Microregional Effects of Gemcitabine in HCT-116 Xenografts

Abstract

To examine the tumor microregional effects after gemcitabine administration to mice, we mapped the location of proliferating and hypoxic cells relative to vasculature in human colon cancer xenografts. The S-phase marker bromodeoxyuridine was used as a surrogate of drug effect and administered 2 hours before tumor excision, whereas vessel position and perfusion were assessed via staining for CD31 and intravenous injection of carbocyanine, respectively. Hypoxia was detected using pimonidazole. Images of the four markers were overlaid to reveal the spatial relationship between proliferation, vasculature, and hypoxia and to examine the microregional effects. Within 1 day after administration of 240 mg/kg of gemcitabine, proliferation throughout the tumor was completely inhibited. Over time, a reemergence of dividing cells occurred in relation to the distance from vasculature. Microregional analysis revealed that cells located distal to vasculature commenced cycling sooner than cells located proximal to vasculature. A similar trend was seen after multiple doses of gemcitabine (40 mg/kg on days 1, 4, 7, and 10). The possibility that the effect of gemcitabine could be attributed to changes in oxygenation was discounted after examining the vessel perfusion and patterns of hypoxia. The effect of gemcitabine was examined in multilayered cell culture, and at doses <30 mol/L, a gradient in proliferation between the exposed and unexposed sides was observed. We show a differential effect on cell proliferation in relation to vasculature and conclude that cells distal to blood vessels are less affected by gemcitabine probably because of limited penetration.

Antiangiogenic effect of gemcitabine following metronomic administration in a pancreas cancer model

“…7) that are well below the previously reported peak plasma concentration (100 Amol/L) of gemcitabine at the maximum tolerated dose (17). These results suggest that following a metronomic schedule, gemcitabine may have an antitumor effect.…”

Tissue Penetration and Activity of Camptothecins in Solid Tumor Xenografts

“…HT29 tumor xenografts have been characterized as having a more mature vascular phenotype as compared with the HCT116 model in terms of collagen and smooth muscle actin association with blood vessels (28). The two tumor types have been previously used to model drug penetration and were selected as they exhibited clearly demarcated regions under the influence of individual vessels and hence allowed for clearer interpretation of the interplay between microregional drug delivery and activity (29)(30)(31)(32). In addition to the tumor-based studies, an in vitro 3D tissue disk assay was used.…”

Chemotherapy Rescues Hypoxic Tumor Cells and Induces Their Reoxygenation and Repopulation—An Effect That Is Inhibited by the Hypoxia-Activated Prodrug TH-302

“…Repopulation of tumor cells following radiotherapy is well documented but repopulation following chemotherapy has not been studied extensively. Limited studies have found that the rate of proliferation of surviving tumor cells may increase following chemotherapy (19)(20)(21)(22). The objectives of the present study Reoxygenation and repopulation at 24 hours in PC-3 tumors treated with pimonidazole and: saline (control; black), docetaxel (8 mg/kg; blue), TH-302 (150 mg/kg; purple) or combination (orange).…”

“…In the present study, we found that combined treatment inhibited proliferation in the reoxygenated compartment-an important finding as it provides support for the activation of TH-302 in hypoxic tissues and its ability to reduce repopulation from this region. Huxham and colleagues reported that gemcitabine treatment of HCT-116 tumors induced proliferation of cells located at the border of necrotic (presumably hypoxic) regions (19). Fung and colleagues also reported that cell proliferation (repopulation) occurred in regions close to hypoxia following chemotherapy (3).…”