Cell-penetrating peptides provide a unique platform to create a new generation of
cancer therapeutics with enhanced efficacy and diminished toxicity. In our study, enhanced expression of
toll-like receptor 2 (TLR2) was observed in
acute myeloid leukemia (AML) cells. Screening of a
phage display peptide library using Biopanning and Rapid Analysis of Selective Interactive
Ligands (BRASIL) identified a TLR2-binding
peptide motif, Pep2. We show that the TLR2-binding
peptide motif targeted and penetrated into
leukemia cells in a TLR2-dependent manner. Moreover, a synthetic, chimeric
peptide composed of the TLR2-binding motif linked to a programmed cell death-inducing sequence, D(
KLAKLAK)2, induced apoptosis in AML cells with high TLR2 expression (TLR2(high)) but not in
chronic myeloid leukemia (CML) cells with low TLR2 expression (TLR2(low)). The antileukemia activity of this chimeric
peptide was confirmed in
leukemia patient samples and an animal model of
myeloid leukemia, as the development of
leukemia was significantly delayed in mice with TLR2(high) AML compared to TLR2(low) CML NOD/SCID mice. TUNEL assays on bone marrow tissue slices revealed that the chimerical
peptide induced
leukemia cell apoptosis in a TLR2-dependent manner. Together, our findings indicate that TLR2 is a potential therapeutic target for the prevention and treatment of AML, and the prototype, Pep2-D(KLAKLAK)2, is a promising
drug candidate in this setting.