SIAH ubiquitin ligases regulate breast cancer cell migration and invasion independent of the oxygen status

Seven-in-absentia homolog (SIAH) proteins are evolutionary conserved RING type E3 ubiquitin ligases responsible for the degradation of key molecules regulating DNA damage response, hypoxic adaptation, apoptosis, angiogenesis, and cell proliferation. Many studies suggest a tumorigenic role for SIAH2. In breast cancer patients SIAH2 expression levels correlate with cancer aggressiveness and overall patient survival. In addition, SIAH inhibition reduced metastasis in melanoma. The role of SIAH1 in breast cancer is still ambiguous; both tumorigenic and tumor suppressive functions have been reported. Other studies categorized SIAH ligases as either pro- or antimigratory, while the significance for metastasis is largely unknown. Here, we re-evaluated the effects of SIAH1 and SIAH2 depletion in breast cancer cell lines, focusing on migration and invasion. We successfully knocked down SIAH1 and SIAH2 in several breast cancer cell lines. In luminal type MCF7 cells, this led to stabilization of the SIAH substrate Prolyl Hydroxylase Domain protein 3 (PHD3) and reduced Hypoxia-Inducible Factor 1α (HIF1α) protein levels. Both the knockdown of SIAH1 or SIAH2 led to increased apoptosis and reduced proliferation, with comparable effects. These results point to a tumor promoting role for SIAH1 in breast cancer similar to SIAH2. In addition, depletion of SIAH1 or SIAH2 also led to decreased cell migration and invasion in breast cancer cells. SIAH knockdown also controlled microtubule dynamics by markedly decreasing the protein levels of stathmin, most likely via p27(Kip1). Collectively, these results suggest that both SIAH ligases promote a migratory cancer cell phenotype and could contribute to metastasis in breast cancer.

An AMP-activated protein kinase-stabilizing peptide ameliorates adipose tissue wasting in cancer cachexia in mice

Cachexia represents a fatal energy-wasting syndrome in a large number of patients with cancer that mostly results in a pathological loss of skeletal muscle and adipose tissue. Here we show that tumor cell exposure and tumor growth in mice triggered a futile energy-wasting cycle in cultured white adipocytes and white adipose tissue (WAT), respectively. Although uncoupling protein 1 (Ucp1)-dependent thermogenesis was dispensable for tumor-induced body wasting, WAT from cachectic mice and tumor-cell-supernatant-treated adipocytes were consistently characterized by the simultaneous induction of both lipolytic and lipogenic pathways. Paradoxically, this was accompanied by an inactivated AMP-activated protein kinase (Ampk), which is normally activated in peripheral tissues during states of low cellular energy. Ampk inactivation correlated with its degradation and with upregulation of the Ampk-interacting protein Cidea. Therefore, we developed an Ampk-stabilizing peptide, ACIP, which was able to ameliorate WAT wasting in vitro and in vivo by shielding the Cidea-targeted interaction surface on Ampk. Thus, our data establish the Ucp1-independent remodeling of adipocyte lipid homeostasis as a key event in tumor-induced WAT wasting, and we propose the ACIP-dependent preservation of Ampk integrity in the WAT as a concept in future therapies for cachexia.

Abstract 223: Comparison of human-specific versus cross-reactive Complex I inhibitor for in vivo tumor efficacy

Mitochondria are both key regulators of energy supply and apoptotic cell death. The mitochondrial electron transport chain (ETC) consists of four enzyme complexes that transfer electrons from NADH to oxygen. During electron transfer, the ETC (Complex I to IV) pumps protons into the inter-membrane space, generating a gradient across the inner mitochondrial membrane that is used by Complex V to drive ATP synthesis. Recent publications have shown that tumor cells harboring specific mutations (LKB1, mIDH and others) are more sensitive to Complex I inhibition, compared to cells that do not have these mutations. We have identified an optimized human/mouse cross-reactive Complex I inhibitor that allows profiling of Complex I inhibitors in pharmacological models. We have pursued different approaches based on the literature, an unbiased screen and in-house results generated with the human-specific Complex I inhibitor BAY 872243 to identify sensitive in vivo tumor models. However, using the cross-reactive Complex I inhibitor we were unable to identify sensitive models apart from weakly sensitive LKB1-deficient tumors (A549, G361) when animals were treated at maximum tolerated dose (MTD). In addition, all approaches for combination therapy failed to improve efficacy in vivo. Direct comparison of human-specific Complex I inhibitor BAY 87-2243 and cross-reactive inhibitor BAY179 in a sensitive LKB1-deficient melanoma model, G361, demonstrated that inhibition of Complex I specifically in the tumor is a valid approach as it results in tumor growth inhibition of ∼50%. However, cross-reactive compounds do not reach exposures at MTD to generate comparable effects.

Citation Format: Sven Christian, Carolyn Algire, Wolfgang Schwede, Jeffrey S. Mowat, Alexander Ehrmann, Stephan Menz, Marcus Bauser, Andrea Haegebarth. Comparison of human-specific versus cross-reactive Complex I inhibitor for in vivo tumor efficacy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 223.

Abstract 4746: Pharmacological characterization of BAY-876, a novel highly selective inhibitor of glucose transporter (GLUT)-1 in vitro and in vivo

One hallmark of cancer is the accelerated metabolism, high energy requirements, and increased glucose uptake by the tumor cells, the latter being the first and rate-limiting step for glucose metabolism. Glucose transport into the tumor cell is mediated by facilitative high-affinity glucose transporter (GLUT) proteins. Among the 14 GLUT proteins, expression of GLUT1 in normal organs is nearly exclusively restricted to the blood brain barrier, while other GLUTs are also expressed in a wide variety of vital organs such as liver and heart. Interestingly, GLUT1 expression is highly regulated by hypoxia-inducible factor (HIF)-1α, a key driver of tumor progression. In line with this finding, GLUT1 over-expression was found to be associated with tumor progression and poor overall survival in various tumor indications. Consequently, GLUT1 represents a potential target for cancer treatment. Therefore, we have developed a highly-selective GLUT1 inhibitor, namely BAY-876, with selectivity over GLUT2, 3, and 4 of 4700-, 800-, and 135-fold, respectively. We here show for the first time the pharmacological characterization of BAY-876, comprising inhibition of glucose-uptake, anti-proliferative activity in vitro, and anti-tumor efficacy in vivo in models of different tumor indications in monotherapy as well as first results on the combinability of BAY-876. Furthermore, at the therapeutic dose, BAY-876 treatment did not show any relevant finding on the behavior of treated mice in the Irwin test, assuming no or only minor effects on brain function. In conclusion, BAY-876 is the first GLUT1-selective inhibitor which reduces glucose uptake and growth of tumor cells with sufficient tolerability at the efficacious dose in preclinical models.

Citation Format: Charlotte Kopitz, Luisella Toschi, Carolyn Algire, Mélanie Héroult, Anna-Lena Frisk, Kirstin Meyer, Arndt Schmitz, Eleni Lagkadinou, Heike Petrul, Iring Heisler, Roland Neuhaus, Bernd Buchmann, Herbert Himmel, Marcus Bauser, Andrea Haegebarth, Karl Ziegelbauer. Pharmacological characterization of BAY-876, a novel highly selective inhibitor of glucose transporter (GLUT)-1 in vitro and in vivo. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4746.

Targeting mitochondrial complex I using BAY 87-2243 reduces melanoma tumor growth

Background

Numerous studies have demonstrated that functional mitochondria are required for tumorigenesis, suggesting that mitochondrial oxidative phosphorylation (OXPHOS) might be a potential target for cancer therapy. In this study, we investigated the effects of BAY 87-2243, a small molecule that inhibits the first OXPHOS enzyme (complex I), in melanoma in vitro and in vivo.

Results

BAY 87-2243 decreased mitochondrial oxygen consumption and induced partial depolarization of the mitochondrial membrane potential. This was associated with increased reactive oxygen species (ROS) levels, lowering of total cellular ATP levels, activation of AMP-activated protein kinase (AMPK), and reduced cell viability. The latter was rescued by the antioxidant vitamin E and high extracellular glucose levels (25 mM), indicating the involvement of ROS-induced cell death and a dependence on glycolysis for cell survival upon BAY 87-2243 treatment. BAY 87-2243 significantly reduced tumor growth in various BRAF mutant melanoma mouse xenografts and patient-derived melanoma mouse models. Furthermore, we provide evidence that inhibition of mutated BRAF using the specific small molecule inhibitor vemurafenib increased the OXPHOS dependency of BRAF mutant melanoma cells. As a consequence, the combination of both inhibitors augmented the anti-tumor effect of BAY 87-2243 in a BRAF mutant melanoma mouse xenograft model.

Conclusions

Taken together, our results suggest that complex I inhibition has potential clinical applications as a single agent in melanoma and also might be efficacious in combination with BRAF inhibitors in the treatment of patients with BRAF mutant melanoma.

Electronic supplementary material

The online version of this article (doi:10.1186/s40170-015-0138-0) contains supplementary material, which is available to authorized users.

Abstract 1126: Differential effects of metformin and phenformin vs. other complex 1 inhibitors in vitro and in vivo

Biguanides, such as metformin and phenformin, are currently under investigation for their potential use as anti-neoplastic therapy. Recent publications suggest that both metformin and phenformin exert effects through inhibition of Complex 1 in the electron transport chain. We investigated the effects of metformin and phenformin compared to rotenone, in vitro, and known Complex 1 inhibitor BAY 872243, in vitro and in vivo.

As expected, rotenone and BAY 872243 showed strong inhibition of Complex I in cell-based and enzymatic assays with IC50 values in the nanomolar range. The high affinity binding to Complex I was also reflected by induction of cellular reactive oxygen species (ROS) with EC50 values in the nanomolar range. In contrast, the biguanides neither inhibited Complex I in cell-based and biochemical assays, nor led to an induction of ROS at concentrations up to 300 μM.

In vivo exposure analysis shows that at the maximal tolerated dose (100 mg/kg QD i.p for phenformin and 350 mg/kg i.p QD for metformin), neither metformin nor phenformin had plasma exposure levels over the IC50 for proliferation in vitro. Recent reports have suggested that biguanides, via the inhibition of Complex 1 and subsequent reduction in oxygen consumption, can be used to re-oxygenate tumor areas prior to radiation therapy. Pimonidazole staining demonstrated that metformin and phenformin effectively eliminated hypoxic regions in NCI-H460 xenografts in a time course dependent manner that reflected the exposure. In contrast to the biguanides, BAY 87-2243 effectively eliminated hypoxic regions up to 24 hours post compound administration. Finally, both phenformin and metformin had minimal effects on inhibition of tumor growth, even in LKB1-deleted xenografts which have been reported to be especially sensitive to biguanides. In conclusion, our in vitro experiments on the mode of action of biguanides raise questions as whether the in vivo effects on hypoxic tumor regions are related to direct inhibition of Complex I.

Citation Format: Carolyn Algire, Alexander Ehrmann, Sven Christian, Roland Neuhaus, Stephan Menz, Wolfgang Schwede, Michael Haerter, Andrea Haegebarth. Differential effects of metformin and phenformin vs. other complex 1 inhibitors in vitro and in vivo. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1126. doi:10.1158/1538-7445.AM2015-1126

TSC22D4 is a molecular output of hepatic wasting metabolism

In mammals, proper storage and distribution of lipids in and between tissues is essential for the maintenance of energy homeostasis. Here, we show that tumour growth triggers hepatic metabolic dysfunction as part of the cancer cachectic phenotype, particularly by reduced hepatic very-low-density-lipoprotein (VLDL) secretion and hypobetalipoproteinemia. As a molecular cachexia output pathway, hepatic levels of the transcription factor transforming growth factor beta 1-stimulated clone (TSC) 22 D4 were increased in cancer cachexia. Mimicking high cachectic levels of TSC22D4 in healthy livers led to the inhibition of hepatic VLDL release and lipogenic genes, and diminished systemic VLDL levels under both normal and high fat dietary conditions. Liver-specific ablation of TSC22D4 triggered hypertriglyceridemia through the induction of hepatic VLDL secretion. Furthermore, hepatic TSC22D4 expression levels were correlated with the degree of body weight loss and VLDL hypo-secretion in cancer cachexia, and TSC22D4 deficiency rescued tumour cell-induced metabolic dysfunction in hepatocytes. Therefore, hepatic TSC22D4 activity may represent a molecular rationale for peripheral energy deprivation in subjects with metabolic wasting diseases, including cancer cachexia.

Metformin reduces endogenous reactive oxygen species and associated DNA damage

Pharmacoepidemiologic studies provide evidence that use of metformin, a drug commonly prescribed for type II diabetes, is associated with a substantial reduction in cancer risk. Experimental models show that metformin inhibits the growth of certain neoplasms by cell autonomous mechanisms such as activation of AMP kinase with secondary inhibition of protein synthesis or by an indirect mechanism involving reduction in gluconeogenesis leading to a decline in insulin levels and reduced proliferation of insulin-responsive cancers. Here, we show that metformin attenuates paraquat-induced elevations in reactive oxygen species (ROS), and related DNA damage and mutations, but has no effect on similar changes induced by H(2)0(2), indicating a reduction in endogenous ROS production. Importantly, metformin also inhibited Ras-induced ROS production and DNA damage. Our results reveal previously unrecognized inhibitory effects of metformin on ROS production and somatic cell mutation, providing a novel mechanism for the reduction in cancer risk reported to be associated with exposure to this drug.

Metformin abolishes increased tumor (18)F-2-fluoro-2-deoxy-D-glucose uptake associated with a high energy diet

Insulin regulates glucose uptake by normal tissues. Although there is evidence that certain cancers are growth-stimulated by insulin, the possibility that insulin influences tumor glucose uptake as assessed by ( 18) F-2-Fluoro-2-Deoxy-d-Glucose Positron Emission Tomography (FDG-PET) has not been studied in detail. We present a model of diet-induced hyperinsulinemia associated with increased insulin receptor activation in neoplastic tissue and with increased tumor FDG-PET image intensity. Metformin abolished the diet-induced increases in serum insulin level, tumor insulin receptor activation and tumor FDG uptake associated with the high energy diet but had no effect on these measurements in mice on a control diet. These findings provide the first functional imaging correlate of the well-known adverse effect of caloric excess on cancer outcome. They demonstrate that, for a subset of neoplasms, diet and insulin are variables that affect tumor FDG uptake and have implications for design of clinical trials of metformin as an antineoplastic agent.

Effects of castration on insulin levels and glucose tolerance in the mouse differ from those in man

BACKGROUND

Plasma insulin concentration is increased in prostate cancer patients during androgen deprivation therapy (ADT) and hyperinsulinemia has been associated with aggressive prostate cancer behavior. To investigate the possible role of castration-induced hyperinsulinemia as a mechanism that may attenuate the beneficial effects of ADT in patients with prostate cancer, a murine model would be useful. We therefore investigated long-term metabolic effects of castration in several mouse models.

METHODS

We studied the long-term influence of castration on energy intake, body weight, glucose tolerance, plasma-insulin, plasma insulin-like growth factor-1 (IGF-1), plasma adiponectin, and plasma leptin in C57BL/6, Swiss nu/nu, and CB17 scid mice receiving various diets. In each case, mice were randomized to have either bilateral orchiectomy or a sham operation.

RESULTS

Energy intake, body weight, blood glucose levels in glucose tolerance test, plasma insulin, plasma IGF-1, and plasma leptin level in all had a trend to be decreased in castrated as compared to sham operated mice. Plasma adiponectin level was increased in the castrated mice.

CONCLUSIONS

The effects of castration on glucose, insulin, and related markers in several mouse models studied does not coincide with clinical observations; further studies in this area will require clinical research and/or the use of alternate models such as the dog.

Metformin blocks the stimulative effect of a high-energy diet on colon carcinoma growth in vivo and is associated with reduced expression of fatty acid synthase

The molecular mechanisms responsible for the association of obesity with adverse colon cancer outcomes are poorly understood. We investigated the effects of a high-energy diet on growth of an in vivo colon cancer model. Seventeen days following the injection of 5x10(5) MC38 colon carcinoma cells, tumors from mice on the high-energy diet were approximately twice the volume of those of mice on the control diet. These findings were correlated with the observation that the high-energy diet led to elevated insulin levels, phosphorylated AKT, and increased expression of fatty acid synthase (FASN) by the tumor cells. Metformin, an antidiabetic drug, leads to the activation of AMPK and is currently under investigation for its antineoplastic activity. We observed that metformin blocked the effect of the high-energy diet on tumor growth, reduced insulin levels, and attenuated the effect of diet on phosphorylation of AKT and expression of FASN. Furthermore, the administration of metformin led to the activation of AMPK, the inhibitory phosphorylation of acetyl-CoA carboxylase, the upregulation of BNIP3 and increased apoptosis as estimated by poly (ADP-ribose) polymerase (PARP) cleavage. Prior work showed that activating mutations of PI3K are associated with increased AKT activation and adverse outcome in colon cancer; our results demonstrate that the aggressive tumor behavior associated with a high-energy diet has similar effects on this signaling pathway. Furthermore, metformin is demonstrated to reverse the effects of the high-energy diet, thus suggesting a potential role for this agent in the management of a metabolically defined subset of colon cancers.

Abstract 65: Metformin inhibits in vivo growth of MC38 colon carcinoma in the absence of LKB1 expression

There is evidence that metformin has anti-neoplastic activity in diabetic cancer patients. In hepatocytes, metformin administration leads to the LKB1-dependent activation of AMPK and inhibition of gluconeogenesis which can lower insulin levels. In neoplastic cells in vitro, metformin-induced activation of AMPK leads to inhibition of both protein synthesis and cell proliferation. Our previous results showed that metformin inhibits LLC1 tumor growth in mice on a high energy diet that induced hyperinsulinemia, while having no effect on tumor growth of mice on a control diet, thus raising questions regarding the roles of direct AMPK mediated anti-neoplastic effects of metformin vs indirect anti-neoplastic effects attributable to reduction of insulin levels.

We extended this work using MC38 colon carcinoma with shRNA to knockdown LKB1 (LKB1-). As expected, knockdown of LKB1 conferred resistance to the in vitro growth inhibitory actions of metformin. We proceeded with an in vivo study to compare growth of MC38-LKB1- and MC38 control tumors in mice on either a high energy or control diet, with or without metformin. Metformin was administered daily and the experiment was carried out with each mouse bearing a MC38-LKB1- tumor on one flank and a MC38 control tumor on the other. Metformin had no effect on the insulin levels of mice on the control diet, but significantly reduced the insulin levels of mice on the high energy diet. Tumors of mice on the high energy diet were twice the volume of tumors of mice on the control diet, regardless of LKB1 status. Metformin significantly inhibited growth of both MC38-LKB1- and MC38 control tumors in mice on the high energy diet. These observations suggest that despite its direct in vitro growth inhibitory activity involving activation of AMPK, the anti-neoplastic activity of the drug in vivo, in the context of hyperinsulinemia, is attributable to the actions of the drug on the liver. Consistent with this conclusion, we observed that metformin administration reduced insulin receptor activation in both MC38-LKB1- and MC38 control tumors of mice on the high energy diet.

In addition, metformin attenuated tumor growth in MC38-LKB1- cells in mice on the control diet, but had no effect on MC38 control cells. Immunoblotting confirmed that unlike MC38 control cells, LKB1- cells did not undergo autophagy in the presence of metformin. We confirmed these results in vitro and found that MC38-LKB1- treated with metformin, in conditions of low glucose, underwent apoptosis whereas LKB1- cells treated with metformin in conditions of high glucose were insensitive to metformin. MC38 control cells were equally sensitive to the growth inhibitory effects of metformin at both high and low glucose conditions. These results suggest that metformin and similar compounds deserve clinical evaluation, but that their activity may be restricted to subsets based on molecular pathology of the tumor and metabolic status of the host.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 65.

Loss of function of PTEN alters the relationship between glucose concentration and cell proliferation, increases glycolysis, and sensitizes cells to 2-deoxyglucose

PTEN loss of function enhances proliferation, but effects on cellular energy metabolism are less well characterized. We used an inducible PTEN expression vector in a PTEN-null glioma cell line to examine this issue. While proliferation of PTEN-positive cells was insensitive to increases in glucose concentration beyond 2.5mM, PTEN-null cells significantly increased proliferation with increasing glucose concentration across the normal physiologic range to approximately 10mM, coinciding with a shift to glycolysis and "glucose addiction". This demonstrates that the impact of loss of function of PTEN is modified by glucose concentration, and may be relevant to epidemiologic results linking hyperglycemia to cancer risk and cancer mortality.

Dependence of malignant proliferation associated with loss of PTEN on glucose concentration in the hyperglycemic range: Relevance to population studies linking hyperglycemia to unfavorable cancer prognosis

11113

Background: Loss of function of the tumor suppressor PTEN enhances malignant proliferation, but effects on cellular energy metabolism are less well characterized. Population studies show that the metabolic syndrome (characterized by hyperglycemia, hyperinsulinism, and obesity) is increasingly prevalent in affluent societies and is associated with adverse outcome of many cancers, but the molecular basis for this is poorly understood. Methods: We used a tetracycline-inducible PTEN expression vector in the PTEN-null U251 glioma cell line to characterize effects of PTEN on cellular energy metabolism. Results: Forced expression of PTEN led to decreased phospho-AKTSer473, decreased hexokinase II and HIF-1 alpha levels, and increased p53 levels. While proliferation of PTEN-positive cells was insensitive to variation in glucose concentration at levels higher than 2.5 mM, PTEN-null cells significantly increased proliferation with increasing glucose concentration across normal physiologic range to ∼10 mM. PTEN-null cells consumed more glucose than PTEN-positive cells (17.2 ± 2.0 vs. 8.8 ± 1.5 mM/million cells/48 hrs) and produced more lactate (35.9 ± 4.8 vs. 10.7 ± 2.3 mM/million cells/48 hrs). When cells were incubated in presence of 2-deoxy-glucose (2-DG), growth inhibition was greater for PTEN-null cells (47.4% inhibition relative to control without 2-DG) compared with PTEN-positive cells (10.8% inhibition relative to control without 2-DG). Conclusions: Loss of function of PTEN leads to increased glycolysis, and increased dependence on glucose availability. Only in the presence of glucose in the hyperglycemic range are maximal adverse effects of loss of PTEN on cellular proliferation and survival seen. This provides a novel mechanism to explain at least in part the relationship between hyperglycemia and cancer mortality observed in several large population studies. The data also suggest that PTEN status is relevant to selection of tumors likely to respond to experimental therapies that exploit glucose dependency.

No significant financial relationships to disclose.

Metformin attenuates the stimulatory effect of a high-energy diet on in vivo LLC1 carcinoma growth

We investigated the effects of metformin on the growth of lewis lung LLC1 carcinoma in C57BL/6J mice provided with either a control diet or a high-energy diet, previously reported to lead to weight gain and systemic insulin resistance with hyperinsulinemia. Forty-eight male mice were randomized into four groups: control diet, control diet+metformin, high-energy diet, or high-energy diet+metformin. Following 8 weeks on the experimental diets, selected groups received metformin in their drinking water. Three weeks following the start of metformin treatment, mice were injected with 0.5x10(6) LLC1 cells and tumor growth was measured for 17 days. By day 17, tumors of mice on the high-energy diet were nearly twice the volume of those of mice on the control diet. This effect of diet on tumor growth was significantly attenuated by metformin, but metformin had no effect on tumor growth of the mice on the control diet. Metformin attenuated the increased insulin receptor activation associated with the high-energy diet and also led to increased phosphorylation of AMP kinase, two actions that would be expected to decrease neoplastic proliferation. These experimental results are consistent with prior hypothesis-generating epidemiological studies that suggest that metformin may reduce cancer risk and improve cancer prognosis. Finally, these results contribute to the rationale for evaluation of the anti-neoplastic activity of metformin in hyperinsulinemic cancer patients.

Similar Effects of Osmolarity, Glucose, and Phosphate on Cleavage past the 2-Cell Stage in Mouse Embryos from Outbred and F1 Hybrid Females1

One-cell-stage embryos derived from most random-bred and inbred female mice exhibit an in vitro developmental block at the two-cell stage in classical embryo culture media. However, embryos derived from many F1 hybrids develop easily past the two-cell stage under the same conditions. This has given rise to the commonly accepted idea that there exist blocking and nonblocking types of female mice, with only the former being prone to a two-cell block. Recently, culture media have been improved to the point that even embryos prone to the two-cell block will develop past the block in vitro, making it possible to study its etiology. Here, we show that either increased osmolarity or increased glucose/phosphate levels induced the expected two-cell block in random-bred CF1 embryos and the two-cell block at increased osmolarities could be rescued by the organic osmolyte glycine. Surprisingly, one-cell embryos from B6D2F1 (BDF1) F1 hybrid females, considered to be nonblocking, also became blocked at the two-cell stage when osmolarity or glucose/phosphate levels were increased. They were also similarly rescued by glycine from the osmolarity-induced block. The most evident difference was that the purportedly nonblocking embryos became blocked at a higher threshold of osmolarity or glucose/phosphate level than those considered prone to this developmental block. Thus, both blocking and nonblocking embryos actually exhibit a similar two-cell block to development.