Objective: Cell resistance to doxorubicin and its toxicity to healthy tissue reduce its efficiency. The
use of cell-penetrating peptides as drug delivery system along with doxorubicin is a strategy to reduce its side
effects. In this study, the influence of poly-L-arginine on doxorubicin cytotoxicity, its cellular uptake and
doxorubicin-induced apoptosis on human prostate cancer DU145 cells are assessed.
Methods: The cytotoxicity of doxorubicin and poly-L-arginine, alone and in combination, in DU145 cells was
evaluated at different exposure times using MTT assay. The influence of poly-L-arginine on doxorubicin delivery
into cells was evaluated by fluorescence microscopy and ultraviolet spectroscopy. DAPI and ethidium bromide-
acridine orange stainings, flow cytometry using annexin V/propidium iodide, western blot analysis with
anti-p21 antibody and caspase-3 activity were used to examine the influence of poly-L-arginine on doxorubicininduced
Results: Poly-L-arginine had no cytotoxicity at low concentrations and short exposure times. Poly-L-arginine
increased the cytotoxic effect of doxorubicin in DU145 cells in a time-dependent manner. But no significant
reduction was found in HFF cell viability. Poly-L-arginine seems to facilitate doxorubicin uptake and increase
its intracellular concentration. 24h combined treatment of cells with doxorubicin (0.5 µM) and poly-L-arginine
(1 µg ml-1) caused a small increase in doxorubicin-induced apoptosis and significantly elevated necrosis in
DU145 cells as compared to each agent alone.
Conclusion: Our results indicate that poly-L-arginine at lowest and highest concentrations act as proliferationinducing
and antiproliferative agents, respectively. Between these concentrations, poly-L-arginine increases the
cellular uptake of doxorubicin and its cytotoxicity through induction of necrosis.