Sodium Multivitamin Transporter-Targeted Fluorochrome Facilitates Enhanced Metabolic Evaluation of Tumors Through Coenzyme-R Dependent Intracellular Signaling Pathways.

BACKGROUND

Intraoperative molecular imaging (IMI)-guided resections have been shown to improve oncologic outcomes for patients undergoing surgery for solid malignancies. The technology utilizes fluorescent tracers targeting cancer cells without the use of any ionizing radiation. However, currently available targeted IMI tracers are effective only for tumors with a highly specific receptor expression profile, and there is an unmet need for IMI tracers to label a broader range of tumor types. Here, we describe the development and testing of a novel tracer (CR)-S0456) targeted to the sodium multivitamin transporter (SMVT).

METHODS

Preclinical models of fibrosarcoma (HT-1080), lung (A549), breast (4T1), and renal cancers (HEK-293 T) in vitro and in vivo were used for assessment of (CR)-S0456 specific tumor labeling via sodium-mediated SMVT uptake in dipotassium phosphate or choline chloride-containing media buffer. Additionally, pharmacologic inhibition of multiple intracellular coenzyme-R obligate signaling pathways, including holocarboxylase synthetase (sulconazole nitrate), PI3K/AKT/mTOR (omipalisib), and calmodulin-dependent phosphatase (calmidazolium), were investigated to assess (CR)-S0456 uptake kinetics. Human fibrosarcoma-bearing xenografts in athymic nude mice were used for tumor and metabolic-specific labeling. Novel NIR needle confocal laser endomicroscopic (nCLE) intratumoral sampling was performed to demonstrate single-cell specific labeling by CR-S0456.

RESULTS

CR-S0456 localization in vitro correlated with highly proliferative cell lines (MTT) and doubling time (p < 0.05) with the highest microscopic fluorescence detected in aggressive human fibrosarcomas (HT-1080). Coenzyme-R-specific localization was demonstrated to be SMVT-specific after competitive inhibition of internal localization with excess administration of pantothenic acid. Inhibiting the activity of SMVT by affecting sodium ion hemostasis prevented the complete uptake of CR-S0456. In vivo validation demonstrated (CR)-S0456 localization to xenograft models with accurate identification of primary tumors as well as margin assessment down to 1 mm tumor volume. Systemic treatment of xenograft-bearing mice with a dual PI3K/mTOR inhibitor suppressed intratumoral cell signaling and (CR)-S0456 uptake via a reduction in SMVT expression. Novel analysis of in vivo intratumoral cytologic fluorescence using near-infrared confocal laser endomicroscopy demonstrated the absence of coenzyme-R-mediated NIR fluorescence but not fibroblast activation protein (FAP)-conjugated fluorochrome, indicating specific intracellular inhibition of coenzyme-R obligate pathways.

CONCLUSION

These findings suggest that a SMVT-targeted NIR contrast agent can be a suitable tracer for imaging a wide range of malignancies as well as evaluating metabolic response to systemic therapies, similar to PET imaging with immune checkpoint inhibitors.