Temporal effects of the novel antitumour pyridyl cyanoguanidine (CHS 828) on human lymphoma cells

Role of coenzymes in cancer metabolism

Cancer is a heterogeneous set of diseases characterized by the rewiring of cellular signaling and the reprogramming of metabolic pathways to sustain growth and proliferation. In past decades, studies were focused primarily on the genetic complexity of cancer. Recently, increasing number of studies have discovered several mutations among metabolic enzymes in different tumor cells. Most of the enzymes are regulated by coenzymes, organic cofactors, that function as intermediate carrier of electrons or functional groups that are transferred during the reaction. However, the precise role of cofactors is not well elucidated. In this review, we discuss several metabolic enzymes associated to cancer metabolism rewiring, whose inhibition may represent a therapeutic target. Such enzymes, upon expression or inhibition, may impact also the coenzymes levels, but only in few cases, it was possible to direct correlate coenzymes changes with a specific enzyme. In addition, we also summarize an up-to-date information on biological role of some coenzymes, preclinical and clinical studies, that have been carried out in various cancers and their outputs.

NAD+ salvage pathway in cancer metabolism and therapy

Nicotinamide adenine dinucleotide (NAD⁺) is an essential coenzyme for various physiological processes including energy metabolism, DNA repair, cell growth, and cell death. Many of these pathways are typically dysregulated in cancer cells, making NAD⁺ an intriguing target for cancer therapeutics. NAD⁺ is mainly synthesized by the NAD⁺ salvage pathway in cancer cells, and not surprisingly, the pharmacological targeting of the NAD⁺ salvage pathway causes cancer cell cytotoxicity in vitro and in vivo. Several studies have described the precise consequences of NAD⁺ depletion on cancer biology, and have demonstrated that NAD+ depletion results in depletion of energy levels through lowered rates of glycolysis, reduced citric acid cycle activity, and decreased oxidative phosphorylation. Additionally, depletion of NAD⁺ causes sensitization of cancer cells to oxidative damage by disruption of the anti-oxidant defense system, decreased cell proliferation, and initiation of cell death through manipulation of cell signaling pathways (e.g., SIRT1 and p53). Recently, studies have explored the effect of well-known cancer therapeutics in combination with pharmacological depletion of NAD⁺ levels, and found in many cases a synergistic effect on cancer cell cytotoxicity. In this context, we will discuss the effects of NAD⁺ salvage pathway inhibition on cancer cell biology and provide insight on this pathway as a novel anti-cancer therapeutic target.

Complex role of nicotinamide adenine dinucleotide in the regulation of programmed cell death pathways

Over the past few years, a growing body of experimental observations has led to the identification of novel and alternative programs of regulated cell death. Recently, autophagic cell death and controlled forms of necrosis have emerged as major alternatives to apoptosis, the best characterized form of regulated cell demise. These recently identified, caspase-independent, forms of cell death appear to play a role in the response to several forms of stress, and their importance in different pathological conditions such as ischemia, infection and inflammation has been recognized. The functional link between cell metabolism and survival has also been the matter of recent studies. Nicotinamide adenine dinucleotide (NAD(+)) has gained particular interest due to its role in cell energetics, and as a substrate for several families of enzymes, comprising poly ADP-ribose polymerases (PARPs) and sirtuins, involved in numerous biological functions including cell survival and death. The recently uncovered diversity of cell death programs has led us to reevaluate the role of this important metabolite as a universal pro-survival factor, and to discuss the potential benefits and limitations of pharmacological approaches targeting NAD(+) metabolism.

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.

Regression of orthotopic neuroblastoma in mice by targeting the endothelial and tumor cell compartments

BACKGROUND

High-risk neuroblastoma has an overall five-year survival of less than 40%, indicating a need for new treatment strategies such as angiogenesis inhibition. Recent studies have shown that chemotherapeutic drugs can inhibit angiogenesis if administered in a continuous schedule. The aim of this study was primarily to characterize tumor spread in an orthotopic, metastatic model for aggressive, MYCN-amplified neuroblastoma and secondarily to study the effects of daily administration of the chemotherapeutic agent CHS 828 on tumor angiogenesis, tumor growth, and spread.

METHODS

MYCN-amplified human neuroblastoma cells (IMR-32, 2 x 10(6)) were injected into the left adrenal gland in SCID mice through a flank incision. Nine weeks later, a new laparotomy was performed to confirm tumor establishment and to estimate tumor volume. Animals were randomized to either treatment with CHS 828 (20 mg/kg/day; p.o.) or vehicle control. Differences between groups in tumor volume were analyzed by Mann-Whitney U test and in metastatic spread using Fisher's exact test. Differences with p < 0.05 were considered statistically significant.

RESULTS

The orthotopic model resembled clinical neuroblastoma in respect to tumor site, growth and spread. Treatment with CHS 828 resulted in tumor regression (p < 0.001) and reduction in viable tumor fraction (p < 0.001) and metastatic spread (p < 0.05) in correlation with reduced plasma levels of the putative tumor marker chromogranin A (p < 0.001). These effects were due to increased tumor cell death and reduced angiogenesis. No treatment-related toxicities were observed.

CONCLUSION

The metastatic animal model in this study resembled clinical neuroblastoma and is therefore clinically relevant for examining new treatment strategies for this malignancy. Our results indicate that daily scheduling of CHS 828 may be beneficial in treating patients with high-risk neuroblastoma.

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.

Pharmacokinetic–pharmacodynamic modelling of the schedule-dependent effect of the anti-cancer agent CHS 828 in a rat hollow fibre model

N-(6-Chlorophenoxyhexyl)-N'-cyano-N''-4-pyridylguanidine (CHS 828) is a novel anticancer agent that shows schedule-dependent effects in vitro and in vivo, as well as in Phase I clinical trials. A rat hollow fibre model was used to investigate whether this dependency is due to pharmacokinetic and/or pharmacodynamic factors. The effect on two cell lines, MDA-MB-231 (breast cancer) and CCRF-CEM (leukaemia) were studied after CHS 828 was administered orally as a single dose or in a 5-day schedule, at different total dose levels. The 5-day schedules were associated with greater effects on both cell lines compared with single doses. A one-compartment pharmacokinetic model, with a half-life of 2.3h and a consecutive zero- and first-order process to describe dissolution and absorption, fit the concentration data. Pharmacokinetics were dose-dependent, as the fraction absorbed decreased with increasing dose. Clearance increased with accumulative exposure. Twenty hours after administration, concentrations started to increase again, probably due to coprophagy. Pharmacokinetic-pharmacodynamic models characterized the cell growth and cell kill over time and showed that schedule-dependent antitumour effects were present also when the dose-dependent pharmacokinetics were accounted for. The prolonged schedules of CHS 828 were therefore associated with greater antitumour effects than single doses of the same total exposure.

Antitumoural effects of the pyridyl cyanoguanidine CHS 828 on three different types of neuroendocrine tumours xenografted to nude mice

CHS 828, a cyanoguanidine with potent experimental antitumoural activity, inhibits activation of nuclear factor-kappaB. In the present study, marked antitumoural activity of peroral CHS 828 was shown against three different human neuroendocrine tumours, midgut carcinoid (GOT1), pancreatic carcinoid (BON), and medullary thyroid carcinoma (GOT2), transplanted in nude mice. Our results indicate that CHS 828 can be a candidate drug for treatment of neuroendocrine tumours.

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.

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.

Activity of CHS 828 in primary cultures of human hematological and solid tumors in vitro

CHS 828 is a pyridyl cyanoguanidine that has shown promising preclinical anticancer activity against various experimental tumor models and is presently being tested in a phase II trial in man. In the present study the fluorometric microculture cytotoxicity assay was used for in vitro evaluation of CHS 828 activity in primary cell cultures from hematological and solid tumors. In total, 156 samples from various diagnoses were tested with 72-h continuous drug exposure. CHS 828 showed high relative in vitro activity against tumor cells from chronic lymphocytic leukemia as well as from acute leukemia and high-grade lymphoma. Activity was also observed in several solid tumor cell samples, although the group as a whole appeared less responsive. CHS 828 was significantly more active against hematological malignancies compared to normal lymphocytes. Correlation analysis with standard drugs revealed low to moderate correlation coefficients. The results show that CHS 828 has potent antitumor activity against primary cultures of human tumor cells from patients and might have a unique mechanism of action.

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

N-(6-(4-chlorophenoxy)hexyl)-N'-cyano-N"-4-pyridylguanidine (CHS 828), with promising antitumoral effects in vitro and in vivo, is currently in clinical Phase I and II studies. Its exact mechanism of action is unclear, but previous studies indicate that CHS 828 induces a controlled, delayed mode of cell death. The characteristics of the cell death process were investigated in vitro in the apoptosis-prone cell line U-937 GTB. Mitochondria showed hyperpolarization at 24 to 32 h and a subsequent late disruption of mitochondria membrane potential (Deltapsi(m)). Between 44 and 72 h of CHS 828 exposure, there was an increasing frequency of terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) positive cells indicative of apoptosis, but caspase-3 was only modestly increased and caspases-8 and -9 showed no activation upon CHS 828 exposure. Furthermore, the morphology of exposed cells did not conform to classical apoptosis, and viability and morphology were unaffected by inhibition of caspases. Thus, CHS 828 induces several unexpected features in this system, suggesting a potentially novel mechanism of action.