M. Kashi Reddy

Synthesis and biological evaluation of 3,5-diaryl isoxazoline/isoxazole linked 2,3-dihydroquinazolinone hybrids as anticancer agents

A series of new 3,5-diaryl isoxazoline/isoxazole linked 2,3-dihydro quinazolinone hybrids with different linker architectures have been designed and synthesized. These compounds have been evaluated for their anticancer activity. One of the compounds 4c amongst this series has shown promising anticancer activity. Further some detailed biological assays relating to the cell cycle aspects and tubulin depolymerization activity have been examined with a view to understand the mechanism of action of this conjugate.

Remarkable enhancement in the DNA-binding ability of C2-fluoro substituted pyrrolo(2,1-c)(1,4)benzodiazepines and their anticancer potential

C2-Fluoro substituted DC-81, and its dimers that comprise of two C2-fluoro substituted DC-81 subunits tethered to their C8-position through simple alkane spacers as well as piperazine moiety side-armed with symmetrical alkyloxy spacers have been designed and synthesized. These fluoro substituted pyrrolo[2,1-c][1,4]benzodiazepines have shown remarkable DNA-binding ability and most of them possess promising anticancer activity, having GI(50) values in micromolar to nanomolar concentration range. DNA thermal denaturation studies show that some of these compounds (14a-c and 15) increase the DeltaT(m) values in the range of 28.9-38 degrees C, and this is further confirmed by the restriction endonuclease studies. This study illustrates the importance of introducing fluoro substitution at the C2-position apart from the incorporation of a piperazine ring in between the alkyloxy linker for enhancement of the DNA-binding ability in comparison to DSB-120 and SJG-136 (DeltaT(m)=10.2 and 25.7 degrees C). Moreover, the variations in the DNA-binding ability with respect to fluoro substitution in this class of dimers has been investigated by molecular modeling studies. Some representative C2-fluoro substituted dimers (8a and 14a) have also exhibited significant anticancer activity in the 60 cancer cell line assay of the National Cancer Institute (NCI).

2-Anilinonicotinyl linked 1,3,4-oxadiazole derivatives: Synthesis, antitumour activity and inhibition of tubulin polymerization

A series of 2-anilinonicotinyl linked 1,3,4-oxadiazoles was synthesized and evaluated for their antitumour activity against various cancer cell lines, inhibition of tubulin polymerization and cell cycle effects. Some of these compounds showed good antiproliferative activity with GI50 values ranging from 4.57 to 97.09 μM in the human cancer cell lines and one of the compounds 5m showed potent antitumour efficacy in all the cell lines tested. This compound also inhibited tubulin polymerization under both in vitro and in vivo conditions. Analysis of tubulin by Western blot experiments demonstrated that 5m depolymerizes microtubules by causing disturbances in the ratio of soluble versus polymerized tubulin in cells, leading to the cell cycle arrest at G2/M phase of the cell cycle followed by activation of caspase-3 activity and apoptotic cell death.

Synthesis and apoptosis inducing ability of new anilino substituted pyrimidine sulfonamides as potential anticancer agents

A series of anilino substituted pyrimidine sulfonamides were prepared and evaluated for their anticancer activity. These sulfonamides showed promising activity with IC(50) values ranging from 5.6 to 12.3 μM. The detailed biological aspects of some of the promising compounds (3d, 3e and 3g) on the K562 cell line were studied. Interestingly, compounds induced G1 cell cycle arrest and down regulation of G1 phase cell cycle regulatory proteins such as cyclin D1, CDK4. These compounds also exhibited inhibition of NF-κB as well as its downstream target gene Akt1 and the phosphorylated form of AKt ser 474 proteins. One of the representative compound 3e could be considered as the potential lead for its development as a new anticancer agent.

Synthesis, anticancer activity and apoptosis inducing ability of bisindole linked pyrrolo[2,1-c][1,4]benzodiazepine conjugates.

A series of bisindole-pyrrolobenzodiazepine conjugates (5a-f) linked through different alkane spacers was prepared and evaluated for their anticancer activity. All compounds exhibited significant anticancer potency and the most potent compounds 5b and 5e were taken up for detailed studies on MCF-7 cell line. Cell cycle effects were examined apart from investigating the inhibition of tubulin polymerization for compounds 2a, 2b, 5b and 5e at 2μM. FACS analysis showed that at higher concentrations (4 and 8μM) there was an increase of sub-G1 phase cells and decrease of G2/M phase cells, thus indicating that compounds 5b and 5e are effective in causing apoptosis in MCF-7 cells. It was also observed that compounds 5b and 5e showed the down regulation of histone deacetylase protein levels such as HDAC1, 2, 3, 8 and increase in the levels of p21, followed by apoptotic cell death. The apoptotic nature of these compounds was further evidenced by increased expression of cleaved-PARP and active caspase-7 in MCF-7 cells.

2-Anilinonicotinyl linked 2-aminobenzothiazoles and [1,2,4]triazolo[1,5-b] [1,2,4]benzothiadiazine conjugates as potential mitochondrial apoptotic inducers

A series of N-(2-anilino-pyridyl) linked 2-amino benzothiazoles (4a-n) and [1,2,4]triazolo [1,5-b]benzothiadiazine conjugates (5a-j) have been designed, synthesized and evaluated for their antiproliferative activity. Some of these compounds (4h-k, 4n, and 5e) have exhibited potent cytotoxicity specifically against human leukemia HL-60 cell lines with IC(50) values in the range of 0.08-0.70 μM. All these compounds were tested for their effects on the cell cycle perturbations and induction of apoptosis. Morphological evidences of apoptosis, including fragmentation of nuclei and inter nucleosomal DNA laddering formation were clearly observed after 24h exposure to compound 4i. Flow cytometry analysis revealed that compound 4i showed drastic cell cycle perturbations due to concentration dependant increase in the sub-G0 region which comprises of both the apoptotic and debris fraction, thus implying the extent of cell death. These compounds trigger the mitochondrial apoptotic pathway that results in the loss of mitochondrial membrane potential through activation of multiple caspases followed by activation of caspase-3, and finally cleavage of PARP. Further the mechanism of cell death was analysed by fluorescent microscopic analysis and also by scanning electron microscopy. The cytotoxicity of 4i correlated with induction of apoptosis, caspases activation and DNA damage and thus indicating the apoptotic pathway of anticancer effect of these compounds.

Design, synthesis and biological evaluation of imidazopyridine/imidazopyrimidine-benzimidazole conjugates as potential anticancer agents

A series of imidazopyridine/imidazopyrimidine-benzimidazole conjugates (11a–t) were synthesized and evaluated for their antiproliferative activity. All of these conjugates showed moderate to improved cytotoxic activity against the human cervical (Hela), lung (A549), prostate (DU-145) and melanoma (B-16) cancer cell lines. Among them, conjugates 11i and 11p showed significant antiproliferative activity against lung cancer cell line A549 with IC50 values 1.48 and 1.92 μM, respectively. Flow cytometric analysis revealed that these conjugates induced cell cycle arrest at G2/M phase in the A549 cell line leading to caspase-3-dependent apoptotic cell death. The tubulin polymerization assay (IC50 of 11i is 2.06 μM and 11p is 2.26 μM) and immuofluorescence analysis displayed that these conjugates effectively inhibit microtubule assembly at both the molecular and cellular levels in A549 cells. Further, Hoechst staining, caspase-3 activation assay, DNA fragmentation analysis and Annexin V-FITC assay also suggested that these compounds induced cell death by apoptosis. Furthermore, molecular docking studies indicated that these conjugates efficiently interact and bind with tubulin protein. Overall, the present study demonstrates that the synthesis of imidazopyridine/imidazopyrimidine-benzimidazole conjugates as promising tubulin inhibitors with G2/M phasecell cycle arrest and apoptotic-inducing ability.

Synthesis of Aryl‐Substituted Naphthalene‐Linked Pyrrolobenzodiazepine Conjugates as Potential Anticancer Agents with Apoptosis‐Inducing Ability

A library of new aryl‐substituted naphthalene C8‐linked pyrrolo[2,1‐c][1,4]benzodiazepine (PBD) conjugates with various linker architectures were designed, synthesized, and evaluated for their anticancer activity against a panel of 11 human cancer cell lines. All 32 conjugates show anticancer potential, with some of them exhibiting particularly high activity (0.01–0.19 μM). Thermal denaturation studies showed effective DNA binding capacity relative to DC‐81. In assays for biological activity relating to cell‐cycle distribution, these PBD conjugates induce G0/G1‐phase arrest and also cause an increase in the levels of p53 and caspase‐9 proteins, followed by apoptotic cell death. One conjugate in particular is the most promising candidate of the series, with the potential to be selected for further studies, either alone or in combination with existing anticancer therapies.

Synthesis and biological evaluation of anilino substituted pyrimidine linked pyrrolobenzodiazepines as potential anticancer agents.

A series of new anilino substituted pyrimidine linked pyrrolo[2,1-c][1,4]benzodiazepine (PBD) conjugates were prepared and evaluated for their anticancer activity. The effects of four promising PBD conjugates on cell cycle of cancerous cell line A375 were investigated. These compounds showed the characteristic features of apoptosis like enhancement in the levels of p53, release of cytochrome c, and cleavage of PARP.

Design and Synthesis of Aminostilbene–Arylpropenones as Tubulin Polymerization Inhibitors

A series of aminostilbene—arylpropenones were designed and synthesized by Michael addition and were investigated for their cytotoxic activity against various human cancer cell lines. Some of the investigated compounds exhibited significant antiproliferative activity against a panel of 60 human cancer cell lines of the US National Cancer Institute, with 50 % growth inhibition (GI50) values in the range from <0.01 to 19.9 μM. One of the compounds showed a broad spectrum of antiproliferative efficacy on most of the cell lines, with a GI50 value of <0.01 μM. All of the synthesized compounds displayed cytotoxicity against A549 (non‐small‐cell lung cancer), HeLa (cervical carcinoma), MCF‐7 (breast cancer), and HCT116 (colon carcinoma) with 50 % inhibitory concentration (IC50) values ranging from 0.011 to 8.56 μM. A cell cycle assay revealed that these compounds arrested the G2/M phase of the cell cycle. Two compounds exhibited strong inhibitory effects on tubulin assembly with IC50 values of 0.71 and 0.79 μM. Moreover, dot‐blot analysis of cyclin B1 demonstrated that some of the congeners strongly induced cyclin B1 protein levels. Molecular docking studies indicated that these compounds occupy the colchicine binding site of tubulin.