Month: January 2024

Dibenzothiophene S-oxides are important in various biochemical processes. However, their synthesis using conventional methods is not easy. Researchers from Tokyo University of Science have now developed an innovative two-step process involving a Suzuki–Miyaura coupling of 2-bromoaryl-substituted sulfinate esters, followed by intramolecular electrophilic sulfinylation. This method can facilitate the facile synthesis of polysubstituted dibenzothiophene oxides without damaging highly reactive functional groups. The resulting compounds can find applications in fields like drug development and biochemical research.

Organic compounds in the field of chemistry range from simple hydrocarbons to complex molecules, with diverse functional groups added to the main carbon backbone. These functional groups impart the compounds distinct chemical properties as well as participate in various chemical transformations, making them important precursors for the synthesis of diverse compounds. Scientists have, therefore, actively engaged in creating molecules that feature novel and highly reactive functional groups.

One such class of compounds are dibenzothiophenes and their derivatives containing S-oxide or S,S-dioxide moieties (sulfur atoms bonded to one and two oxygen atoms respectively). These compounds are of special interest in the fields of pharmaceutical sciences, materials chemistry, and chemical biology. Dibenzothiophenes consist of benzene rings fused to a thiophene ring—a five-membered ring with four carbon atoms and one sulfur atom. When dibenzothiophene S-oxides are exposed to UV light, they release atomic oxygen, which is useful for DNA cleavage and oxidation of adenosine-S’-phosphosulfate kinase, an enzyme involved in cellular processes. Additionally, the S–O bond can be activated to introduce different functional groups, enabling the creation of a wide range of molecules with diverse properties and applications. The conventional method of producing functionalized dibenzothiophene S-oxides involves thiophene ring formation followed by subsequent S-oxidation. However, this reaction is challenging to carry out.

To address this, Associate Professor Suguru Yoshida, Ms. Yukiko Kumagai, Mr. Akihiro Kobayashi, and Mr. Keisuke Nakamura from Tokyo University of Science (TUS) have developed a simple two-step method of synthesizing dibenzothiophene S-oxides. The method involves Suzuki–Miyaura coupling of 2-bromoaryl-substituted sulfinate esters, followed by an intramolecular electrophilic sulfinylation.

The details of the method, published in the journal Chemical Communications on 10 January 2024, opens possibilities for creating a variety of important sulfur-containing molecules in the life sciences that were traditionally difficult to synthesize using conventional methods.

“Dibenzothiophene oxides are attracting attention in the field of chemical biology, and several researchers have developed a reaction using dibenzothiophene oxide, which can now be synthesized using this method. We expect this research to elucidate life phenomena involving reactive oxygen species,” explains Dr. Yoshida, while talking about this study.

The Suzuki–Miyaura coupling is a widely used organic reaction between boronic acids and organic halides, leading to the formation of a new carbon–carbon bond. In the proposed method, sulfinate esters react first with arylboronic acids in the presence of a palladium catalyst. Next, the intermediate biaryl compounds are activated with Tf2O, leading to subsequent cyclization by electrophilic activation.

Compared to the conventional oxidation method of synthesizing dibenzothiophene, this innovative approach developed by Dr. Yoshida and his team can accommodate a wide range of functional groups, including highly reactive ones, enabling the synthesis of polysubstituted dibenzothiophene oxides not achievable earlier. Using the method, the researchers synthesized dibenzothiophene oxides having an o-silylaryl triflate moiety, a compound useful as an aryne generation site, but tends to get easily damaged when produced using conventional methods. The o-silylaryl triflate moiety serves as a useful reactive intermediate and can undergo various transformations to produce highly substituted arenes. The proposed method, therefore, not only simplifies the synthesis method but also opens doors for a diverse range of dibenzothiophene S-oxides and their derivatives.

The novel method is a significant step forward in the field of chemical biology. Going ahead, the researchers anticipate that these compounds can find useful applications in diverse research areas, paving the way for innovations and discoveries. “The proposed method can enable the synthesis of polysubstituted benzothiophene oxides, which are expected to be useful in a wide range of research fields,” concludes Dr. Yoshida.

Consistent manufacturing and production of monoclonal antibodies (mAbs) is critical, and their functional profiles depend on cell culture conditions. Now, researchers from Japan have investigated the role of intracellular polyamines on N-glycan profiles of mAbs. They found that polyamine depletion led to an ER stress response in CHO cells, leading to an increase in galactosylation of mAbs. Supplementation of spermidine recovered N-glycan profiles. These findings will contribute to the stable production of antibody-based drugs.

Monoclonal antibodies (mAbs) are laboratory-designed proteins that mimic the immune system’s antibodies. To date, many therapeutic mAbs belonging to the immunoglobulin G (IgG) class of antibodies, have been approved for the treatment of cancer and autoimmune diseases. Cell lines such as the Chinese hamster ovary (CHO) cells are generally used to produce mAbs. Notably, the production and manufacture of mAbs are regulated by critical quality attributes (CQAs) to ensure their safety and efficacy in treatment.

An important CQA for mAbs is the N-linked glycosylation present at a specific position (Asn297). N-linked glycans consist of N-acetylglucosamine (GlcNAc), mannose (Man), fucose (Fuc), galactose (Gal), and sialic acid. The heterogeneity of the N-linked glycan profiles of mAbs can be attributed to the different numbers and linkages of additional saccharides. The composition of N-linked glycans affects the overall therapeutic efficacy, targeting ability, and immune-specificity of these antibodies. For example, antibody-dependent cellular cytotoxicity (ADCC) is influenced by the fucosylation and galactosylation of N-linked glycans. Complement-dependent cytotoxicity (CDC) is also affected by the galactosylation and sialylation of N-linked glycans. Hence, it’s crucial to meticulously regulate N-linked glycan profiles throughout the manufacturing process because the heterogeneity of the N-linked glycan profile of mAbs depends on the cell culture duration and changes in nucleotide sugars and glycosylation enzyme levels.

Recently, Dr. Kyohei Higashi, Associate Professor at Tokyo University of Science (TUS) in Japan, along with a team of researchers including Dr. Rin Miyajima and Dr. Masahiro Komeno, conducted a study to explore the effects of polyamines on N-linked glycan profiles of mAbs in CHO DP-12 cells. Their work was made available online on November 3, 2023 in the Journal of Biotechnology.

“Because the carbohydrate structure of mAbs changes depending on the state of the cells, we were interested in investigating the relationship between intracellular polyamines and the carbohydrate structure of mAbs from CHO cells.” explained Dr. Higashi, when asked about the motivation behind the research.

Polyamines (putrescine, PUT; spermidine, SPD; and spermine, SPM) are present in millimolar concentrations in all living organisms and play essential roles in normal cell growth and differentiation. PUT, SPD, and SPM contained two, three, and four amino groups, respectively. PUT is synthesized from ornithine (ORN) by ornithine decarboxylase (ODC), a rate-limiting enzyme in the polyamine biosynthesis pathway. SPD is synthesized from putrescine by spermidine synthase, and spermine is synthesized from spermidine by spermine synthase. Intracellular polyamine levels are regulated at various steps, including synthesis, degradation, and transport, and are affected by external stimuli, aging, and diseases. Because CHO cells lack arginase activity to produce ORN from arginine, they cannot produce polyamines in serum-free media, resulting in a decrease in intracellular polyamine levels, which causes a low growth rate and cell viability during long-term cultivation.

Intracellular polyamine levels can also be decreased by treatment with α-difluoromethylornithine (DFMO), an inhibitor of ODC. The depletion of intracellular polyamines by DFMO can be reversed by the addition of SPD to the growth media of CHO cells.

Upon introducing DFMO to the CHO cells, the team observed that IgG antibody galactosylation surged, along with an increase in the levels of β1,4-galactosyl transferase 1 (B4GALT1) mRNA. This mRNA is pivotal in governing the IgG galactosylation mechanism within CHO cells. What’s more, IgG production decreased by approximately 30% in DFMO-treated cells.

Dr. Higashi hypothesized that the decrease in IgG production was a result of endoplasmic stress (ER) stress response caused by polyamine depletion. During ER stress response, protein folding ceases, resulting in the arrest of the normal function of cells. Chaperone proteins assist in the correct folding of other protein classes and play a crucial role under both normal and stress conditions. The results of the ER stress response study confirmed the increased expression levels of chaperones for glycoprotein folding, in polyamine-depleted cells.

The team further observed that upon using tunicamycin, an ER stress inducer inhibiting N-glycosylation, ER stress from polyamine depletion triggered B4GALT1 mRNA expression, increasing IgG galactosylation in CHO cells.

The ability to maintain antibody glycosylation profiles via polyamine modulation has numerous implications. Controlled glycosylation is crucial for optimizing therapeutic proteins, such as antibodies, ensuring the stable production of antibodies in a uniform manner of biological activities, and potentially decreasing the manufacturing cost. Supplementation of polyamine could be accomplished by the addition only of SPD to serum-free medium, offer an easy and costless method to maintain the glycan structure of mAbs produced by CHO cells cultured in the serum-free medium. This insight might influence cell line development and bioproduction, facilitating the creation of biosimilars.

“Introducing polyamines, particularly SPD, to serum-free culture medium for CHO cells may contribute to consistent manufacturing and quality control of antibody production. We hope that this research will contribute to the stable production of antibody drugs and lead to lower drug prices” concludes Dr. Higashi.