Cyclic nucleotides in experimental and human brain tumors

Risk factors and a new nomogram for predicting brain metastasis from lung cancer: a retrospective study

Objective

This study aims to establish and validate a new nomogram for predicting brain metastasis from lung cancer by integrating data.

Methods

266 patients diagnosed as lung cancer between 2016 and 2018 were collected from Guangdong Academy of Medical Sciences. The first 70% of patients were designated as the primary cohort and the remaining patients were identified as the internal validation cohort. Univariate and multivariable logistics regression were applied to analyze the risk factors. Independent risk factors were used to construct nomogram. C-index was used to evaluate the prediction effect of nomogram.100 patients diagnosed as lung cancer between 2018 and 2019 were collected for external validation cohorts. The evaluation of nomogram was carried out through the distinction and calibration in the internal validation cohort and external validation cohort.

Results

166 patients were diagnosed with brain metastasis among the 266 patients. The gender, pathological type (PAT), leukocyte count (LCC) and Fibrinogen stage (FibS) were independent risk factors of brain metastasis. A novel nomogram has been developed in this study showed an effective discriminative ability to predict the probability of lung cancer patients with brain metastasis, the C-index was 0.811.

Conclusion

Our research provides a novel model that can be used for predicting brain metastasis of lung cancer patients, thus providing more credible evidence for clinical decision-making.

An integrative view on sex differences in brain tumors

Sex differences in human health and disease can range from undetectable to profound. Differences in brain tumor rates and outcome are evident in males and females throughout the world and regardless of age. These observations indicate that fundamental aspects of sex determination can impact the biology of brain tumors. It is likely that optimal personalized approaches to the treatment of male and female brain tumor patients will require recognizing and understanding the ways in which the biology of their tumors can differ. It is our view that sex-specific approaches to brain tumor screening and care will be enhanced by rigorously documenting differences in brain tumor rates and outcomes in males and females, and understanding the developmental and evolutionary origins of sex differences. Here we offer such an integrative perspective on brain tumors. It is our intent to encourage the consideration of sex differences in clinical and basic scientific investigations.

Regulation of connexin 43 and microRNA expression via β2-adrenoceptor signaling in 1321N1 astrocytoma cells

Connexin 43 (Cx43) is the main gap junction protein in astrocytes and exerts the same effects on growth inhibition in astrocytoma and glioma as microRNA-146a (miR-146a) in glioma. β2-adrenergic receptor (AR) signaling modulates Cx43 expression in myocytes via components downstream of protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac). However, it remains to be elucidated how expression of Cx43 is modulated in astrocytes. In the present study, 1321N1 astrocytoma cells were treated with β2-AR signaling agents in order to evaluate the expression of Cx43 and miRNAs. RNA and protein were extracted from the cells for use in reverse transcription-quantitative polymerase chain reaction and western blot analysis, respectively. The results revealed that clenbuterol increased miR-146a level and upregulated Cx43 expression via cAMP/PKA at the mRNA and protein level. Pre-inhibition of adenyl cyclase decreased expression of Cx43 and miR-146a. PKA activation and overexpression of miR-146a in A-1321N1 cells increased the expression of Cx43. β2-AR stimulation and 6Bnz, a PKA activator, suppressed oncomiRs miR-155 and miR-27a, while 8-(4-chlorophenylthio)-2'-O-methyladenosine-3',5'-cyclic monophosphate, an Epac activator, increased their levels. The current findings demonstrated that β2-AR signaling has growth inhibitory effects via modulation of the cAMP/PKA pathway in A-1321N1 cells through increasing the expression level of Cx43 and miR-146a as well as decreasing miR-155 and miR-27a levels. Thus, stimulation of the β2-AR and PKA signaling pathway may be a useful approach for astrocytoma therapy.

Selective β2 adrenergic agonist increases Cx43 and miR-451 expression via cAMP-Epac

It has been demonstrated that connexin 43 (Cx43) and microRNAs have significant roles in glioma. Cyclic adenosine monophosphate (cAMP) is suggested to be a regulator of connexins and microRNAs. However, it remains elusive whether cAMP and exchange protein directly activated by cAMP (Epac2), have a regulatory effect on Cx43 and microRNA-451 (miR-451) in astrocytoma cells. We treated 1321N1 astrocytoma cells with a selective β2 adrenergic agonist and a selective Epac activator with and without adenyl cyclase and protein kinase A inhibition. Cx43 and miR-451 expression were measured. Next, we evaluated the effect of miR-451 overexpression on Cx43 expression. Cell proliferation was measured using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The results demonstrated that cAMP-Epac2 increased Cx43 and miR-451 expression. However, the alteration of miR-451 expression required a higher dose of drugs. Overexpression of miR-451 had no significant effect on Cx43 expression. The MTT assay showed that cAMP-Epac stimulation and miR-451 overexpression had a synergic inhibitory effect on cell proliferation. These findings may expand our understanding of the molecular biology of glioma and provide new potential therapeutic targets.

Treating brain tumors with PDE4 inhibitors

Speculation regarding dysregulation of cAMP metabolism in oncogenesis has existed since the discovery of cAMP more than 50 years ago. Recent data confirm the relevance of disordered cAMP metabolism to the genesis of multiple cancers and suggest that the mechanism might involve altered expression and activity of phosphodiesterases (PDEs). These discoveries coincide with the rapid development and clinical evaluation of PDE inhibitors for non-cancer indications. Thus, the time is ripe to evaluate PDE inhibitors as cancer chemotherapeutics. Here we highlight recent evidence that abnormal regulation of cAMP levels might be a determinant of brain tumorigenesis and that altered PDE expression is one the mechanisms of its dysregulation. Recent preclinical and clinical experience with inhibitors of PDE4 indicates that this might be a promising approach to brain tumor therapy.

{Beta}2-adrenergic receptor agonists inhibit the proliferation of 1321N1 astrocytoma cells

Astrocytomas and glioblastomas have been particularly difficult to treat and refractory to chemotherapy. However, significant evidence has been presented that demonstrates a decrease in astrocytoma cell proliferation subsequent to an increase in cAMP levels. The 1321N1 astrocytoma cell line, as well as other astrocytomas and glioblastomas, expresses β(2)-adrenergic receptors (β(2)-ARs) that are coupled to G(s) activation and consequent cAMP production. Experiments were conducted to determine whether the β(2)-AR agonist (R,R')-fenoterol and other β(2)-AR agonists could attenuate mitogenesis and, if so, by what mechanism. Receptor binding studies were conducted to characterize β(2)-AR found in 1321N1 and U118 cell membranes. In addition, cells were incubated with (R,R')-fenoterol and analogs to determine their ability to stimulate intracellular cAMP accumulation and inhibit [(3)H]thymidine incorporation into the cells. 1321N1 cells contain significant levels of β(2)-AR as determined by receptor binding. (R,R')-fenoterol and other β(2)-AR agonists, as well as forskolin, stimulated cAMP accumulation in a dose-dependent manner. Accumulation of cAMP induced a decrease in [(3)H]thymidine incorporation. There was a correlation between concentration required to stimulate cAMP accumulation and inhibit [(3)H]thymidine incorporation. U118 cells have a reduced number of β(2)-ARs and a concomitant reduction in the ability of β(2)-AR agonists to inhibit cell proliferation. These studies demonstrate the efficacy of β(2)-AR agonists for inhibition of growth of the astrocytoma cell lines. Because a significant portion of brain tumors contain β(2)-ARs to a greater extent than whole brain, (R,R')-fenoterol, or some analog, may be useful in the treatment of brain tumors after biopsy to determine β(2)-AR expression.

Targeted inhibition of cyclic AMP phosphodiesterase-4 promotes brain tumor regression

PURPOSE

As favorable outcomes from malignant brain tumors remain limited by poor survival and treatment-related toxicity, novel approaches to cure are essential. Previously, we identified the cyclic AMP phosphodiesterase-4 (PDE4) inhibitor Rolipram as a potent antitumor agent. Here, we investigate the role of PDE4 in brain tumors and examine the utility of PDE4 as a therapeutic target.

EXPERIMENTAL DESIGN

Immunohistochemistry was used to evaluate the expression pattern of a subfamily of PDE4, PDE4A, in multiple brain tumor types. To evaluate the effect of PDE4A on growth, a brain-specific isoform, PDE4A1 was overexpressed in xenografts of Daoy medulloblastoma and U87 glioblastoma cells. To determine therapeutic potential of PDE4 inhibition, Rolipram, temozolomide, and radiation were tested alone and in combination on mice bearing intracranial U87 xenografts.

RESULTS

We found that PDE4A is expressed in medulloblastoma, glioblastoma, oligodendroglioma, ependymoma, and meningioma. Moreover, when PDE4A1 was overexpressed in Daoy medulloblastoma and U87 glioblastoma cells, in vivo doubling times were significantly shorter for PDE4A1-overexpressing xenografts compared with controls. In long-term survival and bioluminescence studies, Rolipram in combination with first-line therapy for malignant gliomas (temozolomide and conformal radiation therapy) enhanced the survival of mice bearing intracranial xenografts of U87 glioblastoma cells. Bioluminescence imaging indicated that whereas temozolomide and radiation therapy arrested intracranial tumor growth, the addition of Rolipram to this regimen resulted in tumor regression.

CONCLUSIONS

This study shows that PDE4 is widely expressed in brain tumors and promotes their growth and that inhibition with Rolipram overcomes tumor resistance and mediates tumor regression.

Blocking CXCR4-mediated cyclic AMP suppression inhibits brain tumor growth in vivo

The chemokine CXCL12 and its cognate receptor CXCR4 regulate malignant brain tumor growth and are potential chemotherapeutic targets. However, the molecular basis for CXCL12-induced tumor growth remains unclear, and the optimal approach to inhibiting CXCR4 function in cancer is unknown. To develop such a therapeutic approach, we investigated the signaling pathways critical for CXCL12 function in normal and malignant cells. We discovered that CXCL12-dependent tumor growth is dependent upon sustained inhibition of cyclic AMP (cAMP) production, and that the antitumor activity of the specific CXCR4 antagonist AMD 3465 is associated with blocking cAMP suppression. Consistent with these findings, we show that pharmacologic elevation of cAMP with the phosphodiesterase inhibitor Rolipram suppresses tumor cell growth in vitro and, upon oral administration, inhibits intracranial growth in xenograft models of malignant brain tumors with comparable efficacy to AMD 3465. These data indicate that the clinical evaluation of phosphodiesterase inhibitors in the treatment of patients with brain tumors is warranted.

Local interstitial chemotherapy with sustained release bucladesine in de novo glioblastoma multiforme: a preliminary study

This clinical study was designed to evaluate the safety and efficacy of the sustained release form of dibutryl adenosine-3',5'-cyclic monophosphate (dB-cAMP, bucladesine) placed in the tumor resection cavity at the time of recurrence of the de novo glioblastoma multiforme (GBM) patients. In a randomized prospective manner, 40 patients who were diagnosed as GBM in their first operations were included in this study. Four different therapy protocols were used: First group of 10 patients had tumor resection only. Second group assessed had only systemic chemotherapy as six i.v. infusions of fotémustine after tumor resection. Third group had implantation of bucladesine-loaded biodegradable polymeric sustained release (bcl-SR) pellets while the last group received six i.v. infusions of systemic fotémustine as in the second group in addition to local implantation of bcl-SR pellets. A biodegradable polymer, poly-DL-lactide-co-glycolide with molecular weight of 80000, was used as carrier matrix for the drug with an approximately 4-5 months of release time. Maximal doses of 20 mg of bucladesine with a mean dose of 15.5 mg were implanted. No bone marrow suppression occurred and there were no wound infections as far as the local bucladesine-loaded polymer therapy is concerned. In this randomized prospective trial of local interstitial chemotherapy with long acting bcl-SR did show a statistically significant delay of recurrence on the treatment of GBM patients. Best treatment results obtained from the local bcl-SR + systemic fotémustine treated group in which survival rate estimated by the Kaplan-Meier method was 70% in de novo GBM at 12 months.

An experimental trial of cyclic nucleotides on multicellular spheroids derived from human brain tumours

The effects of cyclic nucleotides, dibutyryl cyclic adenosine monophosphate and dibutyryl cyclic guanosine monophosphate (db-cAMP and db-cGMP), on the growth rate of multicellular tumour spheroids were evaluated by comparing the growth delay and colony forming efficiency in vitro. Multicellular tumour spheroids were derived directly from human brain tumours. To compare the chemotherapeutic effect of cyclic nucleotides, CCNU was used as a known effective cytotoxic drug on malignant gliomas. Significant growth delay was obtained by db-cAMP (p less than 0.001) while CCNU was tumouricidal rather then producing a delay in growth of the tumour spheroids. Db-cGMP found not to be effective in decreasing the growth rate of the tumour spheroids in vitro (p greater than 0.2). The role of cyclic nucleotides in brain tumours is discussed on a review basis.