Fatty acid mimetic PBI-4547 restores metabolic homeostasis via GPR84 in mice with non-alcoholic fatty liver disease

Non-alcoholic Fatty Liver Disease (NAFLD) is the most common form of liver disease and is associated with metabolic dysregulation. Although G protein-coupled receptor 84 (GPR84) has been associated with inflammation, its role in metabolic regulation remains elusive. The aim of our study was to evaluate the potential of PBI-4547 for the treatment of NAFLD and to validate the role of its main target receptor, GPR84. We report that PBI-4547 is a fatty acid mimetic, acting concomitantly as a GPR84 antagonist and GPR40/GPR120 agonist. In a mouse model of diet-induced obesity, PBI-4547 treatment improved metabolic dysregulation, reduced hepatic steatosis, ballooning and NAFLD score. PBI-4547 stimulated fatty acid oxidation and induced gene expression of mitochondrial uncoupling proteins in the liver. Liver metabolomics revealed that PBI-4547 improved metabolic dysregulation induced by a high-fat diet regimen. In Gpr84^−/− mice, PBI-4547 treatment failed to improve various key NAFLD-associated parameters, as was observed in wildtype littermates. Taken together, these results highlight a detrimental role for the GPR84 receptor in the context of meta-inflammation and suggest that GPR84 antagonism via PBI-4547 may reflect a novel treatment approach for NAFLD and its related complications.

PBI-4050 Reduces Stellate Cell Activation and Liver Fibrosis through Modulation of Intracellular ATP Levels and the Liver Kinase B1/AMP-Activated Protein Kinase/Mammalian Target of Rapamycin Pathway

Hepatic fibrosis is a major cause of morbidity and mortality for which there is currently no effective therapy. We previously showed that 2-(3-pentylphenyl)acetic acid (PBI-4050) is a dual G protein-coupled receptor GPR40 agonist/GPR84 antagonist that exerts antifibrotic, anti-inflammatory, and antiproliferative action. We evaluated PBI-4050 for the treatment of liver fibrosis in vivo and elucidated its mechanism of action on human hepatic stellate cells (HSCs). The antifibrotic effect of PBI-4050 was evaluated in carbon tetrachloride (CCl₄)- and bile duct ligation-induced liver fibrosis rodent models. Treatment with PBI-4050 suppressed CCl₄-induced serum aspartate aminotransferase levels, inflammatory marker nitric oxide synthase, epithelial to mesenchymal transition transcription factor Snail, and multiple profibrotic factors. PBI-4050 also decreased GPR84 mRNA expression in CCl₄-induced injury, while restoring peroxisome proliferator-activated receptor γ (PPARγ) to the control level. Collagen deposition and α-smooth muscle actin (α-SMA) protein levels were also attenuated by PBI-4050 treatment in the bile duct ligation rat model. Transforming growth factor-β-activated primary HSCs were used to examine the effect of PBI-4050 and its mechanism of action in vitro. PBI-4050 inhibited HSC proliferation by arresting cells in the G0/G1 cycle phase. Subsequent analysis demonstrated that PBI-4050 signals through a reduction of intracellular ATP levels, activation of liver kinase B1 (LKB1) and AMP-activated protein kinase (AMPK), and blockade of mammalian target of rapamycin (mTOR), resulting in reduced protein and mRNA levels of α-SMA and connective tissue growth factor and restored PPARγ mRNA expression. Our findings suggest that PBI-4050 may exert antifibrotic activity in the liver through a novel mechanism of action involving modulation of intracellular ATP levels and the LKB1/AMPK/mTOR pathway in stellate cells, and PBI-4050 may be a promising agent for treating liver fibrosis.

Abstract 672: PBI-1402, a first-in-class erythropoiesis regulating agent, inhibits tumor growth and metastasis of murine mastocytoma and does not overshoot hemoglobin: Comparison with erythropoietin

BACKGROUND: PBI-1402 reduces the need for transfusion and increases hemoglobin (Hb) level and red blood cell count (RBC) in chemotherapy-induced anemia (CIA) by a mechanism of action distinct from erythropoietin (EPO).

AIM: The objective was to compare the effect of PBI-1402 and EPO on modulation of tumor growth.

METHODS: The effect of PBI-1402 (200 mg/kg, oral, once a day) or EPO (200 or 2000 U/kg, s.c. injection, twice a week) was studied in a subcutaneous P815 mastocytoma model. P815 cells express both PBI-1402 and EPO receptors. Tumor growth, metastasis, serum nitric oxide (NO) and hematocrit (Ht) were assessed.

RESULTS: P815 tumor growth is rapid and metastasizes to the liver. Inflammation is also associated with P815 tumor growth. PBI-1402 significantly reduced tumor growth (T/C=37%) and invasion as demonstrated by a 33% reduction of mice with liver metastasis. In comparison, EPO had no effect (200 U/kg, equivalent dose used in CKD treatment). However, high dose EPO (2000 U/kg, equivalent dose used in human cancer treatment) exacerbated tumor growth (T/C: 135%). Both doses of EPO induced a significant increase in the percentage of mice with liver metastasis (2X, 200 U/kg, and 3X, 2000 U/kg) compared to control. PBI-1402 treatment had no effect on NO and did not overshoot normal hematocrit. However, treatment with high dose EPO significantly increased NO and Ht levels (Table 1).

CONCLUSION: These results suggest that oral treatment with PBI-1402 may inhibit growth and metastasis of cancer cells. As an important safety feature, PBI-1402 does not induce overshoot of hemoglobin. In contrast to EPO, PBI-1402 may offer the advantage of reducing tumor growth and metastasis while preventing anemia induced by chemotherapy. In conclusion, PBI-1402 has the potential to be a safe erythropoiesis-regulating agent useful in treating anemia in cancer patients.

Abstract 3534: PBI-1402, a first-in-class erythropoiesis regulating agent, possesses differentiation properties and demonstrates synergistic anticancer activity in combination with chemotherapy

Background: PBI-1402 reduces the need for transfusion and increases hemoglobin (Hb) level and red blood cell count (RBC) in chemotherapy-induced anemia (CIA) patients by a mechanism of action which is distinct from erythropoietin (EPO). The PBI-1402 receptor is also expressed on certain cancer cells such as leukemia (K562), lung (LL-2), prostate (PC-3) and pancreas (Panc-02).

Aim: The objective of this study was to determine the role of the PBI-1402 receptor on tumor growth.

Methods: Cell proliferation and differentiation of K562 (human erythroleukemia) was studied in presence of PBI-1402 or EPO using 2,7-diaminofluorene for hemoglobin quantification. The effect of oral administration of PBI-1402 in combination with chemotherapy agents (gemcitabine or cyclophosphamide) was studied in subcutaneous syngeneic Panc02, LL-2 and xenogeneic PC-3 models.

Results: PBI-1402 inhibits proliferation of K562 cells and promotes differentiation of the remaining cells. K562 cells express both EPO and PBI-1402 receptors. EPO increases phosphorylation of ERK1/2 and Stat3 (linked to cell proliferation) while PBI-1402 decreases it in a dose dependent manner. The antitumor efficacy of oral administration of PBI-1402 was studied in combination with gemcitabine in subcutaneous LL2 and Panc02 as well as in orthotopic Panc02 cancers. In subcutaneous Panc02, gemcitabine induced a significant inhibition (p<0.05) of tumor growth from day 27 to 34 with T/C from 55% to 78%. PBI-1402 induced a significant inhibition (p<0.05) of tumor growth from day 23 to 44 with T/C from 26% to 58%. The combination therapy induced a significant (p<0.05) inhibition of tumor growth and T/C<40% from day 23 to 37 when compared to control and at day 23, 25 and 30 to 39 when compared to gemcitabine alone. In orthotopic Panc02, mice treated with gemcitabine or a combination of gemcitabine and PBI-1402 displayed prolonged survival (71 and 88 days, respectively) compared to control (48 days). In LL-2 cancer, at day 25, mice treated with PBI-1402 or gemcitabine alone had a T/C of 94% and 72%, respectively. Mice treated with a combination of gemcitabine plus PBI-1402 displayed a significant (synergistic) reduction of tumor growth (T/C: 33%). The effect of PBI-1402 alone or in combination with cyclophosphamide was also studied in a xenograft prostate PC-3 tumor. Mice treated with PBI-1402 or cyclophosphamide alone have a significant T/C<40% from day 21 to 56 and day 35 to 56, respectively. Mice treated with a combination of cyclophosphamide plus PBI-1402 displayed tumor regression from day 21 to 56.

Conclusion: These results suggest that PBI-1402 has the potential to inhibit the growth of lung, prostate and pancreatic cancer by induction of cell differentiation. PBI-1402-differentiated cancer cells appear to be more susceptible to chemotherapeutic agents.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3534. doi:10.1158/1538-7445.AM2011-3534