Pseudolaric Acid B (PAB), diterpenoid isolated from the root bark of Pseudolarix kaempferi Gordon tree (Pinaceae), exhibits an anti-proliferative and apoptotic activity in various cancer cell lines but to date, the effects of PAB on head and neck cancer (HNC) cell lines remain to be elucidated. In this study, we showed that PAB significantly inhibited the viability and caspase-dependent apoptosis in HN22 cell line. PAB-induced apoptosis is through inducing death receptor 5 (DR5) together with the increase in the expression of cleaved caspase-8. It also inhibited the proliferations and induced apoptosis through DR5 in other three HNC cell lines (HSC3, Ca9.22, and HSC4). Extending our in vitro findings, we found that ethanol extract of Pseudolarix kaempferi (2.5 mg/kg/day) reduced tumor growth in a xenograft model bearing HN22 cell line without any change in body weight. DR5 were also found to be increased in tumors tissue of PAB-treated mice without any apparent histopathological changes in liver or kidney tissues. Taken together, PAB may be a potential lead compound for chemotherapeutic agents against head and neck cancer.

− Pseudolaric acids of Pseudolarix kaempferi (Pinaceae) have been known as diterpenoids with potent anti-fungal-, anti-microbial, and cytotoxic activities. In the present study, the five MeOH extracts were prepared from the five plant part (root bark, stem bark, leaf, the inner part of root, and cone) to find the relation between the concentration of pseudolaric acids and cytotoxicity. Pseudolaric acids B and C were isolated from the root bark of P. kaempferi to use them as standard compounds. The five extracts were tested on cytotoxicity against six cancer cell lines, A549 (lung), HCT116 (colon), MDA-MB-231 (breast), SNU638 (stomach), and SK-hep-1 (liver) by SRB assay, but against K562 (leukemia) by SRB-or MTT assay. HPLC quantification were performed on a Shisheido Capcell PAK C18 column (5 µm, 4.6 mm × 250 mm) using 254 nm wavelength. The cytotoxicity (IC 50 , 0.36 µg/ml on K562 cell lines) of the root bark extract was potent and the content (101.1 mg/g extract) of pseudolaric acid B was very high in the root bark. These results suggest that the MeOH extract obtained from the root bark could be developed as the anti-cancer agent with a high quantity of pseudolaric acid B.