biostudies-literatureTun JOUniversity of the PhilippinesDepartment of Science and Technology, Republic of the PhilippinesE536https://www.ebi.ac.uk/biostudies/studies/S-EPMC6780817biostudies-literatureUnknown17(9)Renieramycin M (RM) is a KCN-stabilized tetrahydroisoquinoline purified from the blue sponge Xestospongia sp., with nanomolar IC50s against several cancer cell lines. Our goal is to evaluate its combination effects with doxorubicin (DOX) in estrogen receptor positive MCF-7 breast cancer cells. MCF-7 cells were treated simultaneously or sequentially with various combination ratios of RM and DOX for 72 h. Cell viability was determined using the MTT assay. Synergism or antagonism was determined using curve-shift analysis, combination index method and isobologram analysis. Synergism was observed with pharmacologically achievable concentrations of DOX when administered simultaneously, but not sequentially. The IC95 values of RM and DOX after combination were reduced by up to four-fold and eightMarine drugsSynergistic Cytotoxicity of Renieramycin M and Doxorubicin in MCF-7 Breast Cancer Cells.PMC6780817in-house grant of GPCDDHP Project 3Suwanborirux KTun JOSalvador-Reyes LAVelarde MCConcepcion GPSaito NfalseSynergistic Cytotoxicity of Renieramycin M and Doxorubicin in MCF-7 Breast Cancer Cells.Renieramycin M (RM) is a KCN-stabilized tetrahydroisoquinoline purified from the blue sponge Xestospongia sp., with nanomolar IC50s against several cancer cell lines. Our goal is to evaluate its combination effects with doxorubicin (DOX) in estrogen receptor positive MCF-7 breast cancer cells. MCF-7 cells were treated simultaneously or sequentially with various combination ratios of RM and DOX for 72 h. Cell viability was determined using the MTT assay. Synergism or antagonism was determined using curve-shift analysis, combination index method and isobologram analysis. Synergism was observed with pharmacologically achievable concentrations of DOX when administered simultaneously, but not sequentially. The IC95 values of RM and DOX after combination were reduced by up to four-fold and eight2019-01-01T00:00:00Z2019 Sep2025-04-20T00:26:03.287Z2019-11-07T08:04:25ZS-EPMC67808173152745310.3390/md17090536