Cytotoxicity and cellular accumulation of a new cis-diammineplatinum (II) complex containing procaine in murine L1210 cells sensitive and resistant to cis-diamminedichloroplatinum (II)

Inhibition of cell growth, induction of apoptosis and mechanism of action of the novel platinum compound cis-diaminechloro-[2-(diethylamino) ethyl 4-amino-benzoate, N(4)]-chloride platinum (II) monohydrochloride monohydrate

Cis-diaminechloro-[2-(diethylamino) ethyl 4-amino-benzoate, N(4)]-chloride platinum (II) monohydrochloride monohydrate (DPR) is a new platinum triamine complex obtained from the synthesis of cisplatin and procaine. In this paper we analyzed, adopting a disease-oriented strategy, the tumour selectivity of this compound, its ability to induce apoptosis and its mechanism of interaction with DNA. The inhibition of cell proliferation was evaluated by the MTT assay using a panel of 51 tumour cell lines. Some of them were also evaluated for the induction of apoptosis by 4'-6-diamidine-2'-phenylindole (DAPI) staining, Western blot of p53 protein and agarose gel electrophoresis of ladder DNA. Finally, interstand cross-links (ISCL) were evaluated by ethidium bromide fluorescence technique. When evaluated by the MTT assay, DPR showed a high selective activity for neuroblastoma, small cell lung cancer (SCLC), ovarian cancer and leukemia cell lines. The comparison of mean graphs of DPR and cisplatin suggested that our compound possesses a mechanism of action similar to that, at least in part, of its parent compound. Moreover, DPR showed itself to be a good trigger of programmed cell death, as demonstrated by DAPI staining, activation of p53 protein and agarose gel electrophoresis of ladder DNA. Finally, the study of the formation of ISCLs demonstrated that DPR, despite being a monofunctional platinum compound, is able to form bifunctional adducts through the release of procaine residue. Data presented here suggest that DPR is an antitumour agent able to trigger apoptosis, and that it is endowed with a peculiar mechanism(s) of action and a special selective activity against two tumours, namely neuroblastoma and SCLC, which are still characterized by a low incidence of long-term survivors.

Transplacental passage of Pt after treatment with the new triamine complex cis-diaminechloro-[2-(diethylamino) ethyl 4-amino-benzoate, N4]-chloride platinum (II) monohydrochloride monohydrate

Cis-diaminechloro-[2-(diethylamino) ethyl 4-amino-benzoate, N4]-chloride platinum (II) monohydrochloride monohydrate (DPR) is a monofunctional Pt triamine complex synthesized starting from cisplatin and procaine hydrochloride, characterized by a good antitumor activity coupled with low toxic effects and able to impair prenatal development of mice but at doses outside or just in the upper range of therapeutic doses. In the present paper the transplacental passage of DPR-derived Pt was investigated in CD1 mice on days 9, 13, 16 and 18 of pregnancy, 24 h after ip administration of 21 mg/kg DPR. For comparison, groups of mice were treated with an equivalent Pt-containing dose of cisplatin (10.7 mg/kg). Similarly to cisplatin, small amounts of Pt were detected in fetuses on day 9. From day 13 of gestation the concentration of DPR- and cisplatin-derived Pt increased up to the highest fetal concentrations detected on day 16. On day 18 the concentration of Pt decreased. Most importantly, on days 13-18 of pregnancy cisplatin-derived Pt was always significantly higher than that assayed after DPR administration. In addition, on day 13 of pregnancy Pt exposure of fetuses was significantly higher when dams were treated with cisplatin (AUC(0.5-24)= 3.40 vs. 4.95 microg.h/g). Finally, it is worth noting that serum decay of Pt after DPR or cisplatin administration in adult female mice was similar with AUC0.13-2h s of 7.5 and 6.6 microg.h/ml, respectively. When we determined the concentration of Pt into the main organs of fetuses from dams treated with either DPR or cisplatin on day 18 of gestation, we observed a different organ distribution. In fact, while the concentration of DPR-derived Pt was greater in the heart (1.08+/-0.30 vs. 0.78 +/- 0.35 microg/g, p <0.10), an opposite situation was found in the kidney (0.51+/-0.20 vs. 0.69 +/- 0.22 microg/g, p <0.05). In conclusion, our data show that DPR may pass through the placenta with an efficiency significantly lower than that of cisplatin. This finding may represent one of the possible causes of the lower embryotoxic/teratogenic effect of DPR as compared to cisplatin.

Preclinical in vitro evaluation of hematotoxicity of the cisplatin-procaine complex DPR

We evaluated in vitro the inhibitory effect of cis-diaminechloro-[2-(diethylamino) ethyl 4-amino-benzoate, N4]-chlorideplatinum(II) monohydrochloride monohydrate (DPR) on colony formation by granulocyte/macrophage (CFU-GM) peripheral blood progenitor cells, representing a method to quantitate the toxicity of drugs to the hematopoietic system, and human leukemic cell lines. The results were compared with those obtained exposing cells to cisplatin and carboplatin. Our data showed that while DPR had a significantly better cytotoxic activity than cisplatin and carboplatin against HL60 and K562, and than carboplatin against Molt 4 cells, it showed 12 and 43 times less inhibitory effect on CFU-GM than cisplatin and carboplatin, respectively. These results suggest that the myelosuppressive activity of DPR could be lower than that of cisplatin and carboplatin, and, furthermore, that leukemic cells represent a preferential target for its cytotoxic activity compared to normal committed hemopoietic progenitor cells. All our results speak in favor of a better therapeutic index for DPR than for the other platinum compounds considered here.

Reduction of cisplatin hepatotoxicity by procainamide hydrochloride in rats

In preceding papers, we proposed that procainamide hydrochloride, a class I antiarrhythmic agent, was able to protect mice and rats from cisplatin-induced nephrotoxicity and that it could exert its action through accumulation in kidneys followed by coordination with cisplatin (or its hydrolysis metabolites) and formation of a less toxic platinum compound similar to the new platinum(II) triamine complex cis-diamminechloro-[2-(diethylamino)ethyl 4-amino-benzoate, N4]-chlorideplatinum(II) monohydrochloride monohydrate, obtained by the reaction of cisplatin with procaine hydrochloride. Hepatotoxicity is not considered as a dose-limiting toxicity for cisplatin, but liver toxicity can occur when the antineoplastic drug is administered at high doses. Here, we report that procainamide hydrochloride, at an i.p. dose of 100 mg/kg, reduces cisplatin-induced hepatotoxicity, as evidenced by the normalization of plasma activity of glutamic oxalacetic transaminase and gamma-glutamyl transpeptidase, as well as by histological examination of the liver tissue. Twenty-four hours after i.p. treatment with the combination of 7.5 mg/kg cisplatin and 100 mg/kg procainamide, a significant increase of procainamide (+56%, P<0.05), total platinum (+31%, P<0.05), platinum-DNA adducts (+31%, P<0.05) and percent DNA-DNA interstrand cross-links (+69%, P<0.02) was found in liver tissue, as compared to animals treated with cisplatin alone. Moreover, in accordance with these findings, we also observed a slightly lower concentration and cumulative excretion of platinum in the feces. Since mitochondrial injury is considered a central event in the early stages of the nephrotoxic effect of cisplatin, the distribution of platinum in these subcellular organelles obtained from hepatocytes was determined after treatment with cisplatin with or without procainamide hydrochloride, together with platinum concentration in their cytosolic fraction. Our data show that the coadministration of procainamide hydrochloride produced a rearrangement of subcellular platinum distribution in hepatocytes with a slight decrease in mitochondria (-15%, P<0.10) and a slight increase in the cytosolic fraction (+40%, P<0.10) of platinum content, compared to the treatment with cisplatin alone. In analogy with our previous results in the kidney, confirmed here by our data in vitro, we suggest that the hepatoprotective activity of procainamide hydrochloride is linked to the formation of a less toxic platinum complex, which leads to inactivation of cisplatin itself and/or its highly toxic hydrolysis metabolites and to a different subcellular distribution of platinum.

Activity and DNA binding of new organoamidoplatinum (II) complexes

Two series of organoamidoplatinum (II) complexes were synthesized [Class 1, Pt(NRCH2)2L2 and Class 2, Pt(NRCH2CH2NR2')L(X)] and their antitumour activity examined by a range of in vitro, cellular and animal studies. All Class 1 compounds exhibited activity comparable to cisplatin in mouse leukemia L1210 cells, but were at least 8-fold more active against the cisplatin-resistant L1210/R line. The lead compound 1a (R=p-HC6F4) caused nearly complete tumour regression in the ADJ/PC6 mouse tumour model. Compound 1a exhibited similar DNA reactivity to cisplatin, resulting in virtually identical DNA sequence specificity as cisplatin, and had similar time and concentration dependency of interstrand crosslinks. Compared with cisplatin, la showed 3-fold greater cellular uptake into human ovarian carcinoma 2008 cells, and this was dramatically enhanced to 17-fold in the cisplatin-resistant 2008/R line. The activity of 1a, therefore, appears to be due at least in part to a greater cellular uptake into tumour cells, particularly cisplatin-resistant cells, and once in the cell it reacts with DNA in a similar manner to that of cisplatin. The enhanced uptake and enhanced cytotoxicity of Class 1 compounds, and 1a in particular, may be due to a greater hydrophobicity compared with cisplatin. The activity of the Class 2 compounds, especially in the cisplatin-resistant cell lines, is unusual because they have trans amine ligands, and further study of both classes of compounds is warranted.

Effect of the cisplatin-procaine complex DPR in combination with several anticancer agents on murine P388 leukemic cells in vitro and in vivo

We evaluated in vitro the antiproliferative activity of DPR (Fig. 1), a new cisplatin-derived compound, in combination with five conventional anticancer drugs: the antimetabolites 5-fluorouracil (5FU) and methotrexate (MTX), the alkylating agent mitomycin C (MMC), the antimicrotubule agent taxol (TAX) and the intercalating agent of the antracycline group doxorubicin (DOX), against murine P388 leukemic cells. MTT assay was used to determine growth inhibition after incubation of cells for 72 hours in the presence of single or combined drugs. The additive, synergistic or antagonistic nature of the combined drug effect was determined using the isobole method. In our cellular model, synergism was the prevailing result observed when DPR was combined with MMC. Conversely, antagonism was observed when DPR was combined with TAX. When DPR was administered together with the other antineoplastic drugs, the final effect was dependent on the concentrations of single agents. The study in vitro of the association between DPR and MMC was extended in vivo in BDF-1 female mice bearing i.p. P388 leukemic cells. Our data in vivo confirmed those obtained in vitro, demonstrating the therapeutic advantage of the association of ineffective doses of DPR (2 and 7 mg/kg) and MMC (3.2 mg/kg) over the administration of MMC alone.

Cisplatin combined with the new cisplatin-procaine complex DPR: in vitro and in vivo studies

The administration of combinations of platinum compounds is considered as a useful alternative therapeutic strategy to avoid the complications of toxic events during cancer chemotherapy in order to obtain a therapeutic advantage. On the basis of previous in vitro and in vivo findings, suggesting an antitumour activity of the new cisplatin-derived compound cis-diamminechloro-[2-(diethylamino)ethyl 4-amino-benzoate, N4]-chlorideplatinum(II) monohydrochloride monohydrate (DPR), we investigated the effectiveness of the combination of cisplatin (DDP) and DPR in vitro on murine leukaemic cells, which were either sensitive (P388) or resistant (L1210/DDP) to DDP, and on the murine M5076 reticulum cell sarcoma, and in vivo in BDF1 female mice transplanted with P388 leukaemic cells or cisplatin-resistant L1210/DDP leukaemic cells. The contemporaneous exposure in vitro to both platinum compounds gave a significantly higher cell growth inhibition than that expected on the basis of dose-response curves for single agents in all tumour models tested. In vivo, the combinations of DDP plus DPR elicited significant enhancement over the activity of the drugs alone both in the ascitic and solid P388 models. The combined treatment of 10 mg/kg DDP and 14 mg/kg DPR yielded 62.5% tumour-free mice compared with 6.2% with 10 mg/kg DDP alone, the best single agent. It is noteworthy that the combined application of DDP and DPR was also very effective in the solid cisplatin-resistant L1210/DDP model, inducing a significant reduction in the volume of tumour. A therapeutic advantage was achieved with combination treatments that had no effect on platinum-mediated body weight loss and were generally well tolerated by the mice. At equitoxic concentrations of DPR and carboplatin, the treatment with DDP plus DPR proved to have a higher efficacy against this tumour model compared to that observed after the combined treatment with DDP and carboplatin. In summary, the combination of DDP and DPR showed a therapeutic advantage over single drug treatment and has demonstrated promise at the preclinical level in its ability to circumvent acquired resistance to DDP both in vitro and in vivo.

Comparison of the toxicities of cisplatin and a new cisplatin-procaine complex to rat renal cortical slices

1. Procaine has previously been shown to diminish the nephrotoxicity of cisplatin and the nephrotoxic effects of cisplatin and a new cisplatin complex (cis-diamminechloro-[2-(diethylamino) ethyl-4-aminobenzoate, N4]-chlorideplatinum (II) monohydrochloride monohydrate; DPR), that contains procaine hydrochloride were compared with rat renal cortical slices. 2. Cisplatin at 1 mM caused toxicity to the slices, as shown by an increase in the leakage of aspartate aminotransferase and lactate dehydrogenase from the slices into the incubation medium and a decrease in the reduction of a tetrazolium dye (MTT assay). Addition of procaine (1 mM) protected against cisplatin-induced toxicity. DPR either at 1 mM or at 4 mM had no effect either on the enzyme leakage or MTT reduction by the renal slices, but DPR at 10 mM produced a similar magnitude of enzyme leakage to cisplatin (1 mM). 3. DPR lowered the concentration of ATP and glutathione (GSH) in the slices but was less potent than cisplatin. Thiobarbituric acid reactive substances, indicators of lipid peroxidation, released into the medium were increased by the highest concentration of DPR (10 mM), which suggests that DPR has the potential to cause oxidative stress. 4. The results suggest that DPR was far less toxic than either cisplatin alone or a mixture of cisplatin and procaine.

Purification and characterization of acetylcholinesterase from desert cobra (Walterinnesia aegyptia) venom

Acetylcholinesterase (AChE) has been identified and purified from the venom of desert cobra (W aegyptia) to apparent homogeneity using a TSK G 3000 SW gel filtration column and a Mono Q anion-exchange column. AChE was purified to homogeneity as established by sodium dodecylsulfate/polyacrylamide gel electrophoresis. The specific activity of AChE was 357 IU/mg with acetylthiocholine iodide as substrate. The denatured W aegyptia venom AChE displayed a molecular mass of 67000 +/- 3000 Da suggesting it was a single polypeptide. Isoelectric focusing of AChE revealed that the enzyme exists in different isoforms, with isoelectric points ranging between pH 7.4-7.9. The kinetic parameters (Km and Vmax) and IC50 of AChE inhibition by procaine, tetracaine and physostigmine were investigated in the present study.