After more than five decades since its initial discovery, scientists have finally achieved a significant breakthrough by successfully synthesizing verticillin A in a laboratory setting, a complex molecule derived from fungi that has long held promise as a potential agent against cancer. This achievement, spearheaded by researchers at the Massachusetts Institute of Technology (MIT), marks a pivotal moment in the field of synthetic chemistry and opens new avenues for therapeutic development. The intricate molecular structure of verticillin A has historically presented formidable challenges to chemists, with even minor variations from related compounds rendering it substantially more difficult to construct.
Professor Mohammad Movassaghi, a leading figure in MIT’s chemistry department, articulated the profound learning gained from this endeavor, stating, "We now possess a far deeper understanding of how minute alterations in molecular architecture can exponentially amplify the complexity of synthetic pathways." He further elaborated, "Our current technological capabilities not only allow us to access these compounds for the first time in over half a century since their isolation but also empower us to engineer numerous bespoke variants, thereby facilitating more in-depth investigations." These advanced synthetic techniques are crucial for unlocking the full therapeutic potential of molecules that were previously beyond reach.
Initial laboratory evaluations, employing human cancer cell lines, revealed a particular verticillin A derivative that exhibited remarkable efficacy against diffuse midline glioma, a particularly aggressive form of pediatric brain cancer. The research team, however, strongly emphasized the necessity for further rigorous testing to ascertain the compound’s viability for clinical application. The collaborative effort involved a multidisciplinary approach, with Professor Jun Qi from the Dana-Farber Cancer Institute and Harvard Medical School serving as a senior author alongside Movassaghi. The foundational work for this publication, appearing in the esteemed Journal of the American Chemical Society, was led by Walker Knauss, a doctoral candidate at MIT, with significant contributions from Xiuqi Wang, a specialist in medicinal chemistry and chemical biology at Dana-Farber, and Mariella Filbin, the research director of the Pediatric Neurology-Oncology Program at Dana-Farber/Boston Children’s Cancer and Blood Disorders Center.
The inherent difficulty in producing verticillin A stems from its exceptionally complex chemical scaffolding. First identified and isolated from fungal sources in 1970, this compound is naturally produced by fungi as a defensive mechanism against pathogens. While verticillin A and its fungal relatives have been subjects of interest for their potential antimicrobial and anti-cancer properties, their structural complexity has consistently thwarted attempts at efficient laboratory synthesis.
A significant precursor to the current breakthrough was the 2009 report from Movassaghi’s laboratory detailing the synthesis of (+)-11,11′-dideoxyverticillin A. This structurally similar compound features ten distinct rings and eight stereogenic centers, which are carbon atoms bonded to four different chemical groups. The precise spatial arrangement, or stereochemistry, of these groups is paramount to the molecule’s function and reactivity. Despite this earlier success, the direct synthesis of verticillin A itself remained an elusive goal. The critical distinction between verticillin A and (+)-11,11′-dideoxyverticillin A lies in the presence of two additional oxygen atoms in the former. These seemingly minor additions, however, dramatically alter the molecule’s behavior during chemical transformations, rendering it considerably more fragile and sensitive. As Movassaghi explained, "Those two oxygens greatly limit the window of opportunity that you have in terms of doing chemical transformations. It makes the compound so much more fragile, so much more sensitive, so that even though we had had years of methodological advances, the compound continued to pose a challenge for us."
The synthesis of both verticillin A and its dideoxy counterpart involves the strategic coupling of two identical molecular fragments to form a larger structure known as a dimer. In the earlier synthesis of (+)-11,11′-dideoxyverticillin A, the dimerization step was performed relatively late in the process, followed by the formation of four critical carbon-sulfur bonds. However, applying this exact sequence to verticillin A proved unsuccessful. The late-stage introduction of the carbon-sulfur bonds failed to achieve the correct stereochemistry, necessitating a complete overhaul of the synthetic strategy and the order of chemical reactions.
"What we learned was the timing of the events is absolutely critical. We had to significantly change the order of the bond-forming events," Movassaghi emphasized. The newly developed synthetic route commences with a derivative of an amino acid, specifically beta-hydroxytryptophan. From this starting point, the researchers meticulously constructed the molecule in a series of staged reactions, progressively incorporating various chemical functional groups, including alcohols, ketones, and amides, while maintaining stringent control over the stereochemistry at each stage. To facilitate this precise control, a precursor containing two carbon-sulfur bonds and a disulfide linkage was introduced early in the synthetic sequence. Due to the inherent reactivity of disulfide bonds, they required temporary protection, achieved by converting them into a stabilized pair of sulfides, to prevent structural degradation during subsequent chemical transformations. Following the dimerization step, these protected disulfide groups were regenerated. Movassaghi highlighted the exceptional nature of this dimerization process, noting, "This particular dimerization really stands out in terms of the complexity of the substrates that we’re bringing together, which have such a dense array of functional groups and stereochemistry." The entire synthetic pathway from the beta-hydroxytryptophan starting material to the final verticillin A molecule comprises 16 distinct chemical steps.
With the successful laboratory synthesis of verticillin A now a reality, the research team was also able to adapt their methodology to create a range of derivatives. A dedicated team at Dana-Farber subjected these novel compounds to rigorous testing against various forms of diffuse midline glioma (DMG), a rare and often aggressive pediatric brain tumor for which treatment options are currently limited. Notably, the most pronounced anti-cancer effects were observed in DMG cell lines that exhibit elevated levels of a protein known as EZHIP. This protein plays a crucial role in regulating DNA methylation, a process that has previously been identified as a potential therapeutic target for DMG.
Professor Qi underscored the significance of identifying the molecular targets of these compounds, stating, "Identifying the potential targets of these compounds will play a critical role in further understanding their mechanism of action, and more importantly, will help optimize the compounds from the Movassaghi lab to be more target specific for novel therapy development." The verticillin derivatives appear to exert their anti-cancer effects by interacting with EZHIP in a manner that enhances DNA methylation, thereby inducing programmed cell death in the malignant cells. Among the most potent compounds identified in these initial experiments were N-sulfonylated variants of both (+)-11,11′-dideoxyverticillin A and verticillin A. The process of N-sulfonylation, which involves the addition of a functional group containing sulfur and oxygen, was found to significantly improve the stability of these molecules.
"The natural product itself is not the most potent, but it’s the natural product synthesis that brought us to a point where we can make these derivatives and study them," Movassaghi commented, emphasizing that the synthetic capability is the true enabler of further drug discovery efforts. Moving forward, researchers at Dana-Farber are committed to further elucidating the precise mechanisms by which these verticillin derivatives operate. Their future research plans include evaluating these compounds in preclinical animal models of pediatric brain cancers. Professor Qi expressed optimism for the future, stating, "Natural compounds have been valuable resources for drug discovery, and we will fully evaluate the therapeutic potential of these molecules by integrating our expertise in chemistry, chemical biology, cancer biology, and patient care. We have also profiled our lead molecules in more than 800 cancer cell lines, and will be able to understand their functions more broadly in other cancers." The scientific endeavor was supported by funding from the National Institute of General Medical Sciences, the Ependymoma Research Foundation, and the Curing Kids Cancer Foundation, underscoring the broad collaborative interest in advancing cancer therapeutics.
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