Changes in 2-fluoro-2-deoxy-D-glucose incorporation, hexokinase activity and lactate production by breast cancer cells responding to treatment with the anti-HER-2 antibody trastuzumab.

INTRODUCTION Changes in 2-[(18)F]-fluoro-2-deoxy-D-glucose (FDG) incorporation by tumors, detected using positron emission tomography, during response to chemotherapy are utilized clinically in patient management. Here, the effect of treatment with growth-inhibitory doses of the anti-human epidermal growth factor receptor-2 antibody trastuzumab (Herceptin) on the incorporation of FDG by breast tumor cells was measured along with hexokinase (HK) and glucose transport to determine the potential of FDG-positron emission tomography in predicting response to these biological anti-cancer therapies and their modulatory effects on the steps involved in FDG incorporation. METHODS The sensitivity to trastuzumab of three breast tumor cell lines, SKBr3, MDA-MB-453 and MDA-MB-468, expressing human epidermal growth factor receptor-2 at high, medium and low levels, respectively, was determined using MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay over a 6-day period, and a clonogenic assay was carried out after 7- and 10-day exposures. FDG incorporation by cells treated with growth-inhibitory doses of trastuzumab was carried out after 4 h and 2, 4 and 6 days of treatment. Glucose transport (rate of uptake of the non-metabolizable analogue [(3)H]O-methyl-D-glucose), HK activity and lactate production were measured on cells treated with inhibitory doses of trastuzumab for 6 days. RESULTS The IC(50) doses for SKBr3 and MDA-MB-453 and the IC(20) dose for MDA-MB-468 after 6 days of treatment with trastuzumab were 0.25, 1 and 170 μg/ml, respectively. FDG incorporation by SKBr3 and MDA-MB-453 cells was found to be decreased using IC(50) doses of trastuzumab for 6 days. At the IC(50) doses, FDG incorporation was also decreased at 4 days and, in the case of MDA-MB-453, even after 4 h of treatment. Decreased FDG incorporation corresponded with decreased HK activity in these cells. Lactate production, previously suggested to be a potential measure of response, was found to be significantly decreased by SKBr3 and MDA-MB-453 cells responding to trastuzumab. CONCLUSION FDG incorporation at the tumor cell level is modulated by treatment with growth-inhibitory doses of trastuzumab due to modulation of HK activity. Changes in lactate production may also be a useful determinant of response to trastuzumab.