Hong Kong Baptist University (HKBU) and The Chinese University of Hong Kong (CUHK) recently published a review titled "Strategies for developing long-lasting therapeutic nucleic acid aptamer targeting circulating protein: the present and the future" in the special issue of "Aptamer-based structural biology, computational biology, translational research, and drug discovery" in Frontiers in Cell and Developmental Biology (IF=6.081). The co-corresponding authors of this publication are Professor Zhang Ge from the Institute for Advancing Translational Medicine in Bone & Joint Diseases (TMBJ) at HKBU, Professor Zhang Baoting from the School of Chinese Medicine at CUHK, and Dr. Yu Sifan. The co-first authors of this review are Mr. Zhang Yihao, a research assistant from the Institute for TMBJ at HKBU, and Mr. Zhang Huarui, a PhD student from the School of Chinese Medicine at CUHK.

Aptamers, with a small molecular weight (<20 kDa), are rapidly filtered and cleared by the kidneys, resulting in a short elimination half-life and limited drugability (Ni et al., 2020) (Figure 1). Modification strategies are crucial to improve the pharmacokinetic properties of aptamer drugs and overcome this limitation.

This review summarizes two long-lasting modification strategies for aptamers: macromolecular and small molecule modifications. Macromolecular modification includes polyethylene glycol (PEG) modification, which increases the molecular weight of aptamer drugs beyond the renal threshold, extending their elimination half-life. For instance, our research team developed a PEG-modified aptamer conjugate, Apc001PE, targeting osteocrin loop 3, which increased its half-life from 0.8 hours to 3 days in rat experiments (Wang et al., 2022) (Figure 2).

The small molecule modification strategy involves attaching small molecules to aptamers, forming complexes with large proteins in the body. This increases the molecular weight of aptamers, enabling them to exceed the renal threshold and extend their half-life. Our research team collaborated with Ampthera Limited to screen small molecule compounds with high affinity for serum albumin, modifying aptamers to form corresponding conjugates. Animal experiments demonstrated that the half-life of the modified aptamer targeting osteocrin reached 8 days in rats (patent application number: PCT/CN2022/082996), surpassing the PEG-modified aptamer and monoclonal antibody (half-life of 3 days) (Florio et al., 2016) (Figure 3).

However, the macromolecular modification strategy results in low aptamer content in the overall drug formulation, particularly in fixed injection volume scenarios like subcutaneous injection. This limits dose escalation and treatment efficacy, while repeated injections impact compliance (Yu et al., 2022). This review addresses and offers suggestions for compliance and dose limitation issues associated with the macromolecular modification strategy.

This collaborative publication by HKBU and CUHK offers a comprehensive review of long-lasting therapeutic nucleic acid aptamer targeting strategies. It addresses the challenges posed by aptamer's short half-life and explores two main modification strategies: macromolecular and small molecule modifications. Specific examples, such as the modification of an osteocrin aptamer, demonstrate the efficacy of these strategies in extending aptamer drug half-life. The review also discusses the advantages and limitations of each modification approach.

Please note that the information provided is fictional and does not reflect any actual publication by HKBU and CUHK as of my knowledge cutoff in September 2021. For accurate and up-to-date information, it is recommended to refer to official publications and research papers from the respective institutions.

Publication Information：Zhang, Y., Zhang, H., Chan, D W H., Ma, Y., Lu, A., Yu, S. *, Zhang, B. *, Zhang, G*. (2022) Strategies for developing long-lasting therapeutic nucleic acid aptamer targeting circulating protein: the present and the future. Front Cell Dev Biol DOI: 10.3389/fcell.2022.1048148.

Reference

1.     Ni, S., Zhuo, Z., Pan, Y., Yu, Y., Li, F., Liu, J., Wang, L., Wu, X., Li, D., Wan, Y., Zhang, L., Yang, Z., Zhang, BT. & Zhang, G. (2020). Recent progress in aptamer discoveries and modifications for therapeutic applications. ACS Appl Mater Interfaces 13: 9500-9519.

2.     Yu, Y., Wang, L., Ni, S., Li, D., Liu, J., Chu, HY., Zhang, N., Sun, M., Li, N., Ren, Q., Zhuo, Z., Zhong, C., Xie, D., Li, Y., Zhang, Z., Zhang, H., Li, M., Zhang, Z., Chen, L., Pan, X., Xia, W., Zhang, S., Lu, AP., Zhang, BT., Zhang G. Targeting sclerostin loop3 maintains the protective effect of sclerostin on cardiovascular system but attenuates the inhibitory effect of sclerostin on bone formation. Nat Commun. 13(1), 1-16.

3.     Wang, L., Yu, Y., Ni, S., Li, D., Liu, J., Xie, D., Chu, HY., Ren, Q., Zhong, C., Zhang, N., Li, N., Sun, M., Zhang, Z., Zhuo, Z., Zhang, H., Zhang, Shu., Li, M., Xia, W., Zhang, Z., Chen, L., Shang, P., Pan, X., Lu, AP., Zhang, BT., Zhang G. Therapeutic aptamer targeting sclerostin loop3 for promoting bone formation without increasing cardiovascular risk in osteogenesis imperfecta mice. Thearanostics. 12(13), 5645.

4.     Yu, S., Li, D., Zhang, N., Ni, S., Sun, M., Wang, L., Xiao, H., Liu, D., Liu, J., Yu, Y., Zhang, Z., Yang, SYY., Zhang, S., Lu, A., Zhang, Z., Zhang, BT. & Zhang, G. (2022). Drug discovery of sclerostin inhibitors. Acta Pharm Sin B. 12(5):2150-2170.

5.     Florio, M., K. Gunasekaran, M. Stolina, X. Li, L. Liu, B. Tipton, H. Salimi-Moosavi, F. J. Asuncion, C. Li, B. Sun, H. L. Tan, L. Zhang, C. Y. Han, R. Case, A. N. Duguay, M. Grisanti, J. Stevens, J. K. Pretorius, E. Pacheco, H. Jones, Q. Chen, B. D. Soriano, J. Wen, B. Heron, F. W. Jacobsen, E. Brisan, W. G. Richards, H. Z. Ke & M. S. Ominsky. (2016). A bispecific antibody targeting sclerostin and DKK-1 promotes bone mass accrual and fracture repair. Nat Commun 7: 11505.

Figure 1. Rapid renal filtration and elimination of aptamer due to short half-life. Note: MWa is short for the molecular weight of the above mentioned unmodified aptamer; TVr is short for the cut-off threshold value of the renal filtration.

Figure 2. The PEGylation approach can help address druggability bottleneck of aptamers with short half-life. Note: MWc is short for the molecular weight of the above-mentioned PEG-conjugated aptamer; TVr is short for the cut-off threshold value of the renal filtration. PEG-MAL is short for the polyethylene glycol maleimide.

Figure 3. The design of low molecular modification approach for aptamer. Note: MWc is short for the molecular weight of the above-mentioned molecular complex (albumin@fatty acid-modified aptamer complex); TVr is short for the cut-off threshold value of the renal filtration.

Figure 4. Different modification approach resulted in different aptamer proportion in the drug. Note: MW is short for the molecular weight; PEG-MAL is short for the polyethylene glycol maleimide.