By Gilang Cahya 
In the realm of scientific inquiry, where the unexpected often serves as a powerful catalyst, a recent breakthrough by researchers at Memorial Sloan Kettering Cancer Center (MSK) and their collaborators at the Icahn School of Medicine at Mount Sinai is poised to significantly advance therapeutic strategies. Their work, born from an experiment yielding results contrary to expectations, has unveiled a novel mechanism for improving therapies that utilize small RNAs to silence disease-causing genes, with particular implications for cancer treatment.
The foundational principle of scientific discovery often hinges on the willingness to embrace the unexpected. As developmental biologist Eric Lai, PhD, aptly described, "Sometimes you do an experiment. 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 sentiment precisely encapsulates the journey of the research team, led by Seungjae Lee, PhD, a postdoctoral fellow in the Lai Lab at MSK’s Sloan Kettering Institute.
Their initial objective was to investigate the role of a protein known as ALAS1 in the biogenesis of small regulatory RNAs called microRNAs. The prevailing scientific understanding suggested that ALAS1 was integral to the production of microRNAs. Consequently, the researchers anticipated that removing ALAS1 from cellular environments would lead to a discernible decrease in microRNA levels. However, the experimental outcomes defied these predictions. Instead of a reduction, the team observed a surprising and significant increase in microRNA abundance.
This counterintuitive finding was not merely an anomaly; it marked the identification of an unrecognized function for ALAS1, extending beyond its well-established role in heme biosynthesis. Heme, a critical component in numerous biological processes, including oxygen transport via hemoglobin, energy production, and, as now understood, microRNA synthesis, had long been the primary focus of ALAS1 research. The study’s findings, published in the prestigious journal Science, have now illuminated a dual nature for this vital protein.
The Precision of Small RNA Gene Silencing
To fully appreciate the implications of this discovery, it is essential to understand the mechanism of small RNAs in gene regulation. Both microRNAs (miRNAs) and their closely related counterparts, small interfering RNAs (siRNAs), are diminutive RNA molecules, typically measuring between 21 and 22 nucleotides in length. Their biological function is to bind with specific messenger RNAs (mRNAs), the molecular intermediaries that carry genetic instructions from DNA to the cell’s protein-making machinery. Upon binding, miRNAs and siRNAs effectively "silence" these target mRNAs, preventing them from being translated into proteins.
The cellular process by which longer RNA molecules are processed into these precise, active small RNA products involves a complex cascade of enzymatic and protein factors. Scientists have masterfully deciphered this intricate "bucket brigade" of molecular players, leveraging this knowledge to engineer small RNAs as potent therapeutic agents. These engineered small RNAs can be designed to target and silence specific genes responsible for initiating or perpetuating various diseases.
The therapeutic potential of this technology was dramatically underscored by the U.S. Food and Drug Administration (FDA) approval of patisiran in 2018. This marked the first siRNA drug to receive regulatory clearance, offering a lifeline to patients suffering from hereditary transthyretin amyloidosis, a debilitating genetic disorder. Since then, a growing number of siRNA drugs have gained approval, with many more progressing through rigorous clinical trials. The medical community views siRNA-based medicines with immense optimism, foreseeing their application in treating both rare genetic conditions and more prevalent diseases. These siRNA drugs are often referred to as RNAi (RNA interference) drugs, a testament to their mechanism of interfering with messenger RNA accumulation.
ALAS1: A "Moonlighting" Enzyme Revealed
Within the confines of the Lai Lab, Dr. Lee’s meticulous experimentation provided the first tangible evidence of ALAS1’s unconventional role. The observation that removing ALAS1 led to an amplification of microRNA levels, while the absence of other enzymes within the heme biosynthesis pathway had no discernible effect on microRNA production, was a critical turning point.
"This told us that ALAS1 has another job outside of helping to make heme, which no one had realized," Dr. Lee stated, underscoring the groundbreaking nature of their finding.
Dr. Lai further elaborated on this revelation, characterizing it as a "moonlighting" function, a term used in molecular biology to describe proteins that perform more than one distinct role. "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 "secret role" represented a significant departure from established biochemical understanding.
Bridging Cell Culture and Animal Models: A Collaborative Leap
The implications of this "moonlighting" enzyme spurred immediate collaboration. Recognizing the need to validate these findings beyond cell culture and into more complex biological systems, the MSK researchers joined forces with a team at the Icahn School of Medicine at Mount Sinai. This group, comprising experts in heme regulation and ALAS genes, included Makiko Yasuda, MD, PhD, Robert Desnick, MD, PhD, and postdoctoral fellow Sangmi Lee, PhD. Their specialized expertise, particularly in developing custom animal models, proved instrumental in advancing the research.
The collaborative effort facilitated the translation of the initial cell-based discoveries into in vivo studies using mice. The results were consistent and compelling: in these animal models, depleting ALAS, specifically within liver cells, triggered a global increase in microRNA levels. This solidified the hypothesis that ALAS1 acts as a regulatory rheostat for microRNA production.
"The emerging picture is that ALAS acts as a brake on the production of microRNAs," Dr. Lai explained. This analogy vividly illustrates the newly identified inhibitory role of ALAS1. He continued, "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."
Enhancing siRNA Drug Efficacy: A Promising Therapeutic Avenue
The strategic insight derived from this research points towards a novel therapeutic strategy: manipulating ALAS1 activity to amplify the effectiveness of existing and future siRNA drugs. In theory, this approach could enhance the potency of siRNA therapies against any gene that is aberrantly overactive in disease states, including oncogenes implicated in cancer development.
"But we’re not quite there yet," Dr. Lai cautioned, tempering immediate expectations. He highlighted current limitations in siRNA drug development, noting that their efficacy is not uniform across all targets, and their delivery to specific tissues remains a challenge. Presently, all six FDA-approved siRNA drugs are designed to target hepatocytes, the primary functional cells of the liver. This concentration in liver-targeted therapies is attributed to the liver’s role as a biological filter, making it a relatively accessible organ for drug delivery.
As a proof-of-concept, the research team successfully demonstrated in mice that not only could they reduce ALAS levels in liver cells, leading to an increase in microRNAs, but this intervention also significantly boosted the gene-silencing capability of a model siRNA compound administered to the animals.
An intriguing coincidence further bolsters this therapeutic avenue. One of the six FDA-approved siRNA drugs, givosiran, functions by inhibiting ALAS1 itself, specifically for the treatment of acute hepatic porphyrias. Drs. Yasuda and Desnick were involved in the preclinical and clinical development of givosiran, underscoring the safety and efficacy of ALAS1 inhibition in humans. This existing therapeutic application raises the distinct possibility of combining an ALAS1-inhibiting agent, such as givosiran or a similar compound, with other siRNA drugs to enhance their overall effectiveness. Dr. Lai posited that this combination strategy could potentially be applicable to any siRNA-based therapy.
The potential benefits of such an approach are multifaceted. Enhanced efficacy could translate to the possibility of using lower drug doses, thereby potentially reducing side effects and improving cost-effectiveness. Furthermore, a deeper understanding of ALAS1’s regulatory role might unlock the ability to target cell types beyond the liver, broadening the scope of siRNA therapies.
The Indispensable Value of Discovery Science
The narrative of this scientific breakthrough is intrinsically linked to the broader ecosystem of fundamental research. The very foundation of microRNA biology, upon which this new discovery is built, was laid by the pioneering work of Gary Ruvkun, PhD, and Victor Ambros, PhD. Their groundbreaking discovery of microRNAs and their role in gene regulation in the early 1990s earned them the Nobel Prize in Physiology or Medicine in December 2024. It is noteworthy that Dr. Lai conducted his undergraduate thesis research in Dr. Ruvkun’s lab during that formative period, a period he credits with igniting his passion for developmental biology and small RNAs.
"Dr. Ruvkun didn’t start out looking for microRNAs," Dr. Lai reflected. "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 example serves as a powerful illustration of the profound impact of curiosity-driven, discovery science. "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," he emphasized.
In an era marked by societal and governmental discourse surrounding the allocation of public funding for scientific research, Dr. Lai stressed the critical importance of maintaining robust support for foundational research. "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."
The research 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 also filed a patent application pertaining to their methods for enhancing RNAi therapy efficacy by targeting ALAS1/ALAS2 (WO2024148236A1). Additionally, Drs. Yasuda and Desnick are co-inventors on a patent related to RNAi therapy for acute hepatic porphyrias and report pharmaceutical consulting work.
