Synergistic interaction between tetra-arsenic oxide and paclitaxel in human cancer cells in vitro.

Similar to arsenic trioxide (As2O3), tetra-arsenic oxide (As4O6, TAO) has shown anti-proliferative and apoptosis-inducing effects against human leukemic and solid tumor cells. In order to assess the increase in efficacy, we evaluated the combinatory interaction of TAO combined with paclitaxel, 5-FU or cisplatin and studied its mechanism of action in the cell lines of human gastric, cervix and head and neck tumors. Two agents were combined at equitoxic ratios based on the IC50 of each drug. Efficacy improvement was evaluated using a combination index and isobologram at 50% inhibition level. Apoptosis induction and expression of apoptosis-related proteins was determined and the effect on microtubule polymerization was monitored. TAO combined with paclitaxel showed synergistic interaction in all three of gastric, cervix and head and neck cancer cell lines. On the other hand, TAO when combined with 5-FU or cisplatin showed an antagonistic interaction in head and neck or cervix cancer cell lines, respectively. Simultaneous treatment with TAO with paclitaxel resulted in an increased percentage of apoptotic cells and a significant increase in PARP cleavage and caspase-3 activation in the gastric and cervix cancer cells compared to TAO alone as well as the antagonistic groups (TAO with 5-FU or cisplatin). TAO suppressed the tubulin polymerization in the presence and absence of paclitaxel in a concentration-dependent manner, suggesting mitotic catastrophe as a potential mechanism of the synergism with paclitaxel. Overall, the present study suggests that TAO may have a greater potential as an anti-cancer agent against human gastric, cervix and head and neck tumors, in combination with paclitaxel. The synergistic interaction with paclitaxel may be associated with increased apoptosis via inhibition of paclitaxel-induced tubulin polymerization. Further detailed studies of combinatory mechanisms and evaluation using in vivo models are warranted.

Antitumor and normal cell protective effect of PKC412 in the athymic mouse model of ovarian cancer.

N-benzoyl-staurosporine (PKC412) is a selective inhibitor of protein kinase C, and it inhibits the growth of human cancer cells. In this study, we examined the antitumor effect of PKC412, given singly and in combination with paclitaxel, on tumor regression and chemotherapeutic side effects by assessing tumor burden and cytokine production responses in vivo. Twenty-six nude mice intraperitoneally inoculated with SKOV3 cells were treated differently in 4 treatment groups: PKC412 plus paclitaxel (n = 7), paclitaxel-only (n = 6), PKC412-only (n = 6), and controls (n = 7). At autopsy, we found that PKC412 itself slightly reduced the mass of tumor but did not fully inhibit tumor formation. The incidence of evident disease was decreased when PKC412 was combined with paclitaxel (43%). From the body weight of the tumor-bearing mice, we observed that PKC412 plus paclitaxel treated mice were less wasted than paclitaxel-only treated mice (18.1 g vs 22.4 g, p = 0.001). We measured intracellular TNFalpha, IFNgamma, IL-4, and IL-10 in stimulated mouse splenocytes using flow cytometry to determine if PKC412 inhibited cytokine production in T cells. TNFalpha, IFNgamma, and IL-10 production were all significantly inhibited in the paclitaxel-treated mice. The inhibitory effects on cytokine production by paclitaxel were compensated with PKC412 combination (p = 0.008, 0.035, 0.014, respectively). From this study, we deduce that PKC412 may have clinical applications in promoting tumor regression in ovarian cancer when combined with paclitaxel. Moreover, PKC412 is able to prevent weight loss and immunosuppression induced by paclitaxel because it rescues normal proliferating cells from cytotoxic effects.