Distinctive profile of antiproliferative activity and interaction with doxorubicin of a new indole alkaloid P1 from <i>Petasites hybridus</i> in molecularly diverse breast cancer cell lines.

Abstract

e12581 Background: Despite the efficacy of anthracyclines in breast cancer (BC) treatment, their use is limited by cardiotoxicity and resistance mechanisms. Secondary plant metabolites offer a reservoir for novel cytostatics. We investigated the in vitro activity of a novel indole alkaloid (P1), isolated from Petasites hybridus, and its interaction with doxorubicin (DOX) across clinically relevant BC subtypes. Methods: Cytotoxicity was evaluated using the MTT assay (48h exposure) in three human BC cell lines: MDA-MB-453 (HER2+, ER-/PR-), BT-474 (Luminal B/HER2+), and BT-20 (Triple-Negative BC), compared to primary normal skin fibroblasts as a non-malignant control. Half-maximal inhibitory concentrations (IC50) were determined. Drug interaction landscapes were analyzed using the Zero Interaction Potency (ZIP) model via SynergyFinderPlus software. Interaction was classified based on Synergy Scores (SS): &gt;10 (synergy), -10 to 10 (additive), &lt;-10 (antagonism). Results: P1 exerted dose-dependent antiproliferative effects in all BC lines. IC50 values were 31.74±3.8 µM for MDA-MB-453, 39.70±2.4 µM for BT-20, and 49.23±5.2 µM for BT-474. Notably, P1 demonstrated selective toxicity towards cancer cells; viability of all BC lines was significantly lower than that of normal fibroblasts at P1 concentrations &gt;22 µM (p&lt;0.05), indicating a favorable therapeutic window. DOX showed expected high potency (IC50 0.51–10.4 µM) but exhibited significant antagonism when combined with P1 in HER2+ cell lines: mean SS was -14.98 for BT-474 and -8.23 for MDA-MB-453 (reaching &lt;-17 at high doses). Conversely, in the TNBC line BT-20, the combination was additive (mean SS -2.66), suggesting no interference with DOX efficacy. Conclusions: The novel indole alkaloid P1 demonstrates selective cytostatic activity against breast cancer cells sparing normal fibroblasts. The drug interaction profile is highly subtype-dependent: while P1 antagonizes DOX in HER2+ models, likely due to cell cycle interference, it shows additive potential in triple-negative breast cancer. These findings position P1 as a promising lead compound for TNBC therapy requiring further mechanistic elucidation. Comparative IC50 and interaction scores. Cell Line Molecular Subtype P1 IC50 (µM) Interaction with Doxorubicin (Mean Synergy Score) Interpretation MDA-MB-453 HER2+ 31.74 ± 3.8 -8.23 Antagonism BT-474 Luminal B / HER2+ 49.23 ± 5.2 -14.98 Antagonism BT-20 Triple-Negative 39.70 ± 2.4 -2.66 Additive