64Cu-ATSM Predicts Efficacy of Carbon Ion Radiotherapy Associated with Cellular Antioxidant Capacity

Abstract

Carbon ion radiotherapy is an emerging cancer treatment modality that has a greater therapeutic window than conventional photon radiotherapy. To maximize the efficacy of this extremely scarce medical resource, it is important to identify predictive biomarkers of higher carbon ion relative biological effectiveness (RBE) over photons. We addressed this issue by focusing on cellular antioxidant capacity and investigated 64Cu(II)-diacetyl-bis(N4-methylthiosemicarbazone) (64Cu-ATSM), a potential radioligand that reflects an over-reduced intracellular environment. We found that the carbon ion RBE correlated with 64Cu-ATSM uptake both in vitro and in vivo. High RBE/64Cu-ATSM cells showed greater steady-state levels of antioxidant proteins and increased capacity to scavenge reactive oxygen species in response to X-rays than low RBE/64Cu-ATSM counterparts; this upregulation of antioxidant systems was associated with downregulation of TCA cycle intermediates. Furthermore, inhibition of nuclear factor erythroid 2-related factor 2 (Nrf2) sensitized high RBE/64Cu-ATSM cells to X-rays, thereby reducing RBE values to levels comparable to those in low RBE/64Cu-ATSM cells. These data suggest that the cellular activity of Nrf2-driven antioxidant systems is a possible determinant of carbon ion RBE predictable by 64Cu-ATSM uptake. These new findings highlight the potential clinical utility of 64Cu-ATSM imaging to identify high RBE tumors that will benefit from carbon ion radiotherapy.

Radiosensitization by the Selective Pan-FGFR Inhibitor LY2874455

“…First, we examined the radiosensitizing effects of LY2874455 on radioresistant human cancer cells. For this purpose, we screened in-house radiosensitivity data from 20 cell lines of various origins and selected H1703, A549, and H1299, which showed the lowest sensitivity to photons [ 14 , 21 , 22 ]. H1703 harbors an amplification of FGFR1 and wild-type FGFR2–4, whereas A549 and H1299 harbor wild-type FGFR1–4 [ 12 ].…”

“…Activated ERK also increases the expression of NRF2 [ 39 ], a master regulator of cellular antioxidant systems [ 40 ]. The induction of DSBs by photons relies predominantly on the so-called indirect effect, which involves the radiolysis of water, followed by the production of reactive oxygen species [ 14 ]. From this standpoint, the radiosensitizing effects of LY2874455 may be due, at least partially, to the suppression of NRF2 upregulation, potentially contributing to the enhancement of the indirect effect.…”

“…Cells were irradiated with X-rays using an MX-160Labo (160 kVp, 1.06 Gy/min; mediXtec, Matsudo, Japan) [ 14 ]. Mouse tumor xenografts were irradiated with X-rays using a TITAN-225S (200 kVp, 1.30 Gy/min, Shimadzu, Otsu, Japan) [ 14 ].…”

“…Colonies of ≥50 cells were recorded using an inverted microscope. The surviving fractions were fitted to the linear–quadratic model, and D X (i.e., the dose that provides X% survival) was calculated [ 14 , 16 ].…”

“…Growth of tumor xenografts was assessed as described previously [ 14 ]. Cells (5 × 10 6 cells) prepared in 100 µL of 0.5% methylcellulose (FUJIFILM) were inoculated subcutaneously into the right thigh of 6-week-old BALB/c female nude mice (Japan SLC, Hamamatsu, Japan).…”