Cytotoxic analogs of luteinizing hormone-releasing hormone containing doxorubicin or 2-pyrrolinodoxorubicin, a derivative 500-1000 times more potent.

Abstract

Doxorubicin (DOX) and its daunosaminemodified derivative, 2-pyrrolino-DOX, which is 500-1000 times more active than DOX, were incorporated into agonistic and antagonistic analogs of luteinizing hormone-releasing hormone (LH-RH). The conjugation of DOX with LH-RH analogs was performed by using N-(9-fluorenylmethoxycarbonyl)-DOX-14-0-hemiglutarate, a dicarboxylic acid ester derivative of DOX. Coupling this derivative covalently to the[where Nal(2) = 3-(2-naphthyl)alanine, Pal(3) = 3-(3-pyridyl)alanine, and Phe(4CI) = 4-chlorophenylalanine] was followed by the removal of the 9-fluorenylmethoxycarbonyl protective group to yield cytotoxic derivatives of LH-RH analogs containing DOX. From these DOX containing LH-RH hybrids, intensely potent analogs with daunosamine-modified derivatives of DOX can be readily formed. Thus, cytotoxic LH-RH agonist containing DOX (AN-152) can be converted in a 66% yield by a reaction with a 30-fold excess of 4-iodobutyraldehyde in N,Ndimethylformamide into a derivative having 2-pyrrolino-DOX (AN-207). Hybrid molecules AN-152 and AN-207 fully preserve the cytotoxic activity of their radicals, DOX or 2-pyrrolino-DOX, respectively, in vitro, and also retain the high binding affinity of the peptide hormone portion of the conjugates to rat pituitary receptors for LH-RH. These highly potent cytotoxic analogs of LH-RH were designed as targeted anti-cancer agents for the treatment of various tumors that possess receptors for the carrier peptide. Initial in vivo studies show that the hybrid molecules are much less toxic than the respective cytotoxic radicals incorporated and significantly more active in inhibiting tumor growth.

Recovery of pituitary function after treatment with a targeted cytotoxic analog of luteinizing hormone-releasing hormone

“…This powerful cytotoxic agent was linked covalently to agonist [D-Lys 6 ]LH-RH to form a cytotoxic LH-RH analog, . The hybrid molecule thus obtained, fully retains cytotoxic activity of AN-201 as well as hormonal and binding properties of the peptide carrier in vitro (18). We have also shown that AN-207 can inhibit growth of various tumors including prostate cancers in rats (19).…”

“…Because gonadotroph cells of pituitary possess high affinity receptors for LH-RH, it is important to determine whether these analogs would damage pituitary functions. It was previously shown that the cytotoxic LH-RH analog AN-207 used in this study fully preserves both the high binding affinity to LH-RH receptors and the powerful LH-releasing activity of the carrier molecule [D-Lys 6 ]LH-RH, in rat pituitary cells (18). Because of the incorporation of the intensely potent 2-pyrrolino-DOX radical AN-201, the cytotoxic activity in vitro of AN-207 on MCF-7 human mammary carcinoma cell line possessing LH-RH receptors (22) .…”

“…Targeted cytotoxic LH-RH analogs have been developed in an endeavor to reduce the toxic side effects and increase the efficacy of antineoplastic agents by delivering them more selectively to tumor cells expressing receptors for LH-RH (1,18). Because gonadotroph cells of pituitary possess high affinity receptors for LH-RH, it is important to determine whether these analogs would damage pituitary functions.…”

“…RH), and the carrier [D-Lys 6 ]LH-RH were synthesized and characterized in our laboratory as reported (17,18). LH-RH and GH-RH(1-29)NH 2 were also synthesized in our laboratory, while TRH was obtained from Takeda (Osaka).…”

Enhanced cellular uptake and in vitro antitumor activity of short-chain fatty acid acylated daunorubicin–GnRH-III bioconjugates

“…Schally's laboratory (AN-152) [16], in which doxorubicin is attached to [D- 6 Lys]-GnRH-I, is currently in Phase-II clinical trial on ovarian and endometrial cancer [17,18].…”