Targeted antisense radiotherapy and dose fractionation using a (177)Lu-labeled anti-bcl-2 peptide nucleic acid-peptide conjugate

Preparation and SPECT/CT Imaging of 177Lu-Labeled Peptide Nucleic Acid (PNA) Targeting CITED1: Therapeutic Evaluation in Tumor-Bearing Nude Mice

Purpose

The expression of Cbp/p300-interacting transactivator with Glu/Asp-rich carboxy-terminal domain 1 (CITED1) is upregulated in papillary thyroid carcinoma (PTC) and mediates cell proliferation and migration. To facilitate early diagnosis and monitoring of recurrent or metastatic PTC, we designed ¹⁷⁷Lu-labeled antisense peptide nucleic acid (PNA) targeting CITED1 mRNA to evaluate the therapeutic potential, while analyzing its distribution in nude mice and the characteristics withsingle-photon emission-computed tomography/computed tomography (SPECT/CT) imaging.

Materials and Methods

¹⁷⁷Lu-DOTA-anti-CITED1-PNA (¹⁷⁷Lu-asPNA) was obtained by indirect labeling. High-performance liquid chromatography (HPLC) and thin-layer chromatography (TLC) were used to determine the labeling rate and radiochemical purity. The stability of ¹⁷⁷Lu-asPNA was evaluated by TLC, and the radioactivity count was measured by a γ counter to calculate its uptake capacity in K1 cells. To analyze the distribution of ¹⁷⁷Lu-asPNA in body tissues and organs of nude mice, static single-photon emission-computed tomography (SPECT) imaging and SPECT/CT image fusion were performed. Then, the therapeutic effects of probes were explored by tumor growth curves and survival analysis.

Results

Our probe showed a radiochemical purity of 96.5±0.15% at 1 hr and specific activity of 8.7±0.53 MBq/μg. The uptake rate in the ¹⁷⁷Lu-asPNA group was much higher than that in the ¹⁷⁷Lu-DOTA-nonsense-PNA (¹⁷⁷Lu-nonsense-PNA) and ¹⁷⁷Lu-DOTA groups (P<0.05). The biological distribution showed that the tumor/muscle ratio was at its highest at 24 h (4.98±0.34) post-inoculation, with SPECT/CT imaging showing clear tumor development. By measuring tumor volume of tumor-bearing nude mice, the ¹⁷⁷Lu-asPNA group showed a significant difference in tumor size 9 days after injection (P < 0.05). Kaplan-Meier survival curves showed that the overall survival rate in the ¹⁷⁷Lu-asPNA group was significantly different from those in the DOTA-anti-CITED1-PNA (asPNA) and saline groups (P = 0.002, log-rank test).

Conclusion

¹⁷⁷Lu-asPNA was developed successfully, showing a high labeling rate and good stability. SPECT/CT imaging demonstrated tumor growth in nude mice, which was effectively inhibited by our probe, thus prolonging survival.

Hematologic malignancies: newer strategies to counter the BCL-2 protein

INTRODUCTION

BCL-2 is the founding member of the BCL-2 family of apoptosis regulatory proteins that either induce (pro-apoptotic) or inhibit (anti-apoptotic) apoptosis. The anti-apoptotic BCL-2 is classified as an oncogene, as damage to the BCL-2 gene has been shown to cause a number of cancers, including lymphoma. Ongoing research has demonstrated that disruption of BCL-2 leads to cell death. BCL-2 is also known to be involved in the development of resistance to chemotherapeutic agents, further underscoring the importance of targeting the BCL-2 gene in cancer therapeutics. Thus, numerous approaches have been developed to block or modulate the production of BCL-2 at the RNA level using antisense oligonucleotides or at the protein level with BCL-2 inhibitors, such as the novel ABT737.

METHODS

In this article, we briefly review previous strategies to target the BCL-2 gene and focus on a new approach to silence DNA, DNA interference (DNAi).

RESULTS AND CONCLUSION

DNA interference is aimed at blocking BCL-2 gene transcription. Evaluations of this technology in preclinical and early clinical studies are very encouraging and strongly support further development of DNAi as cancer therapeutics. A pilot phase II clinical trial in patients with relapsed or refractory non-Hodgkin lymphoma, PNT2258 demonstrated clinical benefit in 11 of 13 patients with notable responses in diffuse large B cell lymphoma and follicular lymphoma. By targeting the DNA directly, the DNAi technology promises to be more effective compared with other gene-interference strategies that target the RNA or protein but leaves the dysregulated DNA functional.