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.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.leading to higher redox activity within the cells than the Feonly
NPs, and that this accounts for the preferential effects
of the coated NPs; and/or (2) there is some synergistic effect
of the Au and Fe elements and/or ions within the cells.
Our research also suggests that the resistance to Fe@Au
treatment may rely on the ability to cope with Fe. Fe-resistant
cells may either have a more robust mitochondrial system
or a more effective efflux system, such as ferroportin, to
eliminate the Fe. Ferroportin is a protein that serves as a
transmembrane ion channel to enable Fe efflux from cells36
and is expressed in hepatic cells, macrophages, and also in
enterocytes.37 More research is needed to further investigate
this hypothesis and elucidate the full mechanisms of Fe@Au
sensitivity in cancer cells.