Acute lymphoblastic leukemia (ALL) is one of the most common type of leukemia in children. It is caused by abnormal cell division of the lymphoid progenitor cells in the bone marrow. In the past decade, metformin has gained increased attention for its anti-leukemic potential. Moreover, other chemotherapeutic agents were investigated for the possible superior efficacy over the existing treatments in treating ALL. Several studies examined the effect of cisplatin as a potential candidate for therapy. Here, we investigate the anti-leukemic effect of metformin and cisplatin on 697 cells. Both compounds revealed significant cytotoxic effects. Specifically designed lipid-based cubosomal nanoformulations were used as drug carriers to facilitate compound entry in low doses. Our results indicate that the use of the carrier did not affect cytotoxicity significantly. In addition, combining the drugs in different carriers demonstrated an antagonistic effect through damping the efficacy of both drugs. This was evident from experiments investigating cellular viability, annexin V/PI staining, mitochondrial membrane potential and caspase-3 activity. Taken together, it appears that metformin does not represent a suitable option for sensitizing leukemia cells to cisplatin.