FIGURE 3 from PARP Inhibitors Effectively Reduce MAPK Inhibitor Resistant Melanoma Cell Growth and Synergize with MAPK Inhibitors through a Synthetic Lethal Interaction In Vitro and In Vivo

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posted on 2023-09-06, 17:07 authored by Lisa Marie Fröhlich, Heike Niessner, Birgit Sauer, Sofie Kämereit, Eftychia Chatziioannou, Simon Riel, Tobias Sinnberg, Birgit Schittek

MAPKi resistant cells show decreased ATM expression. A, Immunoblot analysis of A375 R cells treated with 5 μmol/L talazoparib (Tala.) for 24 hours or untreated (Ctr.). Relative protein expression is shown. Actin control was reused from Fig. 2E as the Western blots were performed in the same experiment. B, Immunoblot analysis of chromatin bound fraction of A375 S and R cells after the treatment with 0.005% MMS and 2 μmol/L talazoparib (+) for 6 hours or untreated cells (−). Relative protein expression is shown. C, RT² Profiler PCR Array Human DNA Repair was performed in A375 S versus R. log₂ fold change in the expression of the corresponding genes of R compared with S cells as well as the log₁₀P values of the respective gene expression changes are shown in the volcano plot. Technical triplicates were performed. D, Immunoblot analysis of A375 and Mel1617 S and R cells. Relative protein expression is shown. E, Relative ATM gene expression of A375 and Mel1617 S and R is shown. Unpaired t test was performed to compare the Ctr. with Tala. group. F, IHC of paraffin-embedded tumors of a patient before and after MAPKi resistance stained for ATM. 10X magnification was used. Quantification of the ATM positive cells was performed and % ATM positive cells is shown. G, MUH cell viability assay of HT-144 melanoma cell line treated with different concentrations of talazoparib (Tala.) starting at 50 μmol/L for 72 hours. IC₅₀ level is shown. H, MUH cell viability assay of A375 S and R cells treated with different concentrations of Ku-55933 (Ku.) for 72 hours. Comparison of fits of the nonlinear regression was performed to analyze statistical differences between S and R cells. I, MUH cell viability assay of A375 S cells treated with different concentrations of talazoparib for 72 hours. Cells were additionally treated with a stable concentration of 2 μmol/L Ku-55933 or remained untreated. Comparison of fits of the nonlinear regression was performed to analyze statistical differences between cells treated with Ku-55933 or untreated cells.

Funding

Deutsche Forschungsgemeinschaft (DFG)

History

ARTICLE ABSTRACT

We show that MAPK inhibitor resistant melanoma cells exhibit low ATM expression increasing their sensitivity toward PARP inhibitors and that a combination of MAPK/PARP inhibitors act synthetically lethal in melanoma cells. Our study shows that PARP inhibitor treatment is a valuable therapy option for patients with melanoma, either as a single treatment or as a combination with MAPK inhibitors depending on ATM expression, which could serve as a novel biomarker for treatment response.