Cristina Geroni

Formation and Antitumor Activity of PNU-159682, A Major Metabolite of Nemorubicin in Human Liver Microsomes

Purpose: Nemorubicin (3′-deamino-3′-[2″(S)-methoxy-4″-morpholinyl]doxorubicin; MMDX) is an investigational drug currently in phase II/III clinical testing in hepatocellular carcinoma. A bioactivation product of MMDX, 3′-deamino-3″,4′-anhydro-[2″(S)-methoxy-3″(R)-oxy-4″-morpholinyl]doxorubicin (PNU-159682), has been recently identified in an incubate of the drug with NADPH-supplemented rat liver microsomes. The aims of this study were to obtain information about MMDX biotransformation to PNU-159682 in humans, and to explore the antitumor activity of PNU-159682. Experimental Design: Human liver microsomes (HLM) and microsomes from genetically engineered cell lines expressing individual human cytochrome P450s (CYP) were used to study MMDX biotransformation. We also examined the cytotoxicity and antitumor activity of PNU-159682 using a panel of in vitro-cultured human tumor cell lines and tumor-bearing mice, respectively. Results: HLMs converted MMDX to a major metabolite, whose retention time in liquid chromatography and ion fragmentation in tandem mass spectrometry were identical to those of synthetic PNU-159682. In a bank of HLMs from 10 donors, rates of PNU-159682 formation correlated significantly with three distinct CYP3A-mediated activities. Troleandomycin and ketoconazole, both inhibitors of CYP3A, markedly reduced PNU-159682 formation by HLMs; the reaction was also concentration-dependently inhibited by a monoclonal antibody to CYP3A4/5. Of the 10 cDNA-expressed CYPs examined, only CYP3A4 formed PNU-159682. In addition, PNU-159682 was remarkably more cytotoxic than MMDX and doxorubicin in vitro, and was effective in the two in vivo tumor models tested, i.e., disseminated murine L1210 leukemia and MX-1 human mammary carcinoma xenografts. Conclusions: CYP3A4, the major CYP in human liver, converts MMDX to a more cytotoxic metabolite, PNU-159682, which retains antitumor activity in vivo.

Structure-activity relationship of novel distamycin a derivatives : synthesis and antitumor activity

Abstract Synthesis and biological evaluation of a group of distamycin A derivatives bearing new alkylating moietis is presented.

Cytotoxic α-bromoacrylic derivatives of distamycin analogues modified at the amidino moiety

Abstract The design, synthesis, in vitro and in vivo activities of novel α-bromoacrylic derivatives of distamycin A, modified at the amidino moiety by the replacement with basic or non-basic groups are reported. In spite of the relevance of these modifications of distamycin frame, the new derivatives are potent cytotoxics. The presence of the amidino moiety, is, therefore, not an absolute requirement for the activity. In particular due to a favorable myelotoxicity/cytotoxicity ratio, guanidino derivative PNU 166196 was selected for clinical development.

Cytotoxic halogenoacrylic derivatives of distamycin A

The design, synthesis, in vitro and in vivo activities of a series of halogenoacrylic derivatives of distamycin A are described. The structure-activity relationships indicate a key role of the reactivity of alpha-halogenoacrylic moiety. The reactivity and the putative alkylating mechanism of these compounds are different from those of the nitrogen mustards and possibly based on a Michael type reaction. This supports the hypothesis that these compounds represent a class of minor groove binders mechanistically different from tallimustine.

Novel benzoyl nitrogen mustard derivatives of pyrazole analogues of distamycin A: synthesis and antileukemic activity

The design and synthesis of novel benzoic acid mustard (BAM) derivatives of distamycin A bearing one or more pyrazole rings replacing the pyrrole rings of the latter are described. In vitro and in vivo activities against L1210 leukemia are reported and discussed. Some of these compounds show an activity profile comparable to tallimustine 1. All the compounds bearing the pyrazole ring close to the BAM moiety show reduced cytotoxicity in comparison to derivatives characterized by the BAM linked to a pyrrole: the same effect has not been observed when occurring at the amidine terminus of the oligopeptidic frame.

Down-regulation of the Nucleotide Excision Repair gene XPG as a new mechanism of drug resistance in human and murine cancer cells

BackgroundDrug resistance is one of the major obstacles limiting the activity of anticancer agents. Activation of DNA repair mechanism often accounts for increase resistance to cancer chemotherapy.ResultsWe present evidence that nemorubicin, a doxorubicin derivative currently in clinical evaluation, acts through a mechanism of action different from classical anthracyclines, requiring an intact nucleotide excision repair (NER) system to exert its activity. Cells made resistant to nemorubicin show increased sensitivity to UV damage. We have analysed the mechanism of resistance and discovered a previously unknown mechanism resulting from methylation-dependent silencing of the XPG gene. Restoration of NER activity through XPG gene transfer or treatment with demethylating agents restored sensitivity to nemorubicin. Furthermore, we found that a significant proportion of ovarian tumors present methylation of the XPG promoter.ConclusionsMethylation of a NER gene, as described here, is a completely new mechanism of drug resistance and this is the first evidence that XPG gene expression can be influenced by an epigenetic mechanism. The reported methylation of XPG gene could be an important determinant of the response to platinum based therapy. In addition, the mechanism of resistance reported opens up the possibility of reverting the resistant phenotype using combinations with demethylating agents, molecules already employed in the clinical setting.

Ongoing phase I and II studies of novel anthracyclines

Many anthracyclines are currently in clinical development with the common aim of improving selectivity. This could be achieved by improving tumor drug delivery through the identification and development of molecules with new structure, prodrugs with low molecular weight for selective release and activation, prodrugs with high molecular weight conjugated to antibody with active targeting or macromolecules with enhanced permeability and retention. There are still interfering factors to be defined, in particular chemical, with degradation steps in tumor tissues, biological, related to tumor proteases, pharmacological, with inter-individual tumor differences in the extent of accumulation. Another way to improve selectivity is to activate the drug at the tumor site, a good example of which is provided by Nemorubicin (2″-(S)-methoxymorpholinodoxorubicin hydrochloride) in hepatocellular carcinoma. The favorable characteristics of Nemorubicin in terms of broad spectrum of significant antitumor activity in liver malignancies models, lower cardiotoxicity than Doxorubicin, make Nemorubicin a promising third-generation anthracycline, suitable for intrahepatic administration.

Hematotoxicity on human bone marrow- and umbilical cord blood-derived progenitor cells and in vitro therapeutic index of methoxymorpholinyldoxorubicin and its metabolites

Purpose: MMDX {3′-deamino-3′-[2(S)-methoxy-4-morpholinyl] doxorubicin}, an anthracycline derivative active in vitro and in vivo against multdrug-resistant tumors, is currently under investigation in phase I clinical trials. In vivo it is metabolically activated, resulting in more cytotoxic compounds. We determined in vitro the toxic concentration of a 1-h period of exposure to doxorubicin (DX), MMDX, and bioactivated MMDX on hematopoietic progenitors and tumor cell lines. Methods: DX and MMDX were tested on both bone marrow- (BM) and cord blood (hCB)-derived clonogenic cells, whereas the metabolites were tested on hCB only. All substances were tested on seven tumor cell lines. Results: BM cells proved to be twice as sensitive as hCB cells to cytotoxics, and MMDX was twice as toxic as DX against hCB cells; MMDX activated with normal rat-liver microsomes and with dexamethasone-induced rat microsomes were, respectively, 70 and 230 times more toxic than MMDX. A comparison of the cytotoxic concentrations on hematopoietic progenitors and tumor cells, revealed that DX and MMDX had 5-fold stronger activity on tumor cell lines than on granulocyte/macrophage colony-forming cells (GM-CFCs), whereas bioactivated MMDX showed comparable cytotoxicity against tumor cells and hematopoietic progenitors. Conclusions: MMDX metabolites are very potent but display a lower degree of tumor selectivity than MMDX. Strategies to reduce MMDX metabolization should be developed to optimize the therapeutic index of this new anthracycline.

Brostallicin: a new concept in minor groove DNA binder development.

Brostallicin is a bromoacryloyl derivative of distamycin A, which has shown very promising preclinical activity against a variety of human tumors both in vitro and in vivo. The drug has a limited toxicity towards bone marrow precursor cells in vitro resulting in a therapeutic index much higher than those achieved with other distamycin A derivatives. It retains activity against cancer cells resistant to alkylating agents, topoisomerase I inhibitors and cells with mismatch repair deficiency. Brostallicin has a peculiar mechanism of action involving activation upon binding to glutathione (GSH) catalyzed by glutathione-S-transferase (GST). As a consequence, cells expressing relatively high GST/GSH levels are more susceptible to treatment with brostallicin. Considering that increased levels of GST/GSH are often found in human tumors, this could represent an advantage for the drug in the clinic. Initial clinical studies indicate the tolerability of the drug and allow the determination of the optimal dose for subsequent studies. Some partial response were obtained in these initial phase I studies. Altogether, the results suggest brostallicin to be a new promising anticancer agent with a new mechanism of action. It also raises the possibility to use it in combination with other anticancer drugs currently used.

Novel phenyl nitrogen mustard and half-mustard derivatives of amidino-modified distamycin

Abstract The design, synthesis, and in vitro and in vivo activities of novel benzoyl and cinnamoyl nitrogen mustard and half-mustard derivatives of distamycin A, in which the amidino moiety has been replaced by moieties of different physico-chemical features, are described and structure-activity relationships are discussed. Some amidino-modified derivatives show significant cytotoxicity and antileukemic activity.