Functionalization of Osmium Arene Anticancer Complexes with (Poly)arginine: Effect on Cellular Uptake, Internalization, and Cytotoxicity

Abstract

Attaching peptides to metallodrugs may result in improved biological properties of the complexes. The potential use of cell penetrating peptides (CPPs) as cell delivery vectors is attractive, since directed cell uptake of (metallo)drugs remains a major challenge in anticancer drug design. In this work, we report the synthesis of peptide conjugates of the organometallic Os II anticancer complex [(η 6 -biphenyl)Os(picolinate)Cl] with different arginine (Arg) chain lengths. Complexes conjugated to Arg 5 or Arg 8 at the 5-position of the picoline ring increase Os uptake into A2780 human ovarian cancer cells by ca. 2Â and 10Â, respectively, whereas a single Arg had no effect. Furthermore, a 15-fold increase in binding of Os to DNA, a potential target for these complexes, was observed for Arg 8 compared to the Arg 1 conjugate. The Arg 5 and Arg 8 conjugates exhibited fast kinetics of binding to calf thymus DNA and an ability to precipitate DNA at very low concentrations. In serum-free medium, the Arg 8 complex was cytotoxic (IC 50 33 μM) and appears to be a rare example of a bioactive organometallic peptide conjugate. Experiments on CHO cells deficient in DNA repair suggested that unrepaired DNA damage contributes to the cytotoxicity of the Arg 5 and Arg 8 conjugates. These studies demonstrate the potential for use of cell-and nucleus-penetrating peptides in targeting organometallic arene anticancer complexes.

100 years of metal coordination chemistry: from Alfred Werner to anticancer metallodrugs

“…[57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73][74][75][76] Recently, different groups have investigated the chemical and biological activity of analogous half-sandwich arene osmium complexes. [77][78][79][80][81][82][83][84][85] Osmium, the heavier congener of ruthenium and a third row transition metal, commonly exhibits slower kinetics than ruthenium, and is often considered to be relatively inert. However, it is apparent that it is possible to tune the biochemical reactivity of arene osmium(II) complexes through understanding their aqueous solution chemistry.…”

Identification of the Structural Determinants for Anticancer Activity of a Ruthenium Arene Peptide Conjugate

“…[1][2][3][4][5] In diagnostic and therapeutic metallodrug research, [6] the approach of tagging metal fragments to peptides is an emerging targeting strategy and several recent investigations were dedicated to organometal-peptide conjugation. [7][8][9][10][11][12][13][14][15][16][17] The peptide carrier is typically obtained by solid phase synthesis, and the metallodrug is linked to the peptide either on solid support or in solution after peptide cleavage from the resin. The metal can be conjugated directly via a suitable amino acid, or a linker with metal-chelating properties can be incorporated into the peptide sequence.…”

“…[14] Based on these strategies, encouraging but rare examples of anticancer active metal-peptide bioconjugates were reported with different metal systems including ferrocenoyl-dipeptides, [19] dicobalt hexacarbonyl tagged to alkyne-modified enkephalin, [16] [Mn(Cp)(CO) 3 ] tagged to the cell-penetrating peptides sC18 or hCTA C H T U N G T R E N N U N G (18-32)-k7, [12,15,20] RhA C H T U N G T R E N N U N G (Cp*)-sandwich, [7] gold(I) [21] or platinum(IV) bioconjugates of TAT, pseudoneurotensin or octreotate. [8,22] Surprisingly, only little is known about bioconjugates of anticancer half-sandwich ruthenium(II) and osmium(II) organometallics with peptide carriers [9,23] or pendant amino acids. [24,25] This is probably related to synthetic difficulties arising from hydrolysis of the metal À halido bond in aqueous solution, which is a crucial activation parameter for these Abstract: Organometallic RuA C H T U N G T R E N N U N G (arene)peptide bioconjugates with potent in vitro anticancer activity are rare.…”

“…[26] The few existing investigations show that loading of the metalloA C H T U N G T R E N N U N G drug on a peptide carrier is associated with a decrease in antiproliferative activity compared to the non-conjugated small metallodrug. [9,23] In particular, conjugation of an OsA C H T U N G T R E N N U N G (arene) picolinate moiety to an octaarginine sequence led to a substantial activity decrease and moderate cytotoxicity was only obtained in protein depleted fetal calf serum. [9] Moreover, conjugation of an imidazole-modified dicarba analogue of octreotide to a Ru-A C H T U N G T R E N N U N G (arene)(triphenylphosphine) moiety also resulted in modest cytotoxic activity, which was approximately fourfold lower than that of the analogous small anticancer metallodrug.…”

“…[9,23] In particular, conjugation of an OsA C H T U N G T R E N N U N G (arene) picolinate moiety to an octaarginine sequence led to a substantial activity decrease and moderate cytotoxicity was only obtained in protein depleted fetal calf serum. [9] Moreover, conjugation of an imidazole-modified dicarba analogue of octreotide to a Ru-A C H T U N G T R E N N U N G (arene)(triphenylphosphine) moiety also resulted in modest cytotoxic activity, which was approximately fourfold lower than that of the analogous small anticancer metallodrug. [23] The apparent lack of anticancer active organometallic Ru-peptide conjugates from potent metallodrugs prompted us to investigate an appropriate model system with the aim of identifying its cytotoxicity-determining building block(s).…”