Abstract:
The synthesis and in vitro evaluation of four mesoporphyrin IX-peptide conjugates designed to
target EGFR, over-expressed in colorectal and other cancers, are reported. Two peptides with known affinity
for EGFR, LARLLT (1) and GYHWYGYTPQNVI (2), were conjugated to mesoporphyrin IX (MPIX, 3)
via one or both the propionic side chains, directly (4, 5) or with a triethylene glycol spacer (7, 8). The
conjugates were characterized using NMR, MS, CD, SPR, UV-vis and fluorescence spectroscopies. Energy
minimization and molecular dynamics suggest different conformations for the conjugates. SPR studies show
that conjugate 4, bearing two LARLLT with no PEG spacers, has the greatest affinity for binding to EGFR,
followed by conjugate 7 with two PEG and two LARLLT sequences. Molecular modeling and docking
studies suggest that both conjugates 4 and 7 can bind to monomer and dimer EGFR in open and closed
conformations. The cytotoxicity and cellular targeting ability of the conjugates were investigated in human
HEp2 cells over-expressing EGFR. All conjugates showed low dark- and photo-toxicities. The cellular uptake
was highest for conjugates 4 and 8 and lowest for 7 bearing two LARLLT linked via PEG groups, likely due
to decreased hydrophobicity. Among the conjugates investigated, 4 is the most efficient EGFR-targeting
agent, and therefore the most promising for the detection of cancers that over-express EGFR.
