A. Scheme for development of a new model of breast cancer autoresistance to trastuzumab. In order to generate a preclinical model of acquired resistance to trastuzumab, HER2 gene-amplified SKBR3 cells were exposed for approximately 3 months to 20 μg/ml trastuzumab (Phase I, top panel). At this point, SKBR3/Tzb20 cells regained morphology similar to the parental (trastuzumab-sensitive) SKBR3 cell line. SKBR3/Tzb20 cells were then continuously grown in culture medium supplemented with 185 μg/ml trastuzumab over a period time of at least one month (Phase II, bottom panel). At this point, SKBR3/Tzb100 cells gained new cell morphology. Cells were then maintained in 100 μg/ml trastuzumab, a concentration of trastuzumab at which SKBR3 parental cells are strongly impaired in their metabolic status. More than 8 months later, SKBR3/Tzb100 cells normally proliferate in the presence of 100 μg/ml trastuzumab. B. Synergy analyses of the interaction between oleuropein aglycone and Tzb against in Tzb-conditioned (high-dose resistant) SKBR3/Tzb100 cells. The nature of the interaction between oleuropein aglycone and trastuzumab was evaluated by the isobologram technique as described in Figure 3.