By Gilang Cahya 
In the relentless pursuit of scientific understanding, the most profound breakthroughs often emerge not from meticulously planned outcomes, but from the unexpected detours that unravel the fabric of what we thought we knew. For a collaborative team of researchers from Memorial Sloan Kettering Cancer Center (MSK) and the Icahn School of Medicine at Mount Sinai, a seemingly perplexing experimental result has opened a significant new avenue for enhancing the efficacy of gene-silencing therapies, with far-reaching implications for treating a spectrum of diseases, including cancer.
The genesis of this discovery lies in a standard laboratory experiment. Developmental biologist Eric Lai, PhD, a leading figure in the research, described the serendipitous nature of scientific progress: "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 perfectly encapsulates the journey that led to the uncovering of a previously unrecognized role for the protein ALAS1.
The research, spearheaded by Seungjae Lee, PhD, a postdoctoral fellow in Dr. Lai’s laboratory at MSK’s Sloan Kettering Institute, initially focused on understanding how ALAS1 contributes to the biogenesis of microRNAs. MicroRNAs are crucial regulators of gene expression, acting as tiny molecular architects that fine-tune the activity of thousands of genes within our cells. The team’s hypothesis was straightforward: removing ALAS1 from cells would lead to a corresponding decrease in microRNA levels, as ALAS1 was known to be involved in processes related to RNA production, particularly through its well-established role in heme biosynthesis.
However, the experimental results defied expectations. Instead of a decline, the researchers observed a surprising and significant increase in microRNA levels when ALAS1 was depleted. This counterintuitive finding served as a critical pivot point, prompting a deeper investigation into the true function of ALAS1.
The Unveiling of a "Moonlighting" Enzyme
The unexpected surge in microRNA production upon ALAS1 removal pointed towards a function for the protein that was entirely independent of its canonical role in synthesizing heme. Heme, an iron-containing molecule, is a vital component in numerous biological processes, including oxygen transport within hemoglobin, energy production in mitochondria, and, as this research now reveals, the intricate pathways governing microRNA maturation.
Further experimentation by Dr. Lee and his colleagues confirmed that this effect was specific to ALAS1. When other enzymes integral to the heme biosynthesis pathway were removed from cells, microRNA levels remained largely unaffected. This crucial distinction underscored the discovery: ALAS1 possessed a "moonlighting" function, a term used in biology to describe proteins that perform multiple, distinct roles.
"This told us that ALAS1 has another job outside of helping to make heme, which no one had realized," Dr. Lee stated. Dr. Lai elaborated on this concept, describing it as a "secret role regulating microRNAs that’s not connected to its normal role in heme synthesis." This revelation marked a significant advancement in our understanding of cellular regulatory networks.
The Power of Small Interfering RNAs (siRNAs)
To fully appreciate the potential impact of this discovery, it is essential to understand the mechanism and therapeutic promise of small RNAs, specifically microRNAs and their close relatives, small interfering RNAs (siRNAs). Both are diminutive RNA molecules, typically measuring 21 to 22 nucleotides in length. Their primary function is to bind to specific messenger RNA (mRNA) molecules, effectively silencing the genes they encode by preventing protein synthesis.
This gene-silencing capability has been ingeniously harnessed by scientists to develop a novel class of therapeutics known as RNA interference (RNAi) drugs. By designing siRNAs that specifically target the mRNAs of disease-causing genes, researchers can therapeutically silence these aberrant genes, thereby mitigating disease progression.
The landmark approval of patisiran (Onpattro) by the U.S. Food and Drug Administration (FDA) in 2018 for the treatment of hereditary transthyretin amyloidosis heralded a new era in RNA-based medicine. Since then, several other siRNA drugs have received regulatory approval, with a robust pipeline of candidates progressing through clinical trials. These therapies hold immense potential for treating both rare genetic disorders and more common acquired diseases.
Collaborative Synergy and Animal Model Validation
The significance of the ALAS1 discovery prompted a crucial collaboration between the MSK team and specialists in heme regulation and ALAS genes at the Icahn School of Medicine at Mount Sinai. This partnership brought together Makiko Yasuda, MD, PhD, Robert Desnick, MD, PhD, and their postdoctoral fellow Sangmi Lee, PhD, whose expertise in custom animal models proved invaluable.
This collaborative effort allowed the researchers to transition their findings from cell culture experiments to a more complex biological system. In custom-designed mouse models, the depletion of ALAS, particularly in liver cells, consistently resulted in a global increase in microRNA levels, corroborating the cell-based observations.
"The emerging picture is that ALAS acts as a brake on the production of microRNAs," Dr. Lai explained. "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 New Therapeutic Strategy
The implication of ALAS1 acting as a "brake" on microRNA production is profound for the development of RNAi therapeutics. If ALAS1 can be effectively inhibited, the resulting surge in microRNAs could potentially enhance the silencing activity of therapeutic siRNAs. This could be particularly beneficial for targeting genes that are overexpressed or dysregulated in various diseases, including oncogenes that drive the proliferation of cancer cells.
However, Dr. Lai cautioned that this therapeutic strategy is still in its early stages. "But we’re not quite there yet," he stated. "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, all FDA-approved siRNA drugs are administered to target hepatocytes, the primary cell type in the liver, due to the organ’s natural filtering function and ease of drug delivery.
To validate their hypothesis, the research team conducted a proof-of-concept study. They demonstrated that not only could they deplete ALAS in mouse liver cells, leading to an increase in microRNAs, but this intervention also significantly amplified the silencing efficacy of a model siRNA compound administered to the mice. This experimental success provides a strong foundation for the potential of combining ALAS1 inhibition with existing siRNA therapies.
A Fortuitous Connection: Givosiran and the Future of Combination Therapies
Remarkably, one of the six FDA-approved siRNA drugs, givosiran (Givlaari), functions by targeting and inhibiting ALAS1 to treat acute hepatic porphyrias, a group of rare genetic disorders affecting heme biosynthesis. Drs. Yasuda and Desnick were instrumental in the preclinical and clinical development of givosiran, adding a layer of serendipity and immediate clinical relevance to the current discovery.
The established safety and efficacy of givosiran in humans directly in the clinic provides a compelling precedent for using ALAS1-targeting agents to enhance other siRNA drugs. Dr. Lai suggested that this combination strategy could be broadly applicable to any siRNA therapy, offering a universal mechanism to boost gene silencing.
The potential benefits of such a combined approach are manifold. Enhanced efficacy could translate to lower required doses of siRNA drugs, potentially reducing side effects and improving cost-effectiveness. Furthermore, a better understanding of ALAS1’s role might unlock the possibility of targeting cell types beyond the liver, expanding the therapeutic reach of RNAi medicines to a wider range of diseases and tissues.
The Enduring Importance of Foundational Discovery Science
The narrative of this discovery is deeply intertwined with the philosophy of curiosity-driven research. Dr. Lai drew a parallel between his team’s unexpected finding and the seminal work of Harvard geneticist Gary Ruvkun, PhD, and Victor Ambros, PhD, who were awarded the Nobel Prize in Physiology or Medicine in December 2024 for their discovery of microRNAs and their role in gene regulation in the early 1990s.
Dr. Lai, who conducted his undergraduate thesis research in Dr. Ruvkun’s lab, credits his mentor’s work for igniting his passion for developmental biology and small RNAs. He highlighted that Dr. Ruvkun’s initial research was not focused on human disease but on the fundamental biology of nematodes, tiny soil-dwelling worms. This pursuit of fundamental knowledge, devoid of immediate therapeutic goals, ultimately unveiled a completely new paradigm of gene control and paved the way for a revolutionary 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 asserted. He emphasized the critical need for sustained public and governmental support for foundational research, particularly in an era marked by societal and political discourse surrounding the allocation of scientific funding. "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."
This discovery serves as a potent reminder that the most impactful medical advancements often originate from the relentless exploration of fundamental biological questions, driven by curiosity and a commitment to understanding the intricate workings of life itself. The unexpected turn in a laboratory experiment at MSK, amplified by the collaborative spirit of scientific inquiry, has not only illuminated a novel regulatory pathway but also charted a promising course towards more effective and accessible gene-silencing therapies for patients worldwide.
Funding and Intellectual Property
The research underpinning this discovery 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 detailing their novel methods for enhancing the efficacy of RNAi therapy by targeting ALAS1/ALAS2 (WO2024148236A1). Additionally, Drs. Yasuda and Desnick are co-inventors on a patent related to RNAi therapy for acute hepatic porphyrias. They have also reported pharmaceutical consulting activities.