Development of a method based on ultra high performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry for studying the in vitro metabolism of phosphorothioate oligonucleotides

A Bioanalytical Liquid Chromatography Tandem Mass Spectrometry Approach for the Quantification of a Novel Antisense Oligonucleotide Designed for Parkinson's Disease: A Rat Brain Biodistribution Study

Antisense oligonucleotides (ASOs) represent a unique category of therapeutics targeting disease-related RNAs. Since this new therapeutic category emerged, the immediate need to analyze ASOs in clinically relevant biological matrices has led to several methodologies, such as ligand binding assays and imaging techniques. To overcome issues in specificity and provide exact quantitative data for ASOs, a new LC-MS/MS method was developed to analyze in brain tissue a novel 4-10-4 gapmer ASO with the potential for treating Parkinson's disease with phosphorothioated backbone and 2'-O-(2-methoxyethyl) modifications. The sample pretreatment protocol to extract the ASO from brain tissue employed solid phase extraction (SPE) and protein digestion. The LC-MS/MS method was fully optimized, validated and applied to quantify the target ASO in brain tissue samples following an in vivo brain distribution study. The method has a Lower Limit Of Quantification of 1 ng/mg and was applied to the study's samples, demonstrating satisfactory sensitivity and providing valuable information about the ASO's distribution in different brain regions over 45 days.

Separation and identification of oligonucleotides impurities and degradation products by reversed phase ultra-high performance liquid chromatography using phenyl-bonded stationary phases without ion pairs - A step towards sustainability

This manuscript discusses the development of a reversed-phase ultra high-performance liquid chromatography (RP UHPLC) method based on phenyl-bonded stationary phases without ion-pairs for the separation and identification of oligonucleotides. The elimination of ion-pair reagents makes the proposed protocol as more compliant to the principles of green chemistry, compared to the traditional ion-pair reversed-phase liquid chromatography methods (IP RP LC). In detail, three phenyl-based stationary phases were tested, namely a C18/AR (a C18 stationary phase with the addition of aromatic groups), a Phenyl-hexyl, and a Diphenyl. Generally, the retention of oligonucleotides increases with the increase of salt concentration and the decrease of the pH, thus confirming the significant impact of van der Waals interactions, salting-out effect, and π-electrons interactions in the retention mechanism. The highest retention and best peak symmetry were observed for the C18/AR stationary phase, while the lowest retention for the Phenyl-hexyl, with retention influenced by the type of salt in the mobile phase. The obtained methods using C18/AR stationary phases allow for the effective separations of positional isomers and for identifying impurities and degradation products using RP UHPLC Q-TOF-MS in a comparatively short time. The application of RP UHPLC Q-TOF-MS provides reasonable selectivity for the resolution of 33 impurities and two degradation products. Both groups of compounds are mainly 3'N and 5'N-shortmers, but in the case of impurities, modifications of cyclic phosphate and phosphate groups were also identified. Nevertheless, Diphenyl and Phenyl-Hexyl may be applied to separate modified oligonucleotides with higher salt concentrations. The proposed separation methods without ion-pair reagents contribute to a more sustainable approach in oligonucleotide analysis.

Development of the Method for Nusinersen and Its Metabolites Identification in the Serum Samples of Children Treated with Spinraza for Spinal Muscular Atrophy

The application of oligonucleotides as drugs for different genetic diseases is increasing rapidly. Since 2016 they are used during spinal muscular atrophy treatment with the use of nusinersen oligonucleotide. The purpose of this study was to improve methods for the analysis of serum samples of patients treated with nusinersen. The results showed that liquid-liquid extraction (with phenol/chloroform) is insufficient and an additional purification step using solid-phase extraction is necessary. The best results were obtained for microextraction by packed sorbents. Important parameters in the optimization of the method were mainly the type of amine in the mobile phase and the stationary phase. Both influenced the selectivity of metabolite separation and thus their correct identification; while amine type impacted also the intensity of signals. Finally, the highest resolution of separation and the highest peak areas were obtained for N,N-dimethylbutylamine or N,N-diisopropylthylamine with an octadecyl column with a terminal aryl group. Over a dozen of metabolites were successfully identified with the use of methods developed during the study. The 3′ exonucleases and 5′ exonucleases were mainly responsible for nusinersen metabolism, consequently, 3′end shortmers, and 5′end shortmers were observed, as well as metabolites with simultaneous loss of bases at both ends of the sequence. However, some depurination and depyrimidination products were also identified. To the best of our knowledge, this is the first report on nusinersen and its metabolite identification in serum samples by liquid chromatography and mass spectrometry.

Oligonucleotides Isolation and Separation—A Review on Adsorbent Selection

Oligonucleotides have many important applications, including as primers in polymerase chain reactions and probes for DNA sequencing. They are proposed as a diagnostic and prognostic tool for various diseases and therapeutics in antisense therapy. Accordingly, it is necessary to develop liquid chromatography and solid phase extraction methods to separate oligonucleotides and isolate them from biological samples. Many reviews have been written about the determination of these compounds using the separation technique or sample preparation for their isolation. However, presumably, there are no articles that critically review the adsorbents used in liquid chromatography or solid phase extraction. The present publication reviews the literature from the last twenty years related to supports (silica, polymers, magnetic nanoparticles) and their modifications. The discussed issues concern reversed phase (alkyl, aromatic, cholesterol, mixed ligands), ion-exchange (strong and weak ones), polar (silica, polyhydroxy, amide, zwitterionic), and oligonucleotide-based adsorbents.

High-sensitivity workflow for LC-MS-based analysis of GalNAc-conjugated oligonucleotides: a case study

Aim: Mass-selective quantitation is a powerful attribute of LC-MS as a platform for bioanalysis. Here, a sensitive LC-MS approach has been validated for an oligonucleotide having chemical modifications (e.g., N-acetylgalactosamine [GalNAc] conjugated), to distinguish between the conjugated and unconjugated forms of the oligonucleotide, thereby enabling a nuanced view of the pharmacokinetic profile. Results: A high-sensitivity methodology for mass-specific measurement of AZD8233, a GalNAc-conjugated 16-mer oligonucleotide, using LLE-SPE with optimized LC conditions and detection of a low-mass fragment ion was successfully validated in the range of 0.20-100 ng/ml in human plasma. Conclusion: The AZD8233 LC-MS methodology adds valuable insight on the GalNAc linker's in vivo stability to the program and should be broadly applicable to oligonucleotides requiring high sensitivity and mass-selective measurement for quantitative discrimination from metabolites and endogenous interferences.

Distribution and biotransformation of therapeutic antisense oligonucleotides and conjugates

Drug properties of antisense oligonucleotides (ASOs) differ significantly from those of traditional small-molecule therapeutics. In this review, we focus on ASO disposition, mainly as characterized by distribution and biotransformation, of nonconjugated and conjugated ASOs. We introduce ASO chemistry to allow the following in-depth discussion on bioanalytical methods and determination of distribution and elimination kinetics at low concentrations over extended periods of time. The resulting quantitative data on the parent oligonucleotide, and the identification and quantification of formed metabolites define the disposition. Proper quantitative understanding of disposition is pivotal for nonclinical to clinical predictions, supports communication with health agencies, and increases the probability of delivering optimal ASO therapy to patients.

Hydrophilic interaction in solid-phase extraction of antisense oligonucleotides

The presented studies aimed to develop a new and simple extraction method based on hydrophilic interaction for antisense oligonucleotides with different modifications. For this purpose, solid-phase extraction cartridges with unmodified silica were used. All extraction steps were performed by utilizing water, acetonitrile, acetone or their mixtures. The results obtained show that a high content (95%) of organic solvent, used during sample loading, is critical to achieve a successful extraction, while elution with pure water allows effective oligonucleotides desorption. The recovery values were greater than 90% in the case of unmodified DNA, phosphorothioate, 2'-O-(2-methoxyethyl) and 2'-O-methyl oligonucleotides. For the mixture of phosphorothioate oligonucleotide and its two synthetic metabolites, the recovery values for the standard solutions were in the range of 70-75%, while for spiked human plasma, 45-50%. The developed method is simple, may be performed in a short time and requires simple solvents like water or acetonitrile/acetone, thus showing promise as an alternative to chaotropic salt-based or ion pair-based SPE methods.

In vivo and in vitro studies of antisense oligonucleotides - a review

The potential of antisense oligonucleotides in gene silencing was discovered over 40 years ago, which resulted in the growing interest in their chemistry, mechanism of action, and metabolic pathways. This review summarizes the selected mechanisms of antisense drug action, as well as therapeutics which are to date approved by the Food and Drug Administration and European Medicines Agency. Moreover, bioanalytical methods used for ASO pharmacokinetics and metabolism studies are briefly summarized. Special attention is paid to the primary pharmacokinetic properties of the different chemistry classes of antisense oligonucleotides. Moreover, in vivo and in vitro metabolic pathways of these compounds are widely described with the emphasis on the different animal models as well as in vitro models, including tissues homogenates, enzyme solutions, and human liver microsomes.

Studying in vitro metabolism of the first and second generation of antisense oligonucleotides with the use of ultra-high-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry

The aim of the present investigation was the analysis and identification of antisense oligonucleotide metabolism products after incubation with human liver microsomes regarding four different oligonucleotide modifications. Separation and detection methods based on the use of liquid chromatography coupled with quadrupole time-of-flight mass spectrometry were developed for this purpose. Firstly, the optimization of mass spectrometer parameters was done to select those which ensure the highest possible sensitivity of oligonucleotide analysis. This step was conducted for two chromatographic modes-ion pair chromatography and hydrophilic interaction liquid chromatography-due to their common application in oligonucleotide analysis. Based on sensitivity results, ion pair chromatography coupled with mass spectrometry was selected for the separation of model oligonucleotide mixtures in order to verify its selectivity for N-deleted metabolite separation. Next, the developed method was applied in the examination of oligonucleotides in vitro metabolism. First, wide optimization of incubation parameters was conducted including the concentration of the reaction buffer components. Obtained results indicated that both 3'-exonucleases and 5'-exonucleases contributed to the biotransformation of oligonucleotides. Moreover, it may be concluded that the number of metabolites depends on oligonucleotide modification and consequently its resistance to enzymatic attack. Thus, the number of the oligonucleotide metabolites decreased with the decrease of the resultant polarity of oligonucleotide caused by chemical modification. Graphical abstract.

Optimizing sample preparation workflow for bioanalysis of oligonucleotides through liquid chromatography tandem mass spectrometry

Liquid chromatography tandem mass spectrometry has been a widely used technique for quantifying oligonucleotides in biological samples. However, lack of simple and efficient sample cleanup approach remains a challenge. Our study aimed to evaluate the major factors during the sample pretreatment process for developing optimal sample preparation workflow for oligonucleotides. In this study, we have employed a model formed with rat plasma containing a 16 mer oligonucleotide standard in order to comprehensively optimize the sample preparation procedures. These included liquid-liquid extraction (LLE), solid-phase extraction (SPE), protein precipitation (PPT) and LLE combined with SPE. LLE with phenol: dichloromethane (2:1, v:v) was found to be the most efficient sample cleanup procedure with low cost and less toxicity. Followed by the extraction, ethanol precipitation (-80 °C, 5 min) was determined to be the optimal drying conditions. Also, mass spectrometric parameters were tuned to optimal conditions. It was found that the central composite design suite was proved to be highly practical for optimizing MS parameters. Finally, the thoroughly optimized sample preparation workflow was fully validated. The developed assay provided a quantitative range of 0.25-1000 nM, with accuracy and precision were < 7.45% and < 12.20%, respectively. Matrix effect and carryover were also evaluated and no significant effect was observed.

Introducing an In Vitro Liver Stability Assay Capable of Predicting the In Vivo Pharmacodynamic Efficacy of siRNAs for IVIVC

There has been a renewed interest in therapeutic small interfering RNAs (siRNAs) over the past few years. This is particularly the result of successful and efficient delivery of N-acetylgalactosamine (GalNAc)-conjugated siRNAs to the liver. In general, the lead selection process for siRNA drugs is faster and more straightforward than traditional small molecules. Nevertheless, many siRNAs of different sequences and chemical modification patterns must still be evaluated before arriving at a final candidate. One of the major difficulties in streamlining this workflow is the well-known phenomenon that the in vitro data obtained from oligonucleotides transfected into cells are not directly predictive of their in vivo activity. Consequently, all oligonucleotides with some degree of in vitro activity are typically screened in vivo before final lead selection. Here, we demonstrate that the stability of liver-targeting GalNAc-conjugated siRNAs in a mouse liver homogenate shows an acceptable correlation to their in vivo target knockdown efficacy. Therefore, we suggest the incorporation of an in vitro liver homogenate stability assay during the lead optimization process for siRNAs. The addition of this assay to a flow scheme may decrease the need for animal studies, and it could bring cost savings and increase efficiency in siRNA drug development.

In vitro metabolism of 2'-ribose unmodified and modified phosphorothioate oligonucleotide therapeutics using liquid chromatography mass spectrometry

Antisense oligonucleotides (ASOs) have been touted as an emerging therapeutic class to treat genetic disorders and infections. The evaluation of metabolic stability of ASOs during biotransformation is critical due to concerns regarding drug safety. Because the effects of the modifications in ASOs on their metabolic stabilities are different from unmodified ASOs, studies that afford an understanding of these effects as well as propose proper methods to determine modified and unmodified ASO metabolites are imperative. An LC-tandem mass spectrometry method offering good selectivity with a high-quality separation using 30 mm N,N-dimethylcyclohexylamine and 100 mm 1,1,1,3,3,3-hexafluoro-2-propanol was utilized to identify each oligonucleotide metabolite. Subsequently, the method was successfully applied to a variety of in vitro systems including endo/exonuclease digestion, mouse liver homogenates, and then liver microsomes, after which the metabolic stability of unmodified versus modified ASOs was compared. Typical patterns of chain-shortened metabolites generated by mainly 3'-exonucleases were observed in phosphodiester and phosphorothioate ASOs, and endonuclease activity was identically observed in gapmers that showed relatively more resistance to nuclease degradation. Overall, the degradation of each ASO occurred more slowly corresponding to the degree of chemical modifications, while 5'-exonuclease activities were only observed in gapmers incubated in mouse liver homogenates. Our findings provide further understanding of the impact of modifications on the metabolic stability of ASOs, which facilitates the development of future ASO therapeutics.

Application of hydrophilic interaction liquid chromatography coupled with tandem mass spectrometry for the retention and sensitivity studies of antisense oligonucleotides

The aim of the present investigation was application of hydrophilic interaction liquid chromatography as an alternative chromatographic approach for the study of antisense oligonucleotides. The influence of several mobile phases, differing with the salt type, their concentration and pH value on the retention and the separation of antisense oligonucleotides has been examined for this purpose. Four different stationary phases were also applied including unmodified silica, silica modified with the use of sulfobetaine groups, polyhydroxy and aminopropyl groups. Such wide range of tested conditions has been useful in better understanding of the retention mechanism of tested compounds. The results obtained during this investigation indicated that greater retention, greater peaks symmetry, as well as more effective separation of oligonucleotides, were obtained for the zwitterionic stationary phase. Moreover, the optimization of tandem mass spectrometry parameters with the use of Central Composite Design was performed and different mobile phases were tested to choose that one, which provided the greatest antisense oligonucleotides peak areas in Multiple Reaction Monitoring mode and consequently, the greatest possible sensitivity. Hydrophilic interaction liquid chromatography was compared with the ion pair chromatography, commonly used in the analysis of oligonucleotides. Both techniques were compared in terms of selectivity of separation as well as the sensitivity of their determination. Obtained results proved that ion pair chromatography provided better results in terms of separation efficiency and peak areas in Multiple Reaction Monitoring for tested conditions. However, these results do not preclude application of hydrophilic interaction liquid chromatography as an alternative chromatographic approach for the oligonucleotides analysis especially when a mobile phase without ion pair reagents is required.

Discovery of a novel deaminated metabolite of a single-stranded oligonucleotide in vivo by mass spectrometry

Aim: A novel single-stranded deaminated oligonucleotide metabolite resulting from a REVERSIR™ oligonucleotide was discovered and identified in monkey liver after subcutaneous administration. Results & methodology: REVERSIR-A and its metabolites were extracted from biological matrices by solid phase extraction and analyzed using LC coupled with high-resolution MS under negative ionization mode. A novel 9-mer metabolite of REVERSIR-A, resulting from deamination of the 3' terminal 2'-O-methyl-adenosine nucleotide to 2'-O-methyl-inosine, was discovered at significant levels in monkey liver. The metabolite's identity was confirmed by LC-MS/MS. Conclusion: This report describes the first observation of a long-chain deaminated metabolite of a single-stranded REVERSIR oligonucleotide in vivo in monkey liver.

Automated determination of early eluting oligonucleotide impurities using ion-pair reversed-phase liquid chromatography high resolution-mass spectrometry

A new method is presented for the automated determination of early eluting (E.E.) oligonucleotide impurities analyzed by IP-RP HPLC HRMS. E.E. are impurities shorter than the main drug component and are primarily formed by the mechanisms of coupling failure, and depurination. The method is based on the detection of the theoretically derived most abundant mass of an impurity in the experimental data. An exhaustive list of candidate impurities and their formulas is automatically generated using the parent sequence and the known mechanisms of impurity formation. The approach accounts for possible modifications in the individual oligonucleotide sequence moieties (e.g., linkage, sugar, and base, 3', and 5' ends). The detected ion signal is summed to provide four nested levels of impurity breakdown information. The approach allows for the rapid determination of relationships and trends of impurities in samples generated by different manufacturing processes and conditions. Representative examples are given to illustrate the capabilities and utility of the approach in synthesis and purification process optimization applications.

Assay determination by mass spectrometry for oligonucleotide therapeutics

Phosphorothioate oligonucleotide drugs typically contain product-related impurities that are difficult to resolve chromatographically from the parent oligonucleotide due to the size of these compounds and the large number of stereoisomers that comprise the parent. The presence of co-eluting impurities hinders the process of determining assay based on chromatographic separation alone. A mass spectrometry-based purity assessment of the main chromatography peak can be used to quantify co-eluting impurities and enable the accurate determination of assay, but a more direct measure of assay was desired due to the complexity of measuring all co-eluting impurities by mass spectrometry. Therefore, we developed an assay method that utilizes the specificity of mass spectrometry to measure the amount of active pharmaceutical ingredient in a sample, which eliminates the need for chromatographic separation of impurities from the product. This procedure uses a single quadrupole mass spectrometer and incorporates an internal standard that is co-sprayed with the analyte to compensate for the drift commonly associated with mass spectrometry-based quantitation. Using the mass spectrometry response ratio for sample to internal standard enables the method to achieve excellent linearity (R²  = 0.998), repeatability (relative standard deviation = 0.5%), intermediate precision (0.6%), and accuracy, with measured assay values consistently within 2.0% of expected. The results indicate the method possesses the accuracy and precision required for measuring assay in clinical and commercial stage pharmaceutical products. Since the method is based on the specificity of the mass spectrometer, and does not rely on chromatographic separation of impurities, the procedure should be applicable to a wide variety of oligonucleotide therapeutics regardless of sequence or chemical modifications.

Analysis of antisense oligonucleotides with the use of ionic liquids as mobile phase modifiers

The main goal of this study was the investigation of the impact of several ionic liquids, commonly used as free silanol suppressors, on the retention and separation of phosphorothioate oligonucleotides. Three various stationary phases (octadecyl, octadecyl with embedded polar groups and pentafluorophenyl) as well as ionic liquids with the concentration range of 0.1-7 mM were used for this purpose. The results obtained during this study showed that the increase in concentration of ionic liquids results in increasing retention of the oligonucleotides. Such an effect was observed regardless of the stationary phase used. Moreover, elongation of the alkyl chain in the structure of ionic liquids caused an increase of antisense oligonucleotide retention factors. The results obtained during retention studies confirmed that addition of ionic liquids to the mobile phase influences antisense oligonucleotide retention in a way similar to the case of commonly used ion pair reagents such as amines. A method of oligonucleotide separation was also developed. The best selectivity was obtained for the octadecyl stationary phase since separation of mixtures of antisense oligonucleotides and their metabolites differing in sequence length was successful. It has to be pointed out that ionic liquids were used for the first time as mobile phase additives for oligonucleotide analysis.

Development of liquid chromatography tandem mass spectrometry method to quantify cyclobutane pyrimidine dimer photolyase activity by detection of 15mer oligonucleotide as reaction product

Ultraviolet radiation from sunlight causes DNA damage in skin cells by formation of photoproducts, mainly cyclobutane pyrimidine dimers (CPD), which are reverted by exogenous CPD-photolyase, preventing photoaging and skin cancer. High performance liquid chromatography tandem mass spectrometry method for quantification of CPD-photolyase activity was developed to search new enzymes sources for dermatology or clinical studies. The method was based in the enzymatic conversion of a 15mer oligonucleotide, containing a center cyclobutane thymidine dimer, to the restored 15mer oligonucleotide. Three ion pair reagent were evaluated by response surface methodology to increase mass intensities. Additionally, chromatographic separation of oligonucleotides was performed. The selected mobile phase was 15 mM diisopropylethylamine/20 mM hexafluoroisopropanol in methanol. The method allowed total separation between the oligonucleotides studied (resolution of 2.3) by using the core shell technology, which reduce the diffusion time of the analyte into the column, increasing the efficiency and minimizing the analysis time at 7 min. The mass spectrometry detection allowed a high selectivity and sensitivity. This is the first time where MRM modality has been employed with this specific purpose. Oligonucleotides recovery from reaction mixture was ∼ 94% and the limit of quantification was 13.4 nM for 15mer. The method was evaluated with a recombinant CPD-photolyase from Synechococcus leopoliensis using purified and crude protein extract. CPD-photolyase could be measured in terms of activity for enzymatic kinetics studies, for evaluation of UV-R effects in (micro)organisms and to identify new enzymes.

Metabolite Profiling of the Antisense Oligonucleotide Eluforsen Using Liquid Chromatography-Mass Spectrometry

Eluforsen (previously known as QR-010) is a 33-mer 2′-O-methyl modified phosphorothioate antisense oligonucleotide targeting the F508del mutation in the gene encoding CFTR protein of cystic fibrosis patients. In this study, eluforsen was incubated with endo- and exonucleases and mouse liver homogenates to elucidate its in vitro metabolism. Mice and monkeys were used to determine in vivo liver and lung metabolism of eluforsen following inhalation. We developed a liquid chromatography-mass spectrometry method for the identification and semi-quantitation of the metabolites of eluforsen and then applied the method for in vitro and in vivo metabolism studies. Solid-phase extraction was used following proteinase K digestion for sample preparation. Chain-shortened metabolites of eluforsen by 3′ exonuclease were observed in mouse liver in an in vitro incubation system and by either 3′ exonuclease or 5′ exonuclease in liver and lung samples from an in vivo mouse and monkey study. This study provides approaches for further metabolite characterization of 2′-ribose-modified phosphorothioate oligonucleotides in in vitro and in vivo studies to support the development of oligonucleotide therapeutics.

A new approach to preparation of antisense oligonucleotide samples with microextraction by packed sorbent

Our research focused on applying microextraction by packed sorbent to extracting antisense oligonucleotides from serum samples. The tested sorbents included poly(styrene-co-divinylbenzene), octyl, octadecyl, and unmodified silica gel. As nonpolar sorbents were used for highly-polar molecules, this required ion-pair mode. Comprehensive optimization of extraction conditions was performed for 20-mer phosphorothioate oligonucleotide. Several parametres - the number of "draw-eject" cycles during the conditioning and load step, the amine type and concentration, and the volume of elution mixture - and the influence they had on recovery were studied for nonpolar sorbents, which made it possible to obtain high (ca. 90%) recovery values. The most influential parameter turned out to be the volume of elution mixture. Similar optimization was performed for silica sorbents; however, despite optimization of various parameters, the recovery values stayed relatively low. The optimized procedures for nonpolar sorbents were applied in extraction of six different oligonucleotides of various length and with different structure modifications. The highest recoveries were obtained for octyl and octadecyl sorbents, ranging between 80-99%. The developed microextraction method was used to extract phosphorothioate and 2'-O-(2-methoxyethyl) oligonucleotides and their two synthetic metabolites from enriched human plasma, with recoveries around 70-80%.

Development of a detection method for antisense oligonucleotides in mouse kidneys by matrix-assisted laser desorption/ionization imaging mass spectrometry

RATIONALE

Oligonucleotide therapeutics have recently gained much attention, but its pharmacokinetic evaluation methods are still not sufficient, and, in particular, more tools are needed to evaluate their tissue distribution and metabolites. We developed a matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS)-based method to evaluate the tissue distribution of oligonucleotide therapeutics.

METHODS

We used an antisense oligonucleotide containing locked nucleic acids (LNA-A). Various washing protocols were examined using mouse kidney homogenate sections. Next, we applied a two-step matrix preparation strategy. As a first step, 3-hydroxypicolinic acid (3-HPA) matrix containing citrate and amines was sprayed using an airbrush and subsequently 3-HPA matrix containing citrate only was sprayed using the ImagePrep. Finally, kidney sections prepared from LNA-A-dosed mice were treated with our optimized method and analyzed with MALDI-IMS.

RESULTS

The selected washing method made it possible to detect LNA-A with MALDI-IMS and, furthermore, our developed matrix pretreatment method enhanced signal intensity approximately two-fold. MALDI-IMS revealed that LNA-A localized in a portion presumed to be the renal cortex. We also obtained information on LNA-A metabolites, which showed the same distribution profile as LNA-A in kidneys.

CONCLUSIONS

This study shows that MALDI-IMS can be applied to evaluate the tissue distribution of oligonucleotide therapeutics. Our method can evaluate the tissue distribution along with metabolites and has the potential to help the development of novel oligonucleotide therapeutics.

Application of ion pair chromatography coupled with mass spectrometry to assess antisense oligonucleotides concentrations in living cells

Antisense oligonucleotides (ASOs) are synthetic bioactive compounds used as therapeutic agents in clinical trials. They act by binding to complementary sequences of the targeted nucleic acids in cells. Assessing the efficiency of ASO delivery to cells or tissues and the stability of these compounds in different biological systems is important. To answer these questions, we developed a new, quick and reliable method to determine the concentrations of different types of ASOs in treated cells. Ultra-high performance liquid chromatography coupled with mass spectrometry was used for the first time for the separation and determination of the studied compounds in total RNA extracts. To develop a method with the highest possible sensitivity, a central composite design was used to comprehensively optimize the MS parameters. Moreover, the effects of the type and concentration of the ion pair reagent on sensitivity were also examined. Finally, a mobile phase containing methanol, hexafluoroisopropanol and N,N-dimethylbutylamine was selected. The optimized method allowed good linearity, accuracy, precision and sensitivity of ASO detection. Next, these compounds were delivered into cells via transfection at a concentration of 25 nM or 125 nM in 1 mL of cell culture medium. After 48 hours, total RNA was isolated from the treated cells and analyzed with the use of the newly developed method. For the cells treated with a higher concentration of ASO composed of phosphorothioate 2'-O-methyl RNA units, the concentration in solution was 0.96 ± 0.06 μM, while in the case of shorter ASO composed of locked nucleic acid units, it was 0.72 ± 0.06 μM in the total RNA extract.

Semi-quantitative determination of co-eluting impurities in oligonucleotide drugs using ion-pair reversed-phase liquid chromatography mass spectrometry

Continued improvements in understanding RNA biology have led to significant success in the development of antisense oligonucleotide therapeutics, and several oligonucleotide drugs have now been approved. Manufacturing of oligonucleotides may be associated with the production of impurities. Current methods for quantification of impurities that co-elute with the main drug component rely on manual ion extraction and integration of the characteristic mass signal of each impurity. For certain applications however, especially those involving large sets of samples such as those generated in the optimization of oligonucleotide manufacturing processes, a rapid method that provides semi-quantitative determination of impurity levels would be sufficient. In this work, an automated approach has been developed to rapidly determine the relative amounts of co-eluting impurities in oligonucleotide samples. The most abundant mass in the isotopic distribution is automatically calculated from the impurity formula and used to detect the presence of the impurities. The principles of the approach are described, and representative examples are given. Impurities determined in different manufacturing lots are compared directly, and by principal component analysis. The ability of the method to determine impurity levels across large sample sets is illustrated for an oligonucleotide drug purification study.

Development of SPE method for the extraction of phosphorothioate oligonucleotides from serum samples

AIM

Comprehensive development of a method for SPE extraction of antisense phosphorothioate oligonucleotide and its metabolites and their determination with the use of UHPLC.

RESULTS

Polymer-based adsorbent and high percentage of methanol in elution solvent provided high recoveries compared with silica-based octadecyl cartridge. As to the type and concentration of ion pair reagent and organic solvent, the mixture of 5 mM of N,N-dimethylbutylamine/150 mM of 1,1,1,3,3,3-hexafluoroisopropanol and methanol was selected. Relatively high recoveries in the range of 79.2-81.2% with the SDs of 3.4-6.2% were obtained for the oligonucleotide and its metabolites extracted from human serum.

CONCLUSION

The developed method may be successfully applied for routine analysis of antisense oligonucleotides in serum since it is relatively easy, quick and reliable.

Review on sample preparation methods for oligonucleotides analysis by liquid chromatography

Antisense oligonucleotides have been successfully investigated for the treatment of different types of diseases. Detection and determination of antisense oligonucleotides and their metabolites are necessary for drug development and evaluation. This review focuses mainly on the first step of the analysis of oligonucleotides i.e. the sample preparation stage, and in particular on the techniques used for liquid chromatography and liquid chromatography coupled with mass spectrometry. Exceptional sample preparation techniques are required as antisense oligonucleotides need to be determined in complex biological matrices. The text discusses general issues in oligonucleotide sample preparation and approaches to their solution. The most popular techniques i.e. protein precipitation, protein enzyme digestion and liquid-liquid extraction are reviewed. Solid phase extraction methods are discussed and the issues connected with the application of each method are highlighted. Other newly reported promising techniques are also described. Finally, there is a summary of actually used techniques and the indication of the direction of future research.

Review on investigations of antisense oligonucleotides with the use of mass spectrometry

Antisense oligonucleotides have been investigated as potential drugs for years. They inhibit target gene or protein expression. The present review summarizes their modifications, modes of action, and applications of liquid chromatography coupled with mass spectrometry for qualitative and quantitative analysis of these compounds. The most recent reports on a given topic were given prominence, while some early studies were reviewed in order to provide a theoretical background. The present review covers the issues of using ion-exchange chromatography, ion-pair reversed-phase high performance liquid chromatography and hydrophilic interaction chromatography for the separation of antisense oligonucleotides. The application of mass spectrometry was described with regard to the ionization type used for the determination of these potential therapeutics. Moreover, the current approaches and applications of mass spectrometry for quantitative analysis of antisense oligonucleotides and their metabolites as well as their impurities during in vitro and in vivo studies were discussed. Finally, certain conclusions and perspectives on the determination of therapeutic oligonucleotides in various samples were briefly described.

Identification of GalNAc-Conjugated Antisense Oligonucleotide Metabolites Using an Untargeted and Generic Approach Based on High Resolution Mass Spectrometry

Antisense oligonucleotides linked by phosphorothioates are an important class of therapeutics under investigation in various pharmaceutical companies. Antisense oligonucleotides may be coupled to high-affinity ligands (triantennary N-acetyl galactosamine = GalNAc) for hepatocyte-specific asialoglycoprotein receptors (ASGPR) to enhance uptake to hepatocytes and to increase potency. Since disposition and biotransformation of GalNAc-conjugated oligonucleotides is different from unconjugated oligonucleotides, appropriate analytical methods are required to identify main cleavage sites and degradation products of GalNAc conjugated and unconjugated oligonucleotides in target cells. A highly sensitive method was developed to identify metabolites of oligonucleotides using capillary flow liquid chromatography with column switching coupled to a high resolution Orbitrap Fusion mass spectrometer. Detection of GalNAc-conjugated oligonucleotides and their metabolites was achieved by combining full scan MS with two parallel MS² experiments, one data-dependent scan and an untargeted MS² experiment (all ion fragmentation) applying high collision energy. In the all ion fragmentation scan, a diagnostic fragment originating from the phosphorothioate backbone (O₂PS-: m/z 94.936) was formed efficiently upon collisional activation. Based on this fragment an accurate determination of metabolites of oligonucleotides was achieved, independent of their sequence or conjugation in an untargeted but highly selective manner. The method was effectively applied to investigate uptake and metabolism of GalNAc-conjugated oligonucleotides in incubations of primary rat hepatocytes; the elucidation of expected and unexpected degradation products was achieved in subnanomolar range.

The impact of ion-pairing reagents on the selectivity and sensitivity in the analysis of modified oligonucleotides in serum samples by liquid chromatography coupled with tandem mass spectrometry

Present study highlights the usage of various ion-pairing agents and their impact on the process of separation and ionization of oligonucleotides in the fortified human serum samples. What is more, retention studies involved different stationary phases, including: octadecyl, phenyl, pentafluorophenyl groups and ligands with embedded polar groups. It was proved that retention of oligonucleotides strongly depends on the alkyl chain branching in the structure of ion pairing reagent. Furthermore ion-pairing agents build of straight alkyl chain are more easily adsorbed on the stationary phase modified with octadecyl groups, while branching of alkyl chain caused more effective adsorption of studied compounds at phenyl groups compared to octadecyl ones. The lowest limit of quantification values were obtained for 5mMN,N-dimethylbutylamine, while the highest values are characteristic for hexylamine. Moreover it was shown that a 2-fold increase of ion-pairing agent concentration results in higher LOQ. The greatest sensitivity was obtained for 2.5mMN,N-dimethylbutylamine/150mM hexafluoroisopropanol. On the other hand Hypersil GOLD aQ column was the most appropriate in terms of time and separation effectiveness. The developed method was successfully used for the determination of studied oligonucleotides and their metabolites in human serum samples. The compounds were separated in just 3.5min with high sensitivity (0.09-0.16ng).

Application of hydrophilic interaction liquid chromatography coupled with mass spectrometry in the analysis of phosphorothioate oligonucleotides in serum

Most of synthetic, modified oligonucleotides are candidates for therapeutics. Consequently, their quick, reliable and sensitive analysis has become a critical challenge for scientists. The main aim of the present study was an investigation of the influence of stationary phase type, mobile phase salt and its concentration on the separation and determination of the selected compounds by hydrophilic interaction liquid chromatography coupled with electrospray ionization tandem mass spectrometry. Three different columns, together with ammonium acetate and formate, were applied for this purpose. The separation of mixtures of phosphorothioate oligonucleotides and their synthetic metabolites was successfully performed. Moreover, an attempt to isolate these compounds from human serum samples was also made together with their separation, qualification and quantification by hydrophilic interaction liquid chromatography and tandem mass spectrometry. The method developed during the study appeared to be effective and sensitive, due to the limit of quantification which equaled 142-165ppb.