An inhibitor of nonhomologous end-joining abrogates double-strand break repair and impedes cancer progression.

DNA Ligase IV is responsible for sealing of double-strand breaks (DSBs) during nonhomologous end-joining (NHEJ). Inhibiting Ligase IV could result in amassing of DSBs, thereby serving as a strategy toward treatment of cancer. Here, we identify a molecule, SCR7 that inhibits joining of DSBs in cell-free repair system. SCR7 blocks Ligase IV-mediated joining by interfering with its DNA binding but not that of T4 DNA Ligase or Ligase I. SCR7 inhibits NHEJ in a Ligase IV-dependent manner within cells, and activates the intrinsic apoptotic pathway. More importantly, SCR7 impedes tumor progression in mouse models and when coadministered with DSB-inducing therapeutic modalities enhances their sensitivity significantly. This inhibitor to target NHEJ offers a strategy toward the treatment of cancer and improvement of existing regimens.

Synthesis of Novel Pyrazole-Oxindole Conjugates with Cytotoxicity in Human Cancer Cells via Apoptosis.

A novel series of pyrazole-oxindole conjugates were prepared and characterized as potential cytotoxic agents by FT-IR, NMR and HR-MS. The cytotoxic activity of these compounds was tested in the Jurkat acute T cell leukemia, CEM acute lymphoblastic leukemia, MCF10 A mammary epithelial and MDA-MB 231 triple negative breast cancer cell lines. Among the tested conjugates, 5-methyl-3-((3-(1-phenyl)-3-(p-tolyl)-1H-pyrazol-4-yl)methylene)indolin-2-one 6h emerged as the most cytotoxic with a CC50 of 4.36+/-0.2 µM against Jurkat cells. The mechanism of cell death induced by 6h was investigated through the Annexin V-FITC assay via flow cytometry. Reactive oxygen species (ROS) accumulation, mitochondrial health and the cell cycle progression were also evaluated in cells exposed to 6h. Results demonstrated that 6h induces apoptosis in a dose-response manner, without generating ROS and/or altering mitochondrial health. In addition, 6h disrupted the cell cycle distribution causing an increase in DNA fragmentation (Sub G0-G1), and an arrest in the G0-G1 phase. Taken together, the 6h compound revealed a strong potential as an antineoplastic agent evidenced by its cytotoxicity in leukemia cells, the activation of apoptosis and restriction of the cell cycle progression.

A Coumarin-Imidazothiadiazole Derivative, SP11 Abrogates Tumor Growth by Targeting HSP90 and Its Client Proteins.

Despite several treatment options for blood cancer, mortality remains high due to relapse and the disease's aggressive nature. Elevated levels of HSP90, a molecular chaperone essential for protein folding, are associated with poor prognosis in leukemia and lymphoma. HSP90 as a target for chemotherapy has been met with limited success due to toxicity and induction of heat shock. This study tested the activity of an HSP90 inhibitor, SP11, against leukemic cells, mouse lymphoma allograft, and xenograft models. SP11 induced cytotoxicity in vitro in leukemic cell lines and induced cell death via apoptosis, with minimal effect on normal cells. SP11 induced cell death by altering the status of HSP90 client proteins both in vitro and in vivo. SP11 reduced the tumor burden in allograft and xenograft mouse models without apparent toxicity. The half-life of SP11 in the plasma was approximately 2 h. SP11 binding was observed at both the N-terminal and C-terminal domains of HSP90. C-terminal binding was more potent than N-terminal binding of HSP90 in silico and in vitro using isothermal calorimetry. SP11 bioavailability and minimal toxicity in vivo make it a potential candidate to be developed as a novel anticancer agent.

Synthesis, Molecular Docking and Preliminary Antileukemic Activity of 4-Methoxybenzyl Derivatives Bearing Imidazo[2,1-b][1,3,4]thiadiazole.

In this study, we synthesized 22 compounds in a series with various substitution on imidazo[2,1-b][1,3,4]thiadiazole. The potential cytotoxic activity of these compounds investigated in leukemia cell lines by Differential Nuclear Staining (DNS). Our results identified two compounds, 2-(4-methoxybenzyl)-6-(2-oxo-2H-chromen-3-yl)imidazo[2,1-b][1,3,4]thiadiazol-5-yl thiocyanate and 6-(4-chlorophenyl)-2-(4-methoxybenzyl)imidazo[2,1-b][1,3,4]thiadiazole-5-carbaldehyde, exhibited the most cytotoxic effect against murine leukemia cells (L1210), human T-lymphocyte cells (CEM) and human cervix carcinoma cells (HeLa) with IC50 values ranging between 0.79 and 1.6 µM. The results indicate that 2-(4-methoxybenzyl)-6-(2-oxo-2H-chromen-3-yl)imidazo[2,1-b][1,3,4]thiadiazol-5-yl thiocyanate is inducing phosphatidylserine externalization and caspase-3 activation which are both a hallmark of apoptosis. Docking studies showed that 2-(4-methoxybenzyl)-6-(2-oxo-2H-chromen-3-yl)imidazo[2,1-b][1,3,4]thiadiazol-5-yl thiocyanate binds within the active sites of transforming growth factor beta (TGF-ß) type I receptor kinase domain by strong hydrogen binding and hydrophobic interactions.

ST09, A Novel Curcumin Derivative, Blocks Cell Migration by Inhibiting Matrix Metalloproteases in Breast Cancer Cells and Inhibits Tumor Progression in EAC Mouse Tumor Models.

PURPOSE: Curcumin is known for its anticancer and migrastatic activity in various cancers, including breast cancer. Newer curcumin derivatives are being explored to overcome limitations of curcumin like low bioavailability, stability, and side effects due to its higher dose. In this study, the synthesis of ST09, a novel curcumin derivative, and its antiproliferative, cytotoxic, and migrastatic properties have been explored both in vitro and in vivo. METHODS: After ST09 synthesis, anticancer activity was studied by performing standard cytotoxicity assays namely, lactate dehydrogenase (LDH) release assay, 3-(4, 5-dimethylthiazol-2-yl)-2-5-diphenyletrazolium bromide (MTT), and trypan blue exclusion assay. Annexin-FITC, cell cycle analysis using flow cytometry, and Western blotting were performed to elucidate cell death mechanisms. The effect on the inhibition of cell migration was studied by transwell migration assay. An EAC (Ehrlich Ascites carcinoma) induced mouse tumor model was used to study the effect of ST09 on tumor regression. Drug toxicity was measured using aspartate aminotransferase (AST), alanine aminotransferase (ALT), blood urea nitrogen (BUN), and flow-cytometry based lymphocyte count. Histological analysis was performed for assessment of any tissue injury post ST09 treatment. RESULTS: ST09 shows an approximate 100-fold higher potency than curcumin, its parent compound, on breast tumor cell lines MCF-7 and MDA-MB231. ST09 arrests the cell cycle in a cell type-specific manner and induces an intrinsic apoptotic pathway both in vitro and in vivo. ST09 inhibits migration by downregulating matrix metalloprotease 1,2 (MMP1,2) and Vimentin. In vivo, ST09 administration led to decreased tumor volume in a mouse allograft model by boosting immunity with no significant drug toxicity. CONCLUSION: ST09 exhibits antiproliferative and cytotoxic activity at nanomolar concentrations. It induces cell death by activation of the intrinsic pathway of apoptosis both in vitro and in vivo. It also inhibits migration and invasion. This study provides evidence that ST09 can potentially be developed as a novel antitumor drug candidate for highly metastatic and aggressive breast cancer.

Investigation of anti-cancer and migrastatic properties of novel curcumin derivatives on breast and ovarian cancer cell lines.

BACKGROUND: Curcumin is known for its multitude of medicinal properties, including anti-cancer and migrastatic activity. Efforts to overcome poor bioavailability, stability, and side effects associated with the higher dose of curcumin has led to the development of newer derivatives of curcumin. Thus, the focus of this study is to screen novel curcumin derivatives, namely ST03 and ST08, which have not been reported before, for their cytotoxicity and migrastatic property on cancer cells. METHODS: Anti-cancer activity of ST03 and ST08 was carried out using standard cytotoxicity assays viz., LDH, MTT, and Trypan blue on both solid and liquid cancer types. Flow cytometric assays and western blotting was used to investigate the cell death mechanisms. Transwell migration assay was carried out to check for migrastatic properties of the compounds. RESULTS: Both the compounds, ST03 and ST08, showed ~ 100 fold higher potency on liquid and solid tumour cell lines compared to its parent compound curcumin. They induced cytotoxicity by activating the intrinsic pathway of apoptosis in the breast (MDA-MB-231) and ovarian cancer cell lines (PA-1) bearing metastatic and stem cell properties, respectively. Moreover, ST08 also showed inhibition on breast cancer cell migration by inhibiting MMP1 (matrix metalloproteinase 1). CONCLUSION: Both ST03 and ST08 exhibit anti-cancer activity at nanomolar concentration. They induce cell death by activating the intrinsic pathway of apoptosis. Also, they inhibit migration of the cancer cells by inhibiting MMP1 in breast cancer cells.

Identification and characterization of novel ligase I inhibitors.

The terminal step of ligation of single and/or double-strand breaks during physiological processes such as DNA replication, repair and recombination requires participation of DNA ligases in all mammals. DNA Ligase I has been well characterised to play vital roles during these processes. Considering the indispensable role of DNA Ligase I, a therapeutic strategy to impede proliferation of cancer cells is by using specific small molecule inhibitors against it. In the present study, we have designed and chemically synthesised putative DNA Ligase I inhibitors. Based on various biochemical and biophysical screening approaches, we identify two prospective DNA Ligase I inhibitors, SCR17 and SCR21. Both the inhibitors blocked ligation of nicks on DNA in a concentration-dependent manner, when catalysed by cell-free extracts or purified Ligase I. Docking studies in conjunction with biolayer interferometry and gel shift assays revealed that both SCR17 and SCR21 can bind to Ligase I, particularly to the DNA Binding Domain of Ligase I with KD values in nanomolar range. The inhibitors did not show significant affinity towards DNA Ligase III and DNA Ligase IV. Further, addition of Ligase I could restore the joining, when the inhibitors were treated with testicular cell-free extracts. Ex vivo studies using multiple assays showed that even though cell death was limited in the presence of inhibitors in cancer cells, their proliferation was compromised. Hence, we identify two promising DNA Ligase I inhibitors, which can be used in biochemical and cellular assays, and could be further modified and optimised to target cancer cells. © 2016 Wiley Periodicals, Inc.

3,5-Bis(3-dimethylaminomethyl-4-hydroxybenzylidene)-4-piperidone and related compounds induce glutathione oxidation and mitochondria-mediated cell death in HCT-116 colon cancer cells.

This study aims at investigating the cytotoxicity and some of the modes of action of 3,5-bis(3-dimethylamino-4-hydroxybenzylidene)-4-piperidone trihydrochloride 3 and two related compounds 2 (which lacks the dimethylaminomethyl groups) and 4 (which has an additional dimethylaminoethyl substituent in both aryl rings) in order to ascertain the contribution of dimethylaminoethyl substituent to bioactivity. The bioactivities of 2-4 were compared with curcumin 5. Both 2 and 3 displayed submicromolar GI50 values towards HCT-116 cells and were significantly more potent than 4, 5 and 5-fluorouracil (5-FU). All of the compounds displayed greater toxicity towards HCT-116 cells than human CRL-1790 non-malignant colon cells. In HCT-116 cells, the compounds 2, 3 and 5 increased the ratio of oxidised to reduced glutathione and destabilized the mitochondrial membrane potential. Both 2 and 5 produced an increase in mitochondrial superoxide and a burst in intracellular reactive oxygen species in HCT 116 cells. In addition, 2 and 4 stimulated respiration in rat liver mitochondria while 2 and 5 induced mitochondrial swelling. The results suggest that 2 and 5 cause oxidation or cross-linking of the thiols which control the mitochondrial permeability transition.

SYNTHESIS AND CYTOTOXIC EVALUATION OF SOME 2-{4-[(2-OXO-1,2-DIHYDRO-3H-INDOL-3-YLIDENE)METHYL] PHENOXY}-N-PHENYLACETAMIDE.

A series of 2-oxindole derivatives were synthesized and evaluated for cytotoxic activity against different human and murine cancer cell lines and cancer chemopreventive activity. Among the tested compounds VS-06, 08, 12 and 17 displayed cytotoxic activity in the range of 5.0 to 8.5 pM against human T-lymphocyte cells (CEM). Results showed that molecules with electron withdrawing substituent at 4 position of N-phenylacetamide group exhibited an increase in activity against the human tumor cell line CEM. The cancer chemo- preventive effect of VS-01 (IC50 = 451 nM) displayed equipotent activity in comparison to standard oleanolic acid (IC50 = 449 nM).

SYNTHESIS OF IMIDAZO[2,1-b][1,3,4]THIADIAZOLE DERIVATIVES AS POSSIBLE BIOLOGICALLY ACTIVE AGENTS.

A series of 2-(4-methylbenzyl)-5,6-substituted-imidazo[2,1-b][1,3,4]thiadiazole derivatives were synthesized, characterized and evaluated for antiproliferative activity and cancer chemopreventive activity. Results showed that molecules with formyl and thiocyanate substiments at the 5 position exhibited an increase in activity against the full panel of 60 human tumor cell lines at a minimum of five concentrations at 10-fold dilutions. Derivative 22 displayed significant in vino anticancer activity against colon cancer (MID GI50 = 0.75 µM). The cancer chemopreventive effect of 19 (IC50 = 489 nM) was almost equipotent to standard oleanolic acid (IC50 = 449 nM).

SYNTHESIS AND PHARMACOLOGICAL ACTIVITY OF IMIDAZO[2,1- b][1,3,4]THIADIAZOLE DERIVATIVES.

In this paper, a series of imidazo[2,l-b][1,3,4]thiadiazoles have been prepared by reacting 2-amino-1,3,4-thiadiazole with various phenacyl bromides in alcohol. The structures of all the derivatives were con- firmed by IR, NMR and mass spectroscopy. All the derivatives have been tested for cytostatic activity against human T-lymphocyte cells (CEM), human cervix carcinoma cells (HeLa), murine leukemia cell line (L1210), and antiviral activity. Among the tested compounds, derivatives 5b, 5c, and 7a were cytostatic between 49-63 mM against Hela and 7g was cytotoxic at 23 mM against L1210 and CEM cell lines. Compounds 5h and 7h emerged as antiviral agents with slight activity against influenza A and B.

SYNTHESIS AND ANTIINFLAMMATORY ACTIVITY OF SOME IMIDAZO[2,1-b][1,3,4]THIADIAZOLE DERIVATIVES.

A number of imidazo[2,1-b][1,3,4]thiadiazole derivatives having alkyl and aryl moieties attached to positions 2 and 6 of imidazo[2,1-b][1,3,4]thiadiazole nucleus, respectively, were prepared and characterized by IR, NMR and mass spectroscopy. Antiinflammatory activity was evaluated by carrageenan-induced rat paw edema assay. By 5th hours, all compounds demonstrated anti-inflammatory activity similar or higher than that of standard NSAID, ibuprofen.

Synthesis and antiproliferative activity of imidazo[2,1-b][1,3,4]thiadiazole derivatives.

A series of 2,5,6-substituted imidazo[2,1-b][1,3,4]thiadiazole derivatives have been prepared and were tested for antiproliferative activity on cancer cells at the National Cancer Institute. Results showed that molecules with a benzyl group at position 2, exhibited an increase in activity for the introduction of a formyl group at the 5 position. The compound 2-benzyl-5-formyl-6-(4-bromophenyl)imidazo[2,1-b][1,3,4]thiadiazole 22 has been chosen for understanding the mechanism of action by various molecular and cellular biology studies. Results obtained from cell cycle evaluation analysis, analysis of mitochondrial membrane potential and Annexin V-FITC by flow cytometric analysis, ROS production and expression of apoptotic and DNA-repair proteins suggested that compound 22 induced cytotoxicity by activating extrinsic pathway of apoptosis, however, without affecting cell cycle progression.

Synthesis of thiocarbohydrazide and carbohydrazide derivatives as possible biologically active agents.

ABSTRACT: A series of new ß-isatin aldehyde-N,N'-thiocarbohydrazone, bis-ß-isatin thiocarbohydrazones, bis-ß-isatin carbohydrazones was synthesized by condensation of 5-substituted isatin with thiocarbohydrazide or carbohydrazide. The chemical structures of the newly synthesized compounds were confirmed by FT-IR, 1H NMR, and mass spectral analysis. The synthesized compounds were evaluated for in vitro antiviral activity against various strains of DNA and RNA viruses, but exhibited moderate antiviral activity compared with the reference compounds. Among all the compounds 6c exhibited the highest chemoprevention activity in a two-stage mouse-skin carcinogenesis test.

Synthesis and biological evaluation of 2-(5-substituted-1-((diethylamino)methyl)-2-oxoindolin-3-ylidene)-N-substituted-hydrazinecarbothioamides.

ABSTRACT: Various 5-substituted-2-(1-((diethylamino)methyl)-2-oxoindolin-3-ylidene)hydrazinecarbothioamide (4a, b) and 5-substituted-2-(1-((diethylamino)methyl)-2-oxoindolin-3-ylidene)-N-(phenyl-4-substituted)hydrazinecarbothioamide (5a-h) derivatives were synthesized. The compounds were screened for cytotoxicity against human HeLa and CEM T-lymphocytes as well as murine L1210 cells. The compounds were also screened for ß-lactamase inhibitory activity, antiviral, antibacterial, and antifungal activity against various strains of microorganisms. Several of these compounds were endowed with low micromolar 50 %-cytostatic concentration (IC50) values, and some were virtually equally potent as melphalan. The most potent inhibitors against the murine leukemia cells (L1210) were also the most inhibitory against human T-lymphocyte (CEM) tumor cells. Derivative 2-(1-((diethylamino)methyl)-2-oxoindolin-3-ylidene)-N-(4-methoxyphenyl)hydrazinecarbothioamide 5c emerged as the most potent cytostatic compound among the tested compounds. Derivatives 4b, 5a, 5b, and 5d showed antiviral activity against HEL cell cultures (IC50 11-20 µM). Moderate antimicrobial activity was observed for all derivatives. The encouraging cytostatic and antiviral activity data provide an adequate rationale for further modification of these molecular scaffolds. GRAPHICAL ABSTRACT: Derivative 5c (1.9-4.4 µM) emerged as the most potent cytostatic compound among the tested compounds. Derivatives 4b, 5a, 5b, and 5d showed antiviral activity against HEL cell cultures (IC50 11-20 µM).

Synthesis, Cytotoxicity Evaluation and Molecular Docking of Fluorine Containing Hexahydroquinoline-3-Carbonitrile Derivatives.

BACKGROUND: Fluorine containing hexahydroquinoline-3-carbonitrile derivatives were found to have potent cytotoxicity. Furthermore, fluorine can modulate pharmacokinetic and pharmacodynamic profile of drugs. Hence, new derivatives containing fluorine were explored as potential cytotoxic agents. OBJECTIVE: Difluoro substituted compounds containing aromatic/heteroaromatic rings were designed, synthesized and screened for in vitro cytotoxicity on cancer cell lines. The active compounds were subjected to docking on Mcl-1 and ADME/T prediction. METHODS: The synthesized compounds were characterized using various spectral techniques like FT-IR, 1H NMR, 13C NMR and Mass spectra. Compounds were screened for cytotoxicity on NCI-60 cell lines at the National Cancer Institute. The active compounds were evaluated additionally by MTT and SRB assay. RESULTS: Compounds (6l and 6o) showed maximum cytotoxicity with (% GI) of 69 and 63.7 at 10 µM drug concentration, respectively. Compound 6i showed potent cytotoxicity with GI50 of 7.2 µM against Ishikawa cell line. Compound 6o was nearly as active as a reference with IC50 of 9.39 µM and 13.54 µM against HT-29 and HCT-116, respectively, and compound 6l also showed equal potency to that of reference with IC50 of 9.66 µM against Caco-2. Compounds 6i, 6o and 6l showed high docking scores, suggesting their cytotoxicity. Furthermore, ADME/T prediction revealed that all the compounds had drug-likeness properties. CONCLUSION: Enhanced lipophilic interaction of compounds due to the presence of fluorine in compounds 6i and 6l was revealed during the docking study. Compound 6i can be explored as a lead molecule against other endometrial cancer in futuristic drug development.

Synthesis, Anticancer Evaluation and Molecular Docking of Hexahydroquinoline Derivatives as Mcl-1 Inhibitors and Apoptosis Inducers.

BACKGROUND: Hexahydroquinoline as a small molecule was reported for good cytotoxicity and affinity towards Mcl-1. Hence, new compounds were explored as Mcl-1 inhibitors to be potent anticancer agents. OBJECTIVE: Compounds were synthesized and screened for cytotoxicity. The active compound was evaluated for cell cycle analysis, Mcl-1 inhibition, caspase-3, and caspase-9 activation. Further compounds were docked with Mcl-1 to confirm the mechanism of cytotoxicity. METHODS: Compounds were confirmed by spectral techniques and screened for cytotoxicity at National Cancer Institute (USA). The active derivatives were screened by SRB and MTT. In addition, the potent compound was studied for apoptosis and cell cycle analysis by PI staining, Mcl-1 inhibition by TR-FRET assay, and activation assay of caspase-3 and caspase-9 with the Elisa technique. RESULTS: Compounds 6a and 6b exhibited the highest growth inhibition of 86.28% and 93.20% against SR and HOP- 62, respectively. Compound 6a showed higher cytotoxicity (IC50 = 0.4 µM) against THP-1 and HL-60. It showed 15- fold higher apoptosis compared to control by arresting cells at the Sub-G1 in the cell cycle. It also showed a potent inhibition with IC50 of 1.5 µM against the anti-apoptotic protein Mcl-1, which may induce apoptosis. Furthermore, apoptosis was evidenced by an increase in cleaved caspase-3 and caspase-9 to 4.20 and 3 folds, respectively higher than control. The docking score of compound 6a was in good agreement with the Mcl-1 inhibition assay. CONCLUSION: Compound 6a inhibited anti-apoptotic protein Mcl-1 and induced activation of pro-apoptotic proteins caspase-3 and caspase-9. These dual results suggested the mechanism of apoptosis and cytotoxicity.

Curcumin derivative 1, 2-bis [(3E, 5E)-3, 5-bis [(2-chlorophenyl) methylene]-4-oxo-1-piperidyl] ethane-1, 2-dione (ST03) induces mitochondria mediated apoptosis in ovarian cancer cells and inhibits tumor progression in EAC mouse model.

Curcumin is known for its anticancer properties, but its clinical application is limited due to its poor bioavailability and chemical stability. In this study we report the curcumin derivative, ST03 (1,2-bis[(3E,5E)-3,5-bis[(2-chlorophenyl)methylene]-4-oxo-1-piperidyl]ethane-1,2-dione) exhibits ∼ 14 fold better bioavailability compared to curcumin and is detectable in plasma up to 12 h. ST03 induces ROS, activates the intrinsic apoptotic pathway as evident by disruption of mitochondrial membrane potential, and induction of proapoptotic proteins in ovarian cancer lines PA1 and A2780. ST03 also blocked the migration of ovarian cancer cells. ST03 exerted its antitumor effect in-vivo in the EAC mouse model by activating the intrinsic apoptotic pathway. Our findings demonstrate ST03, a curcumin derivative, with better bioavailability and stability with no discernable toxicity in vivo to be a promising drug candidate for anticancer therapies.

Synthesis, in vitro cytotoxicity, molecular docking and ADME study of some indolin-2-one linked 1,2,3-triazole derivatives.

In pursuit of an anticancer lead, a library of 1,2,3-triazole derivatives (7a-x) was prepared, characterized and screened for in vitro cytotoxicity in different cell lines. Most of the compounds proved to be cytotoxic with IC50 values in the low micromolar range. Further studies showed that the most active compound 7c induces caspase-dependent apoptosis in Jurkat cells by activating both the intrinsic and the extrinsic apoptotic pathways and perturbs cell-cycle progression. Moreover, 7c did not show any genotoxic activity. Molecular docking simulations were performed against epidermal growth factor receptor (EGFR). Docking experiments showed that, compounds 7c, 7o and 7 v bind within active sites of epidermal growth factor receptor EGFR (Pdb ID: 6P8Q) by strong hydrogen bonds with residue MET793, Pi-Sulfur with residue MET790 and Pi-Alkyl type interactions with residues LEU788, ALA743. The SwissADME webserver investigation suggested that most of the synthesized compounds follow the rules of drug-likeness.

Three novel piperidones exhibit tumor-selective cytotoxicity on leukemia cells via protein degradation and stress-mediated mechanisms.

BACKGROUND: Cancer is an ongoing worldwide health problem. Although chemotherapy remains the mainstay therapy for cancer, it is not always effective and has detrimental side effects. Here, we present piperidone compounds P3, P4, and P5 that selectively target cancer cells via protein- and stress-mediated mechanisms. METHODS: We assessed typical apoptotic markers including phosphatidylserine externalization, caspase-3 activation, and DNA fragmentation through flow cytometry. Then, specific markers of the intrinsic pathway of apoptosis including the depolarization of the mitochondria and the generation of reactive oxygen species (ROS) were investigated. Finally, we utilized western blot techniques, RT-qPCR, and observed the cell cycle profile after compound treatment to evaluate the possible behavior of these compounds as proteasome inhibitors. For statistical analyses, we employed the one-way ANOVA followed by Bonferroni post hoc test. RESULTS: P3, P4, and P5 induce cytotoxic effects towards tumorigenic cells, as opposed to non-cancerous cells, at the low micromolar range. Compound treatment leads to the activation of the intrinsic pathway of apoptosis. The accumulation of poly-ubiquitinated proteins and the pro-apoptotic protein Noxa, both typically observed after proteasome inhibition, occurs after P3, P4, and P5 treatment. The stress-related genes PMAIP1, ATF3, CHAC1, MYC, and HMOX-1 were differentially regulated to contribute to the cytotoxic activity of P3-P5. Finally, compound P5 causes cell cycle arrest at the G2/M phase. CONCLUSION: Taken together, compounds P3, P4, and P5 exhibit strong potential as anticancer drug candidates as shown by strong cytotoxic potential, activation of the intrinsic pathway of apoptosis, and show typical proteasome inhibitor characteristics.