Lino Colombo

Small Molecule Integrin Antagonists in Cancer Therapy

Integrins are a large family of dimeric receptors composed by alpha and beta subunits that, once bound to extra-cellular matrix (ECM) proteins, regulate a variety of cellular processes such as cell motility, migration, and proliferation. The integrins transduce signals from inside-out and outside-in the cell, thus representing the cellular link to the external environment. For these properties, integrin activation has been involved in pathological processes like tumor growth and metastasis formation. Recent advances in the elucidation of the crystallographic structures of the alphavbeta3 and alphaIIbeta3 integrins are promoting studies focused to the search of small molecule antagonists that can block the integrin binding to ECM and inhibit the biological effects exerted by these receptors. In this review we will focus on small molecule antagonists of alphavbeta3 and alphavbeta5 integrin as tools for cancer therapy while other integrins will only be briefly mentioned. Cilengitide (cyclic peptidic alphavbeta3 and alphavbeta5 antagonist) is currently in clinical trials for anti cancer therapy. Combination of integrin alphavbeta3 antagonists and other traditional therapeutic approaches may represent a future strategy to inhibit tumor growth and metastasis spreading.

Camphor-derived 2-stannyl-N-Boc-1,3-oxazolidine: A new chiral formylanion equivalent for the asymmetric synthesis of 1,2-diols

Abstract Optically pure 2-tributylstannyl-N-Boc-1,3-oxazolidine 6 , prepared from the camphor-derived aminoalcohol 5 , was converted to diastereomerically pure 2-acyl derivatives 8 in three steps. Reaction of these ketones with Grignard reagents at −78°C proceeded with high stereoselectivity affording tertiary carbinols which gave 1,2-diols with >96% ee after hydrolysis and reduction of the intermediate α-hydroxy aldehydes. A new deblocking procedure of the t-Boc group is also described.

CONFORMATIONALLY CONSTRAINED DIPEPTIDES : SYNTHESIS OF 7,5- AND 6,5-FUSED BICYCLIC LACTAMS BY STEREOSELECTIVE RADICAL CYCLIZATIONS

Abstract A study of radical cyclizations of β-substituted α-N-acetyl acrylamide have been performed: high level of regio- and stereoselectivity was obtained.

Chiral 2-lithio-13-dioxolanes and -2-lithiooxazolidines: New formyl anion equivalents

Abstract The preparation of enantiomerically pure 2-lithio-1,3-dioxolanes and 2-lithiooxazolidines and their use as formyl anion equivalents in addition reactions to aldehydes are described.

Synthesis of new bicyclic lactam peptidomimetics by ring-closing metathesis reactions

Abstract An efficient and versatile synthetic method for the preparation of new fused bicyclic lactams 3a and 3b is described. The spirane cyclopentane nucleus was easily installed by diallylation of the pyroglutamate derivative 18 followed by ring-closing metathesis (RCM). A more practical and stereoselective method for the allylation of the α-methoxy carbamate 21 , involving the use of InCl3 as a Lewis acid, was developed. In the crucial coupling reaction of the diastereomeric mixture of cis- and trans-pirrolidine derivatives 5a and 5b with N-Cbz vinyl phenylalanine only the cis isomer was found to react. An RCM reaction on the dipeptides 25a and 25b followed by catalytic hydrogenation, gave the final epimeric bicyclic lactams 3a and 3b . The same synthetic sequence on the model compound 7 , lacking the spiro cyclopentane nucleus, is also reported.

Practical stereoselective synthesis of conformationally constrained unnatural proline-based amino acids and peptidomimetics

Abstract A practical synthetic scheme was developed to prepare both the cis- and trans-fused stereoisomers of N-Boc- l -octahydroindole-2-carboxylic acid ( l -Oic) methyl ester. Key event of the synthetic sequence was the ring-closing metathesis of a suitable diallylated proline derivative. This is the first reported practical synthesis of the trans-fused isomer. Functionalization of the octahydroindole nucleus by electrochemical oxidation followed by acid-catalysed allylation paved the way for the preparation of reverse-turn dipeptide mimics.

Synthesis of 7,5-fused bicyclic lactams by stereoselective radical cyclization

Abstract 7,5-Fused bicyclic lactams of type 1 were synthesised by a route involving the radical cyclization of the intermediate 2 . High level of stereoselection was obtained in this reaction.

A small-molecule RGD-integrin antagonist inhibits cell adhesion, cell migration and induces anoikis in glioblastoma cells

In cancer cells integrins modulate important cellular events that regulate the metastasic cascade which involves detachment from the tumor mass, dissemination and attachment to the oncogenic niche. The α5β1, αvβ3 and αvβ5 integrins are widely expressed in different cancer types and recognize the tripeptide Arg-Gly-Asp (RGD) motif present in several extracellular matrix proteins. In human glioblastoma, αvβ3 integrin expression correlates with tumor grade, suggesting that this integrin may play a crucial role in the highly infiltrative behavior of high grade gliomas. However, few selective RGD-like antagonists have been developed and few studies have investigated their effects in in vitro models of human glioblastoma. In this study, we investigated several cellular effects and the underlying molecular mechanisms exerted by a new small-molecule RGD antagonist, 1a-RGD, in the U251 and U373 human glioblastoma cell lines. Treatment with 1a-RGD (20 μM) demonstrated a weak effect on cell viability and cell proliferation but strongly inhibited cell attachment and cell migration together with actin cytoskeleton disassembly. Prolonged 1a-RGD treatment (72 h) induced anoikis, assessed by Annexin staining and nucleosome assay, particularly in the detached cells. When integrin-linked transduction pathways were investigated, 1aRGD was found to exert a marked reduction in focal adhesion kinase (FAK) phosphorylation without affecting the AKT- and ERK-dependent pathways. Our data indicate that 1a-RGD, probably via modulation of the FAK-dependent pathway, inhibits cell migration and attachment and induces anoikis in glioblastoma cells. This novel finding suggests that the development of an RGD-like molecule may represent a promising tool for the pharmacological approach aimed at reducing the malignancy of glioblastoma cells.

Practical stereoselective synthesis of α-d-C-mannosyl-(R)-alanine

Abstract α- d - C -Mannosyl-( R )-alanine 2 was synthesized in only four steps starting from the known acetonide protected d - ribo -hex-1-enitol 4 and N -benzoylalanine. The key C–C bond formation between the sugar and the amino acid moieties was effected through a Claisen rearrangement of the intermediate oxazole 7 , derived from the ester 6 .

Synthesis of substituted conformationally constrained 6,5- and 7,5-fused bicyclic lactams as dipeptide mimics

Using a convenient and practical route we report the preparation of a series of rigid surrogates of amino acids and dipeptides for application within constrained peptide analogues, and for employment as input for combinatorial science. These substituted 2-oxo-1-azabicycloalkane amino acids have the potential of replicating the backbone geometry and side-chain function of dipeptide residues like serine, lysine, glutamate, and related amino acids.