Antagonistic Pharmacological Interaction between Sirtuin Inhibitor Cambinol and Paclitaxel in Triple-Negative Breast Cancer Cell Lines: An Isobolographic Analysis

Breast cancer (BC) is a heterogeneous disease with different intrinsic subtypes. The most aggressive subtype of BC–triple-negative breast cancer (TNBC) is characterized by high heterogeneity and metastasis rate, poor prognosis and lack of therapeutic targets due to the absence of estrogen receptor, progesterone receptor and human epidermal growth factor receptor 2. Targeted therapies have been approved for many other cancers and even other subtypes of BC, but treatment options for TNBC are still mainly limited to chemotherapy. Therefore, new, more effective treatment regimens are needed. Combined chemotherapy with two or more active agents is considered a promising anti-neoplasm tool in order to achieve better therapeutic response and reduce therapy-related adverse effects. The study demonstrated an antagonistic effect commonly used in TNBC therapy cytostatic drug-paclitaxel (PAX) and sirtuin inhibitor: cambinol (CAM) in BT-549, MDA-MB-468 and HCC1937 TNBC cell lines. The type of pharmacological interaction was determined by a precise and rigorous pharmacodynamic method-isobolographic analysis. The cytotoxic and anti-proliferative effects of CAM used alone or combined with PAX were determined utilizing 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and 5-bromo-2′-deoxyuridine (BrdU) assays, respectively. Induction of apoptosis in TNBC cell lines after PAX and CAM treatment applied individually or in combination was determined by flow cytometry (FACS) as a number of cells with active caspase-3. It has been observed that both agents used separately inhibit cell proliferation and induce apoptosis; however, applying them in combination ameliorated antiproliferative and pro-apoptotic effects in all analyzed TNBC cell lines. Our results demonstrate that CAM and PAX used in combination act antagonistically, limiting anti-cancer efficacy and showing the importance of preclinical testing.

Assessment of Pharmacological Interactions between SIRT2 Inhibitor AGK2 and Paclitaxel in Different Molecular Subtypes of Breast Cancer Cells

Breast carcinoma (BC) is the most commonly diagnosed type of cancer in women in the world. Although the advances in the treatment of BC patients are significant, numerous side effects, severe toxicity towards normal cells as well as the multidrug resistance (MDR) phenomenon restrict the effectiveness of the therapies used. Therefore, new active compounds which decrease the MDR, extend disease-free survival, thereby ameliorating the effectiveness of the current treatment regimens, are greatly needed. Histone deacetylase inhibitors (HDIs), including sirtuin inhibitors (SIRTi), are the epigenetic antitumor agents which induce a cytotoxic effect in different types of cancer cells, including BC cells. Currently, combined forms of therapy with two or even more chemotherapeutics are promising antineoplastic tools to obtain a better response to therapy and limit adverse effects. Thus, on the one hand, much more effective chemotherapeutics, e.g., sirtuin inhibitors (SIRTi), are in demand; on the other hand, combinations of accepted cytostatics are trialed. Thus, the aim of our research was to examine the combination effects of a renowned cytotoxic drug paclitaxel (PAX) and SIRT2 inhibitor AGK2 on the proliferation and viability of the T47D, MCF7, MDA-MB-231, MDA-MB-468, BT-549 and HCC1937 BC cells. Moreover, cell cycle arrest and apoptosis induction were explored. The type of pharmacological interactions between AGK2 and PAX in different molecular subtypes of BC cells was assessed using the advanced isobolographic method. Our findings demonstrated that the tested active agents singly inhibited viability and proliferation of BC cells as well as induced cell cycle arrest and apoptosis in the cell-dependent context. Additionally, AGK2 increased the antitumor effect of PAX in most BC cell lines. We observed that, depending on the BC cell lines, the combinations of tested drugs showed synergistic, additive or antagonistic pharmacological interaction. In conclusion, our studies demonstrated that the consolidated therapy with the use of AGK2 and PAX can be considered as a potential therapeutic regimen in the personalized cure of BC patients in the future.