Fungal Prime Editing Platform fPE7max Unlocks Silent Gene Clusters, Yields Three Novel Anti-Cancer Lead Compounds
Key Insights
Researchers at the University of Pennsylvania developed fPE7max (search), the first prime editing tool adapted for filamentous fungi, achieving editing efficiency approaching 90%.
The platform awakened silent biosynthetic gene clusters, yielding 18 complex molecules — eight entirely new to science — with three demonstrating selective anti-cancer activity in cell assays.
One novel molecule showed selective toxicity against human breast, hepatic, and leukemia (search) cancer cell lines, providing new lead compounds for drug discovery.
A first-of-its-kind genome-editing platform for filamentous fungi has cracked open one of drug discovery's most underexplored vaults, yielding 18 complex molecules from previously dormant chemical pathways — including three that selectively kill cancer cells in laboratory assays.
The tool, called fPE7max (search), was developed by chemical engineer Xue "Sherry" Gao and colleagues at the University of Pennsylvania's School of Engineering and Applied Science and was published July 2, 2026, in Nature Biotechnology. It represents the first successful adaptation of prime editing — a precision gene-editing technology that rewrites DNA without cutting both strands — to the class of thread-like molds responsible for producing penicillin, statins, and cyclosporine.
"This neglect is kind of remarkable considering how fungi have shaped modern medicine," said Gao. "From the serendipitous discovery of penicillin to cholesterol-lowering statins, we owe many recent breakthroughs in longevity to fungal chemistry. But despite this, the vast majority of the fungal kingdom remains a black box."
The Scale of the Unexplored Fungal Chemical Repertoire
The pharmaceutical track record of filamentous fungi is extraordinary. Penicillin came from Penicillium notatum; statins were derived from fungal enzymes first characterized by Akira Endo in the 1970s; cyclosporine, the immunosuppressant that made routine organ transplantation possible, was isolated from Tolypocladium inflatum. Yet analysis of more than 11,000 fungal genomes has identified nearly 294,000 biosynthetic gene clusters (BGCs), and fewer than 1% of them can be matched to any known compound. The rest have never been activated in any experimental setting.
The core problem is ecological. Filamentous fungi produce their most chemically interesting compounds in the wild, where they compete with bacteria and hostile environments. Under sterile, nutrient-rich laboratory conditions, the genetic programs driving secondary metabolite production are turned off. Switching those pathways back on requires editing the regulatory genes that govern them — specifically a master control gene called laeA (search), a histone methyltransferase that acts as an upstream switch for a vast network of chemical production pathways.
Why Previous Tools Fell Short
Standard gene-editing tools, including CRISPR-Cas9, introduce double-strand breaks in DNA and rely on the cell's own repair machinery to incorporate changes. In filamentous fungi, that repair process is error-prone, generating unintended mutations that disrupt downstream experiments. Prime editing, developed in 2019 by David Liu's group at the Broad Institute, sidesteps this problem by nicking only one DNA strand and using a tethered reverse transcriptase to write new genetic information directly into the targeted site. However, prime editing had never been made to work in filamentous fungi — until now.
How fPE7max (search) Solved Two Critical Barriers
The Penn team cleared two distinct technical barriers. The first was guide RNA fragility. Prime editing relies on a prime editing guide RNA (pegRNA) that directs the editing machinery to a specific genomic location. For large edits, pegRNAs become unwieldy and degrade before completing the job. The team's solution was a stabilizing protein called fLa, which binds to and shields the pegRNA, allowing fPE7max (search) to handle insertions as large as 1 kilobase and deletions as large as 10 kilobases.
The second barrier was the cell's mismatch repair (MMR) pathway, which identifies and reverses changes to DNA that look like mistakes — including deliberate edits. To overcome this, the team incorporated a protein component that transiently suppresses the MMR machinery using RNA interference, giving the new genetic code time to become permanently incorporated.
The resulting platform achieves editing efficiency approaching 90% across multiple filamentous fungal species, handling everything from single-base substitutions to kilobase-scale structural changes.
What Emerged When the Pathways Awakened
To demonstrate fPE7max (search)'s capabilities, the team targeted the upstream open reading frames (uORFs) that naturally suppress laeA (search) translation. These uORFs function as molecular brakes: the ribosome encounters them before the main laeA coding sequence and stalls, producing little or no functional LaeA protein under standard conditions. By using fPE7max to precisely delete those translational roadblocks, the team allowed laeA to be translated normally, activating downstream silent biosynthetic gene clusters across several different fungal species.
"We isolated 18 distinct complex molecules, eight of which possessed chemical structures entirely new to science," said Chunxiao Sun, a postdoctoral researcher in the Gao Lab and the study's first author. "Of these uncovered molecules, three exhibited promising anti-cancer properties. These molecules can serve as lead compounds for disease treatment, providing a vital new pipeline for drug discovery."
One novel molecule showed selective toxicity against human breast, hepatic, and leukemia (search) cancer cell lines.
From Lead Compounds to Clinical Relevance
The three anti-cancer molecules are early-stage leads that have demonstrated activity in controlled cell-based assays — the first rung of a long ladder. The path from a cell assay lead to an approved drug typically spans 10 to 15 years and involves extensive testing in animal models, chemical structure optimization, toxicology studies, and multiple phases of clinical trials, with most candidates failing at some stage. Nothing in the current findings establishes clinical relevance, and none of the compounds should be understood as a near-term treatment.
Beyond Cancer: Implications for Antibiotic Discovery
The current study focuses on anti-cancer activity because that is what the initial chemical harvest revealed. But the biosynthetic gene clusters that fPE7max (search) can activate are not limited to anti-cancer chemistry. The same pathways that fungi evolved to compete with bacteria encode antibiotics and antifungals — and the field of novel antibiotic discovery faces a recognized public health emergency, with existing antibiotics increasingly ineffective against resistant bacterial strains and the pipeline of new antibiotics having slowed dramatically since the mid-20th century.
From Serendipity to Systematic Exploration
For decades, natural product discovery in filamentous fungi has been governed by chance. Gao's team plans to deploy fPE7max (search) across a much wider range of fungal species, moving from an opportunistic model to systematic optimization.
"It's a compelling proof-of-concept demonstrating that the next generation of life-saving therapeutics might already exist in nature," Gao said.
The shift from serendipity to systematic exploration is the deepest implication of fPE7max (search). The fungal chemical repertoire is not a fixed set of known drugs but an enormous, largely unexplored library of molecular structures with unknown properties — and this platform may be the most reliable key to that library yet developed.