Quantitative Analysis of the Potency of Equimolar Two-Drug Combinations and Combi-Molecules Involving Kinase Inhibitors In Vitro: The Concept of Balanced Targeting

The median-effect principle proposed by Chou and Talalay is the most effective approach to parameterize interactions between several agents in combination. However, this method cannot be used to evaluate the effectiveness of equimolar drug combinations, which are comparative references for dual-targeting molecular design. Here, using data acquired through the development of “combi-molecules” blocking two kinases (e.g., EGFR-c-Src and EGFR-c-Met), we established potency indices for equimolar and dual-targeted inhibitors. If the fold difference (κ) between the IC50 of the two individual kinase inhibitors was >6, the IC50 of their equimolar combination resembled that of the more potent inhibitor. Hence, the “combi-targeting” of the two kinases was considered “imbalanced” and the combination ineffective. However, if κ ≤ 6, the IC50 of the combination fell below that of each individual drug and the combi-targeting was considered “balanced” and the combination effective. We also showed that combi-molecules should be compared with equimolar combinations only under balanced conditions and propose a new parameter Ω for validating their effectiveness. A multi-targeted drug is effective if Ω < 1, where Ω is defined as the IC50 of the drug divided by that of the corresponding equimolar combination. Our study provides a methodology to determine the in vitro potency of equimolar two-drug combinations as well as combi-/hybrid molecules inhibiting two different kinase targets.

N-Phenyl-1,2,3,4-tetrahydroisoquinoline: An Alternative Scaffold for the Design of 17β-Hydroxysteroid Dehydrogenase 1 Inhibitors

17β-Hydroxysteroid dehydrogenases catalyse interconversion at the C17 position between oxidized and reduced forms of steroidal nuclear receptor ligands. The type 1 enzyme, expressed in malignant cells, catalyses reduction of the less-active estrone to estradiol, and inhibitors have therapeutic potential in estrogen-dependent diseases such as breast and ovarian cancers and in endometriosis. Synthetic decoration of the nonsteroidal N-phenyl-1,2,3,4-tetrahydroisoquinoline (THIQ) template was pursued by using Pomeranz-Fritsch-Bobbitt, Pictet-Spengler and Bischler-Napieralski approaches to explore the viability of this scaffold as a steroid mimic. Derivatives were evaluated biologically in vitro as type 1 enzyme inhibitors in a bacterial cell homogenate as source of recombinant protein. Structure-activity relationships are discussed. THIQs possessing a 6-hydroxy group, lipophilic substitutions at the 1- or 4-positions in combination with N-4'-chlorophenyl substitution were most favourable for activity. Of these, one compound had an IC₅₀ of ca. 350 nM as a racemate, testifying to the applicability of this novel approach.

Nonsteroidal sulfamate derivatives as new therapeutic approaches for Neurofibromatosis 2 (NF2)

BACKGROUND

Neurofibromatosis 1 and 2, although involving two different tumour suppressor genes (neurofibromin and merlin, respectively), are both cancer predisposition syndromes that disproportionately affect cells of neural crest origin. New therapeutic approaches for both NF1 and NF2 are badly needed. In promising previous work we demonstrated that two non-steroidal analogues of 2-methoxy-oestradiol (2ME2), STX3451(2-(3-bromo-4,5-dimethoxybenzyl)-7-methoxy-6-sulfamoyloxy-1,2,3,4-tetrahydroisoquinoline), and STX2895 (7-Ethyl-6-sulfamoyloxy-2-(3,4,5-trimethoxybenzyl)-1,2,3,4-tetrahydroisoquinoline) reduced tumour cell growth and induced apoptosis in malignant and benign human Neurofibromatosis 1 (NF1) tumour cells. In earlier NF1 mechanism of action studies we found that in addition to their effects on non-classical hormone-sensitive pathways, STX agents acted on the actin- and myosin-cytoskeleton, as well as PI3Kinase and MTOR signaling pathways. Tumour growth in NF2 cells is affected by different inhibitors from those affecting NF1 growth pathways: specifically, NF2 cells are affected by merlin-downstream pathway inhibitors. Because Merlin, the affected tumour suppressor gene in NF2, is also known to be involved in stabilizing membrane-cytoskeletal complexes, as well as in cell proliferation, and apoptosis, we looked for potentially common mechanisms of action in the agents' effects on NF1 and NF2. We set out to determine whether STX agents could therefore also provide a prospective avenue for treatment of NF2.

METHODS

STX3451 and STX2895 were tested in dose-dependent studies for their effects on growth parameters of malignant and benign NF2 human tumour cell lines in vitro. The mechanisms of action of STX3451 and STX2895 were also analysed.

RESULTS

Although neither of the agents tested affected cell growth or apoptosis in the NF2 tumour cell lines tested through the same mechanisms by which they affect these parameters in NF1 tumour cell lines, both agents disrupted actin- and myosin-based cytoskeletal structures in NF2 cell lines, with subsequent effects on growth and cell death.

CONCLUSIONS

Both STX3451 and STX2895 provide new approaches for inducing cell death and lowering tumour burden in NF2 as well as in NF1, which both have limited treatment options.

Thermodynamic, kinetic, and structural parameterization of human carbonic anhydrase interactions toward enhanced inhibitor design

The aim of rational drug design is to develop small molecules using a quantitative approach to optimize affinity. This should enhance the development of chemical compounds that would specifically, selectively, reversibly, and with high affinity interact with a target protein. It is not yet possible to develop such compounds using computational (i.e., in silico) approach and instead the lead molecules are discovered in high-throughput screening searches of large compound libraries. The main reason why in silico methods are not capable to deliver is our poor understanding of the compound structure-thermodynamics and structure-kinetics correlations. There is a need for databases of intrinsic binding parameters (e.g., the change upon binding in standard Gibbs energy (ΔGint), enthalpy (ΔHint), entropy (ΔSint), volume (ΔVintr), heat capacity (ΔCp,int), association rate (ka,int), and dissociation rate (kd,int)) between a series of closely related proteins and a chemically diverse, but pharmacophoric group-guided library of compounds together with the co-crystal structures that could help explain the structure-energetics correlations and rationally design novel compounds. Assembly of these data will facilitate attempts to provide correlations and train data for modeling of compound binding. Here, we report large datasets of the intrinsic thermodynamic and kinetic data including over 400 primary sulfonamide compound binding to a family of 12 catalytically active human carbonic anhydrases (CA). Thermodynamic parameters have been determined by the fluorescent thermal shift assay, isothermal titration calorimetry, and by the stopped-flow assay of the inhibition of enzymatic activity. Kinetic measurements were performed using surface plasmon resonance. Intrinsic thermodynamic and kinetic parameters of binding were determined by dissecting the binding-linked protonation reactions of the protein and sulfonamide. The compound structure-thermodynamics and kinetics correlations reported here helped to discover compounds that exhibited picomolar affinities, hour-long residence times, and million-fold selectivities over non-target CA isoforms. Drug-lead compounds are suggested for anticancer target CA IX and CA XII, antiglaucoma CA IV, antiobesity CA VA and CA VB, and other isoforms. Together with 85 X-ray crystallographic structures of 60 compounds bound to six CA isoforms, the database should be of help to continue developing the principles of rational target-based drug design.

3,17β-Bis-sulfamoyloxy-2-methoxyestra-1,3,5(10)-triene and Nonsteroidal Sulfamate Derivatives Inhibit Carbonic Anhydrase IX: Structure-Activity Optimization for Isoform Selectivity

3,17β-Bis-sulfamoyloxy-2-methoxyestra-1,3,5(10)-triene (STX140), a bis-sulfamate derivative of the endogenous steroid 2-methoxyestradiol, has shown promising anticancer potency both in vitro and in vivo, with excellent bioavailability. Its activity against taxane-resistant xenografts makes it a potential drug candidate against triple-negative breast cancer (TNBC). These properties are linked to the ability of STX140 to act in a multitargeting fashion in vivo as a microtubule disruptor, leading to cell cycle arrest and with both proapoptotic and anti-angiogenic activities. Carbonic anhydrase IX (CA IX) is a well-established biomarker for aggressive cancers, including TNBC. This study reports, for the first time, the inhibitory activities of a series of steroidal and nonsteroidal sulfamate derivatives against CA IX in comparison to the ubiquitous CA II, with some compounds demonstrating 100-200-fold selectivity for CA IX over CA II. X-ray crystallographic studies of four of the most promising compounds reveal that isoform-specific residue interactions are responsible for the high specificity.

Tetrahydroisoquinoline Sulfamates as Potent Microtubule Disruptors: Synthesis, Antiproliferative and Antitubulin Activity of Dichlorobenzyl-Based Derivatives, and a Tubulin Cocrystal Structure

Tetrahydroisoquinoline (THIQ) 6-O-sulfamate-based anticancer agents, inspired by the endogenous steroid 2-methoxyestradiol and its sulfamate derivatives, are further explored for antiproliferative and microtubule disruptor activity. Based on recently designed C3-methyl C7-methoxy-substituted THIQ derivatives, compounds with mono- and dichloro-substitutions on the pendant N-benzyl ring were synthesized and evaluated. Although improved antiproliferative activity was observed, for example, 4a versus 4b and 4b versus 8c, it was relatively modest. Compound 8c, a 2',5'-dichlorobenzyl derivative was, however, identified as a promising antiproliferative agent with in vitro activities exceeding that of the parent steroid (e.g., GI₅₀ 90 nM in DU-145 cells) and was highly potent against a range of tumor cell lines (e.g., GI₅₀ 26 nM for OVCAR-3). 8c inhibited the polymerization of tubulin in vitro with an IC₅₀ only twofold less potent than combretastatin A-4 and inhibited colchicine binding to tubulin. Tubulin polymerization assays showed the parent THIQ 4a to be only a very weak inhibitor, but a striking potency difference was seen between compounds with C2' methoxy and chloro substituents, whereas this was much smaller when these substituents were positioned at C5'. To confirm the target in atomic detail and because 8c is a racemic mixture, an achiral parent THIQ 6-O-sulfamate derivative 10 was successfully cocrystallized with the αβ-tubulin heterodimer. The derivative 10 binds at the colchicine site on tubulin, the first example of this compound class investigated in such detail, with its sulfamate group interacting with residues beyond the reach of colchicine itself, similar to a recently reported quinazolinone sulfamate derivative, 6a. The structure also suggests that for racemic C3-methyl-substituted THIQ derivatives, such as 8c, the (S)-enantiomer is likely to be preferentially accommodated within the colchicine site for steric reasons. The results further confirm the potential of nonsteroidal THIQ sulfamate derivatives for oncology and suggest that the mechanism of microtubule destabilization for the THIQ compound class is to prevent the curved-to-straight conformational transition of tubulin required for polymerization.

Modes of cell death induced by tetrahydroisoquinoline-based analogs in MDA-MB-231 breast and A549 lung cancer cell lines

Background

A and B rings of the steroidal microtubule disruptor, 2-methoxyestradiol, and its analogs can be mimicked with a tetrahydroisoquinoline (THIQ) core. THIQs are cytotoxic agents with potential anticancer activities. The aim of this in vitro study was to investigate the modes of cell death induced by four nonsteroidal THIQ-based analogs, such as STX 2895, STX 3329, STX 3451 and STX 3450, on MDA-MB-231 metastatic breast and A549 epithelial lung carcinoma cells.

Materials and methods

Cytotoxicity studies determined the half-maximal growth inhibitory concentration of the analogs to be at nanomolar concentrations without the induction of necrosis. Light and fluorescent microscopy determined that compounds caused microtubule depolymerization and displayed morphological hallmarks of apoptosis.

Results

Flow cytometric analyses confirmed apoptosis induction as well as an increased G₂/M phase on cell cycle analysis. Furthermore, intrinsic pathway signaling was implicated due to increased cytochrome c release and a decrease in mitochondrial transmembrane potential. Potential involvement of autophagy was observed due to increased acidic vacuole formation and increased aggresome activation factor.

Conclusion

Thus, it can be concluded that these four THIQ-based analogs exert anti-proliferative and antimitotic effects, induce apoptosis and involve autophagic processes. Further investigation into the efficacy of these potential anticancer drugs will be conducted in vitro and in vivo.

Quinazolinone-Based Anticancer Agents: Synthesis, Antiproliferative SAR, Antitubulin Activity, and Tubulin Co-crystal Structure

Quinazolinone-based anticancer agents were designed, decorated with functional groups from a 2-methoxyestradiol-based microtubule disruptor series, incorporating the aryl sulfamate motif of steroid sulfatase (STS) inhibitors. The steroidal AB-ring system was mimicked, favoring conformations with an N-2 substituent occupying D-ring space. Evaluation against breast and prostate tumor cell lines identified 7b with DU-145 antiproliferative activity (GI₅₀ 300 nM). A preliminary structure-activity relationship afforded compounds (e.g., 7j GI₅₀ 50 nM) with activity exceeding that of the parent. Both 7b and 7j inhibit tubulin assembly in vitro and colchicine binding, and 7j was successfully co-crystallized with the αβ-tubulin heterodimer as the first of its class, its sulfamate group interacting positively at the colchicine binding site. Microtubule destabilization by 7j is likely achieved by preventing the curved-to-straight conformational transition in αβ-tubulin. Quinazolinone sulfamates surprisingly showed weak STS inhibition. Preliminary in vivo studies in a multiple myeloma xenograft model for 7b showed oral activity, confirming the promise of this template.

Insights into the binding mode of sulphamates and sulphamides to hCA II: crystallographic studies and binding free energy calculations

Sulphamate and sulphamide derivatives have been largely investigated as carbonic anhydrase inhibitors (CAIs) by means of different experimental techniques. However, the structural determinants responsible for their different binding mode to the enzyme active site were not clearly defined so far. In this paper, we report the X-ray crystal structure of hCA II in complex with a sulphamate inhibitor incorporating a nitroimidazole moiety. The comparison with the structure of hCA II in complex with its sulphamide analogue revealed that the two inhibitors adopt a completely different binding mode within the hCA II active site. Starting from these results, we performed a theoretical study on sulphamate and sulphamide derivatives, demonstrating that electrostatic interactions with residues within the enzyme active site play a key role in determining their binding conformation. These findings open new perspectives in the design of effective CAIs using the sulphamate and sulphamide zinc binding groups as lead compounds.

Accessing simply-substituted 4-hydroxytetrahydroisoquinolines via Pomeranz-Fritsch-Bobbitt reaction with non-activated and moderately-activated systems

Background: 1,2,3,4-Tetrahydroisoquinolines (THIQs) are common motifs in alkaloids and in medicinal chemistry. Synthetic access to THIQs via the Pomeranz–Fritsch–Bobbit (PFB) methodology using mineral acids for deactivated, electron-poor aromatic systems, is scarcely represented in the literature. Here, the factors controlling the regiochemical outcome of cyclization are evaluated.

Results: A double reductive alkylation was telescoped into a one-pot reaction delivering good to excellent yields of desired aminoacetals for cyclization. Cyclization of activated systems proceeded smoothly under standard PFB conditions, but for non-activated systems the use of HClO₄ alone was effective. When cyclization was possible in both para- and ortho-positions to the substituent, 7-substituted derivatives were formed with significant amounts of 5-substituted byproduct. The formation of the 4-hydroxy-THIQs vs the 4-methoxy-THIQ products could be controlled through modification of the reaction concentration. In addition, while a highly-activated system exclusively cyclized to the indole, this seems generally highly disfavored. When competition between 6- and 7-ring formation was investigated in non-activated systems, 5,7,8,13-tetrahydro-6,13-methanodibenzo[c,f]azonine was exclusively obtained. Furthermore, selective ring closure in the para-position could be achieved under standard PFB conditions, while a double ring closure could be obtained utilizing HClO₄.

Conclusion: Reactivity differences in aminoacetal precursors can be employed to control cyclization using the PFB methodology. It is now possible to select confidently the right conditions for the synthesis of N-aryl-4-hydroxy-1,2,3,4-tetrahydroisoquinolines.

Recent Advances in chemistry and pharmacology of 2-methoxyestradiol: An anticancer investigational drug

2-Methoxyestradiol (2ME2), an estrogen hormone metabolite is a potential cancer chemotherapeutic agent. Presently, it is an investigational drug under various phases of clinical trials alone or in combination therapy. Its anticancer activity has been attributed to its antitubulin, antiangiogenic, pro-apoptotic and ROS induction properties. This anticancer drug candidate has been explored extensively in last twenty years for its detailed chemistry and pharmacology. Present review is an update of its chemistry and biological activity. It also extends an assessment of potential of 2ME2 and its analogues as possible anticancer drug in future.

Targeted NF1 cancer therapeutics with multiple modes of action: small molecule hormone-like agents resembling the natural anticancer metabolite, 2-methoxyoestradiol

Background:

Both the number and size of tumours in NF1 patients increase in response to the rise in steroid hormones seen at puberty and during pregnancy. The size of tumours decreases after delivery, suggesting that hormone-targeting therapy might provide a viable new NF1 treatment approach. Our earlier studies demonstrated that human NF1 tumour cell lines either went through apoptosis or ceased growth in the presence of 2-methoxyoestradiol (2ME2), a naturally occurring anticancer metabolite of 17-β estradiol. Previous reports of treatment with sulfamoylated steroidal and non-steroidal derivatives of 2ME2 showed promising reductions in tumour burden in hormone-responsive cancers other than NF1. Here we present the first studies indicating that 2ME2 derivatives could also provide an avenue for treating NF1, for which few treatment options are available.

Methods:

STX3451, (2-(3-Bromo-4,5-dimethoxybenzyl)-7-methoxy-6-sulfamoyloxy-1,2,3,4-tetrahydroisoquinoline), a non-steroidal sulphamate analogue of 2ME2, was tested in dose-dependent studies of malignant and benign NF1 human tumour cell lines and cell lines with variable controlled neurofibromin expression. The mechanisms of action of STX3451 were also analysed.

Results:

We found that STX3451-induced apoptosis in human malignant peripheral nerve sheath tumour (MPNST) cell lines, even in the presence of elevated oestrogen and progesterone. It inhibits both PI3 kinase and mTOR signalling pathways. It disrupts actin- and microtubule-based cytoskeletal structures in cell lines derived from human MPNSTs and in cells derived from benign plexiform neurofibromas. STX3451 selectively kills MPNST-derived cells, but also halts growth of other tumour-derived NF1 cell lines.

Conclusion:

STX3451 provides a new approach for inducing cell death and lowering tumour burden in NF1 and other hormone-responsive cancers with limited treatment options.

Discovery and Development of the Aryl O-Sulfamate Pharmacophore for Oncology and Women's Health

In 1994, following work from this laboratory, it was reported that estrone-3-O-sulfamate irreversibly inhibits a new potential hormone-dependent cancer target steroid sulfatase (STS). Subsequent drug discovery projects were initiated to develop the core aryl O-sulfamate pharmacophore that, over some 20 years, have led to steroidal and nonsteroidal drugs in numerous preclinical and clinical trials, with promising results in oncology and women's health, including endometriosis. Drugs have been designed to inhibit STS, e.g., Irosustat, as innovative dual-targeting aromatase-steroid sulfatase inhibitors (DASIs) and as multitargeting agents for hormone-independent tumors, such as the steroidal STX140 and nonsteroidal counterparts, acting inter alia through microtubule disruption. The aryl sulfamate pharmacophore is highly versatile, operating via three distinct mechanisms of action, and imbues attractive pharmaceutical properties. This Perspective gives a personal view of the work leading both to the therapeutic concepts and these drugs, their current status, and how they might develop in the future.

In vivo and in vitro properties of STX2484: a novel non-steroidal anti-cancer compound active in taxane-resistant breast cancer

BACKGROUND

STX2484 is a novel non-steroidal compound with potent anti-proliferative activity. These studies aimed to identify STX2484's mechanism of action, in vivo efficacy and activity in taxane-resistant breast cancer models.

METHODS

Effects of STX2484 and paclitaxel on proliferation, cell cycle and apoptosis were assessed in vitro in drug-resistant (MCF-7(DOX)) and non-resistant cells (MCF-7(WT)). STX2484 efficacy in βIII tubulin overexpression in MCF-7 cells was also determined. Anti-angiogenic activity was quantified in vitro by a co-culture model and in vivo using a Matrigel plug assay. An MDA-MB-231 xenograft model was used to determine STX2484 efficacy in vivo.

RESULTS

STX2484 is a tubulin disruptor, which induces p53 expression, Bcl2 phosphorylation, caspase-3 cleavage, cell cycle arrest and apoptosis. In addition, STX2484 is a potent anti-angiogenic agent in vitro and in vivo. In breast cancer xenografts, STX2484 (20 mg kg(-1) p.o.) suppressed tumour growth by 84% after 35 days of daily dosing, with limited toxicity. In contrast to paclitaxel, STX2484 efficacy was unchanged in two clinically relevant drug-resistant models.

CONCLUSIONS

STX2484 is an orally bioavailable microtubule-disrupting agent with in vivo anti-angiogenic activity and excellent in vivo efficacy with no apparent toxicity. Crucially, STX2484 has superior efficacy to paclitaxel in models of clinical drug resistance.

Optimisation of tetrahydroisoquinoline-based chimeric microtubule disruptors

Tetrahydroisoquinoline (THIQ)-based "chimeric" microtubule disruptors were optimised through modification of the N-benzyl motif, in concert with changes at C3 and C7, resulting in the identification of compounds with improved in vitro antiproliferative activities (e.g. 15: GI50 20 nM in DU-145). The broad anticancer activity of these novel structures was confirmed in the NCI 60-cell line assay, with 12 e,f displaying MGM values in the 40 nM region. In addition, their profiles as inhibitors of tubulin polymerisation and colchicine binding to tubulin were confirmed. Compound 15, for example, inhibited tubulin polymerisation with an IC50 of 1.8 μM, close to that of the clinical drug combretastatin A-4, and also proved effective at blocking colchicine binding. Additionally, compound 20 b was identified as the only phenol in the series to date showing both better in vitro antiproliferative properties than its corresponding sulfamate and excellent antitubulin data (IC50=.6 μM). Compound 12 f was selected for in vivo evaluation at the NCI in the hollow fibre assay and showed very good activity and wide tissue distribution, illustrating the value of this template for further development.

Synthesis, anti-tubulin and antiproliferative SAR of steroidomimetic dihydroisoquinolinones

A SAR translation strategy adopted for the discovery of tetrahydroisoquinolinone (THIQ)-based steroidomimetic microtubule disruptors has been extended to dihydroisoquinolinone (DHIQ)-based compounds. A steroid A,B-ring-mimicking DHIQ core was connected to methoxyaryl D-ring mimics through methylene, carbonyl, and sulfonyl linkers, and the resulting compounds were evaluated against two cancer cell lines. The carbonyl-linked DHIQs in particular exhibit significant in vitro antiproliferative activities (e.g., 6-hydroxy-7-methoxy-2-(3,4,5-trimethoxybenzoyl)-3,4-dihydroisoquinolin-1(2H)-one (16 g): GI₅₀ 51 nm in DU-145 cells). The broad anticancer activity of DHIQ 16 g was confirmed in the NCI 60-cell line assay giving a mean activity of 33 nm. Furthermore, 6-hydroxy-2-(3,5-dimethoxybenzoyl)-7-methoxy-3,4-dihydroisoquinolin-1(2H)-one (16 f) and 16 g and their sulfamate derivatives 17 f and 17 g (2-(3,5-dimethoxybenzoyl)-7-methoxy-6-sulfamoyloxy-3,4-dihydroisoquinolin-1(2H)-one and 7-methoxy-2-(3,4,5-trimethoxybenzoyl)-6-sulfamoyloxy-3,4-dihydroisoquinolin-1(2H)-one, respectively) show excellent activity against the polymerization of tubulin, close to that of the clinical combretastatin A-4, and bind competitively at the colchicine binding site of tubulin. Compounds 16 f and 17 f were also shown to demonstrate in vitro anti-angiogenic activity. Additionally, X-ray and computational analyses of 17 f reveal that electrostatic repulsion between the two adjacent carbonyl groups, through conformational biasing, dictates the adoption of a “steroid-like” conformation that may partially explain the excellent in vitro activities.

Synthesis, antitubulin, and antiproliferative SAR of C3/C1-substituted tetrahydroisoquinolines

The syntheses and antiproliferative activities of novel substituted tetrahydroisoquinoline derivatives and their sulfamates are discussed. Biasing of conformational populations through substitution on the tetrahydroisoquinoline core at C1 and C3 has a profound effect on the antiproliferative activity against various cancer cell lines. The C3 methyl-substituted sulfamate (±)-7-methoxy-2-(3-methoxybenzyl)-3-methyl-6-sulfamoyloxy-1,2,3,4-tetrahydroisoquinoline (6 b), for example, was found to be ∼10-fold more potent than the corresponding non-methylated compound 7-methoxy-2-(3-methoxybenzyl)-6-sulfamoyloxy-1,2,3,4-tetrahydroisoquinoline (4 b) against DU-145 prostate cancer cells (GI50 values: 220 nM and 2.1 μM, respectively). Such compounds were also found to be active against a drug-resistant MCF breast cancer cell line. The position and nature of substitution of the N-benzyl group in the C3-substituted series was found to have a significant effect on activity. Whereas C1 methylation has little effect on activity, introduction of C1 phenyl and C3-gem-dimethyl substituents greatly decreases antiproliferative activity. The ability of these compounds to inhibit microtubule polymerisation and to bind tubulin in a competitive manner versus colchicine confirms the mechanism of action. The therapeutic potential of a representative compound was confirmed in an in vivo multiple myeloma xenograft study.

Tetrahydroisoquinolinone-based steroidomimetic and chimeric microtubule disruptors

A structure-activity relationship (SAR) translation strategy was used for the discovery of tetrahydroisoquinoline (THIQ)-based steroidomimetic and chimeric microtubule disruptors based upon a steroidal starting point. A steroid A,B-ring-mimicking THIQ core was connected to methoxyaryl D-ring ring mimics through methylene, carbonyl and sulfonyl linkers to afford a number of steroidomimetic hits (e.g., 7-methoxy-2-(3- methoxybenzyl)-6-sulfamoyloxy-1,2,3,4-tetrahydroisoquinoline (20 c) GI₅₀=2.1 μM). Optimisation and control experiments demonstrate the complementary SAR of this series and the steroid derivatives that inspired its design. Linkage of the THIQ-based A,B-mimic with the trimethoxyaryl motif prevalent in colchicine site binding microtubule disruptors delivered a series of chimeric molecules whose activity (GI₅₀=40 nM) surpasses that of the parent steroid derivatives. Validation of this strategy was obtained from the excellent oral activity of 7-methoxy-6-sulfamoyloxy-2-(3,4,5-trimethoxybenzyl)-1,2,3,4-tetrahydroisoquinoline relative to a benchmark steroidal bis- sulfamate in an in vivo model of multiple myeloma.

Sulfatase inhibitors: a patent review

INTRODUCTION

Steroid sulfatase (STS) converts sulfated hormones to free hormones of importance in hormone-dependent diseases such as breast cancer and endometriosis. Carbohydrate sulfatases degrade complex carbohydrates as part of normal cellular turnover; certain lysosomal storage disorders (LSDs) involve defective processing of sulfated glycosaminoglycans by mutant sulfatases.

AREAS COVERED

Aryl sulfamates have been developed as STS inhibitors, and STX64 and PGL2001 are under evaluation in Phase I and II clinical trials for treatment of endometrial and metastatic breast and prostate cancers and endometriosis. Dual-acting compounds have emerged that are aromatase inhibitors (AIs), selective estrogen receptor antagonists, or inhibitors of microtubule polymerization. Sulfamidase inhibitors as pharmacological chaperones to assist maturation of folding-defective mutants for the treatment of Sanfilippo type A disease are under investigation. Coverage: The patent literature after the mid-1990s.

EXPERT OPINION

The failure of STX64 in a Phase II monotherapy clinical trial should not dissuade further investigations in multidrug regimens, particularly in combination with AIs. The recent development of dual-acting compounds may enhance the potential for success in the clinic. Further investigations into aryl sulfamates are required to clarify the molecular mechanism of action; additionally, new reversible sulfatase inhibition concepts are needed for the development of pharmacological chaperones for sulfatase LSDs.

Steroidomimetic Tetrahydroisoquinolines for the Design of New Microtubule Disruptors

Structure–activity relationship translation offers an expeditious means for discovery of new active series. This approach was applied to discover tetrahydroisoquinoline (THIQ)-based steroidomimetic microtubule disruptors. The two A-ring elements of a three-point steroidal pharmacophore were incorporated into a THIQ-based A,B-ring mimic to which an H-bond acceptor was attached as the third motif. Optimization of the representative 6c through conformational biasing delivered a 10-fold gain in activity and a new series of microtubule disruptors (e.g., 9c) with antiproliferative activity in the nanomolar range. The THIQ derivatives match, or surpass, the activities of the steroidal series and exhibit improved physicochemical properties.