By Gilang Cahya 
In the dynamic landscape of scientific exploration, the unexpected often serves as a potent catalyst for groundbreaking discoveries. This principle has been vividly illustrated by a recent study from researchers at Memorial Sloan Kettering Cancer Center (MSK) and their collaborators at the Icahn School of Medicine at Mount Sinai. Their investigation into the intricate mechanisms of small RNA gene regulation yielded surprising results, opening a novel avenue to enhance therapies that utilize small RNAs to silence disease-causing genes, with significant implications for cancer treatment and a range of other genetic disorders.
The research, spearheaded by Seungjae Lee, PhD, a postdoctoral fellow in the laboratory of developmental biologist Eric Lai, PhD, at MSK’s Sloan Kettering Institute, initially focused on understanding the role of a protein known as ALAS1 in the production of microRNAs. MicroRNAs are a class of small regulatory RNA molecules crucial for gene expression. The team hypothesized that by removing ALAS1 from cells, they would observe a corresponding decrease in microRNA levels. However, the experimental outcome defied these expectations, revealing an increase in microRNAs instead.
"Sometimes you do an experiment," Dr. Lai explained, reflecting on the serendipitous nature of scientific progress. "You think you’re testing one idea, but when it doesn’t turn out the way you planned, it can lead you to find something else that’s much more interesting." This counterintuitive finding illuminated a previously unrecognized function of ALAS1, extending beyond its well-established role in heme biosynthesis. Heme, an iron-containing porphyrin, is fundamental to numerous biological processes, including oxygen transport by hemoglobin, cellular energy production, and, as this research demonstrates, the intricate machinery of microRNA biogenesis.
The comprehensive findings of this collaborative effort were recently published in the esteemed scientific journal Science, marking a significant advancement in the field of molecular biology and therapeutic development.
The Power of Small RNA Snippets in Gene Silencing
To fully appreciate the impact of this discovery, it is essential to understand the fundamental role of small RNAs in cellular regulation and their therapeutic potential. MicroRNAs, along with related small interfering RNAs (siRNAs), are diminutive RNA molecules, typically comprising just 21 to 22 nucleotides. Their primary function is to bind to specific messenger RNA (mRNA) molecules, thereby repressing their translation into proteins. This sophisticated mechanism allows cells to finely tune gene expression, acting as critical regulators of cellular processes, development, and disease.
The conversion of longer RNA precursors into these potent small RNA effectors involves a complex enzymatic cascade, often referred to as a "bucket brigade." Scientists have ingeniously harnessed this biological pathway to develop a novel class of therapeutics. By designing synthetic siRNAs that are complementary to the mRNA of disease-causing genes, these RNA interference (RNAi) drugs can effectively silence the aberrant gene expression.
The therapeutic promise of RNAi was first recognized with the U.S. Food and Drug Administration (FDA) approval of patisiran in 2018. This groundbreaking siRNA drug treats hereditary transthyretin amyloidosis, a debilitating genetic disorder. Since then, several other siRNA drugs have received regulatory approval, with a growing pipeline of candidates progressing through clinical trials. These therapies are demonstrating remarkable efficacy against a spectrum of conditions, ranging from rare genetic diseases to more prevalent chronic illnesses. The potential applications are vast, offering hope for conditions previously considered intractable.
Unveiling the "Moonlighting" Function of ALAS1
The research team’s unexpected observation that ALAS1 depletion led to increased microRNA levels prompted further investigation. Dr. Lee’s meticulous experiments revealed that while the absence of ALAS1 significantly altered microRNA abundance, the removal of other enzymes involved in the heme biosynthesis pathway had no discernible effect. This crucial distinction provided compelling evidence that ALAS1 possesses a distinct functional role separate from its canonical involvement in heme production.
"This told us that ALAS1 has another job outside of helping to make heme, which no one had realized," Dr. Lee stated, highlighting the significance of their findings.
Dr. Lai further elaborated on this concept, describing ALAS1’s newly discovered role as a "moonlighting" function – a term used in biochemistry to describe a protein that performs more than one distinct function. "And here we discovered that ALAS1 has this secret role regulating microRNAs that’s not connected to its normal role in heme synthesis," he added. This revelation suggested that ALAS1 acts as a key regulator in the microRNA production pathway, independent of its heme-related duties.
A Collaborative Effort to Enhance siRNA Drug Efficacy
The implications of this discovery spurred a vital collaboration between the MSK researchers and a team at the Icahn School of Medicine at Mount Sinai. This group, comprising experts in heme regulation and ALAS gene biology, including Makiko Yasuda, MD, PhD, Robert Desnick, MD, PhD, and postdoctoral fellow Sangmi Lee, PhD, brought specialized knowledge and resources to the project. Their expertise was instrumental in transitioning the research from cellular models to custom animal models.
In these specially developed mouse models, the researchers observed a consistent phenomenon: the depletion of ALAS, specifically in liver cells, resulted in a global increase in microRNA levels. This experimental validation in a more complex biological system solidified the team’s hypothesis.
"The emerging picture is that ALAS acts as a brake on the production of microRNAs," Dr. Lai summarized. "So we thought, now that we know how to remove this brake, maybe we can use that to improve the efficacy of siRNA drugs and their ability to silence their target genes."
The theoretical framework suggests that by manipulating ALAS1 activity, it might be possible to enhance the potency of siRNA drugs. This could be particularly beneficial for targeting genes that are overexpressed in diseases, including oncogenes that drive cancer progression. The ability to amplify the silencing effect of siRNA drugs could translate into more effective treatments for a wider range of conditions.
However, Dr. Lai cautioned that significant challenges remain. "But we’re not quite there yet," he noted. "Therapeutic siRNA drugs don’t work well enough against all targets and are currently limited in where they can be used in the body." Currently, approved siRNA drugs primarily target hepatocytes, the main cell type in the liver, due to the organ’s role as a biological filter and its accessibility for drug delivery. The six FDA-approved siRNA drugs all target liver cells.
Proof-of-Concept in Animal Models and Therapeutic Synergies
To demonstrate the practical applicability of their findings, the research team conducted a proof-of-concept study. They successfully depleted ALAS in mouse liver cells, confirming the expected increase in microRNA levels. Crucially, this depletion also enhanced the gene-silencing efficacy of a model siRNA compound administered to the mice. This experiment provided tangible evidence that manipulating ALAS1 activity can indeed amplify the effectiveness of siRNA therapeutics.
Intriguingly, one of the existing FDA-approved siRNA drugs, givosiran, targets and inhibits ALAS1 to treat acute hepatic porphyrias. Drs. Yasuda and Desnick played a pivotal role in the preclinical and clinical development of givosiran, underscoring their deep understanding of ALAS1’s role in human health. The fact that an siRNA targeting ALAS1 is already safely and effectively used in humans opens up a compelling possibility: combining such an agent with other siRNA drugs could synergistically boost their therapeutic power. Dr. Lai believes this approach could be broadly applicable to any siRNA therapy, regardless of its specific target.
The potential benefits of such a combined therapeutic strategy are manifold. Enhanced siRNA drug efficacy could lead to improved cost-effectiveness by allowing for lower therapeutic doses. This, in turn, could reduce the risk of adverse side effects and potentially expand the therapeutic window, making these drugs more accessible and tolerable for patients. Furthermore, improved efficacy might enable the targeting of cell types beyond the liver, broadening the scope of siRNA-based treatments for a wider array of diseases.
The Enduring Importance of Discovery Science
The narrative of ALAS1’s "moonlighting" function and its implications for RNA therapeutics serves as a powerful testament to the value of curiosity-driven research, often referred to as discovery science. This philosophy was recently underscored by the Nobel Prize in Physiology or Medicine awarded in December 2024 to Harvard geneticist Gary Ruvkun, PhD, and Victor Ambros, PhD, for their pioneering discovery of microRNAs and their role in gene regulation in the early 1990s.
Dr. Lai’s own academic journey has been profoundly shaped by his undergraduate thesis research in Dr. Ruvkun’s lab, where he explored another class of gene regulators. He credits Dr. Ruvkun for igniting his passion and directing his career trajectory. "I got my first real exposure to how science was actually done and gained lifelong interests in developmental biology and small RNAs," Dr. Lai remarked, emphasizing how his mentor’s recent accolade highlights the profound impact of foundational, curiosity-driven investigations.
"Dr. Ruvkun didn’t start out looking for microRNAs," Dr. Lai elaborated. "Like Dr. Ambros, he was investigating the development of nematodes, these tiny worms that live in the soil. And not only did this unveil an entirely new paradigm for how genes are controlled, the field they started eventually resulted in a novel class of human therapies." This historical perspective underscores the unpredictable yet transformative power of basic scientific inquiry.
In a broader societal context, the story of microRNAs and ALAS1’s hidden talents directly addresses ongoing debates about scientific funding priorities. "When people ask why we’re not spending all of our research dollars directly studying diseases like cancer, why we’re funding research into cells and processes in model organisms like fruit flies, yeast, and bacteria — this is a great example of how discovery science fuels the biggest breakthroughs," Dr. Lai asserted. He stressed the critical need for sustained public and governmental support for foundational research, particularly amidst societal and political uncertainties regarding the allocation of research funding. "And I think it is especially critical to keep this conversation active, given how much uncertainty and disagreement there is in society and government about how much to publicly fund scientific research and in what areas. Hopefully, there will be continued support to keep the engine of foundational research strong."
Funding and Intellectual Property
The research detailed in this publication was made possible through significant financial support from various institutions. Grants from the National Institutes of Health (R01DK134783, R01-GM083300, P30-CA008748), a Cooperative Centers of Excellence in Hematology pilot grant (10040500-05S1), and a NYSTEM training award (C32559GG) were instrumental in facilitating this complex investigation.
Recognizing the potential of their findings, the researchers have filed a patent application related to their novel methods for enhancing RNAi therapy efficacy by targeting ALAS1/ALAS2 (WO2024148236A1). Additionally, Drs. Yasuda and Desnick are co-inventors on a patent concerning RNAi therapy for acute hepatic porphyrias and have reported pharmaceutical consulting work, further indicating their active engagement in translating scientific discoveries into clinical applications.
