DNA polymerase lambda (polλ) is a recently identified DNA polymerase whose cellular function remains elusive. Here we show, that polλ participates at the molecular level in a chromosomal context, in the repair of DNA double strand breaks (DSB) via non-homologous end joining (NHEJ) in mammalian cells. The expression of a catalytically inactive form of polλ (polλDN) decreases the frequency of NHEJ events in response to I-Sce-I-induced DSB whereas inactivated forms of its homologues polβ and polμ do not. Only events requiring DNA end processing before ligation are affected; this defect is associated with large deletions arising in the vicinity of the induced DSB. Furthermore, polλDN-expressing cells exhibit increased sensitization and genomic instability in response to ionizing radiation similar to that of NHEJ-defective cells. Our data support a requirement for polλ in repairing a subset of DSB in genomic DNA, thereby contributing to the maintenance of genetic stability mediated by the NHEJ pathway.

Purpose MDM2 and CDK4 are frequently co-amplified in well-differentiated/dedifferentiated liposarcoma (WDLPS/DDLPS). We aimed to determine whether combined MDM2/CDK4 targeting is associated with higher antitumour activity than a single agent in preclinical models of DDLPS.Experimental designDDLPS cells were exposed to RG7388 (MDM2 antagonist) and palbociclib (CDK4 inhibitor), and apoptosis and signalling/survival pathway perturbations were monitored by flow cytometry and Western blotting. Xenograft mouse models were used to assess tumour growth and survival. Treatment efficacy was assessed by Western blotting, histopathology and tumour volume.ResultsRG7388 and palbociclib together exerted a greater antitumour effect than either drug alone, with significant differences in cell viability after a 72-h treatment with RG7388 and/or palbociclib. The combination treatment significantly increased apoptosis compared to the single agents. We then analysed the in vivo antitumour activity of RG7388 and palbociclib in a xenograft model of DDLPS. The combination regimen reduced the tumour growth rate compared with a single agent alone and significantly increased the median progression-free survival.ConclusionsOur results provide a strong rationale for evaluating the therapeutic potential of CDK4 inhibitors as potentiators of MDM2 antagonists in DDLPS and justify clinical trials in this setting.

The present study was conducted to evaluate the antioxidant, anti-inflammatory, and antiproliferative activities of organic fractions from Cystoseira sedoides (Desfontaines) C. Agardh . Various fractions of C. sedoides (chloroform (F-CHCl3), ethyl acetate (F-AcOEt), and methanol (F-MeOH)) were screened for total phenol content, as well as antioxidant activity, using the stable radical 1,1-diphenyl-2-picrylhydrazyl (DPPH), and assays for determining the reducing power of these fractions. The anti-inflammatory properties of these fractions were assessed using the carrageenan-induced rat paw oedema model. The antiproliferative activity of C. sedoides fractions was evaluated on normal Madin-Darby canine kiney (MDCK), and fibroblast cells and on cancer cell lines (A549, MCF7, and HCT15), using the ability of the cells to metabolically reduce 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) formazan dyes. The F-CHCl3 and F-AcOEt fractions showed significant total phenolic content at 55.09 and 61.30 mg gallic-acid equivalent/g dried sample, respectively. Using the DPPH method, the F-CHCl3 and the F-AcOEt fractions exhibited the strongest radical scavenging activity, with IC50 120 µg/mL for F-CHCl3 and 121 µg/mL for F-AcOEt, which approaches the activity of the powerful antioxidant standard, Trolox (IC50 = 90 µg/mL). The reducing power of the samples was in the following order: F-AcOEt > F-CHCl3 > F-MeOH fraction. The F-CHCl3 and F-AcOEt fractions of C. sedoides tested at different doses (25 and 50 mg/kg, intraperitoneally (i.p)), exhibited a dose-dependent reduction of rat paw oedema. The percentage of inhibition of oedema, 3 h after carrageenan injection, ranged from 67.71% to 73.49% and from 67.74% to 74.58%, for F-CHCl3 and F-AcOEt, respectively. Their effects are comparable with that of lysine acetylsalicylate (300 mg/kg body mass; i.p.), which is used as a reference drug with the ability to inhibit oedema by 66.14%. Our results revealed that the F-CHCl3 and F-AcOEt fractions from C. sedoides showed important antiproliferative properties towards all of the cancer cell lines studied here, as judged by their IC50 values, which ranged from 52.6 to 66.5 µg/mL for A549; 22.4 to 70.2 µg/mL for MCF7, and 250.6 to 255.3 µg/mL for HCT15. Moreover, no visible destruction or alteration of normal cells was observed, even at 500 µg/mL F-CHCl3 or F-AcOEt. These results suggest that C. sedoides fractions might be used as a potential source of natural antioxidant, anti-inflammatory, and antitumor agents. The purification and determination of the chemical structures of the compounds in these active fractions are under investigation. The results could provide a compound(s) with a promising role in future medicines and nutrition, when used either as a drug or a dietary supplement.