The mitogen-activated protein kinase (MAPK) pathway, consisting of the Ras-Raf-MEK-ERK signaling cascade, regulates genes that control cellular development, differentiation, proliferation, and apoptosis. Within the cascade, multiple isoforms of Ras and Raf each display differences in functionality, efficiency, and, critically, oncogenic potential. According to the NCI, over 30% of all human cancers are driven by Ras genes. This dysfunctional signaling is implicated in a wide variety of leukemias and solid tumors, both with and without viral etiology. Due to the strong evidence of Ras-Raf involvement in tumorigenesis, many have attempted to target the cascade to treat these malignancies. Decades of unsuccessful experimentation had deemed Ras undruggable, but recently, the approval of Sotorasib as the first ever KRas inhibitor represents a monumental breakthrough. This advancement is not without novel challenges. As a G12C mutant-specific drug, it also represents the issue of drug target specificity within Ras pathway; not only do many drugs only affect single mutational profiles, with few pan-inhibitor exceptions, tumor genetic heterogeneity may give rise to drug-resistant profiles. Furthermore, significant challenges in targeting downstream Raf, especially the BRaf isoform, lie in the paradoxical activation of wild-type BRaf by BRaf mutant inhibitors. This literature review will delineate the mechanisms of Ras signaling in the MAPK pathway and its possible oncogenic mutations, illustrate how specific mutations affect the pathogenesis of specific cancers, and compare available and in-development treatments targeting the Ras pathway.

Circadian rhythms regulate many aspects of behavior and physiological processes, and, through external signals, help an organism entrain to its environment. These rhythms are driven by circadian clocks in many cells and tissues within our bodies, and are synchronized by a central pacemaker in the brain, the suprachiasmatic nucleus. Peripheral oscillators include the liver, whose circadian clock controls persistent daily rhythms in gene expression and in liver-specific functions such as metabolic homeostasis and drug metabolism. Chronic circadian clock disruption, as in rotating shiftwork, has been linked to disorders including obesity, diabetes, and cardiovascular disease. The mouse primary hepatocyte culture model allows the examination of circadian rhythms in these cells. This article describes a transgenic mouse model that uses a bioluminescent reporter to examine the circadian properties of a core clock gene Period2. Hepatocytes are isolated using a modified collagenase perfusion technique and cultured in a sandwich configuration, then sealed in a buffered medium containing luciferin for detection of whole-culture or single-cell bioluminescence. After synchronization by a medium change, cultures demonstrate coherent circadian period and phase measures of bioluminescence from the PERIOD2::LUCIFERASE reporter.