Nicholas Farrell

Biomedical uses and applications of inorganic chemistry. An overview

Abstract This article serves as an overview of the topics covered in this special issue dealing with aspects of biomedical inorganic chemistry. Topics include metal ions in disease (the use of chelating agents), metalloproteins as drug targets, organelles as targets (the mitochondrion), metal–drug interactions, metal-based chemotherapuetic drugs, and radioisotopes in medicine. The current activity and topical importance of these various areas are briefly discussed.

Transferring the concept of multinuclearity to ruthenium complexes for improvement of anticancer activity.

Multinuclear platinum anticancer complexes are a proven option to overcome resistance of established anticancer compounds. Transferring this concept to ruthenium complexes led to the synthesis of dinuclear Ru(II)-arene compounds containing a bis(pyridinone)alkane ligand linker. A pronounced influence of the spacer length on the in vitro anticancer activity was found, which is correlated to the lipophilicity of the complexes. IC(50) values in the same dimension as for established platinum drugs were found in human tumor cell lines. No cross-resistance to oxoplatin, a cisplatin prodrug, was observed for the most active complex in three resistant cell lines; in fact, a 10-fold reversal of sensitivity in two of the oxoplatin-resistant lines was found. (Bio)analytical characterization of the representative examples showed that the ruthenium complexes hydrolyze rapidly, forming predominantly diaqua species that exhibit affinity toward transferrin and DNA, indicating that both proteins and nucleobases are potential targets.

Cellular pharmacology of polynuclear platinum anti-cancer agents

Study of the cellular pharmacology of the dinuclear platinum complexes, BBR3005 ([¿trans-PtCl(NH3)2¿2H2N(CH2)6NH2]2+), BBR3171 ([¿cis-PtCl(NH3)2¿2H2N(CH2)6NH2]2+) and the trinuclear platinum complex, BBR3464 ([¿trans-PtCl(NH3)2¿2 mu-¿trans-Pt(NH3)2(H2N(CH2)6NH2)2¿]4+) was undertaken in wild type and cisplatin-resistant L1210 murine leukemia cell lines. All complexes are potent cytotoxic agents against the wild type cell line. Only BBR3464 shows enhanced activity against the cisplatin-resistant cell line following a brief exposure. This enhanced activity is attributable, in part, to preserved accumulation, which contrasts with diminished accumulation of cisplatin and both dinuclear platinum complexes. The cisplatin-resistant cell line is relatively tolerant of DNA adducts induced by both cisplatin and BBR3464, but BBR3464 is much less affected. All complexes induce DNA interstrand cross-links. Di/trinuclear complex-induced interstrand cross-linking peaks early, suggesting rapid genomic access and interaction. Subsequent decay suggests susceptibility to DNA repair mechanisms. Peak and area-under-the-curve values for interstrand cross-linking among the complexes correlate poorly with cytotoxic effects, especially in the cisplatin-resistant cell line. This suggests that all interstrand cross-linking adducts are not equal in their cytotoxic effect, or other, non-interstrand cross-linking adducts are significant. BBR3464 has been selected for clinical development largely on the basis of results from in vivo activity and toxicity studies. These results show BBR3464 to have unique properties in the context of acquired cisplatin-resistance that enhance its candidacy as a potential anticancer agent.

DNA Binding and Chemistry of Dinuclear Platinum Complexes

Abstract This Comment summarises the chemistry and DNA binding of dinuclear platinum-amine, or bis(platinum), complexes, a new class of potent antitumor agents. In these structures, the Pt coordination spheres are bridged by variable-length diamine chains. The DNA binding of these species produces an array of structurally distinct adducts not available to mononuclear analogs such as cis-[PtCl2(NH3)2]. The possibility of tri- and tetra-substitution inherent in the dinuclear structure poses interesting challenges for design of complexes capable of specific DNA binding. Besides the utility of the dinuclear structure in design of novel antitumor agents, the unique DNA binding modes of these species allow their use as probes of DNA structure and conformation.

The cellular basis of the efficacy of the trinuclear platinum complex BBR 3464 against cisplatin-resistant cells

Multinuclear platinum compounds have been designed to circumvent the cellular resistance to conventional mononuclear platinum-based drugs. In this study we performed a comparative study of cisplatin and of the triplatinum complex BBR 3464 in a human osteosarcoma cell system (U2-OS) including an in vitro selected cisplatin-resistant subline (U2-OS/Pt). BBR 3464 was extremely potent in comparison with cisplatin in U2-OS cells and completely overcame resistance of U2-OS/Pt cells. In both cell lines, BBR 3464 accumulation and DNA-bound platinum were higher than those observed for cisplatin. On the contrary, a low frequency of interstrand cross-links after exposure to BBR 3464 was found. Differently from the increase of DNA lesions induced by cisplatin, kinetics studies indicated a low persistence of interstrand cross-link formation for BBR 3464. Western blot analysis of DNA mismatch repair proteins revealed a marked decrease of expression of PMS2 in U2-OS/Pt cells, which also exhibited microsatellite instability. Studies on DNA mismatch repair deficient and proficient colon carcinoma cells were consistent with a lack of influence of the DNA mismatch repair status on BBR 3464 cytotoxicity. In conclusion, the cytotoxic potency and the ability of the triplatinum complex to overcome cisplatin resistance appear to be related to a different mechanism of DNA interaction (formation of different types of drug-induced DNA lesions) as compared to conventional mononuclear complexes.

Comparison of cytotoxicity and cellular accumulation of polynuclear platinum complexes in L1210 murine leukemia cell lines.

The antitumor activity of the trinuclear Phase I clinical agent, BBR3464, is matched by that of polyamine-linked dinuclear complexes. The cytotoxicity and cellular accumulation of three polynuclear platinum complexes: [¿trans-PtCl(NH3)2¿2 mu-¿trans-Pt(NH3)2(H2N(CH2)6-NH2)2¿]4+ (BBR3464), [¿trans-PtCl(NH3)2¿2(H2N(CH2)3NH2(CH2)4NH2)]3+ (BBR3571), and [¿trans-PtCl(NH3)2¿2(H2N(CH2)6-NH2)]2+ (BBR3005), were studied in a series of murine L1210 cell lines and compared with cisplatin. Besides murine L1210 cell lines sensitive (/0) and resistant (/DDP) to cisplatin, the efficacy of the compounds in a cell line rendered resistant to BBR3464 (/3464) was examined. Finally, to examine possible uptake pathways of these novel charged complexes, cytotoxicity in a cell line resistant to the polyamine synthesis inhibitor, methylglyoxal-bis(guanylhydrazone) (/MGBG), was studied. Cytotoxicity profiles of BBR3571 most closely matched that of BBR3464. Both agents showed significantly reduced cytotoxicity in L1210/ BBR3464. The cytotoxicity of neither agent was affected by the polyamine uptake-deficient cell line and indeed both complexes showed significantly enhanced cytotoxicity in L1210/MGBG relative to wild-type L1210/0. The cellular uptake of both BBR3464 and BBR3571 was enhanced in L1210/DDP. These studies suggest that the chemical feature of a diamine linker containing an internal charge contributes significantly to the anticancer profiles of both the trinuclear platinum complex, BBR3464, which incorporates a charged platinum into a diamine linker, and the dinuclear platinum complex, BBR3571, which incorporates only a naturally occurring polyamine as diamine linker.

Polynuclear platinum anticancer drugs are more potent than cisplatin and induce cell cycle arrest in glioma

We have evaluated the efficacy of the multinuclear platinum chemotherapeutics BBR3464, BBR3571, and BBR3610 against glioma cells in culture and animal models and investigated their mechanism of action at the cellular level. In a clonogenic assay, BBR3610, the most potent compound, had an IC90 dose (achieving 90% colony formation inhibition) that was 250 times lower than that of cisplatin for both LNZ308 and LN443 glioma cells. In subcutaneous xenografts of U87MG glioma cells, BBR3610 approximately doubled the time it took for a tumor to reach a predetermined size and significantly extended survival when these cells were implanted intracranially. Analysis of apoptosis and cell cycle distribution showed that BBR compounds induced G2/M arrest in the absence of cell death, while cisplatin predominantly induced apoptosis. Interestingly, the BBR compounds and cisplatin both induced extracellular signal-regulated kinase 1/2 phosphorylation, and inhibition of this pathway at the level of MEK antagonized the induction of G2/M arrest or apoptosis, respectively. Analysis of Chk1 and Chk2 status did not show any differential effects of the drugs, and it is thus unlikely to underlie the difference in response. Similarly, the drugs did not differentially modulate survivin levels, and knockdown of survivin did not convert the response to BBR3610 to apoptosis. Together, these findings support continued development of BBR3610 for clinical use against glioma and provide a framework for future investigation of mechanism of action.

NanoSIMS multi-element imaging reveals internalisation and nucleolar targeting for a highly-charged polynuclear platinum compound

Simultaneous multi-element imaging using NanoSIMS (nano-scale secondary ion mass spectrometry), exploiting the novel combination of (195)Pt and (15)N in platinum-am(m)ine antitumour drugs, provides information on the internalisation and subcellular localisation of both metal and ligands, and allows identification of ligand exchange.

Platinum complexes with one radiosensitizing ligand

Complexes of platinum II containing a single radiosensitizer ligand and an amino or ammine substituent shows superior binding to DNA and are useful in chemotherapy and sensitization of hypoxic tumors to radiation. The chemotherapeutic value of these compounds is enhanced by administration of vasoactive agents.

A comparison of DNA binding profiles of dinuclear platinum compounds with polyamine linkers and the trinuclear platinum phase II clinical agent BBR3464

Abstract. The DNA binding profiles of three bis Pt(II) polyamine-linked compounds, [{trans-PtCl(NH3)2}2{µ-spermine-N1,N12}]4+, [{trans-PtCl(NH3)2}2{µ-spermidine-N1,N8}]3+, and [{trans-PtCl(NH3)2}2{µ-BOC-spermidine}]2+, were compared with that of a novel trinuclear phase II clinical agent, [{trans-PtCl(NH3)2}2{µ-trans-Pt(NH3)2(H2N(CH2)6NH2)2}]4+. All of the compounds bind preferentially in a bifunctional manner, according to unwinding of supercoiled DNA circles. The kinetics of binding of these compounds corresponds to their relative charge (2+ to 4+). The preference for the formation of interstrand crosslinks, however, does not follow a charge-based pattern. By studying the results of DNA polymerase extension products on a DNA template modified by the compounds, and by incorporating the complementary method of RNA transcription mapping, it was possible to determine the nucleotide bases that are preferred sites of binding. The stop sites due to platinum adducts were determined, and some preliminary observations concerning the range and type of crosslinks were established. It can be concluded that dinuclear Pt compounds are similar to their trinuclear counterpart, and that charge differences do not contribute solely to the variances between the compounds.