Written by | Jiang Kuan is responsible for editing | Zhou Yebin
Retinoblastoma (Rb) is the most common intraocular malignancy in children, with a global incidence of about 1/15,000 to 1/20,000, and about 9,000 new neonatal cases per year. Advances in chemotherapy for retinoblastoma have greatly improved the eye preservation and survival rate of children, and the commonly used treatment is melphalan. Because the eyeball has a special protective mechanism and there is no vascular structure in vitreous, the current melphalan chemotherapy regimen for retinoblastoma is to inject directly through vitreous every week or every two weeks in order to achieve sufficient drug concentrations in the retina and vitreous.
However, the administration of this intraocular chemotherapy is more complicated and requires better medical resources and professional physicians to achieve it. This is difficult to do in many developing countries, and there are risks associated with this traumatic topical administration. In addition to severely affecting vision, retinoblastoma is prone to extraocular metastasis in the middle and advanced stages, such as metastasis into the brain with a very high fatality rate. Children in developing countries are also more difficult to detect and treat early. Combining these factors, retinoblastoma still imposes a serious social and family burden. Therefore, for this intraocular malignancy, safer and more effective treatment, especially anti-metastatic therapy, is still an urgent clinical problem to be solved. If effective treatment of fundus diseases can be achieved through simple and convenient eye drops administration, it will greatly improve the compliance and safety of patients, especially infants and young children.
On April 1, 2022, the team of Wei Gang and Zhan Changyou of Fudan University jointly published a study entitled Topology instillation of cell-penetrating peptide-conjugated melphalan blocks metastases of retinoblastoma at Biomaterals. For the first time, a membrane-permeabilant covalent conjugate eye drops for the treatment of retinoblastoma was reported, which could achieve a tumor inhibition effect comparable to that of intravitreal injection administration by eye drops, and with the help of the "outside-in" enveloping drug absorption method of eye drops, it achieved a highly effective anti-intraocular tumor metastasis effect, which was significantly better than intravitreal injection administration.
Based on the high-efficiency eye permeation peptide Q8W and N9WPenetratin (89WP) obtained by the team's previous structural modification for the membrane-penetrating peptide Penetratin, the covalent conjugate of peptide 89WP and the anti-retinoblastoma drug Melphalan (Melphalan) was successfully constructed by polypeptide solid phase synthesis technology.
Molecular structure and solubility of 89WP-Mel
Due to the strong hydrophobicity of mephalan, propylene glycol, ethanol, etc. need to be added to the commercial preparation as a co-solvent, and there are certain safety hazards in long-term eye applications, and the hydrophilic polypeptide 89WP can greatly improve its solubility in water after coupling with melphalan, reaching more than 5,000 times that of prototype drugs. As an eye drop, the conjugate does not require the use of multiple organic solvents in the prototype drug formulation to help dissolve, reducing the risk of possible eye irritation.
In a mouse model of retinoblastoma, the researchers compared the administration of mephalan eye drops, intravitreal injection, and 89WP-Mel eye drops and found that 89WP-Mel eye drops achieved comparable anti-intraocular tumor proliferation effects as intravitreal injection of melphalan (including high-dose impact therapy and high-frequency maintenance therapy).
89WP-Mel Eye Drops Tumor Suppressant Effect (Scale, 0.5 mm)
Although experiments have shown that intravitreal injection of melphalan has a similar tumor suppression effect to 89WP-Mel eye drops, the researchers found that mice injected with melphalan had more accidental deaths. Combined with the results of brain immunohistochemical slices, it was confirmed that the cause of death in mice was brain metastasis in intraocular tumors. Further studies showed that compared with the injection group, the proportion of intraocular tumor brain metastases in the eye drop group was lower, and the survival rate was significantly improved compared with the injection group.
Brain metastasis of intraocular tumors (brown area) and brain metastases of mice in various drug delivery groups (scale, 1 mm)
So how is 89WP-Mel distributed in the eyeball? Multi-dimensional in vitro evaluation confirmed that the ability of peptide covalent conjugates to penetrate eye tissue was significantly enhanced compared with free small molecules. Taking the ability of the sclera permeation of the in vivo rabbit eye as an example, the apparent transmittance coefficient of the covalent conjugate is more than 7 times that of the corresponding small molecule. Taking the fluorescent probe as the tracer, the distribution of covalent conjugates in the mouse eye increased significantly, and was mainly distributed in the posterior segment of the eye, and there was less distribution in the cornea of the anterior segment, and the result of combining the covalent conjugates on the sclera permeability of the ex vivo rabbit eye was significantly better than that of the cornea, confirming that it was mainly absorbed through the posterior segment of the scleral pathway to reach the fundus.
Distribution behavior of peptide covalent conjugates on ex vivo rabbit cornea, scleral permeation and post-eye drops.
The results of the evaluation of cell level and in vitro safety show that the covalent conjugate 89WP-Mel has good safety against normal eye cells, and no eye tissue or organ toxicity is seen after long-term eye drops, and there are no side effects such as bone marrow suppression.
In summary, using the peptide covalent coupling strategy, this study for the first time realized the safe and effective treatment of chemotherapy drug eye drops for intraocular tumors, and with the help of the "outward-in" enveloping drug absorption method, eye drops showed unique anti-intraocular tumor metastasis advantages compared with intravitreal injection administration, providing a new strategy for non-invasive treatment for children with retinoblastoma. In addition, the peptide covalent coupling strategy has also been confirmed to promote the posterior ocular delivery of different hydrophilic and hydrophobic small molecules, which is expected to achieve efficient ocular absorption of a variety of ophthalmic small molecule drugs.
Comparison of ocular drug absorption patterns by different routes of administration. Eye drops: absorbed from the outside to the inside, injectable: chase diffusion from the inside out.
The first author of this paper is Jiang Kuan, a postdoctoral fellow at the School of Basic Medicine of Fudan University, and Professor Wei Gang of the School of Pharmacy of Fudan University and Zhan Changyou, a researcher at the School of Basic Medicine, as co-corresponding authors of the article.
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