Cell death with atypical features induced by the novel antitumoral drug CHS 828, in human U-937 GTB cells

Photolabile ruthenium complexes to cage and release a highly cytotoxic anticancer agent

CHS-828 (N-(6-(4-chlorophenoxy)hexyl)-N'-cyano-N″-4-pyridyl guanidine) is an anticancer agent with low bioavailability and high systemic toxicity. Here we present an approach to improve the therapeutic profile of the drug using photolabile ruthenium complexes to generate light-activated prodrugs of CHS-828. Both prodrug complexes are stable in the dark but release CHS-828 when irradiated with visible light. The complexes are water-soluble and accumulate in tumour cells in very high concentrations, predominantly in the mitochondria. Both prodrug complexes are significantly less cyototoxic than free CHS-828 in the dark but their toxicity increases up to 10-fold in combination with visible light. The cellular responses to light treatment are consistent with release of the cytotoxic CHS-828 ligand.

Apoptosis induced by NAD depletion is inhibited by KN-93 in a CaMKII-independent manner

Nicotinamide phosphoribosyltransferase (NAMPT) is a key enzyme that catalyzes the synthesis of nicotinamide mononucleotide from nicotinamide (Nam) in the salvage pathway of mammalian NAD biosynthesis. Several potent NAMPT inhibitors have been identified and used to investigate the role of intracellular NAD and to develop therapeutics. NAD depletion induced by NAMPT inhibitors depolarizes mitochondrial membrane potential and causes apoptosis in a range of cell types. However, the mechanisms behind this depolarization have not been precisely elucidated. We observed that apoptosis of THP-1 cells in response to NAMPT inhibitors was reduced by the Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) inhibitor KN-93 via an unknown mechanism. The inactive analog of KN-93, KN-92, exhibited the same activity, but the CaMKII-inhibiting cell-permeable autocamtide-2-related inhibitory peptide II did not, indicating that the inhibition of THP-1 cell apoptosis was not dependent on CaMKII. In evaluating the mechanism of action, we confirmed that KN-93 did not inhibit decreases in NAD levels but did inhibit decreases in mitochondrial membrane potential, indicating that KN-93 exerts inhibition upstream of the mitochondrial pathway of apoptosis. Further, qPCR analysis of the Bcl-2 family of proteins showed that Bim is efficiently expressed following NAMPT inhibition and that KN-92 did not inhibit this expression. The L-type Ca(2+) channel blockers verapamil and nimodipine partially inhibited apoptosis, indicating that part of this effect is dependent on Ca(2+) channel inhibition, as both KN-93 and KN-92 are reported to inhibit L-type Ca(2+) channels. On the other hand, KN-93 and KN-92 did not markedly inhibit apoptosis induced by anti-cancer agents such as etoposide, actinomycin D, ABT-737, or TW-37, indicating that the mechanism of inhibition is specific to apoptosis induced by NAD depletion. These results demonstrate that NAD depletion induces a specific type of apoptosis that is effectively inhibited by the KN-93 series of compounds.

Target enzyme mutations are the molecular basis for resistance towards pharmacological inhibition of nicotinamide phosphoribosyltransferase

Background

Inhibitors of nicotinamide phosphoribosyltransferase (NAMPT) are promising cancer drugs currently in clinical trials in oncology, including APO866, CHS-828 and the CHS-828 prodrug EB1627/GMX1777, but cancer cell resistance to these drugs has not been studied in detail.

Methods

Here, we introduce an analogue of CHS-828 called TP201565 with increased potency in cellular assays. Further, we describe and characterize a panel of cell lines with acquired stable resistance towards several NAMPT inhibitors of 18 to 20,000 fold compared to their parental cell lines.

Results

We find that 4 out of 5 of the resistant sublines display mutations of NAMPT located in the vicinity of the active site or in the dimer interface of NAMPT. Furthermore, we show that these mutations are responsible for the resistance observed. All the resistant cell lines formed xenograft tumours in vivo. Also, we confirm CHS-828 and TP201565 as competitive inhibitors of NAMPT through docking studies and by NAMPT precipitation from cellular lysate by an analogue of TP201565 linked to sepharose. The NAMPT precipitation could be inhibited by addition of APO866.

Conclusion

We found that CHS-828 and TP201565 are competitive inhibitors of NAMPT and that acquired resistance towards NAMPT inhibitors can be expected primarily to be caused by mutations in NAMPT.

Efficacy of combining GMX1777 with radiation therapy for human head and neck carcinoma

PURPOSE

Rapidly metabolizing tumor cells have elevated levels of nicotinamide phosphoribosyltransferase, an enzyme involved in NAD(+) biosynthesis, which serves as an important substrate for proteins involved in DNA repair. GMX1777, which inhibits nicotinamide phosphoribosyltransferase, was evaluated in two human head and neck cancer models in combination with radiotherapy.

EXPERIMENTAL DESIGN

Effects of GMX1777-mediated radiosensitization were examined via metabolic and cytotoxicity assays in vitro; mechanism of action, in vivo antitumor efficacy, and radiosensitization were also investigated.

RESULTS

IC(50) values of GMX1777 for FaDu and C666-1 cells were 10 and 5 nmol/L, respectively, which interacted synergistically with radiotherapy. GMX1777 induced a rapid decline in intracellular NAD(+) followed by ATP reduction associated with significant cytotoxicity. These metabolic changes were slightly increased with the addition of radiotherapy, although poly(ADP-ribose) polymerase activity was significantly reduced when GMX1777 was combined with radiotherapy, thereby accounting for the synergistic cytotoxicity of these two modalities. Systemic GMX1777 administration with local tumor radiotherapy caused complete disappearance of FaDu and C666-1 tumors for 50 and 20 days, respectively. There was also significant reduction in tumor vascularity, particularly for the more sensitive FaDu model. [(18)F]FDG-positron emission tomography/computed tomography images showed reduction in [(18)F]FDG uptake after GMX1777 administration, showing decreased glucose metabolism in vivo.

CONCLUSIONS

Our data represent the first report showing that GMX1777 plus radiotherapy is an effective therapeutic strategy for head and neck cancer, mediated via pleiotropic effects of inhibition of DNA repair and tumor angiogenesis, while sparing normal tissues. Therefore, GMX1777 combined with radiotherapy definitely warrants clinical evaluation in human head and neck cancer patients.

Structure-activity relationship analysis of cytotoxic cyanoguanidines: selection of CHS 828 as candidate drug

Background

N-(6-(4-chlorophenoxy)hexyl)-N'-cyano-N''-4-pyridyl guanidine) (CHS 828) is the first candidate drug from a novel group of anti-tumour agents – the pyridyl cyanoguanidines, shown to be potent compounds interfering with cellular metabolism (inhibition of nicotinamide phosphoribosyl transferase) and NF-κB signalling. Substituted cyanoguanidines are also found in anti-hypertensive agents such as the potassium channel opener pinacidil (N-cyano-N'-(4-pyridyl)-N''-(1,2,2-trimethylpropyl)guanidine) and histamine-II receptor antagonists (e.g. cimetidine, N-cyano-N'-methyl-N''-[2-[[(5-methylimidazol-4-yl]methyl]thio]ethyl)guanidine). In animal studies, CHS 828 has shown very promising activity, and phase I and II studies resulted in further development of a with a water soluble prodrug.

Findings

To study the structural requirements for cyanoguanidine cytotoxicity a set of 19 analogues were synthesized. The cytotoxic effects were then studied in ten cell lines selected for different origins and mechanisms of resistance, using the fluorometric microculture cytotoxicity assay (FMCA). The compounds showed varying cytotoxic activity even though the dose-response curves for some analogues were very shallow. Pinacidil and cimetidine were found to be non-toxic in all ten cell lines. Starting with cyanoguanidine as the crucial core it was shown that 4-pyridyl substitution was more efficient than was 3-pyridyl substitution. The 4-pyridyl cyanoguanidine moiety should be linked by an alkyl chain, optimally a hexyl, heptyl or octyl chain, to a bulky end group. The exact composition of this end group did not seem to be of crucial importance; when the end group was a mono-substituted phenyl ring it was shown that the preferred position was 4-substitution, followed by 3- and, finally, 2-substitution as the least active. Whether the substituent was a chloro, nitro or methoxy substituent seemed to be of minor importance. Finally, the activity patterns in the ten cell lines were compared. Substances with similar structures correlated well, whilst substances with large differences in molecular structure demonstrated lower correlation coefficients.

Conclusion

According to this structure-activity relationship (SAR) study, CHS 828 meets the requirements for optimal cytotoxic activity for this class of compounds.

Anticancer agent CHS-828 inhibits cellular synthesis of NAD

Malignant cells display increased demands for energy production and DNA repair. Nicotinamide adenine dinucleotide (NAD) is required for both processes and is also continuously degraded by cellular enzymes. Nicotinamide phosphoribosyltransferase (Nampt) is a crucial factor in the resynthesis of NAD, and thus in cancer cell survival. Here, we establish the cytotoxic mechanism of action of the small molecule inhibitor CHS-828 to result from impaired synthesis of NAD. Initially, we detected cross-resistance in cells between CHS-828 and a known inhibitor of Nampt, FK866, a compound of a structurally different class. We then showed that nicotinamide protects against CHS-828-mediated cytotoxicity. Finally, we observed that treatment with CHS-828 depletes cellular NAD levels in sensitive cancer cells. In conclusion, these results strongly suggest that, like FK866, CHS-828 kills cancer cells by depleting NAD.

Phase I study and pharmacokinetic of CHS-828, a guanidino-containing compound, administered orally as a single dose every 3 weeks in solid tumours: an ECSG/EORTC study

CHS 828 is a new guanidino-containing drug. The aim of this study was to determine the maximum tolerated dose (MTD), the recommended dose and the toxicity of CHS 828. CHS 828 was given orally once every 3 weeks. The starting dose was 50 mg, which was escalated to 500 mg. A total of 107 courses was administered to 37 patients. At the 500-mg dose level, two of three patients experienced dose-limiting toxicities (DLT) (grade 3 mucositis and grade 4 thrombocytopenia), establishing this as the MTD. One of seven patients treated at 420 mg dose experienced DLT (grade 4 leucopenia, grade 4 mucositis and grade 4 diarrhoea), and this was considered the recommended dose for phase II studies. Vomiting, haematuria, leucopenia and thrombocytopenia were other significant toxicities. The pharmacokinetics of CHS 828 showed large variations both between and within patients. No objective responses were seen. A dose of 420 mg of CHS 828 administered every 3 weeks is the recommended dose, while 500 mg is the MTD.

Multiparametric evaluation of apoptosis: Effects of standard cytotoxic agents and the cyanoguanidine CHS 828

A multiparametric high-content screening assay for measurement of apoptosis was developed. HeLa cells and lymphoma U-937 cells were exposed to cytotoxic drugs in flat-bottomed optical microtiter plates. After incubation, the DNA-binding dye Hoechst 33342, fluorescein-tagged probes that covalently bind active caspases and chloromethyl-X-rosamine to detect mitochondrial membrane potential (MMP) were added. Image acquisition and quantitative measurement of fluorescence in a defined number of cells per well was performed using the automated image capture and analysis instrument ArrayScan. The usefulness of the assay was tested in cells exposed to standard cytotoxic drugs as well as in experimental cytotoxic cyanoguanidine CHS 828. A time- and dose-dependent activation of caspase-3, decrease in MMP, and increase in nuclear fragmentation and condensation were observed for the standard drugs, with the ability to correlate the parameters on a single cell basis. CHS 828 induced caspase-3 activation and reduction in MMP with modest changes in nuclear morphology. The method described was considered to be a rapid and information-rich apoptosis assay suitable both for correlating morphological and biochemical apoptotic events in single cells as well as for screening and evaluation of novel substances with apoptosis-inducing capabilities.

Synthesis and in vitro cytotoxicity of 5-substituted 2-cyanoimino-4-imidazodinone and 2-cyanoimino-4-pyrimidinone derivatives

A series of 5-substituted 2-cyanoimino-4-imidazodinone and 2-cyanoimino-4-pyrimidinone derivatives were synthesized and their anticancer cytotoxicity were evaluated in in vitro assay. It was found that the bulky aryl functionality in the 5-position of the 2-cyanoimino-4-imidazolidinone compounds was essential for the cytotoxicity of these heterocyclic compounds. Some of the derivatives exhibited modest cytotoxicity against a variety of cancer cell lines. One of the derivatives, [1-[6-(4-chlorophenoxy)hexyl]-5-oxo-4-phenyl-3-(4-pyridyl)tetrahydro-1H-2-imidazolyliden]aminomethanenitrile (Compound 11), exhibited the most potent cytotoxic activity with IC(50) in the nanomolar range. The cytotoxicity of these derivatives was selection with no apparent toxic effect toward normal fibroblasts.

Cytotoxic effect in vivo and in vitro of CHS 828 on human myeloma cell lines

CHS 828 is a pyridyl cyanoguanidine with promising antitumor activity both in vitro and in vivo, and has previously been found especially active against tumor cells obtained from patients with B cell chronic lymphocytic leukemia. In the present study the cytotoxic effect in vitro of CHS 828 was investigated on a panel of 10 human myeloma cell lines using the fluorometric microculture cytotoxicity assay. CHS 828 induced a concentration-dependent, but variable decrease in tumor cell survival in the cell line panel with inhibitory concentrations 50% (IC50) in the range 0.01-0.3 microM. These concentrations are below those achievable in vivo. There was no detectable dependence on P-glycoprotein-mediated or GSH-associated drug resistance and the drug showed low to moderate cross-resistance with standard drugs, including melphalan, vincristine and doxorubicin. Furthermore, sensitivity to CHS 828 showed no apparent relationship to growth factor dependence, tumor progression or phenotypic variability. CHS 828 was also tested in vivo using a hollow fiber model in rats with three of the cell lines. The results indicate a high cytotoxic activity of CHS 828. Overall, the results show a high cytotoxic activity of CHS 828 in the myeloma models, which might warrant its further development against myeloma.

Development and characterization of two human tumor sublines expressing high-grade resistance to the cyanoguanidine CHS 828

The cyanoguanidine CHS 828 has shown promising antitumor properties and is currently in early clinical trials, although the mechanism of action still is largely unknown. In this study, resistant sublines of the histiocytic lymphoma cell line U-937 GTB and the myeloma line RPMI 8226 were developed by culturing under gradually increasing concentrations of CHS 828 until reaching 25 times the parental line EC50s. The new phenotypes demonstrate more than 400-fold resistance to CHS 828 and cross-resistance to six cyanoguanidine analogs, but no resistance to nine standard drugs of different mechanistic classes or to the cytotoxic guanidines m-iodobenzylguanidine and methylglyoxal-bis(guanylhydrazone). The resistant phenotypes were stable for several months even if cultivated in drug-free medium and no difference in proliferation, ultrastructural or morphologic appearance in the sublines could be detected. Neither was decreased accumulation of tritium-labeled CHS 828 observed. Furthermore, the new U-937 phenotype was not accompanied by changes in differentiation or an altered cell-cycle distribution. In the myeloma cell line, esterase activity was shown to be moderately enhanced. Two-dimensional protein electrophoresis was undertaken to unmask possible resistance-mediating proteins and/or the target molecule(s) for CHS 828. In the myeloma cell line, lambda light chain immunoglobulin (down-regulated) and a fatty acid-binding protein (up-regulated) were identified. The findings presented here indicate that development of specific cellular alterations is responsible for the gained CHS 828 resistance.

The combination of the antitumoural pyridyl cyanoguanidine CHS 828 and etoposide in vitro--from cytotoxic synergy to complete inhibition of apoptosis

1. The present study was aimed at elucidating the apoptosis inhibitory properties of the cyanoguanidine CHS 828. CHS 828 exhibits impressive cytotoxic activity in vitro and in vivo. Apoptosis is not its main mode of cytotoxic effect, and we have previously proposed a dual mechanism, where CHS 828 inhibits its own cell death pathways. 2. Etoposide on the other hand, is a well-established anticancer agent with documented effect in a number of malignancies, induces apoptosis through extensively studied caspase dependent pathways. 3. Here we studied the combined effect of the two drugs in the human lymphoma cell line U-937 GTB. Cytotoxicity was evaluated as total viability measured by the fluorometric microculture cytotoxicity assay (FMCA). Caspase activity was assessed by colorimetric detection of specific cleavage products for caspases 3, 8 and 9, respectively. Morphology was evaluated in May-Grünwald/Giemsa stained preparations. Interaction analysis based on FMCA results of simple combination exposure revealed impressive synergistic effect on cell kill. 4. Detailed investigations of the kinetics involved showed that short pre-exposure (0-12 h) to CHS 828 enhanced caspase activation by etoposide, while longer pre-exposure (18-48 h) inhibited both caspase activation and apoptotic morphology otherwise induced by etoposide. The present results support the theory that CHS 828 block specific cell death pathways. 5. The synergistic results are promising for future combination trials in animals, however, different dosing schedules should be considered, in order to investigate whether the above findings translate into the in vivo setting.

In vitro activity of the novel cytotoxic agent CHS 828 in childhood acute leukemia

CHS 828, a pyridyl cyanoguanidine, is a new drug candidate now in phase I/II trials, that has shown promising anticancer activity in experimental tumor models and primary cultures of cancer cells from patients. In this study the fluorometric microculture cytotoxicity assay was used for evaluation of CHS 828 in primary cell cultures from children with acute leukemia. The activity of and interaction with the standard drugs, doxorubicin, melphalan, etoposide and cytosine arabinoside (Ara-C), were also assessed. Samples from 65 patients, 42 with acute lymphocytic leukemia (ALL) and 23 with acute myelocytic leukemia (AML) were tested with 72-h continuous drug exposure. There was 50% cell kill at very low CHS 828 concentrations; median IC50 was 0.01 microM in ALL and 0.03 in AML samples (NS) with large interindividual variability in both groups. ALL samples were significantly more sensitive than AML samples to melphalan, doxorubicin and etoposide, but not to Ara-C. In AML samples, combinations between CHS 828 and each of the four standard drugs resulted in significantly lower cell survival than either drug alone. This was also observed in ALL samples, except for Ara-C. Using the additive interaction model, CHS 828 showed a synergistic effect with melphalan in 67%, doxorubicin in 47%, etoposide in 38% and Ara-C in 14% of AML samples. In most ALL samples subadditive effects were found. Further exploration of CHS 828 in childhood leukemia is warranted, especially in AML.

Modulation of pyridyl cyanoguanidine (CHS 828) induced cytotoxicity by 3-aminobenzamide in U-937 GTB cells

The role of the nuclear enzyme poly(ADP-ribose) polymerase (PARP) and the ADP-ribosylation inhibitor 3-aminobenzamide (3-ABA) in the cytotoxicity induced by the novel antitumoral cyanoguanidine CHS 828 was investigated in the human lymphoma cell line U-937 GTB. Exposing cells to CHS 828 and 3-ABA in combination resulted in a 100-fold higher IC(50) compared to exposure to CHS 828 alone. CHS 828 did not activate PARP, measured as PARP-activity and formation of poly(ADP-ribose). The ATP-levels and levels of extracellular acidification rate of cells exposed to CHS 828 in combination with 3-ABA were maintained for a longer period than for cells exposed to CHS 828 alone. To characterize the mode of cell death, caspase-3 activity and gross morphology were assessed. 3-ABA increased and delayed the caspase-3 activity in cells exposed to CHS 828. Cells exposed to high concentrations of CHS 828 showed a necrotic morphology, while high concentrations of CHS 828 in combination with 3-ABA switched the mode of cell death, generating an apoptotic morphology. The results indicate that the cytotoxicity and morphology induced by CHS 828 is not due to PARP activation but can be modulated by the ADP-ribosylation inhibitor 3-ABA.