Targeting of
cytotoxic agents represents a modern approach to the treatment of various
cancers, that improves the efficacy and reduces peripheral toxicity. Recently we developed a powerful cytotoxic analog of
luteinizing hormone-releasing hormone (
LHRH),
AN-207, designed to be targeted to
tumors that express
LHRH receptors. This analog consists of the superactive derivative of
doxorubicin (DOX),
2-pyrrolino-DOX (AN-201), linked to [D-Lys6]
LHRH carrier. In the present study we investigated the cytocidal effects of
AN-207 and
AN-201 on the
LHRH receptor-positive ES-2
ovarian cancer cells. The targeting of
AN-207 to ES-2 cells in the presence of
LHRH receptor-negative UCI-107
ovarian cancer cells was also evaluated by semi-quantitative polymerase chain reaction (PCR) amplification of microsatellite markers.
Ligand competition assays showed a single class of high-affinity and low-capacity binding sites in ES-2 cells with a mean dissociation constant (KD) of 3.93 +/- 0.1 nM and a mean maximal binding capacity (Bmax) of 271 +/- 26.1 fmol/mg
membrane protein. Kinetic assays indicated that
AN-207 caused cell death in a concentration- and time-dependent manner in ES-2 cells, but not in UCI-107 cells, while the kinetics of cytotoxic effects of
AN-201 were similar in both cell lines. To investigate targeting, ES-2 cells were co-cultured with UCI-107 cells, treated with 10 nM
AN-207 or
AN-201 for different times and then cultured for 48 h in the absence of
cytotoxic agents. Genomic
DNA was extracted for microsatellite analyses using different markers. Semi-quantitative analyses of the intensity of the alleles that correspond to each cell line indicated that
AN-207 was selectively targeted to ES-2 cells, while
AN-201 showed no selectivity for either cell line. These results extend our previous findings that
AN-207 can be targeted to
ovarian cancers and other
tumors that express receptors for
LHRH. Cytotoxic analogs of
LHRH, such as
AN-207, should be considered for treatment of
LHRH receptor-positive
tumors.