Having acquired DpT azides 1-4, we investigated the antiproliferative activities of the synthesized expected HER2 expression was validated by Western blot (see Figure ). For the MTT assay, we chose a prolonged incubation time of 120 h, as it had been shown that cancer cells are not as sensitive to thiosemicarbazones at shorter incubation times. As illustrated in Figure , both unmodified parent DpTs (i.e., Dp44mT and DpC) were found to be similarly active in the low nanomolar range against both cell lines, with slightly better activity observed against MCF-7 cells. However, the four azide-functionalized DpTs displayed notable differences in cytotoxicity: a 5-to-7-fold decrease in activity was observed in SK-BR-3 compared to MCF-7 for each compound. The cytotoxicity of the Dp44mT-derived compounds 1 and 3 appeared mostly retained against MCF-7 cells, with a slight decrease in activity against SK-BR-3 cells. In contrast, the DpC azides 2 and 4 showed notably higher IC50 values in both cell lines, especially in SK-BR-3, where the decrease in potency was most pronounced. Interestingly, the position of the linker on the DpT scaffold had no discernible effect on the potency, as all the derivatives showed IC50 values comparable to their regioisomers. In general, despite functionalization, all azide-bearing compounds continued to suppress cellular viability in the nanomolar range upon functionalization, and the cytotoxicity was more prominent in MCF-7 cells than in SK-BR-3 cells.