Reversal of boswellic acid analog BA145 induced caspase dependent apoptosis by PI3K inhibitor LY294002 and MEK inhibitor PD98059.

PI3K/Akt and ERK pathways are important for growth and proliferation of many types of cancers. Therefore, PI3K inhibitor LY294002 (LY) and MEK1/2 inhibitor PD98059 (PD) are used to sensitize many types of cancer cell lines to chemotherapeutic agents, where AKT and ERK pathways are over activated. However, in this study, we show for the first time that PD could protect the leukemia cells independent of ERK pathway inhibition, besides, we also report a detailed mechanism for antiapoptotic effect of LY in HL-60 cells against the cytotoxicity induced by a boswellic acid analog BA145. Apoptosis induced by BA145 is accompanied by downregulation of PI3K/Akt and ERK pathways in human myelogenous leukemia HL-60 cells, having activating N-Ras mutation. Both LY and PD protected the cells against mitochondrial stress caused by BA145, and reduced the release of cytochrome c and consequent activation of caspase-9. LY and PD also diminished the activation of caspase-8 without affecting the death receptors. Besides, LY and PD also reversed the caspase dependent DNA damage induced by BA145. Further studies revealed that LY and PD significantly reversed the inhibitory effect of BA145 on cell cycle regulatory proteins by upregulating hyperphosphorylated retinoblastoma, pRB (S795) and downregulating p21 and cyclin E. More importantly, all these events were reversed by caspase inhibition by Z-VAD-fmk, suggesting that both LY and PD act at the level of caspases to diminish the apoptosis induced by BA145. These results indicate that inhibitors of PI3K/Akt and ERK pathways can play dual role and act against chemotherapeutic agents.

Tubulin inhibitors from an endophytic fungus isolated from Cedrus deodara.

From an endophytic fungus, a close relative of Talaromyces sp., found in association with Cedrus deodara, four compounds including two new ones (2 and 4) were isolated and characterized. The structures of two compounds (1 and 4) were confirmed by X-ray crystallography. The compounds displayed a range of cytotoxicities against human cancer cell lines (HCT-116, A-549, HEP-1, THP-1, and PC-3). All the compounds were found to induce apoptosis in HL-60 cells, as evidenced by fluorescence and scanning electron microscopy studies. Also, the compounds caused significant microtubule inhibition in HL-60 cells.

NF-κB down-regulation and PARP cleavage by novel 3-α-butyryloxy-ß-boswellic acid results in cancer cell specific apoptosis and in vivo tumor regression.

The present study relates to the induction of apoptosis thereof cytotoxicity and anti-cancer activity displayed by semi-synthetic analog of Boswellic acid i.e. 3-α-Butyryloxy-ß-boswellic acid (BOBA). The cytotoxicity data revealed the differential sensitivity of cancer cell lines towards BOBA which may display its impact against different types of cancers. Considering the inhibitory potential of BOBA, we further sought to understand the target for BOBA deciphering the mechanism of action leading to apoptotic cell death and it was for the first time reported about the triterpenoid ring especially the ß-boswellic acid derivative is targeting PI3K pathway. Our data revealed that BOBA treatment provides evidence about the apoptotic nature showing the potential of targeting mitochondria dependent pathways during apoptosis in HL-60 cells. BOBA induced hypo-diploid sub-G(1) DNA population in HL-60 cells as was also evident from the pattern of DNA fragmentation and mitochondrial membrane potential (ΛΨm) loss. Morphological analysis under fluorescent and scanning electron microscopy displayed typical features such as cell shrinkage, membrane blebbing, chromatin condensation and nuclear fragmentation. These events paralleled with the down-regulation of NF-κB and induced PARP cleavage. Furthermore, it is noteworthy that BOBA also depicted significant growth inhibition in Ehrlich Ascitic Tumour (EAT), Ehrlich Ascitic Carcinoma (EAC) and Sarcoma- 180 tumour models. Taken together, BOBA treatment may represent as potential agent to the currently available anticancer agents in both prophylactic and/or therapeutic applications. Also, our findings may open up a new perspective in the construction of novel anticancer agents based on boswellic acids that will facilitate the development of these agents for anticancer therapeutics.

PARP cleavage and perturbance in mitochondrial membrane potential by 3-α-propionyloxy-ß-boswellic acid results in cancer cell death and tumor regression in murine models.

BACKGROUND: Apoptotic induction in cancer cells has become a major focus of anticancer therapeutics. In this regard, ß-boswellic acids, naturally occurring pentacyclic triterpenes, have demonstrated antiproliferative and cytotoxic effects against different types of cancers. Surprisingly, not much has been reported regarding the chemical modifications or preparation of structural analogs of the key constituents of ß-boswellic acid. AIM: The anticancer activity of 3-α-propionyloxy-ß-boswellic acid (POBA) was investigated and this article reports for the first time that the triterpenoid ring of the boswellic acid derivative POBA is targeting the PI3K pathway. MATERIALS & METHODS: Induction of apoptosis of the semi-synthetic derivative of ß-boswellic acid-POBA in vitro was analyzed using a battery of human cancer cell lines followed by cell cycle phase distribution, further validated by DNA fragmentation, and was found to cause mitochondrial membrane potential loss with ultrastructural changes, as observed by electron microscopy studies and expression study using PARP cleavage, as well as validated by in vivo anti-tumor activity. RESULTS: The cytotoxicity data revealed the sensitivity of various human cancer cell lines of varied tissue origin to ß-boswellic acid, which robustly induced cell cycle arrest, DNA fragmentation and loss of mitochondrial membrane potential. Morphological studies of the effects of POBA revealed loss of surface projections, chromatin condensation, apoptotic body formation and POBA-mediated PARP cleavage. For in vivo therapeutic experiments, murine tumor models were treated with POBA and the treatment resulted in a significantly higher level of growth inhibition and apoptosis was significantly induced. CONCLUSION: These findings demonstrate that acyl substituents/groups in the main skeleton of ß-boswellic acid have the potential to be potent chemotherapeutic agents.

Potentiation of the antitumor effect of 11-keto-ß-boswellic acid by its 3-α-hexanoyloxy derivative.

We recently discovered that a propionyloxy derivative of 11-keto-ß-boswellic acid (PKBA) showed better anticancer potential than other boswellic acids including AKBA, encompassing the importance of acyl group at the 3-α-hydroxy position of KBA. In continuation of our previous work, other higher derivatives (with increasing alkoxy chain length at 3-α-hydroxy position) including butyryloxy (BKBA) and hexanoyloxy (HKBA) derivatives of KBA were synthesized. The respective IC(50) values of BKBA and HKBA in HL-60 cells were found to be 7.7 and 4.5 µg/ml. IC(50) value of HKBA was comparatively lower than that of BKBA, and further lower than that of the previously reported derivative (PKBA, IC(50) 8.7 µg/ml). In order to compare the anticancer potential of HKBA with PKBA, detailed in vitro pro-apoptotic and in vivo anticancer studies were carried out. The induction of apoptosis by HKBA was measured using various parameters including fluorescence and scanning electron microscopy, DNA fragmentation and Annexin V-FITC binding. The extent of DNA damage was measured using neutral comet assay. HKBA was further evaluated for its effect on DNA cell cycle and mitochondria where it was found to arrest cells in G(2)/M phase and also induced loss of mitochondrial membrane potential. These events were associated with increased expression of cytosolic cytochrome c and cleavage of PARP. Target based studies showed that HKBA inhibited the enzymatic activity of topoisomerases I and II at low doses than that of PKBA. In vivo studies also revealed a low dose inhibitory effect of HKBA on ascitic and solid murine tumor models.

A propionyloxy derivative of 11-keto-ß-boswellic acid induces apoptosis in HL-60 cells mediated through topoisomerase I & II inhibition.

Boswellic acids have invariably been reported for their antiproliferative potential in various cell systems. In the present study the growth inhibitory effect of propionyloxy derivative of 11-keto-ß-boswellic acid (PKBA; a semisynthetic analogue of 11-keto-ß-boswellic acid) on HL-60 promyelocytic leukemia cells is being reported for the first time. In the preliminary studies, in vitro cytotoxicity of PKBA was investigated against eight human cancer cell lines viz., IMR-32, SF-295 (both neuroblastoma), PC-3 (prostate), Colo-205 (colon), MCF-7 (breast), OVCAR-5 (ovary), HL-60, Molt-4 (both leukemia) and their respective IC(50) values were found to be 5.95, 7.11, 15.2, 14.5, 15, 15.9, 8.7 & 9.5µg/ml, respectively. For determining the mechanism of cell death in HL-60 cells, PKBA was subjected to different mechanistic studies. DNA relaxation assay of PKBA revealed inhibition of both topoisomerases I & II. The fragmentation analysis of DNA revealed typical ladders indicating the cytotoxic effect to be mediated by induction of apoptosis. The morphologic studies of PKBA showed the presence of true apoptotic bodies. Apoptosis was confirmed further by flow-cytometric detection of sub-G(1) peaks and enhanced annexin-V-FITC binding of the cells. The activation of apoptotic cascade by PKBA in HL-60 cells was found to be associated with the loss of mitochondrial membrane potential, release of cytochrome c, activation of initiator and executioner caspases and cleavage of poly ADP ribose polymerase (PARP). In vivo studies of PKBA revealed anti-tumoral activity against both ascitic and solid murine tumor models. These studies thus demonstrate PKBA to induce apoptosis in HL-60 cells due to the inhibition of topoisomerases I and II.