Cell experiment:

5×103 MCF7::pcDNA.3 and MCF7::C1199 cells are plated in 96-wells plates and 24 hours later are treated for 72 hours with different concentrations of 17-β-Estradiol to evaluate hormone response. To evaluate the reversion of 4-hydroxytamoxifen (Tam) resistance by 1A-116, MCF7::C1199 cells are treated with Tam (0.01 μM, 0.1 μM and 1 μM), 1A-116 (4 μM) or combination of both for 72 hours. Cell growth is measured by colorimetric crystal violet assay. The analysis of hormone-dependent growth and Tam resistance reversion is determined using PRISM 6, Version 6.01. Results shown correspond to the average of three independent experiments[1].

Animal experiment:

Specific pathogen-free female BALB/c inbred mice with an age of 8 to 10 weeks and an average weight of 20 g, are used. They are housed in plastic cages under standard conditions and have access to rodent chow and water ad libitum. On day 0, 2×105 viable F3II cells in 0.3 mL Dulbecco’s modified Eagle medium (DMEM) are injected into the lateral tail vein. Mice are injected i.p at daily doses of 3 mg/kg body weight 1A-116 or vehicle. Treatment is carried out from day 0 to day 21. On day 21 mice are sacrificed and lungs are excised and immediately fixed in Bouin’s solution. Superficial lung nodules are counted under dissection microscope[2].

1A-116 is a specific Rac1 inhibitor.

1A-116 shows lesser effect on MCF7::pcDNA.3 cells than on MCF7::C1199 cells. 1A-116 treatment decreases phospho-PAK1 levels in a time-dependent manner. The presence of 1A-116 reverts the PAK1 phosphorylation induced by 4-hydroxytamoxifen (Tam). The presence of 1A-116 also effectively reverts Rac1-PAK1-mediated estrogen receptor (ER) phosphorylation at Ser305[1]. 1A-116 shows a significant increase in antiproliferative activity on F3II cells, showing an IC50 value of 4 µM. A-116 also dramatically impairs Rac1 activation at low micromolar range (1 µM)[2].

Daily treatment of mice with compound 1A-116 at 3mg/kg body weight/day reduces about 60% the formation of total metastatic lung colonies. A significant antitumor activity is obtained for macronodules (more than 1 mm in diameter) by treatment with 1A-116 in this highly aggressive breast cancer model. The treatment with 1A-116 reduces the total lung weight compare to the control group, leading to a total weight similar to the average pulmonary weight of Balb/c mice[2].

[1]. Gonzalez N, et al. Pharmacological inhibition of Rac1-PAK1 axis restores tamoxifen sensitivity in human resistant breast cancer cells. Cell Signal. 2017 Jan;30:154-161. [2]. Cardama GA, et al. Preclinical development of novel Rac1-GEF signaling inhibitors using a rational design approach in highly aggressive breast cancer cell lines. Anticancer Agents Med Chem. 2014;14(6):840-51.