engleski

Tumor Accumulation and Biodistribution of a Thermally Responsive Cell Cycle Inhibitory Polypeptide in Vivo

Elastin-like Polypeptide (ELP) is a macromolecular carrier for various therapeutic peptides that has the ability to penetrate tumor vasculature which is mediated by a cell-penetrating peptide. ELP is a biopolymer consisting of pentapeptide repeats in the motif Val-Pro-Gly-Xaa-Gly where Xaa is any amino acid except proline. The polymer is soluble at normal physiological temperature but aggregates above 41° C. Peptides without carriers have very short half-lives, so ELP not only allows for longer circulation time, but its thermal properties allow the peptide to accumulate inside the tumor when heated. Bac7-ELP1-p21 is an ELP conjugate that uses Bac7 to penetrate the nucleus and p21 to inhibit the cell cycle at G1/S. This construct can be actively targeted to the tumor site using focused infrared light that heats the tumor to 41-42° C. In this study, tumor accumulation and biodistribution of fluorescently labeled Bac7-ELP1-p21 was monitored in a mouse subcutaneous xenograft model of S2013 pancreatic cancer by whole animal imaging using the IVIS® system. Luciferase transfected S2013 pancreatic cells were used to establish the tumor, allowing monitoring tumor growth by quantifying luciferase signal over a period of time. The animals were intravenously injected with Alexa750 labeled Bac7-ELP1-p21. Animals were imaged for fluorescence signal at 1, 2, 3, 4, 6, 8, 24, 48, and 72h after treatment to monitor the level of protein with respect to time. This allowed for the detection and quantification of the protein level throughout the whole body. Tumor uptake of intravenously administered Bac7-ELP1-p21 was examined in both heated and unheated tumors. Using both luminescence and fluorescence data, protein levels inside the tumor were compared to the whole body. Bac7-ELP1-p21 accumulates 3-fold more inside the heated tumor than the unheated tumor, and it is still present inside the tumor 72h after treatment. Fusing a therapeutic peptide to macromolecular carriers results in its improved pharmacokinetics and accumulation of the peptide preferentially in the tumor tissue due to passive targeting. Furthermore, this passive targeting is further improved due to externally induced hyperthermia. This approach will allow us to use lower concentrations of drug systemically and therefore reduce side effects in normal tissues.

p21; In vivo imaging; Pancreatic cancer

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