Carboplatin dosage: prospective evaluation of a simple formula based on renal function

A dosage formula has been derived from a retrospective analysis of carboplatin pharmacokinetics in 18 patients with pretreatment glomerular filtration rates (GFR) in the range of 33 to 136 mL/min. Carboplatin plasma clearance was linearly related to GFR (r = 0.85, P less than .00001) and rearrangements of the equation describing the correlation gave the dosage formula dose (mg) = target area under the free carboplatin plasma concentration versus time curve (AUC) x (1.2 x GFR + 20). In a prospective clinical and pharmacokinetic study the formula was used to determine the dose required to treat 31 patients (GFR range, 33 to 135 mL/min) with 40 courses of carboplatin. The target AUC was escalated from 3 to 8 mg carboplatin/mL/min. Over this AUC range the formula accurately predicted the observed AUC (observed/predicted ratio 1.24 +/- 0.11, r = 0.886) and using these additional data, the formula was refined. Dose (mg) = target AUC x (GFR + 25) is now the recommended formula. AUC values of 4 to 6 and 6 to 8 mg/mL. min gave rise to manageable hematological toxicity in previously treated and untreated patients, respectively, and hence target AUC values of 5 and 7 mg/mL min are recommended for single-agent carboplatin in these patient groups. Pharmacokinetic modeling demonstrated that the formula was reasonably accurate regardless of whether a one- or two-compartment model most accurately described carboplatin pharmacokinetics, assuming that body size did not influence nonrenal clearance. The validity of this assumption was demonstrated in 13 patients where no correlation between surface area and nonrenal clearance was found (r = .31, P = .30). Therefore, the formula provides a simple and consistent method of determining carboplatin dose in adults. Since the measure of carboplatin exposure in the formula is AUC, and not toxicity, it will not be influenced by previous or concurrent myelosuppressive therapy or supportive measures. The formula is therefore applicable to combination and high-dose studies as well as conventional single-agent therapy, although the target AUC for carboplatin will need to be redefined for combination chemotherapy.

Parallel Optimization of Potency and Pharmacokinetics Leading to the Discovery of a Pyrrole Carboxamide ERK5 Kinase Domain Inhibitor

The nonclassical extracellular signal-related kinase 5 (ERK5) mitogen-activated protein kinase pathway has been implicated in increased cellular proliferation, migration, survival, and angiogenesis; hence, ERK5 inhibition may be an attractive approach for cancer treatment. However, the development of selective ERK5 inhibitors has been challenging. Previously, we described the development of a pyrrole carboxamide high-throughput screening hit into a selective, submicromolar inhibitor of ERK5 kinase activity. Improvement in the ERK5 potency was necessary for the identification of a tool ERK5 inhibitor for target validation studies. Herein, we describe the optimization of this series to identify nanomolar pyrrole carboxamide inhibitors of ERK5 incorporating a basic center, which suffered from poor oral bioavailability. Parallel optimization of potency and in vitro pharmacokinetic parameters led to the identification of a nonbasic pyrazole analogue with an optimal balance of ERK5 inhibition and oral exposure.

Structure-Based Design of Potent and Orally Active Isoindolinone Inhibitors of MDM2-p53 Protein-Protein Interaction

Inhibition of murine double minute 2 (MDM2)-p53 protein-protein interaction with small molecules has been shown to reactivate p53 and inhibit tumor growth. Here, we describe rational, structure-guided, design of novel isoindolinone-based MDM2 inhibitors. MDM2 X-ray crystallography, quantum mechanics ligand-based design, and metabolite identification all contributed toward the discovery of potent in vitro and in vivo inhibitors of the MDM2-p53 interaction with representative compounds inducing cytostasis in an SJSA-1 osteosarcoma xenograft model following once-daily oral administration.

2-Arylamino-6-ethynylpurines are cysteine-targeting irreversible inhibitors of Nek2 kinase

Renewed interest in covalent inhibitors of enzymes implicated in disease states has afforded several agents targeted at protein kinases of relevance to cancers. We now report the design, synthesis and biological evaluation of 6-ethynylpurines that act as covalent inhibitors of Nek2 by capturing a cysteine residue (Cys22) close to the catalytic domain of this protein kinase. Examination of the crystal structure of the non-covalent inhibitor 3-((6-cyclohexylmethoxy-7H-purin-2-yl)amino)benzamide in complex with Nek2 indicated that replacing the alkoxy with an ethynyl group places the terminus of the alkyne close to Cys22 and in a position compatible with the stereoelectronic requirements of a Michael addition. A series of 6-ethynylpurines was prepared and a structure activity relationship (SAR) established for inhibition of Nek2. 6-Ethynyl-N-phenyl-7H-purin-2-amine [IC50 0.15 μM (Nek2)] and 4-((6-ethynyl-7H-purin-2-yl)amino)benzenesulfonamide (IC50 0.14 μM) were selected for determination of the mode of inhibition of Nek2, which was shown to be time-dependent, not reversed by addition of ATP and negated by site directed mutagenesis of Cys22 to alanine. Replacement of the ethynyl group by ethyl or cyano abrogated activity. Variation of substituents on the N-phenyl moiety for 6-ethynylpurines gave further SAR data for Nek2 inhibition. The data showed little correlation of activity with the nature of the substituent, indicating that after sufficient initial competitive binding to Nek2 subsequent covalent modification of Cys22 occurs in all cases. A typical activity profile was that for 2-(3-((6-ethynyl-9H-purin-2-yl)amino)phenyl)acetamide [IC50 0.06 μM (Nek2); GI50 (SKBR3) 2.2 μM] which exhibited >5-10-fold selectivity for Nek2 over other kinases; it also showed > 50% growth inhibition at 10 μM concentration against selected breast and leukaemia cell lines. X-ray crystallographic analysis confirmed that binding of the compound to the Nek2 ATP-binding site resulted in covalent modification of Cys22. Further studies confirmed that 2-(3-((6-ethynyl-9H-purin-2-yl)amino)phenyl)acetamide has the attributes of a drug-like compound with good aqueous solubility, no inhibition of hERG at 25 μM and a good stability profile in human liver microsomes. It is concluded that 6-ethynylpurines are promising agents for cancer treatment by virtue of their selective inhibition of Nek2.

Selective DNA-PKcs inhibition extends the therapeutic index of localized radiotherapy and chemotherapy

Potentiating radiotherapy and chemotherapy by inhibiting DNA damage repair is proposed as a therapeutic strategy to improve outcomes for patients with solid tumors. However, this approach risks enhancing normal tissue toxicity as much as tumor toxicity, thereby limiting its translational impact. Using NU5455, a newly identified highly selective oral inhibitor of DNA-dependent protein kinase catalytic subunit (DNA-PKcs) activity, we found that it was indeed possible to preferentially augment the effect of targeted radiotherapy on human orthotopic lung tumors without influencing acute DNA damage or a late radiation-induced toxicity (fibrosis) to normal mouse lung. Furthermore, while NU5455 administration increased both the efficacy and the toxicity of a parenterally administered topoisomerase inhibitor, it enhanced the activity of doxorubicin released locally in liver tumor xenografts without inducing any adverse effect. This strategy is particularly relevant to hepatocellular cancer, which is treated clinically with localized drug-eluting beads and for which DNA-PKcs activity is reported to confer resistance to treatment. We conclude that transient pharmacological inhibition of DNA-PKcs activity is effective and tolerable when combined with localized DNA-damaging therapies and thus has promising clinical potential.

Identification of a novel orally bioavailable ERK5 inhibitor with selectivity over p38α and BRD4

Extracellular regulated kinase 5 (ERK5) signalling has been implicated in driving a number of cellular phenotypes including endothelial cell angiogenesis and tumour cell motility. Novel ERK5 inhibitors were identified using high throughput screening, with a series of pyrrole-2-carboxamides substituted at the 4-position with an aroyl group being found to exhibit IC50 values in the micromolar range, but having no selectivity against p38α MAP kinase. Truncation of the N-substituent marginally enhanced potency (∼3-fold) against ERK5, but importantly attenuated inhibition of p38α. Systematic variation of the substituents on the aroyl group led to the selective inhibitor 4-(2-bromo-6-fluorobenzoyl)-N-(pyridin-3-yl)-1H-pyrrole-2-carboxamide (IC50 0.82 μM for ERK5; IC50 > 120 μM for p38α). The crystal structure (PDB 5O7I) of this compound in complex with ERK5 has been solved. This compound was orally bioavailable and inhibited bFGF-driven Matrigel plug angiogenesis and tumour xenograft growth. The selective ERK5 inhibitor described herein provides a lead for further development into a tool compound for more extensive studies seeking to examine the role of ERK5 signalling in cancer and other diseases.

Glucocorticoids and selumetinib are highly synergistic in RAS pathway-mutated childhood acute lymphoblastic leukemia through upregulation of BIM

New drugs are needed for the treatment of relapsed acute lymphoblastic leukemia and preclinical evaluation of the MEK inhibitor, selumetinib, has shown that this drug has excellent activity in those leukemias with RAS pathway mutations. The proapoptotic protein, BIM is pivotal in the induction of cell death by both selumetinib and glucocorticoids, suggesting the potential for synergy. Thus, combination indices for dexamethasone and selumetinib were determined in RAS pathway-mutated acute lymphoblastic leukemia primagraft cells in vitro and were indicative of strong synergism (combination index <0.2; n=5). Associated pharmacodynamic assays were consistent with the hypothesis that the drug combination enhanced BIM upregulation over that achieved by a single drug alone. Dosing of dexamethasone and selumetinib singly and in combination in mice engrafted with primary-derived RAS pathway-mutated leukemia cells resulted in a marked reduction in spleen size which was significantly greater with the drug combination. Assessment of the central nervous system leukemia burden showed a significant reduction in the drug-treated mice, with no detectable leukemia in those treated with the drug combination. These data suggest that a selumetinib-dexamethasone combination may be highly effective in RAS pathway-mutated acute lymphoblastic leukemia. An international phase I/II clinical trial of dexamethasone and selumetinib (Seludex trial) is underway in children with multiply relapsed/refractory disease.

Preclinical evaluation of the first intravenous small molecule MDM2 antagonist alone and in combination with temozolomide in neuroblastoma

High‐risk neuroblastoma, a predominantly TP53 wild‐type (wt) tumour, is incurable in >50% patients supporting the use of MDM2 antagonists as novel therapeutics. Idasanutlin (RG7388) shows in vitro synergy with chemotherapies used to treat neuroblastoma. This is the first study to evaluate the in vivo efficacy of the intravenous idasanutlin prodrug, RO6839921 (RG7775), both alone and in combination with temozolomide in TP53 wt orthotopic neuroblastoma models. Detection of active idasanutlin using liquid chromatography‐mass spectrometry and p53 pathway activation by ELISA assays and Western analysis showed peak plasma levels 1 h post‐treatment with maximal p53 pathway activation 3–6 h post‐treatment. RO6839921 and temozolomide, alone or in combination in mice implanted with TP53 wt SHSY5Y‐Luc and NB1691‐Luc cells showed that combined RO6839921 and temozolomide led to greater tumour growth inhibition and increase in survival compared to vehicle control. Overall, RO6839921 had a favourable pharmacokinetic profile consistent with intermittent dosing and was well tolerated alone and in combination. These preclinical studies support the further development of idasanutlin in combination with temozolomide in neuroblastoma in early phase clinical trials.

What's new?

Long‐term survival of high‐risk neuroblastoma patients currently averages than 50%. New therapies that both improve survival and reduce treatment toxicity are urgently needed. MDM2 antagonists are a novel class of anti‐cancer agents that stabilize the p53 pathway and lead to tumour suppression. In this preclinical study, the authors tested a prodrug of the MDM2 inhibitor idasanutlin in mice. They found that this compound inhibited tumour growth and increased survival, especially in combination with temozolomide. These results support the further development of idasanutlin plus temozolomide in clinical trials for neuroblastoma.

A successful collaboration between academia, biotech and pharma led to discovery of erdafitinib, a selective FGFR inhibitor recently approved by the FDA

The winners of the Malcolm Campbell Memorial Prize for 2019 discuss the discovery of erdafitinib.

Highly Potent Clickable Probe for Cellular Imaging of MDM2 and Assessing Dynamic Responses to MDM2-p53 Inhibition

MDM2 is a key negative regulator of the p53 tumor suppressor. Direct binding of MDM2 to p53 represses the protein's transcriptional activity and induces its polyubiquitination, targeting it for degradation by the proteasome. Consequently, small molecule inhibitors that antagonize MDM2-p53 binding, such as RG7388, have progressed into clinical development aiming to reactivate p53 function in TP53 wild-type tumors. Here, we describe the design, synthesis, and biological evaluation of a trans-cyclooctene tagged derivative of RG7388, RG7388-TCO, which showed high cellular potency and specificity for MDM2. The in-cell reaction of RG7388-TCO with a tetrazine-tagged BODIPY dye enabled fluorescence imaging of endogenous MDM2 in SJSA-1 and T778 tumor cells. RG7388-TCO was also used to pull down MDM2 by reaction with tetrazine-tagged agarose beads in SJSA-1 lysates. The data presented show that RG733-TCO enables precise imaging of MDM2 in cells and can permit a relative assessment of target engagement and MDM2-p53 antagonism in vitro.

TP53 mutant MDM2-amplified cell lines selected for resistance to MDM2-p53 binding antagonists retain sensitivity to ionizing radiation

Non-genotoxic reactivation of the p53 pathway by MDM2-p53 binding antagonists is an attractive treatment strategy for wild-type TP53 cancers. To determine how resistance to MDM2/p53 binding antagonists might develop, SJSA-1 and NGP cells were exposed to growth inhibitory concentrations of chemically distinct MDM2 inhibitors, Nutlin-3 and MI-63, and clonal resistant cell lines generated. The p53 mediated responses of parental and resistant cell lines were compared. In contrast to the parental cell lines, p53 activation by Nutlin-3, MI-63 or ionizing radiation was not observed in either the SJSA-1 or the NGP derived cell lines. An identical TP53 mutation was subsequently identified in both of the SJSA-1 resistant lines, whilst one out of three identified mutations was common to both NGP derived lines. Mutation specific PCR revealed these mutations were present in parental SJSA-1 and NGP cell populations at a low frequency. Despite cross-resistance to a broad panel of MDM2/p53 binding antagonists, these MDM2-amplified and TP53 mutant cell lines remained sensitive to ionizing radiation (IR). These results indicate that MDM2/p53 binding antagonists will select for p53 mutations present in tumours at a low frequency at diagnosis, leading to resistance, but such tumours may nevertheless remain responsive to alternative therapies, including IR.

Sensitizing Ewing sarcoma to chemo- and radiotherapy by inhibition of the DNA-repair enzymes DNA protein kinase (DNA-PK) and poly-ADP-ribose polymerase (PARP) 1/2

Background

DNA-PK and PARP inhibitors sensitize cancer cells to chemo- and radiotherapy. ETS transcription factors (EWS-FLI1) have been described as biomarkers for PARP-inhibitor sensitivity. Sensitivity to single agent PARP inhibitors has so far been limited to homologous recombination repair (HRR) deficient tumors, exploiting synthetic lethality.

Results

In clonogenic assays, single agent rucaparib LD₅₀ values for continuously exposed cells were similar to those observed in HRR-defective cells (CAPAN-1 cell line, BRCA2 defective); however, both ES cell lines (TC-71, CADO-ES1) had functional HRR. In vivo rucaparib administration (10 mg/kg daily) showed no responses. In clonogenic assays, rucaparib enhanced temozolomide, camptothecin and radiation cytotoxicity, which was most profound for temozolomide (15–29 fold enhancement). NU7441 increased the cytotoxicity of etoposide, doxorubicin and radiation.

Materials and Methods

We assessed PARP1/2 (rucaparib) and DNA-PK (NU7441) inhibitors in Ewing sarcoma (ES) cell lines by performing growth inhibition and clonogenic assays. HRR was measured by RAD51 focus formation. Single agent rucaparib was assessed in an in vivo orthotopic model.

Conclusions

Single agent rucaparib ES sensitivity in vitro was not replicated in vivo. DNA-PK and PARP inhibitors are good chemo-/radiosensitizers in ES. The future of these inhibitors lies in their combination with chemo-/radiotherapy, which needs to be evaluated in clinical trials.

PARP inhibitor rucaparib induces changes in NAD levels in cells and liver tissues as assessed by MRS

Poly(adenosine diphosphate ribose) polymerases (PARPs) are multifunctional proteins which play a role in many cellular processes. Namely, PARP1 and PARP2 have been shown to be involved in DNA repair, and therefore are valid targets in cancer treatment with PARP inhibitors, such as rucaparib, currently in clinical trials. Proton magnetic resonance spectroscopy (¹ H-MRS) was used to study the impact of rucaparib in vitro and ex vivo in liver tissue from mice, via quantitative analysis of nicotinamide adenosine diphosphate (NAD⁺ ) spectra, to assess the potential of MRS as a biomarker of the PARP inhibitor response. SW620 (colorectal) and A2780 (ovarian) cancer cell lines, and PARP1 wild-type (WT) and PARP1 knock-out (KO) mice, were treated with rucaparib, temozolomide (methylating agent) or a combination of both drugs. ¹ H-MRS spectra were obtained from perchloric acid extracts of tumour cells and mouse liver. Both cell lines showed an increase in NAD⁺ levels following PARP inhibitor treatment in comparison with temozolomide treatment. Liver extracts from PARP1 WT mice showed a significant increase in NAD⁺ levels after rucaparib treatment compared with untreated mouse liver, and a significant decrease in NAD⁺ levels in the temozolomide-treated group. The combination of rucaparib and temozolomide did not prevent the NAD⁺ depletion caused by temozolomide treatment. The ¹ H-MRS results show that NAD⁺ levels can be used as a biomarker of PARP inhibitor and methylating agent treatments, and suggest that in vivo measurement of NAD⁺ would be valuable.

Abstract LB-300: In vivo evaluation of the intravenous MDM2-p53 antagonist RO6839921 alone and in combination with temozolomide in TP53 wild-type orthotopic models of neuroblastoma

Background. Neuroblastoma is a predominantly TP53 wt tumor which supports the use of MDM2-p53 antagonists as a novel therapy for neuroblastoma patients. This is the first study to evaluate the efficacy of RO6839921, an IV prodrug of RG7388, alone and in combination with temozolomide in TP53 wild-type orthotopic models of neuroblastoma.

Methods. Studies were conducted using a well-established orthotopic model of neuroblastoma, implanted with SHSY5Y-Luc (TP53 wt; non-MYCN amplified) and NB1691-Luc (TP53 wt; MYCN and MDM2 amplified) cells, and randomized into control, intravenous RO6839921, oral temozolomide or RO6839921 and temozolomide in combination. Tumor growth was monitored using bioluminescence imaging. Active RG7388 in plasma and tumor samples were detected using liquid chromatography-mass spectrometry, and p53 pathway activation assessed by MIC-1 ELISA assays, Western analysis and/or immunohistochemistry for p53, p21 and cleaved caspase 3.

Results. Pharmacokinetic and pharmacodynamic analysis of RO6839921 observed peak plasma levels of active RG7388 at 1h posttreatment with maximal activation of the p53 pathway observed 3-6h posttreatment. RO6839921 had a favorable pharmacodynamic profile consistent with intermittent dosing. Assessment of anti-tumor efficacy demonstrated that RO6839921 was as effective as temozolomide and that RO6839921 in combination with temozolomide led to significantly greater tumor growth inhibition and survival than either agent given alone. RO6839921 alone and in combination with temozolomide was well tolerated.

Conclusions. These preclinical studies support the evaluation of combining RO6839921 with temozolomide in early phase clinical trials of neuroblastoma patients with wt TP53.

Citation Format: Lindi Chen, Fabio Pastorino, Philip Berry, Jennifer Bonner, Katrina Wood, Gareth Veal, Mirco Ponzoni, John Lunec, David R. Newell, Deborah A. Tweddle. In vivo evaluation of the intravenous MDM2-p53 antagonist RO6839921 alone and in combination with temozolomide in TP53 wild-type orthotopic models of neuroblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-300. doi:10.1158/1538-7445.AM2017-LB-300

Structure-guided design of purine-based probes for selective Nek2 inhibition

Nek2 (NIMA-related kinase 2) is a cell cycle-dependent serine/threonine protein kinase that regulates centrosome separation at the onset of mitosis. Overexpression of Nek2 is common in human cancers and suppression can restrict tumor cell growth and promote apoptosis. Nek2 inhibition with small molecules, therefore, offers the prospect of a new therapy for cancer. To achieve this goal, a better understanding of the requirements for selective-inhibition of Nek2 is required. 6-Alkoxypurines were identified as ATP-competitive inhibitors of Nek2 and CDK2. Comparison with CDK2-inhibitor structures indicated that judicious modification of the 6-alkoxy and 2-arylamino substituents could achieve discrimination between Nek2 and CDK2. In this study, a library of 6-cyclohexylmethoxy-2-arylaminopurines bearing carboxamide, sulfonamide and urea substituents on the 2-arylamino ring was synthesized. Few of these compounds were selective for Nek2 over CDK2, with the best result being obtained for 3-((6-(cyclohexylmethoxy)-9H-purin-2-yl)amino)-N,N-dimethylbenzamide (CDK2 IC50 = 7.0 μM; Nek2 IC50 = 0.62 μM) with >10-fold selectivity. Deletion of the 6-substituent abrogated activity against both Nek2 and CDK2. Nine compounds containing an (E)-dialkylaminovinyl substituent at C-6, all showed selectivity for Nek2, e.g. (E)-6-(2-(azepan-1-yl)vinyl)-N-phenyl-9H-purin-2-amine (CDK2 IC50 = 2.70 μM; Nek2 IC50 = 0.27 μM). Structural biology of selected compounds enabled a partial rationalization of the observed structure activity relationships and mechanism of Nek2 activation. This showed that carboxamide 11 is the first reported inhibitor of Nek2 in the DFG-in conformation.

Cyclin-Dependent Kinase (CDK) Inhibitors: Structure-Activity Relationships and Insights into the CDK-2 Selectivity of 6-Substituted 2-Arylaminopurines

Purines and related heterocycles substituted at C-2 with 4'-sulfamoylanilino and at C-6 with a variety of groups have been synthesized with the aim of achieving selectivity of binding to CDK2 over CDK1. 6-Substituents that favor competitive inhibition at the ATP binding site of CDK2 were identified and typically exhibited 10-80-fold greater inhibition of CDK2 compared to CDK1. Most impressive was 4-((6-([1,1'-biphenyl]-3-yl)-9H-purin-2-yl)amino) benzenesulfonamide (73) that exhibited high potency toward CDK2 (IC50 0.044 μM) but was ∼2000-fold less active toward CDK1 (IC50 86 μM). This compound is therefore a useful tool for studies of cell cycle regulation. Crystal structures of inhibitor-kinase complexes showed that the inhibitor stabilizes a glycine-rich loop conformation that shapes the ATP ribose binding pocket and that is preferred in CDK2 but has not been observed in CDK1. This aspect of the active site may be exploited for the design of inhibitors that distinguish between CDK1 and CDK2.

Enhanced anti-tumour activity of the combination of the novel MEK inhibitor WX-554 and the novel PI3K inhibitor WX-037

PURPOSE

Tumours frequently have defects in multiple oncogenic pathways, e.g. MAPK and PI3K signalling pathways, and combinations of targeted therapies may be required for optimal activity. This study evaluated the novel MEK inhibitor WX-554 and the novel PI3K inhibitor WX-037, as single agents and in combination, in colorectal carcinoma cell lines and tumour xenograft-bearing mice.

METHODS

In vitro growth inhibition, survival and signal transduction were measured using the Sulforhodamine B, clonogenic and Western blotting assays, respectively, in HCT116 and HT29 cell lines. In vivo anti-tumour efficacy and pharmacokinetic properties were assessed in HCT116 and HT29 human colorectal cancer xenograft tumour-bearing mice.

RESULTS

The combination of WX-554 and WX-037 exhibited marked synergistic growth inhibition in vitro, which was associated with increased cytotoxicity and enhanced inhibition of ERK and S6 phosphorylation, compared to either agent alone. Pharmacokinetic analyses indicated that there was no PK interaction between the two drugs at low doses, but that at higher doses, WX-037 may delay the tumour uptake of WX-554. In vivo efficacy studies revealed that the combination of WX-037 and WX-554 was non-toxic and exhibited marked tumour growth inhibition greater than observed with either agent alone.

CONCLUSION

These studies show for the first time that combination treatment with the novel MEK inhibitor WX-554 and the novel PI3K inhibitor WX-037 can induce synergistic growth inhibition in vitro, which translates into enhanced anti-tumour efficacy in vivo.

Sulfatase-2: a prognostic biomarker and candidate therapeutic target in patients with pancreatic ductal adenocarcinoma

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is the fifth most common cause of cancer death in the UK. Its poor prognosis is attributed to late detection and limited therapeutic options. Expression of SULF2, an endosulfatase that modulates heparan sulfate proteoglycan 6-O-sulfation and is reportedly tumourigenic in different types of cancer, was investigated.

METHODS

SULF2 expression was determined immunohistochemically in archival surgical resection tissue sections from 93 patients with a confirmed histological diagnosis of PDAC between 2002 and 2008 followed for a median of 9 years. Relationships with clinico-pathological parameters and patient survival were explored.

RESULTS

The majority of PDACs showed positive SULF2 staining in tumour cells and intratumoural or tumour-adjacent stroma. Greater than 25% SULF2-positive tumour cells was present in 60% of cancers and correlated with tumour stage (P=0.002) and perineural invasion (P=0.024). SULF2 intensity was scored moderate or strong in 81% of cancers and positively correlated with vascular invasion (P=0.015). High SULF2 expression, defined as >50% SULF2-positive tumour cells and strong SULF2 staining, was associated with shorter time to radiological progression (P=0.018, HR 1.98, CI 1.13-3.47). Similarly, by multivariate analysis, high SULF2 expression was independently associated with poorer survival (P=0.004, HR 2.10, CI 1.26-3.54), with a median survival of 11 months vs 21 months for lower PDAC SULF2.

CONCLUSIONS

Elevated SULF2 in PDAC was associated with advanced tumour stage, vascular invasion, shorter interval to radiological progression and shorter overall survival. SULF2 may have roles as a prognostic biomarker and as a therapeutic target for patients with PDAC.

Combined PI3K and CDK2 inhibition induces cell death and enhances in vivo antitumour activity in colorectal cancer

BACKGROUND

The phosphatidylinositol-3-kinase/mammalian target of rapamycin (PI3K/mTOR) pathway is commonly deregulated in human cancer, hence many PI3K and mTOR inhibitors have been developed and have now reached clinical trials. Similarly, CDKs have been investigated as cancer drug targets.

METHODS

We have synthesised and characterised a series of 6-aminopyrimidines identified from a kinase screen that inhibit PI3K and/or mTOR and/or CDK2. Kinase inhibition, tumour cell growth, cell cycle distribution, cytotoxicity and signalling experiments were undertaken in HCT116 and HT29 colorectal cancer cell lines, and in vivo HT29 efficacy studies.

RESULTS

2,6-Diaminopyrimidines with an O(4)-cyclohexylmethyl substituent and a C-5-nitroso or cyano group (1,2,5) induced cell cycle phase alterations and were growth inhibitory (GI50<20 μM). Compound 1, but not 2 or 5, potently inhibits CDK2 (IC50=0.1 nM) as well as PI3K, and was cytotoxic at growth inhibitory concentrations. Consistent with kinase inhibition data, compound 1 reduced phospho-Rb and phospho-rS6 at GI50 concentrations. Combination of NU6102 (CDK2 inhibitor) and pictilisib (GDC-0941; pan-PI3K inhibitor) resulted in synergistic growth inhibition, and enhanced cytotoxicity in HT29 cells in vitro and HT29 tumour growth inhibition in vivo.

CONCLUSIONS

These studies identified a novel series of mixed CDK2/PI3K inhibitors and demonstrate that dual targeting of CDK2 and PI3K can result in enhanced antitumour activity.

High-Throughput Screening and Hit Validation of Extracellular-Related Kinase 5 (ERK5) Inhibitors

The extracellular-related kinase 5 (ERK5) is a promising target for cancer therapy. A high-throughput screen was developed for ERK5, based on the IMAP FP progressive binding system, and used to identify hits from a library of 57 617 compounds. Four distinct chemical series were evident within the screening hits. Resynthesis and reassay of the hits demonstrated that one series did not return active compounds, whereas three series returned active hits. Structure-activity studies demonstrated that the 4-benzoylpyrrole-2-carboxamide pharmacophore had excellent potential for further development. The minimum kinase binding pharmacophore was identified, and key examples demonstrated good selectivity for ERK5 over p38α kinase.

Design and synthesis of biphenyl and biphenyl ether inhibitors of sulfatases

Inhibitors of sulfatase-2 are putative anticancer agents, but the discovery of potent small molecules targeting this enzyme has proved challenging. Based on molecular modelling, two series of sulfatase-2 inhibitors have been developed with biphenyl and biphenyl ether scaffolds judiciously substituted with sulfamate, carboxylate and other polar groups (e.g. amino). Inhibition of aryl sulfatase A and B was also determined. The biphenyl ether derivatives were less selective for sulfatase-2 over aryl sulfatase B than the biphenyl series. All biphenyl ether derivatives inhibited aryl sulfatase A, whereas only amino derivatives inhibited aryl sulfatase B significantly. In the biphenyl series few derivatives exhibited activity against aryl sulfatase B. The trichloroethylsulfamate group was identified as a new pharmacophore enabling potent inhibition of all of the sulfatases studied.

Pre-clinical evaluation of the MDM2-p53 antagonist RG7388 alone and in combination with chemotherapy in neuroblastoma

Neuroblastoma is a predominantly p53 wild-type (wt) tumour and MDM2-p53 antagonists offer a novel therapeutic strategy for neuroblastoma patients. RG7388 (Roche) is currently undergoing early phase clinical evaluation in adults. This study assessed the efficacy of RG7388 as a single-agent and in combination with chemotherapies currently used to treat neuroblastoma in a panel of neuroblastoma cell lines. RG7388 GI₅₀ concentrations were determined in 21 p53-wt and mutant neuroblastoma cell lines of varying MYCN, MDM2 and p14^ARF status, together with MYCN-regulatable Tet21N cells. The primary determinant of response was the presence of wt p53, and overall there was a >200-fold difference in RG7388 GI₅₀ concentrations for p53-wt versus mutant cell lines. Tet21N MYCN+ cells were significantly more sensitive to RG7388 compared with MYCN− cells. Using median-effect analysis in 5 p53-wt neuroblastoma cell lines, selected combinations of RG7388 with cisplatin, doxorubicin, topotecan, temozolomide and busulfan were synergistic. Furthermore, combination treatments led to increased apoptosis, as evident by higher caspase-3/7 activity compared to either agent alone. These data show that RG7388 is highly potent against p53-wt neuroblastoma cells, and strongly supports its further evaluation as a novel therapy for patients with high-risk neuroblastoma and wt p53 to potentially improve survival and/or reduce toxicity.

Pre-clinical use of isogenic cell lines and tumours in vitro and in vivo for predictive biomarker discovery; impact of KRAS and PI3KCA mutation status on MEK inhibitor activity is model dependent

Studies to identify predictive biomarkers can be carried out in isogenic cancer cell lines, which enable interrogation of the effect of a specific mutation. We assessed the effects of four drugs, the PI3K-mammalian target of rapamycin inhibitor dactolisib, the PI3K inhibitor pictrelisib, and the MEK (MAPK/ERK Kinase) inhibitors PD 0325901 and selumetinib, in isogenic DLD1 parental, KRAS(+/-), KRAS(G13D/-), PIK3CA(+/-) and PIK3CA(E545K/-) colorectal carcinoma cell lines. Importantly, we found substantial differences in the growth of these cells and in their drug sensitivity depending on whether they were studied under 2D (standard tissue culture on plastic) or 3D (in vitro soft agar and in vivo xenograft) conditions. DLD1 KRAS(+/-) and DLD1 PIK3CA(+/-) cells were more sensitive to MEK inhibitors than parental, DLD1 KRAS(G13D/-) and DLD1 PIK3CA(E545K/-) cells under 2D conditions, whereas DLD1 KRAS(G13D/-) and DLD1 PIK3CA(E545K/-) xenografts were sensitive to 10 mg/kg daily ×14 PD 0325901 in vivo (p ≤ 0.02) but tumours derived from parental DLD1 cells were not. These findings indicate that KRAS and PIK3CA mutations can influence the response of DLD1 colorectal cancer cell lines to MEK and PI3K inhibitors, but that the effect is dependent on the experimental model used to assess drug sensitivity.

Tumor cells with KRAS or BRAF mutations or ERK5/MAPK7 amplification are not addicted to ERK5 activity for cell proliferation

ERK5, encoded by MAPK7, has been proposed to play a role in cell proliferation, thus attracting interest as a cancer therapeutic target. While oncogenic RAS or BRAF cause sustained activation of the MEK1/2-ERK1/2 pathway, ERK5 is directly activated by MEK5. It has been proposed that RAS and RAF proteins can also promote ERK5 activation. Here we investigated the interplay between RAS-RAF-MEK-ERK and ERK5 signaling and studied the role of ERK5 in tumor cell proliferation in 2 disease-relevant cell models. We demonstrate that although an inducible form of CRAF (CRAF:ER*) can activate ERK5 in fibroblasts, the response is delayed and reflects feed-forward signaling. Additionally, oncogenic KRAS and BRAF do not activate ERK5 in epithelial cells. Although KRAS and BRAF do not couple directly to MEK5-ERK5, ERK5 signaling might still be permissive for proliferation. However, neither the selective MEK5 inhibitor BIX02189 or ERK5 siRNA inhibited proliferation of colorectal cancer cells harbouring KRAS(G12C/G13D) or BRAF(V600E). Furthermore, there was no additive or synergistic effect observed when BIX02189 was combined with the MEK1/2 inhibitor Selumetinib (AZD6244), suggesting that ERK5 was neither required for proliferation nor a driver of innate resistance to MEK1/2 inhibitors. Finally, even cancer cells with MAPK7 amplification were resistant to BIX02189 and ERK5 siRNA, showing that ERK5 amplification does not confer addiction to ERK5 for cell proliferation. Thus ERK5 signaling is unlikely to play a role in tumor cell proliferation downstream of KRAS or BRAF or in tumor cells with ERK5 amplification. These results have important implications for the role of ERK5 as an anti-cancer drug target.

Identification and Characterization of an Irreversible Inhibitor of CDK2

Irreversible inhibitors that modify cysteine or lysine residues within a protein kinase ATP binding site offer, through their distinctive mode of action, an alternative to ATP-competitive agents. 4-((6-(Cyclohexylmethoxy)-9H-purin-2-yl)amino)benzenesulfonamide (NU6102) is a potent and selective ATP-competitive inhibitor of CDK2 in which the sulfonamide moiety is positioned close to a pair of lysine residues. Guided by the CDK2/NU6102 structure, we designed 6-(cyclohexylmethoxy)-N-(4-(vinylsulfonyl)phenyl)-9H-purin-2-amine (NU6300), which binds covalently to CDK2 as shown by a co-complex crystal structure. Acute incubation with NU6300 produced a durable inhibition of Rb phosphorylation in SKUT-1B cells, consistent with it acting as an irreversible CDK2 inhibitor. NU6300 is the first covalent CDK2 inhibitor to be described, and illustrates the potential of vinyl sulfones for the design of more potent and selective compounds.

Searching for Dual Inhibitors of the MDM2-p53 and MDMX-p53 Protein-Protein Interaction by a Scaffold-Hopping Approach

Two libraries of substituted benzimidazoles were designed using a 'scaffold-hopping' approach based on reported MDM2-p53 inhibitors. Substituents were chosen following library enumeration and docking into an MDM2 X-ray structure. Benzimidazole libraries were prepared using an efficient solution-phase approach and screened for inhibition of the MDM2-p53 and MDMX-p53 protein-protein interactions. Key examples showed inhibitory activity against both targets.

SKP2 is a direct transcriptional target of MYCN and a potential therapeutic target in neuroblastoma

SKP2 is the substrate recognition subunit of the ubiquitin ligase complex which targets p27(KIP1) for degradation. Induced at the G1/S transit of the cell cycle, SKP2 is frequently overexpressed in human cancers and contributes to malignancy. We previously identified SKP2 as a possible MYCN target gene and hence hypothesise that SKP2 is a potential therapeutic target in MYCN amplified disease. A positive correlation was identified between MYCN activity and SKP2 mRNA expression in Tet21N MYCN-regulatable cells and a panel of MYCN amplified and non-amplified neuroblastoma cell lines. In chromatin immunoprecipitation and reporter gene assays, MYCN bound directly to E-boxes within the SKP2 promoter and induced transcriptional activity which was decreased by the removal of MYCN and E-box mutation. Although SKP2 knockdown inhibited cell growth in both MYCN amplified and non-amplified cells, cell cycle arrest and apoptosis were induced only in non-MYCN amplified neuroblastoma cells. In conclusion these data identify SKP2 as a direct transcriptional target of MYCN and supports SKP2 as a potential therapeutic target in neuroblastoma.

Regioselective sulfamoylation at low temperature enables concise syntheses of putative small molecule inhibitors of sulfatases

Regioselective sulfamoylation of primary hydroxyl groups enabled a 5-step synthesis (overall yield 17%) of the first reported small molecule inhibitor of sulfatase-1 and 2, ((2S,3R,4R,5S,6R)-4,5-dihydroxy-2-methoxy-6-((sulfamoyloxy)methyl)tetrahydro-2H-pyran-3-yl)sulfamic acid, which obviated the use of hydroxyl protecting groups and is a marked improvement on the reported 9-step synthesis (overall yield 9%) employing hazardous trifluoromethylsulfonyl azide. The sulfamoylation methodology was used to prepare a range of derivatives of 1, and inhibition data was generated for Sulf-2, ARSA and ARSB.

Pharmacologic biomarkers in the development of stratified cancer medicine

Clinical pharmacologic research plays a vital role in cancer drug development. In recent years, biomarker studies have become integral to this process, specifically the use of pharmacologic biomarkers in the development of targeted therapies and their translation to clinical practice. In this overview, we discuss the validation of pharmacodynamics (PD) biomarkers and highlight the circulating tumor DNA as a promising cancer biomarker to illustrate how PD biomarkers can be powerful tools for guiding treatment strategies. We provide insights into PD biomarker approaches for future development of novel therapies and their role in cancer medicine. See all articles in this CCR focus section, "Progress in pharmacodynamic endpoints."

Synthesis and Activity of Putative Small-Molecule Inhibitors of the F-Box Protein SKP2

The tetrahydropyran 4-(((3-(2,2-dimethyltetrahydro-2H-pyran-4-yl)-4-phenylbutyl)amino)methyl)-N,N-dimethylaniline was reported to disrupt the SCFSKP2 E3 ligase complex. Efficient syntheses of this tetrahydropyran derivative and analogues, including the des-dimethyl derivative 4-(((3-(tetrahydro-2H-pyran-4-yl)-4-phenylbutyl)amino)methyl)-N,N-dimethylaniline, are described. The enantiomers of the des-dimethyl compound were obtained using Evans’ chiral auxiliaries. Structure–activity relationships for these tetrahydropyrans and analogues have been determined by measurement of growth-inhibitory activities in HeLa cells, which indicated a non-specific mechanism of action that correlates with inhibitor lipophilicity. However, preliminary data with (R)- and (S)-4-(((3-(tetrahydro-2H-pyran-4-yl)-4-phenylbutyl)amino)methyl)-N,N-dimethylaniline showed enantioselective inhibition of the degradation of p27 in a cell-based assay that acts as a reporter of SKP2 activity.

Abstract 5451: Profiling inhibitors of MDM2:p53 and MDMX:p53 in relation to MDMX protein levels

Pharmacological antagonism of the interaction between MDM2 and/or MDMX with p53 has been pursued as a therapeutic strategy to restore p53 tumour suppressor activity in wild type TP53 tumours with amplification or over-expression of these negative regulators. The majority of small molecule approaches described to date inhibit MDM2 binding to p53, which has E3 ligase activity and through ubiquitination targets p53 for degradation. However, MDMX, although devoid of E3 ligase activity itself, forms heterodimers with MDM2 and augments its activity to induce polyubiquitination of p53. Further complexity in this regulatory network arises from the fact that MDM2 is a target gene of p53 transcription, and that MDM2 can also control the stability of MDMX. Since MDMX is widely reported to confer resistance to established MDM2:p53 antagonists, this study aimed to examine the activity of MDM2:p53 selective inhibitors across a panel of wild-type TP53 cell lines with variable MDM2 and MDMX protein expression, and to contrast this with recently described inhibitors with mixed MDM2:p53 and MDMX:p53 activity.

Growth inhibition studies (72h) were performed using XTT assays, but with verification by orthogonal methods (SRB, clonogenic assays). Gene expression was determined at the level of mRNA and protein. The selectivity of all inhibitors was confirmed initially in p53 wild-type and non-functional paired cell lines.

As anticipated, MDM2:p53 selective inhibitors (nutlin-3a, MI-773, RG7112) were active in MDM2 amplified cell lines with low MDMX expression (SJSA-1 and T778; GI50 range 0.2 to 1 uM). However, a similar level of activity was also evident in cell lines with low/medium MDM2 in the presence of medium/high MDMX expression (Pre B 697, A375, HCT116, MRK-NU1, and NGP cells: GI50 range 0.2 to 2 uM). Appreciable resistance was only evident in Jeg3 and MCF-7 cells (low MDM2 and high MDMX), averaged compound GI50 values ranging from 9 - 10 uM in Jeg3 and 6 - 14 uM in MCF-7. Whilst a concentration dependent degradation of MDMX was observed in some sensitive cell lines with medium/high MDMX expression, in others no change was evident, suggesting that there are multiple determinants of cellular sensitivity to such inhibitors. Importantly, the mixed MDM2:p53 and MDMX:p53 antagonist RO-5963, displayed a different spectrum of activity, with least growth inhibition evident in SJSA-1 and T778 MDM2 amplified cell lines, and activity being retained in MDMX amplified Jeg3 cells.

These studies support the concept that targeting MDMX may provide a different spectrum of antitumour activity to selective MDM2:p53 inhibition. However, MDMX protein levels per se do not constitute a universal resistance factor to selective MDM2:p53 inhibitors and, beyond MDM2 amplification, the identification of additional markers of sensitivity is warranted for this class of agent.

Citation Format: Sue Tudhope, Yan Zhao, Anita Wittner, Elaine Wilmore, Annalisa Bertoli, Santosh Adhikari, Suzannah J. Harnor, Fabio Del Bello, Alessandro Piergentili, John Lunec, Ian R. Hardcastle, Roger J. Griffin, Bernard R. Golding, Celine Cano, David R. Newell, Stephen R. Wedge. Profiling inhibitors of MDM2:p53 and MDMX:p53 in relation to MDMX protein levels. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5451. doi:10.1158/1538-7445.AM2014-5451

Abstract 2744: The novel and contrasting roles of ATM and DNA-PK in the response of cells to microtubule-targeting anticancer agents

Ataxia telangiectasia mutated (ATM) and DNA-dependent protein kinase (DNA-PK) are DNA-damage activated kinases that play vital roles in the DNA double-strand break repair pathways homologous recombination (HR) and non-homologous end joining (NHEJ), respectively. ATM and DNA-PK have both been shown to have roles in addition to DNA repair, including localising at the centrosome during mitosis and mitotic regulation. This latter role led to the hypothesis that inhibition of ATM and DNA-PK, using the small molecule inhibitors KU55933 and NU7441, respectively, will sensitise cells to agents that interfere with formation of the mitotic spindle, e.g. microtubule-targeting agents. Here we investigated the sensitisation effects of the ATM inhibitor KU55933 to microtubule-targeting agents in paired sensitive and multidrug-resistant cells.

In growth inhibition studies, KU55933 (10μM) sensitised CCRF-CEM leukaemia cells 4-fold to vincristine, and sensitised vincristine-resistant CCRF-CEM VCR/R cells 40-fold to vincristine. We have previously shown that inhibition of DNA-PK sensitises parental and multidrug-resistant (MDR) cells to microtubule-targeting agents and that DNA-PK is activated in response to these agents (Mould E, Proc Ann Meet AACR 2013; 54: #3329). The DNA-PK inhibitor increased vincristine-induced caspase 3/7 activation 2-fold after 24 hours, similar to the increase seen in combination with the positive control mitoxantrone. In contrast, KU55933 did not increase vincristine-induced caspase 3/7-mediated apoptosis, indicating a different mechanism of increased cell death. Vincristine-induced DNA-PK autophosphorylation (ser2056) (Western blotting) was abrogated by NU7441. However, the microtubule-targeting agents had no effect on ATM autophosphorylation (ser1981). Ongoing studies include confocal microscopy to determine localisation of ATM and DNA-PK during spindle formation, and the effects of microtubule-targeting agents and ATM/DNA-PK inhibitors on localisation, to further elucidate the novel roles of these kinases.

We have also demonstrated that 1μM NU7441 induced a 2.1-fold (p=0.04) increase in vincristine accumulation in MDR1-overexpressing cells and that NU7441 is a dual DNA-PK MDR1 inhibitor. Due to the increased sensitisation observed in MDR cells, the effect of KU55933 on drug accumulation was investigated. LC-MS studies demonstrated that both 1μM and 10μM KU55933 increased intracellular vincristine accumulation 1.5-fold and 2.7-fold, respectively, in MDR1-overexpressing cells, indicating that KU55933 acts as a dual ATM and MDR1 inhibitor.

These results highlight the complexity of the roles of ATM and DNA-PK and extend the therapeutic potential of targeting these kinases in combination with chemotherapeutic agents.

Citation Format: Emily V.A. Mould, Stephanie E.A. Burnell, Philip L. Berry, David R. Newell, Elaine Willmore. The novel and contrasting roles of ATM and DNA-PK in the response of cells to microtubule-targeting anticancer agents. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2744. doi:10.1158/1538-7445.AM2014-2744

Structurally diverse MDM2-p53 antagonists act as modulators of MDR-1 function in neuroblastoma

BACKGROUND

A frequent mechanism of acquired multidrug resistance in human cancers is overexpression of ATP-binding cassette transporters such as the Multi-Drug Resistance Protein 1 (MDR-1). Nutlin-3, an MDM2-p53 antagonist, has previously been reported to be a competitive MDR-1 inhibitor.

METHODS

This study assessed whether the structurally diverse MDM2-p53 antagonists, MI-63, NDD0005, and RG7388 are also able to modulate MDR-1 function, particularly in p53 mutant neuroblastoma cells, using XTT-based cell viability assays, western blotting, and liquid chromatography-mass spectrometry analysis.

RESULTS

Verapamil and the MDM2-p53 antagonists potentiated vincristine-mediated growth inhibition in a concentration-dependent manner when used in combination with high MDR-1-expressing p53 mutant neuroblastoma cell lines at concentrations that did not affect the viability of cells when given alone. Liquid chromatography-mass spectrometry analyses showed that verapamil, Nutlin-3, MI-63 and NDD0005, but not RG7388, led to increased intracellular levels of vincristine in high MDR-1-expressing cell lines.

CONCLUSIONS

These results show that in addition to Nutlin-3, other structurally unrelated MDM2-p53 antagonists can also act as MDR-1 inhibitors and reverse MDR-1-mediated multidrug resistance in neuroblastoma cell lines in a p53-independent manner. These findings are important for future clinical trial design with MDM2-p53 antagonists when used in combination with agents that are MDR-1 substrates.

8-Substituted O(6)-cyclohexylmethylguanine CDK2 inhibitors: using structure-based inhibitor design to optimize an alternative binding mode

Evaluation of the effects of purine C-8 substitution within a series of CDK1/2-selective O(6)-cyclohexylmethylguanine derivatives revealed that potency decreases initially with increasing size of the alkyl substituent. Structural analysis showed that C-8 substitution is poorly tolerated, and to avoid unacceptable steric interactions, these compounds adopt novel binding modes. Thus, 2-amino-6-cyclohexylmethoxy-8-isopropyl-9H-purine adopts a "reverse" binding mode where the purine backbone has flipped 180°. This provided a novel lead chemotype from which we have designed more potent CDK2 inhibitors using, in the first instance, quantum mechanical energy calculations. Introduction of an ortho-tolyl or ortho-chlorophenyl group at the purine C-8 position restored the potency of these "reverse" binding mode inhibitors to that of the parent 2-amino-6-cyclohexylmethoxy-9H-purine. By contrast, the corresponding 8-(2-methyl-3-sulfamoylphenyl)-purine derivative exhibited submicromolar CDK2-inhibitory activity by virtue of engineered additional interactions with Asp86 and Lys89 in the reversed binding mode, as confirmed by X-ray crystallography.

Synthesis of 3′-deoxy-3′-fluorothymidine (FLT) 5′-O-glucuronide: a reference standard for imaging studies with [18F]FLT

The de novo synthesis of 3′-deoxy-3′-fluorothymidine-5′-O-glucuronide enabled both the analysis of this reference standard by HPLC and identification of the metabolite in a blood sample from a patient administered [¹⁸F]FLT.

The enhanced in vivo activity of the combination of a MEK and a PI3K inhibitor correlates with [18F]-FLT PET in human colorectal cancer xenograft tumour-bearing mice

Combined targeting of the MAPK and PI3K signalling pathways in cancer may be necessary for optimal therapeutic activity. To support clinical studies of combination therapy, 3′-deoxy-3′-[¹⁸F]-fluorothymidine ([¹⁸F]-FLT) uptake measured by Positron Emission Tomography (PET) was evaluated as a non-invasive surrogate response biomarker in pre-clinical models. The in vivo anti-tumour efficacy and PK-PD properties of the MEK inhibitor PD 0325901 and the PI3K inhibitor GDC-0941, alone and in combination, were evaluated in HCT116 and HT29 human colorectal cancer xenograft tumour-bearing mice, and [¹⁸F]-FLT PET investigated in mice bearing HCT116 xenografts. Dual targeting of PI3K and MEK induced marked tumour growth inhibition in vivo, and enhanced anti-tumour activity was predicted by [¹⁸F]-FLT PET scanning after 2 days of treatment. Pharmacodynamic analyses using the combination of the PI3K inhibitor GDC-0941 and the MEK inhibitor PD 0325901 revealed that increased efficacy is associated with an enhanced inhibition of the phosphorylation of ERK1/2, S6 and 4EBP1, compared to that observed with either single agent, and maintained inhibition of AKT phosphorylation. Pharmacokinetic studies indicated that there was no marked PK interaction between the two drugs. Together these results indicate that the combination of PI3K and MEK inhibitors can result in significant efficacy, and demonstrate for the first time that [¹⁸F]-FLT PET can be correlated to the improved efficacy of combined PI3K and MEK inhibitor treatment.

Diaryl- and triaryl-pyrrole derivatives: inhibitors of the MDM2-p53 and MDMX-p53 protein-protein interactions†Electronic supplementary information (ESI) available: Experimental details for compound synthesis, analytical data for all compounds and intermediates. Details for the biological evaluation. Further details for the modeling. Table of combustion analysis data. See DOI: 10.1039/c3md00161jClick here for additional data file

Screening identified 2-(3-((4,6-dioxo-2-thioxotetrahydropyrimidin-5(2H)-ylidene)methyl)-2,5-dimethyl-1H-pyrrol-1-yl)-4,5,6,7-tetrahydrobenzo[b]thiophene-3-carbonitrile as an MDM2-p53 inhibitor (IC50 = 12.3 μM). MDM2-p53 and MDMX-p53 activity was seen for 5-((1-(4-chlorophenyl)-2,5-diphenyl-1H-pyrrol-3-yl)methylene)-2-thioxodihydropyrimidine-4,6(1H,5H)-dione (MDM2 IC50 = 0.11 μM; MDMX IC50 = 4.2 μM) and 5-((1-(4-nitrophenyl)-2,5-diphenyl-1H-pyrrol-3-yl)methylene)pyrimidine-2,4,6(1H,3H,5H)-trione (MDM2 IC50 = 0.15 μM; MDMX IC50 = 4.2 μM), and cellular activity consistent with p53 activation in MDM2 amplified cells. Further SAR studies demonstrated the requirement for the triarylpyrrole moiety for MDMX-p53 activity but not for MDM2-p53 inhibition.

1-substituted (Dibenzo[b,d]thiophen-4-yl)-2-morpholino-4H-chromen-4-ones endowed with dual DNA-PK/PI3-K inhibitory activity

Analogues of (dibenzo[b,d]thiophen-4-yl)-2-morpholino-4H-chromen-4-one (NU7441), a potent inhibitor of DNA-dependent protein kinase (DNA-PK; IC50 = 42 ± 2 nM), have been synthesized in which water-solubilizing groups [NHCO(CH₂)nNR¹R², where n = 1 or 2 and the moiety R¹R²N was derived from a library of primary and secondary amines, e.g., morpholine] were placed at the 1-position. Several of the newly synthesized compounds exhibited high potency against DNA-PK and potentiated the cytotoxicity of ionizing radiation (IR) in vitro 10-fold or more (e.g., 2-(4-ethylpiperazin-1-yl)-N-(4-(2-morpholino-4-oxo-4H-chromen-8-yl)dibenzo[b,d]thio-phen-1-yl)acetamide, 39; DNA-PK IC₅₀ = 5.0 ± 1 nM, IR dose modification ratio = 13). Furthermore, 39 was shown to potentiate not only IR in vitro but also DNA-inducing cytotoxic anticancer agents, both in vitro and in vivo. Counter-screening against other members of the phosphatidylinositol 3-kinase (PI-3K) related kinase (PIKK) family unexpectedly revealed that some of the compounds were potent mixed DNA-PK and PI-3K inhibitors.

Preclinical evaluation of a novel ATM inhibitor, KU59403, in vitro and in vivo in p53 functional and dysfunctional models of human cancer

Ataxia telangiectasia mutated (ATM) kinase signals DNA double-strand breaks (DSB) to cell-cycle arrest via p53 and DNA repair. ATM-defective cells are sensitive to DSB-inducing agents, making ATM an attractive target for anticancer chemo- and radiosensitization. KU59403 is an ATM inhibitor with the potency, selectivity, and solubility for advanced preclinical evaluation. KU59403 was not cytotoxic to human cancer cell lines (SW620, LoVo, HCT116, and MDA-MB-231) per se but significantly increased the cytotoxicity of topoisomerase I and II poisons: camptothecin, etoposide, and doxorubicin. Chemo- and radiosensitization by ATM inhibition was not p53-dependent. Following administration to mice, KU59403 distributed to tissues and concentrations exceeding those required for in vitro activity were maintained for at least 4 hours in tumor xenografts. KU59403 significantly enhanced the antitumor activity of topoisomerase poisons in mice bearing human colon cancer xenografts (SW620 and HCT116) at doses that were nontoxic alone and well-tolerated in combination. Chemosensitization was both dose- and schedule-dependent. KU59403 represents a major advance in ATM inhibitor development, being the first compound to show good tissue distribution and significant chemosensitization in in vivo models of human cancer, without major toxicity. KU59403 provides the first proof-of-principle preclinical data to support the future clinical development of ATM inhibitors.

Abstract 565: An investigation into the potential therapeutic benefit of targeting Skp2 in neuroblastoma

Background: S-phase kinase-associated protein 2 (Skp2) is a component of an E3 ubiquitin ligase complex which targets several key regulators of the G1/S transition of the cell cycle. Skp2 is overexpressed in many cancers and has been implicated in tumourigenesis due to its ability to degrade the cyclin-dependent kinase inhibitors p27Kip1 and p21Cip1, promote S phase entry and induce growth. We identified Skp2 as a possible MYCN target gene in neuroblastoma (Bell et al, Cell Cycle, 2007), and other groups have reported an increase in Skp2 transcript levels in aggressive MYCN- amplified neuroblastoma (Westermann et al, Clinical Cancer Res 2007). As MYCN amplification is a well-established poor prognostic marker we hypothesise that targeting Skp2 may be a potential therapeutic approach for neuroblastoma, especially the MYCN-amplified subtype.

Methods: The relationship between MYCN and Skp2 was investigated using the SHEP Tet21N-regulatable MYCN expression system and Skp2 siRNA. The effects of Skp2 knockdown on downstream proteins (p21, p27), cell cycle arrest and cell apoptosis were analysed using western blotting, flow cytometry, and the caspase-3/7 glow assay, respectively.

Results: A decrease in Skp2 and subsequent increase in p27 and p21 levels was seen in SHEP Tet21N cells when MYCN expression was suppressed. A G1 arrest was also induced by MYCN removal, an effect mirrored after Skp2 knockdown in Tet21N MYCN+ cells. Skp2 knockdown increased both p27 and p21 levels in non-MYCN amplified SHSY5Y cells and MYCN amplified IMR-32 cells. Both cell lines had ∼20% reduction (p&lt;0.01) in growth after 72 hours knockdown compared to the scrambled control. However, only SHSY5Y cells showed a G1 arrest (p&lt;0.05) and increase in caspase activity (p&lt;0.05).

Conclusions: These data further establish the relationship between MYCN and Skp2. The effect of Skp2 knockdown on growth arrest and apoptosis suggest it would be a valid therapeutic target in neuroblastoma.

Citation Format: Laura Evans, Elaine Willmore, Deborah A. Tweddle, David R. Newell. An investigation into the potential therapeutic benefit of targeting Skp2 in neuroblastoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 565. doi:10.1158/1538-7445.AM2013-565

Characterisation of a Tip60 specific inhibitor, NU9056, in prostate cancer

Tip60 (KAT5) is a histone acetyltransferase (HAT enzyme) involved in multiple cellular processes including transcriptional regulation, DNA damage repair and cell signalling. In prostate cancer, aggressive cases over-express Tip60 which functions as an androgen receptor co-activator via direct acetylation of lysine residues within the KLKK motif of the receptor hinge region. The purpose of this study was to identify and characterise a Tip60 acetylase inhibitor. High-throughput screening revealed an isothiazole that inhibited both Tip60 and p300 HAT activity. This substance (initially identified as 4-methyl-5-bromoisothiazole) and other isothiazoles were synthesised and assayed against Tip60. Although an authentic sample of 4-methyl-5-bromoisothiazole was inactive against Tip60, in an in vitro HAT assay, 1,2-bis(isothiazol-5-yl)disulfane (NU9056) was identified as a relatively potent inhibitor (IC(50) 2 µM). Cellular activity was confirmed by analysis of acetylation of histone and non-histone proteins in a prostate cancer cell line model. NU9056 treatment inhibited cellular proliferation in a panel of prostate cancer cell lines (50% growth inhibition, 8-27 µM) and induced apoptosis via activation of caspase 3 and caspase 9 in a concentration- and time-dependent manner. Also, decreased androgen receptor, prostate specific antigen, p53 and p21 protein levels were demonstrated in response to treatment with NU9056. Furthermore, pre-treatment with NU9056 inhibited both ATM phosphorylation and Tip60 stabilization in response to ionising radiation. Based on the activity of NU9056 and the specificity of the compound towards Tip60 relative to other HAT enzymes, these chemical biology studies have identified Tip60 as a potential therapeutic target for the treatment of prostate cancer.

Chemosensitization of cancer cells by KU-0060648, a dual inhibitor of DNA-PK and PI-3K

DNA double-strand breaks (DSB) are the most cytotoxic lesions induced by topoisomerase II poisons. Nonhomologous end joining (NHEJ) is a major pathway for DSB repair and requires DNA-dependent protein kinase (DNA-PK) activity. DNA-PK catalytic subunit (DNA-PKcs) is structurally similar to PI-3K, which promotes cell survival and proliferation and is upregulated in many cancers. KU-0060648 is a dual inhibitor of DNA-PK and PI-3K in vitro. KU-0060648 was investigated in a panel of human breast and colon cancer cells. The compound inhibited cellular DNA-PK autophosphorylation with IC(50) values of 0.019 μmol/L (MCF7 cells) and 0.17 μmol/L (SW620 cells), and PI-3K-mediated AKT phosphorylation with IC(50) values of 0.039 μmol/L (MCF7 cells) and more than 10 μmol/L (SW620 cells). Five-day exposure to 1 μmol/L KU-0060648 inhibited cell proliferation by more than 95% in MCF7 cells but only by 55% in SW620 cells. In clonogenic survival assays, KU-0060648 increased the cytotoxicity of etoposide and doxorubicin across the panel of DNA-PKcs-proficient cells, but not in DNA-PKcs-deficient cells, thus confirming that enhanced cytotoxicity was due to DNA-PK inhibition. In mice bearing SW620 and MCF7 xenografts, concentrations of KU-0060648 that were sufficient for in vitro growth inhibition and chemosensitization were maintained within the tumor for at least 4 hours at nontoxic doses. KU-0060648 alone delayed the growth of MCF7 xenografts and increased etoposide-induced tumor growth delay in both in SW620 and MCF7 xenografts by up to 4.5-fold, without exacerbating etoposide toxicity to unacceptable levels. The proof-of-principle in vitro and in vivo chemosensitization with KU-0060648 justifies further evaluation of dual DNA-PK and PI-3K inhibitors.

Abstract 919: Design and preclinical pharmacological evaluation of a cleavable succinate ester solubilizing group for isoindolinone MDM2-p53 protein-protein interaction inhibitors

The potent and selective MDM2-p53 antagonist 4-chloro-3-(4-chlorophenyl)-3-((1-(hydroxymethyl)cyclopropyl)methoxy)-2-(4-nitrobenzyl)isoindolin-1-one 1 displays promising activity in cellular tumour models; however, poor solubility precludes in vivo investigations.(Bioorg. Med. Chem. Letters 2011, 21, 5916-5919) A water-soluble succinate ester of 1 was designed as a pro-drug, based on an understanding of the interaction of the parent compound 1 with MDM2, and the cellular pharmacology and in vivo pharmacokinetics of the ester 2 were defined. Compound 2 was synthesised and evaluated as an antagonist of MDM2- and MDMX-p53 using ELISA assays. Cell growth inhibition induced by 2 and 1 were compared in paired p53 functional and p53 non-functional HCT116, A2780 and SJSA-1 cell lines. Conversion of 2 into 1 was studied in human and mouse plasma in vitro, as was uptake into tumour cells, by HPLC analysis. The pharmacokinetics of 2 was studied in vivo in tumour-bearing mice. Unexpectedly, the succinate ester 2 was 7-fold more potent than the parent compound 1 as an MDM2-p53 binding antagonist in cell-free assays (IC50 values 20 ± 13 nM versus 95 ± 96 nM, respectively) and maintained &gt;100-fold selectivity for MDM2 over MDMX antagonism. In cell growth inhibition assays (GI50) 2 was 2.3-, 6.1- and 8.6-fold more potent in paired p53 functional versus non-functional HCT116, A2780 and SJSA-1 cell lines, respectively. As anticipated, the solubility of 2 (65 µM) was greatly improved over 1 (6.5 µM), and the succinate ester was converted to the parent compound in mouse plasma (&gt;90% in 60 min), although interestingly not in human plasma. Following incubation of tumour cell lines with 2, both the pro-drug and parent compound could be detected. Administration of 2 to A2780 tumour-bearing mice i.v. at 10 mg/kg generated plasma concentrations approaching those required for cell growth inhibition (≥ 3 μM), and oral administration at 100 mg/kg resulted in 2 bio-availability of 7%, and an 1 AUC that was estimated to be 21% of the equivalent i.v. dose of 2. However, a major unidentified metabolite was observed which compromised the in vivo utility of the succinate ester 2. Protein-protein interaction inhibitors as exemplified by MDM2-p53 binding antagonists are a major new class of antitumour agent. However, targeting hydrophobic protein-protein interactions can result in molecules with poor physicochemical properties. A cleavable succinate ester approach can be applied to address this problem without compromising target interaction or cellular activity, as in the current study. Although additional metabolite pathways may limit the utility of this approach, the improved potency gained by addition of a solubilising group provides valuable information for further lead optimisation. (This work was supported by the CR-UK)

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 919. doi:1538-7445.AM2012-919

The synergistic interaction of MEK and PI3K inhibitors is modulated by mTOR inhibition

BACKGROUND

Combined targeting of MAPK and PI3K signalling pathways may be necessary for optimal therapeutic activity in cancer. This study evaluated the MEK inhibitors AZD6244 and PD0325901, alone and in combination with the dual mTOR/PI3K inhibitor NVP-BEZ235 or the PI3K inhibitor GDC-0941, in three colorectal cancer cell lines.

METHODS

Growth inhibition, survival and signal transduction were measured using the Sulforhodamine B assay, clonogenicity and western blotting, respectively, in HCT116, HT29 and DLD1 cell lines.

RESULTS

All MEK/PI3K inhibitor combinations exhibited marked synergistic growth inhibition; however, GDC-0941 displayed greater synergy in combination with either MEK inhibitor. NVP-BEZ235 exhibited stronger inhibition of 4EBP1 phosphorylation, and similar inhibition of S6 and AKT phosphorylation, compared with GDC-0941. Both PD0325901 and AZD6244 inhibited ERK phosphorylation, and with MEK/PI3K inhibitor combinations inhibition of S6 phosphorylation was increased. The reduced synergy exhibited by NVP-BEZ235 in combination with MEK inhibitors, compared with GDC-0941, may be due to inhibition of mTOR, and the addition of the mTORC1/2 inhibitor KU0063794 compromised the synergy of GDC-0941:PD0325901 combinations.

CONCLUSION

These studies confirm that dual targeting of PI3K and MEK can induce synergistic growth inhibition; however, the combination of specific PI3K inhibitors, rather than dual mTOR/PI3K inhibitors, with MEK inhibitors results in greater synergy.

Further characterisation of the cellular activity of the DNA-PK inhibitor, NU7441, reveals potential cross-talk with homologous recombination

PURPOSE

Inhibition of DNA repair is emerging as a new therapeutic strategy for cancer treatment. One promising target is DNA-PK, a pivotal kinase in double-strand break repair. The purpose of this study was to further characterise the activity of the DNA-PK inhibitor NU7441, giving some new insights into the biology of DNA-PK.

METHODS

We used NU7441, a potent DNA-PK inhibitor, to evaluate potential pharmacodynamic markers of DNA-PK inhibition, inhibition of DNA repair and chemo- and radio-potentiation in isogenic human cancer cells proficient (M059-Fus1) and deficient (M059 J) in DNA-PK.

RESULTS

NU7441 strongly inhibited DNA-PK in cell lines (IC(50) = 0.3 μM) but only weakly inhibited PI3 K (IC(50) = 7 μM). The only available anti-phospho-DNA-PK antibody also recognised some phosphoprotein targets of ATM. NU7441 caused doxorubicin- and IR-induced DNA DSBs (measured by γ-H2AX foci) to persist and also slightly decreased homologous recombination activity, as assessed by Rad51 foci. Chemo- and radio-potentiation were induced by NU7441 in M059-Fus-1, but not in DNA-PK-deficient M059 J cells. DNA-PK was highly expressed in a chronic lymphocytic leukaemia sample but undetectable in resting normal human lymphocytes, although it could be induced by PHA-P treatment. In K652 cells, DNA-PK expression was not related to cell cycle phase.

CONCLUSION

These data confirm NU7441 not only as a potent chemo- and radio-sensitiser clinical candidate but also as a powerful tool to study the biology of DNA-PK.

Potent, selective inhibitors of fibroblast growth factor receptor define fibroblast growth factor dependence in preclinical cancer models

We describe here the identification and characterization of 2 novel inhibitors of the fibroblast growth factor receptor (FGFR) family of receptor tyrosine kinases. The compounds exhibit selective inhibition of FGFR over the closely related VEGFR2 receptor in cell lines and in vivo. The pharmacologic profile of these inhibitors was defined using a panel of human tumor cell lines characterized for specific mutations, amplifications, or translocations known to activate one of the four FGFR receptor isoforms. This pharmacology defines a profile for inhibitors that are likely to be of use in clinical settings in disease types where FGFR is shown to play an important role.

Thiothymidine combined with UVA as a potential novel therapy for bladder cancer

BACKGROUND

Thiothymidine (S(4)TdR) can be incorporated into DNA and sensitise cells to DNA damage and cell death following exposure to UVA light. Studies were performed to determine if the combination of S(4)TdR and UVA could be an effective treatment for bladder cancer.

METHODS

Uptake and incorporation of S(4)TdR was determined in rat and human bladder tumour cell lines. Measures of DNA crosslinking and apoptosis were also performed. In vivo activity of the combination of S(4)TdR and UVA was investigated in an orthotopic model of bladder cancer in rats.

RESULTS

Thiothymidine (200 μM) replaced up to 0.63% of thymidine in rat and tumour bladder cancer cells. The combination of S(4)TdR (10-200 μM) and UVA (1-5 kJ m(-2)) caused apoptosis and cell death at doses that were not toxic alone. Addition of raltitrexed (Astra Zeneca, Alderley Edge, Cheshire, UK) increased the incorporation of S(4)TdR into DNA (up to 20-fold at IC(5)) and further sensitised cells to UVA. Cytotoxic effect was associated with crosslinking of DNA, at least partially to protein. Intravenous administration of S(4)TdR, in combination with UVA delivered directly to the bladder, resulted in an antitumour effect in three of five animals treated.

CONCLUSION

These data indicate that the combination of S(4)TdR and UVA has potential as a treatment for bladder cancer, and give some insight into the mechanism of action. Further work is necessary to optimise the delivery of the two components.

Preclinical in vitro and in vivo evaluation of the potent and specific cyclin-dependent kinase 2 inhibitor NU6102 and a water soluble prodrug NU6301

To facilitate the evaluation of CDK2 (cyclin-dependent kinase 2) as a cancer target, the in vitro and in vivo properties of NU6102 (O⁶-cyclohexylmethyl-2-(4'-sulphamoylanilino)purine) and a water soluble prodrug (NU6301) were investigated. NU6102 selectively inhibited the growth of CDK2 WT (wild type) versus KO MEFs (knockout mouse embryo fibroblasts) (GI₅₀ (concentration required to inhibit cell growth by 50%) 14 μM versus >30 μM), and was more growth-inhibitory in p53 mutant or null versus p53 WT cells (p=0.02), and in Rb (retinoblastoma protein) WT SKUT-1B versus SKUT 1 Rb deficient cells (p=0.01). In SKUT-1B cells NU6102 induced a G2 arrest, inhibition of Rb phosphorylation and cytotoxicity (LC₅₀ 2.6 μM for a 24h exposure). The prodrug NU6301 rapidly generated NU6102 in vitro in mouse plasma, and tumour NU6102 levels in vivo consistent with activity in vitro. Eight or 12 hourly dosing of 120 mg/kg NU6301 for 10 days was well tolerated in SKUT-1B tumour-bearing mice and inhibited Rb phosphorylation in tumour tissue. Two (8 hourly dosing) and 3 (12 hourly dosing) day tumour growth delay was observed (p=0.04 and p=0.007, respectively) following NU6301 administration. NU6102 and its prodrug NU6301 have pharmacological properties consistent with CDK2 inhibition, and represent useful tool molecules for the evaluation of CDK2 as a target in cancer.