Preclinical Characterization of 5-Amino-4-Oxo-[6-¹¹C]Hexanoic Acid as an Imaging Probe to Estimate Protoporphyrin IX Accumulation Induced by Exogenous Aminolevulinic Acid

Abstract

Preoperative noninvasive imaging to estimate the quantity and spatial distribution of protoporphyrin IX (PpIX) accumulation in tumors induced by 5-aminolevulinic acid (ALA) administration is expected to improve the efficacy of ALA-based fluorescence-guided resection and photo-and sonodynamic therapies. PpIX synthesis from exogenous ALA has been reported to be regulated by ALA influx or ALA dehydratase (ALAD) activity, which catalyzes the first step of the synthesis. In this study, we characterized the properties of a 11 C-labeled ALA analog, 5-amino-4-oxo-[6-11 C]hexanoic acid ( 11 C-MALA), as a PET tracer to estimate PpIX accumulation. Methods: In vitro uptake of 11 C-MALA and 3 H-ALA was determined in 5 tumor cell lines after 10-min incubation with each tracer at 37°C. The expression levels of ALAD were determined by Western blot analysis. In vivo distribution and dynamic PET studies were conducted in tumor-bearing mice. In vitro and in vivo accumulation of ALA-induced PpIX was determined by measuring fluorescence in extracts of cells or tumors. Results: In vitro uptake of 11 C-MALA in 5 tumor cell lines was correlated with ALAD expression levels and PpIX accumulation. In vivo biodistribution and dynamic PET studies showed that 11 C-MALA was rapidly incorporated into tumors, and the tumor-to-muscle ratio of 11 C-MALA at 1 min after injection was significantly correlated with that of 3 H-ALA. 11 C-MALA in tumors was continuously decreased thereafter, and the elimination rate of 11 C-MALA from AsPC-1 tumors with the highest ALAD expression level was slower than from other tumors with lower expression levels. These results suggest that the influx and intracellular retention of 11 C-MALA reflect ALA influx and ALAD expression levels, respectively. Tumor accumulation of 11 C-MALA at 60 min after injection was strongly correlated with PpIX accumulation in tumor tissues. Conclusion: 11 C-MALA PET has the potential to noninvasively estimate the quantitative and spatial accumulation of exogenous ALA-induced PpIX.

Mechanistic study of PpIX accumulation using the JFCR39 cell panel revealed a role for dynamin 2-mediated exocytosis

“…There are still many factors to be considered in the detailed mechanisms involved in the accumulation of PpIX by cancer cells, and thus extensive research is currently being carried out. At the level of basic research, many reports have been published on the accumulation of PpIX in different types of human cancer cell lines derived from a wide variety of tissues, such as brain tumor 24 , hepatic cancer 25 , gastric cancer 26 , melanoma 27 , ovarian cancer 28 , cervical cancer 29 , breast cancer 30 , prostate cancer 31 , colon cancer 32 , lung cancer 33 , bladder cancer 34 , oral cancer 35 , pancreatic cancer 36 , esophageal cancer 37 and osteosarcoma 38 .…”

Sonodynamic Therapy: Advances and Challenges in Clinical Translation

“…Future challenges to improve this technique involve notably obtaining a deeper knowledge and efficient methods to handle cavitation. First, additional Accuracy is slightly reduced when using dual-frequencies; US power is not the only relevant parameter: exposure configuration and timing are important Treatment monitoring US contrast agents loaded with sensitizers and gas for cavitation imaging 84 ; SDT process monitoring by positron emission tomography 86 ; Association of sensitizers with manganese ions for high magnetic resonance imaging performance 87 Most of studies did not report proper cavitation monitoring mechanistic studies have to be conducted on the sonodynamic effect. A better understanding of the interaction of sonosensitizers with cavitation will help adapt cavitation generation to optimize the resulting effects while limiting unnecessary energy deposition of undesired mechanical effects.…”

“…Future challenges to improve this technique involve notably obtaining a deeper knowledge and efficient methods to handle cavitation. First, additional 59 ; nonphotosensitive sensitizers such as IR-780 iodide 62 or DEG 61 Increase local toxicity and reduce systemic toxicity Target selectivity NPe 6 : 5-fold concentration in tumors compared to surrounding muscle tissue 13,63 ; combination with monoclonal antibody 17,65 NPe 6 sonosensitivity is lower than other sensitizers such as ALA-5; combination with antibody permits selective effect Increase stimuli-response reactivity Hydrophilization of sensitizers 68 ; ROS-triggered drug delivery 73 ; combination with oxygen-loaded microbubbles 71 or silicon nanoparticles 72 ROS-triggered drug delivery provides a selective antitumoral effect Cavitation generation Dual-frequency sonication 4,80 ; confocal US 81 ; shorter, high-amplitude bursts, followed by sustaining bursts 82 Accuracy is slightly reduced when using dual-frequencies; US power is not the only relevant parameter: exposure configuration and timing are important Treatment monitoring US contrast agents loaded with sensitizers and gas for cavitation imaging 84 ; SDT process monitoring by positron emission tomography 86 ; Association of sensitizers with manganese ions for high magnetic resonance imaging performance 87 Most of studies did not report proper cavitation monitoring mechanistic studies have to be conducted on the sonodynamic effect. A better understanding of the interaction of sonosensitizers with cavitation will help adapt cavitation generation to optimize the resulting effects while limiting unnecessary energy deposition of undesired mechanical effects.…”

“…Cavitation activity monitoring could enable monitoring at step C . To image the sonodynamic process at step D, a 11 C‐labeled ALA analogue, 5‐amino‐4‐oxo‐[6‐ 11 C]hexanoic acid, was used as a positron emission tomography tracer to estimate PpIX accumulation . The tumor accumulation of 5‐amino‐4‐oxo‐[6‐ 11 C]hexanoic acid correlated well with the accumulation of PpIX in tumor tissues.…”