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Abstract: Inula racemosa Hook.f. commonly known as Pushkarmula (Compositae) has been used as a traditional drug in India, China and Europe. In the present study, 95% ethanolic extract of roots and its fractions (n-hexane, chloroform, n-butanol and aqueous) were evaluated for in vitro cytotoxicity against cancer cell lines of colon, ovary, prostate, lung, CNS and leukemia. The n-hexane fraction containing alantolactone and isoalantolactone as its major constituents was further studied for its mode of action in HL-60 cells. The lowest IC50 value of n-hexane fraction was 10.25μg/ml for Colo-205, a colon cancer cell line whereas, 17.86μg/ml was the highest IC50 value observed against CNS cancer cell line SF-295. Further studies on HL-60 cells treated with n-hexane fraction at 10, 25 and 50μg/ml for 6h, revealed that it induces apoptosis through intrinsic as well as extrinsic pathways by generating reactive oxygen species (ROS) intermediates. Mitochondrial dysfunction prompted the release of cytochrome c, translocation of pro-apoptotic protein (Bax), activation of caspase cascade, resulting in the cleavage of some specific substrates for caspase-3 such as poly (ADP-ribose) polymerase (PARP), which eventually leads to apoptosis. The results of present study strongly support further research and development of bioactive constituents from Inula racemosa as potential anticancer agent with possible therapeutic implication. [ABSTRACT FROM AUTHOR]

Leukemia is one of the deadliest types of cancer. Lack of effective treatment strategies has resulted in an extensive quest for new therapeutic molecules against it. This study explores the molecular mechanism of anticancer activity of P16, a semisynthetic analog of parthenin, against the human acute lymphoblastic leukemia MOLT-4 cells. P16 displayed antiproliferative activity in different cancer cell lines; however, MOLT-4 cells showed highest sensitivity for P16 with IC50 value of 0.6 μM. Further studies revealed that P16 induced cell death by apoptosis. It caused mitochondrial stress, which was mediated by the translocation of Bax from cytosol to mitochondria and release of cytochrome c into the cytosol and consequent activation of caspase-9. However, P16 was also able to activate caspase-8, thus involving both extrinsic and intrinsic pathways of apoptosis. Further, activation of caspase-3 led to cleavage of its target proteins PARP-1 and ICAD, which resulted in apoptotic DNA damage. P16 induced apoptosis was accompanied by the down-regulation of important leukemic cell survival proteins like pAKT (S473), pAKT (T308), pP70S6K, pCRAF, and pERK1/2. However, inhibition of caspases by Z-VAD-FMK reversed the down-regulatory effect of P16 on pAKT (S473) and pP70S6K, as evident by the cell viability assay and flow cytometric analysis but this inhibition did not completely reverse the antiproliferative effect of P16, thereby indicating the role of additional factors apart from caspases in P16 induced apoptosis in MOLT-4 cells. Owing to its antiproliferative potential against leukemia cells, P16 can further be explored as an effective therapeutics against leukemia. [ABSTRACT FROM AUTHOR]