In this study, we evaluated the antiproliferative activity of the biopolymer p21-ELP1-Bac, a p21-derived peptide delivered via an elastin-like polypeptide (ELP1) carrier and a cell-penetrating peptide (CPP), across three glioblastoma cell lines: U87, GBM43, and GBM6. This evidence concerns the gene ELP1 and glioblastoma.