An orally active antitumor cyclohexanediamine-Pt(IV) complex: trans,cis,cis-bis(n-valerato)(oxalato)(1R,2R-cyclohexane diamine)Pt(IV)

A platinum(IV) prodrug strategy to overcome glutathione-based oxaliplatin resistance

Clinical efficacy of oxaliplatin is frequently limited by severe adverse effects and therapy resistance. Acquired insensitivity to oxaliplatin is, at least in part, associated with elevated levels of glutathione (GSH). In this study we report on an oxaliplatin-based platinum(IV) prodrug, which releases L-buthionine-S,R-sulfoximine (BSO), an inhibitor of glutamate-cysteine ligase, the rate-limiting enzyme in GSH biosynthesis. Two complexes bearing either acetate (BSO-OxOAc) or an albumin-binding maleimide (BSO-OxMal) as second axial ligand were synthesized and characterized. The in vitro anticancer activity of BSO-OxOAc was massively reduced in comparison to oxaliplatin, proving its prodrug nature. Nevertheless, the markedly lower intracellular oxaliplatin uptake in resistant HCT116/OxR cells was widely overcome by BSO-OxOAc resulting in distinctly reduced resistance levels. Platinum accumulation in organs of a colorectal cancer mouse model revealed higher tumor selectivity of BSO-OxMal as compared to oxaliplatin. This corresponded with increased antitumor activity, resulting in significantly enhanced overall survival. BSO-OxMal-treated tumors exhibited reduced GSH levels, proliferative activity and enhanced DNA damage (pH2AX) compared to oxaliplatin. Conversely, pH2AX staining especially in kidney cells was distinctly increased by oxaliplatin but not by BSO-OxMal. Taken together, our data provide compelling evidence for enhanced tumor specificity of the oxaliplatin(IV)/BSO prodrug.

Structure-Activity Relationships of Triple-Action Platinum(IV) Prodrugs with Albumin-Binding Properties and Immunomodulating Ligands

Chemotherapy with platinum complexes is essential for clinical anticancer therapy. However, due to side effects and drug resistance, further drug improvement is urgently needed. Herein, we report on triple-action platinum(IV) prodrugs, which, in addition to tumor targeting via maleimide-mediated albumin binding, release the immunomodulatory ligand 1-methyl-d-tryptophan (1-MDT). Unexpectedly, structure-activity relationship analysis showed that the mode of 1-MDT conjugation distinctly impacts the reducibility and thus activation of the prodrugs. This in turn affected ligand release, pharmacokinetic properties, efficiency of immunomodulation, and the anticancer activity in vitro and in a mouse model in vivo. Moreover, we could demonstrate that the design of albumin-targeted multi-modal prodrugs using platinum(IV) is a promising strategy to enhance the cellular uptake of bioactive ligands with low cell permeability (1-MDT) and to improve their selective delivery into the malignant tissue. This will allow tumor-specific anticancer therapy supported by a favorably tuned immune microenvironment.

A cancer specific oxaliplatin-releasing Pt(iv)-prodrug

A highly efficient cancer specific Pt(iv) prodrug was developed.

trans,cis,cis-bis(benzoato)dichlorido(cyclohexane-1R,2R-diamine)platinum(IV): a prodrug candidate for the treatment of oxaliplatin-refractory colorectal cancer

The gold standard for the treatment of metastatic colorectal cancer consists of combination chemotherapy. Over time, however, the development of chemoresistant tumor clones leads to relapse. It may be possible to overcome oxaliplatin chemoresistance in colorectal cancer cells by exploiting a complex obtained from the insertion of the cyclohexane-1R,2R-diamine carrier ligand (the same diamine present in oxaliplatin) into an octahedral Pt(IV) scaffold with high lipophilicity conferred by two benzoate axial ligands. Herein we report the synthesis, characterization (including X-ray structure), biological activity, and cellular accumulation of trans,cis,cis-bis(benzoato)dichlorido(cyclohexane-1R,2R-diamine)platinum(IV) complex in a panel of several human cancer cell lines, including a colon carcinoma cell line resistant to oxaliplatin. The compound under investigation shows the best performance in terms of in vitro anti-proliferative activity and ability to overcome chemoresistance, with respect to oxaliplatin and some other Pt(II) reference complexes. This result is likely related to the high lipophilicity shown by the title compound that favors its cellular accumulation by passive diffusion.

Synthesis and cytotoxicity of new platinum(IV) complexes of mixed carboxylates

In order to develop new antitumor platinum(IV) complexes with highly tuned lipophilicity, a series of (diamine)Pt(IV) complexes of the formula [Pt(IV)(dach)L(3)L'] or [Pt(IV)(dach)L(2)L"(2)] (dach=trans-(+/-)-1,2-diaminocyclohexane; L=acetato, propionato; L'=acetato, propionato, valerato or pivalato; L"=trifluoroacetato) have been synthesized by electrophilic substitution of the tris(carboxylato)hydroxoplatinum(IV) complexes, [Pt(IV)(dach)L(3)OH] (L=acetato, propionato), with various carboxylic anhydrides such as acetic, trifluoroacetic, pivalic and valeric anhydrides. The present platinum(IV) complexes were fully characterized by means of elemental analyses, 1H NMR, mass and IR spectroscopies. The complexes 8 and 10, satisfying the appropriate range of lipophilicity (logP=0.18-1.54), exhibited high activity (ED(50), 5.1 and 1.3 microM, respectively) compared with other complexes, which implies that the lipophilicity is an important factor for the antitumor activity of this series of complexes.

Electrophilic substitution of (diamine)tetrahydroxoplatinum(IV) with carboxylic anhydrides. Synthesis and characterization of (diamine)platinum(IV) complexes of mixed carboxylates

A novel series of (diamine)platinum(IV) complexes of mixed carboxylates have been synthesized by electrophilic substitution of the tetrahydroxoplatinum(IV) complex (dach)Pt(OH)4 (dach = trans-(+/-)-1,2-diaminocyclohexane) with three different carboxylic anhydrides, pivalic, acetic, and trifluoroacetic anhydrides. Consecutive two-step acylations with two different carboxylic anhydrides in acetone or dichloromethane gave the mixed carboxylate complexes (dach)Pt(O2CR)x(O2CR')4 - x (R = C(CH3)3 or CF3, R' = CH3, x = 1-4) including all the possible stereoisomers, which could be separated and identified by means of HPLC, column chromatography, 1H NMR, and X-ray crystallography. From analysis of the reaction products we have found that the positions of electrophilic substitution of (dach)Pt(OH)4 were influenced by the kinds of carboxylic anhydrides exhibiting different electrophilicity or steric effects. The initial substitution by the first reactant occurs more favorably on axial OH, but in the case of pivalic anhydride, equatorial substitution is favored probably because of the bulkiness of the pivalate group. Such a result seems to be related to their stereochemical factors rather than to differences in electrophilicity. The lipophilicity of the title complexes was affected not only by the carbon numbers of substituents but also by the conformation of the resulting compound.

Synthesis and antitumor activity of the metformin platinum (IV) complex. Crystal structure of the tetrachloro(metformin)platinum (IV) dimethylsulfoxide solvate

The synthesis of (metformin) tetrachloroplatinum (IV) was investigated (metformin is N,N-dimethylbiguanide). It crystallizes with one dimethylsulfoxide molecule as solvate in the monoclinic system, space group P2(1)/n (No. 14) with Z = 4. The cell dimensions are: a = 13.136(7), b = 9.424(2), c = 14.009(8) A, beta = 111.96(4) degrees, V = 1608.4(2) A3. Of the 4269 independent nonzero reflections collected, 1979 with I > 3 sigma (I) were considered and used in the calculations. The structure was refined to R = 0.043 and wR = 0.045. The platinum coordination is octahedral, built up from four chloride anions and one bidentate chelating ligand via the two imine nitrogen atoms cis position. The distances and angles are typical of six-membered rings that have similar donor atoms. The complex was evaluated in vitro and in vivo on murine P388 leukemia. It was found to be as potent as cis-dichlorodiammine platinum (II), CDDP, in inhibiting the proliferation of the sensitive P388 cells. However the resistant P388/CDDP cells were threefold more sensitive to the compound than to CDDP. The two compounds induced a similar perturbation in the G2+M phases of the cell-cycle. The complex was less active than CDDP in vivo on P388 leukemia when administered i.p. (intra peritoneal) on day 1.