Antihypoxic Potentiation of Standard Therapy for Experimental Colorectal Liver Metastasis through Myo-Inositol Trispyrophosphate

Cefmetazole sodium as an allosteric effector that regulates the oxygen supply efficiency of adult hemoglobin

Allosteric effectors play an important role in regulating the oxygen supply efficiency of hemoglobin for blood storage and disease treatment. However, allosteric effectors that are approved by the US FDA are limited. In this study, cefmetazole sodium (CS) was found to bind adult hemoglobin (HbA) from FDA library (1338 compounds) using surface plasmon resonance imaging high-throughput screening. Using surface plasmon resonance (SPR), the interaction between CS and HbA was verified. The oxygen dissociation curve of HbA after CS interaction showed a significant increase in P50 and theoretical oxygen-release capacity. Acid-base sensitivity (SI) exhibited a decreasing trend, although not significantly different. An oxygen dissociation assay indicated that CS accelerated HbA deoxygenation. Microfluidic modulated spectroscopy showed that CS changed the ratio of the alpha-helix to the beta-sheet of HbA. Molecular docking suggested CS bound to HbA's β-chains via hydrogen bonds, with key amino acids being N282, K225, H545, K625, K675, and V544.The results of molecular dynamics simulations (MD) revealed a stable orientation of the HbA-CS complex. CS did not significantly affect the P50 of bovine hemoglobin, possibly due to the lack of Valβ1 and Hisβ2, indicating that these were the crucial amino acids involved in HbA's oxygen affinity. Competition between the 2,3-Diphosphoglycerate (2,3-DPG) and CS in the HbA interaction was also determined by SPR, molecular docking and MD. In summary, CS could interact with HbA and regulate the oxygen supply efficiency via forming stable hydrogen bonds with the β-chains of HbA, and showed competition with 2,3-DPG.Communicated by Ramaswamy H. Sarma.

Desulfovibrio desulfuricans and its derived metabolites confer resistance to FOLFOX through METTL3

BACKGROUND

Chemoresistance is a critical factor contributing to poor prognosis in clinical patients with cancer undergoing postoperative adjuvant chemotherapy. The role of gut microbiota in mediating resistance to tumour chemotherapy remains to be investigated.

METHODS

Patients with CRC were categorised into clinical benefit responders (CBR) and no clinical benefit responders (NCB) based on chemotherapy efficacy. Differential bacterial analysis using 16S rRNA sequencing revealed Desulfovibrio as a distinct microbe between the two groups. Employing a syngeneic transplantation model, we assessed the effect of Desulfovibrio on chemotherapy by measuring tumour burden, weight, and Ki-67 expression. We further explored the mechanisms underlying the compromised chemotherapeutic efficacy of Desulfovibrio using metabolomics, western blotting, colony formation, and cell apoptosis assays.

FINDINGS

In comparison, Desulfovibrio was more abundant in the NCB group. In vivo experiments revealed that Desulfovibrio colonisation in the gut weakened the efficacy of FOLFOX. Treatment with Desulfovibrio desulfuricans elevates serum S-adenosylmethionine (SAM) levels. Interestingly, SAM reduced the sensitivity of CRC cells to FOLFOX, thereby promoting the growth of CRC tumours. These experiments suggest that SAM promotes the growth and metastasis of CRC by driving the expression of methyltransferase-like 3 (METTL3).

INTERPRETATION

A high abundance of Desulfovibrio in the intestines indicates poor therapeutic outcomes for postoperative neoadjuvant FOLFOX chemotherapy in CRC. Desulfovibrio drives the manifestation of METTL3 in CRC, promoting resistance to FOLFOX chemotherapy by increasing the concentration of SAM.

FUNDING

This study is supported by Wuxi City Social Development Science and Technology Demonstration Project (N20201005).

Hypoxia as a potential inducer of immune tolerance, tumor plasticity and a driver of tumor mutational burden: Impact on cancer immunotherapy

In cancer patients, immune cells are often functionally compromised due to the immunosuppressive features of the tumor microenvironment (TME) which contribute to the failures in cancer therapies. Clinical and experimental evidence indicates that developing tumors adapt to the immunological environment and create a local microenvironment that impairs immune function by inducing immune tolerance and invasion. In this context, microenvironmental hypoxia, which is an established hallmark of solid tumors, significantly contributes to tumor aggressiveness and therapy resistance through the induction of tumor plasticity/heterogeneity and, more importantly, through the differentiation and expansion of immune-suppressive stromal cells. We and others have provided evidence indicating that hypoxia also drives genomic instability in cancer cells and interferes with DNA damage response and repair suggesting that hypoxia could be a potential driver of tumor mutational burden. Here, we reviewed the current knowledge on how hypoxic stress in the TME impacts tumor angiogenesis, heterogeneity, plasticity, and immune resistance, with a special interest in tumor immunogenicity and hypoxia targeting. An integrated understanding of the complexity of the effect of hypoxia on the immune and microenvironmental components could lead to the identification of better adapted and more effective combinational strategies in cancer immunotherapy. Clearly, the discovery and validation of therapeutic targets derived from the hypoxic tumor microenvironment is of major importance and the identification of critical hypoxia-associated pathways could generate targets that are undeniably attractive for combined cancer immunotherapy approaches.

Hypoxia, a Targetable Culprit to Counter Pancreatic Cancer Resistance to Therapy

Pancreatic ductal adenocarcinoma (PDAC) is the most common type of pancreatic cancer, and it is a disease of dismal prognosis. While immunotherapy has revolutionized the treatment of various solid tumors, it has achieved little success in PDAC. Hypoxia within the stroma-rich tumor microenvironment is associated with resistance to therapies and promotes angiogenesis, giving rise to a chaotic and leaky vasculature that is inefficient at shuttling oxygen and nutrients. Hypoxia and its downstream effectors have been implicated in immune resistance and could be contributing to the lack of response to immunotherapy experienced by patients with PDAC. Paradoxically, increasing evidence has shown hypoxia to augment genomic instability and mutagenesis in cancer, suggesting that hypoxic tumor cells could have increased production of neoantigens that can potentially enable their clearance by cytotoxic immune cells. Strategies aimed at relieving this condition have been on the rise, and one such approach opts for normalizing the tumor vasculature to reverse hypoxia and its downstream support of tumor pathogenesis. An important consideration for the successful implementation of such strategies in the clinic is that not all PDACs are equally hypoxic, therefore hypoxia-detection approaches should be integrated to enable optimal patient selection for achieving improved patient outcomes.

Normalization of lipid oxidation defects arising from hypoxia early posthepatectomy prevents liver failure in mouse

Surgical liver failure (SLF) develops when a marginal amount of hepatic mass is left after surgery, such as following excessive resection. SLF is the commonest cause of death due to liver surgery; however, its etiology remains obscure. Using mouse models of standard hepatectomy (sHx) (68%, resulting in full regeneration) or extended hepatectomy (eHx) (86%/91%, causing SLF), we explored the causes of early SLF related to portal hyperafflux. Assessing the levels of HIF2A with or without oxygenating agent inositol trispyrophosphate (ITPP) indicated hypoxia early after eHx. Subsequently, lipid oxidation (PPARA/PGC1α) was downregulated and associated with persisting steatosis. Mild oxidation with low-dose ITPP reduced the levels of HIF2A, restored downstream PPARA/PGC1α expression along with lipid oxidation activities (LOAs), and normalized steatosis and other metabolic or regenerative SLF deficiencies. Promotion of LOA with L-carnitine likewise normalized the SLF phenotype, and both ITPP and L-carnitine markedly raised survival in lethal SLF. In patients who underwent hepatectomy, pronounced increases in serum carnitine levels (reflecting LOA) were associated with better recovery. Lipid oxidation thus provides a link between the hyperafflux of O₂-poor portal blood, the metabolic/regenerative deficits, and the increased mortality typifying SLF. Stimulation of lipid oxidation-the prime regenerative energy source-particularly through L-carnitine may offer a safe and feasible way to reduce SLF risks in the clinic.

New potential treatment for cardiovascular disease through modulation of hemoglobin oxygen binding curve: Myo-inositol trispyrophosphate (ITPP), from cancer to cardiovascular disease

The human body is a highly aerobic organism, which needs large amount of oxygen, especially in tissues characterized by high metabolic demand, such as the heart. Inadequate oxygen delivery underlies cardiovascular diseases, such as coronary artery disease, heart failure and pulmonary hypertension. Hemoglobin, the oxygen-transport metalloprotein in the red blood cells, gives the blood enormous oxygen carrying capacity; thus oxygen binding to hemoglobin in the lungs and oxygen dissociation in the target tissues are crucial points for oxygen delivery as well as potential targets for intervention. Myo-inositol trispyrophosphate (ITPP) acts as an effector of hemoglobin, shifting the oxygen dissociation curve to the right and increasing oxygen release in the target tissues, especially under hypoxic conditions. ITPP has been successfully used in cancer studies, demonstrating anti-cancer properties due to prevention of tumor hypoxia. Currently it is being tested in phase 2 clinical trials in humans with various tumors. First preclinical evidence also indicates that it can successfully alleviate myocardial hypoxia and prevent adverse left ventricular and right ventricular remodeling in post-myocardial infarction heart failure and pulmonary hypertension. The aim of the article is to summarize the current knowledge on ITTP, as well as to determine the prospects for its potential use in the treatment of many cardiovascular disorders.

Akkermansia Muciniphila Potentiates the Antitumor Efficacy of FOLFOX in Colon Cancer

FOLFOX (oxaliplatin, fluorouracil and calcium folinate) is the first-line chemotherapy regimen for colon cancer therapy in the clinic. It provides superior efficacy than oxaliplatin alone, but the underlying mechanism remains unclear. In the present study, pharmacomicrobiomics integrated with metabolomics was conducted to uncover the role of the gut microbiome behind this. First, in vivo study demonstrated that FOLFOX exhibited better efficacy than oxaliplatin alone in colon cancer animal models. Second, 16S rDNA gene sequencing analysis showed that the abundance of Akkermansia muciniphila (A. muciniphila) remarkably increased in the FOLFOX treated individuals and positively correlated with the therapeutic effect. Third, further exploration confirmed A. muciniphila colonization significantly enhanced the anti-cancer efficacy of FOLFOX. Last, metabolomics analysis suggested dipeptides containing branched-chain amino acid (BCAA) might be responsible for gut bacteria mediated FOLFOX efficacy. In conclusion, our study revealed the key role of A. muciniphila in mediating FOLFOX efficacy, and manipulating A. muciniphila might serve as a novel strategy for colon cancer therapy.

Phase Ib dose-escalation study of the hypoxia-modifier Myo-inositol trispyrophosphate in patients with hepatopancreatobiliary tumors

Hypoxia is prominent in solid tumors and a recognized driver of malignancy. Thus far, targeting tumor hypoxia has remained unsuccessful. Myo-inositol trispyrophosphate (ITPP) is a re-oxygenating compound without apparent toxicity. In preclinical models, ITPP potentiates the efficacy of subsequent chemotherapy through vascular normalization. Here, we report the results of an unrandomized, open-labeled, 3 + 3 dose-escalation phase Ib study (NCT02528526) including 28 patients with advanced primary hepatopancreatobiliary malignancies and liver metastases of colorectal cancer receiving nine 8h-infusions of ITPP over three weeks across eight dose levels (1'866-14'500 mg/m2/dose), followed by standard chemotherapy. Primary objectives are assessment of the safety and tolerability and establishment of the maximum tolerated dose, while secondary objectives include assessment of pharmacokinetics, antitumor activity via radiological evaluation and assessment of circulatory tumor-specific and angiogenic markers. The maximum tolerated dose is 12,390 mg/m2, and ITPP treatment results in 32 treatment-related toxicities (mostly hypercalcemia) that require little or no intervention. 52% of patients have morphological disease stabilization under ITPP monotherapy. Following subsequent chemotherapy, 10% show partial responses while 60% have stable disease. Decreases in angiogenic markers are noted in ∼60% of patients after ITPP and tend to correlate with responses and survival after chemotherapy.

A novel patient-derived orthotopic xenograft (PDOX) mouse model of highly-aggressive liver metastasis for identification of candidate effective drug-combinations

Liver metastasis is a recalcitrant disease that usually leads to death of the patient. The present study established a unique patient-derived orthotopic xenograft (PDOX) nude mouse model of a highly aggressive liver metastasis of colon cancer. The aim of the present study was to demonstrate proof-of-concept that candidate drug combinations could significantly inhibit growth and re-metastasis of this recalcitrant tumor. The patient’s liver metastasis was initially established subcutaneously in nude mice and the subcutaneous tumor tissue was then orthotopically implanted in the liver of nude mice to establish a PDOX model. Two studies were performed to test different drugs or drug combination, indicating that 5-fluorouracil (5-FU) + irinotecan (IRI) + bevacizumab (BEV) and regorafenib (REG) + selumetinib (SEL) had significantly inhibited liver metastasis growth (p = 0.013 and p = 0.035, respectively), and prevented liver satellite metastasis. This study is proof of concept that a PDOX model of highly aggressive colon-cancer metastasis can identify effective drug combinations and that the model has future clinical potential.

Nano Codelivery of Oxaliplatin and Folinic Acid Achieves Synergistic Chemo-Immunotherapy with 5-Fluorouracil for Colorectal Cancer and Liver Metastasis

FOLFOX, the combinational strategy of folinic acid (FnA), 5-fluorouracil (5-Fu), and oxaliplatin (OxP), has been used as standard treatment of colorectal cancer (CRC) for decades. Despite the improved survival, patients still suffer from drawbacks such as low efficacy, high toxicity, and long course of treatment. New strategies to address these issues are needed to further clinical benefits. In this study, a nanoprecipitate (C₂₆H₃₅N₉O₇Pt) was formed by the active form of OxP ([Pt(DACH)(H₂O)₂]²⁺) and FnA, which was formulated into an aminoethyl anisamide targeted PEGylated lipid nanoparticle within microemulsions using nanoprecipitation technique. The resultant formulation (namely Nano-Folox) significantly promoted the blood circulation and tumor accumulation of platinum drug and FnA in an orthotopic CRC mouse model. Emerging evidence indicates that OxP can not only provide anticancer cytotoxic effects but also induce immunogenic cell death (a type of apoptosis that primes anticancer immune responses). Consequently, Nano-Folox demonstrated favorable chemo-immunotherapeutic activities in orthotopic CRC mice. In addition, when compared to FOLFOX the significantly stronger chemo-immunotherapeutic responses were achieved by the combination of Nano-Folox and 5-Fu without showing toxicity. Moreover, the anti-PD-L1 monoclonal antibody enhanced Nano-Folox/5-Fu for decreased liver metastases in mice. These results indicate the potential of Nano-Folox-based combination strategy for the treatment of CRC.

Remembering the Host in Tuberculosis Drug Development

New therapeutics to augment current approaches and shorten treatment duration are of critical importance for combating tuberculosis (TB), especially those with novel mechanisms of action to counter the emergence of drug-resistant TB. Host-directed therapy (HDT) offers a novel strategy with mechanisms that include activating immune defense mechanisms or ameliorating tissue damage. These and related concepts will be discussed along with issues that emerged from the workshop organized by the Stop TB Working Group on New Drugs, held at the Gordon Research Conference for Tuberculosis Drug Development in Lucca, Italy in June 2017, titled "Strategic Discussion on Repurposing Drugs & Host Directed Therapies for TB." In this review, we will highlight recent data regarding drugs, pathways, and concepts that are important for successful development of HDTs for TB.

Relaxin-FOLFOX-IL-12 triple combination therapy engages memory response and achieves long-term survival in colorectal cancer liver metastasis

Induction of memory T cell response is inefficient in colorectal cancer (CRC) liver metastasis following existing therapies due to abundant stroma and immunosuppressive environment within the metastatic liver, which leads to fast disease progression, high recurrence rate, and short survival. Two fundamental steps are involved to elicit extensive memory T cell response: stimulation of naive T cells with robust and persistent antigen signals; and maintenance of differentiated memory T cells with survival factors. Here, we demonstrate a rational design of triple combination regimen, including relaxin (RLN), FOLFOX (combination of 5-fluorouracil, leucovorin, and oxaliplatin), and IL-12, successfully stimulates central memory T cells and achieves long-term survival in an aggressive experimental CRC liver metastasis model. Sequential administration of FOLFOX and IL-12 gene therapy following stromal deactivation by RLN gene therapy completely cured established CRC liver metastases in ~50% of mice and provided long-lasting protection against tumor recurrence. The study here may highlight the potential of evoking memory response as a curative therapy for the treatment of CRC liver metastasis.

Impact of myo-inositol trispyrophosphate (ITPP) on tumour oxygenation and response to irradiation in rodent tumour models

Tumour hypoxia is a well-established factor of resistance in radiation therapy (RT). Myo-inositol trispyrophosphate (ITPP) is an allosteric effector that reduces the oxygen-binding affinity of haemoglobin and facilitates the release of oxygen by red blood cells. We investigated herein the oxygenation effect of ITPP in six tumour models and its radiosensitizing effect in two of these models. The evolution of tumour pO₂ upon ITPP administration was monitored on six models using 1.2 GHz Electron Paramagnetic Resonance (EPR) oximetry. The effect of ITPP on tumour perfusion was assessed by Hoechst staining and the oxygen consumption rate (OCR) in vitro was measured using 9.5 GHz EPR. The therapeutic effect of ITPP with and without RT was evaluated on rhabdomyosarcoma and 9L-glioma rat models. ITPP enhanced tumour oxygenation in six models. The administration of 2 g/kg ITPP once daily for 2 days led to a tumour reoxygenation for at least 4 days. ITPP reduced the OCR in six cell lines but had no effect on tumour perfusion when tested on 9L-gliomas. ITPP plus RT did not improve the outcome in rhabdomyosarcomas. In 9L-gliomas, some of tumours receiving the combined treatment were cured while other tumours did not benefit from the treatment. ITPP increased oxygenation in six tumour models. A decrease in OCR could contribute to the decrease in tumour hypoxia. The association of RT with ITPP was beneficial for a few 9L-gliomas but was absent in the rhabdomyosarcomas.

Impact of associating liver partition and portal vein ligation for staged hepatectomy (ALPPS) on growth of colorectal liver metastases

BACKGROUND

Associating liver partition and portal vein ligation for staged hepatectomy induces an unprecedented liver hypertrophy and enables resection of otherwise unresectable liver tumors. The effect of associating liver partition and portal vein ligation for staged hepatectomy on tumor proliferation, however, remains a concern. This study investigated the impact of associating liver partition and portal vein ligation for staged hepatectomy on growth of colorectal metastases in mice and in humans.

METHODS

The effect of associating liver partition and portal vein ligation for staged hepatectomy and 90% portal vein ligation on colorectal liver and lung metastases was investigated in mice. In vivo tumor progression was assessed by magnetic resonance imaging, histology, and survival experiments. The effects of associating liver partition and portal vein ligation for staged hepatectomy, portal vein ligation, and control sera on cultures of several colorectal cancer cell lines (MC38 and CT26) were tested in vitro. Additionally, the international associating liver partition and portal vein ligation for staged hepatectomy registry enabled us to identify patients with remaining tumor in the future liver remnant after associating liver partition and portal vein ligation for staged hepatectomy stage 1.

RESULTS

Two and 3 weeks after associating liver partition and portal vein ligation for staged hepatectomy stage 1, portal vein ligation, or sham surgery, liver magnetic resonance images showed similar numbers (P=.14/0.82), sizes (P=.45/0.98), and growth kinetics (P=.58/0.68) of intrahepatic tumor. Tumor growth was not different between the associating liver partition and portal vein ligation for staged hepatectomy and portal vein ligation groups after completion of stage 2. Median survival after tumor cell injection was similar after sham surgery (36 days; 95% confidence interval; 27-57 days), completion of associating liver partition and portal vein ligation for staged hepatectomy (42 days; 95% confidence interval; 35-49 days), and portal vein ligation (39 days; 95% confidence interval; 34-43 days, P=.237). Progression of pulmonary metastases and in vitro cell proliferation were comparable among groups. Observations in humans failed to identify any accelerated tumor growth in the future liver remnant within the regenerative phase after associating liver partition and portal vein ligation for staged hepatectomy stage 1.

CONCLUSION

The accelerated regeneration process associated with associating liver partition and portal vein ligation for staged hepatectomy does not appear to enhance growth of colorectal metastases.

The 150 most important questions in cancer research and clinical oncology series: questions 76-85 : Edited by Chinese Journal of Cancer

Since the beginning of 2017, Chinese Journal of Cancer has published a series of important questions in cancer research and clinical oncology to promote cancer research and accelerate collaborations. In this article, 10 questions are presented as followed. Question 76. How to develop effective therapeutics for cancer cachexia? Question 77. How can we develop preclinical animal models to recapitulate clinical situations of cancer patients for more effective anti-cancer drug development? Question 78. How can we develop novel effective therapeutics for pancreatic cancer and hepatocellular carcinoma? Question 79. What are the true beneficial mechanisms of antiangiogenic therapy in cancer patients? Question 80. How to approach the complex mechanisms of interplay among various cellular and molecular components in the tumor microenvironment? Question 81. Can tissue oxygenation improve the efficacy of conventional chemotherapy on cancer? Question 82. Can tissue oxygenation improve the efficacy of radiotherapy on digestive system tumors including liver cancer? Question 83. Can we integrate metabolic priming into multimodal management of liver cancer? Question 84. Has the limit of anti-androgen strategy in prostate cancer treatment been reached by the new generation of anti-androgen drugs? Question 85. Can we identify individuals with early-stage cancers via analyzing their clinical and non-clinical information collected from social media, shopping history, and clinical, pathological, and molecular traces?

The Allosteric Hemoglobin Effector ITPP Inhibits Metastatic Colon Cancer in Mice

OBJECTIVE

To test the effects of enhanced intracellular oxygen contents on the metastatic potential of colon cancer.

BACKGROUND

Colorectal cancer is the commonest gastrointestinal carcinoma. Distant metastases occur in half of patients and are responsible for most cancer-related deaths. Tumor hypoxia is central to the pathogenesis of metastases. Myo-Inositoltrispyrophosphate (ITPP), a nontoxic, antihypoxic compound, has recently shown significant benefits in experimental cancer, particularly when combined with standard chemotherapy. Whether ITPP protects from distant metastases in primary colon cancer is unknown.

METHODS

ITPP alone or combined with FOLFOX was tested in a mouse model with cecal implantation of green fluorescent protein-labeled syngeneic colorectal cancer cells. Tumor development was monitored through longitudinal magnetic resonance imaging-based morphometric analysis and survival. Established serum markers of tumor spread were measured serially and circulating tumor cells were detected via fluorescence measurements.

RESULTS

ITPP significantly reduced the occurrence of metastases as well as other indicators of tumor aggressiveness. Less circulating tumor cells along with reduction in malignant serum markers (osteopontin, Cxcl12) were noted. The ITPP benefits also affected the primary cancer site. Importantly, animals treated with ITPP had a significant survival benefit compared with respective controls, while a combination of FOLFOX with ITPP conferred the maximum benefits, including dramatic improvements in survival (mean 86 vs 188 d).

CONCLUSIONS

Restoring oxygen in metastatic colon cancer through ITPP inhibits tumor spread and markedly improves animal survival; an effect that is enhanced through the application of subsequent chemotherapy. These promising novel findings call for a clinical trial on ITPP in patients with colorectal cancer, which is under way.

Should modulation of p50 be a therapeutic target in the critically ill?

INTRODUCTION

A defining feature of human hemoglobin is its oxygen binding affinity, quantified by the partial pressure of oxygen at which hemoglobin is 50% saturated (p50), and the variability of this parameter over a range of physiological and environmental states. Modulation of this property of hemoglobin can directly affect the degree of peripheral oxygen offloading and tissue oxygenation. Areas covered: This review summarizes the role of hemoglobin oxygen affinity in normal and abnormal physiology and discusses the current state of the literature regarding artificial modulation of p50. Hypoxic tumors, sickle cell disease, heart failure, and transfusion medicine are discussed in the context of recent advances in hemoglobin oxygen affinity manipulation. Expert commentary: Of particular clinical interest is the possibility of maintaining adequate end-organ oxygen availability in patients with anemia or compromised cardiac function via an increase in systemic p50. This increase in systemic p50 can be achieved with small molecule drugs or a packed red blood cell unit processing variant called rejuvenation, and human trials are needed to better understand the potential clinical benefits to modulating p50.

Hypoxia-driven Hif2a coordinates mouse liver regeneration by coupling parenchymal growth to vascular expansion

Interaction between sinusoidal endothelial cells and hepatocytes is a prerequisite for liver function. Upon tissue loss, both liver cell populations need to be regenerated. Repopulation occurs in a coordinated pattern, first through the regeneration of parenchyme (hepatocytes), which then produces vascular endothelial growth factor (VEGF) to enable the subsequent angiogenic phase. The signals that instruct hepatocytes to induce timely VEGF remain unidentified. Given that liver is highly vascularized, we reasoned that fluctuations in oxygenation after tissue loss may contribute to the coordination between hepatocyte and sinusoidal endothelial cell proliferation. To prevent drops in oxygen after hepatectomy, mice were pretreated with inositol trispyrophosphate (ITPP), an allosteric effector of hemoglobin causing increased O₂ release from heme under hypoxic conditions. ITPP treatment delayed liver weight gain after hepatectomy. Comparison with controls revealed the presence of a hypoxic period around the peak of hepatocyte mitosis. Inhibition of hypoxia led to deficient hepatocyte mitosis, suppressed the regenerative Vegf wave, and abrogated the subsequent reconstruction of the sinusoidal network. These ITPP effects were ongoing with the reduction in hepatocellular hypoxia inducible factor 2a (Hif2a). In contrast, Hif1a was unaffected by ITPP. Hif2a knockdown phenocopied all effects of ITPP, including the mitotic deficiencies, Vegf suppression, and angiogenic failure.

CONCLUSIONS

Oxygen is a key regulator of liver regeneration. Hypoxia-inherent to the expansion of parenchyme-activates Hif2a to couple hepatocyte mitosis with the angiogenic phase. Hif2a acts as a safeguard to initiate sinusoidal reconstruction only upon successful hepatocyte mitosis, thereby enforcing a timely order onto cell type-specific regeneration patterns. These findings portray the hypoxia-driven Hif2a-Vegf axis as a prime node in coordinating sinusoidal endothelial cell-hepatocyte crosstalk during liver regeneration. (Hepatology 2016;64:2198-2209).