Adding Histidine Tags to Cancer-Killing Peptides Helps Them Enter Tumor Cells | Research

The takeaway

A simple histidine tag modification improved the ability of pro-apoptotic peptides to penetrate and kill lung cancer cells in laboratory tests.

IC50 of 33.3 µM
His-tagged KLAK peptide inhibited lung cancer cell growth at this concentration, with confirmed apoptosis induction and improved cellular uptake

What the researchers found

Adding a histidine tag (His-tag) to pro-apoptotic peptides improved their ability to enter cancer cells in laboratory tests. The KLAK-H peptide showed the strongest anticancer effect against A-549 lung cancer cells, with an IC50 of 33.3 µM, while the EGFR-targeted version NRPD-KLAK-H had an IC50 of 40.9 µM.

Both KLAK-H and NRPD-KLAK-H successfully entered cancer cells (confirmed by immunofluorescence) and induced apoptosis (confirmed by TUNEL assays). However, the CTMP4-based peptides showed poor cellular uptake regardless of targeting modifications.

Interestingly, the EGFR-targeting component (NRPD) did not enhance the anticancer effect as expected — the simpler His-tagged KLAK peptide actually performed slightly better than the targeted version. This suggests that short poly-histidine sequences alone can meaningfully improve cellular uptake of pro-apoptotic peptides.

Why it matters

Getting cancer-killing peptides inside tumor cells is one of the biggest challenges in peptide drug development. This study shows that a simple chemical modification — adding a histidine tag — can improve cellular uptake of pro-apoptotic peptides without complex targeting systems. While the EGFR-targeting strategy didn't work as hoped, the His-tag finding offers a practical approach to enhancing peptide delivery for cancer therapy.

The numbers in context

KLAK-H IC50: 33.3 µM · NRPD-KLAK-H IC50: 40.9 µM · Tested on A-549 lung cancer cells · His-tag improved internalization · CTMP4 variants: poor uptake

How the study worked

Researchers designed pro-apoptotic peptides with His-tag modifications and EGFR-targeting sequences, then tested them against A-549 non-small cell lung cancer cells. Cell viability was measured using MTT assays, apoptosis was confirmed with TUNEL assays, and cellular uptake was visualized with immunofluorescence microscopy.

Who was studied

In vitro study using A-549 non-small cell lung cancer cell line — no human or animal subjects

What this study cannot tell us

This is an in vitro study using a single cancer cell line (A-549). The IC50 values (33–41 µM) are relatively high for drug candidates, which may limit clinical applicability. No animal testing was performed. The EGFR-targeting strategy did not improve efficacy over the non-targeted version, raising questions about the design approach. Selectivity for cancer cells over normal cells was not thoroughly assessed.

How to read the evidence

This is an early-stage in vitro study testing peptide modifications against a single cancer cell line. While the findings are interesting, they represent proof-of-concept work that requires extensive further validation in animal models and additional cell lines.

When this study was published

Published in 2025, this is a very recent contribution to the rapidly growing field of peptide-based cancer therapeutics and drug delivery modification strategies.

The bigger picture

Peptide-based cancer therapies are gaining momentum, but delivering peptides into cells remains a major bottleneck. This study adds to the evidence that simple chemical modifications can significantly improve peptide uptake. The His-tag approach is inexpensive and easy to implement, making it a practical tool for peptide drug development — even if more sophisticated targeting strategies require further refinement.

Questions still open

Could His-tagged KLAK peptides show selectivity for cancer cells over healthy cells in more comprehensive testing?
Why did the EGFR-targeting modification not improve anticancer effects despite EGFR being overexpressed on A-549 cells?
Would His-tag modification improve cellular uptake of other classes of therapeutic peptides beyond pro-apoptotic sequences?

Common questions

What is a His-tag and why does it help peptides enter cells?

A His-tag is a short string of histidine amino acids added to a peptide. Histidine has a positive charge at the slightly acidic pH found near many cell surfaces, which helps the peptide interact with and cross the negatively charged cell membrane. It's a simple modification commonly used in laboratory research that appears to improve how well therapeutic peptides can get inside cells.

Could this lead to a new cancer treatment?

It's very early — this was a lab study on cells in a dish. The finding that a simple His-tag improves peptide uptake is promising, but the peptides would need to be tested in animals, optimized for stability and selectivity, and eventually tested in human clinical trials. The IC50 values are also relatively high, meaning the peptides would need to be made more potent for practical use.

Read the original research

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

Apoptosis : an international journal on programmed cell death, 30(11-12), 3105-3114

View on PubMed ↗Publisher’s paper ↗

Citation

González-Cruz, Aldo O; Pérez-Trujillo, José Juan; Balderas-Rentería, Isaías; Villa-Cedillo, Sheila Adela; De-León-Covarrubias, Ulises Edgardo; Arredondo-Espinoza, Eder. (2025). His-tagged pro-apoptotic peptides: enhancing cell internalization and anticancer effect in vitro.. Apoptosis : an international journal on programmed cell death, 30(11-12), 3105-3114. https://doi.org/10.1007/s10495-025-02180-3