Abstract

Introduction: Drug resistance in cancer becomes a barrier to cancer cure and they are insensitive towards a drug, which requires patients to change to a new set of treatments. It was reported that minor pre-existing drug resistance is present in patients during diagnosis. Although changing treatment options is the only way to eradicate drug-resistant cells, a new theory called Adaptive Therapy (AT) focuses on survival competition between sensitive and resistant cells in treatment-free period. During this period, sensitive cells will outgrow resistant cells for space. Thus, AT possesses the potential to delay the emergence of resistance. This in vitro study was done with sensitive and resistant non-small cell lung cancer (NSCLC) cell lines against afatinib. Continuous (96 hours exposed) and intermittent treatment (24 hours, followed by a 72-hour treatment-free period) in a direct co-culture of 0.1% and 0.5% resistance cells. Methods: Separate cell viability assays over 96 hours for sensitive and resistant NSCLC cell lines were evaluated. Cell counting was done at 96- and 192-hours of experiment and quantitative PCR (qPCR) with specific primers against sensitive and resistant cells was performed to determine the remaining population. Results: The sensitive cell line has a lower IC₅₀ value than the resistance cell line (0.3 nM against 300 nM). At 96- and 192-hours, concentrations at 1.0 and 2.0 nM showed higher cell counts for intermittent than continuous by 5000 cells, and qPCR showed gene expression of resistance cells are higher than sensitive cells. Conclusion: This preliminary study showed that AT was not able to be established to delay the emergence of NSCLC resistance in vitro. One of the shortcomings is that the resistant cells proliferate 24 hours faster than sensitive cells, and this does not reflect the reported scenario in patients and opposes one of the parameters to achieve AT. Thus this study gave resistant cells the advantage to be dominant.

Keywords: Drug resistance, Continuous therapy, Adaptive therapy, Non-small cell lung cancer