Figure 1.

Induction of Rab25 Is Involved in Acquired Tumor Radioresistance

(A) Increased Rab25 expression in radioresistant lung cancer cells (H157R, H358R, and A549R) and NPC cells (CNE2R) derived from the surviving residues of corresponding wild-type counterparts treated by radiation with fractionated doses.

(B) Schematic (top) and IHC staining of Rab25 in A549 xenografts treated with or without local irradiation, 2 Gy per day for 2 days (bottom). The average Rab25-positive cells in tumors were quantified and are shown in the right bar graph. Scale bar, 50 μm. n = 3, mean ± SD, ∗p < 0.05.

(C) Schematic diagram for establishment of radioresistant xenograft model. CNE2 cells were injected subcutaneously into the right flanks of nude mice, and when tumors reached a volume of approximately 200 mm³, radiotherapy was delivered to the local tumor (5 Gy per day for 2 days; total dose = 10 Gy). On day 5 after last irradiation, the tumors were removed and one part of tumor tissues was fixed for IHC analysis and another part of tumor tissues was inoculated subcutaneously into the right flank of another mouse (P1). When the volume of the re-planted tumors in the P1 mice reached approximately 200 mm³, radiotherapy was delivered again with the same dose, and such treatment was repeated for 11 cycles (P11). The radiosensitivity of tumors from P1 and P11 mice was measured by transplanting the tumors from P1 and P11 mice and irradiating with 5 Gy × 2 when tumor reached 200 mm³.

(D) Representative IHC staining of Rab25 in P1 and P11tumors (left). The average Rab25-positive cells in tumors were quantified (six fields were randomly selected for each xenograft) and shown in the right. Scale bar, 50 μm. n = 18, mean ± SD, ∗∗p < 0.01.