Detection of aberrant locomotor activity in a mouse model of lung cancer via home cage monitoring

Abstract

Introduction: Lung cancer is the first cause of cancer death in the world, due to a delayed diagnosis and the absence of efficacy therapies. KRAS mutation occurs in 25% of all lung cancers and the concomitant mutations in LKB1 determine aggressive subtypes of these tumors. The improvement of therapeutical options for KRASG12C mutations has increased the possibility of treating these tumors, but resistance to these therapies has emerged. Preclinical animal models permit the study of tumors and the development of new therapies. The DVC system was used to measure circadian activity changes indicative of lung cancer progression in KRAS and KRAS-LKB1 transgenic mouse models.

Material and methods: KRAS and KRAS-LKB1 conditional transgenic animal models were bred and genotyped. The tumors were inducted using adeno-CRE-recombinase system. The mice were housed in a Digital Ventilated Cage (DVC^®) rack measuring the locomotor activity continuously for 24/7. The progression of the tumors was monitored with MRI. The DVC system evaluated a reduction in animal locomotion during the tumor progression.

Results: KRAS and KRAS-LKB1 mutations were induced, and the tumor formation and progression were monitored over time. As expected, the onset of the tumors in the two different breeds occurred at different times. DVC system registered the locomotion activity of the mice during the light and dark phases, reporting a strong reduction, mainly, in the dark phase. In KRAS-LKB1 models, the locomotion reduction appeared more pronounced than in KRAS models.

Discussions: Transgenic animal models represent a fundamental tool to study the biology of cancers and the development of new therapies. The tumors induced in these models harbor the same genotypical and phenotypical characteristics as their human counterparts. DVC methods permit a home cage monitoring system useful for tracking animal behavior continuously 24 hours a day, 7 days a week. DVC system could determine disease progression by monitoring a single animal activity in a cage and also using group-housed animals. For these reasons, the DVC system could play a crucial role in identifying diseases at early stages and in testing new therapeutic approaches with a higher likelihood of efficacy.

Keywords: KRAS/LKB1; MRI; NSCLC; biomarker; home cage monitoring; locomotion; transgenic animal models; translational models.

Figure 1

Cross-section of MRI analysis of the lungs from KRAS/LKB1 mutated mice. The arrows show the presence of nodules. Images were acquired weekly for 4 weeks, showing the progression of lesions over time. The arrows indicate the presence of nodules in the lungs. This scan was derived only from KRAS/LKB1 mice. The first scan was referred to T0. The scan in the middle was referred to T1. The last scan was referred to T2.

Figure 2

Frontal-section of MRI analysis of the lungs from KRAS/LKB1-mutant mice and KRAS-mutant mice. Images were captured 55 days after the initiation of DVC analysis. The arrows indicate the presence of nodules in the lungs. These scans were performed for both genotypes. The scans A–D were derived from KRAS/LKB1 mice. The last two scans (E, F) were derived from KRAS-mutated mice.

Figure 3

Daily activity of all the cages (KRAS/LKB1 and KRAS) in light and dark conditions. Each panel depicts daily average activity across 81 days, in cages of KRAS/LKB1 and KRAS mice. KRAS/LKB1 mutated mice started the measurement after about 28 days from the birth, while KRAS mice started the measurement after about 60 days from the birth. The blue lines show the activity during the dark phase, while the green lines represent activity during the light phase. The dashed orange line and axis represents the number of animals inside the cage, which changed over time.

Figure 4

Average weekly activity normalized per cage density. Average weekly normalized activity (± SD) over light (left panel) and dark (right panel) phases across 11 weeks of observation and between two genotypes. N of cages per group: KRAS/LKB1 = 5, KRAS = 3.

Figure 5

Coefficients of the Linear Regression analysis of daily activity over time during weeks 8-11. Slope of the linear regression computed for the day and night time daily activity points in weeks 8-11. N of cages per group: KRAS/LKB1 = 5, KRAS = 2.