Experimental solid tumour activity of N-[2-(dimethylamino)ethyl]-acridine-4-carboxamide

DNA-Binding Anticancer Drugs: One Target, Two Actions

Amsacrine, an anticancer drug first synthesised in 1970 by Professor Cain and colleagues, showed excellent preclinical activity and underwent clinical trial in 1978 under the auspices of the US National Cancer Institute, showing activity against acute lymphoblastic leukaemia. In 1984, the enzyme DNA topoisomerase II was identified as a molecular target for amsacrine, acting to poison this enzyme and to induce DNA double-strand breaks. One of the main challenges in the 1980s was to determine whether amsacrine analogues could be developed with activity against solid tumours. A multidisciplinary team was assembled in Auckland, and Professor Denny played a leading role in this approach. Among a large number of drugs developed in the programme, N-[2-(dimethylamino)-ethyl]-acridine-4-carboxamide (DACA), first synthesised by Professor Denny, showed excellent activity against a mouse lung adenocarcinoma. It underwent clinical trial, but dose escalation was prevented by ion channel toxicity. Subsequent work led to the DACA derivative SN 28049, which had increased potency and reduced ion channel toxicity. Mode of action studies suggested that both amsacrine and DACA target the enzyme DNA topoisomerase II but with a different balance of cellular consequences. As primarily a topoisomerase II poison, amsacrine acts to turn the enzyme into a DNA-damaging agent. As primarily topoisomerase II catalytic inhibitors, DACA and SN 28049 act to inhibit the segregation of daughter chromatids during anaphase. The balance between these two actions, one cell cycle phase specific and the other nonspecific, together with pharmacokinetic, cytokinetic and immunogenic considerations, provides links between the actions of acridine derivatives and anthracyclines such as doxorubicin. They also provide insights into the action of cytotoxic DNA-binding drugs.

Synthesis of 9-Aminoacridine Derivatives as Anti-Alzheimer Agents

In the present study, some 9-aminoacridine derivatives have been synthesized by condensation of 9-aminoacridine with substituted phenacyl, benzoyl, and benzyl halides (RM1-RM6). Compounds were investigated for acetylcholinesterase and butyrylcholinesterase inhibition potential, considering these enzymes playing a key role in Alzheimer's disease. All derivatives showed better inhibition of enzymes than the standard galantamine, whereas except RM4, all exhibit better results than tacrine, a well-known acridine derivative used for the treatment of Alzheimer's disease.

Novel DNA topoisomerase IIα inhibitors from combined ligand- and structure-based virtual screening

DNA topoisomerases are enzymes responsible for the relaxation of DNA torsional strain, as well as for the untangling of DNA duplexes after replication, and are important cancer drug targets. One class of topoisomerase inhibitors, “poisons”, binds to the transient enzyme-DNA complex which occurs during the mechanism of action, and inhibits the religation of DNA. This ultimately leads to the accumulation of DNA double strand breaks and cell death. Different types of topoisomerases occur in human cells and several poisons of topoisomerase I and II are widely used clinically. However, their use is compromised by a variety of side effects. Recent studies confirm that the inhibition of the α-isoform of topoisomerase II is responsible for the cytotoxic effect, whereas the inhibition of the β-isoform leads to development of adverse drug reactions. Thus, the discovery of agents selective for topoisomerase IIα is an important strategy for the development of topoisomerase II poisons with improved clinical profiles. Here, we present a computer-aided drug design study leading to the identification of structurally novel topoisomerase IIα poisons. The study combines ligand- and structure-based drug design methods including pharmacophore models, homology modelling, docking, and virtual screening of the National Cancer Institute compound database. From the 8 compounds identified from the computational work, 6 were tested for their capacity to poison topoisomerase II in vitro: 4 showed selective inhibitory activity for the α- over the β-isoform and 3 of these exhibited cytotoxic activity. Thus, our study confirms the applicability of computer-aided methods for the discovery of novel topoisomerase II poisons, and presents compounds which could be investigated further as selective topoisomerase IIα inhibitors.

Tumour tissue selectivity in the uptake and retention of SN 28049, a new topoisomerase II-directed anticancer agent

PURPOSE

A variety of anticancer drugs, including doxorubicin and mitoxantrone, have structures in which a DNA-intercalating chromophore is linked to a positively charged side chain. These drugs generally inhibit tumour growth and survival by poisoning the enzyme DNA topoisomerase II. SN 28049, a benzonaphthyridine derivative with these properties, has curative activity against the Colon 38 tumour in mice. Previous pharmacokinetic studies have demonstrated tumour-selective retention with approximately 20-fold higher area under the concentration-time curve (AUC) for tumour tissue as compared to normal tissues. We have investigated here whether such retention is tumour specific.

METHODS

Plasma and tissue pharmacokinetics were assessed in the murine Lewis lung (LL3) tumour in C57 BL/6 mice and in xenografts of the NZM4, NZM10 and NZM52 human melanoma lines in Balb/c Rag-1 immunodeficient mice. The in vitro cellular localisation of SN 28049 in murine and human cell lines was studied by confocal fluorescence microscopy.

RESULTS

A 260-fold variation, from 8.9 μM h (NZM4) to 2,334 μM h (Colon 38), was found among the different tumours. Only small variations were observed in the corresponding plasma AUC (2.9-5 μM h). Moreover, in vivo activity, as measured by tumour growth delay, varied from 1 day (NZM4) to curative (Colon 38), consistent with the tumour pharmacokinetic data. In cultured cell lines, SN 28049 was found in cytoplasmic bodies, suggesting that drug sequestration could contribute to tumour pharmacokinetics.

CONCLUSION

SN 28049 shows dramatic differences in both tumour AUC and antitumour activity against different tumours. These differences point to the presence of a tumour-specific uptake and retention mechanism.

Novel activity of acriflavine against colorectal cancer tumor cells

A high-throughput screen of the cytotoxic activity of 2000 molecules from a commercial library in three human colon cancer cell lines and two normal cell types identified the acridine acriflavin to be a colorectal cancer (CRC) active drug. Acriflavine was active in cell spheroids, indicating good drug penetration and activity against hypoxic cells. In a validation step based on primary cultures of patient tumor cells, acriflavine was found to be more active against CRC than ovarian cancer and chronic lymphocytic leukemia. This contrasted to the activity pattern of the CRC active standard drugs 5-fluorouracil, irinotecan and oxaliplatin. Mechanistic studies indicated acriflavine to be a dual topoisomerase I and II inhibitor. In conclusion, the strategy used seems promising for identification of new diagnosis-specific cancer drugs.

Intracellular trafficking as a determinant of AS-DACA cytotoxicity in rhabdomyosarcoma cells

BACKGROUND

Rhabdomyosarcoma (RMS) is a malignant soft tissue sarcoma derived from skeletal muscle precursor cells, which accounts for 5-8% of all childhood malignancies. Disseminated RMS represents a major clinical obstacle, and the need for better treatment strategies for the clinically aggressive alveolar RMS subtype is particularly apparent. Previously, we have shown that the acridine-4-carboxamide derivative AS-DACA, a known topoisomerase II poison, is potently cytotoxic in the alveolar RMS cell line RH30, but is 190-fold less active in the embryonal RMS cell line RD. Here, we investigate the basis for this selectivity, and demonstrate in these RMS lines, and in an AS-DACA- resistant subclone of RH30, that AS-DACA-induced cytotoxicity correlates with the induction of DNA double strand breaks.

RESULTS

We show that inhibition of the multidrug-resistance associated protein (MRP1) has no effect on AS-DACA sensitivity. By exploiting the pH-dependent fluorescence properties of AS-DACA, we have characterized its intracellular distribution, and show that it concentrates in the cell nucleus, as well as in acidic vesicles of the membrane trafficking system. We show that fluorescence microscopy can be used to determine the localization of AS-DACA to the nuclear and cytoplasmic compartments of RMS cells grown as spheroids, penetrance being much greater in RH30 than RD spheroids, and that the vesicular signal leads the way into the spheroid mass. EEA1 and Rab5 proteins, molecular markers expressed on early-endosomal vesicles, are reduced by >50% in the sensitive cell lines.

CONCLUSION

Taking the evidence as a whole, suggests that endosomal vesicle trafficking influences the toxicity of AS-DACA in RMS cells.

Molecular modeling study of intercalation complexes of tricyclic carboxamides with d(CCGGCGCCGG)₂ and d(CGCGAATTCGCG)₂

Tricyclic dyes with different mesoatoms such as xanthenes (fluorescein, eosin) anthracenes and acridines (proflavine) approved by the Food and Drug Administration (FDA) for use in foods, pharmaceuticals and cosmetic preparations interact with DNA, and some of them do so through intercalation. Hyperchem 7.5, Spartan 04, Yasara 10.5.14 program packages and molecular modeling, molecular mechanics and dynamics techniques with the oligonucleotides d(CCGGCGCCGG)2 and d(CGCGAATTCGCG)2 were utilized in order to examine the mode of binding to DNA of a range of tricyclic carboxamides bearing N,N-dimethylaminoethyl side chain, i.e., 9-amino-DACA, anthracene, acridine-1-carboxamide, acridine-4-carboxamide (DACA), azacridine, phenazine, pyridoquinoxaline, oxopyridoquinoxaline, phenoxazine and xanthenone or N,N-dimethylaminobutyl moiety, i.e., phenazine and acridine. The bicyclic quinoline-8-carboxamide was also examined for comparison reasons. On the basis of our data, prerequisite for the interaction between protonated N,N-dimethylaminoethyl moiety and guanine is the formation of only one internal hydrogen bond between carboxamide and peri NH + in the case of 9-amino-DACA or peri N in the cases of DACA, azacridine, phenazine and pyridoquinoxaline. The presence of an additional internal hydrogen bond between oxygen carboxamide and protonated N,N-dimethylamino group in the cases of tricyclic systems bearing peri NH (phenoxazine) or O (xanthenone) group, prevents the interaction between side chain and guanine. Also, the formation of one internal hydrogen bond between oxygen carboxamide and protonated N,N-dimethylamino group inhibits the interaction between side chain and guanine in the case of acridine-1-carboxamide. Our findings are in accordance with previously reported results obtained from the kinetic studies of the binding of acridine and related tricyclic carboxamides to DNA.

In vivo and in vitro assessment of the action of SN 28049, a benzonaphthyridine derivative targeting topoisomerase II, on the murine Colon 38 carcinoma

AIM

SN 28049 (N-[2-(dimethylamino)ethyl]-2,6-dimethyl-1-oxo-1,2-dihydrobenzo[b]-1,6-naphthyridine-4-carboxamide) is a new DNA binding drug that targets topoisomerase II. SN 28049 is curative against the murine Colon 38 adenocarcinoma (CT38) while etoposide, another topoisomerase II-directed drug, shows minimal activity; we investigated the basis for this difference in vivo and in vitro.

METHODS

Colon 38 tumours were grown in C57Bl mice and in immunodeficient mice. Tumour sections were examined by staining and TUNEL assays. A new cell line (Co-38P) derived from the in vivo tumour was developed and responses were analysed using flow cytometry.

RESULTS

Both SN 28049 and etoposide induced similar tumour histological changes, reducing mitotic index and increasing apoptotic index 8 h after administration. At later times however, SN 28049-treated tumours showed further progressive morphological changes while etoposide-treated tumours reverted to their original growth characteristics. The effects of SN 28049 on tumour growth were delayed and attenuated when Colon 38 tumours were grown in immunodeficient mice. SN 28049 and etoposide both induced dose-dependent increases of γ-phosphorylation of histone H2AX and cell cycle perturbation of the Co-38P cell line, indicative of DNA damage, although SN 28049 had 30-fold higher activity. Following 1-hour drug exposure of Co-38P cells, SN 28049 was more effective that etoposide in inducing persistent cycle arrest for the same degree of DNA damage.

CONCLUSION

The superior antitumour activity of SN 28049 may result from its ability to induce long term cycle arrest. Host immune responses contribute to the curative activity of SN 28049 and this could result from the induction of cycle arrest.

Mechanism of interaction of small transcription inhibitors with DNA in the context of chromatin and telomere

Small molecules from natural and synthetic sources have long been employed as human drugs. The transcription inhibitory potential of one class of these molecules has paved their use as anticancer drugs. The principal mode of action of these molecules is via reversible interaction with genomic DNA, double and multiple stranded. In this article we have revisited the mechanism of the interaction in the context of chromatin and telomere. The established modes of association of these molecules with double helical DNA provide a preliminary mechanism of their transcription inhibitory potential, but the scenario assumes a different dimension when the genomic DNA is associated with proteins in the transcription apparatus of both prokaryotic and eukaryotic organisms. We have discussed this altered scenario as a prelude to understand the chemical biology of their action in the cell. For the telomeric quadruplex DNA, we have reviewed the mechanism of their association with the quadruplex and resultant cellular consequence.

Action of SN 28049, a new DNA binding topoisomerase II-directed antitumour drug: comparison with doxorubicin and etoposide

AIM

We have examined the cellular action of SN 28049 (N-[2-(dimethylamino)ethyl]-2,6-dimethyl-1-oxo-1,2-dihydrobenzo[b]-1,6-naphthyridine-4-carboxamide), a DNA binding drug with curative activity against the Colon 38 transplantable murine carcinoma, on human tumour cells. Its action has been compared with that of two topoisomerase II-targetted drugs, etoposide and doxorubicin.

METHODS

The NZM3 melanoma and HCT116 colon carcinoma cell lines, each expressing wild-type p53, were cultured and responses were compared by flow cytometry, electrophoresis, microscopy, and growth of tumour xenografts.

RESULTS

Responses of NZM3 cells to all three drugs, as measured by histone H2AX γ-phosphorylation, induction of the p53 pathway and cell cycle arrest, were comparable and typical of those of topoisomerase II poisons. Xenografts of NZM3 cells responded to SN 28049 with a tumour growth delay of 16 days. In contrast, HCT116 cells had an attenuated DNA damage response to the drugs and SN 28049 had no in vivo activity, consistent with low topoisomerase II activity. However, SN 28049 inhibited HCT116 cell growth in vitro and activated the p53 pathway to induce a state with G(2)/M-phase DNA content, low mitotic index and a high proportion of binucleate cells. Treated cells expressed cyclin E and the senescence marker β-galactosidase but showed low expression of cyclin B and survivin. In comparison, etoposide caused little p53 expression or cycle arrest, and doxorubicin had an intermediate effect.

CONCLUSION

The action of SN 28049 in NZM3 cells is typical of a topoisomerase II poison, but the low topoisomerase IIα activity of HCT116 cells allowed the detection of a second antiproliferative action of SN 28049 in which cells undergo post-mitotic cycle arrest and induction of p53.

In vitro assessment of novel transcription inhibitors and topoisomerase poisons in rhabdomyosarcoma cell lines

PURPOSE

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children. Current chemotherapy regimes include the topoisomerase II poison etoposide and the transcription inhibitor actinomycin D. Poor clinical response necessitate identification of new agents to improve patient outcomes.

METHODS

We assessed the in vitro cytotoxicity (MTT assay) of DNA intercalating agents in five established human RMS cell lines. These include novel classes of transcription inhibitors and topoisomerase poisons, previously shown to have potential as anti-cancer agents.

RESULTS

Amongst the former agents, bisintercalating bis(9-aminoacridine-4-carboxamides) linked through the 9-position, and bis(phenazine-1-carboxamides) linked via their side chains, are compared with established transcription inhibitors. Amongst the latter, monofunctional acridine-4-carboxamides related to N-[2-(dimethylamino)ethyl]acridine-4-carboxamide, DACA, are compared with established topoisomerase poisons.

CONCLUSIONS

Our findings specifically highlight the topoisomerase poison 9-amino-DACA, its 5-methylsulphone derivative, AS-DACA, and the bis(phenazine-1-carboxamide) transcription inhibitor MLN944/XR5944, currently in phase I trial, as candidates for further research into new agents for the treatment of RMS.

The role of topoisomerases and RNA transcription in the action of the antitumour benzonaphthyridine derivative SN 28049

PURPOSE

SN 28049 (N-[2-(dimethylamino)ethyl]-2,6-dimethyl-1-oxo-1,2-dihydrobenzo[b]-1,6-naphthyridine-4-carboxamide) is a DNA intercalating drug that binds selectively to GC-rich DNA and shows curative activity against the Colon 38 adenocarcinoma in mice. We wished to investigate the roles of topoisomerase (topo) I, topo II and RNA transcription in the action of SN 28049.

METHODS

We used clonogenic assays to study the cytotoxicity of SN 28049; RNA interference and enzyme assays to examine the role of topo I in SN 28049 action; 3H uridine incorporation and reporter assays to study its effects on transcription; and RT-PCR to examine its ability to reduce endogenous h-TERT expression.

RESULTS

In clonogenic assays, SN 28049 showed a biphasic cytotoxic dose response curve in H460 cells typical of acridine derivatives such as N-[2-(dimethylamino)ethyl]acridine-4-carboxamide (DACA) although it was approximately 16-fold more potent. Down-regulation of topo IIalpha in HTETOP cells reduced the cytotoxicity of SN 28049, establishing its action as a topo IIalpha poison. Surprisingly, down-regulation of topo I in H460 cells by RNA interference sensitised them to the actions of SN 28049 and other topo II poisons. SN 28049 also inhibited topo I-mediated relaxation of supercoiled plasmid DNA. SN 28049 was also an inhibitor of transcription in HEK293 cells and was more potent at reducing luciferase expression from a GC-rich SP-1 binding promoter than from a non-GC-rich AP-1 binding promoter. The drug also reduced luciferase reporter gene expression driven by the SP-1-binding survivin promoter as well as reducing endogenous h-TERT expression in HEK293 cells whose promoter also contains SP-1 binding sites.

CONCLUSION

We conclude that SN 28049 has a complex action that may involve poisoning of topo IIalpha, suppression of topo I and inhibition of gene transcription from promoters with SP-1 sites. These actions may contribute to the promising experimental solid tumour anticancer activity of SN 28049.

Synthesis and cytotoxic activities of 8-alkyl or 8-aryl-8,9-dihydro-7H-isoindolo[5,6-g]quinoxaline-7,9-diones

A series of 8-alkyl- and 8-aryl-8,9-dihydro-7H-isoindolo[5,6- g]quinoxaline-7,9-diones were synthesized using sultine chemistry as a key step in good yield. These compounds were evaluated for their in vitro cytotoxicity against six human cancer cell lines (HCT15, SK-OV-3, A549, SNB19, MCF7 and MCF7/ADR).

QSAR analysis of substituted bis[(acridine-4-carboxamide)propyl]methylamines using optimized block-wise variable combination by particle swarm optimization for partial least squares modeling

In the current work, we employed optimized block-wise variable combination (OBVC) by particle swarm optimization (PSO) based on partial least squares (PLS) modeling for variable combination and compared it to the traditional methods. It has been demonstrated that the modified PSO is a useful tool for searching optimized variable combination. Quantitative structure-activity relationship (QSAR) model has been formulated for a set of DNA binding topoisomerase (topo) (substituted bis[(acridine-4-carboxamide)propyl]methylamines) on murine Lewis lung carcinoma (LL(c)) cells. The spatial descriptors especially Jurs descriptors play important roles in predicting the compound's inhibitory activity to murine LL(c) cells, and polar interactions are the principal binding strength between compounds and murine LL(c) cells. In addition, rotatable bonds in molecules and molar refractivity of the compounds will markedly affect the compounds' inhibitory activity.

Synthesis and cytotoxic activity of carboxamide derivatives of benzo[b][1,6]naphthyridin-(5H)ones

A previous reaction leading to 2-substituted 6-methyl-1-oxo-1,2-dihydrobenzo[b][1,6]naphthyridine-4-carboxylic acids has been extended to encompass a broad range of 2-substituents. Derived carboxamides, particularly 4-N-[2-(dimethylamino)ethyl], were tested for growth inhibitory properties. Potent cytotoxicity against murine P388 leukemia and Lewis lung carcinoma (LLTC) was retained for compounds bearing a remarkably diverse range of 2-substituents with a number having IC50 values <10 nM. Five of the new compounds were tested in vivo against subcutaneous colon 38 tumors in mice; a single dose (1.8 mg/kg) proved curative for the 2-(4-fluorophenyl) derivative, a further increase in potency over the very effective 2-methyl analogue reported previously.

Synthesis andin vitro cytotoxicity of 1,3-dioxoindan-2-carboxylic acid arylamides

A series of 1,3-dioxoindan-2-carboxylic acid arylamides were synthesized and evaluated for in vitro cytotoxicity against four human cancer cell lines (HOP62, SK-OV-3, MD-MB-468 and T-47D). The most active was compound 3e (1.2 microM against SK-OV-3 cell line) bearing a 4-methyl substituent.

Synthesis of C8-linked pyrrolo[2,1-c][1,4]benzodiazepine-acridone/acridine hybrids as potential DNA-binding agents

Pyrrolobenzodiazepine hybrids linked to acridone/acridine ring systems at C8-position have been designed and prepared that exhibit significant DNA-binding affinity, and a representative compound shows promising in vitro anticancer activity.

NF-kappa B activation in vivo in both host and tumour cells by the antivascular agent 5,6-dimethylxanthenone-4-acetic acid (DMXAA)

5,6-Dimethylxanthenone-4-acetic acid (DMXAA), a new anticancer agent developed in this centre, has an antivascular action and causes regression of transplantable murine tumours that is mediated partially by the intratumoral production of tumour necrosis factor (TNF). DMXAA activates the nuclear factor-kappaB (NF-kappaB) transcription factor, which is involved in TNF synthesis and has also been suggested to mediate resistance to TNF. We wished to determine whether tumour cell NF-kappaB activation modulated the in vitro and in vivo effects of DMXAA. We compared the response of the 70Z/3 pre-B lymphoma cell line with that of its mutant 1.3E2 sub-line, which has a defective gamma-subunit of IKK, the kinase that phosphorylates IkappaB leading to NF-kappaB activation. As shown by electrophoretic mobility shift assays (EMSAs), DMXAA induced in vitro translocation of NF-kappaB (p50 and p65 subunits) into the nucleus of 70Z/3 cells, but not of 1.3E2 cells. However, when the cell lines were then grown as subcutaneous tumours in mice and treated with DMXAA (25 mg/kg), activation of NF-kappaB was found in nuclear extracts prepared from both 70/Z3 and 1.3E2 tumours, as well as from Colon 38 tumours that were used for comparison. This suggests that DMXAA induces NF-kappaB responses in host components of the tumour. Tumours grown from both 70Z/3 and 1.3E2 cells were found to regress completely following DMXAA treatment. Thus, the antitumour action of DMXAA appears to be independent of the ability of the target tumour cell population to induce NF-kappaB expression. Moreover, activation of NF-kappaB in the tumour cell did not confer resistance to DMXAA-induced therapy.

Synthesis and cytotoxic activity of carboxamide derivatives of benzo[b][1,6]naphthyridines

The reaction of 4-dimethylaminomethylene-6-methyl-4H-pyrano[4,3-b]quinoline-1,3-dione with a range of primary amines gave rise to a series of 2-substituted 6-methyl-1-oxo-1,2-dihydrobenzo[b][1,6]naphthyridine-4-carboxylic acids. The derived 4-N-[2-(dimethylamino)ethyl]carboxamides were tested for growth inhibitory properties against murine P388 leukemia, Lewis lung carcinoma (LLTC), and human Jurkat leukemia cell lines. Most compounds were potent cytotoxins, with some having IC(50) values less than 10 nM. Five were tested in vivo against subcutaneous colon 38 tumors in mice, and a single dose (3.9 mg/kg) proved to be curative for the 2-methyl and 2-(3,4-dimethoxyphenyl) derivatives in this refractory model.

Use of positron emission tomography in pharmacokinetic studies to investigate therapeutic advantage in a phase I study of 120-hour intravenous infusion XR5000

PURPOSE

XR5000 (N-[2-(dimethylamino)ethyl]acridine-4-carboxamide) is a topoisomerase I and II inhibitor. Because the cytotoxicity of XR5000 increases markedly with prolonged exposure, we performed a phase I study of weekly XR5000 by 120-hour continuous infusion over 3 weeks.

PATIENTS AND METHODS

Twenty-four patients with advanced solid cancer were treated at seven dose levels (700 to 4,060 mg/m2/120 hrs) for a total of 67 cycles. Three patients underwent positron emission tomography (PET) studies at the maximum-tolerated dose (MTD) to evaluate normal tissue and tumor carbon-11 radiolabeled XR5000 ([11C]XR5000) pharmacokinetics.

RESULTS

The dose-limiting toxicity was National Cancer Institute Common Toxicity Criteria (version 1) grade 4 chest and abdominal pain affecting the single patient receiving 4,060 mg/m2/120 hours, and the MTD was 3,010 mg/m2/120 hours. Other grade 3-4 toxicities, affecting single patients at the MTD, were myelosuppression (grade 4), raised bilirubin, vomiting, and somnolence (all grade 3). There was one partial response (adenocarcinoma of unknown primary); the remainder had progressive disease. [11C]XR5000 distributed well into the three tumors studied by PET. Tumor uptake (maximum concentration or area under the concentration versus time curve [AUC]) was less than in normal tissue in which the tumors were located. Tumor exposure (AUC; mean +/- SD in m2/mL/sec) increased when [(11)C]XR5000 was administered during an infusion of XR5000 (0.242 +/- 0.4), compared with [11C]XR5000 given alone (0.209 +/- 0.04; P <.05), indicating that tumor drug exposure was not saturated [corrected].

CONCLUSION

The recommended dose for XR5000 in phase II studies is 3,010 mg/m2/120 hours. PET studies with 11C-labeled drug were feasible and demonstrated in vivo distribution into tumors. Saturation of tumor exposure was not reached at the MTD.

Synthesis and antitumor activity of conjugates of muramyldipeptide or normuramyldipeptide with hydroxyacridine/acridone derivatives

A series of MDP (muramyldipeptide) or nor-MDP (normuramyldipeptide) analogues modified at the C-terminus post of the molecule by a formation of an ester bond between the carboxylic group of isoglutamine and the hydroxyl function of the respective derivatives of 4-carboxamide-acridine/9-acridone or 1-nitro-9-hydroxyalkylaminoacridines were synthesized as potential anticancer agents. The compounds O-(1-O-benzyl-N-acetyl-muramyl-l-alanyl-d-gamma-isoglutaminyl)-9-(ethylamino)-1-nitroacridine ester 3j and O-(1-O-benzyl-N-acetyl-muramyl-l-alanyl-d-gamma-isoglutaminyl)-9-propylamino-1-nitroacridine ester 3k exhibited high in vitro cytotoxic activity against a panel of human cell lines, prostate cancer and AIDS-related lymphoma (ARL). Analogue 3j was also active in vivo in the hollow fiber assay. Antitumor activity of both compounds were tested in vivo against difference human tumor xenograft, but only analogue 3k showed in vivo activity against sc UACC-62 melanoma in mice.

Synthesis and cytotoxic activity of N-(2-diethylamino)ethylcarboxamide and other derivatives of 10H-quindoline

A series of mono- and dimeric N-methylquindoline carboxamides were prepared by Friedlander condensation between methyl 2-amino-3-formyl benzoate and 3-acetoxy-1-acetylindoles, followed by exhaustive methylation with methyl iodide to give N-methylquindoline esters. Direct amination of these, or hydrolysis to the acids and amine coupling via intermediate imidazolides gave the desired carboxamides. The compounds were evaluated in a panel of cell lines in culture. The monomeric compounds showed similar structure-activity relationships to the known indeno[1,2-b]quinolines, with a 4-methyl group increasing potency several-fold. Bis analogues linked through the carboxamide were more cytotoxic than the corresponding monomers in the human leukemia lines, but N-N linked dimers were generally less potent, except for a tetracationic derivative. The most potent monomeric analogue showed moderate growth delay (ca. 5 days) against sub-cutaneously implanted colon 38 tumors in mice.

Kinetic studies of the binding of acridinecarboxamide topoisomerase poisons to DNA: implications for mode of binding of ligands with uncharged chromophores

We have used stopped-flow spectrophotometry and the sodium dodecyl sulfate sequestration technique to study the kinetics of dissociation of DNA complexes of the mixed topoisomerase I/II poison N-[2-(dimethylamino)ethyl]acridine-4-carboxamide (termed DACA) and a range of related linear tricyclic carboxamides with neutral chromophores. Complexes of DACA and related acridine and phenazinecarboxamides bearing an N,N-dimethylaminoethyl side chain dissociate from calf thymus DNA by a kinetic pathway involving four discernible steps in a manner similar to complexes of N-[(2-dimethylamino)ethyl]-9-aminoacridine-4-carboxamide (termed 9-amino-DACA). We infer from these findings that the side chains of DACA, its phenazine homologue, and 9-amino-DACA make comparable interactions with the DNA base pairs. In the case of 9-amino-DACA, a selective topoisomerase II poison, these are known, by crystallographic analysis, to involve hydrogen-bonding interactions between the protonated dimethylammonium group of the side chain and the O6/N7 atoms of guanine and to include a bridging water molecule hydrogen bonded to the carboxamide group and a phosphate oxygen. By contrast, we find that other linear tricyclic carboxamides with neutral chromophores which lack a peri nitrogen atom and are biologically inactive dissociate from DNA by a different mechanism in which it appears their side chains fail to interact with guanine. We conclude that the ability of the carboxamide group to lie preferentially in the plane of the chromophore, so facilitating the dimethylammonium-guanine hydrogen bond and ensuring maintenance of the water-bridged carboxamide-phosphate interaction, is a critical requirement for antitumor activity among ligands of the linear tricyclic carboxamide class. However, unlike the situation for 9-amino-DACA, for ligands with uncharged chromophores containing peri nitrogen atoms such as DACA, this outcome is possible with the 4-carboxamide group rotated cis or trans with respect to the ring nitrogen. This difference may have relevance to the ability of DACA to be a dual poison of both topoisomerases I and II.

Crystal structure of 9-amino-N-[2-(4-morpholinyl)ethyl]-4-acridinecarboxamide bound to d(CGTACG)2: implications for structure-activity relationships of acridinecarboxamide topoisomerase poisons

The structure of the complex formed between d(CGTACG)2 and 9-amino-N-[2-(4-morpholinyl)ethyl]-4-acridinecarboxamide, an inactive derivative of the antitumour agents N-[2-(dimethylamino)ethyl]acridine-4-carboxamide (DACA) and 9-amino-DACA, has been solved to a resolution of 1.8 A using X-ray crystallography. The complex crystallises in the space group P6(4 )and the final structure has an overall R factor of 21.9%. A drug molecule intercalates between each of the CpG dinucleotide steps with its side chain lying in the major groove, and its protonated morpholino nitrogen partially occupying positions close to the N7 and O6 atoms of guanine G2. The morpholino group is disordered, the major conformer adopting a twisted boat conformation that makes van der Waals contact with the O4 oxygen of thymine T3. A water molecule forms bridging hydrogen bonds between the 4-carboxamide NH and the phosphate group of guanine G2. Sugar rings are found in alternating C3'-exo/C2'-endo conformations except for cytosine C1 which is C3'-endo. Intercalation perturbs helix winding throughout the hexanucleotide compared with B-DNA, steps 1 and 2 being unwound by 10 and 8 degrees, respectively, while the central TpA step is overwound by 11 degrees. An additional drug molecule lies at the end of each DNA helix linking it to the next duplex to form a continuously stacked structure. The protonated morpholino nitrogen of this 'end-stacked' drug hydrogen bonds to the N7 atom of guanine G6, and its conformationally disordered morpholino ring forms a C-H...O hydrogen bond with the guanine O6 oxygen. In both drug molecules the 4-carboxamide group is internally hydrogen bonded to the protonated N10 atom of the acridine ring. We discuss our findings with respect to the potential role played by the interaction of the drug side chain and the topoisomerase II protein in the poisoning of topoisomerase activity by the acridinecarboxamides.

Phase II study of XR 5000, an inhibitor of topoisomerases I and II, in advanced colorectal cancer

XR 5000 is one of a series of tricyclic carboxamide-based cytotoxic agents. It binds to DNA by intercalation and stimulates DNA cleavage by inhibition of both topoisomerase I and II, thus possibly overcoming the resistance resulting from downregulation of either enzyme. Twenty patients with advanced or metastatic colorectal cancer, unpretreated for metastatic disease, received XR 5000 at the dose of 3010 mg/m(2) in a 120-h central intravenous (i.v.) infusion every 3 weeks. Response was evaluated every two cycles. No complete (CR) or partial responses (PR) were observed in eligible patients (response rate, 0 of 19, 0%; 95% confidence interval (CI): 0-18%). 5 patients had stable disease, which lasted from 79 to 157 days. Haematological toxicity was low, since only one grade 4 neutropenia and two grade 3 anaemia were observed. Other treatment-related grade 3-4 toxicities were: deep venous thrombosis (2 cases), liver toxicity, diarrhoea, anorexia, dyspnoea, chest pain, infection (1 case each). Despite the good toxicity profile, these results do not support further trials with XR 5000 in metastatic colorectal cancer.

Synthesis and cytotoxic activity of 7-oxo-7H-dibenz[f,ij]isoquinoline and 7-oxo-7H-benzo[e]perimidine derivatives

A series of 7-oxo-7H-dibenz[f,ij]isoquinoline and 7-oxo-7H-benzo[e]perimidines bearing cationic side chains were prepared from aminoanthraquinones. The perimidines were prepared from 1-aminoanthraquinone by initial condensation with urea or dimethylacetamide. A series of 2-, 4-, 8-, and 11-carboxy derivatives of the dibenzisoquinolines were prepared from aminoanthraquinonecarboxylic acids. The cationic derivatives were prepared from these via amide, amine, or methylene linkers to study the effects of side chain positioning on biological activity. Within the series of carboxamide-linked compounds, the order of increasing cytotoxicity was 8- < 4- < 2- < 11-. The 2- and 4-carboxamides showed substantial growth delays against in vivo subcutaneous colon 38 tumors in mice, but the 11-carboxamide had curative activity in this refractory model and is being investigated further.

Pharmacokinetic evaluation of N-[2-(dimethylamino)ethyl]acridine-4-carboxamide in patients by positron emission tomography

PURPOSE

To evaluate tumor, normal tissue, and plasma pharmacokinetics of N-[2-(dimethylamino)ethyl]acridine-4-carboxamide (DACA). The study aimed to determine the pharmacokinetics of carbon-11-labeled DACA ([11C]DACA) and evaluate the effect of pharmacologic doses of DACA on radiotracer kinetics.

PATIENTS AND METHODS

[11C]DACA (at 1/1,000 phase I starting dose) was administered to 24 patients with advanced cancer (pre-phase I) or during a phase I trial of DACA in five patients. Positron emission tomography (PET) was performed to assess pharmacokinetics and tumor blood flow. Plasma samples were analyzed for metabolite profile of [11C]DACA.

RESULTS

There was rapid systemic clearance of [11C]DACA over 60 minutes (1.57 and 1.46 L x min(-1) x m(-2) in pre-phase I and phase I studies, respectively) with the production of several radiolabeled plasma metabolites. Tumor, brain, myocardium, vertebra, spleen, liver, lung, and kidneys showed appreciable uptake of 11C radioactivity. The area under the time-versus-radioactivity curves (AUC) showed the highest variability in tumors. Of interest to potential toxicity, maximum radiotracer concentrations (Cmax) in brain and vertebra were low (0.67 and 0.54 m(2) x mL(-1), respectively) compared with other tissues. A moderate but significant correlation was observed for tumor blood flow with AUC (r = 0.76; P =.02) and standardized uptake value (SUV) at 55 minutes (r = 0.79; P =.01). A decrease in myocardial AUC ( P =.03) and splenic and myocardial SUV ( P =.01 and.004, respectively) was seen in phase I studies. Significantly higher AUC, SUV, and Cmax were observed in tumors in phase I studies.

CONCLUSION

The distribution of [11C]DACA and its radiolabeled metabolites was observed in a variety of tumors and normal tissues. In the presence of unlabeled DACA, pharmacokinetics were altered in myocardium, spleen, and tumors. These data have implications for predicting activity and toxicity of DACA and support the use of PET early in drug development.

N4-(omega-Aminoalkyl)-1-[(omega-aminoalkyl)amino]-4- acridinecarboxamides: novel, potent, cytotoxic, and DNA-binding agents

A series of DNA-binding potential antitumor agents, (omega-aminoalkyl)-4-acridinecarboxamides, has been prepared either by reduction of the corresponding (omega-aminoalkyl)-9-oxo-9, 10-dihydro-4-acridinecarboxamides with aluminum amalgam or by aminolysis of the corresponding (omega-aminoalkyl)-1-chloro-4-acridinecarboxamides with the suitable amine. The noncovalent DNA-binding properties of these compounds have been examined using a fluorometric technique. In vitro cytotoxic potencies of these derivatives toward six tumor cell lines, including human colon adenocarcinoma (HT29) and human ovarian carcinoma (A2780-sensitive, A2780cisR cisplatin-resistant, CH1-sensitive, CH1cisR cisplatin-resistant, and SKOV-3) cells, are described and compared to that of reference drugs. One highly DNA affinic analogue (3a) has been identified with a useful broad spectrum of cytotoxic activity in the 4-7 nM range (mean IC(50) of 6 nM).

A novel form of intercalation involving four DNA duplexes in an acridine-4-carboxamide complex of d(CGTACG)(2)

The structures of the complexes formed between 9-amino-[N:-(2-dimethyl-amino)butyl]acridine-4-carboxamide and d(CG(5Br)UACG)(2) and d(CGTACG)(2) have been solved by X-ray crystallography using MAD phasing methodology and refined to a resolution of 1.6 A. The complexes crystallised in space group C222. An asymmetric unit in the brominated complex comprises two strands of DNA, one disordered drug molecule, two cobalt (II) ions and 19 water molecules (31 in the native complex). Asymmetric units in the native complex also contain a sodium ion. The structures exhibit novel features not previously observed in crystals of DNA/drug complexes. The DNA helices stack in continuous columns with their central 4 bp adopting a B-like motif. However, despite being a palindromic sequence, the terminal GC base pairs engage in quite different interactions. At one end of the duplex there is a CpG dinucleotide overlap modified by ligand intercalation and terminal cytosine exchange between symmetry-related duplexes. A novel intercalation complex is formed involving four DNA duplexes, four ligand molecules and two pairs of base tetrads. The other end of the DNA is frayed with the terminal guanine lying in the minor groove of the next duplex in the column. The structure is stabilised by guanine N7/cobalt (II) coordination. We discuss our findings with respect to the effects of packing forces on DNA crystal structure, and the potential effects of intercalating agents on biochemical processes involving DNA quadruplexes and strand exchanges. NDB accession numbers: DD0032 (brominated) and DD0033 (native).

Synthesis of substituted indeno[1,2-b]quinoline-6-carboxamides, [1]benzothieno[3,2-b]quinoline-4-carboxamides and 10H-quindoline-4-carboxamides: evaluation of structure-activity relationships for cytotoxicity

New substituted indeno[1,2-b]quinoline-6-carboxamides, [1]benzothieno[3,2-b]quinoline-4-carboxamides and 10H-quindoline-4-carboxamides were prepared from methyl 2-amino-3-formylbenzoate by a new Friedlander synthesis. Evaluation of these carboxamides for cytotoxicity in a panel of cell lines showed that small lipophilic substituents in the non-carboxamide ring, in a pseudo-peri position to the side chain, significantly increased cytotoxic potency while retaining a pattern of cytotoxicity consistent with a non-topo II mode of action. The methyl-substituted indeno[1,2-b]quinoline-6-carboxamide demonstrated substantial effectiveness (20-day growth delays) in a sub-cutaneous colon 38 in vivo tumor model. This is comparable to that reported for the dual topo I/II inhibitor DACA that is in clinical trial.

Acridinecarboxamide topoisomerase poisons: structural and kinetic studies of the DNA complexes of 5-substituted 9-amino-(N-(2-dimethylamino)ethyl)acridine-4-carboxamides

For a series of antitumor-active 5-substituted 9-aminoacridine-4-carboxamide topoisomerase II poisons, we have used X-ray crystallography and stopped-flow spectrophotometry to explore relationships between DNA binding kinetics, biological activity, and the structures of their DNA complexes. The structure of 5-F-9-amino-[N-(2-dimethylamino)ethyl]-acridine-4-carboxamide bound to d(CGTACG)(2) has been solved to a resolution of 1.55 A in space group P6(4). A drug molecule intercalates between each of the CpG dinucleotide steps, its protonated dimethylamino group partially occupying positions close to the N7 and O6 atoms of guanine G2 in the major groove. A water molecule forms bridging hydrogen bonds between the 4-carboxamide NH and the phosphate group of the same guanine. Intercalation unwinds steps 1 and 2 by 12 degrees and 8 degrees, respectively compared with B-DNA, whereas the central TpA step is overwound by 10 degrees. Nonphenyl 5-substituents, on average, decrease mean DNA dissociation rates by a factor of three, regardless of their steric, hydrophobic, H-bonding, or electronic properties. Cytotoxicity is enhanced on average 4-fold and binding affinities rise by 3-fold, thus there is an apparent association between kinetics, affinity, and cytotoxicity. Taken together, the structural and kinetic studies imply that the main origin of this association is enhanced stacking interactions between the 5-substituent and cytosine in the CpG binding site. Ligand-dependent perturbations in base pair twist angles and their consequent effects on base pair-base pair stacking interactions may also contribute to the stability of the intercalated complex. 5-Phenyl substituents modify dissociation rates without affecting affinities, and variations in their biological activity are not correlated with DNA binding properties, which suggests that they interact directly with the topoisomerase protein.

Comparative QSAR studies on substituted bis-(acridines) and bis-(phenazines)-carboxamides: a new class of anticancer agents

Quantitative structure-activity relationships have been formulated for two sets of DNA binding topoisomerase agents (bis-acridines and bis-phenazines) acting on murine P388 leukemia cells, murine Lewis lung carcinoma (LL(C)) cells and human Jurkat leukemia wild-type (JL(C)) cells. For the acridines, all three QSARs (1-3) show only a (small negative) hydrophobic effect. In sharp contrast, the phenazines in all three studies (4-6) show a strong hydrophobic effect, with the optimum ClogP being near 7.3 for all examples. This suggests that, despite the structural similarity of the compounds, different modes of enzyme and/or DNA binding may be involved.

Bis(phenazine-1-carboxamides): structure-activity relationships for a new class of dual topoisomerase I/II-directed anticancer drugs

Ring-substituted bis(phenazine-1-carboxamides), linked by a -(CH(2))(3)NMe(CH(2))(3)- chain, were prepared from the corresponding substituted phenazine-1-carboxylic acids by reaction of the intermediate imidazolides with bis(3-aminopropyl)methylamine. The compounds were evaluated for growth inhibitory activity in a panel of tumor cell lines, including P388 leukemia, Lewis lung carcinoma, and wild-type (JL(C)) and mutant (JL(A) and JL(D)) forms of human Jurkat leukemia. The latter mutant lines are resistant to topoisomerase (topo) II targeted agents because of lower levels of the enzyme. Analogues with small, lipophilic substituents (e.g., Me, Cl) at the 9-position were the most potent inhibitors, superior to the corresponding dimeric bis(acridine-4-carboxamides) (bis-DACA analogues). Several of the compounds were preferentially (up to 2-fold) more cytotoxic toward the mutant Jurkat lines than the wild-type. To test whether this selectivity was related to topoisomerase action, the most potent of the compounds (9-methyl) was evaluated in a cell-free system. It poisoned topo I at drug concentrations of 0.25 and 0.5 microM and inhibited the catalytic activity of both topo I and topo II at concentrations of 1 and 5 microM, respectively. Results from the NCI human tumor cell line panel showed the compounds had preferential activity toward colon tumor lines (on average 9.5-fold more active in the HT29 line than in the cell line panel as a whole). Several analogues produced significant growth delays in the relatively refractory subcutaneous colon 38 tumor model in vivo. In particular, the 9-methyl compound was substantially more potent in this tumor model than the clinical dual topo I/II poison DACA (total dose 90 versus 400 mg/kg) with comparable activity. The bis(phenazine-1-carboxamides) are a new and interesting class of dual topo I/II-directed anticancer drugs.

Phase I and pharmacokinetic study of DACA (XR5000): a novel inhibitor of topoisomerase I and II. CRC Phase I/II Committee

DACA, also known as XR5000, is an acridine derivative active against both topoisomerase I and II. In this phase I study, DACA was given as a 3-h intravenous infusion on 3 successive days, repeated every 3 weeks. A total of 41 patients were treated at 11 dose levels between 9 mg m(-2) d(-1) and the maximum tolerated dose of 800 mg m(-2) day(-1). The commonest, and dose-limiting, toxicity was pain in the infusion arm. One patient given DACA through a central venous catheter experienced chest pain with transient electrocardiogram changes, but no evidence of myocardial infarction. At the highest dose levels, several patients also experienced flushing, pain and paraesthesia around the mouth, eyes and nose and a feeling of agitation. Other side-effects, such as nausea and vomiting, myelosuppression, stomatitis and alopecia, were uncommon. There was one minor response but no objective responses. DACA pharmacokinetics were linear and did not differ between days 1 and 3. The pattern of toxicity seen with DACA is unusual and appears related to the mode of delivery. It is possible that higher doses of DACA could be administered using a different schedule of administration.

Synthesis and in vitro cytotoxicity of 1-azaanthraquinone-3-carboxamides

Five 1-azaanthraquinone-3-carboxamides were synthesized and evaluated in vitro cytotoxicity against four human cancer cell lines. The most active compound, 7b, exhibited cytotoxic activity comparable to doxorubicin.