Correction: BMC Complement Med Ther 23, 111 (2023)

https://doi.org/10.1186/s12906-023-03933-w

Following the publication of the original article [1], it was noted that due to a typesetting error the figure images were paired incorrectly and some information was lost. The correct Figs. 1, 2, 3 and 4 are given below.

Fig. 1
figure 1

Protocatechuic aldehyde synergistically enhances DTIC cytotoxicity to melanoma cells. A Dose-response curves for PA, DTIC or DTIC combined with a certain concentration of PA for 72 h in A375 and SK-MEL-28 cells. B Dose-response curves for A375 and SK-MEL-28 cells treated with a range of concentrations of PA, DTIC or their combinations. C Synergy scores were calculated from the data represented in B for PA combined with DTIC for A375 and SK-MEL-28 cells. The left panel represents the synergy scores from ZIP model. The right panel represents the synergy scores from Bliss model. **** p<0.0001

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Fig. 2
figure 2

Combination of PA and DTIC increased DNA-double strand breaks and apoptosis in A375 and SK-MEL-28 cells. A The double-strand breaks in A375 and SK-MEL-28 cells were assessed by neutral comet assay. B Quantification of DNA percentages in comet tails in A. C γ-H2AX levels after 72 h of treatment with DMSO, PA, DTIC or combination of PA and DTIC in A375 and SK-MEL-28 cells. D Quantification of the relative γ-H2AX levels in C. E Cell apoptosis was analyzed by flow cytometry. The combined treatment showed the most apoptosis induction. F Quantification of apoptosis ratios in E. G Cleaved caspase-3 protein levels after 72 h of treatment with DMSO, PA, DTIC or combination of PA and DTIC in A375 and SK-MEL-28 cells. Right panel represents quantification of the relative cleaved caspase-3 protein levels in G. ns = no significant,*p < 0.05, **p < 0.01,***p < 0.001 and **** p<0.0001

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Fig. 3
figure 3

PA promotes MGMT degradation in melanoma cells. A-B Left panel shows western blot analysis for MGMT levels in A375 and SK-MEL-28 cells after 72h of treatment with DMSO, PA, DTIC or combination of PA and DTIC. Right panel represents the quantification of the MGMT protein levels for the left panel. C MGMT mRNA expression in A375 and SK-MEL-28 after 72 h PA treatment. D-E A375 and SK-MEL-28 were treated with cycloheximide in the presence or absence PA for 0-8 h hours. Western blot showed the MGMT degradation rates. Right panel represents quantification of the MGMT protein levels. F-G A375 and SK-MEL-28 were treated with MG132 combined with cycloheximide in the presence or absence of PA for 0-8 h hours. The MGMT protein levels were analyzed by western blot. Right panel represents quantification of the MGMT protein levels. ns = no significant, *p < 0.05, **p < 0.01,***p < 0.001 and **** p<0.0001

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Fig. 4
figure 4

MGMT is required for PA-mediated synergistic effect. A The shRNA-mediated knockdown of MGMT was validated by western blot. Right panel represents the quantification of the MGMT protein levels in A. B Knockdown of MGMT increased the DTIC sensitivities in A375 and SK-MEL-28 cells. C Dose-response curves for MGMT-depleted melanoma cells treated with PA, DTIC or their combinations. The selected concentrations for treatment are identical with those in Fig. 1B. D Synergy scores were obtained from the data represented in C. The synergy scores were calculated by ZIP model and Bliss model, respectively. *p < 0.05, **p < 0.01 and **** p < 0.0001

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The correct figures and captions have been included in this correction, and the original article has been corrected.