Phosphonium salts exhibiting selective anti-carcinoma activity in vitro
D C Rideout1, T Calogeropoulou, J S Jaworski
1Department of Molecular Biology, Scripps Clinic and Research Foundation, La Jolla, CA 92037.
Abstract:
Tetraphenylphosphonium cation (TPP) and other phosphonium cations selectively inhibited the growth in vitro of human pancreatic carcinoma-derived cells (PaCa-2) and Ehrlich Lettre Ascites cells (ELA) when compared with untransformed monkey kidney epithelial cells (CV-1). In contrast, neither cisplatin nor cytosine arabinoside showed significant selectivity using these lines. Evidence is presented to support the conclusion that the carcinoma-selective antiproliferative activity of phosphonium salts is due to selective accumulation caused by the abnormally high membrane potentials in carcinoma cells. Inhibition of TPP uptake into PaCa-2 and ELA cells by potassium and (for PaCa-2) valinomycin demonstrates that higher membrane potentials account for the carcinoma-selective uptake and cytostatic selectivity of the cation. For TPP chloride and 16 other phosphonium chlorides with a variety of structures, selective inhibition of PaCa-2 growth relative to CV-1 was optimal for the eight falling in a narrow range of octanol/water partition coefficients (between 0.013 and 0.24). A similar optimal selectivity range was observed for ELA cells relative to CV-1. The relationship between partition coefficients and cytostatic selectivity suggests that the rates of diffusion across cytoplasmic and mitochondrial membranes are key factors in the structure/anticarcinoma selectivity relationship for delocalized phosphonium salts in vitro. The relationship could prove useful for the design of other carcinoma-selective delocalized cations.
Insights
Tetraphenylphosphonium (TPP) and related phosphonium cations selectively inhibit cancer cell growth by accumulating in cells with high membrane potentials. This selective uptake mechanism offers potential for designing new anticancer agents.
Area of Science:
- Oncology
- Biochemistry
- Pharmacology
Background:
- Carcinoma cells exhibit abnormally high membrane potentials compared to normal cells.
- Selective accumulation of compounds in cancer cells is a key strategy for targeted therapy.
Purpose of the Study:
- To investigate the selective antiproliferative activity of tetraphenylphosphonium (TPP) cation and other phosphonium salts against carcinoma cells.
- To elucidate the mechanism underlying the selective accumulation and cytostatic effects of phosphonium salts in cancer cells.
Main Methods:
- In vitro growth inhibition assays using human pancreatic carcinoma (PaCa-2) and Ehrlich Lettre Ascites (ELA) cells compared to monkey kidney epithelial (CV-1) cells.
- Assessment of TPP uptake inhibition using potassium and valinomycin.
- Structure-activity relationship analysis based on octanol/water partition coefficients for various phosphonium salts.
Main Results:
- TPP and other phosphonium cations demonstrated selective growth inhibition of PaCa-2 and ELA cells over CV-1 cells.
- Selective accumulation in carcinoma cells, driven by high membrane potentials, was confirmed as the mechanism of action.
- Optimal cytostatic selectivity was observed for phosphonium salts within a specific range of octanol/water partition coefficients (0.013–0.24).
Conclusions:
- Phosphonium cations possess inherent carcinoma-selective antiproliferative activity.
- The high membrane potential of carcinoma cells facilitates selective cation accumulation, leading to cytostatic effects.
- Partition coefficients are critical for optimizing the structure and selectivity of phosphonium-based anticancer agents.
