Brachytherapy Using Elastin-Like Polypeptides with (131)I Inhibit Tumor Growth in Rabbits with VX2 Liver Tumor

Engineered elastin-like polypeptides: An efficient platform for enhanced cancer treatment

Drug delivery systems (DDSs) have recently gained widespread attention for improving drug loading and delivery efficiency in treating many cancers. Elastin-like polypeptides (ELPs) are synthetic peptides derived from a precursor of elastin (tropoelastin), reserving similar structural and physicochemical properties. ELPs have gained a variety of applications in tissue engineering and cancer therapy due to their excellent biocompatibility, complete degradability, temperature-responsive property, controllable sequence and length, and precisely tuned structure and function. ELPs-based drug delivery systems can improve the pharmacokinetics and biodistribution of therapeutic reagents, leading to enhanced antitumor efficacy. In this review, we summarize the recent application of ELPs in cancer treatment, focusing on the delivery of functional peptides, therapeutic proteins, small molecule drugs, and photosensitizers.

Assessment of the hepatic tumor extracellular matrix using elastin-specific molecular magnetic resonance imaging in an experimental rabbit cancer model

To investigate the imaging performance of an elastin-specific molecular magnetic resonance imaging (MRI) probe with respect to the extracellular matrix (ECM) in an experimental hepatic cancer model. Twelve rabbits with hepatic VX2 tumors were examined using 3 T MRI 14, 21, and 28 days after tumor implantation for two subsequent days (gadobutrol, day 1; elastin-specific probe, day 2). The relative enhancement (RE) of segmented tumor regions (central and margin) and the peritumoral matrix was calculated using pre-contrast and delayed-phase T1w sequences. MRI measurements were correlated to histopathology and element-specific and spatially resolved mass spectrometry (MS). Mixed-model analysis was performed to assess the performance of the elastin-specific probe. In comparison to gadobutrol, the elastin probe showed significantly stronger RE, which was pronounced in the tumor margin (day 14–28: P ≤ 0.007). In addition, the elastin probe was superior in discriminating between tumor regions (χ²(4) = 65.87; P < 0.001). MRI-based measurements of the elastin probe significantly correlated with the ex vivo elastinstain (R = .84; P <0 .001) and absolute gadolinium concentrations (ICP-MS: R = .73, P <0 .01). LA-ICP-MS imaging confirmed the colocalization of the elastin-specific probe with elastic fibers. Elastin-specific molecular MRI is superior to non-specific gadolinium-based contrast agents in imaging the ECM of hepatic tumors and the peritumoral tissue.

Brachytherapy using elastin-like polypeptide with different concentrations of 131I for treatment of VX2 liver tumor in rabbits

BACKGROUND

Brachytherapy is a targeted radiation therapy for cancer. The elastin-like peptide (ELP) is a genetically engineered peptide that has unique advantages such as self-assembly, temperature responsiveness, and non-immunogenicity, which make it possible to become the carrier of the radionuclide ¹³¹I.

AIM

To evaluate the effectiveness of brachytherapy in a rabbit model of VX2 liver tumor using elastin-like polypeptide as a radionuclide ¹³¹I carrier and compare the effectiveness of ¹³¹I-ELP at different radioactive concentrations to provide evidence for its clinical application.

METHODS

ELP as a carrier was labeled with ¹³¹I by the iodogen method, and different concentrations of ¹³¹I-ELP were prepared. Under ultrasound guidance, different concentrations of ¹³¹I-ELP and ELP solution were randomly injected into 15 rabbits with VX2 liver tumor for brachytherapy and blank control observation. The rabbits were divided into the following groups: high-dose radiation group (injection with 100 mCi/mL ¹³¹I-ELP; group H, n = 5); low-dose radiation group (injection with 50 mCi/mL ¹³¹I-ELP; group L, n = 5); and blank control group (injection with ELP solution; group C, n = 5). Periodic biochemical and sonographic examinations were performed to assess the therapeutic efficacy after treatment. Single-photon emission computed tomography/computed tomography (SPECT/CT) was additionally performed in the treatment groups. The natural survival time of animals in the three groups was determined. In addition, histopathological examination was performed.

RESULTS

The survival time of animals was the longest in group H (61.4 d ± 10.50 d) and the shortest (39.2 d ± 5.63 d) in group C. The survival time of animals in group L was 52.6 d ± 8.85 d. Significant differences were observed in the survival time among the three groups (P < 0.05). At 7 and 14 d after treatment, SPECT/CT showed that ¹³¹I-ELP was continuously localized in liver tumors in groups H and L. The tumor growth rates in groups H and L were significantly lower than that in group C (P < 0.05). Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) at 14 d after treatment in groups H and L were significantly lower than those in group C (P < 0.05). At 7 d after treatment, ALT level in group L was significantly lower than that in group H (P < 0.05). At 14 d after treatment, AST value in group L was significantly lower than that in group H (P < 0.05), suggesting that group L is better than group H with regard to ameliorating ALT and AST levels (P < 0.05). There were no significant differences in Hb or RBC levels between the three groups at 7 and 14 d after treatment. Histopathological examination showed that normal tissues around the tumor in group H were destroyed; proliferation of cord-like fibers, expansion of hepatic sinus, and dilatation of small bile ducts in the portal area were observed. In group L, no radioactive damage was observed in normal liver tissues around the tumor.

CONCLUSION

¹³¹I-ELP brachytherapy has curative effects in inhibiting tumor growth. ¹³¹I-ELP at a radiation dose of 100 mCi/mL inhibits tumor growth better than ¹³¹I-ELP at a radiation dose of 50 mCi/mL; however, the higher dose causes greater radiation damage to normal liver tissues around the tumor.