Label-free analysis of tenofovir delivery to vaginal tissue using co-registered confocal Raman spectroscopy and optical coherence tomography

Abstract

Vaginally applied microbicide products offer a female-controlled strategy for preventing sexual transmission of HIV. Microbicide transport processes are central to their functioning, and there is a clear need for a better understanding of them. To contribute to that end, we developed an assay to analyze mass transport rates of microbicide molecules within the epithelial and stromal layers of polarized vaginal mucosal tissue during contact with a gel vehicle. The assay utilizes a new diffusion chamber mounted in a custom instrument that combines confocal Raman spectroscopy and optical coherence tomography. This measures depth-resolved microbicide concentration distributions within epithelium and stroma. Data for a tenofovir gel were fitted with a compartmental diffusion model to obtain fundamental transport properties: the molecular diffusion and partition coefficients in different compartments. Diffusion coefficients in epithelium and stroma were computed to be 6.10 ± 2.12 x 10−8 and 4.52 ± 1.86 x 10−7 cm2/sec, respectively. The partition coefficients between epithelium and gel and between stroma and epithelium were found to be 0.53 ± 0.15 and 1.17 ± 0.16, respectively. These drug transport parameters are salient in governing the drug delivery performance of different drug and gel vehicle systems. They can be used to contrast drugs and vehicles during product design, development and screening. They are critical inputs to deterministic transport models that predict the gels’ pharmacokinetic performance, which can guide improved design of products and optimization of their dosing regimens.

Understanding Factors Governing Distribution Volume of Ethyl Cellulose-Ethanol to Optimize Ablative Therapy in the Liver

“…The volume and distribution of the injected solution within the tissue are primary outcomes of the procedure. In principle, these could be measured by imaging serial sections of tissue after injection, e.g., using Raman spectroscopy (distinguishing unlabeled ethanol from tissue) [43]. However, such approaches with unlabeled materials were deemed too time-consuming, given the sample size and spatial resolution necessary for this study.…”

Deducing Mucosal Pharmacokinetics and Pharmacodynamics of the Anti-HIV Molecule Tenofovir from Measurements in Blood

“…First a deterministic computational PK model would be created (if not already available) for the test product, specific to its properties and those of its active pharmaceutical ingredient. Input parameters to the model would be obtained: (a) by direct measurements – for example, rheological properties governing vaginal deployment of the vehicle 43 and solubility and transport properties of the drug 56 ; and (b) by reference to other studies – for example, clearance rate constants in the circulation from different dosing studies of the same drug. If prior pharmacokinetic data already existed for the product, model predictions would be compared to them, and improvements in the model would be implemented to the extent warranted by the data – for example, refinements of values of parameters such as rate constants.…”

Polymer-assisted intratumoral delivery of ethanol: Preclinical investigation of safety and efficacy in a murine breast cancer model

“…A custom-built confocal Raman spectroscope with a 785 nm excitation laser diode (LD785-SH300, Thorlabs Inc., Newton, NJ) was used to capture Raman spectra at the surface of the tumor (30). The least squares fit was performed in MATLAB (MathWorks, Natick, MA) to extract the relative contribution of ethanol and tumor tissue to the measured Raman spectra at the tumor surface, using a previously validated method (30)(31)(32).…”

“…In order to investigate the mechanism for improved safety of EC-ethanol over ethanol, the release (Fig 2A-B) as in previously validated algorithms (30)(31)(32). The D eff of ethanol of 6%EC-ethanol was approximately half that of pure ethanol (3.3 ± 1.5 x 10 -6 cm 2 /s vs. 5.9 ± 1.2 x 10 -6 cm 2 /s ; P<0.05; n=7,6) (Fig 2C).…”