A major limitation of cancer chemotherapy is the inability to escalate doses of an anticancer drug due to intolerable cytotoxic side effects. This limitation can be overcome by using a combination of drugs administered at lower doses. In this study, we investigated the effects of combining two compounds isolated from marine organisms for in vitro cytotoxicity to the MCF-7 breast cancer cell line by the MTT assay. Adociaquinone B, from the marine sponge Xestospongia sp., and heptyl prodigiosin, from the marine bacterium Pseudovibrio denitrificans strain Z143-1, were combined in three molar proportions and the combinatorial effect was determined by isobologram analysis and the fractional inhibitory concentration (FIC) of each compound. To determine if these compounds individually caused apoptosis in MCF-7 cells, we performed brightfield microscopy to investigate cell morphology and Hoechst 33342 staining to check for chromatin condensation. Apoptosis is the preferred mode of cell death in cancer therapy because it causes minimal inflammation. Initial findings of this study suggest a synergistic cytotoxic effect of combinations of these two compounds against MCF-7 breast cancer cells, and their ability to induce apoptosis individually.