In this study, the native sequence of -MSH was used, in which Met was replaced by Nle (SYSNleEHFRWGKPV). Daunomycin was attached to the amino functional groups via non-cleavable oxime linkage. These types of conjugates have many excellent properties to study and compare the bioactivity of the compounds. One of the developed conjugates contained drug molecules on both conjugation site (N-terminal and the side chain of Lys). The two additional conjugates were modified by the drug, either on theN-terminus or on the Lys side chain. The in vitro cytostatic effect on mouse melanoma cells did not show any significant differences among them. However, results indicated that the conjugates with Dau on the side chain of Lys could enter the cells more rapidly and efficiently. In contrast, the in vivo tumor growth inhibition was the most pronounced in the case of Ac-SYSNleEHFRWGK(Dau=Aoa)PV-NH2(Conj2). It is worth mentioning that the dose was normalized to Dau content, thus the injected dose ofConj3was half that ofConj 2. Nevertheless,Conj2, with one molecule of the drug, might be superior to the conjugate containing two molecules of daunomycin. The higher tumor growth inhibition effect ofConj2overConj1where the Dau is connected to theN-terminus, confirms our previous results with Dau-GnRH-III (Glp-His-Trp-Lys(Bu)-His-Asp-Trp-Lys(Dau=Aoa)-Pro-Gly-NH2), suggesting that H-Lys(Dau=Aoa)-OH can release easily from this position by the dipeptidyl-peptidase activity of cathepsin B.

In this study, the native sequence of -MSH was used, in which Met was replaced by Nle (SYSNleEHFRWGKPV). Daunomycin was attached to the amino functional groups via non-cleavable oxime linkage. These types of conjugates have many excellent properties to study and compare the bioactivity of the compounds. One of the developed conjugates contained drug molecules on both conjugation site (N-terminal and the side chain of Lys). The two additional conjugates were modified by the drug, either on theN-terminus or on the Lys side chain. The in vitro cytostatic effect on mouse melanoma cells did not show any significant differences among them. However, results indicated that the conjugates with Dau on the side chain of Lys could enter the cells more rapidly and efficiently. In contrast, the in vivo tumor growth inhibition was the most pronounced in the case of Ac-SYSNleEHFRWGK(Dau=Aoa)PV-NH2(Conj2). It is worth mentioning that the dose was normalized to Dau content, thus the injected dose ofConj3was half that ofConj 2. Nevertheless,Conj2, with one molecule of the drug, might be superior to the conjugate containing two molecules of daunomycin. The higher tumor growth inhibition effect ofConj2overConj1where the Dau is connected to theN-terminus, confirms our previous results with Dau-GnRH-III (Glp-His-Trp-Lys(Bu)-His-Asp-Trp-Lys(Dau=Aoa)-Pro-Gly-NH2), suggesting that H-Lys(Dau=Aoa)-OH can release easily from this position by the dipeptidyl-peptidase activity of cathepsin B.

In this study, the native sequence of -MSH was used, in which Met was replaced by Nle (SYSNleEHFRWGKPV). Daunomycin was attached to the amino functional groups via non-cleavable oxime linkage. These types of conjugates have many excellent properties to study and compare the bioactivity of the compounds. One of the developed conjugates contained drug molecules on both conjugation site (N-terminal and the side chain of Lys). The two additional conjugates were modified by the drug, either on theN-terminus or on the Lys side chain. The in vitro cytostatic effect on mouse melanoma cells did not show any significant differences among them. However, results indicated that the conjugates with Dau on the side chain of Lys could enter the cells more rapidly and efficiently. In contrast, the in vivo tumor growth inhibition was the most pronounced in the case of Ac-SYSNleEHFRWGK(Dau=Aoa)PV-NH2(Conj2). It is worth mentioning that the dose was normalized to Dau content, thus the injected dose ofConj3was half that ofConj 2. Nevertheless,Conj2, with one molecule of the drug, might be superior to the conjugate containing two molecules of daunomycin. The higher tumor growth inhibition effect ofConj2overConj1where the Dau is connected to theN-terminus, confirms our previous results with Dau-GnRH-III (Glp-His-Trp-Lys(Bu)-His-Asp-Trp-Lys(Dau=Aoa)-Pro-Gly-NH2), suggesting that H-Lys(Dau=Aoa)-OH can release easily from this position by the dipeptidyl-peptidase activity of cathepsin B.

In this study, the native sequence of -MSH was used, in which Met was replaced by Nle (SYSNleEHFRWGKPV). Daunomycin was attached to the amino functional groups via non-cleavable oxime linkage. These types of conjugates have many excellent properties to study and compare the bioactivity of the compounds. One of the developed conjugates contained drug molecules on both conjugation site (N-terminal and the side chain of Lys). The two additional conjugates were modified by the drug, either on theN-terminus or on the Lys side chain. The in vitro cytostatic effect on mouse melanoma cells did not show any significant differences among them. However, results indicated that the conjugates with Dau on the side chain of Lys could enter the cells more rapidly and efficiently. In contrast, the in vivo tumor growth inhibition was the most pronounced in the case of Ac-SYSNleEHFRWGK(Dau=Aoa)PV-NH2(Conj2). It is worth mentioning that the dose was normalized to Dau content, thus the injected dose ofConj3was half that ofConj 2. Nevertheless,Conj2, with one molecule of the drug, might be superior to the conjugate containing two molecules of daunomycin. The higher tumor growth inhibition effect ofConj2overConj1where the Dau is connected to theN-terminus, confirms our previous results with Dau-GnRH-III (Glp-His-Trp-Lys(Bu)-His-Asp-Trp-Lys(Dau=Aoa)-Pro-Gly-NH2), suggesting that H-Lys(Dau=Aoa)-OH can release easily from this position by the dipeptidyl-peptidase activity of cathepsin B.