Efficient routes to acenaphthylene-fused polycyclic arenes/heteroarenes and heterocyclic fluoranthene analogues

The acenaphthenone-derived α-oxoketene dithioacetal 2 has been subjected to various [3 + 3] aromatic and heteroaromatic annulation and other heterocyclization reactions previously developed in our laboratory, providing short and efficient routes to a diverse range of known and unknown acenaphtho-annulated linear and angular PAHs, heteroaromatics and five-membered heterocycles in good yields. Thus, benzo- and naphthoannulation of 2 with various allyl and benzyl Grignard reagents afforded substituted fluoranthenes 4a-c and benzo[k]fluoranthene 8, respectively, in good yields. Similarly, the parent benzo[j]fluoranthene 15a and its substituted derivative 16b have been synthesized by base-induced conjugate 1,4-addition of arylacetonitriles to 2, followed by acid-induced cyclization of the conjugate adducts 12a-b to give 13a-b and subsequent further transformations. The adducts obtained by 1,4-addition of anions derived from acetophenone and acenaphthenone were subjected toheterocyclization in the presence of ammonium acetate to give 8-arylacenaphtho[1,2-b]pyridines 18a-b and bis(acenaphtho)-annulated pyridine 20. Heterocyclization of 2 with bifunctional nucleophiles such as 2-picolyllithium and guanidinium nitrate afforded the corresponding acenaphtho[1,2-b]quinolizinium salt 23 and acenaphtho[1,2-d]pyrimidine 24, respectively, in high yields. Finally, acenaphtho[1,2-c]-fused five-membered heterocycles such as 7-(methylthio)acenaphtho[1,2-c]thiophene (25), 7-(methylthio)acenaphtho[1,2-c]furan (27) and 7-(methylthio)acenaphtho[1,2-c]pyrrole-2-carboxylic acid (30) were obtained in good yields by subjection of 2 to Simmons-Smith reaction conditions or by treatment with dimethylsulfonium methylide or glycinate dianion. Some of these newly synthesized PAHs or fused heterocycles were subjected to Raney Ni desulfurization to furnish sulfur-free compounds

Highly diastereoselective [3+2] cyclopenta[b]annulation of indoles with 2-arylcyclopropyl ketones and diesters

A highly diastereoselective Lewis acid (BF3·Et2O or TiCl4) induced [3+2] cycloaddition of substituted and unsubstituted indoles with 2-arylcyclopropyl ketones/diesters yielding cyclopenta[b]indoles in high yields is reported. This methodology has also been extended to tetrahydrocarbazole, cyclopenta[b]- and cyclohepta[b]indoles affording tetracyclic propellane type frameworks in modest yields

Evaluation of the reducing potential of PSMA-containing endosomes by FRET imaging

Aim: Ligand-targeted therapeutics are experiencing increasing use for treatment of human diseases due to their ability to concentrate a desired drug at a pathologic site while reducing accumulation in healthy tissues. For many ligand-targeted drug conjugates, a critical aspect of conjugate design lies in engineering release of the therapeutic payload to occur only after its internalization by targeted cells. Because disulfide bond reduction is frequently exploited to ensure intracellular drug release, an understanding of the redox properties of endocytic compartments can be critical to ligand-targeted drug design. While the redox properties of folate receptor trafficking endosomes have been previously reported, little is known about the trafficking of prostate-specific membrane antigen (PSMA), a receptor that is experiencing increasing use for drug targeting in humans.Methods: To obtain this information, we have constructed a PSMA-targeted fluorescence resonance energy transfer pair that reports on disulfide bond reduction by changing fluorescence from red to green.Results: We show here that this reporter exhibits rapid and selective uptake by PSMA-positive cells, and that reduction of its disulfide bond proceeds steadily but incompletely following internalization. The fact that maximal disulfide reduction reaches only ~50%, even after 24 h incubation, suggests that roughly half of the conjugates must traffic through endosomes that display no reducing capacity.Conclusion: As the level of disulfide reduction differs between PSMA trafficked and previously published folate trafficked conjugates, it also follows that not all internalizing receptors are translocated through similar intracellular compartments. Taken together, these data suggest that the efficiency of disulfide bond reduction must be independently analyzed for each receptor trafficking pathway when disulfide bond reduction is exploited for intracellular drug release

A targeted near-infrared nanoprobe for deep-tissue penetration and imaging of prostate cancer

Fluorescent guided surgery (FGS) has been highlighted as a potential to increase precision of diseased tissue whilst minimising the removal of surrounding healthy tissue, particularly relevant for increasingly prevalent prostate cancer (PCa). There remain challenges in the design of imaging probes presenting high selectivity for tumour tissue, clear visualization and minimal toxicity. Here we report the design and development of a novel NIR-nanoprobe and evaluate its potential in penetration inside PCa tumour tissues. Prostate-specific membrane antigen (PSMA) receptor-targeted near infrared emitting quantum dots (PSMA-NIR-QDot) are demonstrated as deep tissue imaging agents for intraoperative navigation during surgery and improving detection specificity for PCa. Probes were designed and synthesized by conjugating functionalized amino-PEG QDots through a heterobifunctional linker to a DUPA targeted polypeptide construct. Nanoprobes were evaluated in vitro in PSMA+ PCa cell lines for specificity and affinity determined by flow cytometric analysis. The penetration efficacy was tested further on large PCa 3D tumour spheroids (dia ~ 1.2 mm, width ~ 250 µm) by deep tissue multiphoton imaging. The PSMA-NIR-Qdot was found to be an efficient deep tissue penetrating intra-operative guided surgical tool with high affinity (KD = 15 nM) and penetrative capacity. The results have been demonstrated in vitro in 2D and 3D tissue models, mimicking cancer lesions in vivo. The presented deep-tissue imaging NIR nanoprobes target prostatic lesions that (i) bind to PSMA+ tumour with sub-nanomolar affinity and high specificity, (ii) show excellent safety profile in primary cell lines in vitro, and (iii) show high penetrative capacity in 3D prostate tumour model (~ 250 µm tissue depth). These probes may potentially offer vastly improved surgical accuracy for diseased tissue removal.</p

Use of Folate-Conjugated Imaging Agents To Target Alternatively Activated Macrophages in a Murine Model of Asthma

Pro-inflammatory macrophages play a prominent role in such autoimmune diseases as rheumatoid arthritis, Crohn’s disease, psoriasis, sarcoidosis, and atherosclerosis. Because pro-inflammatory macrophages have also been shown to overexpress a receptor for the vitamin folic acid (i.e., folate receptor beta; FR-β), folate-linked drugs have been explored for use in imaging and treatment of these same diseases. To determine whether allergic inflammatory disorders might be similarly targeted with folate-linked drugs, we have examined the characteristics of macrophages that are prominent in the pathogenesis of asthma. We report here that macrophages from the lungs of mice with experimental allergic asthma express FR-β. We further document that these FR-β⁺ macrophages coexpress markers of alternatively activated (M2-type) macrophages, including the mannose receptor and arginase-1. Finally, we demonstrate that folate-conjugated fluorescent dyes and radioimaging agents can be specifically targeted to these asthmatic lung macrophages, with little uptake by macrophages present in healthy lung tissue. These data suggest strategies for the development of novel diagnostic agents for the imaging of asthma and other diseases involving alternatively activated macrophages

Novel solid-phase strategy for the synthesis of ligand-targeted fluorescent-labelled chelating peptide conjugates as a theranostic tool for cancer

In this article, we have successfully designed and demonstrated a novel continuous process for assembling targeting ligands, peptidic spacers, fluorescent tags and a chelating core for the attachment of cytotoxic molecules, radiotracers, nanomaterials in a standard Fmoc solid-phase peptide synthesis in high yield and purity. The differentially protected Fmoc-Lys-(Tfa)-OH plays a vital role in attaching fluorescent tags while growing the peptide chain in an uninterrupted manner. The methodology is versatile for solid-phase resins that are sensitive to mild and strong acidic conditions when acid-sensitive side chain amino protecting groups such as Trt (chlorotrityl), Mtt (4-methyltrityl), Mmt (4-methoxytrityl) are employed to synthesise the ligand targeted fluorescent tagged bioconjugates. Using this methodology, DUPA rhodamine B conjugate (DUPA = 2-[3-(1,3-dicarboxypropyl)ureido]pentanedioic acid), targeting prostate specific membrane antigen (PSMA) expressed on prostate, breast, bladder and brain cancers and pteroate rhodamine B, targeting folate receptor positive cancers such as ovarian, lung, endometrium as well as inflammatory diseases have been synthesized. In vitro studies using LNCaP (PSMA +ve), PC-3 (PSMA −ve, FR −ve) and CHO-β (FR +ve) cell lines and their respective competition experiments demonstrate the specificity of the newly synthesized bioconstructs for future application in fluorescent guided intra-operative imaging

Development of Tumor-Targeted Near Infrared Probes for Fluorescence Guided Surgery

Complete surgical resection of malignant disease is the only reliable method to cure cancer. Unfortunately, quantitative tumor resection is often limited by a surgeon’s ability to locate all malignant disease and distinguish it from healthy tissue. Fluorescence-guided surgery has emerged as a tool to aid surgeons in the identification and removal of malignant lesions. While nontargeted fluorescent dyes have been shown to passively accumulate in some tumors, the resulting tumor-to-background ratios are often poor, and the boundaries between malignant and healthy tissues can be difficult to define. To circumvent these problems, our laboratory has developed high affinity tumor targeting ligands that bind to receptors that are overexpressed on cancer cells and deliver attached molecules selectively into these cells. In this study, we explore the use of two tumor-specific targeting ligands (i.e., folic acid that targets the folate receptor (FR) and DUPA that targets prostate specific membrane antigen (PSMA)) to deliver near-infrared (NIR) fluorescent dyes specifically to FR and PSMA expressing cancers, thereby rendering only the malignant cells highly fluorescent. We report here that all FR- and PSMA-targeted NIR probes examined bind cultured cancer cells in the low nanomolar range. Moreover, upon intravenous injection into tumor-bearing mice with metastatic disease, these same ligand–NIR dye conjugates render receptor-expressing tumor tissues fluorescent, enabling their facile resection with minimal contamination from healthy tissues

DUPA Conjugation of a Cytotoxic Indenoisoquinoline Topoisomerase I Inhibitor for Selective Prostate Cancer Cell Targeting

Prostate-specific membrane antigen (PSMA) is overexpressed in most prostate cancer cells while being present at low or undetectable levels in normal cells. This difference provides an opportunity to selectively deliver cytotoxic drugs to prostate cancer cells while sparing normal cells that lack PSMA, thus improving potencies and reducing toxicities. PSMA has high affinity for 2-[3-(1,3-dicarboxypropyl)­ureido]­pentanedioic acid (DUPA) (<i>K</i>_i = 8 nM). After binding to a DUPA–drug conjugate, PSMA internalizes, unloads the conjugate, and returns to the surface. In the present studies, an indenoisoquinoline topoisomerase I inhibitor was conjugated to DUPA via a peptide linker and a drug-release segment that facilitates intracellular cleavage to liberate the drug cargo. The DUPA–indenoisoquinoline conjugate exhibited an IC₅₀ in the low nanomolar range in 22RV1 cell cultures and induced a complete cessation of tumor growth with no toxicity, as determined by loss of body weight and death of treated mice