Utility of the Ba/F3 Cell System for Exploring On‐target Mechanisms of Resistance to Targeted Therapies for Lung Cancer

The development and approvals of targeted drugs have improved treatment outcomes of patients with NSCLC harboring driver mutations. This progress in oncology is encouraging; however, mechanistic analyses of acquired resistance to these targeted drugs is necessary to further improve patient outcomes. The Ba/F3 cell model is useful to validate the oncogenic roles of these mutations. Furthermore, exploratory studies using Ba/F3 cells with N‐ethyl‐N‐nitrosourea (ENU) mutagenesis will be beneficial to comprehensively detect mutations that could promote resistance to targeted drugs.

Basics of BA/F3 Cells as a Tool to Generate Oncogene‐Dependent Cell Line Models

Ba/F3 is a murine, IL‐3‐dependent, pro‐B cell line, which is a popular system that can resolve the limited availability of lung cancer patient‐derived cells with rare driver mutations. Ba/F3 cells have served as an important tool for oncology research because the removal of IL‐3 causes loss of viability. Ba/F3 cells can grow in the presence of 5 ng/mL IL‐3 with a doubling time of 8 hours. Introduction of a driver gene mutation can render Ba/F3 cells independent of IL‐3 but dependent on the introduced driver gene. Therefore, this simple oncogene dependency creates a straightforward tool for testing the sensitivity of Ba/F3 cells to molecular targeted drugs.

Figure 1. Ba/F3 model and lung cancer cell lines as tools for mechanistic analysis of resistance to molecular targeted drugs.

However, it should be noted that Ba/F3 models have some limitations that should be considered when we evaluate the results obtained from Ba/F3 experiments. First, it is usually difficult to control the expression level (as well as the introduced gene copy number) of the transfected driver gene. Second, because only a single driver mutation is usually introduced into Ba/F3 cells, the established Ba/F3 clone does not carry the WT allele of the driver gene. Third, because Ba/F3 cells do not have innate human genes, it is impossible to evaluate the impacts of heterodimers between introduced oncogenes and other RTKs (for example, EGFR is reported to form heterodimers with other ERBB members such as ERBB3). However, it should be mentioned that the requirement of homodimerization can be evaluable using Ba/F3 models; for example, using NIH‐3T3 cells and Ba/F3 cells, a previous study reported that EGFR L858R mutant required homodimerization for activation but EGFR exon 19 deletion, exon 20 insertion, and L858R/T790M did not require homodimerization.

BA/F3 Cells as a Tool to Identify On‐Target Acquired Resistance Mechanisms

Exposure of transfected Ba/F3 cells to increasing concentrations of molecular targeted drugs will often result in the development of drug resistance. The use of ENU can facilitate and shorten the process of resistance induction. One of the first applications of Ba/F3 cells for identifying secondary resistance mutations was reported by Ercan et al who used ENU mutagenesis and identified an EGFR C797S mutation as a mechanism of osimertinib resistance. Furthermore, Katayama et al used Ba/F3 cells to identify secondary ROS1 mutations that could cause crizotinib or ceritinib resistance.

BA/F3 Cells as a Tool to Explore Novel Agents to Overcome On‐Target Resistance

The Ba/F3 cell model is also useful to examine the roles of secondary mutations with unknown significance that are found in TKI‐refractory patient specimens. Ba/F3 cell lines can be produced with any driver or secondary (or tertiary) mutation and used to evaluate the efficacy of drugs. In the field of lung cancer research, Ba/F3 cells were first used for this purpose, that is, to confirm that the EGFR T790M secondary mutation conferred acquired resistance to gefitinib, a 1G‐EGFR‐TK. Ba/F3 cells with secondary mutations can be used to explore novel TKIs that can overcome drug resistance.

Reference:

Koga T.; et al. Utility of the Ba/F3 cell system for exploring on‐target mechanisms of resistance to targeted therapies for lung cancer. Cancer science, 2022, 113(3): 815.

* For research use only. Not intended for any clinical use.

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Utility of the Ba/F3 Cell System for Exploring On‐target Mechanisms of Resistance to Targeted Therapies for Lung Cancer

Basics of BA/F3 Cells as a Tool to Generate Oncogene‐Dependent Cell Line Models

BA/F3 Cells as a Tool to Identify On‐Target Acquired Resistance Mechanisms

BA/F3 Cells as a Tool to Explore Novel Agents to Overcome On‐Target Resistance

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