The therapeutic effect of surgery in metastatic non-small cell lung cancer has been controversial [50, 51]. During the surgery, many clinical factors might contribute to the metastasis and recurrence of lung cancer surgery. The application of lidocaine during the surgery or preoperational treatment results in a plasma lidocaine micro-environment for lung cancer cell migration and survival. Hence, the potential impact of lidocaine on metastasis and recurrence of lung cancer surgery should be further studied. However, so far, the effect of lidocaine at plasma concentration on cancers was less studied. The doses of lidocaine used in most previous studies are much higher than the clinical plasma concentration. Therefore, although many previous studies demonstrated the effect of lidocaine on lung cancer cells, they fail to convince clinical surgeons that lidocaine exerts a considerable impact on the surgery outcome. Lidocaine is known as a sodium channel blocker. Although the major target of lidocaine, the voltage-gated sodium channels, has been found to play a role in cancer developments , lidocaine might also affect cancer independent of sodium channel blockade.
Although a previous study suggested that lidocaine at the “mM” concentration range inhibited proliferation  and induced apoptosis of A549 , our result showed that, at plasma concentration, lidocaine had almost no effect on cell proliferation, apoptosis, and cell death. The previous study also suggested that the migration of A549 was inhibited by lidocaine at 8 mM, but as shown by our data, the effect of lidocaine on migration was not significant when the doses of lidocaine decreased to 100 µM. Lidocaine at clinical plasma concentrations only reduced CXCL12-induced migration in A549. The western blotting assay showed that lidocaine decreased the expression of CXCR4 especially the membrane expression of CXCR4. We suggested that the reduction of CXCR4 on membrane surface impaired the sensitivity of cells to CXCL12 stimulations. A previous study has suggested that lidocaine can regulate CXCR4 sensitivity to CXCL12 in breast cancer cells MDA-MB-231 , which was similar to A549 according to our results.
Different membrane surface proteins expressed on lung cancer cells as adhesion molecules can be critical in the migration of cells . CD44 has been reported to play roles in the metastasis of non-small cell lung cancer cells . In this study, the expression of CD44 was promoted by CXCL12 stimulation. Our results also showed that the surface expression of CD44 on A549 was up-regulated by lidocaine. However, the lidocaine did not further increase the CD44 expression at the presence of CXCL12 and the increase of CD44 in the lidocaine alone group did not affect cell migration. Thus, we suggested that CD44 was directly up-regulated by lidocaine bypassing the CXCL12/CXCR4 axis but the increase of CD44 was not essential for the migration of A549. In addition, we also determined another critical adhesion molecule for migration, the ICAM-1. The expression of ICAM-1 has been associated with lung cancer progression and prognosis . A previous study reported that lidocaine affects migration of a lung cancer cell line H838 by reducing ICAM-1 . However, in this study, the lidocaine at plasma concentration did not affect ICAM-1 expression. The ICAM-1 expression was up-regulated by CXCR4 activation by CXCL12, hence, we suggested ICAM-1 might be a potential downstream target of lidocaine/CXCR regulation (Fig. 7). Further validation is required in the future.
Another activity that might impact the migration of A549 was the remodeling of the cytoskeleton. The activation of CXCR4 by CXCL12 can trigger intracellular Ca2+ releasing . Subsequently, the released intracellular Ca2+ facilitated many Ca2+-dependent activities that are involved in cytoskeleton remodeling [59, 60]. Results showed that lidocaine significantly reduced the intracellular Ca2+ releasing triggered by CXCL12 stimulated CXCR4 activation. We further determined the level of filamentous actin to observe the rearrangement of cortical actin fibers during CXCL12 stimulation. Actin is an important part of the cytoskeleton in most eukaryotic cells . There are two types of actin: globular G-actin and filamentous F-actin. The G-actin can polymerize into the actin filaments, the F-actin polymer filaments that form the cytoskeleton. Thus, the level of F-actin can indicate the rate of cytoskeleton rearrangement. Our results showed that lidocaine reduced cytoskeleton remodeling by about 50%. Therefore, we suggested that lidocaine inhibited cytoskeleton remodeling via suppressing CXCL12-induced intracellular Ca2+ releasing (Fig. 7). However, lidocaine, as a multiple channel blocker, might have other effects on intracellular Ca2+ level. Many cancer-related ion channels, such as TRP and TPCs , might contribute to lidocaine effects on cancer cells and need further investigation.