# Phaseolus acutifolius Recombinant Lectin Exerts Differential Proapoptotic Activity on EGFR+ and EGFR− Colon Cancer Cells and Provokes T Cell-Assisted Antitumor Responses in Mice

## TL;DR

A plant-based protein from Phaseolus acutifolius kills colon cancer cells and boosts immune responses in mice, especially when T cells are present.

## Contribution

Demonstrates that rTBL-1 induces apoptosis in colon cancer cells and triggers T cell-assisted antitumor effects in mice.

## Key findings

- rTBL-1 shows cytotoxic effects on both EGFR+ and EGFR− colon cancer cells with similar LC50 values.
- rTBL-1 inhibits tumor growth in immunocompetent mice but not in immunodeficient mice, indicating T cell involvement.
- Apoptosis is induced in both cell types, with slower and longer-lasting effects in EGFR+ cells.

## Abstract

Background: rTBL-1, a recombinant lectin from Phaseolus acutifolius, exhibit proapoptotic activity on colon cancer cells and inhibitory properties on colon tumorigenesis in vivo. Apoptosis has been associated with a phospho-EGFR/phospho-p38/phospho-p53 mechanistic axis. Immunogenicity data have been observed in treated animals, but its possible involvement in the antitumor response remained unexplored. Objective: We investigated whether the cytotoxic activity of rTBL-1 depends on EGFR and its capacity to produce antitumor responses on syngeneic colon cancer in mice, with and without T cells, in order to explore its possible involvement in the process. Results:
rTBL-1 exhibited cytotoxic effects in a concentration-dependent manner in both EGFR+ (MC-38) and EGFR− (CT-26) colon cancer cells with LC50 values of 23.50 and 30.01 µg/mL, respectively (p = 0.063). Apoptotic effects were slower and longer-lasting in MC-38 than in CT-26 cells. Significant increases in caspase-3 proteolytic activation and PARP1 cleavage were detected in both cell types, despite PARP1 rheostasis in CT-26 cells. Intralesional treatment with rTBL-1 inhibited the growth of established tumors in immunocompetent BALB/c mice in 27.81% (p = 0.0008) with a benefit in survival (p = 0.022), but not in immunodeficient BALB/c nude mice. Conclusions:
rTBL-1 induces apoptosis in colon cancer cells by EGFR independent mechanisms, although its presence could be related to deeper responses. Unresponsiveness in nude mice indicated that rTBL-1 antitumor effect is the synergistic result of apoptosis induction and T cell-mediated cytotoxicity in the tumor. Future studies will focus on the immunogenic effects triggered by the antitumor activity of rTBL-1 in colon cancer.