Vinblastine is a widely used anticancer drug with undesired side effects. Its conjugation with carrier molecules could be an efficient strategy to reduce these side effects. Besides this, the conjugate could exhibit increased efficiency against resistant cells, e.g., due to the altered internalization pathway. Oligoarginines, as cell-penetrating peptides, can transport covalently attached compounds into different kinds of cells and enhance the efficiency of those compounds. We report here the coupling of vinblastine through its carboxyl group at position 16 with the N-terminal amino function of L-Trp methyl ester. After hydrolysis of the ester group, 17-desacetylvinblastineTrp was conjugated to the N-terminal amino group of oligoarginine via the C-terminal carboxyl group of the Trp moiety in solution. The antitumor effect of conjugates was studied on sensitive and resistant human leukemia (HL-60) cells in vitro. Our data suggest that all conjugates investigated possess an antiproliferative effect against the studied cells. However, the effect was dependent on the number of Arg residues in the conjugates: Arg₈ > Arg₆ ≫ Arg₄. The conjugate with Arg₈ exhibited similar efficicacy as compared with free 17-desacetylvinblastineTrp. The in vitro studies also showed that the tubulin binding ability of vinblastine was essentially preserved even in the octaarginine conjugate. We also observed that two isomers were formed during conjugation. These isomers showed different levels of activity against tubulin polymerization in vitro and in vivo. The 17-desacetylvinblastineTrp-Arg₈-1 isomer conjugate possessed high selectivity against the mitotic spindles. HRMS and NMR data suggest that 17-desacetylvinblastineTrp-Arg₈-1 and 17-desacetylvinblastineTrp-Arg₈-2 are epimers at the tryptophan α carbon atom.

Some Vinca alkaloids (eg, vinblastine, vincristine) have been widely used as antitumor drugs for a long time. Unfortunately, vindoline, a main alkaloid component of Catharanthus roseus (L.) G. Don, itself, has no antitumor activity. In our novel research program, we have prepared and identified new vindoline derivatives with moderate cytostatic activity. Here, we describe the effect of conjugation of vindoline derivative with oligoarginine (tetra-, hexa-, or octapeptides) cell-penetrating peptides on the cytostatic activity in vitro and in vivo. Br-Vindoline-(l)-Trp-OH attached to the N-terminus of octaarginine was the most effective compound in vitro on HL-60 cell line. Analysis of the in vitro activity of two isomer conjugates (Br-vindoline-(l)-Trp-Arg and Br-vindoline-(d)-Trp-Arg suggests the covalent attachment of the vindoline derivatives to octaarginine increased the antitumor activity significantly against P388 and C26 tumour cells in vitro. The cytostatic effect was dependent on the presence and configuration of Trp in the conjugate as well as on the cell line studied. The configuration of Trp notably influenced the activity on C26 and P388 cells: conjugate with (l)-Trp was more active than conjugate with the (d)-isomer. In contrast, conjugates had very similar effect on both the HL-60 and MDA-MB-231 cells. In preliminary experiments, conjugate Br-vindoline-(l)-Trp-Arg exhibited some inhibitory effect on the tumor growth in P388 mouse leukemia tumor-bearing mice. Our results indicate that the conjugation of modified vindoline could result in an effective compound even with in vivo antitumor activity.

Alkaloids U 0600Aromatic Electrophilic Substitutions on Vindoline. -Nitration of 10-bromo derivative (V) leads to the unexpected, anomalous 12-bromo-10-nitrovindoline (VI) and appears to be a further example of the rearrangement discovered by Reverdin. Nitration of the 10-chloro analogue (VII) leads to the expected derivative (VIII). -(GORKA-KERESKENYI, A.; SZABO, L.; HAZAI, L.; LENGYEL, M.; SZANTAY, C. J.; SANTA, Z.; KALAUS, G.; SZANTAY*, C.; Heterocycles 71 (2007) 7, 1553-1563; Dep. Org. Chem. Technol., Budapest Univ. Technol. Econ., H-1521 Budapest, Hung.; Eng.) -K. Woydowski 44-184

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