Anticancer peptides (ACPs) offer a promising alternative to conventional chemotherapy but face challenges, including poor selectivity, limited tumor penetration, low cellular uptake, and rapid degradation in serum. To address these barriers, we developed synthetic mRNAs encoding chimeric ACPs designed for enhanced intracellular delivery and activity. mRNAs for constructs SAK6L9AS(1X), SAK6L9AS(4X), and WTAS-K6L9(4X) were transcribed in vitro and tested against 4T1 breast cancer cells. Cytotoxicity was assessed by cell confluence and MTT assays, while apoptosis was evaluated using caspase 3/7 activation, PI staining, and Annexin V flow cytometry. Our results demonstrate that all SAK6L9AS variants induced robust apoptosis and cellular toxicity in 4T1 cells. Importantly, this work provides the first demonstration of intracellular expression of an mRNA-encoded ACP fused to a cell-penetrating peptide, thereby validating a modular platform for RNA-based delivery of anticancer agents. This study highlights the feasibility of mRNA-encoded peptide therapeutics as a scalable and customizable strategy for cancer treatment. By combining the advantages of mRNA delivery with rational peptide design, ACP chimeras can be expressed directly inside tumor cells, overcoming the limitations of exogenous peptide administration. Our findings support further development of synthetic mRNA therapeutics to generate potent, selective anticancer peptides with reduced systemic toxicity and improved translational potential.