Summary of Primary Culture of Human Lung Cancer Cells

Review Article

Austin J Cancer Clin Res. 2018; 5(1): 1083.

Summary of Primary Culture of Human Lung Cancer Cells

Dai Y¹, Guo S¹, Huang S¹, Zhang J² and Zhang Z²*

¹Second Clinical College, Guangzhou Medical University, China

²Radiology Department, The Second Affiliated Hospital of Guangzhou Medical University, China

*Corresponding author: Zhenfeng Zhang, Radiology Department, Guangzhou Medical University, Haizhuqu District, Guangdong, China

Received: October 25, 2018; Accepted: November 28, 2018; Published: December 05, 2018

Abstract

Lung cancer is one of malignant tumors in the world with the highest morbidity and mortality [1]. Individualized treatment of lung cancer depends on the establishment of primary lung cancer cell lines. Primary cell culture of lung cancer has been studied for more than 30 years, but the success rate is still very low. This article reviews the research on primary culture of lung cancer cells both at home and abroad. The methods of isolation, purification, biological characterization and culture of lung cancer cells were discussed respectively. By comparing the advantages and disadvantages of different primary culture schemes, we hope to get the Enlightenment of better scheme and provide reference value for clinical and cell research.

Keywords: Lung cancer; Methods of primary culture

Introduction

The isolation of lung cancer cells

The use of isolation methods for lung cancer cells will roughly determine the rate of obtaining lung cancer cells, which will be helpful to the purification of lung cancer cells at later stage and the purpose test of relevant cell lines. With regard to the isolation of lung cancer cells, taking into account the simplicity associated with the experiment and the cost of the experiment, the basic method has been continuously adopted by the vast number of experimenters and continue to improve from the more traditional method of direct separation to the collagenase perfusion method created by Seglen. In the following passage, some reasonable improvement experiments will be explained on the basis of the general method.

Non-enzymatic digestion: Direct separation: The direct separation method refers to the general mechanical method to separate the cells in the animal tissue mass and to separate the target cells from the target cells by the appropriate mechanical method. Shearing, oscillating and pressing are often used to disperse the tissue and cells, and centrifugation is used to separate the cells. In the experiment of lung cancer cell separation, the direct separation method will face the defect of low acquisition rate (the direct death of the target cell in mechanical separation), but the cost of the direct separation method is lower and the operation is simpler.

The tissue mass culture: Tissue block culture is one of the methods of cell culture, but it can also be used as an effective method for cell separation because of the migration of non-target cells from the tissue mass in the process of tissue mass culture [2]. According to some operational differences, it mainly includes reverse drying and thin layer culture.

Reverse drying: The obtained tissue was cut into tissue blocks about the size of 1mm³, washed with PBS buffer for 3 times and transferred to the culture bottle at a certain distance. The culture bottle was flipped gently to prevent the tissue mass from sliding, and the culture medium was added to the non-cell growth surface of the culture bottle. Plug the bottle and place it in a 37ºC incubator for 2-3 hours to dry up the small pieces. After taking out the bottle, open the bottle and hold the culture bottle 46 degrees diagonally, gently inject a small amount of culture fluid into the bottom foot of the bottle, then slowly turn the culture bottle over and start the culture. With the increase of cell value, the medium can be added appropriately.

Thin layer culture: The obtained tissue was cut into tissue blocks about the size of 1mm³ and washed with PBS buffer for 3 times and transferred to the culture bottle at a certain distance. After 30 minutes, fresh 2.0 mL medium was injected slowly. Culture the tissue in 37ºC incubator without floating, and replace the new medium every 2-3 days.

Enzyme digestion: Collagenase digestion: Luo Mingzhi systematically divided collagenase conversion methods into three categories: two-step in situ collagenase perfusion method [3], direct collagenase digestion method and semi-in-situ perfusion method. At the same time, the advantages of Polyvinylpyrrolidone (PVP) in the separation of cell mass formed by single cell aggregation are also described. However, in the separation experiment of lung cancer cells, because of the different materials, the corresponding collagenase conversion method is also different. The following is the general method for the isolation of lung cancer cells from lung cancer tissue.

Lung cancer tissue obtained from biopsy is an important source for lung cancer related experiments. About 1 cm3 of lung cancer tissue without necrosis was taken and immediately put into frozen 1640 medium with appropriate concentration of penicillin G and streptomycin to ensure the activity of tissue mass cells. After being transported to the laboratory and removed blood clots, the blood clots were washed with PBS buffer for 2 times, cut into tissue blocks of 1mm³ size, digested with collagenase, bathed in water at 37ºC for one hour, passed through 38 μm sieve to obtain cell suspensions, washed twice, and centrifuged. The cells obtained from the supernatant are diluted into cell suspensions. Perco could also be used for further purification.

Collagenase digestion could simulate the cellular environment. The damage of tissue treated by collagenase is limited and reversible in the process of digesting the stroma of the cells, compared with the conventional mechanical treatment.

The survival rate of the cells treated with this method is greatly improved, and thus the rate of lung cancer cell acquisition will also be increased.

The use of other enzymes: Joseph Seo [4] raised the problem of using enzymes to isolate lung cancer cells. They used many enzymes, such as collagenase, disperse enzyme, trypsin, and so on, but the results were not satisfactory, because it was difficult to get a single cell population after enzyme treatment. In their conclusion, they pointed out two shortcomings:

• The separation of simple cancer cells from fibroblasts was treated only by dissipating enzymes, but a large number of fibroblasts still remained on the disk.

• Trypsin-EDTA simultaneously isolated peripheral fibroblasts with a long time.

Purification methods and biological characters detection of primary lung cancer cells

Purification method of primary lung cancer cells: No matter which method is used to isolate lung cancer cells, there is a problem of lung cancer cell purification, mainly to remove fibroblasts [5]. In primary culture, the elimination of fibroblasts is one of the keys to the success of lung cancer cell culture.

A study indicates [4] that media containing serum or growth factors promote the growth of fibroblasts, making it difficult to purify the required cell population in the co-culture state. H. Baillie- Johnson et al. [6] cultured Small Cell Lung Cancer (SCLC) cell lines and found that when these fibroblasts began to overgrow, to transfer specimens growing in HITES+2.5% FCS to separate HITES alone for some period of time could inhibit fibroblast growth. PingWang et al. [7] found that the culture medium of Defined Keratinocyte-Serum Free Medium (DK-SFM) did support the selective growth of typical epithelial cells and significantly inhibited the growth of fibroblasts coexisting. Joseph Seo et al. [4] indicated that replacing serum with N2 supplements prevented fibroblast proliferation while allowing lung cancer cells to grow. As a result, the N2-supplemented was superior in purification while the BEI medium of 10% FBS was the first-rank culture medium in proliferation.

Most studies are based on the method of trypsin enzymatic digestion and differential attachment to isolate and purify fibroblasts by, so as to purify cancer cells [8]. For example, according to the characteristics that tumor cells are slower than fibroblasts to adhere to the wall, the cell suspensions containing the two types of cells are repeatedly adhered to the wall of dish with nutrient solution without serum, so that the two types of cells separated from each other. The general method of operation is similar to that of cell passage. 1) When the cells have grown to a certain amount, the medium is inhaled. Then digest with 0.25% trypsin/EDTA and observe with microscope. When the fibrocytes have been shed, the digestion is terminated by adding one times the volume of trypsin to the medium. Epithelioid cells continue to adhere to the medium. Wash twice with PBS, add serumfree Most studies are based on the method of trypsin enzymatic digestion and differential attachment to isolate and purify fibroblasts by, so as to purify cancer cells [8]. For example, according to the characteristics that tumor cells are slower than fibroblasts to adhere to the wall, the cell suspensions containing the two types of cells are repeatedly adhered to the wall of dish with nutrient solution without serum, so that the two types of cells separated from each other. The general method of operation is similar to that of cell passage. 1) When the cells have grown to a certain amount, the medium is inhaled. Then digest with 0.25% trypsin/EDTA and observe with microscope. When the fibrocytes have been shed, the digestion is terminated by adding one times the volume of trypsin to the medium. Epithelioid cells continue to adhere to the medium. Wash twice with PBS, add serumfree medium and blow to make cell suspension; 2) Fetch three tissue culture flasks, named separately from A to C; first, the suspension is inoculated in A culture bottle. After half an hour of static culture in the incubator chamber, gently tilt the culture bottle, let the liquid concentrate in the bottle corner, slowly suck out all the culture liquid, and then inoculate it into the B culture bottle. Add a little of the complete culture solution to bottle A and maintain the culture in the incubator chamber. 3) After half an hour of cell culture in B bottle, the culture solution is poured into bottle C in the way of treating bottle A. Then add complete culture solution to bottle B. When all three bottles contain the medium, the culture s continued in the incubator. If the operation is successful, the next day’s observation shows that bottle A is mainly fibroblasts bottle B is mixed with two types of cells, and bottle C is probably mainly cancer cells. If necessary, it can be repeatedly treated until the cancer cell purification.

In addition, some studies use anti-fibroblast columns to isolate fibroblasts [9].

On the other hand, the study by HirokoEndo et al. [10] also demonstrated that using the CTOS (Cancer Tissue-Originated Spheroid) method could obtain primary lung tumor cells of high viability and purity compared with conventional culture methods. CTOS could be a new platform for the study of lung cancer biology. However, it is still necessary to optimize the tissue separation protocol to improve the preparation of CTOS from tiny tissue samples of lung cancer.

Biological characters detection of primary lung cancer cells

Identification of lung cancer cells: Due to the heterogeneity and variability of tumor cells [11], every cancer patient needs to be seen as an individual with a unique disease. In order to achieve an effective individualized strategy in clinical practice, it is important to elucidate the biological behavior characteristics of individual lung cancer cells. In general, the characteristics of lung cancer cells are analyzed and identified to evaluate whether the cells had the main characteristics of tumor cells by means of routine light microscopy, H&E (hematoxylineosin) staining, immunocytochemistry, immunohistochemistry, nude mice xenograft model and soft agarose assay [8,12]. After repeated cell passage, the characteristics of primary lung cancer cells can be altered. Therefore, it is best to describe the biological characteristics of lung cancer cells in early generations.

David P. Kodack et al. [9] developed an immunofluorescence analysis method to identify NSCLC cells in mixed culture using a mixture of cytokeratin 8 and cytokeratin 18 monoclonal antibodies. In addition, they found that exogenous EGF and insulin could reduce the sensitivity of EGFR mutant and ALK-translocated NSCLC cells to EGFR or ALK inhibitors respectively. Therefore, it was essential to remove them from the culture medium before drug sensitivity analysis.

Zengli Zhang et al. [13] established long-term cultivation conditions of Patient-Derived Tumor Spheroid (PDS), which allowed the cytological features and markers of primary tumors to be recapitulated. The PDS established by 3D culture were shown by H&E staining to be tumor cells with high nuclear-cytoplasmic ratios, hyper chromatic nucle and irregular nuclear membrane. Immunostaining showed that their PDS cultures all stained positive for lung tumor marker TTF-1, confirming the origin of adenocarcinoma of the tumor. HE and immunohistochemical staining of multigenerational PDS in their culture also showed that the cytological characteristics of tumor cells remained stable and the clinical markers were consistently retained with serial passaging. In the future, they will conduct further studies on the comprehensive characterization of gene expression profiles and mutations in tumor spheres derived from patients to prove that the model can also generalize the molecular and genetic diversity of NSCLC tumors. The Asian patient-specific NSCLC study is also expected to be carried out.

Citation: Dai Y, Guo S, Huang S, Zhang J and Zhang Z. Summary of Primary Culture of Human Lung Cancer Cells. Austin J Cancer Clin Res. 2018; 5(1): 1083.