Cancer is the second leading cause of death worldwide. Triple-negative breast cancer (TNBC) and glioblastoma (GBM) are among the most aggressive malignancies, characterized by poor prognosis and limited therapeutic options. Overexpression of the epidermal growth factor receptor (EGFR) is frequently observed in both tumors, exceeding 50% in TNBC and representing a common alteration in primary GBM. In this context, EGFR-targeting peptides, such as LARLLT, have emerged as promising tools in precision oncology due to their specificity, affinity, low synthesis cost, and reduced toxicity. So, LARLLT is a potential bioactive EGFR-targeting agent.

To investigate the in vitro effects of the anti-EGFR peptide LARLLT on TNBC (MDA-MB-231) and GBM (U-87 MG) cell lines.

The LARLLT peptide was obtained by solid-phase synthesis employing the Fmoc/tBu approach, followed by purification and characterization using RP-HPLC and mass spectrometry. MDA-MB-231 and U-87 MG cells were maintained under standard culture conditions using RPMI-1640 and DMEM media, respectively, both supplemented with 10% fetal bovine serum (37°C; 5% CO2). Cell proliferation was evaluated by growth curve assays. Cells were seeded in 6-well plates (5 × 104 cells/well) and incubated with LARLLT (116.6 µM). Viable cells were counted using a Neubauer chamber on days 1, 3, 5, and 7, comparing with untreated control (CT). Cell viability was assessed by the MTT assay in MDA-MB-231 cells, which were seeded in 96-well plates (5 × 10³ cells/well) and incubated with LARLLT (11.66 µM). Absorbance readings were obtained on days 1, 5, and 7, and viability was expressed as a percentage relative to CT. Data are presented as mean ± SD. Statistical analyses were performed using Student’s t-test or ANOVA followed by Tukey’s test (significance set at p<0.05).

After synthesis and purification, the LARLLT peptide was obtained in pure form, with compatible molar mass (686 g/mol), showing a single and well-defined chromatographic peak. Growth curve analysis indicated that treatment with the anti-EGFR peptide did not significantly affect cell proliferation in either TNBC or GBM cells under the evaluated conditions. On day 7, cell counts were comparable between treated and CT groups: (i) MDA-MB-231: treated = (3.9 ± 0.2) × 105 versus CT = (4.1 ± 0.1) × 105 [p = 0.0776; n = 6]; (ii) U-87 MG: treated = (2.4 ± 0.3) × 105 versus CT = (2.4 ± 0.4) × 105 [p = 0.7243; n = 6]. Consistently, the MTT assay revealed no significant differences in metabolic activity in MDA-MB-231 cells relative to CT, with viabilities of 109.7 ± 12.3% (day 1), 105.0 ± 16.3% (day 5), and 104.8 ± 12.2% (day 7), showing no statistically significant variation over time [p = 0.6874; n = 8]. MTT assays for the U-87 MG cell line are currently ongoing. The absence of biological effects may be explained by the low peptide concentration used, particularly in the MTT assay, which may be insufficient to elicit measurable modulation of downstream EGFR signaling.

The anti-EGFR peptide LARLLT did not affect cell proliferation or viability in TNBC or GBM cells, indicating that the peptide does not exert cytostatic or cytotoxic effects under the evaluated conditions. These results support its further evaluation at low concentrations in radiolabeling protocols, for applications focused on molecular imaging rather than direct therapeutic intervention.