Noninvasive and nondestructive optical spectroscopic measurement of motexafin gadolinium in mouse tissues: comparison to high-performance liquid chromatography.

Efficient design of anti-cancer treatments involving radiation- and photo-sensitizing therapeutics requires knowledge of tissue-specific drug concentrations. This study investigates the use of the optical pharmacokinetic system (OPS) to measure concentrations of the anti-cancer agent motexafin gadolinium (MGd) in mouse tissues noninvasively and nondestructively using elastic-scattering spectroscopy. The magnitude of MGd absorbance was quantitated by integration of the MGd peak absorbance area, and MGd concentrations were estimated by comparison with standard curves that were validated by high performance liquid chromatography (HPLC). In tissue-simulating phantoms in vitro, MGd peak absorbance area correlated with MGd concentration. Female C.B-17 SCID mice, bearing subcutaneous MDA-MB-231 human breast cancer xenografts, were dosed with 23 mg/kg MGd i.v. At specific times between 5 min and 24h after dosing, noninvasive OPS measurements were made on skin overlaying the subcutaneous tumor and skin on the opposite flank in vivo, and following exsanguination, nondestructive measurements were made on tumor, skin, and internal tissues in situ. OPS measurements on tissues in vivo detected MGd present in both tissue and blood perfusing the tissue. Both the OPS and the HPLC detected selective localization of MGd in malignant tissues compared with surrounding non-malignant tissues, and neither technique detected MGd in brain tissue. Comparison of MGd concentrations measured by HPLC and OPS is complicated by mismatch between measured tissue volumes, heterogeneous spatial distribution of MGd in tissues, and blood-localized MGd at early time points. Tumor-specific MGd concentrations measured by HPLC correlated with those measured by OPS in vivo and in situ. Best fit lines to the concentration estimates (forced through zero) had slopes of 0.900 and 1.185, respectively; however, the variability was significant (r(2)=0.477 and 0.269). The clinical utility of the OPS to quantitate MGd concentrations remains to be validated.