Background: Second mitochondrial activator of caspase (Smac) is a short mitochondrial
peptide. When released from the mitochondria into the cytoplasm, it binds to inhibitor of apoptotic
proteins (IAPs) within the cytoplasm and prevents them from inhibiting apoptosis.
Objective: Delivery of external synthetic Smac peptide into the cytoplasm of malignant cells could greatly improve the efficiency
of apoptosis-inducing chemotherapeutic agents.
Method: In our study different conjugates based on the seven N-terminal amino acids AVPIAQK of Smac (SmacN7)
were produced to obtain a cytoplasm-directed Smac variant. SmacN7 and a point mutant (AVPKAQK) were coupled either
to rhodamine alone or to both rhodamine and undecylic aldehyde, which is an antagonist of the Lily-of-the-valley
fragrance receptor. The fifth conjugate consisted of rhodamine coupled only to undecylic aldehyde, without SmacN7. The
uptake of these five conjugates into three different human cell lines was characterized and quantified by confocal laser
scanning microscopy and flow cytometry. A caspase apoptosis assay was performed for cells incubated with the five different
conjugates after induction of apoptosis.
Results: The coupling of undecylic aldehyde to SmacN7 increased the cellular uptake of the correct and mutant conjugates.
Conclusion: Caspase 3/7 apoptosis tests after induction of apoptosis with staurosporine or UV irradiation showed that the
coupling of SmacN7 with undecylic aldehyde resulted in a greatly increased adjuvant pro-apoptotic effect compared to the
separate components and a mutant SmacN7 peptide sequence in the LNCaP prostate carcinoma cells compared to the benign
prostate hyperplasia (BPH) cells and the human embryonal kidney (HEK) cells.