Tetrazolium-based colorimetric assays underestimat the direct antitumor effects of anti-VEGF agent bevacizumab

Adaptive resistance of tumor cells to anti-vascular endothelial growth factor therapy: A reversible phenomenon

Vascular endothelial growth factor (VEGF) inhibition is an essential targeted strategy for malignant tumors, but its efficacy is severely constrained by drug resistance. The traditional view holds that the target of VEGF inhibition is endothelial cells, and thus compensatory angiogenesis is considered the main mechanism of drug resistance. In this study, we found that tumor cells themselves could develop acquired resistance to VEGF therapy, indicating an independent resistance mechanism apart from angiogenesis. Notably, this acquired resistance was temporary, disappearing completely four days after discontinuing exposure to the drug in vitro. Our findings suggest that tumor cells may also be targets of VEGF inhibition, and their response to treatment should not be overlooked in contributing to drug resistance.

Basic Fibroblast Growth Factor Accumulation in Culture Medium Masks the Direct Antitumor Effect of Anti-VEGF Agent Bevacizumab

The direct antitumor effect of bevacizumab (BEV) has long been debated. Evidence of the direct antitumor activities of drugs are mainly obtained from in vitro experiments, which are greatly affected by experimental conditions. In this study, we evaluated the effect of BEV-containing medium renewal on the results of in vitro cytotoxicity experiments in A549 and U251 cancer cells. We observed starkly different results between the experiments with and without BEV-containing medium renewal. Specifically, BEV inhibited the tumor cell growth in the timely replacement with a BEV-containing medium but promoted tumor cell growth without medium renewal. Meanwhile, compared with the control, a significant basic fibroblast growth factor (bFGF) accumulation in the supernatant was observed in the group without medium renewal but none in that with replaced medium. Furthermore, bFGF neutralization partially reversed the pro-proliferative effect of BEV in the medium non-renewed group, while exogenous bFGF attenuated the tumor cell growth inhibition of BEV in the medium-renewed group. Our data explain the controversy over the direct antitumor effect of BEV in different studies from the perspective of the compensatory autocrine cytokines in tumor cells.

The immunomodulatory effects of metformin in LPS-induced macrophages: an in vitro study

OBJECTIVE

The study aimed to explore the immunomodulatory effects of clinically relevant concentrations of metformin on macrophages during sepsis, which is characterized by an initial hyperinflammatory phase followed by a period of immunosuppression.  METHODS: We employed the RAW 264.7 mouse macrophage cell line as an in vitro model to induce inflammatory responses and immune suppression through primary and secondary stimulation by lipopolysaccharide (LPS). The cells were exposed to clinically relevant concentrations of metformin, and their responses were gauged through cytotoxicity assays, enzyme-linked immunosorbent assay for cytokine quantification, and assessments of intracellular reactive oxygen species (ROS) production. Moreover, to probe the role of AMPK in mediating the effects of metformin, we conducted an AMP-activated protein kinase (AMPK) activity assay and knocked down AMPK using siRNA.  RESULTS: Our study revealed that clinically relevant concentrations of metformin considerably decreased the LPS-induced secretion of tumor necrosis factor-α and interleukin-6, which indicates the suppression of the initial hyperinflammatory response. Furthermore, metformin prevented LPS-induced immunosuppression. Notably, these immunomodulatory effects of metformin were not mediated by the activation of the AMPK pathway, as evidenced by the unaltered AMPK activity and siRNA experiments. The modulation of intracellular ROS levels emerged as the critical mechanism underlying the inhibition of hyperinflammation and impediment of immunosuppression by metformin.

CONCLUSION

A certain therapeutic dose of metformin inhibited hyperinflammatory responses and alleviated immunosuppression in LPS-induced macrophages through the bidirectional modulation of intracellular ROS generation.