Potentiation of irinotecan sensitivity by Se-methylselenocysteine in an in vivo tumor model is associated with downregulation of cyclooxygenase-2, inducible nitric oxide synthase, and hypoxia-inducible factor 1alpha expression, resulting in reduced angiogenesis

Until recently, the use of Se-methylselenocysteine (MSC) as selective modulator of the antitumor activity and selectivity of anticancer drugs including irinotecan, a topoisomerase I poison, had not been evaluated. Therapeutic synergy between MSC and irinotecan was demonstrated by our laboratory in mice bearing human squamous cell carcinoma of the head and neck tumors. In FaDu xenografts, a poorly differentiated tumor-expressing mutant p53, the cure rate was increased from 30% with irinotecan alone to 100% with the combination of irinotecan and MSC. Cellular exposure to cytotoxic concentration of SN-38, the active metabolite of irinotecan (0.1 microM) alone and in combination with noncytotoxic concentration of MSC (10 microM) did not result in additional enhancement of chk2 phosphorylation and downregulation of specific DNA replication-associated proteins, cdc6, MCM2, cdc25A, nor increase in PARP cleavage, caspase activation and the 30-300 kb DNA fragmentation induced by SN-38 treatment. MSC did not alter significantly markers associated with apoptosis, nor potentiate irinotecan-induced apoptosis. These results indicate that apoptosis is unlikely to be one of the main mechanism associated with the observed in vivo therapeutic synergy. In contrast, significant downregulation of cyclooxygenase-2 (COX-2) expression and activity was observed in the cells exposed to SN-38 in combination with MSC compared to SN-38 alone. Moreover, the inhibition of PGE(2) production was also observed in the cells treated with the combination as compared with SN-38 alone. Analysis of tumor tissues at 24 h after treatment with synergistic modality of irinotecan and MSC revealed significant downregulation of COX-2, inducible nitric oxide synthase (iNOS) and hypoxia-induced factor-1alpha expression (HIF 1alpha). Moreover, decreased microvessel density was observed after irinotecan treatment with the addition of MSC. These results suggest that observed therapeutic synergy correlates with the inhibition of neoangiogenesis through the downregulation of COX-2, iNOS and HIF-1alpha expression.

Targeting molecular signals in chk1 pathways as a new approach for overcoming drug resistance

The common clinical problem in the successful treatment of cancer is the resistance of cancer cells to chemotherapeutic drugs. Chemotherapy kills drug-sensitive cells, but leaves behind a higher proportion of drug-resistant cells. The resistance can be due to altered drug accumulation, retention, metabolism and distribution, or to reduced drug-target interaction. More recently, cell cycle progression, DNA mismatch repair (MMR) and cell death have been shown to play an important role in the regulation of cell resistance to anticancer drugs. Chkl regulation pathways, DNA MMR and p73, as well as altered apoptotic cell death involved in the cell resistance toward DNA damaging agents will be reviewed in this article.

The Chk1-Cdc25C regulation is involved in sensitizing A253 cells to a novel topoisomerase I inhibitor BNP1350 by bax gene transfer

Promotion of apoptosis may potentiate the sensitivity of tumor cells to chemotherapeutic agents, thus improving the efficacy of cancer treatment. The transfection of the proapoptotic bax gene, which results in the overexpression of bax protein, augments the growth inhibition of A253 cells by BNP1350. Increased drug response was associated with the induction of DNA fragmentation in the size of 30-200 Kb, generating a cleaved fragment of 18 kDa from full-length 21 kDa bax and the cleavage of PARP. A253/vec cells treated with 0.07 microM(IC50) of BNP1350 accumulated in G2 phase at 24 h after drug removal. In contrast, A253/Bax cells treated with an equimolar concentration of BNP1350 primarily displayed a G1 phase accumulation with a concurrent decrease in G2 phase. Certain cell cycle regulatory protein expression and activities were altered following drug exposure in both cell lines under similar conditions. Cdk2- and cdc2-associated H1 kinase activities were markedly increased in the A253/Bax cell line with marginal increased activity in the A253/vec cell line. A chk1 activity assay was performed with GST-cdc25C (200-256) or GST-cdc25C(S216A) (200-256) fusion proteins as the substrate. Increased chk1 activity was observed in the A253/vec cell line, with little change in the A253/Bax cell line, when exposed to equimolar concentrations of BNP1350 (0.07 microM). A Western blot of immunoprecipitated chk1 indicated that increased chk1 phosphorylation following DNA damage induced by BNP1350 was accompanied by the observed G2 accumulation in the A253/vec cell line, while only a slight increase in chk1 phosphorylation was seen in the A253/Bax cell line. A decreased expression of cdc25C was observed in the BNP1350-treated A253/Bax cells, but not in the A253/vec cell line. Following exposure to BNP1350, increased binding of 14-3-3 proteins to chk1 occurred in both cell lines, with more being observed in the A253/vec cell line. The data have shown that inhibition of the chk1 pathway accompanied by the abrogation of G2 arrest is involved in sensitizing A253 cells to BNP1350 by bax gene transfer. These findings suggest that bax gene transfer sensitizes A253 cells to BNP1350 through apoptosis promoting and G2/M DNA damage checkpoint regulatory pathways.

Preclinical activity of a new platinum analogue, lobaplatin, in cisplatin-sensitive and -resistant human testicular, ovarian, and gastric carcinoma cell lines

Lobaplatin [1,2-diamminomethylcyclobutane-platinum(II) lactate] is a new platinum compound with interesting preclinical activity and apparently no nephro- or neurotoxicity that is currently undergoing clinical phase II studies. Little is known about the cross-resistance between cisplatin and lobaplatin. The activity of this new compound in comparison with cisplatin and carboplatin was evaluated in cisplatin-sensitive and cisplatin-resistant human testicular, gastric, and ovarian carcinoma cell lines using 96 h continuous drug exposure in a sulforhodamine-B assay. In three cisplatin-sensitive testicular carcinoma cell lines, lobaplatin and cisplatin showed comparable antitumor activity. The 50% growth-inhibitory concentrations (IC50 values) determined for cisplatin ranged from 0.1 to 0.4 microM, and those found for lobaplatin ranged from 0.25 to 0.5 microM. Carboplatin showed markedly lower cytotoxicity in all cell lines tested. Lobaplatin was not cross-resistant to cisplatin in a 10-fold cisplatin-resistant testicular carcinoma cell line and showed only weak cross-resistance in a 20-fold cisplatin-resistant ovarian carcinoma cell line. In contrast, complete cross-resistance between cisplatin and lobaplatin occurred in two cisplatin-resistant human gastric carcinoma cell lines, which were 3.3- and 9-fold resistant to cisplatin and 3.1- and 6.5-fold resistant to lobaplatin, respectively. Furthermore, lobaplatin showed significant activity against cisplatin-resistant human ovarian and testicular carcinoma xenografts in vivo. These data indicate a high level of activity for lobaplatin at clinically achievable concentrations in ug-sensitive testicular, ovarian, and gastric carcinoma cell lines and a lack of complete cross-resistance to cisplatin. Further clinical development of lobaplatin is clearly warranted.