Roberta Bortolozzi

MG-2477, a new tubulin inhibitor, induces autophagy through inhibition of the Akt/mTOR pathway and delayed apoptosis in A549 cells

We previously demonstrated that MG-2477 (3-cyclopropylmethyl-7-phenyl-3H-pyrrolo[3,2-f]quinolin-9(6H)-one) inhibits the growth of several cancer cell lines in vitro. Here we show that MG-2477 inhibited tubulin polymerization and caused cells to arrest in metaphase. The detailed mechanism of action of MG-2477 was investigated in a non-small cell lung carcinoma cell line (A549). Treatment of A549 cells with MG-2477 caused the cells to arrest in the G2/M phase of the cell cycle, with a concomitant accumulation of cyclin B. Moreover, the compound induced autophagy, which was followed at later times by apoptotic cell death. Autophagy was detected as early as 12h by the conversion of microtubule associated protein 1 light chain 3 (LC3-I) to LC3-II, following cleavage and lipid addition to LC3-I. After 48h of MG-2477 exposure, phosphatidylserine externalization on the cell membrane, caspase-3 activation, and PARP cleavage occurred, revealing that apoptotic cell death had begun. Pharmacological inhibition of autophagy with 3-methyladenine or bafilomycin A1 increased apoptotic cell death, suggesting that the autophagy caused by MG-2477 played a protective role and delayed apoptotic cell death. Additional studies revealed that MG-2477 inhibited survival signaling by blocking activation of Akt and its downstream targets, including mTOR, and FHKR. Treatment with MG-2477 also reduced phosphorylation of mTOR downstream targets p70 ribosomal S6 kinase and 4E-BP1. Overexpression of Akt by transfection with a Myr-Akt vector decreased MG-2477 induced autophagy, indicating that Akt is involved. Taken together, these results indicated that the autophagy induced by MG-2477 delayed apoptosis by exerting an adaptive response following microtubule damage.

Synthesis and evaluation of 1,5-disubstituted tetrazoles as rigid analogues of combretastatin A-4 with potent antiproliferative and antitumor activity.

Tubulin, the major structural component of microtubules, is a target for the development of anticancer agents. Two series of 1,5-diaryl substituted 1,2,3,4-tetrazoles were concisely synthesized, using a palladium-catalyzed cross-coupling reaction, and identified as potent antiproliferative agents and novel tubulin polymerization inhibitors that act at the colchicine site. SAR analysis indicated that compounds with a 4-ethoxyphenyl group at the N-1 or C-5 position of the 1,2,3,4-tetrazole ring exhibited maximal activity. Several of these compounds also had potent activity in inhibiting the growth of multidrug resistant cells overexpressing P-glycoprotein. Active compounds induced apoptosis through the mitochondrial pathway with activation of caspase-9 and caspase-3. Furthermore, compound 4l significantly reduced in vivo the growth of the HT-29 xenograft in a nude mouse model, suggesting that 4l is a promising new antimitotic agent with clinical potential.

Synthesis and biological evaluation of 2-substituted-4-(3′,4′,5′-trimethoxyphenyl)-5-aryl thiazoles as anticancer agents

Antitumor agents that bind to tubulin and disrupt microtubule dynamics have attracted considerable attention in the last few years. To extend our knowledge of the thiazole ring as a suitable mimic for the cis-olefin present in combretastatin A-4, we fixed the 3,4,5-trimethoxyphenyl at the C4-position of the thiazole core. We found that the substituents at the C2- and C5-positions had a profound effect on antiproliferative activity. Comparing compounds with the same substituents at the C5-position of the thiazole ring, the moiety at the C2-position influenced antiproliferative activities, with the order of potency being NHCH(3) > Me >> N(CH(3))(2). The N-methylamino substituent significantly improved antiproliferative activity on MCF-7 cells with respect to C2-amino counterparts. Increasing steric bulk at the C2-position from N-methylamino to N,N-dimethylamino caused a 1-2 log decrease in activity. The 2-N-methylamino thiazole derivatives 3b, 3d and 3e were the most active compounds as antiproliferative agents, with IC(50) values from low micromolar to single digit nanomolar, and, in addition, they are also active on multidrug-resistant cell lines over-expressing P-glycoprotein. Antiproliferative activity was probably caused by the compounds binding to the colchicines site of tubulin polymerization and disrupting microtubule dynamics. Moreover, the most active compound 3e induced apoptosis through the activation of caspase-2, -3 and -8, but 3e did not cause mitochondrial depolarization.

9-(4-Dimethylaminophenyl)benzo[b]quinolizinium: A Near-Infrared Fluorophore for the Multicolor Analysis of Proteins and Nucleic Acids in Living Cells

The visualization of cell components or processes within cells is an essential task in bioanalytical chemistry. Specifically, the fluorimetric detection of biomacromolecules has developed as a key technique in this research area, mainly because emission spectroscopy is a highly sensitive and straightforward method with relatively few demands on the equipment. As a consequence, several fluorescent probes have been established that enable the selective detection of cells or cellular components. For example, DNA–fluorophore conjugates, peptide-based molecular beacons, groove-binding cyanine dyes, and light-cleavable caged dyes were shown to operate as DNA stains in live cells. Similarly, it was demonstrated that appropriately substituted metallointercalators have a high propensity to bind to cellular DNA and thus enable its fluorimetric detection, or, in some cases, the detection of other cell components. 11] The same principle was applied to detect RNA in nucleoli and the cytoplasm with a 2,7-carbazole derivative. Furthermore, exciton-controlled hybridization-sensitive fluorescent oligonucleotide (ECHO) probes allow multicolor RNA imaging in cells. Recently, a chemosensor has been presented that enables the fluorimetric differentiation of quadruplex DNA from other nucleic acids in cells. Moreover, it has been shown that the fluorimetric discrimination of regions with different polarities may be accomplished in cells with quinoxaline derivatives. Along these lines, the use of near-infrared (NIR, 650–900 nm) fluorescent probes is advantageous for biological applications, because NIR fluorophores exhibit low or almost no phototoxicity, relatively deep penetration into tissue, and negligible interference with the autofluorescence of cells. We have shown recently that benzo[b]quinolizinium derivatives may be functionalized such that the fluorescence is quenched by different independent deactivation pathways and that the association with biomacromolecules results in light-up effects and shifts in the emission energy. In some cases, separate deactivation channels enable the indepenACHTUNGTRENNUNGdent or even simultaneous detection of DNA and metal ions with one chemosensor. In this context, we synthesized 9-(4-dimethylamino)benzo[b]quinolizinium (1a), which exhibits a very low emission quantum yield, presumably caused by deactivation of the excited state by torsional relaxation and photoinduced electron transfer (PET) or charge shift (CS). Notably, some structural features of the derivative 1a resemble aminophenylpyridinium derivatives such as 2, which have been used as fluorescent probes in nerve membranes, and Thioflavin T (3), which has been applied for fluorimetric analysis of amyloid fibril formation. Therefore, we proposed that the derivative 1a may represent a complementary fluorimetric tool for the selective analysis of biomacromolecules, especially considering our experience with the benzo[b]quinolizinium ion as a ligand for DNA and proteins. Herein, we demonstrate that different physiologically relevant host systems are stained with the chemosensor 1a, most remarkably with different emission wavelengths and intensities. In addition, we show that, due to these properties, the chemosensor 1a represents one of the rare examples of probes that stain cells with multicolored fluorescence.

Recent advances in vascular disrupting agents in cancer therapy.

Vascular disrupting agents (VDAs) are an important class of compounds that exhibit selective activity against pre-existing tumor vasculature, causing rapid shutdown of the tumor blood flow and consequent necrosis of the tumor mass. The VDAs can be divided into flavonoid compounds, which are related to flavone acetic acid, and tubulin-binding agents. Tubulin-binding agents represent the largest group of VDAs and are characterized by different chemical structures, although most of them are derivatives of the lead compound combretastatin (CA-4). They demonstrated clinical activity, although recent findings have established that they have insufficient activity as single agents. Several resistance mechanisms occur, such as the resistance of the tumor rim cells, while promising results have been described in combination with other chemotherapeutics.

Design, synthesis, and structure-activity relationships of azolylmethylpyrroloquinolines as nonsteroidal aromatase inhibitors.

A small library of both [2,3-h] and [3,2-f] novel pyrroloquinolines equipped with an azolylmethyl group was designed and synthesized as nonsteroidal CYP19 aromatase inhibitors. The results showed that azolylmethyl derivatives 11, 13, 14, 21, and 22 exhibited an inhibitory potency on aromatase comparable to that of letrozole chosen as a reference compound. When assayed on CYP11B1 (steroid-11β-hydroxylase) and CYP17 (17α-hydroxy/17,20-lyase), compound 22 was found to be the best and most selective CYP19 inhibitor of them all. In a panel of nine human cancer cell lines, all compounds were either slightly cytotoxic or not at all. Docking simulations were carried out to inspect crucial enzyme/inhibitor interactions such as hydrophobic interactions, hydrogen bonding, and heme iron coordination. This study, along with the prediction of the pharmacokinetics of compounds 11, 13, 14, 21, and 22, demonstrates that the pyrroloquinoline scaffold represents a starting point for the development of new pyrroloquinoline-based aromatase inhibitors.

Synthesis, biological evaluation and molecular docking studies of trans-indole-3-acrylamide derivatives, a new class of tubulin polymerization inhibitors

In this study, we synthesized a series of trans-indole-3-acrylamide derivatives (3a-k) and investigated their activity for inhibition of cell proliferation against five human cancer cell lines (HeLa, MCF7, MDA-MB-231, Raji and HL-60) by MTT assay. Compound 3e showed significant antiproliferative activity against both the Raji and HL-60 cell lines with IC50 values of 9.5 and 5.1 μM, respectively. Compound 3e also exhibited moderate inhibitory activity on tubulin polymerization (IC50=17 μM). Flow cytometric analysis of cultured cells treated with 3e also demonstrated that the compound caused cell cycle arrest at the G2/M phase in HL-60 and HeLa cells. Moreover, 3e, the most active compound, caused an apoptotic cell death through the activation of caspase-3. Docking simulations suggested that 3e binds to the colchicine site of tubulin.

Synthesis and in vitro Evaluation of 3H-Pyrrolo[3,2-f]-quinolin-9-one Derivatives That Show Potent and Selective Anti-leukemic Activity

A series of new substituted 7‐phenyl‐3H‐pyrrolo[3,2‐f]quinolin‐9‐ones were synthesized and evaluated for their antiproliferative activity. The most active derivatives showed high selectivity against human leukemia cell lines and potently inhibited their growth, with GI50 values in the nanomolar range. The active compounds strongly blocked tubulin assembly and colchicine binding to tubulin. Their activities were equal to or greater than that of the reference compound combretastatin A‐4. Flow cytometry studies showed that the two most active compounds arrested Jurkat cells in the G2/M cell‐cycle phase in a concentration‐dependent manner. This effect was associated with apoptosis, mitochondrial depolarization, generation of reactive oxygen species, activation of caspase‐3, and cleavage of the enzyme poly(ADP‐ribose) polymerase.

FOXO3a and Posttranslational Modifications Mediate Glucocorticoid Sensitivity in B-ALL.

Glucocorticoids are widely used to treat B acute lymphoblastic leukemia (B-ALL); however, the molecular mechanism underlying glucocorticoid response and resistance is unclear. In this study, the role and regulation of FOXO3a in mediating the dexamethasone response in B-ALL were investigated. The results show that FOXO3a mediates the cytotoxic function of dexamethasone. In response to dexamethasone, it was found that FOXO3a translocates into the nucleus, where it induces the expression of downstream targets, including p27Kip1 and Bim, important for proliferative arrest and cell death in the sensitive RS4;11 and SUP-B15 B-ALL cells. FOXO3a activation by dexamethasone is mediated partially through the suppression of the PI3K/Akt signaling cascade. Furthermore, two posttranslational modifications were uncovered, phosphorylation on Ser-7 and acetylation on Lys-242/5, that associated with FOXO3a activation by dexamethasone. Immunoblot analysis showed that the phosphorylation on Ser-7 of FOXO3a is associated with p38/JNK activation, whereas the acetylation on Lys-242/5 is correlated with the downregulation of SIRT1/2/6 and the induction of the acetyltransferase CBP/p300. Collectively, these results indicate that FOXO3a is essential for dexamethasone response in B-ALL cells, and its nuclear translocation and activation is associated with its phosphorylation on Ser-7 and acetylation on Lys-242/245. These posttranslational events can be exploited as biomarkers for B-ALL diagnosis and as drug targets for B-ALL treatment, particularly for overcoming the glucocorticoid resistance. Implications: FOXO3a and its posttranslational regulation are essential for dexamethasone response, and targeting FOXO3a and sirtuins may enhance the dexamethasone-induced cytotoxicity in B-ALL cells. Mol Cancer Res; 13(12); 1578–90. ©2015 AACR.

Novel 3-Substituted 7-Phenylpyrrolo[3,2-f]quinolin-9(6H)-ones as Single Entities with Multitarget Antiproliferative Activity

A series of chemically modified 7-phenylpyrrolo[3,2-f]quinolinones was synthesized and evaluated as anticancer agents. Among them, the most cytotoxic (subnanomolar GI50 values) amidic derivative 5f was shown to act as an inhibitor of tubulin polymerization (IC50, 0.99 μM) by binding to the colchicine site with high affinity. Moreover, 5f induced cell cycle arrest in the G2/M phase of the cell cycle in a concentration dependent manner, followed by caspase-dependent apoptotic cell death. Compound 5f also showed lower toxicity in nontumoral cells, suggesting selectivity toward cancer cells. Additional experiments revealed that 5f inhibited the enzymatic activity of multiple kinases, including AURKA, FLT3, GSK3A, MAP3K, MEK, RSK2, RSK4, PLK4, ULK1, and JAK1. Computational studies showed that 5f can be properly accommodated in the colchicine binding site of tubulin as well as in the ATP binding clefts of all examined kinases. Our data indicate that the excellent antiproliferative profile of 5f may be derived from its interactions with multiple cellular targets.