Apoptosis-inducing effect of ¹³¹I-K237 on human prostate cancer LNCaP cells

Objective: To assess the in vitro affinity and apoptosis-inducing effect of ¹³¹I-K237 peptide (H-His-Thr-Met-Tyr-Tyr-His-His-Tyr-Gln-His-His-Leu-OH) to LNCaP prostate cancer cell line. Methods: The K237 peptide was radiolabeled with ¹³¹I by the Iodogen method. The radiolabeling efficiency and radiochemical purity after purification were then characterized by TLC in vitro. LNCaP cells were inoculated in 96-well cell plate and divided into following groups (3 duplicate wells for each group): 15 kBq ¹³¹I-K237 was added in the experimental group, different doses of Na¹³¹I (5, 10, 15 kBq) were added in 3 negative control groups, 15 kBq ¹³¹I-K237 with different doses of unlabeled K237 (1, 2, 4, 8, 16 μg/μl) were added in 3 blocking groups, and PBS was added in blank control group. The cellular binding ratios were calculated after 48 h. LNCaP cells were inoculated in 24-well cell plate and divided into 3 groups: ¹³¹I-K237 group,which including 3 different dose subgroups (5, 10, 15 kBq); unlabeled K237 group, which including 3 different dose subgroups (1, 2, 4 μg/μl); blank control group with 100 μl PBS. All the cells were cultured for 48 h, then optical microscopy (OM) and fluorescence microscopy (FM) were used to observe the cell morphology; DNA gel electrophoresis was conducted and flow cytometry (FCM) was used to estimate the apoptotic rate of LNCaP cells. One-way analysis of variance and the least significant difference (ISD)-t test were used to analyze the data. Results: The labeling efficiency of ¹³¹I-K237 was (73.7 ± 3.2)% and the radiochemical purity was (96.7 ± 0.6)% after purification. The binding ratio of experimental group was (95.8 ± 1.5)%, whereas the ratio of negative groups with 5, 10, 15 kBq Na¹³¹I and PBS group was (8.2 ± 0.4)%, (8.3 ± 0.6)%, (8.6 ± 0.5)% and 0, respectively. The binding ratio of ¹³¹I-K237 and LNCaP significantly declined with the increased dose of unlabeled K237 (t = 4.71, P < 0.01). The apoptosis of LNCaP cells cultured with ¹³¹I-K237 was observed. Typical DNA ladder was found by DNA gel electrophoresis. The apoptotic rates of 5, 10, 15 ¹³¹I-K237 groups were (34.1 ± 2.9)%, (37.3 ± 3.4)% and (41.7 ± 3.6)%, respectively; whereas those of unlabeled K237 groups and blank control group were (10.8 ± 1.0)%, (12.5 ± 2.1)%, (13.1 ± 2.4)% and (2.9 ± 0.3)%, respectively. There were significant differences of apoptotic rate among groups (F = 76.31, P < 0.05). The difference among 5, 10, 15 kBq ¹³¹I-K237 groups was statistically significant (t = 3.09, 3.27, 4.52, all P < 0.05). Conclusion: ¹³¹I-K237 can bind to LNCaP cells with highly affinity and has significant apoptosis-inducing efficacy on the prostate cancer cell line. (authors)