Introduction: The importance of the antitumor activity of some antimicrobial peptides
(AMPs) is being increasingly recognized. The antimicrobial peptide, tachyplesin, has been shown
to exhibit anticancer properties and a linear, cysteine deleted analogue (CDT), was found to retain
its antibacterial function.
Objectives: The objective was to test CDT and related analogues against normal mammalian, bacterial,
and cancer cells to determine their effectiveness and then utilize specific assays to determine a
possible mechanism of action.
Methods: We used sequence reversal and D-amino acids to synthesize four CDT analogues by solid
phase peptide synthesis. A number of assays were used including liposome dye-leakage, antibacterial
activity against both Gram-positive and Gram-negative bacterial strains, hemolytic assays,
methyl thiazolyl tetrazolium (MTT), and apoptosis to examine their effectiveness as both AMPs
and anti-cancer peptides (ACPs). We then tested the analogues for their ability to inhibit proliferation
of the human lung cancer cell line, A549.
Results: We found that D-CDT exhibited the best bactericidal properties of those tested and was
not damaging to red blood cells. Both D-CDT and reverse D-CDT showed a dose-dependent reduction
of cell viability. However, D-CDT was most effective with an IC50 of 9.814 μM, a value
9-fold lower than that calculated for reverse D-CDT (90.16 μM). Apoptosis does not appear to be a
mechanism by which D-CDT exerts its anticancer properties since > 100 μM was required to increase
activation of caspase 3. Moreover, the ERK1/2 pathway is also unlikely since only a modest
(20%) decrease of activity was observed with > 100 μM D-CDT. However, D-CDT was found to
operate via a hyaluronan (HA)-dependent mechanism as pretreatment of the cells with hyaluronidase
decreased the cytotoxic effects of D-CDT on A549 cells and increased its IC50 29-fold to
Conclusion: D-CDT is both an effective AMP and ACP, and likely exerts its anticancer effects
through both membranolytic as well as an HA-mediated mechanism.