Abstract SNACC-55

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Feasibility of Rapid Mitoxantrone-DNA Binding Revealed by Diffuse Reflectance Spectroscopy

1Singh-Moon R, 2Bigio I, 1Joshi S
1College of Physicians and Surgeons, Columbia University, New York, NY, USA; 2Boston University, Boston, MA, USA

Introduction: Mitoxantrone (MTO) is an antineoplastic drug with light absorption in the visible-near infrared region.(1) MTO experiences a spectral shift in ms time frame when bound to albumin (8nm) and an additional 7-9nm to nucleic acids, which takes much longer.(2, 3) Diffuse reflectance spectroscopy (DRS) can determine changes in tissue spectra with sub-second sampling.(4) We therefore assessed the feasibility of DRS for simultaneous determination of tissue albumin- and DNA-bound MTO concentrations after IV injection. A DRS-based method for determining MTO-DNA binding could assist in non-invasive monitoring of delivery to the target site.
Methods: After IACUC approval, experiments were conducted in Sprague Dawley rats under isoflurane anesthesia. Tissue drug concentrations were measured from the animals' heel by DRS.(4) MTO (1 mg/1 min) was infused via the tail vein to keep systemic hemodynamics stable. After 12 baseline measurements 600 spectra were obtained over the next hour. The concentrations of MTO states were determined using extinction spectra for albumin and DNA-bound MTO and oxy-and deoxy-hemoglobin obtained from published literature.(2-4) Finally, drug concentration-time curves were fit to a 2-compartment model for IV injection using least squares minimization in conjunction with a Runge-Kutta numerical solver.
Results: Representative curves showing concentration-time clearance of albumin and DNA bound MTO are shown in Figure. Rapid increase in albumin bound MTO concentrations was evident immediately after injection, and binding to DNA was evident early after injection. While concentrations of albumin-bound MTO declined below the level of DRS detection, those of DNA-bound MTO increased slowly but remained stable thereafter. The pharmacokinetic data for albumin and DNA-bound MTO was in good fit with the 2-compartmental model.
Discussion and conclusions: This experiment shows that it is feasible to detect spectral shifts suggestive of MTO binding to DNA - which is the target site of drug delivery and is therefore significant. Further studies are necessary to validate actual tissue uptake by determining MTO concentrations in cell fractions. An optical method monitoring chemotherapeutic drug-DNA concentrations could provide a parameter to assess the effectiveness drug delivery particularly when the drug is caged in nanoparticles. One potential problem with nanoparticle drug delivery is the suboptimal release of the drug. Chemical tissue concentrations usually do not provide such information, while optical methods might easily be able to do.
1. A. Boiardi et al., Ital J Neurol Sci 20, 43 (1999)
2. H. Porumb et. al., Prog Biophys Mol Biol 34, 175-95 (1978)
3. J. Kapuscinski et. al., Biochem Pharmacol 34: 4203-13 (1985)
4. JR Mourant, et al., Phys Med Biol 44: 1397-417 (1999).

Acknowledgements: R 01 CA 127500 and CA 138643

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