Recent advances in biotin-based therapeutic agents for cancer therapy

Biotin receptors, as biomarkers for cancer cells, are overexpressed in various tumor types. Compared to other vitamin receptors, such as folate receptors and vitamin B12 receptors, biotin receptor-based targeting strategies exhibit superior specificity and broader potential in treating aggressive cancers, including ovarian cancer, leukemia, colon cancer, breast cancer, kidney cancer, and lung cancer. These strategies promote biotin transport via receptor-mediated endocytosis, which is triggered upon ligand binding. Biotin, as the ligand of the biotin receptor, can be conjugated to anti-cancer drugs to form targeted therapies that bind to receptors overexpressed on tumor cells, thus increasing drug uptake. Despite these advantages, many candidate drugs have progressed slowly and remain in the preclinical stage, impeding clinical translation. This is mainly due to the effects of various conjugation methods and drug formulations on their functionality and efficacy. Therefore, developing novel biotin-based therapeutics is crucial. The innovation of this strategy lies in its multifunctionality-researchers can use different conjugation methods to design and synthesize these drugs, enabling precise targeting of various tumor types while minimizing toxicity to normal cells. These drugs include small-molecule-biotin conjugates (SMBCs) and nano-biotin conjugates (NBCs). This dual-platform approach represents a significant advancement in targeted therapy, offering unprecedented flexibility in drug design and delivery. Compared to chemotherapy drugs and traditional delivery systems, biotin-based drugs with tumor-specific targeting demonstrate enhanced targeting, improved efficacy, and reduced toxicity. This review examines strategies and applications for enhancing the delivery of chemotherapy drugs to cancer cells, highlighting the need for high-quality conjugates and strategies. It not only summarizes the latest progress but also provides key insights into how this emerging field could revolutionize personalized cancer treatment, especially in the context of precision medicine. Additionally, it offers perspectives on future research directions in this field.

Storage conditions, sample integrity, interferences, and a decision tool for investigating unusual high-sensitivity cardiac troponin results

The current definition of high-sensitivity cardiac troponin (hs-cTn) assays is laboratory-based and their analytical attributes and characteristics have drawn significant attention in the literature at least partly due to the lower concentration cut-offs and changes in concentrations (i.e., deltas) employed in different algorithms and pathways to manage patient care. We propose that pre-analytical conditions such as sample type, storage conditions, and other interferences may also have a significant impact on hs-cTn concentrations and clinical management. The purpose of this literature review is to provide a summary of important pre-analytical and interference studies affecting hs-cTn concentrations. A breakdown of the literature for the major diagnostic companies providing core laboratory instrumentation (i.e., Abbott, Beckman, Ortho, Roche, and Siemens) is also provided. Finally, three cases are highlighted where knowledge of pre-analytical factors aids the hs-cTn clinically discordant investigations. This review highlights the importance of pre-analytical variables, especially storage condition, sample handling, and blood tubes used (i.e., sample type) when interpreting hs-cTn assays. Additional studies are needed to further elaborate on pre-analytical variables (i.e., centrifugation, sample type, stability) and interferences for all hs-cTn assays in clinical use, as knowledge of these variables may aid in hs-cTn clinically discordant investigations.

Interferences in immunoassays: review and practical algorithm

Immunoassays are currently the methods of choice for the measurement of a large panel of complex and heterogenous molecules owing to full automation, short turnaround time, high specificity and sensitivity. Despite remarkable performances, immunoassays are prone to several types of interferences that may lead to harmful consequences for the patient (e.g., prescription of an inadequate treatment, delayed diagnosis, unnecessary invasive investigations). A systematic search is only performed for some interferences because of its impracticality in clinical laboratories as it would notably impact budget, turnaround time, and human resources. Therefore, a case-by-case approach is generally preferred when facing an aberrant result. Hereby, we review the current knowledge on immunoassay interferences and present an algorithm for interference workup in clinical laboratories, from suspecting their presence to using the appropriate tests to identify them. We propose an approach to rationalize the attitude of laboratory specialists when faced with a potential interference and emphasize the importance of their collaboration with clinicians and manufacturers to ensure future improvements.

Mitigation of Biotin Interference in Manual and Automated Immunoassays by Preconjugating Biotinylated Antibodies to the Streptavidin Surface as an Alternative to Biotin Depletion

BACKGROUND

Streptavidin-to-biotin binding is one of the strongest noncovalent interactions in nature and incorporated into many immunoassays. Biotin-streptavidin coupling assays are susceptible to interference from free biotin in patient specimens, which may falsely decrease or increase results. To prevent biotin interference, we evaluated a method to preconjugate biotinylated antibodies to the assay's streptavidin solid surface before adding patient specimen and compared this technique to a biotin depletion protocol.

METHODS

Biotin interference in 3 manual ELISAs and 2 automated immunoassays was established. Mitigation of biotin interference by preincubation was evaluated in each assay by adding biotinylated antibody to the streptavidin-coated surface before adding biotin- or PBS-spiked serum. Lastly, the preincubation method was compared to a biotin-depletion protocol to compare the effectiveness of mitigating biotin interference.

RESULTS

In the presence of 400 µg/L biotin, analyte detection was reduced to 10% to 15% of total in the ELISA assays and to 15.2% in the automated sandwich (thyroglobulin) immunoassay. In the automated competitive (free thyroxine) immunoassay, biotin caused an increased detection of 551.6%. Preconjugation of the biotinylated capture antibody to the streptavidin surface in the ELISA assays resulted in 84% to 99% activity recovery, compared to 84% to 97% by a biotin depletion protocol. Similarly, automated sandwich and competitive immunoassays obtained 97.1% and 116.5% recovery by preconjugation, compared to 95.6% and 100.3% by the depletion method, respectively.

CONCLUSION

This study demonstrates how assay redesign to include preconjugation of biotinylated capture antibody to streptavidin is an effective alternative to biotin-depletion methods to mitigate biotin interference.

A study on the detection of free and bound biotin based on TR-FRET technology

Biotin is widely used in biological applications due to its highly selective and stable interaction with avidin, which highlights the great potential value of the quantitative determination of biotin concentration. However, the currently reported methods have many defects such as complicated operation processes and low sensitivity. Here, the time-resolved fluorescence resonance energy transfer (TR-FRET) assay is introduced to establish a convenient, rapid and sensitive biotin quantitative detection strategy. Europium cryptate (Eu³⁺) acts as an energy donor to label streptavidin, while APC acts as an energy acceptor to label biotin. Biotin in aqueous solution interacts with streptavidin in a competition mode. The obtained biotin detection range is 0.05-100 nM and the optimal limit of detection (LOD) of 0.03 nM biotin is obtained. Furthermore, an enzyme digestion test and a competition mode test were performed to analyze biotin in different states. The method used in this work has greatly improved the sensitivity of biotin quantitative detection and it's for the first time that a systematic study on the difference between free and bound biotin based on concentration results is conducted. It can be further extended to the detection of other biological molecules or multiplex detection of other small molecules.

The prevalence of elevated biotin in patient cohorts presenting for routine endocrinology, sepsis, and infectious disease testing

Elevated blood biotin levels may interfere with some biotin-streptavidin immunoassays, used in clinical laboratories to aid diagnosis. The objective of this study was to determine the prevalence of elevated blood biotin levels in three at risk patient cohorts, where misclassification of disease status would have a high clinical impact. This retrospective, single-center study screened residual, de-identified plasma samples (N = 700) from adult patients undergoing routine thyroid stimulating hormone (TSH) (n = 500), procalcitonin (PCT) (n = 100), or human immunodeficiency virus (HIV) (n = 100) testing using the Elecsys® BRAHMS PCT (Roche Diagnostics), Access TSH (3rd IS) (Beckman Coulter Inc), and ARCHITECT HIV Ag/Ab Combo (Abbott Laboratories) immunoassays, respectively, for elevated levels of biotin (quantified by gas chromatography-time of flight mass spectrometry). Patients taking biotin supplements were included and dosages recorded from medical records. In the overall study cohort, blood biotin levels ranged 0.1-21.3 ng/mL; 44.3% (310/700) of samples were < 1 ng/mL, 54.7% (383/700) were 1-<10 ng/mL, and 1% (7/700) were ≥ 10 ng/mL. The sub-cohorts had similar ranges of biotin levels: 0.5-21.3 ng/mL (TSH), 0.1-12.1 ng/mL (PCT), and 0.3-7.3 ng/mL (HIV). In the 44 patients (6.3% of overall study cohort) who were documented as taking biotin supplements (range of doses, 2.5-10 mg/day), blood biotin levels ranged 0.9-21.3 ng/mL; 2.3% (1/44) of samples were < 1 ng/mL, 86.4% (38/44) were 1-<10 ng/mL, and 11.4% (5/44) were ≥ 10 ng/mL. Most patients who reported taking biotin supplements had blood biotin levels ≥ 1 ng/mL and the highest blood biotin level detected was 21.3 ng/mL.

Toxicologic evaluation of a novel, highly soluble biotin salt, magnesium biotinate

A novel, highly soluble biotin salt, magnesium biotinate (MgB), was assessed for general and genetic toxicity using several toxicologic tests. This battery of tests included in vitro bacterial reverse mutation test, in vitro mammalian micronucleus assay, and oral acute, 14-day, and 90-day repeat-dose toxicity in Sprague-Dawley (SD) rats. The results of the in vitro studies indicate that MgB is not mutagenic, clastogenic, or aneugenic. The acute oral toxicity study established an LD50 ≥ 5000 mg MgB/kg. In the 14-day oral toxicity study, doses of MgB up to 2500 mg MgB/kg/day produced no clinical signs or mortality. In the 90-day oral toxicity study, administration of 600 mg MgB/kg/day resulted in no clinical signs and was determined to be the no-observed-adverse-effect-level (NOAEL), which equates to 39 g biotin/day for a 70 kg human. Since MgB is composed of 93% biotin, the 600 mg NOAEL equates to approximately 1.3 million times the current recommended daily allowance of 30 μg biotin/day and 3900 times supplement levels of 10 mg biotin/day. Based on the toxicologic profile and lack of findings in various in vitro and in vivo studies, MgB may be considered safe for long-term human use.

Prevalence of Detectable Biotin in Five US Emergency Department Patient Cohorts

BACKGROUND

The objective of this study was to estimate the prevalence of biotin supplementation in United States emergency department patients using a multi-site, geographically distributed sampling model.

METHODS

Biotin was measured using an Abbott ARCHITECT Biotin research use only assay in 7118 emergency department patient serum or plasma samples from five US medical centers. Samples with biotin ≥10 ng/mL underwent additional LC-MS/MS confirmatory testing for biotin and its primary metabolites. The overall and site-specific prevalence of detectable biotin was determined using the screening assay while biotin speciation (i.e., prevalence of detectable metabolites) was determined using LC-MS/MS.

RESULTS

Of 7118 samples screened, 291 (4.1%) had biotin ≥10 ng/mL and were considered positive. Across five medical centers, the fraction of positive samples ranged from 2.0% to 5.4%. The maximum biotin concentration observed was 355 ng/mL. Of the 285 positive screens that underwent additional LC-MS/MS testing, 89 (31%) showed detectable biotin, bisnorbiotin, and/or biotin sulfoxide. Biotin, bisnorbiotin, and biotinsulfoxide were detected in 82/89 (92.1%), 61/89 (68.5%), and 18/89 (20.2%) samples, respectively; biotin was detected in the absence of either metabolite in 18/89 (20.2%) samples.

CONCLUSIONS

Using a screening assay, 4.1% of emergency department patient samples were found to be potentially susceptible to interference from biotin. Confirmatory testing showed detectable biotin and/or biotin metabolites in 31% of positive screens (1.3% overall). The prevalence of biotin ≥10 ng/mL varied 2-3-fold across US emergency department patient cohorts. Biotin metabolites were observed in 80% of samples confirmed to have detectable biotin species by LC-MS/MS, suggesting that rigorous assessments of assay susceptibility to biotin interference, often performed using in vitro studies, should consider the potential role of biotin metabolites present in vivo.

The underestimated issue of non-reproducible cardiac troponin I and T results: case series and systematic review of the literature

Cardiac troponins (cTn) are the preferred biomarkers for the evaluation of myocardial injury and play a key role in the diagnosis of acute myocardial infarction (MI). Pre-analytical or analytical issues and interferences affecting troponin T and I assays are therefore of major concern given the risk of misdiagnosis. False positive troponin results have been related to various interferences including anti-troponin antibodies, heterophilic antibodies, or elevated alkaline phosphatase level. On the other hand, false negative results have been reported in the case of a large biotin intake. These interferences are characterized with erroneous but reproducible troponin results. Of interest, non-reproducible results have also been reported in the literature. In other words, if the sample is reanalyzed a second time, a significant difference in troponin results will be observed. These interferences have been named "fliers" or "outliers". Compared to the biotin interference that received major attention in the literature, troponin outliers are also able to induce harmful clinical consequences for the patient. Moreover, the prevalence of outliers in recent studies was found to be higher (0.28-0.57%) compared to the biotin interference. The aim of this systematic review is to warn clinicians about these non-reproducible results that may alter their clinical judgment. Four case reports that occurred in the Clinique of Saint-Luc Bouge are presented to attest this point. Moreover, we aimed at identifying the nature of these non-reproducible troponin results, determining their occurrence, and describing the best way for their identification.

Evaluating the performance of an updated high-sensitivity troponin T assay with increased tolerance to biotin

OBJECTIVES

Biotin >20 ng/mL may interfere with the Elecsys^® Troponin T-high sensitive assay (cTnT-hs; Roche Diagnostics International Ltd). We evaluated the performance of an updated assay, cTnT-hs*, which was designed to reduce biotin interference.

METHODS

cTnT-hs* assay performance was assessed using up to two applications (18 min/9 min) on three analyzers (cobas e 411/cobas e 601/cobas e 801). Biotin interference was determined by measuring recovery in an 11-sample series dilution with biotin ranging from 0-3600 ng/mL. Repeatability/reproducibility were evaluated in five serum sample pools (n=75 each). Method comparisons tested: cTnT-hs* vs. cTnT-hs (18 min/cobas e 601); cTnT-hs* assay 18 vs. 9 min (cobas e 601); cTnT-hs* (18 min) on cobas e 601 vs. cobas e 411 and cobas e 601 vs. cobas e 801. Concordance at the 99th percentile decision limit between cTnT-hs* and cTnT-hs (9 min/cobas e 601) was calculated using 300 lithium-heparin plasma samples and a 14 ng/L assay cutoff.

RESULTS

cTnT-hs* assay (18 min/cobas e 601) recovery was ≥96% for biotin ≤1250 ng/mL. Across all applications/analyzers, coefficients of variation for repeatability/reproducibility with the cTnT-hs* assay were <5% in most serum sample pools (mean cardiac troponin T: 8.528-9484 ng/L). High correlation (Pearson's r=1.000) was demonstrated for all method comparisons. Concordance at the 99th percentile decision limit was high between the cTnT-hs* and cTnT-hs assays.

CONCLUSIONS

The updated cTnT-hs* assay may provide greater tolerance to biotin interference, and shows good analytical and clinical agreement/concordance with the previous cTnT-hs assay.