Screening of New Anti-tumor Drugs

Anti-cancer drugs are also known as anti-neoplastic agents. They take action to quickly divide cancer cells and destroy them. They can be used alone (single-drug therapy) or once (combination therapy). At present, the main types of anti-tumor drugs include cell apoptosis inducer, tumor cytotoxic agent, cellular aging inducer, tumor resistance reversal agent, cell differentiation inducer, tumor chemopreventive agent and tumor metastasis inhibitor. The main sources of anticancer drugs are: effective substances in natural products, synthesis of new chemical substances, emergence of biotherapeutic drugs and new uses of old drugs.

Screening for drugs is a means of discovering new drugs. It is critical to choose screening system after screening the targets. After decades of continuous improvement, the screening of anti-tumor drugs is divided into in vivo and in vitro screening. Currently, substances having antitumor activity are usually screened in vitro and in vitro, and then animal models are screened. In vitro screening is further divided into tumor cell line analysis method and molecular target analysis method. In vivo screening includes spontaneous tumors, induced tumors, and transplanted tumors.

Screening in vitro

• Tumor cell line analysis

Antitumor effects were analyzed by in vitro action using established representative tumor cell lines. Rapid screening of large sample drugs is particularly suitable for the screening of cytotoxic antitumor active substances that can penetrate cell membranes. However, its mechanism of action is still unclear, the false positive rate is high, and it is not suitable for screening by indirect anti-tumor substances produced by other systems acting on the body.

Some cell lines used for in vitro screening of anticancer drugs by the National Cancer Institute are listed below:
Kidney cancer: 786-0, A498, CAKI-1, RXF-393, SN12C, TK-10, UO-31
Breast cancer: MCF-7, MCF7, HS578T, MDA-N, BT-549, T-47D
Colon cancer :COLO205, HCT-116, HCT-15, HT-29, KM12, SW-620, HCC-2998
Nervous system tumor :U-251, SNB-75, SNB-19, SF-268, SF-295, SF-539
Ovarian cancer: IGR-OV1, OVCAR-3, OVCAR-4, OVCAR-5, OVCAR-8, SK-OV-3
Prostate cancer: PC-3, DU-145
Lung cancer: A549, NCI-H226, NCI-H23, NCI-H322M, NCI-H460, NCI-H522, EKVX, HOP-62,HOP-92
Leukemia: HL-60, K562, CCRF-CEM, MOLT-4, RPMI-8226

• Molecular target analysis

Analytical studies were carried out with exact anti-tumor targets, such as tubulin, tyrosine kinase and the like. The advantage of molecular target analysis is that it can be used for drug screening of large samples, and the mechanism of action is clear and targeted. But, the required working conditions are high and costly, which is not conducive to the development of ordinary research rooms. In addition, due to the protection of intellectual property rights, pharmaceutical groups and research institutions often take confidential measures for their own molecular target analysis technology, which is not conducive to widespread application.

Screening in vivo

Drug-based screening of tumor-bearing animals indicates that many substances have strong anti-tumor activity in vitro, but they are often ineffective in vivo, and the causes are very complex. Therefore, every drug that is effective in screening in vitro must be rescreened by an animal model. However, re-screening ineffective substances often has the value of research and development. If they can understand the reasons for their inactivity in the body, they are also expected to be developed and applied. Here, we only introduce the transplanted tumors.

• Subcutaneous tumor model

The subcutaneous tumor model refers to the transplantation of human tumors into immunodeficient animals (nude mice/SCID mice) to study the sensitivity of human tumors to drugs. Subcutaneously transplanted tumor animal models are widely used in cancer research and anticancer drug development due to their simple operation and high tumor formation rate.

According to the Patrick Poulin’s method, the tissues of healthy tissues and tumors were first analyzed, and then the in vivo tissue distribution of the mice was studied. Finally, the Kp values were observed and predicted. Tissue composition analyses established the abundance of lipids and common transporter families in the human tumor xenografts to determine whether the transporter effect or binding to lipids are the predominant distribution mechanism. Finally, in vitro transport studies were performed to further analyze the predictions.

Figure 1 Predicted and observed mean Kp values for human tumor xenografts in mouse (HCT116, H2122, and PC3) for DOC, DOX, MTX, TOP, and 5-FU.⁴

• Ascites tumor model

Ascites tumors can be treated with ascites at any time after transplantation for individual observation and quantitative calculation of cells. According to the method described by Abdel-Rahman et al, venom collection and preparation were first performed, then experimental animals and cancer cell lines were established, and LD50 of co-cultured cells was determined for the third time, and finally in vitro experiments (cell survival assay, DNA extraction and fragmentation) were performed. The time to death of the animal due to the tumor is also very short. These have many advantages in research because of the great value of biological research objects and cancer treatment tests for tumors.

Figure 2 Amoreuxi venom on tumor growth (tumor cell count and viability, ascites volume and PCV) of EAC-bearing mice.⁵

• In situ seeding model

In situ vaccination model refers to inoculation of an organ-derived tumor into an animal organ, such as a human liver cancer tumor inoculated into the liver of a nude mouse. In situ vaccination is not a routine method but is particularly advantageous and is a method of encouragement, which is mainly used for lung, liver, stomach, spleen, etc.

References

• Amany Elamin, Thomas Franz, and Muntaser E Ibrahim.(2017) ‘Identification of Potential Tumor Markers in Sudanese Breast Cancer Patients Using a Proteomic Approach’, Journal of Cancer Science & Therapy, 2017: 494.

• Imen Kahouli, Meenakshi Malhotra, Moulay Alaoui-Jamali and Satya Prakash. (2015) ‘In-Vitro Characterization of the Anti-Cancer Activity of the Probiotic Bacterium Lactobacillus Fermentum NCIMB 5221 and Potential against Colorectal Cancer’, Journal of Cancer Science & Therapy, 2015: 354.

• Silva VAO, Rosa MN, Tansini A, et al. ( 2018) ‘In vitro screening of cytotoxic activity of euphol from Euphorbia tirucalli on a large panel of human cancer-derived cell lines’, Experimental and Therapeutic Medicine, 16(2):557-566.

• Patrick Poulin, Yung-Hsiang Chen, Xiao Ding, Stephen E. Gould, Cornelis Eca Hop, Kirsten Messick, Jason Oh, Bianca M. Lederer. (2015) ‘Prediction of Drug Distribution in Subcutaneous Xenografts of Human Tumor Cell Lines and Healthy Tissues in Mouse: Application of the Tissue Composition-Based Model to Antineoplastic Drugs’, Journal of Pharmaceutical Sciences, 4(104): 1508-1521.

• Salem ML, Shoukry NM, Teleb WK, Abdel-Daim MM, Abdel-Rahman MA. (2016) ‘In vitro and in vivo antitumor effects of the Egyptian scorpion Androctonus amoreuxi venom in an Ehrlich ascites tumor model’, SpringerPlus, 5:570.

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