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Table 1 Relationship of porphyrin phototoxicity and MBR affinity

From: Photodynamic Tumor Therapy: Mitochondrial Benzodiazepine Receptors as a Therapeutic Target

Porphyrin

MBR K i (nM)

D37 (nM)

“Neutral” porphyrin

14

20

Protoporphyrin IX

20

60

Mesoporphyrin IX

40

50

Deuteroporphyrin IX

50

60

Fe-Protoporphyrin IX (heme)

50

>32,000

N-methyl mesoporphyrin IX

90

350

N-methyl protoporphyrin IX

95

400

2,4(4,2)Hydroxyethylvinyl-deuteroporphyrin IX

100

125

Photofrin II

100

153

Hematoporphyrin IX

350

1,000

Zn protoporphyrin IX

375

800

Chlorine E6

500

1,000

Diaspartylprotoporphyrin IX

545

480

2-vinyl,4-hydroxymethyl-deuteroporphyrin IX

900

1650

Ditaurylmesoporphyrin IX

1,000

350

Sn-protoporphyrin IX

2,000

12,000

Coproporphyrin in

2,500

> 10,000

Biliverdin

2,500

>2,500

Coprotoporphyrin IX

5,000

8,000

Diglutamatylmesoporphyrin IX

7,600

2,400

Hexaporphyrin

24,000

> 10,000

Coproporphyrin I

100,000

> 10,000

Pentaporphyrin

> 100,000

> 10,000

Heptaporphyrin

> 100,000

> 10,000

Bilirubin

> 100,000

>2,500

Deuteroporphyrin IX disulfonate

> 100,000

> 10,000

Deuteroporphyrin IX BB Glycol

> 100,000

> 10,000

  1. MBR Ki values for porphyrins and analogs were determined by displacement of [3H] PK11195 binding to rat kidney mitochondria as described. Phototoxicity studies using V79 Chinese hamster lung cells were performed as described in Materials and Methods. D37 values represent doses that reduce survival to 37% of control. values are the inhibitory constants of drugs for MBR. As FeProtoporphyrin IX (heme), a potent MBR ligand is not a photosensitive molecule, it does not cause phototoxicity. With the omission of heme, the D37 and MBR Ki values correlate with a coefficient of 0.827 (p < 0.001). Experiments were performed three times in duplicate and results shown are mean values.