Cellular retinol-binding proteins in head and neck tumors and their adjacent tissues

PARG inhibition limits HCC progression and potentiates the efficacy of immune checkpoint therapy

BACKGROUND & AIMS

Although the treatment of hepatocellular carcinoma (HCC) has been revolutionized by the advent of effective systemic therapies, the prognosis of patients with HCC remains dismal. Herein, we examined the pathophysiological role of PARG and assessed the utility of targeting dePARylation for HCC therapy.

METHODS

The oncogenic function of PARG was evaluated in 2 orthotopic xenograft models and a Parg^flox/flox mice model. The therapeutic efficacy of PARG inhibitors in combination with an anti-PD-1 antibody were assessed in murine orthotopic models. Microarray analysis was used to evaluate the pathological relevance of the PARG/DDB1/c-Myc/MMR axis.

RESULTS

High PARG expression was strongly associated with poor HCC prognosis. Hepatocyte-specific PARG deletion significantly impaired liver tumorigenesis. PARG promoted HCC growth and metastasis through DDB1-dependent modulation of c-Myc. Specifically, PARG dePARylated DDB1 and consequently promoted DDB1 autoubiquitination, thus stabilizing the c-Myc protein in HCC cells. PARG downregulation attenuated c-Myc-induced MMR expression and PARG deficiency was correlated with a favorable prognosis in patients with HCC treated with anti-PD-1-based immunotherapy. In addition, PARG inhibitors could act in synergy with anti-PD-1 antibodies in orthotopic mouse models.

CONCLUSIONS

PARG can act as an oncogene in HCC by modulating PARG/DDB1/c-Myc signaling and could be used as a biomarker to identify patients with HCC who may benefit from anti-PD-1 treatment. Our findings suggest that co-inhibition of PARG and PD-1 is an effective novel combination strategy for patients with HCC.

LAY SUMMARY

The increase in deaths due to hepatocellular carcinoma (HCC) is a growing concern, with the mechanisms responsible for HCC development still incompletely understood. Herein, we identify a novel mechanism by which the protein PARG contributes to HCC development. Inhibition of PARG increased the efficacy of anti-PD-1 therapy (a type of immunotherapy) in HCC. These findings support the future clinical development of PARG inhibitors, potentially in combination with anti-PD-1 inhibitors.

Plasma-specific proteins: their response to surgical trauma and tumour load, and modification of this response by post-operative metabolic support

Concentrations of plasma proteins with short half-life have been suggested as indicators of nutritional state in surgical patients. Trauma also affects the circulating concentrations of these proteins. Serum concentrations of retinol binding protein (RBP), pre-albumin and transferrin were determined pre- and post-operatively on different supporting regimens. The circulating concentration of these liver proteins displayed no differential effect of the supporting regimen during the first 5 post-operative days. None of the patients with tumour demonstrated any indication of hepatic metastases pre-operatively or at the time of laparotomy but, as a group, had lower pre-operative concentrations of RBP (p < 0.001) and pre-albumin (p < 0.01) than patients with no tumour load. In addition 55% of patients (15:27) with tumour had RBP concentrations <3.5 mg/dl; all of the non-tumour bearing patients (13/13) had RBP concentrations >3.5 mg/dl. RBP and pre-albumin appear to act as non-specific tumour markers, but not to serve a useful function as short-term nutritional markers of post-operative support.

Levels of vitamin A and cellular retinol binding protein in human hepatocellular carcinoma and adjacent normal tissue

The levels of vitamin A (retinol) and vitamin E were measured in the blood, in tissues of human hepatocellular carcinoma (HCC), and in adjacent liver parenchyma. The median values of vitamin A were 11.5 micrograms/g (ranging 0-82.5 micrograms/g) in HCC and 52.1 micrograms/g (ranging 0.4-895.2 micrograms/g) in normal liver tissues; the difference was statistically significant (p less than 0.05). By contrast, there was no significant difference in vitamin E levels between the two tissues. Although the levels of vitamin A were significantly lower in HCC in 10 patients, no significant difference was noted in the cellular retinol binding protein levels in the normal and malignant tissues. These results suggest that the decreased levels of vitamin A in HCC are not due to altered cellular retinol binding protein levels in tumors and the different vitamin A blood supply system. We conclude that either the decreased uptake of vitamin A, but not vitamin E, by HCC cells or the lack of vitamin A-storing cells in tumors might be responsible for the low levels of vitamin A in HCC.