Distant organ metastasis is the main cause of death in breast cancer patients. Evidences have shown that mitochondria also play a crucial role in tumor metastasis, except for as apoptosis center. However, the treatment of tumor growth and metastasis was reported to be limited by mitochondria-associated protein Bcl-2, which are gatekeepers of apoptosis and are found to reside in mitochondria mainly. Herein, we designed a mitochondria-targeting doxorubicin delivery system as well as a mitochondrial distributed Bcl-2 function-converting peptide NuBCP-9 delivery system, which are both based on N-(2-hydroxypropyl)methacrylamide copolymers, to achieve a synergistic effect on tumor regression and metastasis inhibition by combination therapy. After mitochondria were damaged by mitochondria-targeting peptide-modified doxorubicin, apoptosis was effectively enhanced by mitochondrial specifically distributed NuBCP-9 peptides, which converted Bcl-2 function from anti-apoptotic to pro-apoptotic and paved the way for the development of mitochondrial impairment. The combination treatment exhibited significant damage to mitochondria, including excess reactive oxygen species (ROS), the permeabilization of mitochondrial outer membrane (MOMP), and apoptosis initiation on 4T1 breast cancer cells. Meanwhile, besides enhanced tumor growth suppression, the combination treatment also improved the inhibition of 4T1 breast cancer metastasis both in vitro and in vivo. By increasing the expression of cytochrome C and decreasing the expression of Bcl-2, metal matrix protease-9 (MMP-9) as well as vascular endothelial growth factor (VEGF), the combination treatment successfully decreased 84% lung metastasis. Overall, our work provided a promising strategy for metastatic cancer treatment through mitochondria-targeting anti-cancer drug delivery and combination with mitochondrial distributed Bcl-2 function-converting peptide.
Therapeutic peptide, NuBCP-9 (N9) as a Bcl-2 functional converter, has been demonstrated to have the remarkable anticancer efficiency in Bcl-2-abundant cancer. However, it faced technical challenges in clinical use, such as the low bioavailability, the easily-destroyed bio-stability, and the insusceptibility to cellular interior. With the potential of mesoporous silica nanoparticles (MSNs) as the promising delivery vehicle of therapeutic macromolecules, we developed a kind of MSNs with the surface coating of folic acid (FA) for cancer cell targeting and with the macropore loading of N9 peptide for cancer therapy. Our results showed that the functional MSNs had the relatively greater biosafety than the naked MSNs in zebrafish models, leading to less than 30% embryo of death at 200 μg/ml, which could further specifically target the folate receptor (FR)-overexpressed cervical cancer HeLa cells instead of FR-negative normal embryonic kidney HEK 293T cells in a FA-competitive manner. N9 peptide with the delivery of functional MSNs could be internalized by HeLa cells, and co-localized with mitochondria in a Bcl-2-dependent manner. Moreover, N9 peptide delivered by FA-modified MSNs displayed the excellent anticancer efficiency with great selectivity, inducing approximately 52% HeLa cells into apoptosis. In summary, our results illustrated the potential of functional MSNs with large pore size as an efficient nanocarrier for the intracellular delivery of peptide drugs with targeting proteins to realize cancer therapy.
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