Can mice be trained to discriminate urine odor of conspecifics with melanoma before clinical symptoms appear?

Abstract

This study sought to determine whether mice can differentiate, through urine odors, conspecifics with melanoma in early stages, when no clinical signs are detectable, from healthy animals. Forty male mice of the B57BL6 strain were urine donors before and after orthotopic inoculation with melanoma cells. Another group (35 males and 31 females), divided into two subgroups were either tested for spontaneous preference for urine odor from donors with melanoma against urine odor of healthy conspecifics, or underwent operant conditioning training to discriminate between the two kinds of urine samples. Open-field and Y-maze tests were used initially to assess any spontaneous preference for urine of either type of donor, and subsequently a Y-maze test was used in discrimination training. During 5-minute tests, it was recorded which sample the mouse approached first, the latency to the first sniffing, the frequency of approaching, and the total duration of sniffing of each urine sample.No significant spontaneous preference for urine samples from animals with melanoma or from healthy animals was observed. However, in the open-field test, the male mice in the first trial more frequently approached the melanoma sample (P < 0.05). Mice were successfully trained to discriminate between urine samples from donors with melanoma (with or without clinical symptoms) versus urine from healthy controls (P < 0.001). Gas chromatography/mass spectrometry analyses showed that, after the inoculation of melanoma cells, the concentration of n-hexane and methylene chloride decreased, ethyl acetate and methyl cyclopentane disappeared, and acetone and 1-methyl-6,7-dioxabicyclo[3.2.1]octane appeared, in urine samples analyzed. The study demonstrated that mice can discriminate the odor of melanoma in the urine of their conspecifics even before visible clinical melanoma symptoms appear. This finding is crucial as a rationale for further studies directed toward developing a noninvasive screening method for the early detection of a cancer, based on detection of volatile organic compounds.