cancer cell

Muller Fabbri, M.D., Ph.D.: The microRNA journey and the future of cancer therapy

cancer cell

Children’s National Hospital welcomes Muller Fabbri, M.D. Ph.D., as associate director for the Center for Cancer and Immunology Research at the Children’s National Research Institute. In this role, he will build and lead the Cancer Biology Program while developing and conducting basic and translational research. Dr. Fabbri will also develop multidisciplinary research projects with various clinical divisions, including oncology, blood and marrow transplantation, pathology and hematology.

Dr. Fabbri shares his journey working with microRNAs, how his work is advancing the field and his vision for the Center for Cancer and Immunology Research at Children’s National.

Q: You have been working with microRNAs for quite some time. How are you exploring the role of microRNAs in cancer?

A: It was well established within the scientific community that a gene, which is a piece of DNA, becomes a piece of RNA and then becomes a protein. This thought process was pretty much a one-way flow of information that we had, going from DNA to protein as part of a cell function. But, almost 30 years ago, it was discovered that this is not entirely true because what happens is that some of these genes that are transcribed into RNA do not become a protein. Instead, they stay as RNA. Some of these RNAs are tiny and have short sequences, which is why they are called microRNAs.

I work primarily on microRNAs and non-coding RNAs and my research studies focus on the role that microRNAs play in cancer. I can take a cancer cell and a healthy cell and observe how these microRNAs are expressed in the two different cell populations. In this way, the microRNAs expressed in cancer cells are profoundly different from the microRNAs expressed in healthy cells.

We conducted a series of studies to observe what happens to a cancer cell if we restore normal levels of certain microRNAs like the ones you would see in a normal cell. We discovered that by restoring some of these microRNAs levels it led to the death of the cancer cells, suggesting that this approach may be used as a cancer treatment. This is one of the research areas that I will further develop at Children’s National as I seek to understand the mechanisms that control microRNA expression and subsequently affect cancer cell proliferation. With this information, we can target these mechanisms and create drugs that interfere with this function and, hopefully, stop cancer cell growth.

Q: Can you tell us about that eureka moment with your best friend during a lunch break?

A: This was a bit of a crazy idea. I will never forget. I shared a theory during a lunch break with a friend. I dared to ask, what if microRNAs worked like hormones? MicroRNAs can be detected in the blood of patients with cancer, and they can be transferred from one cell to another inside of little vesicles called exosomes. If you think about it, I further asked, what other molecules in our body behave like that — i.e. are secreted, circulate in the blood and then transferred to a target cell? My friend replied, “well, those would be hormones.” To which, I added, yes, exactly! Then, why do we not think of RNAs as hormones? And I quote him now, “you are crazy, but if it works it is huge.”

I felt that I had some validation from my best friend, so I decided to invest in this crazy idea, carving extra time on the side while working on my “safe” projects. It was one of those rare cases in science, where in a little over a year, we showed for the first time that microRNAs do not only work the traditional way, but they can also work as hormones. They do have a receptor protein to attach to, and by binding to this protein, they trigger a response in a cell that can be pro-tumoral or anti-tumoral.

Even today, if you open a textbook of endocrinology, under the chapter of hormones, it mentions that there are only two categories, proteins and lipids. Well, it turns out there is a third category, which is nucleic acids because of RNAs.

Q: You mentioned other research areas of interest as it relates to cancer cell biology. What are they?

A: The other line of research that I am developing stems from the original observation that I made in 2012. Cancer cells release tiny vesicles that I like to compare to envelopes containing a written message — the RNA and microRNA. These vesicles released in the surrounding environment contain a message captured by immune cells, known as macrophages. Macrophages act as scavengers in our bodies. In cancer, macrophages are supposed to digest and destroy the cancer cell. However, it turns out that they also have the proper receptor to receive and read the message enclosed in the vesicles. Then, something shocking happens. The macrophage stops fighting the cancer cell and starts producing proteins called cytokines that promote cancer growth. This finding means that we are 180 degrees apart from what we thought at the beginning. A lot of macrophages in the cancer are good news for the patient because they are supposed to kill cancer cells, but because of this mechanism, a lot of macrophages can be bad news since they can also help the cancer cell grow.

My contribution to this discovery was to investigate how the macrophage response is mediated. I discovered that macrophages operate, at least in part, by expressing receptors that bind to microRNAs released by the cancer cell, thereby favoring cancer growth. In the pediatric cancer field we discovered that because of this microRNA–receptor interaction, the pediatric tumor neuroblastoma becomes resistant to chemotherapy. Therefore, one of the strategies we are working on now is to interfere or impair these negative communications between the cancer cell and immune cell. We want to disrupt these communications so the macrophage cannot read the message from the cancer cell anymore and instead keeps doing its job to fight the cancer. We hope that we can leverage this approach to develop novel cancer treatments or create strategies that improves immune cell function in the presence of the patient’s current therapy to enhance an anti-cancer treatment response.

Q: What is your vision for the Center of Cancer and Immunology Research?

A: I am very excited about what I saw at Children’s NationalI was delighted to talk to many faculty members, and I recognized the immense talent within the Center. I would like to help elevate and enhance the cancer biology program focused on solid tumors, and augment the work being done in this space by the cell therapy program. The clinicians are clearly eager to collaborate with the basic scientists including the sharing of samples and ideas, which is not typical of many scientific environments. My other goal is to ensure that the Cancer Biology Program plays a central role in acquiring an NCI-Designated Cancer Center recognition often given to institutions that stand out in scientific leadership and clinical research. Finally, I want to create the first national center that develops extracellular vesicles as an innovative treatment strategy for cancer. Importantly, I think that we have all the resources and connections at Children’s National that are necessary to realize this vision!


illustration of lungs with virus

Segmenting viral bronchiolitis patients to better predict clinical outcomes

illustration of lungs with virus

By evaluating viral bronchiolitis patients at first presentation and categorizing them based on clinical phenotype, the researchers were able to better predict outcomes and disease progression patterns.

Researchers from Children’s National Hospital have recently published a pilot study of children with viral bronchiolitis. By evaluating viral bronchiolitis patients at first presentation and categorizing them based on clinical phenotype, the researchers were able to better predict outcomes and disease progression patterns. Nasal airway cytokine levels were also measured to assess the underlying airway immunobiology of different clinical phenotypes. The researchers believe this novel subdivision of viral bronchiolitis patients based on a robust combination of clinical and molecular assessment can help lead to more individualized care and better patient outcomes.

Viral bronchiolitis is broadly used to group together infants with first-time severe viral respiratory infection, which is the most common cause of early life sick visits and hospitalizations worldwide. However, viral respiratory infections can vary significantly in clinical manifestations, which has raised concern among experts that the use of viral bronchiolitis as a catchall term may be compromising patient care. Children’s National researchers hypothesized that a novel segmentation technique of viral bronchiolitis patients by phenotype at first episode could provide better outcome prediction. In addition, lung X-rays and nasal cytokine profiles could help illuminate the underlying airway disease processes that drive the phenotypical differences observed at bedside.

The study examined 50 children ≤ 2 years old, including 41 patients admitted at Children’s National with PCR-confirmed viral respiratory infection and 9 controls. Researchers examined clinical features at presentation by reviewing each patient’s electronic medical record. Key parameters served as the basis for patient segmentation into three phenotypical groups: hypoxemia, wheezing and mild phenotypes. Patients in the hypoxia group (n = 16) were characterized by their need for supplemental oxygen; patients in the wheezing phenotype (n = 16) were distinguished by wheezing or subcostal retractions and patients in the mild phenotype (n = 9) displayed persistent respiratory symptoms but not hypoxia, wheezing or subcostal retractions. Chest x-rays further revealed that patients in the hypoxia phenotype displayed significantly more lung opacities than the other phenotypes.

As hypothesized, the three phenotype groups displayed distinct clinically relevant outcomes. Patients in the hypoxia group had more severe clinical symptoms at presentation and were significantly more likely to require prolonged hospitalization and pediatric intensive care unit (PICU) settings for treatment. Patients in the wheezing phenotype had shorter hospital stays but were significantly more likely to make a respiratory sick visit after initial discharge, with 69% coming back to the hospital with the same symptoms. Patients in the mild phenotype had the shortest hospital stays and did not require transfer to the PICU.

Nasal cytokine profiles were also assessed for all study subjects. Controls had lower cytokine levels than patients, with no significant difference between phenotype groups. However, wheezing patients with ≥1 recurrent respiratory sick visit had higher nasal levels of type 2 cytokines IL-13 and IL-4, consistent with the pathobiology of allergic asthma. This result adds support for the potential of initial sub-setting in guiding timely intervention.

The researchers hope that the strong results of their pilot study will guide clinicians to revise current practices regarding viral bronchiolitis and personalize care of viral respiratory illnesses from first presentation in order to improve outcomes. Study author and Children’s National pulmonologist Maria Arroyo, M.D., says, “if we can prevent these patients from coming [back] to the hospital just by doing a clinical evaluation the first time that they present with [viral respiratory infection]…that would be very impactful.”

The associated article, “Phenotypical Sub-setting of the First Episode of Severe Viral Respiratory Infection Based on Clinical Assessment and Underlying Airway Disease: A Pilot Study,” was published April 2, 2020 in Frontiers in Pediatrics. Notable authors include Maria Arroyo, M.D., Kyle Salka, M.S., and Gustavo Nino, M.D., M.S.H.S., D.A.B.S.M.

newborn in incubator

How EPO saves babies’ brains

newborn in incubator

Researchers have discovered that treating premature infants with erythropoietin can help protect and repair their vulnerable brains.

The drug erythropoietin (EPO) has a long history. First used more than three decades ago to treat anemia, it’s now a mainstay for treating several types of this blood-depleting disorder, including anemia caused by chronic kidney disease, myelodysplasia and cancer chemotherapy.

More recently, researchers discovered a new use for this old drug: Treating premature infants to protect and repair their vulnerable brains. However, how EPO accomplishes this feat has remained unknown. New genetic analyses presented at the Pediatric Academic Societies 2018 annual meeting that was conducted by a multi-institutional team that includes researchers from Children’s National show that this drug may work its neuroprotective magic by modifying genes essential for regulating growth and development of nervous tissue as well as genes that respond to inflammation and hypoxia.

“During the last trimester of pregnancy, the fetal brain undergoes tremendous growth. When infants are born weeks before their due dates, these newborns’ developing brains are vulnerable to many potential insults as they are supported in the neonatal intensive care unit during this critical time,” says An Massaro, M.D., an attending neonatologist at Children’s National Health System and lead author of the research. “EPO, a cytokine that protects and repairs neurons, is a very promising therapeutic approach to support the developing brains of extremely low gestational age neonates.”

The research team investigated whether micro-preemies treated with EPO had distinct DNA methylation profiles and related changes in expression of genes that regulate how the body responds to such environmental stressors as inflammation, hypoxia and oxidative stress.  They also investigated changes in genes involved in glial differentiation and myelination, production of an insulating layer essential for a properly functioning nervous system. The genetic analyses are an offshoot of a large, randomized clinical trial of EPO to treat preterm infants born between 24 and 27 gestational weeks.

The DNA of 18 newborns enrolled in the clinical trial was isolated from specimens drawn within 24 hours of birth and at day 14 of life. Eleven newborns were treated with EPO; a seven-infant control group received placebo.

DNA methylation and whole transcriptome analyses identified 240 candidate differentially methylated regions and more than 50 associated genes that were expressed differentially in infants treated with EPO compared with the control group. Gene ontology testing further narrowed the list to five candidate genes that are essential for normal neurodevelopment and for repairing brain injury:

“These findings suggest that EPO’s neuroprotective effect may be mediated by epigenetic regulation of genes involved in the development of the nervous system and that play pivotal roles in how the body responds to inflammation and hypoxia,” Dr. Massaro says.

In addition to Dr. Massaro, study co-authors include Theo K. Bammler, James W. MacDonald, biostatistician, Bryan Comstock, senior research scientist, and Sandra “Sunny” Juul, M.D., Ph.D., study principal investigator, all of University of Washington.