## 4 Discussion
In the case of H1975 cells, the IC\({}_{50}\) values for the CV and MTS assays were approximately 10 and 16 \(\upmu\)M, respectively, as described in [PERSON] et al. [44]. Importantly, it should be mentioned that the IC\({}_{50}\) values for MnTnHex in the present study are consistently lower than those observed for cisplatin, which fact is worthwhile to be emphasized. Regarding its role as a chemosensitizer, in the present study, when combined with cisplatin, MnTnHex was able to enhance the cytotoxic impact of this pivotal chemotherapeutic drug. Indeed, in both cell lines, MnTnHex increased the cytotoxicity of cisplatin, being much more effective in H1975 cells. This could be perceived as another beneficial aspect given the resistant pattern of these cells. We recently reported the same impact of MnTnBuOE-2-PyP5+ as a single drug in breast cancer cells, where even without carboplatin, the cytotoxicity of Mn porphyrin in its own right was massive [58]. We also saw a large effect of MnTnBuOE-2-PyP5+ in its own right as paclitaxel in a mouse ovarian xenograft study [59]. Regarding the differences observed in our study between the two NSCLC cell lines, several factors might be involved in their sensitivity to a given anticancer drug, including MnTnHex or cisplatin. The expression levels of the genes that code for H\({}_{2}\)O\({}_{2}\)-detoxifying enzymes may, at least partially, justify the differences observed between cell lines. Other reasons may involve differences between cell lines in terms of other enzymes involved in redox pathways, apoptosis, DNA repair, drug transport, and drug detoxification, among others. Another aspect of this work was the characterization of the cell-cycle distribution of both cell lines treated with MnTnHex combined with cisplatin. For this, we selected a concentration of cisplatin that comprises low cytotoxicity (1 \(\upmu\)M) and concentrations of MnTnHex that, albeit being cytotoxic, did not markedly decrease cell viability (Figure 2). This selection of concentrations was chosen with the purpose of better understanding the effective impact of a two-drug combination. The sub-G1 data revealed the cytotoxic potential of MnTnHex at 1 \(\upmu\)M and recapitulated the impact of this MnP to boost the cytotoxicity of cisplatin in both cell lines. Regarding the cell cycle checkpoints, it is known that cisplatin can interfere at the G1/S and G2/M checkpoints [60]. The second checkpoint is generally more affected since cells trapped in G2/M can enter cell cycle arrest. At the concentration levels tested, we did not find these alterations. Nevertheless, when cisplatin was combined with MnTnHex, a mild but significant increase in the G2/M phase occurred, which may indicate that this combination promotes G2/M cell cycle arrest. However, this effect was only observed in A549 cells. A possible cause may be related to the long incubation period with the compounds. The G2/M arrest may happen early, and arrested cells will either be efficient at repairing damage or induce cell death; thus, at 72 h, these cells might have either died or progressed to G1/G0. MnTnHex induced a significant reduction of collective cell migration on both cell lines. Interestingly, there was a more significant reduction of migration in cells exposed to MnTnHex per se rather than when combined with cisplatin. Nonetheless, MnTnHex, either alone or combined, appears to induce a slightly higher reduction of migration when compared to cisplatin alone. The impact of MnTnHex on migration has already been studied in other types of cancer in combination with chemotherapy and radiotherapy. While in this study, MnTnHex was effective per se in reducing collective cell migration, the same was not observed in renal and breast cancer. In renal cancer, MnTnHex did not affect collective cell migration, although it significantly decreased chemotactic migration [29]. [PERSON] et al. thoroughly analyzed the effect of MnTnHex alone and combined it with dos in breast cancer cell lines (MCF7 and MDA-MB-231).