A Systems Biology Approach Identifies SART1 as a Novel Determinant of Both 5-Fluorouracil and SN38 Drug Resistance in Colorectal Cancer

Chemotherapy response rates for advanced colorectal cancer remain disappointingly low, primarily because of drug resistance, so there is an urgent need to improve current treatment strategies. To identify novel determinants of resistance to the clinically relevant drugs 5-fluorouracil (5-FU) and SN38 (the active metabolite of irinotecan), transcriptional profiling experiments were carried out on pretreatment metastatic colorectal cancer biopsies and HCT116 parental and chemotherapy-resistant cell line models using a disease-specific DNA microarray. To enrich for potential chemoresistance-determining genes, an unsupervised bioinformatics approach was used, and 50 genes were selected and then functionally assessed using custom-designed short interfering RNA(siRNA) screens. In the primary siRNA screen, silencing of 21 genes sensitized HCT116 cells to either 5-FU or SN38 treatment. Three genes (RAPGEF2, PTRF, and SART1) were selected for further analysis in a panel of 5 colorectal cancer cell lines. Silencing SART1 sensitized all 5 cell lines to 5-FU treatment and 4/5 cell lines to SN38 treatment. However, silencing of RAPGEF2 or PTRF had no significant effect on 5-FU or SN38 sensitivity in the wider cell line panel. Further functional analysis of SART1 showed that its silencing induced apoptosis that was caspase-8 dependent. Furthermore, silencing of SART1 led to a downregulation of the caspase-8 inhibitor, c-FLIP, which we have previously shown is a key determinant of drug resistance in colorectal cancer. This study shows the power of systems biology approaches for identifying novel genes that regulate drug resistance and identifies SART1 as a previously unidentified regulator of c-FLIP and drug-induced activation of caspase-8. Mol Cancer Ther; 11(1); 119-31. (C) 2011 AACR.

Inactivation of Rb in stromal fibroblasts promotes epithelial cell invasion

Stromal-derived growth factors are required for normal epithelial growth but are also implicated in tumour progression. We have observed inactivation of the retinoblastoma protein (Rb), through phosphorylation, in cancer-associated fibroblasts in oro-pharyngeal cancer specimens. Rb is well known for its cell-autonomous effects on cancer initiation and progression; however, cell non-autonomous functions of Rb are not well described. We have identified a cell non-autonomous role of Rb, using three-dimensional cultures, where depletion of Rb in stromal fibroblasts enhances invasive potential of transformed epithelia. In part, this is mediated by upregulation of keratinocyte growth factor (KGF), which is produced by the depleted fibroblasts. KGF drives invasion of epithelial cells through induction of MMP1 expression in an AKT- and Ets2-dependent manner. Our data identify that stromal fibroblasts can alter the invasive behaviour of the epithelium, and we show that altered expression of KGF can mediate these functions. © European Molecular Biology Organization.

Phosphoramidates of 2'-beta-D-arabinouridine (AraU) as phosphate prodrugs; design, synthesis, in vitro activity and metabolism

2'-Beta-D-arabinouridine (AraU), the uridine analogue of the anticancer agent AraC, was synthesized and evaluated for antiviral activity and cytotoxicity. In addition, a series of AraU monophosphate prodrugs in the form of triester phosphoramidates (ProTides) were also synthesized and tested against a range of viruses, leukaemia and solid tumour cell lines. Unfortunately, neither the parent compound (AraU) nor any of its ProTides showed antiviral activity, nor potent inhibitory activity against any of the cancer cell lines. Therefore, the metabolism of AraU phosphoramidates to release AraU monophosphate was investigated. The results showed carboxypeptidase Y, hog liver esterase and crude CEM tumor cell extracts to hydrolyse the ester motif of phosphoramidates with subsequent loss of the aryl group, while molecular modelling studies suggested that the AraU l-alanine aminoacyl phosphate derivative might not be a good substrate for the phosphoramidase enzyme Hint-1. These findings are in agreement with the observed disappearance of intact prodrug and concomitant appearance of the corresponding phosphoramidate intermediate derivative in CEM cell extracts without measurable formation of araU monophosphate. These findings may explain the poor antiviral/cytostatic potential of the prodrugs.

Treatment of intestinal Behçet's syndrome with chimeric tumour necrosis factor alpha antibody

Few patients with Behçet's syndrome have gastrointestinal ulceration. Such patients are difficult to treat and have a higher mortality. Faced with refractory symptoms in two patients with intestinal Behçet's, we used the tumour necrosis factor alpha (TNF-alpha) monoclonal antibody infliximab to induce remission. Both women (one aged 27 years, the other 30 years) presented with orogenital ulceration, pustular rash, abdominal pain, bloody diarrhoea due to colonic ulceration, weight loss, and synovitis. One had thrombophlebitis, digital vasculitis, perianal fistula, and paracolic abscess; the other had conjunctivitis and an ulcer in the natal cleft. Treatment with prednisolone, methyl prednisolone, and thalidomide in one and prednisolone, colchicine, and cyclosporin in the other was ineffective. After full discussion, infliximab (3 mg/kg, dose reduced because of recent sepsis in one, and 5 mg/kg in the other) was administered. Within 10 days the ulcers healed, with resolution of bloody diarrhoea and all extraintestinal manifestations. A second infusion of infliximab was necessary eight weeks later in one case, followed by sustained (>15 months) remission on low dose thalidomide. Remission was initially sustained for 12 months in the other but thalidomide had to be stopped due to intolerance, and a good response to retreatment lasted only 12 weeks without immunosuppression, before a third infusion. The cause of Behçet's syndrome is unknown but peripheral blood CD45 gammadelta T cells in Behçet's produce >50-fold more TNF-alpha than controls when stimulated with phorbol myristate acetate and anti-CD3. Infliximab could have a role for inducing remission in Behçet's syndrome.