM and metabolic syndrome; and the novel therapeutic strategy such as metformin, aiming to decrease serum FAs, is beneficial to treat breast cancer in combination with anti-cancer therapies.