Isosteric Substitution Research Articles

Synthesis and Biological Evaluation of New Chalcogen Semicarbazone (S, Se) and Their Azole Derivatives against Chagas Disease.

Chagas disease is caused by the eukaryote parasite Trypanosoma cruzi. Current treatment exhibits limited efficacy and selenium-based compounds emerged as promising candidates for new therapies which is surpassing its bioisoster, sulfur. We designed new thiosemicarbazones, thiazoles, selenosemicarbazones and selenazoles, using isosteric substitution. We synthesized 57 new chalcogen compounds which were evaluated against T. cruzi, C2C12 cells and cruzain, the main target of this parasite. Additionally, human cathepsin L, was tested for selectivity. Three compounds were selected, based on their activity against the intracellular amastigotes (EC50 < 1 μM, SI > 10) and cruzain (IC50 < 100 nM, SI > 5.55) which compared favorably with the approved drug, Benznidazole, and the well-established cruzain inhibitor K777. Seleno-compounds demonstrated enhanced activity and selenazoles showed a decrease in selenium-associated toxicity. Compound 4-methyl-2-(2-(1-(3-nitrophenyl)ethylidene)hydrazineyl)-1,3-selenazole (Se2h) emerged as a promising candidate, and its binding to cruzain was investigated. Pharmacokinetic assessment was conducted, showing a favorable profile for subsequent in vivo assays.

Synthesis, Anticancer Activity, and Docking Studies of Novel Hydroquinone-Chalcone-Pyrazoline Hybrid Derivatives.

A novel series of antitumor hybrids was synthesized using 1,4-benzohydroquinone and chalcone, furane, or pyrazoline scaffolds. This were achieved through isosteric substitution of the aryl group of the chalcone β-carbon with the furanyl moiety and structural modification of the α,β-unsaturated carbonyl system. The potential antitumor activity of these hybrids was evaluated in vivo on MCF-7 breast adenocarcinoma and HT-29 colorectal carcinoma cells, demonstrating cytotoxic activity with IC50 values ranging from 28.8 to 124.6 µM. The incorporation of furan and pyrazoline groups significantly enhanced antiproliferative properties compared to their analogues and precursors (VII-X), which were inactive against both neoplastic cell lines. Compounds 4, 5, and 6 exhibited enhanced cytotoxicity against both cell lines, whereas compound 8 showed higher cytotoxic activity against HT-29 cells. Molecular docking studies revealed superior free-energy values (ΔGbin) for carcinogenic pathway-involved kinase proteins, with our in silico data suggesting that these derivatives could be promising chemotherapeutic agents targeting kinase pathways. Among all the synthesized PIBHQ compounds, derivatives 7 and 8 exhibited the best drug-likeness properties, with values of 0.53 and 0.83, respectively. ADME results collectively suggest that most of these compounds hold promise as potential candidates for preclinical assays.

Confinement and Separation of Benzene from an Azeotropic Mixture Using a Chlorinated B←N Adduct.

Separations of azeotropic mixtures are typically carried out using energy-demanding processes (e.g., distillation). Here, we report the capacity of a self-assembled chlorinated boronic ester-based adduct to confine acetonitrile and benzene in channels upon crystallization. The solvent confinement occurs via a combination of hydrogen bonding and [π···π] interactions. Quantitative separation of benzene from an azeotropic 1:1 mixture of a benzene/acetonitrile (v/v), and methanol is achieved through crystallization with the chlorinated adduct by complementary [C-H···O] and [C-H···π] interactions. Inclusion behavior is rationalized by molecular modeling and crystallographic analysis. The chlorinated boronic ester adduct shows the potential of modularity via isosteric substitution for the separation of challenging chemical mixtures (e.g., azeotropes).

1,2,5‐Azadiborolane as a Building Block for Inorganic–Organic Hybrid Polymers

AbstractThe incorporation of BN units in organic scaffolds by isoelectronic/isosteric substitution of selected CC couples has emerged as an efficient tool to produce new materials with useful properties and functions. The knowledge about BN‐doped inorganic–organic hybrid polymers, however, is still rather scarce. This is especially true for linear or cyclolinear macromolecules that feature longer inorganic chains. Herein, we introduce 1,2,5‐azadiborolane as a polymer building block for the first time. An attempt to apply it for the synthesis of a cyclolinear poly(iminoborane) resulted after only two B−N coupling events in the formation of a molecular compound comprising a chain of three nitrogen and two boron atoms – as confirmed by single‐crystal X‐ray diffractometry. In combination with a p‐phenylene diamine‐based co‐monomer, we accomplished to incorporate the 1,2,5‐azadiborolane into a hybrid polymer of considerable molecular weight that features a B2N3 chain. We additionally synthesized a small molecular model compound for the polymer and characterized it crystallographically as well. Comparison of the UV‐vis spectra of the monomer, the oligomer, and the polymer revealed systematic red‐shifts of the longest‐wavelength absorption band with increasing number of BN units in the chain.

Novel analgesic/anti-inflammatory agents: 1,5-Diarylpyrrole nitrooxyethyl sulfides and related compounds as Cyclooxygenase-2 inhibitors containing a nitric oxide donor moiety endowed with vasorelaxant properties

The design of compounds able to combine the selective inhibition of cyclooxygenase-2 (COX-2) with the release of nitric oxide (NO) is a promising strategy to achieve potent anti-inflammatory agents endowed with an overall safer profile and reduced toxicity upon gastrointestinal and cardiovascular systems. With the aim of generating novel and selective COX-2 inhibiting NO-donors (CINOD) and encouraged by the promising results obtained with our nitrooxy- and hydroxyethyl ethers 11 and 12 reported in previous works, we shifted our attention on the synthesis of isosteric thioanalogs nitrooxy- and hydroxy ethyl sulfides 13a-c and 14a-c, respectively, along with their oxidation products nitrooxy- and hydroxyethyl sulfoxides 15a-c and 16a-c, respectively, also referred to as thio-CINOD. Preliminary data and metabolic analysis highlighted how the isosteric substitution of the ethereal oxygen atom of 11a-c with sulfur in compounds 13a-c, independently from the presence and the number of fluorine atoms in N1-phenyl ring, leads to new selective and highly potent COX-2 inhibitors, capable to induce vasorelaxant responses in vivo. The same behavior is observed with their oxidized counterparts nitrooxyethyl sulfoxides 15a-c, in which the oxidation state of the sulfur atom and the presence of the additional oxygen atom play a substantial role in enhancing compounds activity and vasorelaxation. In addition, the screened compounds proved significantly efficacious in mouse models of inflammation and nociception at the dose of 20 mg/kg.

Benzimidazole-2-Phenyl-Carboxamides as Dual-Target Inhibitors of BVDV Entry and Replication.

Bovine viral diarrhea virus (BVDV), also known as Pestivirus A, causes severe infection mostly in cattle, but also in pigs, sheep and goats, causing huge economical losses on agricultural farms every year. The infections are actually controlled by isolation of persistently infected animals and vaccination, but no antivirals are currently available to control the spread of BVDV on farms. BVDV binds the host cell using envelope protein E2, which has only recently been targeted in the research of a potent and efficient antiviral. In contrast, RdRp has been successfully inhibited by several classes of compounds in the last few decades. As a part of an enduring antiviral research agenda, we designed a new series of derivatives that emerged from an isosteric substitution of the main scaffold in previously reported anti-BVDV compounds. Here, the new compounds were characterized and tested, where several turned out to be potent and selectively active against BVDV. The mechanism of action was thoroughly studied using a time-of-drug-addition assay and the results were validated using docking simulations.

Sulfonamide as amide isostere for fine-tuning the gelation properties of physical gels.

(S)-2-Stearamidopentanedioic acid (C18-Glu) is a known LMW gelator that forms supramolecular gels in a variety of solvents. In this work, we have carried out the isosteric substitution of the amide group by a sulfonamide moiety yielding the new isosteric gelator (S)-2-(octadecylsulfonamido)pentanedioic acid (Sulfo-Glu). The gelation ability and the key properties of the corresponding gels were compared in terms of gelation concentration, gel-to-sol transition temperature, mechanical properties, morphology, and gelation kinetics in several organic solvents and water. This comparison was also extended to (S)-2-(4-hexadecyl-1H-1,2,3-triazol-4-yl)pentanedioic acid (Click-Glu), which also constitutes an isostere of C18-Glu. The stabilizing interactions were explored through computational calculations. In general, Sulfo-Glu enabled the formation of non-toxic gels at lower concentrations, faster, and with higher thermal-mechanical stabilities than those obtained with the other isosteres in most solvents. Furthermore, the amide-sulfonamide isosteric substitution also influenced the morphology of the gel networks as well as the release rate of an embedded antibiotic (vancomycin) leading to antibacterial activity in vitro against Staphylococcus aureus.

Toward a Structural View of hERG Activation by the Small-Molecule Activator ICA-105574.

Outward current conducted by human ether-à-go-go-related gene type 1 (hERG1) K+ channels is important for action potential repolarization in the human ventricle. Rapid, voltage-dependent inactivation greatly reduces outward currents conducted by hERG1 channels and involves conformational changes in the ion selectivity filter (SF). Recently, compounds have been found that activate hERG1 channel function by modulating gating mechanisms such as reducing inactivation. Such activating compounds could represent a novel approach to prevent arrhythmias associated with prolonged ventricular repolarization associated with inherited or acquired long QT syndrome. ICA-105574 (ICA), a 3-nitro-n-(4-phenoxyphenyl) benzamide derivative activates hERG1 by strongly attenuating pore-type inactivation. We previously mapped the putative binding site for ICA to a hydrophobic pocket located between two adjacent subunits. Here, we used the recently reported cryoelectron microscopy structures of hERG1 to elucidate the structural mechanisms by which ICA influences the stability of the SF. By combining molecular dynamics simulations, voltage-clamp electrophysiology, and the synthesis of novel ICA derivatives, we provide atomistic insights into SF dynamics and propose a structural link between the SF and S6 segments. Further, our study highlights the importance of the nitro moiety, at the meta position of the benzamide ring, for the activity of ICA and reveals that the (bio)isosteric substitution of this side chain can switch the activity to weak inhibitors. Our findings indicate that ICA increases the stability of the SF to attenuate channel inactivation, and this action requires a fine-tuned compound geometry.

Two-Dimensional Organic–Inorganic Perovskite Ferroelectric Semiconductors with Fluorinated Aromatic Spacers

Two-dimensional (2D) organic-inorganic perovskites (OIPs), with improved material stability over their 3D counterparts, are highly desirable for device applications. It is their considerable structural diversity that offers an unprecedented opportunity to engineer materials with fine-tuning functionalities. The isosteric substitution of hydrogen by an electronegative fluorine atom has been proposed as a useful route to improve the photovoltaic performance of 2D OIPs, whereas its valuable role in developing ferroelectricity is still waiting for further exploration. Herein, for the first time we applied fluorinated aromatic cations in extending the family of 2D OIP ferroelectrics, and successfully obtained [2-fluorobenzylammonium]2PbCl4 as a high-performance ferroelectric semiconductor. The failures in the nonferroelectric [4-fluorobenzylammonium]2PbCl4 and [3-fluorobenzylammonium]2PbCl4 demonstrate that the selective introduction of fluorine in correct structural positions is particularly essential. This work represents an unprecedented proof-of-concept in the use of fluorinated aromatic cations for the targeted design of excellent 2D OIP ferroelectrics, and is believed to inspire the future development of low-cost, high-efficiency, and stable device applications.

Expanding the limits of amide-triazole isosteric substitution in bisamide-based physical gels.

Gelation of organic solvents using N,N′-((1S,2S)-cyclohexane-1,2-diyl)didodecanamide (C12–Cyc) is driven by its self-assembly via antiparallel hydrogen bonds and van der Waals intermolecular interactions. In this work we carried out a dual isosteric substitution of the two amide groups with 1,2,3-triazole rings affording the corresponding isosteric gelator (click-C12–Cyc). A detailed comparative study in terms of the gelation ability and gel properties demonstrated that the 1,2,3-triazoles can take over all of the functions derived from the amide groups offering a versatile strategy for tuning the properties of the corresponding gels. This is not an obvious outcome because the directional amide groups in C12–Cyc constitute the source of the hydrogen bonds to build the 3D self-assembled network. Furthermore, theoretical calculations revealed that click-C12–Cyc can adopt a wide variety of interacting patterns, whose relative stability depends on the polarity of the environment, this is in good agreement with the experimental data obtained regarding its gelation ability. Other important features of click-C12–Cyc for potential practical applications are its non-cytotoxic character and its phase-selective gelation of water–oil mixtures.

Use of a bis-1,2,3-triazole gelator for the preparation of supramolecular metallogels and stabilization of gold nanoparticles

In this work, a series of functional metallogels have been prepared using a bis-1,2,3-triazole gelator prepared using the isosteric substitution method.

Isosteric Substitution of 4 H-1,2,4-Triazole by 1 H-1,2,3-Triazole in Isophthalic Derivative Enabled Hydrogel Formation for Controlled Drug Delivery.

In this work, we demonstrated that the simple substitution of the 1,2,4-triazole moiety in 5-( 4H-1,2,4-triazol-4-yl)isophthalic acid (5-TIA) by the 1 H-1,2,3-triazol-5-yl unit enables the preparation of a hydrogelator (click-TIA). In sharp contrast to 5-TIA, its isostere click-TIA undergoes self-assembly in water upon sonication, leading to the formation of stable supramolecular viscoelastic hydrogels with a critical gelation concentration of 6 g/L. Hydrogels made of click-TIA as well as hybrid hydrogels made of the mixture click-TIA + 5-TIA (molar ratio 1:0.2) were used to compare different properties of the materials (i.e., rheological properties, thermal properties, mechanical stability, morphology). In terms of toxicity, neither click-TIA nor 5-TIA showed cytotoxic effects on cellular viability of HeLa cells up to 2.3 × 10-3 g/L when compared to untreated cells incubated with DMSO. Furthermore, the hydrogels were used for the encapsulation and in vitro controlled release of oxytetracycline that followed first-order kinetics. For the hydrogel made of click-TIA, a maximum drug release of ∼60% was reached after ∼8 h within a pH range between 6.5 and 10. However, the release rate was reduced to approximately half of its value at pH values between 1.2 and 5.0, whereas the use of hybrid hydrogels made of click-TIA + 5-TIA allowed to reduce the original rate at pH ≤ 6.5.

Isosteric substitution in cationic-amphiphilic polymers reveals an important role for hydrogen bonding in bacterial membrane interactions.

Biomimetic antibacterial polymers, the functional mimics of antimicrobial peptides (AMPs), targeting the bacterial cell membrane have been developed to combat the problem of antibiotic resistance. Amphiphilicity, a balance of cationic charge and hydrophobicity, in these polymers has been shown to be pivotal for their selective interactions with anionic lipid membranes of bacteria instead of zwitterionic mammalian (human erythrocyte) membranes. However, it is unclear if and to what extent hydrogen bonding in amphiphilic antibacterial polymers contributes to this membrane binding specificity. To address this, we employ isosteric substitution of ester with amide moieties that differ in their potency for hydrogen bonding in the side chains of N-alkyl maleimide based amphiphilic polymers. Our studies reveal that amide polymer (AC3P) is a potent antibacterial agent with high membrane-disrupting properties compared to its ester counterpart (EC3P). To understand these differences we performed bio-physical experiments and molecular dynamics (MD) simulations which showed strong interactions of AC3P including hydrogen bonding with lipid head groups of bacterial model lipid bilayers, that are absent in EC3P, make them selective for bacterial membranes. Mechanistic investigations of these polymers in bacteria revealed specific membrane disruptive activity leading to the delocalization of cell division related proteins. This unprecedented and unique concept provides an understanding of bacterial membrane interactions highlighting the role of hydrogen bonding. Thus, these findings will have significant implications in efficient design of potent membrane-active agents.

Amide-triazole isosteric substitution for tuning self-assembly and incorporating new functions into soft supramolecular materials.

The proof-of-concept for the modular synthesis of new functional soft gel materials based on amide-triazole isosteric replacement has been demonstrated. A coassembly approach of isosteric amino acid-based hydrogelators was fruitfully applied for fine-tuning the release of entrapped drugs.

Abstract 5494: Novel 6-substituted pyrrolo[2,3-d]pyrimidine thienoyl antifolate regioisomers target folate receptor alpha positive ovarian cancer cells via inhibition of de novo purine nucleotide biosynthesis.

Abstract Epithelial ovarian cancers (EOC) represent a unique treatment challenge as over 50% of patients are diagnosed with advanced stage disease when surgical and chemotherapeutic interventions prove futile. Approximately 90% of EOC are folate receptor (FR) α positive and FR levels correlate with stage and grade. FRα-targeted therapies represent a rational treatment option for patients with advanced EOC whose treatments fail. There are three primary mechanisms of folate transport in mammalian cells, the reduced folate carrier (RFC), the proton-coupled folate transporter (PCFT) and FRs. RFC is the major transporter for folates and is expressed ubiquitously in normal tissues and tumors. Hence, developing novel antifolates that bypass cellular accumulation by RFC should reduce dose-limiting toxicities. PCFT is expressed in many solid tumors including ovarian cancer and is active at acidic pH. Previous studies established that a novel 2-amino-4-oxo-6-substituted pyrrolo[2,3-d]pyrimidine antifolate with an isosteric thienoyl substitution and a three carbon bridge (AG94) showed selective cellular uptake by FRα and PCFT over RFC. [1,3]Thienoyl regioisomers (AG150 and AG154) of AG94 showed subnanomolar potencies toward both KB nasopharyngeal carcinoma (IC50s = 0.1 and 0.09 nM, respectively) and IGROV1 ovarian carcinoma (IC50s of 0.64 and 0.1nM, respectively). While AG150 and AG154 were substrates for both PCFT and FRs, like AG94, their inhibitory effects at low drug concentrations were mediated primarily via FRα, as indicated by their capacities to bind with high affinities to FRα and protection by excess folic acid. Nucleoside protection assays with adenosine and 5-amino-4-imidazole carboxamide established that the first folate-dependent enzyme in the de novo purine biosynthesis pathway, glycinamide ribonucleotide (GAR) formyltransferase (GARFT), was the primary intracellular target for AG150 and AG154. GARFT targeting was confirmed by in situ metabolic labeling with [14C]glycine and measurement of accumulated [14C]formyl GAR in KB cells, for which IC50s were 1.35 and 1.46 nM, respectively. The purine salvage enzyme methylthioadenosine phosphorylase (MTAP) is frequently co-deleted with CDKN2a in solid tumors including ovarian cancer. Growth inhibitory effects of AG150 and AG154 were reversed in the presence of methylthioadenosine in MTAP-deficient IGROV1 cells transfected with MTAP cDNA. Our results demonstrate potent anti-tumor activities of the 6-pyrrolo[2,3-d]pyrimidine thienoyl regioisomers of AG94, AG150 and AG154, associated with their FRα-mediated cellular uptake and inhibition of GARFT in de novo purine biosynthesis. Preservation of purine salvage including MTAP is likely an important cellular determinant of antitumor efficacy for this class of novel tumor-targeted agents. Citation Format: Shermaine K. Mitchell-Ryan, Lei Wang, Steven Orr, Sita Kugel, Christina Cherian, Aleem Gangjee, Larry H. Matherly. Novel 6-substituted pyrrolo[2,3-d]pyrimidine thienoyl antifolate regioisomers target folate receptor alpha positive ovarian cancer cells via inhibition of de novo purine nucleotide biosynthesis. [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 5494. doi:10.1158/1538-7445.AM2013-5494

Optimizing the control of apoptosis by amide/triazole isosteric substitution in a constrained peptoid

Apoptosis is a biological process relevant to several human diseases that is strongly regulated through protein–protein complex formation. We have previously reported a peptidomimetic compound as potent apoptotic modulator. Structural studies of this compound showed the presence of cis/trans isomers of the exocyclic tertiary amide bond in slow exchange. This information encouraged us to perform an isosteric replacement of the amide bond by a 1,2,3-triazole moiety, where different substitution patterns would mimic different amide rotamers. The syntheses of these restricted analogs have been carried out using the Ugi multicomponent reaction followed by an intramolecular cyclization. Unexpectedly, for one of the proposed structures, a novel β -lactam compound was formed. All compounds showed to efficiently inhibit apoptosis, in vitro and in cellular extracts, with slight differences for the corresponding regioisomers. We propose the binding to Apaf-1 as the inhibition mechanism.

H/F isosteric substitution to attest different equi-energetic molecular conformations in crystals

The sequential replacement of aromatic H-atoms by F-atoms in 1,6-bis(phenylcarbonate) hexa-2,4-diyne allows access to its possible iso-energetic “syn”, “gauche” and “anti” conformations.

Designing Multitarget Anti‐inflammatory Agents: Chemical Modulation of the Lumiracoxib Structure toward Dual Thromboxane Antagonists–COX‐2 Inhibitors

A series of lumiracoxib derivatives were designed to explore the influence of isosteric substitution on balancing COX-2 inhibition and thromboxane A(2) prostanoid (TP) receptor antagonism. The compounds were synthesized through a copper-catalyzed coupling procedure and characterized for their pK(a) values. TP receptor antagonism was assessed on human platelets; COX-2 inhibition was determined on human isolated monocytes and human whole blood. TPα receptor binding of the most promising compounds was evaluated through radioligand binding assays. Some of the isosteric substitutions at the carboxylic acid group afforded compounds with improved TP receptor antagonism; of these, a tetrazole derivative retained good COX-2 inhibitory activity and selectivity. The identification of this tetrazole acting as a balanced dual-acting compound in human whole blood, along with SAR analysis of the synthesized lumiracoxib derivatives, might contribute to the rational design of a new class of cardioprotective anti-inflammatory agents.

Abstract 5740: 124I-CLR1404 and 131I-CLR1404: Broad spectrum diapeutic agents for cancer cell-targeted PET imaging and molecular radiotherapy

Abstract Selective delivery of therapeutic and diagnostic agents to malignant tumors versus normal tissues continues to be an important goal in cancer research and clinical practice. We have been developing cancer specific, iodinated phospholipid ether (PLE) analogs for tumor imaging and molecular radiotherapy. These PLEs localize in cancer cells selectively via plasma membrane lipid rafts, more abundant in cancer cells compared to normal cells, using them as portals of entry. Isosteric iodine substitution in CLR1404 affords either a diagnostic/imaging agent (e.g. using 124I for cancer-selective PET imaging) or a molecular radiotherapeutic agent (e.g. using 131I for cancer-selective cytotoxicity), both of which are in clinical development. We suggest the term “diapeutic” to describe such drugs which can be used in one form to identify and characterize patients who will benefit from a specific therapy and, in another form, to effect that therapy. A fluorescent analog of CLR1404, CLR1501, as well as a radioactive homolog displayed increased, lipid raft-dependent selective uptake and prolonged retention in a wide variety of cancer cell lines in comparison to normal human cells. Intracellular accumulation was observed in organellar membranes (ER, Golgi, mitochondria, autophagosomes). Lipid raft involvement in uptake was supported by co-localization of CLR1501 and lipid raft molecular markers. Lipid raft-dependence of uptake into cancer cells was confirmed by the finding that it was significantly decreased after disruption of lipid rafts with Filipin III. In vivo, nuclear imaging with radioiodinated CLR1404 revealed tumor-selective uptake and retention in 52 of 54 rodent cancer models tested, including human tumor xenograft, transgenic and spontaneous tumor models. In these models, 124I-CLR1404 clearly imaged both primary tumors and metastases. In vivo tumor conspicuity was apparent by 24 hours after i.v. administration and appeared undiminished at 120 hours. In contrast, the extra-tumoral 124I-CLR1404 PET signal decreased dramatically over the same time period as the agent was excreted. By 48 hours, no other tissues or organs showed significant labeling above the background of the blood compartment. Tumor uptake was not seen in models of benign hyperplasia. SPECT/CT imaging after administration of 131I-CLR1404 to cancer patients in the context of a Phase 1a dosimetric clinical trial also demonstrated selective uptake into malignant tumors, including metastases. Used in tandem, these chemically identical isosteres offer a personalized, diapeutic approach to cancer therapy, with 124I-CLR1404 imaging serving as an ideal qualitative and quantitative biomarker for subsequent treatment with 131I-CLR1404. 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 5740. doi:1538-7445.AM2012-5740

Abstract 3831: 131I-CLR1404 and CLR1404: Broad spectrum, cancer-targeted molecular radio- and chemotherapeutic phospholipid ether analogs

Abstract The effectiveness of current approaches to cancer therapy is often limited by off-target toxicity or, if relatively selective, by lack of drug target expression in tumors. To address these shortcomings, structure-activity relationship studies were undertaken and identified a series of iodophenyl-containing phospholipid ether (PLE) analogs that selectively accumulate in cancer cells/cancer stem cells compared to normal cells/stem cells, in vitro and in vivo. Isosteric iodine substitution in CLR1404 affords either a diagnostic/imaging agent (e.g. using 124I for cancer-selective PET imaging) or a molecular radiotherapeutic agent (e.g. using 131I for cancer-selective cytotoxicity), both of which are in clinical development. We suggest the term “diapeutic” to describe such drugs which can be used in one form to identify and characterize patients who will benefit from a specific therapy and, in another form, to effect that therapy. Here we describe the broad-spectrum efficacy of the 131I-labeled homolog of one such diapeutic compound (CLR1404) in human tumor xenograft models in mice including Caki-2 (renal; clear cell carcinoma), HCT-116 (colorectal carcinoma), Ovcar-3 (ovarian adenocarcinoma), MDA-MB-231 (triple negative mammary gland adenocarcinoma, MES-SA/Dx5 (uterine sarcoma), U87 (glioma), Mia Paca-2 (pancreatic carcinoma) and PC-3 (prostate carcinoma). In these models, a single i.v. injection of 131I-CLR1404 (100 αCi, 3.8 μg/mouse) resulted in significant tumor growth suppression and extension of survival. A separate radiotoxicology study in normal rats followed for six months or until death after a single dose of 131I-CLR1404 did not find significant radiation toxicity below 5 mCi suggesting that 131I-CLR1404 may display an acceptable therapeutic index in man. At 100-fold higher mass dose (380 μg/mouse, i.v.) CLR1404, the non-radioactive, 127I-containing homolog, was also highly efficacious in human tumor mouse xenograft models including MDA-MB-231 (triple negative breast cancer) and A549 (non-small cell lung cancer). CLR1404 inhibited proliferation of multiple human cancer cell lines in vitro with an IC50 of ∼5 μM compared to ∼50 μM for growth suppression of normal fibroblasts. Similar concentrations inhibited the PI3K/Akt cell signaling pathway and stimulated pro-apoptotic caspases in human cancer cell lines but not in normal fibroblasts. Thus, 131I-CLR1404 and CLR1404 each combine wide-ranging, cancer cell-selective targeting with cytotoxicity mechanisms known be broadly effective (intracellular radiation or PI3K/Akt inhibition, respectively). As such, both agents have the potential to provide effective, well-tolerated therapy across numerous cancer types. 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 3831. doi:1538-7445.AM2012-3831