Pharmacological and toxicological aspects of 4-demethoxy-3'-deamino-3'-aziridinyl-4'-methylsulphonyl-daunorubicin (PNU-159548): a novel antineoplastic agent.

4-demethoxy-3'-deamino-3'-aziridinyl-4'-methylsulphonyl-daunorubicin (PNU-159548) belongs to a novel class of antitumor compounds (termed alkycyclines) and is currently undergoing Phase II clinical trial. In the present study, we investigated the in vitro and in vivo antitumor activity, the pharmacokinetics, and the toxicological profile of this compound. PNU-159548 showed good cytotoxic activity in murine and human cancer cells growing in vitro, with an average concentration for 50% growth inhibition of 15.8 ng/ml. The drug showed strong antitumor efficacy in vivo after i.v. and p.o. administration against rapidly proliferating murine leukemias and slowly growing transplantable human xenografts. At non-toxic doses, PNU-159548 produced complete regression and cures in ovarian, breast, and human small cell lung carcinomas. Fourteen of 16 models studied, including colon, pancreatic, gastric, and renal carcinomas, astrocytoma and melanoma, were found to be sensitive to PNU-159548. In addition, PNU-159548 was effective against intracranially implanted tumors. Toxicological studies revealed myelosuppression as the main toxicity in both mice and dogs. The maximum tolerated doses, after a single administration, were 2.5 mg/kg of body weight in mice, 1.6 mg/kg in rats, and 0.3 mg/kg in dogs. In the cyclic studies, the maximum tolerated doses were 0.18 mg/kg/day (cumulative dose/cycle: 0.54 mg/kg) in rats and 0.05 mg/kg/day (cumulative dose/cycle: 0.15 mg/kg) in dogs. PNU-159548 showed minimal cardiotoxicity, when compared with doxorubicin in the chronic rat model at a dose level inducing similar myelotoxicity. Animal pharmacokinetics, carried out in mice, rats, and dogs, was characterized by high volumes of distribution, plasma clearance of the same order of the hepatic blood flow, and short terminal half-life. These findings support the conclusion that PNU-159548 is an excellent candidate for clinical trials in the treatment of cancer.

Phenyl sulfur mustard derivatives of distamycin A.

The design, synthesis, and cytotoxic activity of novel benzoyl and cinnamoyl sulfur mustard derivatives of distamycin A are described and structure activity relationships are discussed. These sulfur mustards are more potent cytotoxics than corresponding nitrogen mustards in spite of the lower alkylating power, while their sulfoxide analogues are substantially inactive. Cinnamoyl sulfur mustard derivative (7) proved to be one of the most active distamycin-derived cytotoxics, about 1000 times more potent than melphalan.

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.

The antitumor efficacy of cytotoxic drugs is potentiated by treatment with PNU 145156E, a growth-factor-complexing molecule.

PNU 145156E (formerly FCE 26644) is a noncytotoxic molecule whose antitumor activity is exerted through the formation of a reversible complex with growth/angiogenic factors, thus inhibiting their induction of angiogenesis. We studied in vitro and in vivo the activity of PNU145156E in combination with the four cytotoxic drugs doxorubicin, cyclophosphamide, methoxymorpholinyldoxorubicin (MMDX, FCE 23762, PNU152243), and 9-aminocamptothecin against M5076 murine reticulosarcoma. In vitro, PNU 145156E did not modify the cytotoxicity of the four drugs or the cell-cycle block induced by doxorubicin. In vivo, at the optimal dose of each compound, the antitumor activity was significantly increased in all combinations, with no associated increase in general toxicity being observed. In healthy mice treated with cyclophosphamide or doxorubicin the association with PNU 145156E did not enhance the myelotoxic effect induced by the two cytotoxics. These results indicate that two drugs affecting solid tumor growth through two different mechanisms-growth factor blockage and cell proliferation can be combined, resulting in increased antitumor efficacy with no additive toxicity.

Sequence-specific DNA alkylation of novel tallimustine derivatives.

Three different groups of analogs of the sequence-specific minor groove alkylator tallimustine (2) have been synthesized and investigated. Within group I, the dibromo nitrogen mustard (3) and the half-mustard (4) are more cytotoxic (IC50 = 0.6 and 40 ng/ml respectively) than tallimustine (IC50 = 50.3 ng/ml) against L1210 cells with high reactivity against the region 5'-TTTTGA. The diol derivative (6) and the difluoro nitrogen mustard (5) were not cytotoxic against L1210 cells and did not show any detectable DNA alkylation. The two compounds modified in the propionamidine terminus (7 and 8, group II), showed lower cytotoxic potency (IC50 = 130 and 94 ng/ml respectively) against L1210 cells than tallimustine (IC50 = 50.3 ng/ml) and a loss of in vitro sequence specificity for DNA alkylation. Considering the compounds in which the pyrrole rings were replaced by one (9) or two (10) pyrazole rings, compound 9 was not significantly cytotoxic against L1210 cell line and was apparently unable to produce alkylation on the DNA fragments tested, while compound 10 showed decreased cytotoxicity (IC50 = 114 ng/ml) and no modification in the pattern and intensity of DNA alkylation. The data obtained in this work suggest that it is possible to increase tallimustine potency by modifying the nitrogen mustard moiety. Moreover, the sequence specificity of DNA alkylation appears to be affected by the modification of the propionamidino moiety but not by the isosteric modification of the pyrrole rings. The correlation between cytotoxicity and alkylation pattern suggests that tallimustine exerts its cytotoxicity through DNA sequence-specific alkylation of the adenine located in the sequence 5'-TTTTGA.

Estimation of the haematological toxicity of minor groove alkylators using tests on human cord blood cells.

We evaluated the myelotoxicity and the anti-tumor potential of tallimustine, three of its analogues and carzelesin, with melphalan as reference substance. Tallimustine was tested by clonogenic assays on both human bone marrow (BM) and cord blood (hCB) cells, the other compounds on hCB only. The degree of inhibition of the haemopoietic progenitors GM-CFC, CFC-E and BFU-E was evaluated after exposure to different concentrations. The same schedules were tested on five tumour cell lines. We found that the dose-response curves for tallimustine on BM and hCB cells were similar. Carzelesin was shown to be the most potent of the substances tested and to be the one with the best in vitro therapeutic index; of the distamycin analogues, the one bearing an alpha-bromoacrylic group (FCE 25450) had the best index. For melphalan, tallimustine and carzelesin, the concentration inhibiting the growth of 70% of progenitor cells in vitro (ID70) was similar to the concentrations found in the serum of patients treated at the maximum tolerated dose (MTD). We conclude that hCB cells may be used instead of BM cells for in vitro myelotoxicity tests. Therapeutic indexes can be extrapolated from this model and could help in selecting the most promising analogue for further clinical development. The in vitro-active concentrations are similar to myelotoxic concentrations in patients, suggesting a predictive value for the assay.

Synthesis, solvolytic stability and cytotoxicity of a modified derivative of CPzI, a pyrazole analog of the alkylation subunit of the antitumor agent CC-1065: effect of the nitrogen substitution on the functional reactivity.

The synthesis and the comparative preliminary biological evaluation of a new pyrazole analog (16) of the CC-1065 alkylating unit (CPI) are described. This new derivative showed low cytotoxicity against L1210 murine leukemia (IC50 3064 nM) with respect to reference compound, but contrarily to literature data, was found to be more stable to solvolysis than the natural derivative (+/-)-N-Boc-CPI (pH 3, t1/2 = 212 h vs. 37 h). The results of such investigation showed that alkylation of the pyrazole nitrogen caused a loss of cytotoxic activity in vitro against tumor cells. This experimental observation allowed us to confirm the importance of free N-H for the anticellular activity.

The alkylating antitumor drug tallimustine does not induce DNA repair.

Tallimustine, an alkylating benzoyl mustard derivative of distamycin A (FCE 24517), is a novel anti-tumor agent. Both its cytotoxic activity against human LoVo cells and nicking efficiency on isolated plasmid DNA were studied in relation to hyperthermic treatment and compared to the effect of doxorubicin, a known non-alkylating anti-tumor agent. The results of this analysis indicate that the cytotoxic activity of tallimustine reflects its direct interaction with the DNA target. The ability of tallimustine to induce DNA repair in human primary normal fibroblasts was monitored by determining both the stimulation of unscheduled DNA synthesis (UDS) and the ability to reactivate a plasmid containing a reporter gene, treated in vitro with tallimustine, in comparison with the effect of UV-C irradiation. The results suggest that human cells able to repair UV-damage arc unable to overcome DNA damage induced by tallimustine. Therefore, the hypothesis that the biological activity of tallimustine is related to its alkylating properties is further supported by the temperature studies and strengthened by the observed inability of cells to repair tallimustine-induced DNA damage.

Morpholinylanthracyclines: cytotoxicity and antitumor activity of differently modified derivatives.

The relationship between different chemical modifications on morpholinylanthracyclines and their ability to overcome multidrug resistance (MDR) has been evaluated testing all compounds in vitro on LoVo and LoVo/DX human colon adenocarcinoma cells and in vivo disseminated P388 and P388/DX murine leukemias. Results obtained led us to the following conclusions: 1) the insertion of the morpholinyl or the methoxymorpholinyl group on position 3' of the sugar moiety confers the ability to overcome MDR in vitro and in vivo; conversely, 4' morpholinyl compounds are effective on MDR cells only in vitro and result inactive in vivo on DX-resistant leukemia; 2) all chemical modifications performed on 3' morpholinyl or methoxymorpholinyl derivatives, that is substitutions on the aglycone or on position 2 of the morpholino ring, do not interfere with the activity of the compounds: all derivatives present in fact the same efficacy on sensitive and resistant models. It is concluded that position 3' in the sugar moiety plays a crucial role in the ability of morpholinyl-anthracyclines to overcome MDR.

Decreased tyrosine phosphorylation in tumour cells resistant to FCE 24517 (tallimustine).

Resistance to FCE 24517 is not related to the emergence of any of the most frequently observed phenotypes. We have found that two resistant cell lines (L1210/24517 murine leukaemia and LoVo/24517 human colon adenocarcinoma) present congenital modifications in tyrosyl phosphatase and kinase activities. Moreover, the cytotoxic activity of FCE 24517 is increased in combination with a tyrosine phosphatase inhibitor and decreased in combination with protein kinase inhibitors, this being in agreement with the hypothesis that the activity of this drug is strictly dependent on the presence of tyrosine phosphorylated protein(s).

Flow cytometric detection of glutathione S-transferase isoenzymes by quantitative immunofluorescence under nonsaturating conditions.

The glutathione (GSH)-glutathione S-transferase (GST) detoxification system is an important element in cellular defence against injurious agents and anticancer drugs. GST isoenzymes may represent biochemical markers of neoplastic transformation, and, possibly, drug resistance is associated with altered GST-isoenzyme levels. The ability to measure GST-isoenzymes in cell populations would be useful for several biological and clinical applications. We have developed an immunofluorescence flow cytometric method for the simultaneous detection of different GST-isoenzymes and of DNA in fixed cells. Due to the impossibility of working under saturating conditions for the anti-GST antibody, a normalizing procedure was developed to permit quantitative analysis of single cells labelled with the anti-GST antibody at high dilution. A theoretical model and experimental data supported the use of this procedure. The method proposed is general and could be applied to other antibodies in order to obtain quantitative data outside saturating conditions. The method was challenged in different applications in order to compare it with other classical techniques. First, we characterized sublines resistant to different anticancer drugs with respect to variations of GST isotypes. In a second application, we studied the intercellular heterogeneity of GST content in mouse renal cells. In addition, GST was determined in aneuploid cells from solid tumor biopsies by separation from diploid cells on the basis of DNA content. Finally, GST distribution during cell-cycle progression was studied in two different cell lines by the biparametric analysis of GST/DNA.

Influence of structural modifications at the 3' and 4' positions of doxorubicin on the drug ability to trap topoisomerase II and to overcome multidrug resistance.

To better define the role of the amino sugar in the pharmacological and biochemical properties of anthracyclines related to doxorubicin and daunorubicin, we have investigated the effects of various substituents at the 3'- and 4'-positions of the drug on cytotoxic activity and ability to stimulate DNA cleavage mediated by DNA topoisomerase II. The study shows that the nature of the substituent at the 3'-position but not the 4'-position is critical for drug ability to form cleavable complexes. The amino group at the 3'-position is not essential for cytotoxic and topoisomerase II-targeting activities, because it can be replaced by a hydroxyl group without reduction of activity. However, the presence of bulky substituents at this position (i.e., morpholinyl derivatives) totally inhibited the effects on the enzyme, thus supporting previous observations indicating that the cytotoxic potencies of these particular derivatives are not related to topoisomerase II inhibition. This conclusion is also supported by the observation that 3'-morpholinyl and 3'-methoxymorpholinyl derivatives are able to overcome atypical (i.e., topoisomerase II-mediated) multidrug resistance. Because a bulky substituent at the 4'-position did not reduce the ability to stimulate DNA cleavage, these results support a critical role of the 3'-position in the drug interaction with topoisomerase II in the ternary complex. An analysis of patterns of cross-resistance to the studied derivatives in resistant human tumor cell lines expressing different resistance mechanisms indicated that chemical modifications at the 3'-position of the sugar may have a relevant influence on the ability of the drugs to overcome specific mechanisms of resistance.

Reversal of multidrug resistance by new dihydropyridines with low calcium antagonist activity.

The clinical use of Ca++ antagonist agents as modulators of multidrug resistance is limited by their strong vasodilator activity. This study reports data obtained by testing a series of new 1,4 dihydropyridine derivatives (DHPs) for their in vitro resistance modulating activity and their Ca++ antagonist effect. All the tested DHPs are active to increase doxorubicin activity with dose modifying factor values ranging between 2 and 47 on P388/DX cells and 12 and 36 on LoVo/DX cells. Their resistance modulating action is exerted through an increase of DX intracellular level. The Ca++ antagonist activity of DHPs, evaluated as capacity to inhibit the KCl-induced contractions in isolated Guinea pig ileum strips, is not related to their resistance modulating activity. This finding makes it possible to select, for further in vivo evaluations, compounds IX, X and XI, which have strong ability to overcome multidrug resistance and low Ca++ antagonist effect.

Growth-inhibitory properties of novel anthracyclines in human leukemic cell lines expressing either Pgp-MDR or at-MDR.

The objective of the experiments reported in this paper was the identification of promising anthracycline analogs on the basis of lack of cross-resistance against tumor cells presenting either P-glycoprotein multidrug resistance (Pgp-MDR) or the altered topoisomerase multidrug resistant (at-MDR) phenotype. Differently modified anthracycline analogs known to be active against MDR cells were assayed in vitro against CEM human leukemic cells, and the sublines CEM/VLB100 and CEM/VM-1 exhibiting respectively the Pgp-MDR and the at-MDR phenotype. Two classes of molecules, in which the -NH2 group in C-3' position is substituted with a morpholino, methoxymorpholino (morpholinyl-anthracycline), or an alkylating moiety, present equivalent efficacy in the drug-sensitive and the two drug-resistant sublines. These results indicate that such molecules may exert their cytotoxic effect through a mode of action different from that of "classical" anthracyclines and is not mediated through topoisomerase II inhibition. Both molecules represent novel concepts in the field of new anthracyclines derivatives.

Temperature influences both cytotoxicity and DNA nicking efficiency of the antitumor distamycin analogue FCE24517.

The number of DNA single strand breaks generated by FCE24517 increases exponentially while covalent adducts linearly accumulate at a higher rate. Kinetics studies indicate that the rate of DNA fragmentation is temperature-dependent. The sites of DNA strand breaks do not change in the 30-65 degrees C range. The cytotoxic potency of FCE24517 is also affected by temperature, since a shift up of 6 degrees C during the 4 h exposure of human colon carcinoma cells raises the cytotoxic efficiency fivefold. These results are consistent with the hypothesis that the biological activity of this new drug relates to its electrophilic properties.

Characterisation of a LoVo subline resistant to a benzoyl mustard derivative of distamycin A (FCE 24517).

Human colon adenocarcinoma cells (LoVo) resistant to the new antitumor agent FCE 24517 [benzoyl-mustard derivative of distamycin A] (LoVo/24517) are resistant to the selecting agent and related molecules as well as to vinblastine, with marginal or no resistance to other antitumour drugs. Treatment with verapamil, tamoxifen, nicergoline or cyclosporin A only partially restores the activity of FCE 24517 against LoVo/24517 cells. Such results suggest that resistance mechanisms possible specific for this class of compounds are operating.

Biological profile of FCE 24517, a novel benzoyl mustard analogue of distamycin A.

FCE 24157 (chemically (beta-[1-methyl-4-(1-methyl-4--[1-methyl-4-(4-N,N- bis(2-chloroethyl) amino-benzene-1-carboxy-amido) pyrrole-2-carboxiamido]pyrrole-2-carboxyamido)pyrrole-2-c arboxyamido]) propionamidine, hydrochloride) is a distamycin A (Dista A) derivative bearing a benzoyl mustard moiety instead of the formyl group at the N-terminal. Contrary to Dista A, FCE 24517 has been found to display potent cytotoxic activity on human and murine tumour cell lines. The compound maintains activity on melphalan (L-PAM)-resistant cells, whereas cross-resistance is observed on doxorubicin-(DX)-resistant cells. In vivo, FCE 24517 was found to possess evident antineoplastic activity on a series of murine transplanted solid tumours and human tumour xenografts. The following neoplasms were in fact found to be sensitive to FCE 24517 treatment: M14 human melanoma xenograft, N592 human small cell lung carcinoma, MTV murine mammary carcinoma, Colon 38 murine carcinoma, PO2 murine pancreatic carcinoma and M5076 murine reticulosarcoma. Lower effectiveness was observed against the murine P388 and Gross leukaemia, Lewis lung murine carcinoma, LoVo human colon carcinoma xenografts and A459 human lung adenocarcinoma. Against the murine L1210 leukaemia, FCE 24517 displayed a clear activity only when the tumour was transplanted i.p. and treatment was given i.p., whereas only marginal activity was seen against this leukaemia if transplanted i.v. and the drug was given i.v. As true also in vitro, FCE 24517 was effective against i.p. implanted L1210 leukaemia resistant to L-PAM. The mode(s) of action of this new compound is under active investigation.

Purine and 1-deazapurine ribonucleosides and deoxyribonucleosides: synthesis and biological activity.

A series of 6-(hydroxylamino)purine and -1-deazapurine nucleosides were synthesized and tested for their antitumor and adenosine deaminase inhibitory activity. All the examined molecules displayed an in vitro activity comparable to that of the reference compounds 6-(hydroxylamino)-9-beta-D-ribofuranosylpurine (HAPR) and ara-A, their ID50 ranging from 0.9 microM to approximately 100 microM. The 6-hydroxylamino derivatives of 1-deazapurine 9, 12, and 17 and also the blocked compound 13 are inhibitors of ADA whereas the purine derivatives 4 and 6 and the nitro compounds 11 and 16 are resistant to the enzyme. 7-(Hydroxylamino)-3-(2-deoxy-beta-D-erythro-pentofuranosyl)-3H-imi dazo[4,5- b]pyridine, the less cytotoxic but the most active ADA inhibitor in the series (Ki = 2.7 x 10(-7)), greatly potentiates the antitumor activity of ara-A in vitro.