1-Methyl-3H-pyrazolo[1,2-a]benzo[1,2,3,4]tetrazin-3-ones. Design, synthesis, and biological activity of new antitumor agents

Design and synthesis of novel 1,2,3,4-tetrazines as new anti-leukemia cancer agents

A series of novel 1,2,3,4-tetrazines were designed and synthesized. 1 H-NMR spectroscopy, 13 C NMR spectroscopy, and HRMS were used to determine the structures of this novel compounds. Computational approaches suggested that DHFR is a putative target for the newly synthesized 11 compounds. Extensive molecular dynamics simulations followed by molecular docking simulations were employed to evaluate DHFR as a potential target protein. The anticancer activities of the compounds were evaluated against five different types of leukemia cell lines (Jurkat, Nalm-6, Reh, K562, and Molt-4) and one non-leukemic cell line (Hek293T) by MTT test in vitro and imatinib was used as a control drug. Among these compounds, 3a exhibited the best activity against all the leukemic cell lines, except Reh cell line. For Nalm-6, K562, Jurkat, and Molt-4 cell lines, IC50 values were found to be 15.98, 19.12, 23.15, and 25.80 μM, respectively. Our work focuses on the synthesis of original and novel 1,2,3,4-tetrazine derivatives while contributing to the ongoing effort to discover more potent new antileukemia agents.

Spectroscopic and In Silico Studies on the Interaction of Substituted Pyrazolo[1,2-a]benzo[1,2,3,4]tetrazine-3-one Derivatives with c-Myc G4-DNA

Herein we describe a combined experimental and in silico study of the interaction of a series of pyrazolo[1,2-a]benzo[1,2,3,4]tetrazin-3-one derivatives (PBTs) with parallel G-quadruplex (GQ) DNA aimed at correlating their previously reported anticancer activities and the stabilizing effects observed by us on c-myc oncogene promoter GQ structure. Circular dichroism (CD) melting experiments were performed to characterize the effect of the studied PBTs on the GQ thermal stability. CD measurements indicate that two out of the eight compounds under investigation induced a slight stabilizing effect (2-4 °C) on GQ depending on the nature and position of the substituents. Molecular docking results allowed us to verify the modes of interaction of the ligands with the GQ and estimate the binding affinities. The highest binding affinity was observed for ligands with the experimental melting temperatures (Tms). However, both stabilizing and destabilizing ligands showed similar scores, whilst Molecular Dynamics (MD) simulations, performed across a wide range of temperatures on the GQ in water solution, either unliganded or complexed with two model PBT ligands with the opposite effect on the Tms, consistently confirmed their stabilizing or destabilizing ability ascertained by CD. Clues about a relation between the reported anticancer activity of some PBTs and their ability to stabilize the GQ structure of c-myc emerged from our study. Furthermore, Molecular Dynamics simulations at high temperatures are herein proposed for the first time as a means to verify the stabilizing or destabilizing effect of ligands on the GQ, also disclosing predictive potential in GQ-targeting drug discovery.

[3 + 3] Cycloaddition of Azides with in Situ Formed Azaoxyallyl Cations To Synthesize 1,2,3,4-Tetrazines

A formal [3 + 3] cycloaddition reaction between azides and in situ formed azaoxyallyl cations has been realized. This reaction provided an efficient and practical pathway to synthesize 1,2,3,4-tetrazines in good yields under mild conditions. Biologically active molecules could also be well compatible, highlighting the potential value of this reaction.

New insights into the mechanism of action of pyrazolo[1,2-a]benzo[1,2,3,4]tetrazin-3-one derivatives endowed with anticancer potential

Due to the scarce biological profile, the pyrazolo[1,2-a]benzo[1,2,3,4]tetrazine-3-one scaffold (PBT) has been recently explored as promising core for potential anticancer candidates. Several suitably decorated derivatives (PBTs) exhibited antiproliferative activity in the low-micromolar range associated with apoptosis induction and cell cycle arrest on S phase. Herein, we selected the most active derivatives and submitted them to further biological explorations to deepen the mechanism of action. At first, a DNA targeting is approached by means of flow Linear Dichroism experiments so as to evaluate how small planar molecules might interact with DNA, including the interference with the catalytic cycle of topoisomerase II and the influence on the cleavable complex stabilization (poisoning effect). In support of the experimental data, in silico studies have been achieved to better understand the chemical space of the interactions. Interestingly some meaningful structural features, useful for further developments, were found. The 8,9-di-Cl substituted derivative revealed as the most effective in the intercalative process, as well as on the inhibition of catalytic activity of topoisomerase II. Predicted ADME studies confirm that PBTs are promising as potential drug candidates.

Direct access to non-aromatic 1,2,3,6-tetrahydro-1,2,3,4-tetrazines via [4 + 2] cycloaddition of α-halogeno hydrazones with azodicarboxylic acid derivatives

Construction of non-aromatic 1,2,3,6-tetrahydro-1,2,3,4-tetrazines through [4 + 2] cycloaddition of α-halogeno hydrazones with azodicarboxylic acid derivatives.

Exploring the anticancer potential of pyrazolo[1,2-a]benzo[1,2,3,4]tetrazin-3-one derivatives: the effect on apoptosis induction, cell cycle and proliferation

In order to investigate their anticancer potential, four new pyrazolo[1,2-a]benzo[1,2,3,4]tetrazinone derivatives, designed through the chemometric protocol VLAK, and three of the most active compounds of the previous series have been evaluated on some cellular events including proliferation, apoptosis induction, and cell cycle. The NCI one dose (10 μM) screening revealed that the 8,9-di-methyl derivative showed activity against Leukemia (CCRF-CEM) and Colon cancer cell line (COLO 205), reaching 81% and 45% of growth inhibition (GI), respectively. Replacement of the two methyl groups with two chlorine atoms maintained the activity toward Leukemia cell (CCRF-CEM, GI 77%) and selectively enhanced the activity against COLO 205 attaining a LD50 in the μM range and against SW-620 a GI of 77%. Interestingly, an appreciable growth inhibition of 47% against therapeutically "refractory" Non-Small Cell Lung Cancer (NCI-H522) was observed. Moreover, the apoptosis induction, based on mitochondrial membrane depolarization, was found in the range EC50 3-5 μM on HeLa cell, evidencing a well defined relationship with the related in vitro cell growth inhibitory assays (MTT) performed against other selected tumor cell lines not included in the NCI tumor panel (HeLa, cervix; H292, lung; LAN-5, CNS; CaCo-2, colon; 16HBE, normal human cell lung) and against MCF-7 tumor cell line (breast). Only for the most active compounds, further cell cycle tests on HeLa displayed a cell arrest on S phase. Thus, a promising new class of anticancer candidates, acting as valuable apoptotic inductors, is proposed.