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

Acridine Derivatives as Inhibitors of the IRE1α-XBP1 Pathway Are Cytotoxic to Human Multiple Myeloma

Using a luciferase reporter-based high-throughput chemical library screen and topological data analysis, we identified N-acridine-9-yl-N',N'-dimethylpropane-1,3-diamine (DAPA) as an inhibitor of the inositol requiring kinase 1α (IRE1α)-X-box binding protein-1 (XBP1) pathway of the unfolded protein response. We designed a collection of analogues based on the structure of DAPA to explore structure-activity relationships and identified N(9)-(3-(dimethylamino)propyl)-N(3),N(3),N(6),N(6)-tetramethylacridine-3,6,9-triamine (3,6-DMAD), with 3,6-dimethylamino substitution on the chromophore, as a potent inhibitor. 3,6-DMAD inhibited both IRE1α oligomerization and in vitro endoribonuclease (RNase) activity, whereas the other analogues only blocked IRE1α oligomerization. Consistent with the inhibition of IRE1α-mediated XBP1 splicing, which is critical for multiple myeloma cell survival, these analogues were cytotoxic to multiple myeloma cell lines. Furthermore, 3,6-DMAD inhibited XBP1 splicing in vivo and the growth of multiple myeloma tumor xenografts. Our study not only confirmed the utilization of topological data analysis in drug discovery but also identified a class of compounds with a unique mechanism of action as potent IRE1α-XBP1 inhibitors in the treatment of multiple myeloma. Mol Cancer Ther; 15(9); 2055-65. ©2016 AACR.

Why are we failing to implement imaging studies with radiolabelled new molecular entities in early oncology drug development?

In early drug development advanced imaging techniques can help with progressing new molecular entities (NME) to subsequent phases of drug development and thus reduce attrition. However, several organizational, operational, and regulatory hurdles pose a significant barrier, potentially limiting the impact these techniques can have on modern drug development. Positron emission tomography (PET) of radiolabelled NME is arguably the best example of a complex technique with a potential to deliver unique decision-making data in small cohorts of subjects. However, to realise this potential the impediments to timely inclusion of PET into the drug development process must be overcome. In the present paper, we discuss the value of PET imaging with radiolabelled NME during early anticancer drug development, as exemplified with one such NME. We outline the multiple hurdles and propose options on how to streamline the organizational steps for future studies.

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.

Camptothecin and podophyllotoxin derivatives: inhibitors of topoisomerase I and II - mechanisms of action, pharmacokinetics and toxicity profile

Camptothecins represent an established class of effective agents that selectively target topoisomerase I by trapping the catalytic intermediate of the topoisomerase I-DNA reaction, the cleavage complex. The water-soluble salt camptothecin-sodium - introduced in early trials in the 1960s - was highly toxic in animals, whereas the semisynthetic derivatives irinotecan and topotecan did not cause haemorrhagic cystitis because of their higher physicochemical stability and solubility at lower pH values. Myelosuppression, neutropenia and, to a lesser extent, thrombocytopenia are dose-limiting toxic effects of topotecan. In contrast to the structurally-related topotecan, irinotecan is a prodrug which has to be converted to SN-38, its active form. SN-38 is inactivated by conjugation, thus patients with Gilbert's syndrome and other forms of genetic glucuronidation deficiency are at an increased risk of irinotecan-induced adverse effects, such as neutropenia and diarrhoea. The cytotoxic mechanism of podophyllotoxin is the inhibition of topoisomerase II. Common adverse effects of etoposide include dose-limiting myelosuppression. Hypersensitivity reactions are more common with etoposide and teniposide than with etoposide phosphate because the formulations of the former contain sensitising solubilisers. Leukopenia and thrombocytopenia occur in 65% and 80%, respectively, of patients after administration of conventional doses of teniposide. Anorexia, vomiting and diarrhoea are generally of mild severity after administration of conventional doses of topoisomerase II inhibitors. Clinical pharmacokinetic studies have revealed substantial interindividual variabilities regarding the area under the concentration-time curve values and steady-state concentrations for all drugs reviewed in this article. Irinotecan, etoposide and teniposide are degraded via complex metabolic pathways. In contrast, topotecan primarily undergoes renal excretion. Regarding etoposide and teniposide, the extent of catechol formation over time during drug metabolism may be associated with a higher risk for secondary malignancies.

Linker-modified triamine-linked acridine dimers: synthesis and cytotoxicity properties in vitro and in vivo

The preparation and cytotoxicity properties of a series of N(epsilon)-substituted triamine-linked acridine dimers are described. Most acridine dimer derivatives reveal highly potent in vitro cytotoxicity properties and DNA binding activity. Several acridine dimers were selected to study their action in vivo. These acridine dimers have demonstrated a narrow safe margin, as has adriamycin, but higher maximum tolerate dose (MTD) in comparison with that of adriamycin in ICR mice. The acridine dimers also demonstrated various anit-COLO 205 solid tumor activities in vivo. Compound 1 has shown the most potent solid tumor inhibition.

Phase II study of XR5000 (DACA), an inhibitor of topoisomerase I and II, administered as a 120-h infusion in patients with advanced ovarian cancer

BACKGROUND

XR5000 is a tricyclic carboxamide-based cytotoxic agent that binds to DNA by intercalation and stimulates DNA cleavage by inhibition of both topoisomerase I and II. The aim of the present study was to evaluate the antitumoral activity and safety profile of XR5000 given as second-line chemotherapy in patients with ovarian cancer who had relapsed within 1 year after first-line chemotherapy with taxanes and platinum for advanced disease.

PATIENTS AND METHODS

Patients received XR5000 at the dose of 3010 mg/m(2) through a 120-h central venous infusion every 3 weeks. Toxicity was graded according to the Common Toxicity Criteria (CTC), version 2.0. An independent panel assessed response every two cycles according to the World Health Organization (WHO) criteria. Gehan's rule was used for sample size determination.

RESULTS

Sixteen patients were enrolled; one patient was ineligible because of prior melphalan single agent treatment. Eastern Cooperative Oncology Group (ECOG) performance status was 0 (eight patients), 1 (five patients), or 2 (two patients). The 15 eligible patients received 43 cycles of XR5000 (median 2, range 1-8). Hematological toxicity was mild with only one grade 3 anemia in one patient. Other drug-related toxicities never exceeded grade 3 and included fatigue (four patients), thrombosis (one patient), nausea (one patient), stomatitis (one patient) as well as dyspnea/cough (one patient). One patient who had refused further therapy and controls after the first cycle was not assessable for response evaluation. No objective responses were observed. Four patients experienced stable disease and 10 patients progressive disease. The median time to progression was 42 days (CI 95% 40; 54).

CONCLUSIONS

The complete lack of any objective response does not justify further evaluation of XR5000 in patients with advanced ovarian cancer using this dose and schedule, although the therapy was generally well tolerated.

Bisintercalating Threading Diacridines: Relationships between DNA Binding, Cytotoxicity, and Cell Cycle Arrest

We have synthesized a series of bis(9-aminoacridine-4-carboxamides) linked via the 9-position with neutral flexible alkyl chains, charged flexible polyamine chains, and a semirigid charged piperazine-containing chain. The carboxamide side chains comprise N,N-dimethylaminoethyl and ethylmorpholino groups. The compounds are designed to bisintercalate into DNA by a threading mode, in which the side chains are intended to form hydrogen-bonding contacts with the O6/N7 atoms of guanine in the major groove, and the linkers are intended to lie in the minor groove. By this means, we anticipate that they will dissociate slowly from DNA, and be cytotoxic as a consequence of template inhibition of transcription. The dimers remove and reverse the supercoiling of closed circular DNA with helix unwinding angles ranging from 26 degrees to 46 degrees, confirming bifunctional intercalation in all cases, and the DNA complexes of representative members dissociate many orders of magnitude more slowly than simple aminoacridines. Cytotoxicity for human leukemic CCRF-CEM cells was determined, the most active agents having IC(50) values of 35-50 nM in a range extending over 20-fold, with neither the dimethylaminoethyl nor the ethylmorpholino series being intrinsically more toxic. In common with established transcription inhibitors, the morpholino series, with one exception, have no effect on cell cycle distribution in randomly dividing CCRF-CEM populations. By contrast, the dimethylaminoethyl series, with two exceptions, cause G2/M arrest in the manner of topoisomerase poisons, consistent with possible involvement of topoisomerases in their mode of action. Thus, the cellular response to these bisintercalating threading agents is complex and appears to be determined by both their side chain and linker structures. There are no simple relationships between structure, cytotoxicity, and cell cycle arrest, and the origins of this complexity are unclear given that the compounds bind to DNA by a common mechanism.

Phase II study of XR 5000 (DACA), an inhibitor of topoisomerase I and II, administered as a 120-h infusion in patients with non-small cell lung cancer

XR5000 is a tricyclic carboxamide-based cytotoxic agent that binds to DNA by intercalation and stimulates DNA cleavage by inhibition of both topoisomerase I and II. The aim of this study was to evaluate the antitumoral activity and safety profile of XR5000 given as second-line chemotherapy in patients with advanced non-small cell lung cancer (NSCLC). Patients received XR5000 at the dose of 3010 mg/m(2) as a 120-h central venous infusion every 3 weeks. The 15 patients (median age 56 years, range 48-71 years) enrolled had an Eastern Cooperative Oncology Group (ECOG) performance status of 0 (3 patients), 1 (11 patients) or 2 (1 patient). A total of 32 cycles of XR5000 (median 2, range 1-6) were given to 14 patients. No objective response (assessed according to World Health Organization (WHO) criteria) was documented in the 12 evaluable patients by an external review panel; in 4 out of the 12 patients disease stabilisation was recorded. The following toxicities graded according to the Common Toxicity Criteria (CTC) version 2.0. were observed: one grade 3 and two grade 4 granulocytopenia, one grade 3 and one grade 4 thrombocytopenia, one grade 3 deep venous thrombosis, one grade 3 fatigue, and grade 3 undocumented epileptic seizures which led to death in 2 patients. With only 4 out of 12 patients reaching stable disease when using this dose and regimen, further evaluation of XR5000 in advanced NSCLC is not justified.

Overview of the clinical efficacy of investigational anticancer drugs

The purpose of this overview was to make a broad inventory of investigational drugs for medicinal cancer treatment and, specifically, to indicate the evidence of clinical efficacy. Information was retrieved from electronic database searches in Medline and CANCERLIT and relevant published reviews. As the most recent findings are first reported as conference abstracts, an important basis for identification of new drugs and clinical results was a hand search of 13,392 abstracts from five major recent cancer conferences. A total of 209 investigational approaches or drugs were identified and classified into one of eight groups according to proposed mechanism of action. For 28 drugs/approaches survival data were available from randomized controlled trials. Statistically significant benefit was observed for only 12. In earlier phases no or modest anticancer activity was reported. It is speculated that the expanding knowledge in tumour biology might not easily translate into new substantially better anticancer drugs.

Homocamptothecins: potent topoisomerase I inhibitors and promising anticancer drugs

Homocamptothecins (hCPTs) represent a new generation of antitumor agents targeting DNA topoisomerase I. The expanded seven-membered lactone E-ring that characterizes hCPTs enhances the plasma stability of the drug and reinforces the inhibition of topoisomerase I compared with conventional six-membered CPTs. hCPTs are more efficient than the CPTs at promoting cleavage at T/G sites and induce additional cleavage at C/G sites. Compound BN80765 and its difluoro analogue diflomotecan (DN80915) are potent cytotoxic agents and efficiently induce apoptosis in tumor cells. They display strong antiproliferative activities against specific tumor types. Diflomotecan is remarkably efficient at inhibiting the growth of human colon cancer cells in vivo and, administered orally, it also shows superior activities against human prostate cancers compared with the benchmark products topotecan (TPT) and irinotecan (IRT). Diflomotecan has entered phase I clinical testing and antitumor activity has been observed in patients. This 9,10-difluoro-hCPTs derivative is one of the most promising new members of the 'tecan' family. This review summarizes the recent discoveries in the topoisomerase I field and presents the different camptothecin (CPT) analogues currently evaluated as anticancer agents. The specific properties of hCPTs are highlighted.