BT474 cells are highly sensitive to Chloropyramine hydrochloride (compound 1) treatment, whereby 1 µM concentrations cause a 40% reduction of viability after 48 h of treatment. It is found that at 1 µM concentrations of Chloropyramine hydrochloride, viability of control MCF7-pcDNA3 cells is significantly higher than the viability of MCF7-VEGFR-3 cells (P<0.01) and at 10 µM concentration this difference reaches twofold (P<0.001). In the BT474 cells treatment with Chloropyramine hydrochloride also leads to a concentration-dependent decrease of cell proliferation. When treatment with Chloropyramine hydrochloride is continued for 48 h, the breast cancer cells that overexpressed VEGFR-3 undergo apoptosis. This effect is dose-dependent, with 10 µM Chloropyramine hydrochloride inducing apoptosis in more than 60% of BT474 cells. In our model cell lines MCF7-pcDNA3 and MCF7-VEGFR-3, treatment with 10 µM Chloropyramine hydrochloride for 48 h leads to a 4-fold increase in apoptotic cell death in the cell line that overexpressed VEGFR-3 (18% versus 76 % respectively).

Chloropyramine hydrochloride causes a dramatic reduction of tumor growth in both model systems whereby the tumor size in the treated groups is approximately 20% of the tumor size in vehicle control groups. Doxorubicin administered at 3 mg/kg causes approximately 60% reduction of tumor growth, but has no effect on tumor growth at 0, 3 mg/kg. In contrast, there is a modest effect of Chloropyramine hydrochloride alone (50% reduction of tumor growth). The low-dose combination of Chloropyramine hydrochloride and doxorubicin has a prolonged anti-tumor effect (85% reduction of tumor growth) that is greater than either drug alone.