Multi-parametric functional optical spectroscopy to monitor the metabolic and vascular changes in small head and neck tumors in vivo with radiation stress

Abstract

We demonstrated a portable multi-parametric functional optical spectroscopy to monitor metabolic and vascular changes in small head and neck tumors in vivo with fractional radiation therapy. For the first time, we captured the key metabolic and vascular parameters of head and neck xenograft tumors in vivo prior to and post a total of 10 Gy fractional radiation therapy. Our animal studies showed dramatic vascular and metabolic changes in radioresistant head and neck tumors (rSCC-61) under radiation stress but not in radiosensitive head and neck tumors (SCC-61). Specifically, our data showed that rSCC-61 tumors had increased tissue oxygen saturation (indicating reoxygenation), increased total hemoglobin content (indicating blood perfusion), and increased oxygenated hemoglobin (indicating oxygen supply) post radiation therapy. Our study also showed that rSCC-61 tumors had decreased glucose uptake and increased mitochondrial function post-radiation therapy. In contrast, SCC-61 tumors had minimal changes in either vascular or metabolic parameters post-radiation treatment. These results demonstrated the potential of our portable multi-parametric functional optical spectroscopy to evaluate tumor vascular and metabolic changes under therapeutic stresses for future head and neck cancer research.

Fig. 1.

Timeline for tumor cell injections, optical measurements and fractional RT in this study.

Fig. 2.

(A). Schematic of the optical spectroscopy setup. Bottom left: custom-designed fiber-optics probe; Bottom right: photo of a typical xenograft tumor under optical measurement. (B) photo of the actual spectroscopy system in a stand-alone portable cart.

Fig. 3.

(A) Representative SCC-61 and rSCC-61 tumors measured by our optical spectroscopy; (B) Tumor volumes of SCC-61 and rSCC-61 tumors on day 10 post cell injection; (C) Average diffuse reflectance spectra measured on all five in vivo SCC-61 tumors and five in vivo rSCC-61 tumors; (D) MC model extracted absorption coefficients of five in vivo SCC-61 tumors and five in vivo rSCC-61 tumors; (E) MC model extracted reduced scattering coefficients of five in vivo SCC-61 tumors and five in vivo rSCC-61 tumors. Tumor volume was estimated using the equation: volume = (Length x Width x Height)/2.

Fig. 4.

MC model extracted tissue vascular parameters including (A) StO2, (B) [THB], (C) [HB], (D) [HbO2] for both SCC-61 and rSCC-61 tumors. (E) 2-NBDG uptake kinetics over 60 minutes and (F) boxplot of 2-NBDG uptake at 60 minutes (2-NBDG₆₀). (G) TMRE uptake kinetics over 80 minutes and (H) boxplot of TMRE uptake at 80 minutes (TMRE₈₀). A student t-test was used for all statistical analyses.

Fig. 5.

Tumor volumes of SCC-61 (A) and rSCC-61(E) tumors prior to and post RT. Average diffuse reflectance spectra measured on SCC-61 (B) and rSCC-61 tumors (F), the MC model extracted absorption coefficients of SCC-61 (C) and rSCC-61 (G) tumors and the MC model extracted reduced scattering coefficients of SCC-61 (D) and rSCC-61 (H) tumors prior to and post radiation treatment. Tumor volume was estimated using the equation: volume = (Length x Width x Height) / 2. One animal from the SCC-61 group showed obvious tumor necrosis, therefore, the animal was euthanized before RT treatment per IACUC protocol.

Fig. 6.

MC models extracted tissue vascular parameters including (A and E) StO2, (B and F) [THB], (C and G) [HB], (D and H) [HbO2] for both SCC-61 and rSCC-61 tumors prior to and post RT. A paired Student’s t-test was used for all statistical analyses.

Fig. 7.

(A) 2-NBDG uptake kinetics over 60 minutes and (B) boxplot of 2-NBDG uptake at 60 minutes (2-NBDG₆₀), and (C) TMRE uptake kinetics over 80 minutes and (D) boxplot of TMRE uptake at 80 minutes (TMRE₈₀) in SCC-61 tumors. (E) 2-NBDG uptake kinetics over 60 minutes and (F) boxplot of 2-NBDG uptake at 60 minutes (2-NBDG₆₀) and (G) TMRE uptake kinetics over 80 minutes and (H) boxplot of TMRE uptake at 80 minutes (TMRE₈₀) in rSCC-61 tumor prior to and post RT. A paired Student’s t-test was used for all statistical analyses.