In this study, we investigated the mechanisms of CRC cell resistance to treatments with Fe@Au nanoparticles and directly compared the responses with the Fe@Au-sensitive OECM1 oral cancer cell line. We found that Fe@Au retards growth in both CRC and OECM1 cell lines, but the Fe@Autreated CRC cells are arrested in G1/G0 phase, rather than in the S-phase, as observed in the treated OECM1 cell line.Furthermore, we observed that the mitochondrial responses to the Fe@Au treatment were distinct in different CRC cells, with only Fe@Au-treated Caco-2 cells showing any mitochondrial membrane potential loss within 24 hours (Figure 6).
Furthermore, the mitochondria membrane potential blocker,CsA, could not protect the HT-29 and SW480 cells from the damage caused by Fe@Au; while 3-MA significantly
restored the Fe@Au induced cytotoxicity in Caco-2 cells (P , 0.05). According to the difference in uptake profiles of Fe and Au (Figure 9), as well as to the responses to Fe-only
nanoparticle treatment (Figure 10), Caco-2 cells were found to be more sensitive to Fe alone compared to the other two CRC cell lines. Hence, Fe@Au nanoparticles apparently
induce cytotoxicity in HT-29 and SW480 cells through pathways different to the ones observed in OECM1 cells and to Caco-2 cells. Given these results and the previously
demonstrated importance of Fe in the cancer-preferential cytotoxicity17 that occurs in Fe@Au-sensitive cells, it seems evident that the cells better able to deal with Fe will display
greater resistance to Fe@Au treatment.