Preparation and Evaluation of 177Lu-Labeled Gemcitabine: An Effort Toward Developing Radiolabeled Chemotherapeutics for Targeted Therapy Applications

Targeted Tumor Therapy with Radiolabeled DNA Intercalator: A Possibility? Preclinical Investigations with 177Lu-Acridine

Objective

A DNA intercalating agent reversibly stacks between the adjacent base pairs of DNA and thus is expected to exhibit preferential localization in the tumorous lesions as tumors are associated with enhanced DNA replication. Therefore, radiolabeled DNA intercalators are supposed to have potential to be used in targeted tumor therapy. Working in this direction, an attempt was made to radiolabel 9-aminoacridine, a DNA intercalator, with ¹⁷⁷Lu, one of the most useful therapeutic radionuclides, and study the potential of ¹⁷⁷Lu-acridine in targeted tumor therapy. Experiments. 9-Aminoacridine was coupled with p-NCS-benzyl-DOTA to facilitate radiolabeling, and the conjugate was radiolabeled with ¹⁷⁷Lu. Different reaction parameters were optimized in order to obtain ¹⁷⁷Lu-acridine complex with maximum radiochemical purity. In vitro stability of the radiolabeled complex was studied in normal saline and human blood serum. Biological behavior of the radiolabeled agent was studied both in vitro and in vivo using the Raji cell line and fibrosarcoma tumor-bearing Swiss mice, respectively.

Results

¹⁷⁷Lu-acridine complex was obtained with ~100% radiochemical purity under the optimized reaction conditions involving incubation of 1.5 mg/mL of ligand with ¹⁷⁷Lu (1 mCi, 37 MBq) at 100°C at pH ~5 for 45 minutes. The complex maintained a radiochemical purity of >85% in saline at 6 d and >70% in human serum at 2 d postpreparation. In vitro cellular study showed uptake of the radiotracer (5.3 ± 0.13%) in the Raji cells along with significant cytotoxicity (78.06 ± 2.31% after 6 d). Biodistribution study revealed considerable accumulation of the radiotracer in tumor 9.98 ± 0.13 %ID/g within 1 h postadministration and retention therein till 6 d postadministration 4.00 ± 0.16 %ID/g with encouraging tumor to nontarget organ uptake ratios.

Conclusions

The present study, although preliminary, indicates the potential of ¹⁷⁷Lu-acridine and thus radiolabeled DNA intercalators in targeted tumor therapy. However, further detailed evaluation is required to explore the actual potential of such agents in targeted tumor therapy.

The potential of radiolabeled chemotherapeutics in tumor diagnosis: Preliminary investigations with 68 Ga-gemcitabine

Preclinical Research & Development Gemcitabine, a nucleoside analog, is a well-known chemotherapeutic drug that is used either alone or with other agents to treat a wide variety of cancers. The aim of the present work was to evaluate the potential of ⁶⁸ Ga-labeled gemcitabine for its application in positron emission tomography (PET) imaging of tumorous lesions. Gemcitabine was coupled with p-NCS-benzyl-DOTA in order to facilitate radiolabeling with ⁶⁸ Ga. The gemcitabine-p-NCS-benzyl-DOTA was radiolabeled with ⁶⁸ Ga, obtained from a ⁶⁸ Ge/⁶⁸ Ga radionuclide generator. The radiolabeled product was characterized by high performance liquid chromatography (HPLC) and its tumor specificity was evaluated by biodistribution studies in Swiss mice bearing fibrosarcoma tumors. Preliminary bioevaluation study showed good tumor uptake within 1 hr post-administration [2.5% Injected Activity (IA) per g of tumor] with rapid renal clearance (>90% IA) and a high tumor to muscle ratio. ⁶⁸ Ga-gemcitabine may have potential as a PET agent for tumor imaging.