Robert Chin

Heart-type Fatty Acid-binding Protein Is Essential for Efficient Brown Adipose Tissue Fatty Acid Oxidation and Cold Tolerance

Brown adipose tissue has a central role in thermogenesis to maintain body temperature through energy dissipation in small mammals and has recently been verified to function in adult humans as well. Here, we demonstrate that the heart-type fatty acid-binding protein, FABP3, is essential for cold tolerance and efficient fatty acid oxidation in mouse brown adipose tissue, despite the abundant expression of adipose-type fatty acid-binding protein, FABP4 (also known as aP2). Fabp3−/− mice exhibit extreme cold sensitivity despite induction of uncoupling and oxidative genes and hydrolysis of brown adipose tissue lipid stores. However, using FABP3 gain- and loss-of-function approaches in brown adipocytes, we detected a correlation between FABP3 levels and the utilization of exogenous fatty acids. Thus, Fabp3−/− brown adipocytes fail to oxidize exogenously supplied fatty acids, whereas enhanced Fabp3 expression promotes more efficient oxidation. These results suggest that FABP3 levels are a determinant of fatty acid oxidation efficiency by brown adipose tissue and that FABP3 represents a potential target for modulation of energy dissipation.

High-throughput profiling of influenza A virus hemagglutinin gene at single-nucleotide resolution

Genetic research on influenza virus biology has been informed in large part by nucleotide variants present in seasonal or pandemic samples, or individual mutants generated in the laboratory, leaving a substantial part of the genome uncharacterized. Here, we have developed a single-nucleotide resolution genetic approach to interrogate the fitness effect of point mutations in 98% of the amino acid positions in the influenza A virus hemagglutinin (HA) gene. Our HA fitness map provides a reference to identify indispensable regions to aid in drug and vaccine design as targeting these regions will increase the genetic barrier for the emergence of escape mutations. This study offers a new platform for studying genome dynamics, structure-function relationships, virus-host interactions, and can further rational drug and vaccine design. Our approach can also be applied to any virus that can be genetically manipulated.

Diet1 Functions in the FGF15/19 Enterohepatic Signaling Axis to Modulate Bile Acid and Lipid Levels

We identified a mutation in the Diet1 gene in a mouse strain that is resistant to hyperlipidemia and atherosclerosis. Diet1 encodes a 236 kD protein consisting of tandem low-density lipoprotein receptor and MAM (meprin-A5-protein tyrosine phosphatase mu) domains and is expressed in the enterocytes of the small intestine. Diet1-deficient mice exhibited an elevated bile acid pool size and impaired feedback regulation of hepatic Cyp7a1, which encodes the rate-limiting enzyme in bile acid synthesis. In mouse intestine and in cultured human intestinal cells, Diet1 expression levels influenced the production of fibroblast growth factor 15/19 (FGF15/19), a hormone that signals from the intestine to liver to regulate Cyp7a1. Transgenic expression of Diet1, or adenoviral-mediated Fgf15 expression, restored normal Cyp7a1 regulation in Diet-1-deficient mice. Diet1 and FGF19 proteins exhibited overlapping subcellular localization in cultured intestinal cells. These results establish Diet1 as a control point in enterohepatic bile acid signaling and lipid homeostasis.

SREBP-2-deficient and hypomorphic mice reveal roles for SREBP-2 in embryonic development and SREBP-1c expression

Cholesterol and fatty acid biosynthesis are regulated by the sterol regulatory element-binding proteins (SREBPs), encoded by Srebf1 and Srebf2. We generated mice that were either deficient or hypomorphic for SREBP-2. SREBP-2 deficiency generally caused death during embryonic development. Analyses of Srebf2−/− embryos revealed a requirement for SREBP-2 in limb development and expression of morphogenic genes. We encountered only one viable Srebf2−/− mouse, which displayed alopecia, attenuated growth, and reduced adipose tissue stores. Hypomorphic SREBP-2 mice (expressing low levels of SREBP-2) survived development, but the female mice exhibited reduced body weight and died between 8 and 12 weeks of age. Male hypomorphic mice were viable but had reduced cholesterol stores in the liver and lower expression of SREBP target genes. Reduced SREBP-2 expression affected SREBP-1 isoforms in a tissue-specific manner. In the liver, reduced SREBP-2 expression nearly abolished Srebf1c transcripts and reduced Srebf1a mRNA levels. In contrast, adipose tissue displayed normal expression of SREBP target genes, likely due to a compensatory increase in Srebf1a expression. Our results establish that SREBP-2 is critical for survival and limb patterning during development. Reduced expression of SREBP-2 from the hypomorphic allele leads to early death in females and reduced cholesterol content in the liver, but not in adipose tissue.

The KRAS-Variant and Cetuximab Response in Head and Neck Squamous Cell Cancer: A Secondary Analysis of a Randomized Clinical Trial.

Importance There is a significant need to find biomarkers of response to radiotherapy and cetuximab in locally advanced head and neck squamous cell carcinoma (HNSCC) and biomarkers that predict altered immunity, thereby enabling personalized treatment. Objectives To examine whether the Kirsten rat sarcoma viral oncogene homolog (KRAS)–variant, a germline mutation in a microRNA-binding site in KRAS, is a predictive biomarker of cetuximab response and altered immunity in the setting of radiotherapy and cisplatin treatment and to evaluate the interaction of the KRAS-variant with p16 status and blood-based transforming growth factor &bgr;1 (TGF-&bgr;1). Design, Setting, and Participants A total of 891 patients with advanced HNSCC from a phase 3 trial of cisplatin plus radiotherapy with or without cetuximab (NRG Oncology RTOG 0522) were included in this study, and 413 patients with available samples were genotyped for the KRAS-variant. Genomic DNA was tested for the KRAS-variant in a CLIA-certified laboratory. Correlation of the KRAS-variant, p16 positivity, outcome, and TGF-&bgr;1 levels was evaluated. Hazard ratios (HRs) were estimated with the Cox proportional hazards model. Main Outcomes and Measures The correlation of KRAS-variant status with cetuximab response and outcome, p16 status, and plasma TGF-&bgr;1 levels was tested. Results Of 891 patients eligible for protocol analyses (786 male [88.2%], 105 [11.2%] female, 810 white [90.9%], 81 nonwhite [9.1%]), 413 had biological samples for KRAS-variant testing, and 376 had plasma samples for TGF-&bgr;1 measurement. Seventy patients (16.9%) had the KRAS-variant. Overall, for patients with the KRAS-variant, cetuximab improved both progression-free survival (PFS) for the first year (HR, 0.31; 95% CI, 0.10-0.94; P = .04) and overall survival (OS) in years 1 to 2 (HR, 0.19; 95% CI, 0.04-0.86; P = .03). There was a significant interaction of the KRAS-variant with p16 status for PFS in patients treated without cetuximab. The p16-positive patients with the KRAS-variant treated without cetuximab had worse PFS than patients without the KRAS-variant (HR, 2.59; 95% CI, 0.91-7.33; P = .07). There was a significant 3-way interaction among the KRAS-variant, p16 status, and treatment for OS (HR, for KRAS-variant, cetuximab and p16 positive, 0.22; 95% CI, 0.03-1.66; HR for KRAS-variant, cetuximab and p16 negative, 1.43; 95% CI, 0.48-4.26; HR for KRAS-variant, no cetuximab and p16 positive, 2.48; 95% CI, 0.64-9.65; and HR for KRAS-variant, no cetuximab and p16 negative, 0.61; 95% CI, 0.23-1.59; P = .02). Patients with the KRAS-variant had significantly elevated TGF-&bgr;1 plasma levels (median, 23 376.49 vs 18 476.52 pg/mL; P = .03) and worse treatment-related toxic effects. Conclusions and Relevance Patients with the KRAS-variant with HNSCC significantly benefit from the addition of cetuximab to radiotherapy and cisplatin, and there is a significant interaction between the KRAS-variant and p16 status. Elevated TGF-&bgr;1 levels in patients with the KRAS-variant suggests that cetuximab may help these patients by overcoming TGF-&bgr;1–induced suppression of antitumor immunity. Trial Registration clinicaltrials.gov Identifier: NCT00265941

Inadequate target volume delineation and local–regional recurrence after intensity-modulated radiotherapy for human papillomavirus-positive oropharynx cancer

PURPOSE To perform a spatial analysis of local-regional recurrences, in relation to quantitative dose distribution, among patients treated by intensity-modulated radiotherapy (IMRT) for human papillomavirus (HPV)-positive oropharyngeal cancer. METHODS AND MATERIALS The records of 107 consecutive patients who presented for consideration of re-irradiation for local-regional recurrent disease occurring in a previously irradiated field were reviewed. The original IMRT plans were retrieved for those with HPV-positive disease originating from the oropharynx, and deformable image registration was used to fuse the magnetic resonance imaging (MRI) and positron emission tomography (PET) scans obtained at recurrence to the pre-treatment planning computed tomography (CT) dataset. The recurrent tumor volume (Vrecur) was subsequently identified on axial imaging, and the dose of radiation received by Vrecur was then calculated and analyzed using dose-volume histograms. RESULTS A total of 83 recurrent lesions occurring in 50 oropharyngeal cancer patients were HPV-positive and met inclusion criteria. Using PET-defined Vrecur, thirty-three lesions were classified as in-field recurrences (40%), 35 were marginal misses (41%), and 15 were true misses (18%). Using the MRI-defined Vrecur, thirty-seven lesions were classified as in-field recurrences (45%), 32 were marginal misses (39%), and 14 were true misses (17%). CONCLUSION A significant proportion of local-regional recurrences from HPV-positive oropharyngeal cancer represented geographical misses which possibly could have been prevented with more meticulous attention to IMRT planning. This finding has important implications with respect to ongoing attempts to de-escalate radiation dose for this disease. Our data highlight the importance of robust quality assurance with careful review of target volumes prior to the initiation of IMRT.

Prognostic significance of p16 in squamous cell carcinoma of the larynx and hypopharynx

PURPOSE To evaluate the prognostic significance of p16 expression among patients with squamous cell carcinoma of the larynx (LSCC) and hypopharynx (HSCC). METHODS The medical records of all patients with locally advanced, non-metastatic LSCC/HSCC were reviewed. p16INK4A (p16) protein expression was evaluated on pathological specimens by immunohistochemistry (IHC), and the Kaplan-Meier method was used to estimate overall survival (OS) and locoregional control (LRC). In select cases, p16 expression was correlated to high-risk and low-risk HPV genotypes using in situ hybridization (ISH). RESULTS Thirty-one patients (23 LSCC; 8 HSCC) were identified. Seventeen (54.8%) patients were p16 negative; 14 (45.2%) were p16-positive. The primary treatment modality was radiation therapy for 22 (71.0%) patients and surgery for 9 (29.0%). Nineteen (61.3%) patients were evaluated for high-risk HPV and low-risk HPV genotypes by IHC, of whom 2 (10.5%) patients were positive for high-risk HPV and 1 (5.3%) was positive for low-risk HPV. For high-risk HPV, the positive predictive value (PPV), sensitivity, and specificity of p16 was 20.0%, 100%, and 52.9%. There was no significant difference in the 2-year actuarial rates of OS (91% vs. 64%, p=0.34) or LRC (51% vs. 46%, p=0.69) between the p16-positive and p-16 negative patients. CONCLUSION In this small cohort of 31 LSCC and HSCC patients, p16 was not a significant predictive of either LRC or OS. Furthermore, p16 was poorly correlated with HPV genotyping as identified by ISH.

Effect of daily fraction size on laryngoesophageal dysfunction after chemoradiation for squamous cell carcinomas of the larynx and hypopharynx

The purpose of this study was to determine the effect of fraction size on laryngoesophageal dysfunction among patients treated by chemoradiotherapy for laryngeal and hypopharyngeal cancer.

Hypo-fractionated stereotactic radiotherapy of five fractions with linear accelerator for vestibular schwannomas: a systematic review and meta-analysis

Vestibular schwannomas (VS) are benign tumors stemming from the eighth cranial nerve. Treatment options for VS include conservative management, microsurgery, stereotactic radiosurgery, and fractionated radiotherapy. Though microsurgery has been the standard of care for larger lesions, hypo-fractionated stereotactic radiotherapy (hypo-FSRT) is an emerging modality. However, its clinical efficacy and safety have yet to be established. We conducted a systematic review and meta-analysis of manuscripts indexed in PubMed, Scopus, Web of Science, Embase, and Cochrane databases reporting outcomes of VS cases treated with hypo-FSRT. Five studies representing a total of 228 patients were identified. Across studies, the pooled rates of tumor control, hearing, facial nerve, and trigeminal nerve preservation were 95%, 37%, 97%, and 98%. No instances of malignant induction were observed at median follow-up of 34.8 months. Complications included trigeminal neuropathy (n = 3), maxillary paresthesia (n = 1), neuralgia (n = 1), vestibular dysfunction (n = 1), radionecrosis (n = 1), and hydrocephalus (n = 1). Hypo-FSRT may be another useful approach to manage VS, but studies with extended follow-up times are required to establish long-term safety.

Re-irradiation for recurrent and second primary cancers of the head and neck

PURPOSE To evaluate a single-institutional experience with the use of re-irradiation for recurrent and new primary cancers of the head and neck. METHODS The medical charts of 80 consecutive patients who underwent re-irradiation for local-regionally recurrent or second primary head and neck cancer between November 1998 and December 2015 were analyzed. Multivariate analysis was performed using Cox proportional hazard and logistic regression to determine predictors of clinical outcomes. RESULTS Seventy-six of the 80 patients were evaluable. The median age was 57.5 (range 26.6-84.9); Intensity-modulated radiotherapy (IMRT) was used in 71 (93.4%) patients with a median dose of 60Gy. Thirty-one patients (40.8%) underwent salvage surgery before re-irradiation and 47 (61.8%) received concurrent systemic therapy. The median time interval between radiation courses was 25.3months (range 2-322months). The 2-year estimates of overall survival, progression free survival, locoregional control, and distant control were 51.0%, 31.3%, 36.8% and 68.3%, respectively. Patients who underwent salvage surgery prior to re-irradiation had significantly improved locoregional control, progression free survival, and overall survival (p<0.05, for all). On multivariate analysis, gross tumor volume (GTV) at re-irradiation and interval between radiation courses were associated with improved overall survival. Severe (grade⩾3) late complications were observed in 25 patients (32.8%). CONCLUSIONS Re-irradiation for recurrent or second primary head and neck cancer is feasible and effective in select patients with head and neck cancer. The high observed rate of treatment-related morbidity highlights the continue challenges that accompany this approach.