Growth Inhibition of Human Ovarian Cancers by Cytotoxic Analogues of Luteinizing Hormone-Releasing Hormone

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Abstract
Background: Receptors for luteinizing hormone-releasing hormone (LH-RH) are found in nearly 80% of human ovarian cancers. The chemotherapeutic agent doxorubicin can be linked to [ d -lysine 6 ]LH-RH to form a cytotoxic analogue (AN-152) that may have greater specificity for tumor cells. This study was conducted to investigate the effects of AN-152 on the growth of LHRH receptor-positive OV-1063 human epithelial ovarian cancers. Methods: Nude mice bearing human ovarian tumors, OV-1063 or UCI-107 (LH-RH receptor negative), were injected intraperitoneally with saline (control) or with equimolar doses of AN-152 or doxorubicin; experiments involving mice with OV-1063 tumors also included groups that were administered [ d -lysine 6 ]LH-RH either alone or in combination with doxorubicin. Tumor volume, weight, doubling time, and burden (i.e., tumor weight/body weight) as well as tumor apoptotic and mitotic indices were determined. The levels of receptors for LH-RH and epidermal growth factor (EGF) and their messenger RNAs were measured by use of radioreceptor and reverse transcription-polymerase chain reaction assays, respectively. Results: The growth of OV-1063 ovarian tumors in nude mice, as based on reduction in tumor volume, was inhibited significantly (all P<.05, two-sided) 4 weeks after treatment with AN-152, even at the lowest dose tested (413 nmol/20 g weight); the toxic effects of an equivalent dose of doxorubicin caused substantial mortality. Highaffinity receptors for LH-RH and EGF were found on cell membranes of OV1063 cancers; however, after in vivo treatment with AN-152, LH-RH receptor-binding sites were not detectable and EGF receptors were reduced in number. The growth of UCI-107 ovarian cancers was not inhibited by AN-152. Conclusions: In nude mice bearing LH-RH receptor positive OV-1063 epithelial ovarian cancers, systemic administration of AN-152 is less toxic and inhibits tumor growth better than equimolar doses of doxorubicin.

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