1
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Hwang H, Park KH, Kwon JL, Park HO, Kim J. Analysis of Self-Assembled Micelle Inhibitory RNA (SAMiRNA) Drug Using Ion-Pairing Reversed-Phase Liquid Chromatography Combined with Mass Spectrometry. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2024. [PMID: 38657000 DOI: 10.1021/jasms.4c00081] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/26/2024]
Abstract
Small interfering RNA (siRNA) is known for its ability to silence the expression of specific genes, demonstrating its promising potential as a therapeutic approach. Self-assembled micelle inhibitory RNA (SAMiRNA) is an oligonucleotide duplex developed to overcome the in vivo delivery limitations of siRNA. SAMiRNA has hydrophilic and hydrophobic groups at both ends of a sense strand, forming a spherical nanostructure that enhances the in vivo delivery efficiency. Ion-pairing reversed-phase liquid chromatography (IP-RPLC) is the most commonly used method for the analysis of oligonucleotides. Since SAMiRNA is heavily chemically modified, the behavior of SAMiRNA in IP-RPLC combined with mass spectrometry (MS) is anticipated to differ from that of the conventional siRNA drug. The current investigation using IP-RPLC-MS revealed that a distinct duplex peak along with two minor separate strands of antisense and sense was observed at column temperatures below 35 °C in the IP-RPLC system with a 100 mM ammonium bicarbonate buffer system. At column temperatures higher than 35 °C, however, two fully denatured single strands were observed. The mass spectrum from the chromatographic peak of the SAMiRNA duplex contained signals from the duplex, the antisense, and the sense, probably due to duplex denaturation during the MS ionization process. The current comprehensive analysis results will make a substantial contribution to the future application of IP-RPLC-MS in the analysis of SAMiRNA.
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Affiliation(s)
- Hyojin Hwang
- Department of Chemistry, Chungnam National University, Daejeon 34134, Republic of Korea
| | - Kyu H Park
- Bioneer Corporation, Daejeon 34013, Republic of Korea
| | - Ju-Lee Kwon
- siRNAgen Therapeutics Inc., Daejeon 34302, Republic of Korea
| | - Han-Oh Park
- Bioneer Corporation, Daejeon 34013, Republic of Korea
- siRNAgen Therapeutics Inc., Daejeon 34302, Republic of Korea
| | - Jeongkwon Kim
- Department of Chemistry, Chungnam National University, Daejeon 34134, Republic of Korea
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2
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Ozaki M, Kuwayama T, Shimotsuma M, Hirose T. Separation and purification of short-, medium-, and long-stranded RNAs by RP-HPLC using different mobile phases and C 18 columns with various pore sizes. ANALYTICAL METHODS : ADVANCING METHODS AND APPLICATIONS 2024; 16:1948-1956. [PMID: 38445900 DOI: 10.1039/d4ay00114a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/07/2024]
Abstract
Nucleic acids, which have been employed in medicines for various diseases, are attracting attention as a new pharmaceutical model. Depending on the target substances, nucleic acid medicines with various nucleic acid chain lengths (several tens of nucleotides [nt] to several thousands of nt) exist. The purification of synthesized nucleic acids is crucial as various impurities remain in the crude product after synthesis. Presently, reversed-phase high-performance liquid chromatography (RP-HPLC) represents an effective purification method for nucleic acids. However, the information regarding the HPLC conditions for separating and purifying nucleic acids of various chain lengths is insufficient. Thus, this technical note describes the separation and purification of short-, medium-, and long-stranded nucleic acids (several tens of nt to thousands of nt) by RP-HPLC with various mobile phases and octadecyl-based columns with various pore sizes, such as normal (9-12 nm), wide (30 nm), and super wide (>30 nm) pores.
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Affiliation(s)
- Makoto Ozaki
- Research and Development Department, Nacalai Tesque, Inc., Ishibashi Kaide-cho, Muko-shi, Kyoto 617-0004, Japan.
| | - Tomomi Kuwayama
- Research and Development Department, Nacalai Tesque, Inc., Ishibashi Kaide-cho, Muko-shi, Kyoto 617-0004, Japan.
| | - Motoshi Shimotsuma
- Research and Development Department, Nacalai Tesque, Inc., Ishibashi Kaide-cho, Muko-shi, Kyoto 617-0004, Japan.
| | - Tsunehisa Hirose
- Research and Development Department, Nacalai Tesque, Inc., Ishibashi Kaide-cho, Muko-shi, Kyoto 617-0004, Japan.
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3
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Abdullah AM, Sommers C, Rodriguez JD, Zhang D, Kozak D, Hawes J, Sapru M, Yang K. Decoding Complexity in Synthetic Oligonucleotides: Unraveling Coeluting Isobaric Impurity Ions by High Resolution Mass Spectrometry. Anal Chem 2024; 96:904-909. [PMID: 38158374 PMCID: PMC10794994 DOI: 10.1021/acs.analchem.3c05016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2023] [Revised: 12/06/2023] [Accepted: 12/11/2023] [Indexed: 01/03/2024]
Abstract
Analyzing coeluting impurities with similar masses in synthetic oligonucleotides by liquid chromatography-mass spectrometry (LC-MS) poses challenges due to inadequate separation in either dimension. Herein, we present a direct method employing fully resolved isotopic envelopes, enabled by high resolution mass spectrometry (HRMS), to identify and quantify isobaric impurity ions resulting from the deletion or addition of a uracil (U) or cytosine (C) nucleotide from or to the full-length sequence. These impurities may each encompass multiple sequence variants arising from various deletion or addition sites. The method utilizes a full or targeted MS analysis to measure accurate isotopic distributions that are chemical formula dependent but nucleotide sequence independent. This characteristic enables the quantification of isobaric impurity ions involving sequence variants, a capability typically unavailable in sequence-dependent MS/MS methods. Notably, this approach does not rely on standard curves to determine isobaric impurity compositions in test samples; instead, it utilizes the individual isotopic distributions measured for each impurity standard. Moreover, in cases where specific impurity standards are unavailable, the measured isotopic distributions can be adequately replaced with the theoretical distributions (calculated based on chemical formulas of standards) adjusted using experiment-specific correction factors. In summary, this streamlined approach overcomes the limitations of LC-MS analysis for coeluting isobaric impurity ions, offering a promising solution for the in-depth profiling of complex impurity mixtures in synthetic oligonucleotide therapeutics.
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Affiliation(s)
- A. M. Abdullah
- Division
of Complex Drug Analysis, Office of Testing and Research, Office of
Pharmaceutical Quality, Center for Drug Evaluation and Research, U.S. Food and Drug Administration, St. Louis, Missouri 63110, United States
| | - Cynthia Sommers
- Division
of Complex Drug Analysis, Office of Testing and Research, Office of
Pharmaceutical Quality, Center for Drug Evaluation and Research, U.S. Food and Drug Administration, St. Louis, Missouri 63110, United States
| | - Jason D. Rodriguez
- Division
of Complex Drug Analysis, Office of Testing and Research, Office of
Pharmaceutical Quality, Center for Drug Evaluation and Research, U.S. Food and Drug Administration, St. Louis, Missouri 63110, United States
| | - Deyi Zhang
- Division
of Therapeutic Performance I, Office of Research and Standards, Office
of Generic Drugs, Center for Drug Evaluation and Research, U.S. Food and Drug Administration, Silver Spring, Maryland 20903, United States
| | - Darby Kozak
- Division
of Therapeutic Performance I, Office of Research and Standards, Office
of Generic Drugs, Center for Drug Evaluation and Research, U.S. Food and Drug Administration, Silver Spring, Maryland 20903, United States
| | - Jessica Hawes
- Division
of Systems Biology, National Center for Toxicological Research, U.S. Food and Drug Administration, Jefferson, Arkansas 72079, United States
| | - Mohan Sapru
- Division
of New Drug Product III, Office of New Drug Product, Office of Pharmaceutical
Quality, Center for Drug Evaluation and Research, U.S. Food and Drug Administration, Silver Spring, Maryland 20903, United States
| | - Kui Yang
- Division
of Complex Drug Analysis, Office of Testing and Research, Office of
Pharmaceutical Quality, Center for Drug Evaluation and Research, U.S. Food and Drug Administration, St. Louis, Missouri 63110, United States
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4
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Vosáhlová Z, Kalíková K, Gilar M, Szymarek J, Mazurkiewicz-Bełdzińska M, Studzińska S. Hydrophilic interaction liquid chromatography with mass spectrometry for the separation and identification of antisense oligonucleotides impurities and nusinersen metabolites. J Chromatogr A 2024; 1713:464535. [PMID: 38039623 DOI: 10.1016/j.chroma.2023.464535] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2023] [Revised: 11/24/2023] [Accepted: 11/25/2023] [Indexed: 12/03/2023]
Abstract
With the development of therapeutic oligonucleotides for antisense and gene therapies, the demand for analytical methods also increases. For the analysis of complex samples, for example plasma samples, where the use of mass detection is essential, hydrophilic interaction liquid chromatography is a suitable choice. The aim of the present work was to develop a method for separation and identification of the oligonucleotide impurities and metabolites by hydrophilic interaction liquid chromatography. First of all, the effects of different chromatographic conditions (e.g. pH of the aqueous part of the mobile phase, buffer concentration, column temperature) on the retention and separation of phosphorothioate oligonucleotides standards on the amide stationary phase were investigated. A set of model oligonucleotides containing a fully modified 21mer and its typical impurities (shortmers and oligonucleotides with different number of thiophosphate modifications) was used. The results showed that the concentration of the salt in the mobile phase as well as its pH, are the most influential parameters with regard to peak shape and separation. The knowledge gained was applied to the analysis of an unpurified 18mer oligonucleotides, analogues of the drug nusinersen used for the treatment of spinal muscular atrophy. The successful separation and identification of twenty-six and twenty-eight impurities was performed with the developed HILIC method. The method was applied to analysis of nusinersen metabolites of serum samples of patients treated with Spinraza.
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Affiliation(s)
- Zuzana Vosáhlová
- Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Hlavova 8, 12800, Prague, Czech Republic
| | - Květa Kalíková
- Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Hlavova 8, 12800, Prague, Czech Republic.
| | - Martin Gilar
- Waters Corporation, 34 Maple Street, Milford, MA 01757, USA
| | - Jakub Szymarek
- Department of Developmental Neurology, Medical University of Gdansk, 7 Dębinki Str., PL-80-952, Gdańsk, Poland
| | | | - Sylwia Studzińska
- Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Hlavova 8, 12800, Prague, Czech Republic; Chair of Environmental Chemistry and Bioanalytics, Faculty of Chemistry, Nicolaus Copernicus University in Toruń, 7 Gagarin Str., PL-87-100 Toruń, Poland; Centre for Modern Interdisciplinary Technologies, Nicolaus Copernicus University in Toruń, 4 Wilenska St., 87-100 Toruń, Poland.
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5
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Guimaraes GJ, Saad JG, Annavarapu V, Bartlett MG. Mobile Phase Aging and Its Impact on Electrospray Ionization of Oligonucleotides. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2023; 34:2691-2699. [PMID: 37978939 DOI: 10.1021/jasms.3c00264] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2023]
Abstract
The implementation of fluoroalcohol/alkylamine mobile phase systems in oligonucleotide LC-MS provides a good balance between chromatographic separations and MS sensitivity. Since its introduction, several parameters including mobile phase composition, additive concentration, alkylamine hydrophobicity, and different fluoroalcohols have been carefully evaluated and optimized. While our understanding of this mobile phase system has increased over the years, there are challenges that continue to hinder method performance and remain poorly understood. One of these challenges is the constant loss of MS sensitivity over time, commonly termed mobile phase aging. This study investigates two aging mechanisms associated with loss of MS sensitivity: alkylamine oxidation and aggregate formation. The relationship between pH, organic solvent, oxygen, and mobile phase aging is characterized, and mitigation strategies to extend mobile phase lifetime are discussed.
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Affiliation(s)
- Guilherme J Guimaraes
- Department of Pharmaceutical and Biomedical Sciences, University of Georgia College of Pharmacy, Athens, Georgia 30602, United States
| | - Jack G Saad
- Micromeritics Instrument Company, 4356 Communications Drive, Norcross, Georgia 30093, United States
| | - Vidya Annavarapu
- Department of Pharmaceutical and Biomedical Sciences, University of Georgia College of Pharmacy, Athens, Georgia 30602, United States
| | - Michael G Bartlett
- Department of Pharmaceutical and Biomedical Sciences, University of Georgia College of Pharmacy, Athens, Georgia 30602, United States
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6
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Leśko M, Kaczmarski K, Jora M, Stavenhagen K, Leek T, Czechtizky W, Fornstedt T, Samuelsson J. Strategies for predictive modeling of overloaded oligonucleotide elution profiles in ion-pair chromatography. J Chromatogr A 2023; 1711:464446. [PMID: 37865023 DOI: 10.1016/j.chroma.2023.464446] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2023] [Revised: 09/20/2023] [Accepted: 10/10/2023] [Indexed: 10/23/2023]
Abstract
Due to their potential for gene regulation, oligonucleotides have moved into focus as one of the preferred modalities modulating currently undruggable disease-associated targets. In the course of synthesis and storage of oligonucleotides a significant number of compound-related impurities can be generated. Purification protocols and analytical methods have become crucial for the therapeutic application of any oligonucleotides, be they antisense oligonucleotides (ASOs), small interfering ribonucleic acids (siRNAs) or conjugates. Ion-pair chromatography is currently the standard method for separating and analyzing therapeutic oligonucleotides. Although mathematical modeling can improve the accuracy and efficiency of ion-pair chromatography, its application remains challenging. Simple models may not be suitable to treat advanced single molecules, while complex models are still inefficient for industrial oligonucleotide optimization processes. Therefore, fundamental research to improve the accuracy and simplicity of mathematical models in ion-pair chromatography is still a necessity. In this study, we predict overloaded concentration profiles of oligonucleotides in ion-pair chromatography and compare relatively simple and more advanced predictive models. The experimental system consists of a traditional C18 column using (dibutyl)amine as the ion-pair reagent and acetonitrile as organic modifier. The models were built and tested based on three crude 16-mer oligonucleotides with varying degrees of phosphorothioation, as well as their respective n - 1 and (P = O)1 impurities. In short, the proposed models were suitable to predict the overloaded concentration profiles for different slopes of the organic modifier gradient and column load.
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Affiliation(s)
- Marek Leśko
- Department of Engineering and Chemical Sciences, Karlstad University, SE-651 88 Karlstad, Sweden
| | - Krzysztof Kaczmarski
- Department of Chemical and Process Engineering, Rzeszów University of Technology, PL-35 959 Rzeszów, Poland
| | - Manasses Jora
- Medicinal Chemistry, Research and Early Development, Respiratory and Immunology, BioPharmaceuticals R&D, AstraZeneca, SE-431 50 Mölndal, Sweden
| | - Kathrin Stavenhagen
- Medicinal Chemistry, Research and Early Development, Respiratory and Immunology, BioPharmaceuticals R&D, AstraZeneca, SE-431 50 Mölndal, Sweden
| | - Tomas Leek
- Medicinal Chemistry, Research and Early Development, Respiratory and Immunology, BioPharmaceuticals R&D, AstraZeneca, SE-431 50 Mölndal, Sweden
| | - Werngard Czechtizky
- Medicinal Chemistry, Research and Early Development, Respiratory and Immunology, BioPharmaceuticals R&D, AstraZeneca, SE-431 50 Mölndal, Sweden
| | - Torgny Fornstedt
- Department of Engineering and Chemical Sciences, Karlstad University, SE-651 88 Karlstad, Sweden.
| | - Jörgen Samuelsson
- Department of Engineering and Chemical Sciences, Karlstad University, SE-651 88 Karlstad, Sweden
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7
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Sorensen MJ, Paulines MJ, Maloney TD. Evaluating orthogonality between ion-pair reversed phase, anion exchange, and hydrophilic interaction liquid chromatography for the separation of synthetic oligonucleotides. J Chromatogr A 2023; 1705:464184. [PMID: 37419013 DOI: 10.1016/j.chroma.2023.464184] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2023] [Revised: 06/26/2023] [Accepted: 06/27/2023] [Indexed: 07/09/2023]
Abstract
The orthogonality of separation between ion-pair reversed phase (IP-RP), anion exchange (AEX), and hydrophilic interaction liquid chromatography (HILIC) was evaluated for oligonucleotides. A polythymidine standard ladder was first used to evaluate the three methods and showed zero orthogonality, where retention and selectivity were based on oligonucleotide charge/size under all three conditions. Next, a model 23-mer synthetic oligonucleotide containing 4 phosphorothioate bonds with 2' fluoro and 2'-O-methyl ribose modifications typical of small interfering RNA was used for evaluating orthogonality. The resolution and orthogonality were evaluated between the three modes of chromatography in terms of selectivity differences for nine common impurities, including truncations (n-1, n-2), addition (n + 1), oxidation, and de-fluorination. We first evaluated different ion-pairing reagents that provided the best separation of the key impurities while suppressing diastereomer separation due to phosphorothioate linkages. Although different ion-pairing reagents affected resolution, very little orthogonality was observed. We then compared the retention times between IP-RP, HILIC, and AEX for each impurity of the model oligonucleotide and observed various selectivity changes. The results suggest that coupling HILIC with either AEX or IP-RP provide the highest degree of orthogonality due to the differences in retention for hydrophilic nucleobases and modifications under HILIC conditions. IP-RP provided the highest overall resolution for the impurity mixture, whereas more co-elution was observed with HILIC and AEX. The unique selectivity patterns offered by HILIC provides an interesting alternative to IP-RP or AEX, in addition to the potential for coupling with multidimensional separations. Future work should explore orthogonality for oligonucleotides with subtle sequence differences such as nucleobase modifications and base flip isomers, longer strands such as guide RNA and messenger RNA, and other biotherapeutic modalities such as peptides, antibodies, and antibody-drug-conjugates.
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Affiliation(s)
- Matthew J Sorensen
- Synthetic Molecule Design and Development, Lilly Research Labs, Eli Lilly and Company, Indianapolis, IN 46285, United States
| | - Mellie June Paulines
- Synthetic Molecule Design and Development, Lilly Research Labs, Eli Lilly and Company, Indianapolis, IN 46285, United States
| | - Todd D Maloney
- Synthetic Molecule Design and Development, Lilly Research Labs, Eli Lilly and Company, Indianapolis, IN 46285, United States.
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8
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Lardeux H, Fekete S, Lauber M, D'Atri V, Guillarme D. High-Throughput Chromatographic Separation of Oligonucleotides: A Proof of Concept Using Ultra-Short Columns. Anal Chem 2023. [PMID: 37384898 DOI: 10.1021/acs.analchem.3c01934] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/01/2023]
Abstract
Ion-pairing reversed-phase liquid chromatography (IP-RPLC) is the reference separation technique for characterizing oligonucleotides (ONs) and their related impurities. The aim of this study was to better understand the retention mechanism of ONs, evaluate the applicability of the linear solvent strength (LSS) retention model, and explore the potential of ultra-short columns having a length of only 5 mm for the separation of model ONs. First, the validity of the LSS model was evaluated for ONs having sizes comprised between 3 and 30 kDa, and the accuracy of retention time predictions was assessed. It was found that ONs in IP-RPLC conditions follow an "on-off" elution behavior, despite a molecular weight lower than that of proteins. For most linear gradient separation conditions, a column length between 5 and 35 mm was found to be appropriate. Ultra-short columns of only 5 mm were therefore explored to speed up separations by considering the impact of the instrumentation on the efficiency. Interestingly, the impacts of injection volume and post-column connection tubing on peak capacity were found to be negligible. Finally, it was demonstrated that longer columns would not improve selectivity or separation efficiency, but baseline separation of three model ONs mixtures was enabled in as little as 30 s on the 5 mm column. This proof-of-concept work paves the way for future investigations using more complex therapeutic ONs and their related impurities.
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Affiliation(s)
- Honorine Lardeux
- Institute of Pharmaceutical Sciences of Western Switzerland (ISPSO), University of Geneva, Geneva 1211, Switzerland
- School of Pharmaceutical Sciences, University of Geneva, Geneva 1211, Switzerland
| | - Szabolcs Fekete
- Waters Corporation, located in CMU-Rue Michel Servet 1, Geneva 1211, Switzerland
| | - Matthew Lauber
- Waters Corporation, Milford, Massachusetts 01757, United States
| | - Valentina D'Atri
- Institute of Pharmaceutical Sciences of Western Switzerland (ISPSO), University of Geneva, Geneva 1211, Switzerland
- School of Pharmaceutical Sciences, University of Geneva, Geneva 1211, Switzerland
| | - Davy Guillarme
- Institute of Pharmaceutical Sciences of Western Switzerland (ISPSO), University of Geneva, Geneva 1211, Switzerland
- School of Pharmaceutical Sciences, University of Geneva, Geneva 1211, Switzerland
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9
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Roussis SG, Rentel C. Exploring the use of the desirability function to optimize the separation of oligonucleotide impurities by ion pair-RP LCMS. J Chromatogr B Analyt Technol Biomed Life Sci 2023; 1220:123666. [PMID: 36921438 DOI: 10.1016/j.jchromb.2023.123666] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2023] [Revised: 03/03/2023] [Accepted: 03/06/2023] [Indexed: 03/11/2023]
Abstract
The use of small alkyl amines as ion pair reagents permits enhanced separation of impurities of phosphate diester oligonucleotides, which can be beneficial to quality control applications, and aid elucidation of the mechanisms of impurity formation. In general, however, separation of the individual components that comprise the majority of oligonucleotide impurities requires development of several independent chromatographic methods. Ideally, a single method capable of separating the individual components of all impurity classes would be developed. The mathematical concept of the desirability function has been explored here for its ability to determine the combination of experimental factors that result in a single, globally optimized chromatographic method. The optimized mobile phase, consisting of 1 mM propylamine (PA), 30 mM ammonium bicarbonate (ABC), and 1 mM octanoic acid (C8A), produced excellent agreement between measured and predicted peak resolution values for a set of n - 1 impurities. The relative importance of the mobile phase constituents on the mechanism of separation has been discussed. The approach holds great promise for the improved separation of components in complex chromatographic systems.
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Affiliation(s)
| | - Claus Rentel
- Ionis Pharmaceuticals, Carlsbad, CA 92010, United States
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10
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Separation of phosphorothioate oligonucleotide impurities by WAX HPLC under high organic content elution conditions. Anal Biochem 2022; 659:114956. [PMID: 36270331 DOI: 10.1016/j.ab.2022.114956] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2022] [Revised: 10/11/2022] [Accepted: 10/12/2022] [Indexed: 12/14/2022]
Abstract
The separation of impurities in phosphorothioate diester (PS) oligonucleotides is complicated by (1) the presence of a very large number of diastereoisomers, e.g., 219 for a 20-mer oligonucleotide, (2) peak broadening due to the hydrophobic character of the sulfur atom, and (3) the chemical similarity of the impurities to the parent oligonucleotide and each other. Further difficulties arise due to the chemical nature of oligonucleotides, which display a complex mixture of ionic, hydrophobic, H-bonding, and other functionalities. To minimize hydrophobic interactions and peak broadening due to the PS modification, we have developed a novel method that combines a weak anion exchange (WAX) column with a mobile phase elution system designed to maximize separation by a single ionic/electrostatic interaction. We found that although chaotropes are helpful, the most significant beneficial effect of the hydrophilic WAX column is that high-organic, low-salt mobile phase is required for product elution. Separations are also benefitted by pH gradient effects on stationary phase electrostatic potential and analyte ionization. An extraordinary degree of separation is achieved by the new WAX method in comparison to SAX (strong anion exchange) chromatography. For the first time, the extent of deamination of PS oligonucleotides is directly determined by a chromatography-only method. The approach, representative results, and the mechanisms of separation are discussed.
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