Year: 2015
Type: article
Abstract: MicroRNAs (miRNAs) are small, non-coding RNAs that regulate virtually all biological functions in cells by inhibiting the translation and stability of messenger RNAs (mRNAs) that regulate these functions. Sieving through more than 500 miRNAs that are uniquely deregulated in disease processes is a difficult task. In a study published recently in Genes and Development, Kouri et al use a more directed approach in identifying miR-182 as a master regulator of apoptosis, growth, and differentiation in glioblastoma (GBM). Previous studies had shown that Bcl2L12 plays a role in therapy resistance in glioma, and this oncogene was found to be highly expressed in nearly all GBMs. The authors used genomic datasets from the TCGA and found that miR-182 showed strong inverse correlation with Bcl2L12. The Bcl2L12 UTR contained an evolutionarily conserved miR-182 binding site, and transfection of synthetic miR-182, but not other family members of miR-96–182 cluster, resulted in reduction of luciferase activity from a Bcl2L12 reporter construct, proving that Bcl2L12 is a direct target of miR-182. miR-182 overexpression sensitized glioma cells to apoptosis induced by temozolamide and other RTK inhibitors in a Bcl2L12-dependent manner. To further understand the biological roles of miR-182, the authors examined the consequence of overexpression of miR-182 in glioma-initiating cells (GICs). miR-182-expressing GICs showed reduced growth, stem cell marker expression, and increased differentiation. In silico analyses predicted a network of genes including HIF2A, c-met and WNT5A, and other genes involved in cell death and survival as putative direct targets of miR-182. Of note, the miR-182-HIF2A axis was shown to play a role in stemness and dedifferentiation, and the miR-182-c-met axis controlled cell growth in GICs. Finally, the authors used spherical nucleic acids (SNAs) conjugated with miR-182 for targeting the brain. Intravenous administration of miR-182-based SNAs (182-SNAs) penetrated the blood-brain barrier and caused reduction of tumor burden and improved survival of mice implanted with glioma cells. This was accompanied by a marked apoptosis in 182-SNAs compared with control groups. Importantly, 182-SNAs had no adverse effects on animals, but a strong penetration in the glioma vasculature and parenchyma. This study shows that miR-182 acts as a tumor suppressor in GBM and the development of miR-182-SNAs to target GBM is an attractive strategy. Iron oxide nanoparticles (IONPs), in adequate concentrations, are detectable by MRI, serving as a negative contrast agent (an agent that results in loss of MR signal). A major advantage of IONPs over commonly used contrast agents such as gadolinium chelates is that IONPs can be easily “functionalized” by conjugation to molecules that bind specific targets. This functionalization has two important applications. One is that a target molecule can be specifically imaged in vivo and non-invasively. Another is that functionalization can be used to deliver therapeutic agents to specifically targeted cells based on cell-surface receptors or other membrane molecules. In fact, these applications can be combined so that, for instance, EGFR-expressing cells are imaged and therapeutically targeted in one step. Following this approach, Kaluzova et al recently reported the use of IONPs conjugated to the EGFR antibody cetuximab to image and to treat human glioblastoma cells in vitro and in vivo. In vitro, both transmission electron and fluorescence light microscopy were used to demonstrate that cetuximab-IONPs were bound and internalized by GBM cells. Increased uptake was found in both EGFR and EGFRvIII tumors. This resulted in increased apoptosis in both EGFR-expressing GBM stem-like cells and in human GBM neurospheres. For in vivo studies the authors used convection-enhanced delivery (CED) to circumvent the blood-brain barrier by using a catheter and pressure gradient to directly distribute cetuximab-IONPs into tumors (EGFR-expressing human GBM neurospheres implanted in mouse brains). This direct delivery system has the advantage of providing higher local concentrations of active molecules while reducing systemic toxicity. MRI was used to directly image cetuximab-IONPs, which showed widespread distribution in xenografts and in surrounding brain. Thus, this approach could potentially be used to target infiltrating tumor cells in addition to the primary mass. Treatment with cetuximab-IONPs had a greater anti-tumor effect than either cetuximab or IONP alone and resulted in longer survival. The authors hypothesize that conjugation of IONP to cetuximab enhances uptake compared with free IONPs or cetuximab alone, and that this results in higher intracellular concentrations of IONP leading to more apoptosis. Regardless of the mechanism, the report from Kaluzova et al indicates that functionalized IONPs have the potential to image and enhance killing of targeted subsets of cancer cells. The identification of patients with brain metastases from breast cancer, who are deemed to have a better prognosis and are hence more likely to benefit from more aggressive therapeutic approaches, is critical. Efforts to prognosticate patients with breast cancer with CNS metastases have led to the development of prognostic scores for the stratification of patients to predict overall survival. The primary recursive partitioning analysis for breast cancer by Sperduto et al1 retrospectively evaluated a multi-institutional database of 400 patients who received treatment for newly diagnosed brain metastases from breast cancer. This analysis identified tumor subtype (classified by human epidermal growth factor receptor 2 [HER2], estrogen receptor and progesterone receptor status), Karnofsky performance score (KPS), and age as independent prognostic factors, which were then incorporated into the breast graded prognostic assessment (breast-GPA). Conversely, the number of brain metastases did not emerge as an independent prognostic factor. Given the profound clinical relevance of the number of brain metastases with regard to therapeutic decisions, Subbiah and coworkers2 in a recent issue of Journal of Clinical Oncology sought to validate, expand, and develop a modified breast-GPA. Data were retrospectively gathered from a prospectively maintained institutional database (MD Anderson Cancer Center) : patients with newly diagnosed brain metastases from 1996 to 2013 were identified and collected. Within a cohort of 1,552 patients, the breast-GPA was validated as a prognostic tool for OS (P < .001). In a multivariate model including the breast-GPA and number of brain metastases (>3 v ≤ 3), both were independent predictors of OS. In particular, median survival time was significantly higher in patients with 1 to 3 brain metastases when compared with those with more than 3 brain metastases (13.2 v 6.3 months; P < .001). The authors, therefore, developed the modified breast-GPA integrating the number of brain metastases as a fourth clinical parameter. Recursive partitioning analysis reinforced the prognostic significance of these four factors. Concordance indices were 0.78 (95% CI, 0.77 to 0.80) and 0.84 (95% CI, 0.83 to 0.85) for the breast-GPA and modified breast-GPA, respectively (P < .001). The emergence of number of brain metastases as a significant prognostic factor may be partly attributed to the size of the breast cancer cohort in the present analysis, which was nearly twice that in previously reported studies. Data were not available on number or location of extracranial metastatic sites at the diagnosis of brain metastasis; however, these variables were not an independent prognostic factor in the original GPA or breast-GPA. In conclusion, the modified breast-GPA incorporates four simple clinical parameters of high prognostic significance. This index could have a role in the clinic as part of the clinician's discussion of prognosis and direction of care and as a potential patient selection tool for clinical trials. Patient-reported outcome parameters, such as health-related quality of life (HRQoL) and cognitive function, become more relevant for trials in glioblastoma especially if progression-free survival is prolonged.1,2 Reliable and feasible methods need to be implemented in clinical trials to assess cognitive function and to measure any potential cognitive decline exerted by the therapies administered to slow down or inhibit tumor growth. Brain involvement from systemic tumors, which may develop in 20–40% of all newly diagnosed cancer patients, and ionizing radiotherapy to the whole brain or partial brain radiotherapy, are associated with cognitive impairment in 50–90% of patients.3 Notably, whole-brain and to a lesser extent partial-brain radiotherapy commonly contribute to neurocognitive impairment including executive dysfunction, inattention, and memory deficits.3 Concepts to reduce unwanted cognitive effects include modifications of radiation fields (ie hippocampal sparing), the use of focal or partial radiotherapy instead of whole brain radiotherapy in oligometastatic patients,4,5 and pharmacological interventions. A recent study by the Radiation Therapy Oncology Group (RTOG) suggested benefit from a six-month course of the NMDA receptor antagonist memantine initiated in conjunction with whole-brain radiotherapy for brain metastasis.6 Although there was only an insignificant improvement in the decline in delayed recall in the memantine arm at 24 weeks, in the secondary objectives the memantine arm had significantly longer time to cognitive decline. Superior results were seen in the memantine arm for executive function at 8 and 16 weeks and for processing speed and delayed recognition at 24 weeks.6 Cholinesterase inhibitors are of proven albeit modest benefit in moderate-severe Alzheimer disease with encouraging results in other neurodegenerative disorders. A previous small uncontrolled open-label study of one such agent, donepezil, in patients with a mixture of brain tumors who had previously undergone radiation suggested improvement over a course of 24 weeks.7 Shaw et al reported that scores for cognitive function improved between baseline (pretreatment) and week 24 in the domains of attention/concentration, verbal memory, and figural memory. Additionally, HRQoL improved significantly from baseline to 24 weeks, particularly for brain-specific concerns with a trend for improvement in emotional and social functioning.7 With the background of these results it was logical to perform a double-blind, controlled trial looking at the effect of donepezil in brain tumor patients (66% had primary brain tumors, 27% had brain metastases, and 8% underwent prophylactic cranial irradiation) ≥6 months after partial- or whole-brain irradiation randomly assigned to receive a single daily dose (5 mg for 6 weeks, 10 mg for 18 weeks) of donepezil or placebo.8 The study population of Rapp et al consisted of 198 adults with fractionated radiotherapy at least six months prior to a dose ≥30 Gy, stable tumor, and ECOG performance status ≤2. Treatment groups were well matched on diagnosis (primary tumor, metastasis, or prophylactic), tumor location, age, and time from diagnosis (median 3 years). Approximately 40% in each arm had received whole-brain radiotherapy. Subjects underwent neuropsychological testing at baseline, 12 and 24 weeks (end of study) with a standard battery that included tests of verbal and visuospatial memory, attention, verbal fluency, motor dexterity, and executive functioning. The primary endpoint was overall cognitive performance at 24 weeks based upon a composite score of all tests; secondary endpoints included group comparisons on individual tests. Compliance was good and donepezil was well-tolerated; 74% of patients completed the study. The study was negative for the primary outcome, a composite score at 24 weeks.8 However, both recognition memory and motor speed/dexterity significantly favored the donepezil group over placebo (with the caveat that there was no correction for multiple comparisons). There were significant interactions between pretreatment cognitive function and treatment, with the benefits of donepezil treatment being greater for the patients with more cognitive impairment prior to study treatment. Dependent on the risk-benefit assessment, registration, and reimbursement status, donepezil might be used in some patients with cognitive impairment already prior to a cognitively challenging radiotherapy for a brain tumor. Measures of quality of life and function, which would provide information about clinical significance of the observed improvements, have not yet been reported for the Rapp et al patient cohort.8 Arguably, if these are encouraging, one consideration would be repeating the study in a more symptomatic study population. If benefit is confirmed, further studies might explore combination therapy with memantine. This study also emphasizes the need for structured, population-based data on the prevalence of cognitive decline as a function of primary and secondary brain tumors, radiation volume, time from treatment and risk factors. Further, the outcome focus in clinical trials, especially for patients with good prognosis, needs to be widened to include cognition and HRQoL.
Source: Neuro-Oncology
Language: English
Subfield: Cancer Research
Domain: Life Sciences
Open Access status: bronze
OpenAlex ID: W4238575338