His-tagged pro-apoptotic peptides: enhancing cell internalization and anticancer effect in vitro.

Epidermal growth factor receptor (EGFR) overexpression is commonly found in various solid tumors, including non-small cell lung cancer, where it is associated with poor prognosis and resistance to treatment. Despite the availability of EGFR-targeted therapies, overcoming drug resistance remains a challenge. Tumor-homing cell-penetrating peptides can selectively target cancer cells and improve drug delivery. In this study, we evaluated the anticancer potential of EGFR-targeted pro-apoptotic peptides, specifically NRPD-KLAK-H and NRPD-CTMP4-H, designed to enhance internalization and overcome drug resistance in EGFR-positive cancers, and compared their effects with those of the free His-tagged peptides NRPD-H, KLAK-H, and CTMP4-H. MTT assays showed that KLAK-H and NRPD-KLAK-H exhibited the strongest anticancer effects, significantly inhibiting cell growth in A-549 cell line, with IC₅₀ values of 33.3 µM and 40.9 µM, respectively. TUNEL assays suggested that KLAK-H and NRPD-KLAK-H induced apoptosis in the tested cell lines. Immunofluorescence revealed successful internalization of KLAK-H/NRPD-KLAK-H, but poor uptake of CTMP4-H/NRPD-CTMP4-H. The His-tag modification improved peptide internalization, suggesting that short poly-histidine sequences can enhance cellular uptake of pro-apoptotic KLAK-derived peptides, particularly in cancer cells. Although the proposed EGFR-targeted proapoptotic peptides did not show the expected effect, our findings indicate that His-tagged pro-apoptotic peptides, especially KLAK-H, hold promise as potential cancer treatments.