Anticancer activity of multifunctional Pt(IV) prodrugs

The anticancer activity of Pt(II)-based drugs is limited by severe side effects, resistance and poor pharmacokinetic profile. To overcome these limits Pt(IV) prodrugs can be used: they are activated by reduction within hypoxic tumor environment, releasing the corresponding Pt(II) complex and two axial ligands, which can also be bioactive molecules, providing a synergistic activity with Pt(II) drugs (multi-action agents). The biological properties of such molecules have been reported in this thesis. A cisplatin-based Pt(IV) complex containing the Histone DeAcetylase inhibitor (HDACi) 2-(2-propynyl)octanoate (POA) as axial ligand showed a marked in vitro and in vivo anticancer activity compared with cisplatin and a Pt(IV) compound with two other known HDACis. Also a Pt(IV) derivate bearing POA but based on the oxaliplatin-analogue cis-dichlorido(cyclohexane-1R,2Rdiamine) platinum(II) (or [PtCl2(dach)]) was 1-2 orders of magnitude more active in vitro than the references cisplatin, oxaliplatin and [PtCl2(dach)], due to its high cellular accumulation. It exerted also a marked in vivo anticancer activity, inducing immunogenic cell death on colon cancer. The selectivity towards colon cancer of dach-based complexes was confirmed by the investigation of three couples of asymmetric Pt(IV) species, cisplatin- or dach-based, containing the bioactive axial ligands clofibrate, heptanoate or octanoate. The two series showed a marked in vitro antiproliferative activity (on 2D and 3D models) compared to the Pt(II) counterparts, due to a considerable accumulation in cancer cells. Finally, two cisplatin-based Pt(IV) complexes, containing inhibitors of cyclooxygenase (COX) enzymes as axial ligands, offered good antiproliferative performances, due to their enhanced lipophilicity. However, their biological effects were almost independent from COX-2 expression. In conclusion, the use of bioactive ligands leads to multi-action Pt(IV) complexes with promising pharmacological profile

How to obtain Pt(IV) complexes suitable for the conjugation to nanovectors from the oxidation of [PtCl(terpyridine)]+

Oxidation of [Pt(II)Cl(terpy)]+ (terpy = 2,2’:6’,2”-terpyridine) has been attempted with several oxidizing agents and in different experimental conditions in order to obtain a Pt(IV) complex suitable for the conjugation to nanovectors to be used in drug delivery targeting for anticancer therapy. The best compromise in terms of yield and purity of the final complex was obtained by microwave-assisted reaction at 70 °C in 50% aqueous H2O2 for 2 h. Under these conditions the quantitative formation of [Pt(IV)Cl(OH)2(terpy)]+ was observed. Subsequent synthetic steps were i) functionalization of [Pt(IV)Cl(OH)2(terpy)]+ in the axial position with succinic anhydride to obtain [Pt(IV)Cl(OH)(succinato)(terpy)]+, and ii) reaction of the latter with nonporous silica nanoparticles (SNPs) with an external shell containing primary amino groups to obtain a nanovector able to transport the Pt(IV) antitumor prodrug in form of conjugate Pt-SNP. Finally, the antiproliferative activity and cell accumulation of [Pt(II)Cl(terpy)]+, [Pt(IV)Cl(OH)2(terpy)]+, and Pt-SNP conjugate were measured on three cancer cell lines. Despite highly effective accumulation of Pt-SNP into cells, a modest increase in activity was observed with respect to the molecular species. Further experiments showed that the Pt-SNP conjugate can release [Pt(II)Cl(terpy)]+ upon reduction, but this metabolite may undergo hydrolysis, and the resulting aquo complex could coordinate once again the free amino groups of the SNPs. In the resulting tetraamine form, the Pt(II) complex conjugated to the SNPs cannot completely exert its antiproliferative activity

A new platinum-based prodrug candidate: Its anticancer effects in B50 neuroblastoma rat cells

AIMS: Neuroblastoma is a rare cancer that affects children, mostly under the age of 5. This type of cancer starts in very early forms of immature nerve cells or developing cells found in embryo or fetus. To date cisplatin represents one of the most potent antitumor agent known, however, the onset of systemic side effects and the induction of drug resistance limit its use in the clinic for long-term treatment. In the present study we have analysed the effects of a new compound of platinum(IV) conjugates, named Pt(IV)Ac-POA, which is able to generate a synergistic antineoplastic action when released along with cisplatin upon intracellular Pt(IV) → Pt(II) reduction. MAIN METHODS: To assess the growth inhibition of the compounds under investigation, a cell viability test, i.e. the resazurin reduction assay was used on the B50 neuroblastoma rat cells. Further analysis on the cell cycle and metabolic alterations were carried out through flow cytometry. Morphological changes and activation of different cell death pathways after treatment, were observed at transmission electron microscope and by immunocytochemistry at fluorescence microscopy. Protein expression was examined by western blot analysis. KEY FINDINGS: This compound bearing bioactive axial ligand, such as the active histone deacetylase inhibitor (HDACi) (2-propynyl)octanoic acid (POA), induced cell death through different pathways at a concentration ten times lower than cisplatin. SIGNIFICANCE: The results showed that Pt(IV)Ac-POA could represent a promising improvement of Pt-based chemotherapy against neuroblastoma

Cis,cis,trans-[PtIVCl2(NH3)2(perillato)2], a dual-action prodrug with excellent cytotoxic and antimetastatic activity

Two Pt(iv) conjugates containing one or two molecules of perillic acid (4-isopropenylcyclohexene-1-carboxylic acid), an active metabolite of limonene, were synthesized both with traditional and microwave-assisted methods and characterized. Their antiproliferative activity was tested on a panel of human tumor cell lines. In particular, cis,cis,trans-[PtIVCl2(NH3)2(perillato)2] exhibited excellent antiproliferative and antimetastatic activity on A-549 lung tumor cells at nanomolar concentrations. A number of in vitro biological tests were performed to decipher some aspects of its mechanism of action, including transwell migration and invasion as well as wound healing assay

Can the Self-Assembling of Dicarboxylate Pt(IV) Prodrugs Influence Their Cell Uptake?

The possibility of spontaneous self-assembly of dicarboxylato Pt(IV) prodrugs and the consequences on their uptake in cancer cells have been evaluated in different aqueous solutions. Four Pt(IV) complexes, namely, (OC-6-33)-diacetatodiamminedichloridoplatinum(IV), Ace, (OC-6-33)-diamminedibutanoatodichloridoplatinum(IV), But, (OC-6-33)-diamminedichloridodihexanoatoplatinum(IV), Hex, and (OC-6-33)-diamminedichloridodioctanoatoplatinum(IV), Oct, have been dispersed in i) milliQ water, ii) phosphate buffered saline, and iii) complete cell culture media (RPMI 1640 or DMEM) containing fetal bovine serum (FBS). The samples have been analyzed by dynamic light scattering (DLS) to measure the size and distribution of the nanoparticles possibly present. The zeta potential offered an indication of the stability of the resulting aggregates. In the case of the most lipophilic compounds of the series, namely, Oct and to a lesser extent Hex, the formation of nanosized aggregates has been observed, in particular at the highest concentration tested (10 μM). The cell culture media had the effect to disaggregate these nanoparticles, mainly by virtue of their albumin content, able to interact with the organic chains via noncovalent (hydrophobic) interactions. For Oct, at the highest concentration employed for the uptake tests (10 μM), the combination between passive diffusion and endocytosis of the self-assembled nanoparticles makes the cellular uptake higher than in the presence of passive diffusion only. During the study of cellular uptake on A2780 ovarian cancer cells pretreated with cytochalasin D, a statistically significant inhibition of endocytosis was observed for Oct. In these experimental conditions, the relationship between uptake and lipophilicity becomes almost linear instead of exponential. Since Oct anticancer prodrug is active at nanomolar concentrations, where the aggregation in culture media is almost abolished, this phenomenon should not significantly impact its antiproliferative activity

Pt(IV) Bifunctional Prodrug Containing 2-(2-Propynyl)octanoato Axial Ligand: Induction of Immunogenic Cell Death on Colon Cancer

The synthesis, characterization, and in vitro activity of a cyclohexane-1R,2R-diamine-based Pt(IV) derivative containing the histone deacetylase inhibitor rac-2-(2-propynyl)octanoato, namely, (OC-6-44)-acetatodichlorido (cyclohexane-1R,2R-diamine)(rac-2-(2-propynyl)octanoato)platinum(IV), are reported together with those of its isomers containing enantiomerically enriched axial ligands. These Pt(IV) complexes showed comparable activity, of 2 orders of magnitude higher than reference drug oxaliplatin on three human (HCT 116, SW480, and HT-29) and one mouse (CT26) colon cancer cell lines. In vivo experiments were carried out on immunocompetent BALB/c mice bearing the same syngeneic tumor. The complex (OC-6-44)-acetatodichlorido(cyclohexane-1R,2R-diamine)(rac-2-(2-propynyl)octanoato)platinum(IV) showed higher tumor mass Pt accumulation than oxaliplatin, due to its higher lipophilicity, with negligible nephro- and hepatotoxicities when administered intravenously. A remarkable tumor mass invasion by cytotoxic CD8(+) T lymphocytes, following the Pt(IV) treatment, indicated a strong induction of immunogenic cell death

How to obtain Pt(IV) complexes suitable for conjugation to nanovectors from the oxidation of [PtCl(terpyridine)]+

Oxidation of [Pt(II)Cl(terpy)]+ (terpy = 2,2′:6′,2′′-terpyridine) has been attempted with several oxidizing agents and under different experimental conditions in order to obtain a Pt(IV) complex suitable for the conjugation to nanovectors to be used in drug delivery targeting for anticancer therapy. The best compromise in terms of yield and purity of the final complex was obtained by microwave-assisted reaction at 70 °C in 50% aqueous H2O2 for 2 h. Under these conditions the quantitative formation of [Pt(IV)Cl(OH)2(terpy)]+ was observed. The subsequent synthetic steps were, (i) functionalization of [Pt(IV)Cl(OH)2(terpy)]+ in the axial position with succinic anhydride to obtain [Pt(IV)Cl(OH)(succinato)(terpy)]+ and (ii) reaction of the latter with nonporous silica nanoparticles (SNPs) with an external shell containing primary amino groups to obtain a nanovector able to transport the Pt(IV) antitumor prodrug in the form of a conjugate Pt-SNP. Finally, the antiproliferative activity and cell accumulation of [Pt(II)Cl(terpy)]+, [Pt(IV)Cl(OH)2(terpy)]+, and the Pt-SNP conjugate were measured on three cancer cell lines. Despite highly effective accumulation of Pt-SNP in cells, a modest increase in activity was observed with respect to the molecular species. Further experiments showed that the Pt-SNP conjugate can release [Pt(II)Cl(terpy)]+ upon reduction, but this metabolite may undergo hydrolysis, and the resulting aquo complex could coordinate once again the free amino groups of the SNPs. In the resulting tetraamine form, the Pt(ii) complex conjugated to the SNPs cannot completely perform its antiproliferative activity. © 2017 The Royal Society of Chemistry

An unsymmetric cisplatin-based Pt(IV) derivative containing 2-(2-propynyl)octanoate: A very efficient multi-action antitumor prodrug candidate

The design, synthesis, characterization and biological properties of a Pt(iv) complex containing the very active inhibitor of histone deacetylase (2-propynyl)octanoic acid, POA, as an axial ligand are reported here. The title complex, namely (OC-6-44)-acetatodiamminedichlorido(2-(2-propynyl)octanoato)platinum(iv), 1, containing POA in racemic or in enantiomeric forms, was one/two orders of magnitude more active than cisplatin, depending on the chemo-sensitivity of the cancer cell lines. Moreover, 1 exhibited similar or even better antiproliferative activity than (OC-6-33)-diamminedichloridobis(2-propylpentanoato)platinum(iv), 2, containing two molecules of the well-known histone deacetylase inhibitor 2-propylpentanoic (valproic) acid. The high potency of 1 is likely due to its high cellular accumulation and to the synergism between the DNA-damaging cisplatin and the histone deacetylase inhibitor POA, both released upon the intracellular reduction of 1. Prodrug 1, after oral administration, caused an impressive reduction of the tumor mass (94%) in a model of solid tumor (murine Lewis lung carcinoma), compared to that of the control, whereas (intraperitoneal) cisplatin induced a tumor regression of 75% only. A good accumulation of 1 was observed in the tumor mass. The time course of the body weight attested that cisplatin induced elevated anorexia, whereas treatment with 1 did not induce significant body weight loss throughout the therapeutic experiment

Pt(IV) complexes based on cyclohexanediamines and the histone deacetylase inhibitor 2-(2-propynyl)octanoic acid: synthesis, characterization, cell penetration properties and antitumor activity

The Pt(iv) complexes based on (SP-4-2)-dichlorido(cyclohexane-1,4-diamine)platinum(ii) (kiteplatin) and the histone deacetylase inhibitor 2-(2-propynyl)octanoic acid (POA) were investigated. Since POA contains a chiral carbon, all the possible Pt(iv) isomers were prepared and characterized, and their antiproliferative activity on six cancer cell lines was compared with that of the corresponding Pt(iv) complexes containing the cyclohexane-1R,2R-diamine equatorial ligand. To justify the very good antiproliferative activity (nanomolar IC50), the polarity, lipophilicity, permeability, and cell accumulation of the complexes were studied. Overall, the two series of Pt(iv) complexes showed similar cell penetration properties, being significantly better than that of the Pt(ii) reference compounds. Finally, a representative compound of the whole set of complexes (i.e., that based on cyclohexane-1R,2R-diamine and racemic POA) was tested in vivo on mice bearing Lewis lung carcinoma, showing good tumor growth inhibition with negligible body weight loss