By Gilang Cahya 
In the realm of scientific inquiry, the unexpected is often the harbinger of groundbreaking revelation. For a collaborative team of researchers from Memorial Sloan Kettering Cancer Center (MSK) and the Icahn School of Medicine at Mount Sinai, an experimental outcome that defied their initial hypotheses has opened a promising new avenue for improving therapies that leverage small RNA molecules to silence disease-causing genes, with significant implications for cancer treatment and a spectrum of other conditions.
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, centered on understanding the role of a protein known as ALAS1 in the biogenesis of microRNAs. MicroRNAs are a class of small regulatory RNA molecules that play a crucial role in controlling gene expression. The team’s initial expectation was that the removal of ALAS1 from cells would lead to a decrease in microRNA levels. However, the experimental results presented a stark and surprising counterpoint: microRNA levels actually surged.
"Sometimes you do an experiment," Dr. Lai explained in a recent interview, reflecting on the serendipitous nature of the discovery. "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 fundamental principle of scientific exploration—that unexpected findings can be more valuable than predicted ones—lies at the heart of this latest advancement.
The Unforeseen Role of ALAS1: Beyond Heme Synthesis
The unexpected increase in microRNA levels upon ALAS1 depletion pointed to a previously unrecognized function for the protein. ALAS1, or aminolevulinate synthase 1, has a well-established and vital role in the production of heme. Heme is an essential molecule involved in numerous critical biological processes, including oxygen transport (as the core component of hemoglobin), energy production within cells, and, as this research now reveals, the intricate machinery that generates microRNAs.
The team’s meticulous investigation revealed that the perturbation of other enzymes within the heme biosynthesis pathway did not yield the same effect on microRNA levels. This observation strongly suggested that ALAS1 possesses a "moonlighting" function—a term used in molecular biology to describe proteins that perform more than one distinct role within a cell. The discovery that ALAS1 actively regulates microRNAs, independent of its canonical function in heme synthesis, represents a significant paradigm shift in our understanding of cellular regulatory networks.
"This told us that ALAS1 has another job outside of helping to make heme, which no one had realized," stated Dr. Lee, highlighting the novelty of their findings. Dr. Lai further elaborated, "We can consider this a ‘moonlighting’ function. And here we discovered that ALAS1 has this secret role regulating microRNAs that’s not connected to its normal role in heme synthesis."
The comprehensive findings of this research were recently published in the esteemed scientific journal Science, a testament to their significance and rigorous peer review.
Understanding the Power of Small RNA Snippets in Gene Silencing
To fully appreciate the implications of this discovery, it is crucial to understand how small RNAs exert their regulatory influence. MicroRNAs, along with a related class of molecules called small interfering RNAs (siRNAs), are remarkably small RNA fragments, typically measuring only 21 to 22 nucleotides in length. Their primary function is to bind to specific messenger RNA (mRNA) molecules. mRNA acts as a blueprint, carrying genetic instructions from DNA to the cell’s protein-making machinery. By binding to mRNA, microRNAs and siRNAs effectively "silence" these genetic messages, preventing the production of the corresponding proteins.
The cellular machinery responsible for converting longer RNA molecules into these functional small RNA products is a complex, multi-step process involving numerous enzymatic and regulatory components. Scientists have ingeniously harnessed this knowledge to develop therapeutic strategies that utilize small RNAs, particularly siRNAs, as drugs. These therapeutic siRNAs are designed to target and silence specific disease-causing genes.
The landmark approval of patisiran by the U.S. Food and Drug Administration (FDA) in 2018 marked a pivotal moment in the field, as it was the first siRNA drug to receive regulatory authorization for treating hereditary transthyretin amyloidosis, a debilitating genetic disorder. Since then, the pipeline for siRNA-based therapeutics has expanded significantly, with several more drugs gaining approval and numerous others progressing through various stages of clinical trials. The potential applications are vast, ranging from rare genetic disorders to more common diseases. These RNA interference (RNAi) drugs, as they are sometimes called, hold immense promise for revolutionizing medicine.
A Collaborative Effort to Validate and Expand Findings
Recognizing the profound implications of their discovery, the MSK researchers proactively sought collaboration with experts in heme regulation and ALAS genes at the Icahn School of Medicine at Mount Sinai. This strategic partnership brought together the specialized knowledge of Makiko Yasuda, MD, PhD, Robert Desnick, MD, PhD, and postdoctoral fellow Sangmi Lee, PhD. The Mount Sinai team had developed sophisticated custom animal models, particularly focused on liver-specific heme regulation.
This collaboration enabled the researchers to transition their observations from in vitro cell culture experiments to in vivo studies in animal models. Crucially, the findings in mice mirrored those observed in cell cultures. When ALAS was depleted, specifically in liver cells, a global increase in microRNA levels was observed.
"The emerging picture is that ALAS acts as a brake on the production of microRNAs," Dr. Lai posited. "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."
Towards More Potent and Targeted RNA-Based Therapies
The theoretical implication of this discovery is substantial: by understanding how to modulate ALAS1 activity, scientists may be able to enhance the effectiveness of existing siRNA drugs. This could lead to more potent silencing of problematic genes that are overexpressed in various diseases, including oncogenes that drive cancer progression.
"But we’re not quite there yet," Dr. Lai cautioned, emphasizing the need for continued research. He pointed out that current therapeutic siRNA drugs face limitations. Their efficacy is not uniform across all targets, and their delivery to specific tissues or cell types remains a challenge. For instance, all six FDA-approved siRNA drugs primarily target hepatocytes, the main functional cells of the liver. The liver’s role as a biological filter makes it a relatively accessible target for drug delivery.
As a proof-of-concept, the research team successfully demonstrated in mice that depleting liver cells of ALAS not only increased microRNA levels but also significantly enhanced the gene-silencing activity of a model siRNA compound administered to the animals.
Intriguingly, a coincidental overlap emerged with an existing therapeutic. One of the six approved siRNA drugs is specifically designed to turn off ALAS1 to treat acute hepatic porphyrias, a group of rare genetic disorders affecting heme metabolism. This drug, known as givosiran, has undergone extensive preclinical and clinical trials, demonstrating its safety and efficacy in humans. The existence of an approved siRNA targeting ALAS1 in humans opens up a compelling possibility: combining a similar agent with other siRNA drugs could potentially amplify their therapeutic effects. Dr. Lai suggested that this strategy might be broadly applicable to any siRNA therapy.
The potential benefits of such an approach are multifaceted. If siRNA drugs can be made more effective, they could become more cost-efficient, requiring lower doses to achieve therapeutic outcomes, thereby potentially reducing side effects. Furthermore, enhanced efficacy might also pave the way for targeting cell types beyond the liver, expanding the therapeutic reach of RNAi technology.
The Enduring Value of Fundamental Discovery Science
This remarkable discovery underscores the profound importance of curiosity-driven, fundamental research. 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 microRNA and its role in gene regulation in the early 1990s, serves as a powerful recent testament to this principle. Dr. Lai, who conducted his undergraduate thesis research in Dr. Ruvkun’s lab, credits his mentor with igniting his passion for scientific exploration.
"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 validates the significance of fundamental research. He noted that Dr. Ruvkun, like Dr. Ambros, was not initially searching for microRNAs. Instead, their groundbreaking work stemmed from investigations into the development of nematodes, tiny soil-dwelling worms. This basic research not only unveiled an entirely new paradigm for gene control but ultimately led to the development of a novel class of human therapies.
"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 argued passionately. He stressed the critical need to maintain societal and governmental support for basic scientific research, especially in a climate marked by uncertainty and disagreement regarding public funding for science. "Hopefully, there will be continued support to keep the engine of foundational research strong," he concluded.
Funding and Intellectual Property
The research detailed in this article was supported by 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).
The researchers have filed a patent application covering their novel methods for enhancing the efficacy of RNAi therapy through the modulation of ALAS1/ALAS2 (WO2024148236A1). Additionally, Drs. Yasuda and Desnick are co-inventors on a patent pertaining to RNAi therapy for acute hepatic porphyrias and have reported pharmaceutical consulting activities.
