Induction of apoptosis in
tumor cells specifically within the complex tumor microenvironment is highly desirable to kill them efficiently and to enhance the effects of
chemotherapy. Second mitochondria-derived activator of
caspase (Smac) is a key pro-apoptotic pathway which can be activated with a Smac mimetic
peptide. However, in vivo application of
peptides is hampered by several limitations such as poor pharmacokinetics, rapid elimination, enzymatic degradation, and insufficient intracellular delivery. In this study, we developed a nanosystem to deliver a
Smac peptide to
tumor by passive targeting. We first synthesized a chimeric
peptide that consists of the 8-mer
Smac peptide and a 14-mer
cell penetrating peptide (
CPP) and then encapsulated the Smac-
CPP into polymeric nanoparticles (Smac-
CPP-NPs). In vitro, Smac-
CPP-NPs were rapidly internalized by 4T1 mammary
tumor cells and subsequently released Smac-
CPP into the cells, as shown with fluorescence microscopy. Furthermore, Smac-
CPP-NPs induced apoptosis in
tumor cells, as confirmed with cell viability and
caspase 3/7 assays. Interestingly, combination of Smac-
CPP-NPs with
doxorubicin (dox), a clinically used
cytostatic drug, showed combined effects in vitro in 4T1 cells. The effect was significantly better than that of SMAC-
CPP-NPs alone as well as empty nanoparticles and dox. In vivo, co-treatment with Smac-
CPP-NPs and free dox reduced the
tumor growth to 85%. Furthermore, the combination of Smac-
CPP-NPs and free dox showed reduced proliferating
tumor cells (Ki-67 staining) and increased apoptotic cells (cleaved
caspase-3 staining) in
tumors. In conclusion, the present study demonstrates that the intracellular delivery of Smac-mimetic
peptide using nanoparticle system can be an interesting strategy to attenuate the
tumor growth and to potentiate the therapeutic efficacy of
chemotherapy in vivo.