PC-9

C17:0 Inhibits PC-9 and PC-9/GR Cell Proliferation, Migration, and Clone Formation

Dietary saturated fatty acids may exert antitumor effects, and screening functional fatty acids may provide candidates that may serve as adjuvants in cancer therapy. C14:0, C15:0, C16:0, C17:0, C18:0, C18:1 or C20:0 were directly added into HBE, PC-9 and PC-9/GR cells. As presented in Fig. 1A and B, the results of the MTT assay indicated that these fatty acids did not affect the proliferation of HBE cells, while 4 types of fatty acids (C16:0, C17:0, C18:0, and C20:0) significantly inhibited the proliferation of PC-9 and PC-9/GR cells. Furthermore, C17:0 was identified to be the most effective fatty acid against PC-9 and PC-9/GR cells, and its effects were dose-dependent (Fig. 1C and D). The effect of C17:0 in other lung cancer cells, including A549 and H1975, was also examined. Similarly, the results revealed that C17:0 inhibited cell proliferation in A549 and H1975. These results indicated that C17:0 may be a fatty acid suitable for lung cancer treatment.

The functional role of C17:0 in lung cancer cells was then studied. A wound healing assay indicated that C16:0, C17:0, and C18:0 inhibited the wound closure ratio of PC-9 and PC-9/GR cells (Fig. 2A and B). Furthermore, the impact of C17:0 on cell migration was the greatest among all fatty acids tested. The apoptosis ratio was also determined by flow cytometry. As presented in Fig. 3A, C17:0 induced 16.62 and 29.63% apoptosis in PC-9 cells and PC-9/GR cells respectively. C18:0 also performed similarly in the two cell line variants. In addition, the results of the cell clone formation assay indicated that C17:0 suppressed the proliferation of PC-9 and PC-9/GR cells (Fig. 3B). These results indicated that C17:0 treatment in PC-9 and PC-9/GR cells was able to induce lung cancer cell death.

Fig. 1 C17:0 inhibits PC-9 and PC-9/GR cell proliferation. (Xu C, et al., 2019)

Fig. 2 C17:0 inhibits wound healing in PC-9 and PC-9/GR cells. (Xu C, et al., 2019)

Fig. 3 C17:0 promotes apoptosis, while it inhibits clone formation in PC-9 and PC-9/GR cells. (Xu C, et al., 2019)

Increased Sensitivity of EGFR-TKI-Resistant Cells to Gemcitabine and Vinorelbine

EGFR-tyrosine kinase inhibitors (EGFR-TKIs) are widely used for the treatment of non-small cell lung cancers (NSCLCs) harboring EGFR-activating mutations. PC-9 cells harboring an EGFR-activating mutation (EGFR exon 19 deletion) were used. The established EGFR-TKI-resistant cells were designated as PC-9ER and PC-9GR cells. PC-9ER cells became resistant to erlotinib by acquiring the EGFR T790M gatekeeper mutation (i.e., a mutation that sterically hinders inhibitor interaction), whereas PC-9GR cells became resistant to gefitinib through activation of the FGF2-FGFR1 pathway. First, the resistance of PC-9ER and PC-9GR cells to EGFR-TKIs was confirmed. The proliferation of PC-9 parent cells was inhibited by erlotinib and gefitinib at 0.01 µM; however, the proliferation of PC-9ER and PC-9GR was not significantly inhibited by even 3 mM erlotinib or gefitinib (Fig. 4A). To examine whether EGFR-TKI-resistant cells exhibit altered sensitivity to cytotoxic agents, the sensitivity of PC-9, PC-9ER and PC-9GR cells was evaluated by MTS assay with or without cytotoxic agents. The cytotoxic agents included in the present study were cisplatin, docetaxel, pemetrexed, gemcitabine, and vinorelbine, all of which are widely used in the clinic for the treatment of patients with NSCLC. The sensitivity of EGFR-TKI-resistant cells to cisplatin, docetaxel, and pemetrexed was comparable with that of PC-9 parent cells. By contrast, increased sensitivity of EGFR-TKI-resistant cells to gemcitabine and vinorelbine was observed (Fig. 4B). These results indicated that EGFR-TKI-resistant cells had increased sensitivity to gemcitabine and vinorelbine.

Fig. 4 Sensitivity of EGFR-tyrosine kinase inhibitor-sensitive and resistant cell lines to cytotoxic agents. Results of MTS assay for PC-9, PC-9GR, and PC-9ER cells. (Hamamoto J, et al., 2017)