Cancer Chemotherapy and Pharmacology

, Volume 27, Issue 4, pp 315–319 | Cite as

Mechanism of action of psoralens: isobologram analysis reveals that ultraviolet light potentiation of psoralen action is not additive but synergistic

  • Edward J. Yurkow
  • Jeffrey D. Laskin
Original Articles Psoralens, Isobologram Analysis, Synergism, UV


The combination of psoralens and ultraviolet light (UVA, 320–400 nm), referred to as PUVA, inhibits proliferation of a variety of cell types. In the present studies, we used S-180 cells to investigate the mechanism underlying the antiproliferative actions of PUVA. We found that inhibition of growth of S-180 cells by PUVA was dependent on the concentration of psoralen as well as the dose of UVA light. Neither the psoralens nor UVA light by themselves inhibited cell growth. Several clinically important psoralen analogs inhibited cell growth. The potent phototoxin 4,5′,8-trimethylpsoralen was the most active psoralen analog tested, followed by 5-methoxypsoralen and 8-methoxypsoralen. The angular furocoumarin, 5-methylangelicin, was the least active inhibitor of growth. Multivariate (isobologram) analysis of the growth-inhibition curves revealed that combinations of psoralens and UVA light were not simply additive but synergistic. Similar results were observed when inhibition of DNA synthesis was used as an endpoint for the biological effects of PUVA. These studies are the first to demonstrate that psoralens and UVA light act synergistically. Our results suggest that the synergism between the psoralens and UVA light may be an important property of PUVA that contributes to its therapeutic efficacy in proliferative diseases.


Cell Growth Cancer Research Active Inhibitor Biological Effect Therapeutic Efficacy 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.









5-methylangelicin; UVA, ultraviolet light of 320–400 nm wavelength


psoralens used in combination with UVA light


Dulbecco's Modified Eagle's Medium


phosphate-buffered saline


N-2-hydroxyethylpiperazine-N′-2-ethane-sulfonic acid


level of PUVA treatment that inhibits measurable cellular parameters by 50%




trichloroacetic acid


hypoxanthine-guanine phosphoribosyltransferase


Chinese hamster ovary


ethylenediaminetetraacetic acid


epidermal growth factor


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Copyright information

© Springer-Verlag 1991

Authors and Affiliations

  • Edward J. Yurkow
    • 1
  • Jeffrey D. Laskin
    • 1
  1. 1.Department of Environmental and Community MedicineUniversity of Medicine and Dentistry of New Jersey, UMDNJ-Robert Wood Johnson Medical SchoolPiscatawayUSA

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