Blockage of 2-Deoxy-d-Ribose-Induced Angiogenesis with Rapamycin Counteracts a Thymidine Phosphorylase-Based Escape Mechanism Available for Colon Cancer under 5-Fluorouracil Therapy

Abstract

Purpose: Colorectal neoplasms remain a leading cause of cancer-related deaths. A recognized weakness of conventional 5-fluorouracil (5-FU) therapy relates to expression of the intracellular enzyme, thymidine phosphorylase (TP). Although TP promotes 5-FU cytotoxicity, TP-derived 2-deoxy-D-ribose (dRib) counterproductively stimulates tumor angiogenesis. Here, the newly discovered antiangiogenic drug rapamycin was combined with 5-FU to counteract the potential escape mechanism of dRib-induced angiogenesis.Experimental Design: Orthotopic tumor growth was assessed in rapamycin and 5-FU-treated BALB/c mice with TP-expressing CT-26 colon adenocarcinoma cells. To examine liver metastasis, green-fluorescent protein-transfected CT-26 cells were visualized by fluorescence microscopy after intraportal injection. Cell counting and Ki67 staining were used to determine in vitro and in vivo cell expansion, respectively. In vitro angiogenic effects of dRib were assessed with endothelial cell migration and aortic ring assays. Western blotting detected dRib effects on p70/S6 kinase activation.Results: Rapamycin treatment of mice bearing orthotopic tumors inhibited tumor growth more than did 5-FU, and mice treated with both drugs typically developed no tumors. In the liver metastasis assay, combination therapy blocked metastatic expansion of solitary tumor cells. Interestingly, complex drug activities were suggested by tumorcell proliferation being more sensitive to 5-FU than to rapamycin in vitro, but more sensitive to rapamycin in vivo. With regard to angiogenesis, dRib-induced endothelial cell migration and aortic ring formation were completely abrogated by rapamycin, correlating with blockage of dRib-induced p70/S6 kinase activation in endothelial cells.Conclusions: Inhibition of dRib-induced angiogenesis with rapamycin counteracts a potential TP-based escape mechanism for colorectal cancer under 5-FU therapy, introducing a novel, clinically feasible, combination treatment option for this common neoplasm.

Angiogenic Factor Thymidine Phosphorylase Increases Cancer Cell Invasion Activity in Patients with Gastric Adenocarcinoma

“…The finding that rapamycin inhibits TP-stimulated migration implicates the activation of p70 S6K in this cellular response, which is consistent with other works showing that rapamycin inhibits the migration of vascular smooth muscle cells or endothelial cells (30)(31)(32). In those studies, the effects of rapamycin were primarily mediated by p27 kip , a cell cycle regulator that may be a downstream target of mTOR.…”

Antiangiogenic therapy in human gastrointestinal malignancies

“…81 In addition to its functions as a secreted growth factor, PD-ECGF is involved intracellularly in the metabolism of pyrimidine nucleosides and 5-fluorouracil. 82 Expression of PD-ECGF has been shown in tumour cells, stromal cells, and infiltrating mononuclear cells. 83 It has been hypothesised that human colorectal tumours showing low VEGF expression are more dependent on PD-ECGF as the major proangiogenic factor.…”

Pharmacometrics and delivery of novel nanoformulated PEG-b-poly(ε-caprolactone) micelles of rapamycin

“…Further investigations also revealed that rapamycin has a unique anti-tumor mechanism through the binding with FKBP12 and the inhibition of mammalian target of rapamycin (mTOR), which is a central regulator of proliferation, apoptosis [5,11,37,41], and cell growth by inducing cellcycle arrest in the G 1 phase [7]. These latter pharmaco-logical properties have allowed rapamycin to be recognized recently as a possible chemotherapeutic agent against many solid tumor types including breast [21], colon [15], prostate [50], and renal cell carcinomas [38] with a typical IC 50 < 50 nM.…”