Hypoxia-induced alteration of tracer accumulation in cultured cancer cells and xenografts in mice: implications for pre-therapeutic prediction of treatment outcomes with 99mTc-sestamibi, 201Tl chloride and 99mTc-HL91

Abstract

Weak visualization of tumours in pre-therapeutic scintigrams with technetium-99m sestamibi (MIBI) is likely a predictive sign of unfavourable tumour response to radiotherapy and chemotherapy. However, factors relating to this scintigraphic finding are not well understood. The presence of hypoxic tumour cells is one of the major reasons for therapeutic failure; consequently, we attempted to determine whether oxygenation status affects (99m)Tc-MIBI accumulation in tumour cells. LS180 human colon cancer and T24 human bladder cancer cells were incubated in air or N(2) gas at 37 degrees C. Cellular uptake of (99m)Tc-MIBI was subsequently determined at 15, 60 and 120 min. Uptake of thallium-201 chloride was also assessed. Uptake of (99m)Tc-HL91 was assessed as a hypoxic marker. Accumulation of the tracers in LS180 xenografts was observed in mice treated with 5 mg/kg hydralazine and compared with that in untreated mice. pO(2) in the medium and tumours was measured with O(2) microelectrodes. N(2) gas flow gradually reduced pO(2) in the cell suspension to 1-2 mmHg in 60 min. Cellular uptake of (99m)Tc-MIBI in LS180 cells decreased by approximately 30% in N(2) gas in comparison to that in air throughout the study. Hypoxia had a more prominent influence on (201)Tl uptake, which displayed a reduction of approximately 60% in N(2) gas at 120 min, than on (99m)Tc-MIBI uptake. On the other hand, N(2) gas induced an increase of 170% in (99m)Tc-HL91 uptake at 120 min, indicating the hypoxic condition of cells. The results of in vitro assays employing the T24 cell line were similar to those obtained with the LS180 cell line. Hydralazine treatment markedly reduced (99m)Tc-MIBI and (201)Tl accumulation in LS180 xenografts; moreover, intratumoural pO(2) decreased from 14.5 +/- 6.6 mmHg to 7.6 +/- 6.2 mmHg. (99m)Tc-HL91 accumulation in xenografts was markedly increased by hydralazine. In conclusion, hypoxia reduced accumulation of (99m)Tc-MIBI and (201)Tl in tumour cells. Accordingly, hypoxia may be an important factor in terms of the interpretation of scintigraphic findings obtained with these tracers for pre-therapeutic prediction of tumour response to treatment. Furthermore, the enhanced (99m)Tc-HL91 accumulation in hypoxic tumour cells indicates the usefulness of this tracer in this regard.

Hypoxia imaging predicts success of hypoxia-induced cytosine deaminase/5-fluorocytosine gene therapy in a murine lung tumor model

“…Our results, combined with recent studies using hypoxia imaging in cancer patients, provide evidence that hypoxia imaging using Tc-99m-HL91 is useful to characterize tumor hypoxia and to predict tumor outcome after radiation treatment. [16][17][18] Our findings indicate that Tc99m-HL91 imaging allows identifying tumor hypoxia and predicting success of hypoxia-induced CD gene therapy for cancer.…”

“…19 Moreover, the use of Tc-99m-HL91 has been described for identifying tumor hypoxia in vitro and ex vivo. 17,[19][20][21][22][23][24] The present study demonstrates for the first time, to our knowledge, that Tc99m-HL91 is useful as an imaging biomarker to predict the treatment responses of hypoxia-regulated CD/5-FC gene therapy in a mouse lung tumor model.…”

“…In our result of autoradiography, high uptake of Tc-99m-HL91 corresponded to the histopathologically hypoxic area, consistent with previous reports. [15][16][17][18][19][20][21][22][23][24] Tc-99m-HL91 displays increased retention in hypoxic tumors and is correlated with independent measures of tissue oxygen tension. 15 An oxygen-specific retention mechanism may determine the amount of the radiotracer that is trapped in hypoxic tissues.…”

“…18 In vitro studies have identified hypoxia-selective uptake of Tc-99m-HL91, with a significant increase in the uptake in the hypoxic state compared with the normoxic state. 17,19,20 Animal studies have also shown that Tc99m-HL91 is markedly increased in mice treated with hydralazine compared with controls. 19,20 The aim of this study was to test our hypothesis that Tc-99m-HL91 imaging can be used to identify the efficacy of hypoxia-induced CD gene/5-FC gene therapy for cancer.…”

“…15 Significant correlations between antitumor responses and tumor uptakes of Tc-99m-HL91 were noted. 16,17 A human study demonstrated the diagnostic value of Tc99m-HL91 in the squamous head and neck carcinoma. 18 In vitro studies have identified hypoxia-selective uptake of Tc-99m-HL91, with a significant increase in the uptake in the hypoxic state compared with the normoxic state.…”