Light during darkness, melatonin suppression and cancer progression

Area of Science:

• Oncology
• Endocrinology
• Chronobiology

Background:

• Melatonin's nocturnal surge acts as an oncostatic signal against ER+ liver and breast cancers.
• Cancer progression is linked to linoleic acid (LA) uptake and its metabolism to 13-HODE.
• LA metabolism amplifies growth factor pathways, promoting cell proliferation.

Purpose of the Study:

• To investigate the impact of light exposure during darkness on melatonin's oncostatic effect.
• To determine if light-induced melatonin suppression affects tumor growth and LA metabolism.

Main Methods:

• Studies involved tissue-isolated rat hepatoma 7288CTC, ER+ MCF-7 human breast cancer xenografts, and NMU-induced rat mammary cancers.
• Animals were exposed to constant bright light, dim light during darkness, or a standard 12L:12D photoperiod.
• Tumor growth, melatonin levels, LA uptake, and 13-HODE production were measured.

Main Results:

• Light exposure during darkness significantly reduced melatonin levels.
• Suppressed melatonin correlated with increased tumor growth, LA uptake, and 13-HODE production.
• These effects were observed in both male and female rats across different cancer models.

Conclusions:

• Light exposure during the dark phase eliminates the nocturnal melatonin signal.
• This elimination promotes cancer progression by increasing tumor LA uptake and 13-HODE production.
• Disrupting the nocturnal melatonin signal via light exposure increases cancer risk.