Metal complexes of bleomycin: evaluation of [Rh-105]-bleomycin for use in targeted radiotherapy.

Bleomycin has been used as a carrier for several radioisotopes; however, its potential for clinical use has been limited either by the in vivo stability of the complexes or the half-life of the isotope used. The chemical, biological, and radiological properties of 105Rhodium appear to make it an ideal choice for targeted radiotherapy. The synthesis and purification of a hereto unreported 105Rhodium-bleomycin (105Rh-BLM) complex is described. The stability of this complex in plasma is sufficient to allow targeted delivery of the radioisotope. 57Cobalt-bleomycin was studied under identical conditions for comparative purposes. The suitability of 105Rh-BLM for targeted therapy, which appears to be limited by the renal clearance of this agent, is discussed.

In vitro circumvention of cisplatin resistance by the novel sterically hindered platinum complex AMD473.

A novel sterically hindered platinum complex, AMD473 [cis-aminedichloro(2-methylpyridine) platinum (II)], has been selected for phase I clinical trials due to commence in 1997. AMD473 was rationally designed to react preferentially with nucleic acids over sulphur ligands such as glutathione. This report documents the in vitro circumvention of acquired cisplatin resistance mechanisms in human ovarian carcinoma (HOC) cell lines by AMD473. In a panel of 11 HOC cell lines, AMD473 showed intermediate growth inhibition potency (mean IC50 of 8.1 microM) in comparison to cisplatin (mean IC50 of 2.6 microM) and carboplatin (mean IC50 of 20.3 microM). AMD473 showed only a 30.7-fold increase in IC50 value from the most sensitive to the most resistant HOC cell line, whereas for cisplatin it was 117.9-fold and for carboplatin 119.7-fold. AMD473 also showed significantly (P < 0.05) reduced cross-resistance to cisplatin in a panel of three cell lines with known acquired platinum drug resistance mechanisms (mean RF for AMD473 was 1.9, for cisplatin 9.1). Cellular accumulation of AMD473 was not reduced in two HOC cell lines (A2780cisR and 41McisR), in which reduced cisplatin accumulation is a major mechanism of acquired cisplatin resistance. AMD473 naked-DNA binding was significantly less affected (P < 0.05) than that of cisplatin by the presence of 5 mM glutathione. Also, AMD473 almost completely circumvented acquired cisplatin resistance in a cell line (A2780cisR) with fivefold elevated intracellular glutathione levels compared with the parent A2780 cell line when measured by clonogenic assay (RF 4.5 for AMD473 vs RF 18 for cisplatin). AMD473 also showed a lower increase in IC50 than cisplatin in an A2780 cell line model with artificially elevated glutathione levels. AMD473 DNA binding was slower than that of cisplatin on both naked and cellular DNA. AMD473 also formed DNA interstrand cross-links (ICLs) at a slower rate than cisplatin (peak ICL formation was at 5 h for cisplatin vs > or = 14 h for AMD473) after equitoxic doses were exposed to HOC cells for 2 h. AMD473 ICLs in the CH1 HOC cell line were slowly formed and showed no visible signs of being repaired 24 h after removal of drug. This was paralleled by a slower, longer lasting induction of p53 protein by equitoxic doses of AMD473 in HOC cell lines with wild-type p53. This new class of sterically hindered platinum compound, selected for clinical trial in 1997, may therefore elicit improved clinical response in intrinsically and acquired cisplatin-resistant tumours in the clinic.

Chemical, biochemical and pharmacological activity of the novel sterically hindered platinum co-ordination complex, cis-[amminedichloro(2-methylpyridine)] platinum(II) (AMD473).

cis-[Amminedichloro(2-methylpyridine)] platinum(II) (AMD473) is a novel sterically hindered anti-tumour compound designed to circumvent platinum drug resistance and is due to begin clinical trials in 1997. This paper reports the rationale behind the development of AMD473 with regard to its chemical and DNA binding properties. AMD473 circumvents resistance in vitro in acquired cisplatin resistant human ovarian carcinoma (HOC) cell line models (2 h SRB assay mean resistance factor = 2.8 +/- 1.2 microM for AMD473, versus 6.5 +/- 3.5 microM for cisplatin). AMD473 was chosen from a panel of sterically hindered 'pyridine platinum complexes' due to its reduced reactivity with sulphur ligands, unique DNA binding properties and ability to circumvent several of the major resistance mechanisms that manifest in cisplatin-resistant tumour cell lines. AMD473 hydrolyses more slowly (aquation rate = 1.47 +/- 0.32 x 10(-5) s-1 for AMD473 versus 2.98 +/- 0.6 x 10(-5) s-1 for cisplatin) in water than cisplatin and is also shown to have a reduced preference for reaction with soft nucleophiles such as sulphur ligands. Although AMD473 has similar DNA sequence specificity to cisplatin in DNA extracted from drug-treated tumour cells, several adducts unique to AMD473 were formed on naked plasmid DNA. AMD473 was shown to form DNA interstrand cross-links (ICLs) in both naked pBR322 plasmid and SKOV-3 cellular DNA, although AMD473 formed ICLs at a much slower rate than cisplatin. As steric hindrance was increased from AMD494 (unsubstituted pyridine) through AMD473 to AMD508 (2,6-dimethylpyridine), by addition of methyl groups on the pyridine ligand, cross-link formation rates became slower. By alkaline elution, at equimolar doses, AMD473 ICL formation after 24 h incubation was less than that of cisplatin after 4 h. Understanding the chemical and biochemical properties of these sterically hindered platinum complexes may aid the development of more novel platinum chemotherapeutic agents capable of further improving anti-tumour activity in resistant tumours.

Phase I and pharmacokinetic study of an oral platinum complex given daily for 5 days in patients with cancer.

PURPOSE: We aimed to determine the maximum-tolerated dose (MTD) clinical toxicities, pharmacokinetics, and pharmacodynamics of oral JM216 given once daily for 5 days to cancer patients. PATIENTS AND METHODS: Patients who fulfilled standard phase I trial criteria were enrolled. Oral JM216 was given at doses based on patient body-surface area, on an empty stomach, once daily for 5 consecutive days, as 10-, 50-, and 200-mg hard gelatin capsules and with oral antiemetics. The pharmacokinetics of platinum were studied on days 1 and 5 of the first treatment course using atomic absorption spectrophotometry (AAS). RESULTS: Thirty-two patients received 94 courses of oral JM216 at doses that ranged from 30 to 140 mg/m2 body-surface area for 5 consecutive days. The MTD was 140 mg/m2/d. The dose-limiting toxicities were thrombocytopenia and neutropenia. Hematotoxicity was reversible (nadir, 17 to 21 days; recovery, 28 days), noncumulative, and dependent on the dose and history of previous therapy. There were two instances of neutropenic sepsis. Two-thirds of patients experienced mild nausea, vomiting, or diarrhea. There was no ototoxicity, neurotoxicity, nephrotoxicity, or objective tumor responses. There was a significant correlation between JM216 dose and the day 1 and 5 plasma ultrafiltrate area under the concentration-time curve (AUC; r = .78), which indicates linear pharmacokinetics. There was considerable intersubject pharmacokinetic and pharmacodynamic variability, but a significant sigmoidal relationship between the plasma ultrafiltrate AUC and severity of thrombocytopenia (R2 = .83). CONCLUSION: We recommend JM216 doses of 100 and 120 mg/m2/d x 5 for previously treated and untreated patients, respectively, for phase II trials.

The synthesis of 191Pt labelled JM216, an orally active platinum anti-tumour agent.

The orally active platinum anti-tumour complex JM216[bis-acetatoamminedichlorocyclohexylamineplatinum(IV)] is at present in stage II clinical trials. A procedure for synthesising the complex labelled with 191Pt or 188Pt at the platinum centre has been developed. The purity (shown by HPLC) is 98% and the specific activity (0.3-0.4 Ci/kg) is enough for in vivo and in vitro studies.

cis-Amminedichloro(2-methylpyridine) platinum(II) (AMD473), a novel sterically hindered platinum complex: in vivo activity, toxicology, and pharmacokinetics in mice.

A novel sterically hindered platinum complex, AMD473 [cis-amminedichloro(2-methylpyridine) platinum(II)], designed primarily to be less susceptible to inactivation by thiols, has shown in vitro activity against several ovarian carcinoma cell lines. Notably, AMD473 has shown activity in vitro in human carcinoma cells that have acquired cisplatin resistance due to reduced drug transport (41M/41McisR) or enhanced DNA repair/increased tolerance of platinum-DNA adducts (CH1/CH1cisR). In this study, we show that AMD473, at its maximum tolerated dose of 35-40 mg/kg i.p. administration, produced marked in vivo antitumor activity against a variety of murine (ADJ/PC6 plasmacytoma, L1210 leukemia) and human ovarian carcinoma xenograft models, including several possessing acquired resistance to cisplatin [ADJ/PC6cisR, L1210cisR, CH1cisR, and HX110 (carboplatin-resistant)]. In the ADJ/PC6 model, an increased therapeutic index was noted following oral as opposed to i. p. administration. In a head-to-head comparison using CH1cisR xenografts and equitoxic doses (q7dx4 schedule), comparative growth delays were as follows: AMD473, 34 days; cisplatin, 10.4 days; carboplatin, 6.4 days; and JM216 (p.o. administration), 3.5 days (in a previous experiment, the trans-platinum complex JM335 induced a growth delay of 5.4 days against this model). In this model, oral activity was also noted with a growth delay of 34 days at 400 mg/kg every 7 days (total of four doses). In addition, AMD473 showed promising activity against CH1 xenografts that had regrown following initial treatment with cisplatin (additional growth delay of 30 days over that observed for retreatment with cisplatin). Across the whole panel of cisplatin-sensitive to cisplatin-resistant human ovarian carcinoma xenografts, AMD473 showed improved or at least comparable activity to that observed for an equitoxic dose (4 mg/kg) and schedule of cisplatin. Platinum pharmacokinetics showed that following i.v. administration of 20 mg/kg AMD473 in saline to Balb/c- mice bearing murine plasmacytoma (ADJ/PC6), a biexponential decay was observed in the plasma with a rapid distribution t1/2alpha of 24 min followed by a slow elimination t1/2beta of 44 h. Platinum accumulated in various organs with platinum tissue to plasma area under the curve ratios of 8.6 for liver and kidney, 5.7 for spleen, 3.7 for heart, 5.2 for lung, and 5 for tumor. The plasma and tissue concentration time curve following i.p. administration was similar to that observed following i.v. administration, with a bioavailability of 89%. When AMD473 was given p.o., the platinum absorption was rapid (K01 of 30 min) and the bioavailability was 40%. A less than proportional increase in area under the curve and Cmax was noted in tissue, plasma, and plasma ultrafiltrate following increasing oral doses of AMD473. In vitro, with AMD473, the rate of binding to different plasma proteins was approximately half of that of cisplatin. Following administration of 45 mg/kg i.p. in oil, 33% of the administered platinum was eliminated in the urine after 24 h, and 40% was eliminated after 72 h. Fecal recovery represented 13% of the administered dose after 3 days. Similar results were observed following oral and i.v. administration of 20 mg/kg, but significantly more was excreted in the feces (over 50% of the administered dose) following oral administration of 400 mg/kg, showing that absorption might be a limiting factor by this route of administration. The dose-limiting toxicity for AMD473 in mice was myelosuppression, and no renal toxicity was observed. The promising antitumor activity of AMD473, together with its lack of nephrotoxicity and favorable pharmacokinetic profile, suggests that AMD473 is a good candidate for clinical development. AMD473 is entering Phase I clinical trials under the auspices of the United Kingdom Cancer Research Campaign in 1997.

Ruthenium complexes as nitric oxide scavengers: a potential therapeutic approach to nitric oxide-mediated diseases.

1. Ruthenium(III) reacts with nitric oxide (NO) to form stable ruthenium(II) mononitrosyls. Several Ru(III) complexes were synthesized and a study made of their ability to bind NO, in vitro and also in several biological systems following expression of the inducible isoform of nitric oxide synthase (iNOS). Here we report on the properties of two, related polyaminocarboxylate-ruthenium complexes: potassium chloro[hydrogen(ethylenedinitrilo)tetraacetato]ruthenate+ ++ (=JM1226; CAS no.14741-19-6) and aqua[hydrogen(ethylenedinitrilo)tetraacetato]ruthenium (=JM6245; CAS no.15282-93-6). 2. Binding of authentic NO by aqueous solutions of JM1226 yielded a product with an infrared (IR) spectrum characteristic of an Ru(II)-NO adduct. A compound with a similar IR spectrum was obtained after reacting JM1226 with S-nitroso-N-acetylpenicillamine (SNAP). 3. The effect of JM1226 or JM6245 on nitrite (NO2-) accumulation in cultures of macrophages (RAW 264 line) 18 h after stimulating cells with lipolysaccharide (LPS) and interferon-gamma (IFNgamma) was studied. Activation of RAW264 cells increased NO2- levels in the growth medium from (mean+/-1 s.e.mean) 4.9+/-0.5 microM to 20.9+/-0.4 microM. This was blocked by actinomycin D (10 microM) or cycloheximide (5 microM). The addition of JM1226 or JM6245 (both 100 microM) to activated RAW264 cells reduced NO2- levels to 7.6+/-0.2 microM and 8.8+/-0.6 microM, respectively. N(G)-methyl-L-arginine (L-NMMA; 250 microM) similarly reduced NO2- levels, to 6.1+/-0.2 microM. 4. The effect of JM1226 or JM6245 on NO-mediated tumour cell killing by LPS+IFNgamma-activated macrophages (RAW 264) was studied in a co-culture system, using a non-adherent murine mastocytoma (P815) line as the 'target' cell. Addition of JM1226 or JM6245 (both 100 microM) to the culture medium afforded some protection from macrophage-mediated cell killing: target cell viability increased from 54.5+/-3.3% to 93.2+/-7.1% and 80.0+/-4.6%, respectively (n=6). 5. Vasodilator responses of isolated, perfused, pre-contracted rat tail arteries elicited by bolus injections (10 microl) of SNAP were attenuated by the addition of JM1226 or JM6245 (10(-4) M) to the perfusate: the ED50 increased from 6.0 microM (Krebs only) to 1.8 mM (Krebs + JM6245) and from 7 microM (Krebs only) to 132 microM (Krebs + JM1226). Oxyhaemoglobin (5 microM) increased the ED50 value for SNAP from 8 microM to 200 microM. 6. Male Wistar rats were injected with bacterial LPS (4 mg kg(-1); i.p.) to induce endotoxaemia. JM1226 and JM6245 (both 100 microM) fully reversed the hyporesponsiveness to phenylephrine of tail arteries isolated from animals previously (24 h earlier) injected with LPS. Blood pressure recordings were made in conscious LPS-treated rats using a tail cuff apparatus. A single injection of JM1226 (100 mg kg(-1), i.p.) administered 20 h after LPS (4 mg kg(-1), i.p.) reversed the hypotension associated with endotoxaemia. 7. The results show that JM1226 and JM6245 are able to scavenge NO in biological systems and suggest a role for these compounds in novel therapeutic strategies aimed at alleviating NO-mediated disease states.

Metabolism, protein binding and in vivo activity of the oral platinum drug JM216 and its biotransformation products.

This study evaluates the metabolism of the oral platinum drug JM216 [bis(acetato) amminedichloro (cyclohexylamine)platinum (IV)] following oral administration to Balb C- mice. JM216 was detectable 1 h post administration in mice but not in patients. Also, a late eluting metabolite observed in patients was not detected in mice. JM118 [amminedichloro(cyclohexylamine) platinum (II)], the platinum II species which is the major metabolite in patients was rapidly converted following i.v. administration to a compound having the same retention time as JM383 [bis(acetato)ammine(cyclohexylamine)dihydroxo platinum(IV)] indicating that the levels of JM383 following JM216 administration have probably been overestimated. The metabolite D observed in patients for which a structure has not been assigned, was also detected in mice. However, it did not originate from any of the identified biotransformation products. The protein binding evaluated in plasma, and buffer with physiological levels of albumin and globulin showed that only Platinum (II) species have significant binding and that Jm118 showed the same affinity to albumin and globulin (t 1/2 of 4.2 and 4.8 h) while cisplatin bound more readily to albumin (t 1/2 3.4 h) than globulin IV (t 1/2 8.2 h). JM216 itself failed to bind to either of the proteins tested indicating extensive reduction in patients, animals or plasma incubation medium. JM118 and JM518 [bis(acetato)amminechloro(cyclohexylamine) hydroxoplatinum (IV)] were significantly more active than the platinum IV complexes JM216 and JM383 when given i.p. to ADJ/PC6 plasmacytoma bearing mice (ED90 of 1.0 and 0.4 versus 5.7 and 4.2 mg/kg, TI (therapeutic index) of 14 and 37 versus 5.3 and 4.2). When given orally, JM216 was the most potent drug (ED90 of 5.8 versus 11,12 and 42 mg/kg and TI of 57 versus 12 12 and 16) for JM118 and JM383. There data indicates that JM216 biotransformation products are potent but that the levels of JM383 determined in our analytical conditions could have been overestimated.

Novel trans platinum complexes: comparative in vitro and in vivo activity against platinum-sensitive and resistant murine tumours.

Two pairs of cis/trans platinum complexes, JM118 (cis-ammine(cyclohexylamine) dichloro platinum(II)) and its trans counterpart, JM334 and JM149 (cis-ammine(cyclohexylamine) dichloro-dihydroxo platinum(IV)) and its trans counterpart JM335 have been evaluated (both in vitro and in vivo) against two murine tumour models of historical importance in the discovery of novel platinum drugs; the ADJ/PC6 plasmacytoma and the L1210 leukaemia and sublines selected for resistance to platinum drugs. In vitro, results showed that the trans complexes induced comparable growth inhibitory properties to those observed for cisplatin and their respective cis isomers. Moreover, retention of activity was observed in a series of 5 acquired platinum drug (cisplatin, carboplatin, iproplatin, tetraplatin and JM149)-resistant L1210 sublines whereas at least partial cross-resistance was observed to the cis isomer JM149 in the acquired carboplatin and iproplatin-resistant lines (in addition to being 11-fold resistant in the line selected for resistance to JM149 itself). In vivo, JM355 showed activity against both the ADJ/PC6 and L1210 models of acquired cisplatin resistance. Furthermore, JM355 was active against an ADJ/PC6 subline possessing resistance to iproplatin and a L1210 subline possessing resistance to its cis isomer JM149. Interestingly, the trans platinum(II) counterpart of JM335(JM334) was inactive in vivo. These data indicate that the trans platinum(IV) complex JM335 possess several in vitro growth inhibitory- and in vivo antitumour properties which are distinct from those observed for cisplatin (or its cis isomer). Thus, JM335 contravenes the original structure-activity rules determined for platinum-containing compounds and, because of its level of activity against cisplatin-resistant tumours, establishes the complex as of interest in the search for new platinum drugs active against cisplatin-resistant disease.

The tissue distribution in BALB/c mice of C-14-labeled JM216, an orally active platinum antitumour compound.

The ammine/amine platinum(IV) dicarboxylates have been developed as orally active platinum antitumor agents, and one of these, [PtCl2(NH3)(C6H11NH2) (OCOCH3)2] (JM216), is undergoing clinical trials at present. A synthesis method was developed to radiolabel JM216 with carbon 14 at the carboxylate carbon. The labeling efficiency was 92%, and the purity as shown by high-performance liquid chromathography (HPLC) was 96% after recrystallisation. The radiolabeled JM216 was given orally to BALB/c mice and detailed tissue-distribution data were obtained (blood plasma, kidney, liver, spleen, brain, lung, muscle and skin) for time points of 2 h and 2, 6 and 10 days. Comparison of these data with previously reported data for distribution of platinum obtained by atomic absorption spectroscopy has shown distinct differences, especially for the liver and the kidney. This clearly indicates a difference in behaviour between the labeled ligand and the platinum centre, suggesting detachment of the ligand in vivo.

Biotransformation of the platinum drug JM216 following oral administration to cancer patients.

This study evaluates the metabolic profile of JM216 [bis(acetato)ammine-dichloro(cyclohexylamine) platinum(IV)], the first orally administrable platinum complex, in plasma ultrafiltrates of 12 patients (n = 2-4 time points per patient) following different doses of drug (120, 200, 340, 420, 560 mg/m2). The biotransformation profile was evaluated by high-performance liquid chromatography (HPLC) followed by atomic absorption spectrophotometry (AA). The AA profiles were compared with those previously identified by HPLC on line with mass spectrometry (HPLC-MS) in plasma incubated with JM216. A total of six platinum peaks (Rt = 5.5, 7.2, 10.6, 12.4, 15.6, and 21.6 min, respectively) were observed in patients' plasma ultrafiltrate samples, of which only four appeared during the first 6 h post-treatment. Four of these coeluted with those observed and identified previously in plasma incubation medium. No parent JM216 was detected. The major metabolite seen in patients was the Pt II complex JM118 [cis-amminedichloro-(cyclohexylamine)platinum(II)] and was observed in all the patients. Interestingly, the second metabolite was shown to coelute with the Pt IV species JM383 [bis-acetatoammine(cyclohexylamine)dihydroxoplatinum (IV)]. Both JM118 and JM383 were identified by HPLC-MS in a clinical sample. Peak C, which was a minor product (less than 5% of the free platinum), coeluted with JM559 [bis-acetatoammine-chloro(cyclohexylalamine)hydroxoplatin um(IV)]. The cytotoxicity profile of all three metabolites in a panel of cisplatin-sensitive and -resistant human ovarian carcinoma cell lines was very close to that of the parent drug. In addition, the concentrations of JM118 reached in patients' plasma ultrafiltrate were comparable with the cytotoxic levels of the compound determined in the ovarian carcinoma panel of cell lines. Two metabolites were seen in patients but not in the in vitro incubation medium, suggesting the involvement of a possible enzymatic reaction. Thus, the biotransformation profile following oral administration of JM216 shows a variety of Pt(IV) and Pt(Il) metabolites in plasma that differ significantly from other systemically applied platinum drugs.

Determination of metabolites of a novel platinum anticancer drug JM216 in human plasma ultrafiltrates.

The present study describes the application of on-line liquid chromatography-electrospray ionisation in conjunction with a high resolution magnetic sector mass spectrometer to identify metabolites of a platinum(IV) anticancer drug JM216 [bis(acetato)amminedichloro(cyclohexylamine)platinum(IV)] in human plasma. Four metabolites were identified following incubation of JM216 in human plasma: JM118 [amminedichlorocyclohexylamineplatinum(II)], a platinum(II) complex; JM383 [bis(acetato)amminedihydroxo(cyclohexylamine)platinum(IV)]; JM518 [bis(acetato)amminechloro(cyclohexylamine)hydroxoplatinum (IV)] and its isomer JM559. The platinum complexes mass spectra were dominated by the natriated [M + Na]+ ion. Elemental compositions of these natriated ions were confirmed by accurate mass measurement on a magnetic sector mass spectrometer in the course of LC/MS analysis. This study demonstrates the capability of direct LC-ESI/MS with accurate mass measurement for analysis of platinum complexes in biological samples. Our results suggest that LC-ESI/MS is a powerful technique for structure elucidation of novel metabolites, and could make valuable contributions to drug metabolism research.

DNA-binding properties of novel cis- and trans platinum-based anticancer agents in 2 human ovarian carcinoma cell lines.

We have investigated the comparative initial DNA binding properties of 7 platinum-based anticancer drugs: 5 cis-oriented compounds, cisplatin, tetraplatin (Ormaplatin), JM118 [cis ammine dichloro (cyclohexylamine) platinum (II)], JM216 [bisacetato cis ammine dichloro (cyclohexylamine) platinum (IV)] and JM149 [cis ammine dichloro (cyclohexylamine) trans dihydroxo platinum (IV)], and 2 trans-oriented compounds, transplatin and JM335 [trans ammine dichloro (cyclohexylamine) dihydroxo platinum (IV)] in SKOV-3 and CHI human ovarian carcinoma cells. Unlike transplatin, the trans complex JM335 was comparably cytotoxic to its cis isomer JM149 and cisplatin. No significant correlation was observed between levels of total platinum bound to DNA after exposure to the 7 drugs and cytotoxicity in either cell line. Using a competitive enzyme-linked immunoabsorbent assay, DNA extracted from CH1 cells exposed to the 5 cis platinum drugs was recognized by the monoclonal antibody ICR4 (raised against DNA platinated by cisplatin) in the order JM118 > cisplatin > JM216 > tetraplatin > JM149; a strong positive correlation which just attained statistical significance was observed between recognition by ICR4 and cytotoxicity. In contrast, DNA extracted from CH1 cells exposed to the trans platinum drugs transplatin and JM335 was no more immunoreactive than control DNA. Using alkaline elution, interstrand cross-link levels after exposure to drug did not correlate with cytotoxicity in either cell line. The 5 cis drugs formed interstrand cross-links in both cell lines, whereas transplatin formed very low levels in SKOV-3 and undetectable levels in CH1. JM335 was efficient at forming interstrand cross-links in SKOV-3 but, notably, none were observed in CH1. In contrast, in the CH1 cells, single-strand breaks were observed with JM335 (but not with any other drug). The novel trans complex JM335 was unique, among the platinum drugs studied, in its ability to form both DNA interstrand cross-links and single strand breaks (DNA lesion formation being cell line dependent), a property which may account for its cytotoxicity.

Metabolic studies of an orally active platinum anticancer drug by liquid chromatography-electrospray ionization mass spectrometry.

Bis(acetato)amminedichloro(cyclohexylamine) platinum(IV) (JM216) is a new orally administered platinum complex with antitumor properties, and is currently undergoing phase II clinical trials. When JM216 was incubated with human plasma ultrafiltrate, 93% of the platinum species were protein-bound and 7% were unbound. The unbound platinum complexes in the ultrafiltrates of human plasma were analysed using a liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) method. Apart from the parent drug, four metabolites were identified and characterised. These include JM118 [amminedichloro(cyclohexylamine) platinum(II)], JM383 [bis(acetato)ammine(cyclohexylamine)dihydroxo platinum(IV)] and the two isomers JM559 and JM518 [bis(acetato)amminechloro(cyclohexylamine) hydroxo platinum(IV)]. Their elemental compositions were determined by accurate mass measurement during the LC analysis, to confirm their identities. Quantitation of these metabolites by off-line LC atomic absorption spectroscopy demonstrated that JM118 is the major metabolite in plasma from patients receiving JM216 treatment.

Synthesis and in vitro and in vivo antitumor activity of a series of trans platinum antitumor complexes.

The synthesis of a series of platinum complexes of trans coordination geometry [centered around the general formula, trans-ammine(amine)dichlorodihydroxoplatinum(IV) plus corresponding tetrachloroplatinum(IV) or Pt(II) counterparts] is described as part of a drug discovery program to identify more effective platinum-based anticancer drugs, particularly targeted toward the circumvention of resistance to cisplatin. Complexes have been evaluated for antitumor activity using in vitro and in vivo tumor models. In vitro against a panel of cisplatin-sensitive and -resistant human tumor cell lines (predominantly ovarian), many of the trans platinum complexes studied (e.g., 1, R = cyclohexyl) exhibited comparable potency to cisplatin and also overcame acquired cisplatin resistance, where resistance was due mainly to either reduced drug uptake or enhanced platinum-DNA adduct removal. Moreover, 14 trans complexes showed significant in vivo antitumor activity against the subcutaneous murine ADJ/PC6 plasmacytoma model; all were platinum(IV) complexes, 13/14 possessing axial hydroxo ligands the other possessing axial ethylcarbamato ligands. Where tested, all of their respective platinum(II) or tetrachloroplatinum(IV) counterparts were inactive. Notably, three dihydroxoPt(IV) complexes (18, 29, 34) (R = c-hexyl, c-heptyl, and 1-adamantyl) retained some efficacy against a cisplatin-resistant variant of the ADJ/PC6. Compounds 18 (trans-[PtCl2(OH)2NH3-(RNH2)]) R = c-C6H11, 22, R = Me3C, 27, R = n-C6H13, 28, R = PhCH2, and 36 (trans-[PtBr2(OH)2NH3(c-C6H11NH2)]) also produced evidence of antitumor activity (> 5 days growth delay) against subcutaneously grown advanced stage human ovarian carcinoma xenografts. These data demonstrate that a series of trans-ammine(amine)dichlorodihydroxoplatinum(IV) complexes are active in vivo against both murine and human subcutaneous tumor models and represent potential leads to a new generation of platinum-based anticancer drug.

Bis(acetato)amminedichloro(cyclohexylamine)platinum(IV), an orally active anticancer drug.

The structure of the anticancer drug bis(acetato)-amminedichloro(cyclohexylamine)platinum(IV), [PtCl2-(C2H3O2)2(C6H13N)(NH3)], is reported. The acetato groups are axial to the square plane composed of the chlorine and amine substituents. The cyclohexane ring may sterically hinder one of the acetato groups for metabolic attack. The amine groups are hydrogen bonded to the carbonyl O atoms of the acetato groups.

A phase I and pharmacology study of an oral platinum complex, JM216: dose-dependent pharmacokinetics with single-dose administration.

JM216 [bis-acetato-ammine-dichloro-cyclo-hexylamine-platinum (IV)] is an oral platinum complex with in vivo activity against murine and human tumor models and a lack of nephro- and neurotoxicity in rodents. During a phase I study of a single-dose schedule, JM216 was given in dry-filled hard gelatin capsules by mouth without hydration or diuresis. In all, 37 patients were given a total of 88 courses at doses ranging from 60 to 700 mg/m2. The study was stopped before the MTD was reached because of nonlinear pharmacokinetics. Myelosuppression was manifest by leucopenia or thrombocytopenia and showed marked variability at 420-700 mg/m2. Vomiting was mild and controllable by antiemetics in approximately 50% of courses. The onset of vomiting was delayed to 4 h after during ingestion. There was no nephro-, oto- or neuro-toxicity. A partial response was recorded in a patient with recurrent ovarian cancer, and significant falls in plasma tumour markers (CA125) were seen in two further cases. Plasma pharmacokinetics were linear and showed moderate interpatient variability at dose levels of < or = 120 mg/m2. At dose levels of > or = 200 mg/m2, Cmax and AUC increased less than proportionally to dose. This was associated with greater interpatient pharmacokinetic variability and reduced urinary platinum recovery. A significant sigmoidal relationship existed between ultrafilterable plasma AUC and the percentage of reduction in platelet count (r2 = 0.78). Nonlinear absorption was a limitation to this single-dose schedule of oral NM216; however, little non-haematological toxicity was seen at doses associated with myelosuppression and antitumour activity. Clinical studies of divided dose schedules using doses within the range of pharmacokinetic linearity (< or = 120 mg/m2) are now being investigated.

A novel trans-platinum coordination complex possessing in vitro and in vivo antitumor activity.

As part of a drug discovery program to discover more effective platinum-based anticancer drugs, a series of platinum complexes of trans coordination geometry centered on trans-ammine(cyclohexylaminedichlorodihydroxo)platinum(IV) (JM335) has been evaluated in vitro against a panel of cisplatin-sensitive and cisplatin-resistant human tumor cell lines (predominantly ovarian). In vitro, against 5 human ovarian carcinoma cell lines, JM335 was comparably cytotoxic to cisplatin itself and over 50-fold more potent than transplatin (mean 50% inhibitory concentrations: JM335, 3.1 microM; cisplatin, 4.1 microM; transplatin, 162 microM). With the use of seven pairs of human tumor cell lines (parent and subline with acquired resistance to cisplatin and encompassing all of the known major mechanisms of resistance to cisplatin) JM335 exhibited a different cross-resistance pattern to that of its cis isomer (JM149). JM335 showed non-cross-resistance in six of the seven resistant lines, cross-resistance in the A2780cisR line possibly being associated with high levels of glutathione. Preliminary intracellular DNA binding studies showed that in contrast to transplatin, JM335 was efficient at forming DNA-DNA interstrand cross-links. In vivo, JM335 produced growth delays in excess of 15 days against 4 of 6 human ovarian carcinoma xenografts and was unique among the complexes studied in retaining some efficacy against a cisplatin-resistant subline of the murine ADJ/PC6 plasmacytoma. JM335 is the first trans-platinum complex to demonstrate marked antitumor efficacy against both murine and human s.c. tumor models and represents a significant structural lead to complexes capable of circumventing cross-resistance to cisplatin.

Evaluation of novel ammine/amine platinum (IV) dicarboxylates in L1210 murine leukaemia cells sensitive and resistant to cisplatin, tetraplatin or carboplatin.

Seventeen alkylamine ammine dicarboxylatodichloroplatinum(IV) complexes of general structure c,t,c-[PtCl2(OCOR1)2NH3(RNH2)], where R = aliphatic or alicyclic and R1 = aliphatic or aromatic, have been evaluated against L1210 cell lines with acquired resistance to cisplatin (10-fold), tetraplatin (34-fold) or carboplatin (14-fold) using an in vitro growth-delay assay. All of these compounds overcame cisplatin, tetraplatin and carboplatin resistance. Potency increased as the number of carbon atoms in the axial aliphatic ligands (R1) increased, for example comparing JM216 (R = cyclohexyl, R1 = CH3, IC50 = 1.2 microM) with JM274 (R = cyclohexyl, R1 = n-C4H9, IC50 = 0.05 microM) against the parent sensitive line (L1210/S). The most active compounds were those possessing aromatic ligands at R1, regardless of whether R = aliphatic or alicyclic, for example JM244 (R = n-C3H7, R1 = C6H5, IC50 = 0.028 microM) and JM2644 (R = c-C6H11, R1 = C6H5, IC50 = 0.031 microM) against L1210/S. For an alicyclic alkylamine series in which R is varied from c-C3H7 to C-C7H13, with R1 = n-C3H7 for each compound, cytotoxic potency was maximised at c-C6H11 (JM221, IC50 = 0.06 microM against L1210/S). Preliminary biochemical studies, at equitoxic doses, comparing JM221 (0.1 microM) with cisplatin (0.6 microM) identified five times more platinum associated with JM221 treated cells and 1.5 times more platinum bound to the DNA of JM221-treated cells. The lipophilic properties of some of these platinum(IV) dicarboxylates may contribute to both the potency and circumvention of resistance by these compounds.