See-Voon Seow

Selected cytotoxic chemicals can provoke the immune system to recognize and destroy malignant tumors. Most of the studies on immunogenic cell death are focused on the signals that operate on a series of receptors expressed by dendritic cells to induce tumor antigen-specific T-cell responses. Here, we explored the effects of oxaliplatin, an immunogenic cell death inducer, on the induction of stress ligands and promotion of natural killer (NK) cell-mediated cytotoxicity in human ovarian cancer cells. The results indicated that treatment of tumor cells with oxaliplatin induced the production of type I interferons and chemokines and enhanced the expression of major histocompatibility complex class I-related chains (MIC) A/B, UL16-binding protein (ULBP)-3, CD155 and TNF-related apoptosis-inducing ligand (TRAIL)-R1/R2. Furthermore, oxaliplatin but not cisplatin treatment enhanced susceptibility of ovarian cancer cells to NK cell-mediated cytolysis. In addition, activated NK cells completely abrogated the growth of cancer cells that were pretreated with oxaliplatin. However, cancer cells pretreated with the same concentration of oxaliplatin alone were capable of potentiating regrowth over a period of time. These results suggest an advantage in combining oxaliplatin and NK cell-based therapy in the treatment of ovarian cancer. Further investigation on such potential combination therapy is warranted.

BACKGROUND: The rich biodiversity of medicinal plants and their importance as sources of novel therapeutics and lead compounds warrant further research. Despite advances in debulking surgery and chemotherapy, the risks of recurrence of ovarian cancer and resistance to therapy are significant and the clinical outcomes of ovarian cancer remain poor or even incurable. OBJECTIVE: This study aims to investigate the effects of leaf extracts from a medicinal plant Leea indica and its selected phytoconstituents on human ovarian cancer cells and in combination with oxaliplatin and natural killer (NK) cells. METHODS: Fresh, healthy leaves of L. indica were harvested and extracted in 70% methanol by maceration. The crude extract was partitioned with n-hexane, dichloromethane and ethyl acetate. Selected extracts and compounds were analyzed for their effects on cell viability of human ovarian cancer cells, NK cell cytotoxicity, and stress ligands expression for NK cell receptors. They were also evaluated for their effects on TNF-α and IL-1β production by enzyme-linked immunosorbent assay in lipopolysaccharide-stimulated human U937 macrophages. RESULTS: Leaf extracts of L. indica increased the susceptibility of human ovarian tumor cells to NK cell-mediated cytotoxicity. Treatment of cancer cells with methyl gallate but not gallic acid upregulated the expression of stress ligands. Tumor cells pretreated with combination of methyl gallate and low concentration of oxaliplatin displayed increased levels of stress ligands expression and concomitantly enhanced susceptibility to NK cell-mediated cytolysis. Further, NK cells completely abrogated the growth of methyl gallate-pretreated ovarian cancer cells. The leaf extracts suppressed TNF-α and IL-1β production in human U937 macrophages. Methyl gallate was more potent than gallic acid in down-regulating these cytokine levels. CONCLUSIONS: We demonstrated for the first time that leaf extracts of L. indica and its phytoconstituent methyl gallate enhanced the susceptibility of ovarian tumor cells to NK cell cytolysis. These results suggest that the combined effect of methyl gallate, oxaliplatin and NK cells in ovarian cancer cells warrants further investigation, for example for refractory ovarian cancer. Our work is a step towards better scientific understanding of the traditional anticancer use of L. indica.

Abstract Glutathione-S-transferases have been detected in the insecticide-resistant and susceptible strains of the larvae of Piute/la xylostella, a major pest of cruciferous vegetables. Although there was no significant difference in the enzyme-substrate affinities (Km) for glutathione (GSH) and 1-chloro- 2,4-dinitrobenzene (CDNB), the enzyme was present in almost five-fold excess in the resistant strain than in the susceptible strain. The enzyme in the crude supernatant suffered a marked loss in activity on standing; its activity, however, could be stabilized by thiol reagents such as 2-mercaptoethanol, cysteine or GSH, but not with metal ions.

B7 Abstract
 The main aim of this study is to evaluate the potential application of an immunomodulatory protein, Fve, as an adjuvant for tumor immunotherapy. Using HPV-16 E7 oncoprotein as a model antigen, we have demonstrated that mice co-immunized with E7 and Fve showed enhanced E7-specific antibodies as compared to mice immunized with E7 alone. Furthermore, intracellular cytokine staining revealed that there was an increased expansion of E7-specific IFN-γ-producing CD4+ and CD8+ T cells in the co-immunized mice. Tumor protection assays showed that 60% of mice co-immunized with E7 plus Fve remained tumor free up to 167 days after the TC-1 tumor cells challenge whereas only 20% of the E7-immunized mice remained tumor free. Tumor therapeutic assays showed that E7 plus Fve treatment significantly retarded tumor growth and prolonged survival of tumor bearing mice as compared to those treated by E7 alone. In the metastatic settings, similar enhanced prophylactic and therapeutic anti-tumor effects were observed in the co-immunized mice. Antibody depletion assays illustrated that the CD4+, CD8+ T cells and IFN-γ play critical roles in conferring the anti-tumor effects. Adoptive transfer of purified T cells to the tumor-bearing mice further indicated that T cells play a pivotal role in the therapeutic anti-tumor effects and such effects are correlated to the magnitude of the E7-specific T cell responses. In summary, this study demonstrates that Fve protein has potent adjuvant properties, in driving enhanced antigen-specific humoral and cellular type 1 immune responses, which confer effective anti-tumor effects, representing an attractive vaccination strategy for cancer immunotherapy.