By Gilang Cahya 
In the relentless pursuit of scientific understanding, the unexpected often serves as a potent catalyst for groundbreaking discovery. This principle has once again been underscored by a remarkable finding from a collaborative research effort involving scientists at Memorial Sloan Kettering Cancer Center (MSK) and the Icahn School of Medicine at Mount Sinai. Their work, which stemmed from an experiment yielding results contrary to initial expectations, has unveiled a novel mechanism in the regulation of small RNAs, potentially revolutionizing therapies designed to silence disease-causing genes, including those implicated in various forms of cancer.
The research, published in the prestigious journal Science, centers on the protein ALAS1 and its previously unrecognized role in the intricate world of microRNA production. "Sometimes you do an experiment," explained Eric Lai, PhD, a developmental biologist at MSK and a senior author on the study. "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 serendipitous deviation from expectation has indeed unearthed a significant new facet of biological regulation with profound therapeutic implications.
The Genesis of an Unforeseen Finding
The research team, spearheaded by Seungjae Lee, PhD, a postdoctoral fellow in Dr. Lai’s laboratory at MSK’s Sloan Kettering Institute, embarked on their investigation with a specific hypothesis. They aimed to elucidate how the protein ALAS1 contributes to the synthesis of microRNAs, a class of small regulatory RNA molecules. Their experimental design involved the targeted removal of ALAS1 from cellular models, with the clear expectation that this action would lead to a demonstrable decrease in microRNA levels. However, the laboratory results defied this prediction, presenting the researchers with a startling observation: microRNA levels not only failed to decline but actually increased.
"But instead, we were surprised to see them increase," Dr. Lai recounted, highlighting the pivotal nature of this counterintuitive outcome. This unexpected surge in microRNA production prompted a deeper exploration into the functions of ALAS1, revealing an entirely new role for the protein beyond its well-established involvement in heme biosynthesis. Heme, a critical component in numerous biological processes such as oxygen transport (forming the core of hemoglobin), energy production within cells, and the very synthesis of microRNAs, was thought to be ALAS1’s primary domain. The new findings suggest ALAS1 is a "moonlighting" enzyme, performing a second, independent function in regulating microRNAs.
Understanding the Power of Small RNA Snippets
To fully appreciate the significance of this discovery, it is essential to understand the fundamental role of microRNAs and their close relatives, small interfering RNAs (siRNAs). These molecules are minuscule fragments of RNA, typically comprising only 21 to 22 nucleotides. Their primary function is to bind with specific messenger RNA (mRNA) molecules, effectively "silencing" them and preventing the production of the proteins encoded by these mRNAs. This intricate process is orchestrated by a complex molecular machinery that converts longer RNA precursors into these potent regulatory agents.
The scientific community has adeptly harnessed this knowledge, translating it into a revolutionary class of therapeutics known as RNA interference (RNAi) drugs. These drugs leverage the natural gene-silencing capabilities of small RNAs to target and inhibit the expression of genes responsible for various diseases. A landmark achievement in this field was the U.S. Food and Drug Administration (FDA) approval of patisiran in 2018, the first siRNA drug, which treats hereditary transthyretin amyloidosis, a severe genetic disorder. Since then, several other siRNA drugs have received regulatory approval, with numerous others progressing through clinical trials, offering hope for treating both rare genetic conditions and more prevalent diseases. The potential applications are vast, and the ongoing development signifies a transformative shift in pharmaceutical innovation.
The "Moonlighting" Enzyme: ALAS1’s Dual Identity
The unexpected observation in the Lai Lab—that removing ALAS1 led to an increase, not a decrease, in microRNAs—sparked a series of intensive investigations. Dr. Lee’s further experiments revealed a crucial distinction: while the absence of ALAS1 significantly impacted microRNA levels, removing other enzymes involved in the heme biosynthesis pathway had no discernible effect. This critical observation firmly pointed to ALAS1 possessing a function entirely independent of its known role 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, emphasizing the novelty of this revelation. Dr. Lai further elaborated on this concept, describing it as 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," he added. This identification of a dual role for ALAS1 represents a significant advancement in understanding cellular regulatory networks.
Bridging the Gap: From Cell Culture to Animal Models
To validate and expand upon these initial findings, the MSK researchers sought collaboration with experts in heme regulation and ALAS genes at the Icahn School of Medicine at Mount Sinai. This strategic partnership brought together Makiko Yasuda, MD, PhD, Robert Desnick, MD, PhD, and their postdoctoral fellow, Sangmi Lee, PhD, whose laboratories had developed specialized animal models and possessed deep expertise in these areas. This collaboration proved instrumental in transitioning the research from isolated cell cultures to more complex biological systems.
In custom animal models developed at Mount Sinai, the researchers observed a consistent pattern: the depletion of ALAS, specifically in liver cells, resulted in a global increase in microRNA populations. This finding in a living organism strongly supported the conclusion that ALAS1 acts as a regulator of microRNA biogenesis. "The emerging picture is that ALAS acts as a brake on the production of microRNAs," Dr. Lai elucidated. This understanding immediately led to a compelling therapeutic hypothesis: if ALAS1 acts as a brake, then manipulating its activity could potentially enhance the effectiveness of existing gene-silencing therapies.
Enhancing siRNA Drug Efficacy: A New Therapeutic Frontier
The implications of ALAS1’s "brake" function on microRNA production are far-reaching, particularly for the development and efficacy of siRNA drugs. The research team theorized that by inhibiting ALAS1, they could essentially "release the brake," thereby amplifying the production of microRNAs and potentially boosting the silencing activity of siRNA therapeutics. "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," Dr. Lai explained.
This proposed strategy holds significant promise for a wide range of diseases where gene overactivity contributes to pathology. Potentially, this could include the targeting of oncogenes, which are known drivers of cancer development. While the prospect is exciting, Dr. Lai tempered expectations with a realistic assessment of the current limitations. "But we’re not quite there yet," he cautioned. "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, the FDA-approved siRNA drugs are primarily targeted to hepatocytes within the liver, largely due to the organ’s role as a biological filter, making drug delivery more straightforward.
As a proof-of-concept, the researchers successfully demonstrated in their mouse models that not only could they deplete ALAS in liver cells, leading to the expected increase in microRNAs, but this intervention also significantly enhanced the silencing efficacy of a model siRNA compound administered to the animals. This experimental validation provides a strong foundation for further development.
Remarkably, a serendipitous connection emerged with one of the existing FDA-approved siRNA drugs. This drug, known as givosiran, is used to treat acute hepatic porphyrias by specifically targeting and turning off ALAS1. Drs. Yasuda and Desnick were instrumental in the preclinical and clinical development of givosiran, providing a critical real-world precedent. The established safety and efficacy of an siRNA targeting ALAS1 in humans opens the door to combining such an agent with other siRNA drugs to augment their therapeutic effects. Dr. Lai suggested that this combinational approach could be broadly applicable to any siRNA-based therapy.
The potential benefits of enhancing siRNA drug efficacy are substantial. Improved potency could lead to more cost-effective treatments, allow for lower therapeutic doses thereby reducing the risk of side effects, and potentially expand the range of cell types and tissues that can be effectively targeted beyond the liver. This breakthrough represents a significant step towards unlocking the full therapeutic potential of RNAi technology.
The Enduring Value of Discovery Science
The narrative of this discovery also serves as a powerful testament to the enduring importance of curiosity-driven, fundamental research. In December 2024, the Nobel Prize in Physiology or Medicine was awarded 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 himself was an undergraduate thesis student in Dr. Ruvkun’s lab during that formative period, an experience that he credits with igniting his passion for science.
"I got my first real exposure to how science was actually done and gained lifelong interests in developmental biology and small RNAs," Dr. Lai reflected, underscoring the profound influence of his mentor’s work. He drew a parallel between the Nobel laureates’ journey and the recent findings, emphasizing that breakthroughs often arise from investigations into fundamental biological processes, rather than direct attempts to cure specific diseases. Dr. Ruvkun, he noted, was not initially searching for microRNAs but rather studying the developmental biology of nematodes (tiny soil worms). This fundamental inquiry ultimately unveiled an entirely new paradigm of gene control that has since led to novel 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 asserted. He stressed the critical need to maintain robust support for foundational research, especially in an era of societal and governmental discourse concerning the allocation of public funding for scientific endeavors. "And I think that 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 study 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).
In recognition of the novelty and therapeutic potential of their findings, the researchers have filed a patent application concerning their methods for enhancing the efficacy of RNAi therapy by targeting ALAS1/ALAS2, designated as WO2024148236A1. Furthermore, Drs. Yasuda and Desnick are co-inventors on a patent related to RNAi therapy for acute hepatic porphyrias and also report engaging in pharmaceutical consulting work. These disclosures highlight the significant commercial and clinical interest generated by this groundbreaking research.
