A thin-film interferometry-based label-free immunoassay for the detection of daratumumab interference in serum protein electrophoresis.

BACKGROUND: Daratumumab (DARA) is a fully human anti-CD38 IgG1-κ monoclonal antibody drug used in the treatment of multiple myeloma (MM). While serum protein electrophoresis (SPEP) is an important assay for diagnosis and monitoring of patients with MM, DARA can appear in the γ-region as a single band and interfere with the interpretation of SPEP results. An approach to detect the interference is measuring the quantity of DARA in serum samples and assessing its impact on SPEP results. Immunoassays based on label-free technologies, i.e. label-free immunoassays (LFIA's), can achieve real-time immunometric measurement without attaching a reporter molecule (enzyme, fluorophore, etc.) to the immunocomplex. The recorded time course of the immunocomplex formation allows for quantitation on initial binding rate, which facilitates rapid measurement within a few minutes. Based on the thin-film interferometry (TFI) technology, a rapid LFIA was established for the quantitation of DARA in serum samples. METHODS: The TFI-based LFIA for DARA was validated for imprecision (CV), accuracy, limit of quantitation (LOQ), and analytical measurement range (AMR). Interference to the LFIA was evaluated using a group of protein samples, as well as hemolytic, lipemic, and icteric clinical samples. RESULTS: The precision of the TFI-based LFIA's for DARA ranged from 6.5% to 10.7% (within-run CV), and 7.4% to 11.6% (between-run CV), with a bias of -2.1% to 10.1%. The LOQ was 10 µg/ml (n = 4, CV 9.8%), with an AMR ranging from the LOQ to 1000 µg/ml. The LFIA was used to measure 37 patient samples submitted for SPEP testing. The LFIA results were 100% consistent with the history of DARA use as documented in the medical record. CONCLUSIONS: The TFI-based LFIA was successful at accurately identifying DARA in serum samples and can be used to identify DARA interference in SPEP testing. This work demonstrates the applicability of label-free technologies, particularly the TFI technology, to clinical diagnostic needs. Given the simplicity and the speed of the testing process, the TFI technology provides a unique testing approach for the measurement of proteins in clinical samples.

Transcutaneous ultrasound augments naked DNA transfection of skeletal muscle.

This study was designed to test the hypothesis that transcutaneous ultrasound (US) exposure may augment the transfection efficiency and biological outcome associated with nonviral DNA gene transfer. Hindlimb muscles of New Zealand White rabbits were transfected with the reporter plasmid pCMV-beta, with or without US exposure. Optimization studies employed US exposure at various frequencies, mechanical indices, duty cycles, durations of exposure, and exposure time points. Based on these results, we explored the effect of US exposure on nonviral gene transfer of vascular endothelial growth factor (VEGF, phVEGF165) to promote neovascularization of ischemic hindlimbs. Ultrasound at 1 MHz, 100 W/cm(2), 6% duty cycle, and 5 minutes exposure time, applied immediately following DNA injection, was found to be the most effective among the settings tested, increasing beta-galactosidase expression approximately 20 fold. Compared with US exposure alone, or phVEGF165 only, phVEGF165 + US exposure yielded a statistically significant improvement in revascularization, as determined by calf blood pressure ratio, angiographic score, intravascular Doppler blood flow, and capillary/myocyte ratio. These data demonstrate that ultrasound, when applied directly after intramuscular gene transfer, significantly increases transfection efficiency in vivo. The biological significance of this finding was confirmed by augmented limb perfusion in response to US exposure and naked VEGF DNA.