Dysregulated Amino Acid Sensing Drives Colorectal Cancer Growth and Metabolic Reprogramming Leading to Chemoresistance.

BACKGROUND & AIMS: Colorectal cancer (CRC) is a devastating disease that is highly modulated by dietary nutrients. Mechanistic target of rapamycin complex 1 (mTORC1) contributes to tumor growth and limits therapy responses. Growth factor signaling is a major mechanism of mTORC1 activation. However, compensatory pathways exist to sustain mTORC1 activity after therapies that target oncogenic growth factor signaling. Amino acids potently activate mTORC1 via amino acid-sensing GTPase activity towards Rags (GATOR). The role of amino acid-sensing pathways in CRC is unclear. METHODS: Human colon cancer cell lines, preclinical intestinal epithelial-specific GATOR1 and GATOR2 knockout mice subjected to colitis-induced or sporadic colon tumor models, small interfering RNA screening targeting regulators of mTORC1, and tissues of patients with CRC were used to assess the role of amino acid sensing in CRC. RESULTS: We identified loss-of-function mutations of the GATOR1 complex in CRC and showed that altered expression of amino acid-sensing pathways predicted poor patient outcomes. We showed that dysregulated amino acid-sensing induced mTORC1 activation drives colon tumorigenesis in multiple mouse models. We found amino acid-sensing pathways to be essential in the cellular reprogramming of chemoresistance, and chemotherapeutic-resistant patients with colon cancer exhibited de-regulated amino acid sensing. Limiting amino acids in in vitro and in vivo models (low-protein diet) reverted drug resistance, revealing a metabolic vulnerability. CONCLUSIONS: Our findings suggest a critical role for amino acid-sensing pathways in driving CRC and highlight the translational implications of dietary protein intervention in CRC.

Longitudinal Changes in Exercise Capacity in Patients Who Underwent Ross Procedure and Mechanical Aortic Valve Replacement: Does the Type of Surgery Matter?

The surgical options for significant aortic valve disease include either Ross procedure (RP) or aortic valve replacement (AVR). The exercise stress test is routinely performed in these patients to assess the objective functional capacity. This retrospective study was conducted to evaluate the differences and the longitudinal changes of exercise capacity in patients following the RP and AVR for aortic valve disease. This is an IRB approved retrospective study and included patients who had either RP or AVR performed for aortic valve disease and had at least one exercise stress test performed after the surgical procedure. Patients with other congenital heart disease, pacemaker or defibrillators, and those with inadequate data were excluded. Demographic data including age at surgery, type of surgery and type of aortic valve was collected. Data regarding treadmill cardiopulmonary exercise test (CPET) was also collected. A total of 47 patients met inclusion criteria and were equally represented in each group, i.e. RP [n = 23, 73.9% male, age at surgery 11.2 (4.5-15.9) years] vs. AVR [n = 24, 88% mechanical AVR, 60.9% male, age at surgery 15.1 (12.8-19.4) years]. There was a significant decline in predicted oxygen consumption (%VO2) at time of first post-operative CPET in patients after AVR compared to RP (79 vs. 88%, p = 0.048) over a similar accrued median interval follow-up (4.6 vs. 6.2 years, p = 0.2). The longitudinal follow-up analysis of following AVR (n = 11, 54.5% male, median inter-test duration of 5 years) showed significant decline in peak exercise capacity or VO2 (34.2 vs. 26.2 vs., p = 0.006). In contrast, after RP (n = 12 patients [58.3% male, median inter-test duration 7.1 of years], exercise capacity and other key parameters remained preserved. In this small sentinel study, we report a better initial exercise capacity among patients after RP compared to AVR over an intermediate follow-up. During longitudinal follow-up in a subset of patients, exercise capacity remained preserved amongst the RP group while it further declined in the AVR group.