Abstract: Jin Jialu, Zhu Renshu, Xie Yuyuan, Liu Hongchun Department of Laboratory Medicine, Medical School of Hebi Polytechnic, Hebi 458030, Henan, China （Jin JL, Zhu RS）; Institute for Biological Products Control, Hubei Institute for Food and Drug Control, Wuhan 430064, China（Xie YY）; Department of Clinical Laboratory, the First Affiliated Hospital of Zhengzhou University, Zhengzhou 450052, China （Liu HC） Corresponding author: Liu Hongchun, Email: xingyunerliu@163.com 【Abstract】 Objective To evaluate the antitumor effect of dacarbazine（DTIC）on B16-F1 melanoma after CDK2 gene silencing. Methods Cultured B16-F1 melanoma cells were divided into 4 groups: control group receiving no treatment, CDK2-shRNA group infected with a recombinant lentivirus pUL-CDK2-shRNA, DTIC group cultured in 96-well plates followed 12 hours later by the treatment with 250 μmol/L DTIC, CDK2-shRNA + DTIC group infected with pUL-CDK2-shRNA followed 12 hours later by the treatment with 250 μmol/L DTIC. MTT assay was performed to evaluate the growth inhibition of B16-F1 melanoma cells, and coefficient of drug interaction（CDI） was calculated. AnnexinV-FITC/PI double staining was conducted to detect cell apoptosis. C57BL/6 mice were subcutaneously injected with B16-F1 cells at exponential growth phase into the right groin to establish melanoma-bearing mouse models. Twenty mouse models were randomly and equally divided into 4 groups: control mouse group injected with phosphate-buffered solution（PBS） into tumors, CDK2-shRNA mouse group injected with pUL-CDK2-shRNA into tumors, DTIC mouse group injected with DTIC into the abdominal cavity, and CDK2-shRNA + DTIC mouse group treated with pUL-CDK2-shRNA and DTIC. The animal experiment lasted 18 days, and the tumor growth curve was drawn. After 18-day treatment, all the mice were sacrificed, and tumors were isolated and weighed. The tumor growth inhibition rate was calculated, and the tumor cell apoptosis was detected by terminal deoxynucleotidyl transferase-mediated dUTP nick-end-labeling（TUNEL）. Results After 72-hour culture, compared with the control group, the CDK2-shRNA group, DTIC group, and CDK2-shRNA + DTIC group showed significantly decreased relative cell survival rates （40.6% ± 2.8%, 45.2% ± 3.7%, 28.7% ± 2.1%, respectively; F = 458.04, P < 0.05）, but significantly increased cell apoptosis rates （25.1% ± 3.3%, 15.6% ± 2.2%, 45.6% ± 3.5%, respectively; F = 115.46, P < 0.05）. Additionally, CDK2-shRNA + DTIC group showed significantly lower relative cell survival rates （P < 0.01）, but higher cell apoptosis rates （P < 0.01） compared with the DTIC group. The CDI value was less than 0.7. On the sixth day after the in vivo treatment, the tumor volumes in the control mouse group, CDK2-shRNA mouse group, DTIC mouse group, and CDK2-shRNA + DTIC mouse group were（185.44 ± 68.97） mm3,（83.91 ± 14.33） mm3, （123.70 ± 20.85） mm3, and（34.54 ± 10.72） mm3 respectively. From then on, the CDK2-shRNA mouse group, DTIC mouse group, and CDK2-shRNA + DTIC mouse group showed significantly decreased tumor growth rates compared with the control mouse group （F = 11.819, P < 0.05）, and the tumor growth rate was significantly lower in the CDK2-shRNA + DTIC mouse group than in the DTIC mouse group （P = 0.04）. The calculated tumor growth inhibition rates in the CDK2-shRNA mouse group, DTIC mouse group and CDK2-shRNA + DTIC mouse group were 52.2%, 41.2% and 86.4% respectively. Compared with the control mouse group, the CDK2-shRNA mouse group, DTIC mouse group, and CDK2-shRNA + DTIC mouse group showed significantly increased tumor cell apoptosis indice （32.93% ± 3.72%, 21.62% ± 3.54%, 63.29% ± 4.74% respectively; F = 222.25, P < 0.05）. Moreover, the tumor cell apoptosis index was significantly higher in the CDK2-shRNA + DTIC mouse group than in the DTIC mouse group （P < 0.01）. Conclusion CDK2 gene silencing can enhance the inhibitory effect of DTIC on the growth of melanoma, and show a synergistic effect with DTIC, likely by increasing the apoptosis of tumor cells.