Alkylating benzamides with melanoma cytotoxicity: role of melanin, tyrosinase, intracellular pH and DNA interaction.
N-(2-Dialkylaminoethyl)benzamides have been shown to selectively accumulate in melanoma metastases with high uptake capacity. Therefore, this class of compound has previously been evaluated as a transporter for cytostatic drugs. It has been demonstrated that this significant targeting effect improves the cytotoxicity against melanoma cells. Although these agents are not accumulated by non-melanoma cells, they have been found to be toxic. In order to identify mechanistic reasons for this effect, we investigated the DNA and melanin binding affinities of a selection of four benzamide-drug conjugates, together with their parental cytostatics. An investigation of the influence of the melanin content on the cytotoxicity of these substances in B16 melanoma and Morris hepatoma (MH3924A) cells was performed, together with their influence on melanosomal pH and tyrosinase activity. The suppression of melanin formation with phenylisothiourea and the saturation of melanin binding sites with chloroquine were also investigated. These experiments demonstrated high DNA binding and low melanin affinity, in accordance with the toxicity against tumour cells. Melanin has a concentration-dependent scavenging effect, thereby reducing cytotoxicity. These compounds lead to an increase in the acidic pH of melanosomes, resulting in an increase in tyrosinase activity. The consequence of this reaction chain is an amplification of the scavenging effect for the benzamide-drug conjugates. These effects may be considered as limiting factors for the targeting characteristics of this class of compound, necessitating further modifications to the carrier system.
Wolf
Markus
M
Department of Radiopharmaceutical Chemistry, German Cancer Research Center Heidelberg, Germany.
Bauder-Wüst
Ulrike
U
Haberkorn
Uwe
U
Mier
Walter
W
Eisenhut
Michael
M
D000818:Animals; D018906:Antineoplastic Agents, Alkylating / Q000493:pharmacokinetics / Q000494:pharmacology*; D001549:Benzamides / Q000493:pharmacokinetics / Q000494:pharmacology*; D002470:Cell Survival / Q000187:drug effects; D002699:Chlorambucil / Q000008:administration & dosage / Q000493:pharmacokinetics; D004247:DNA / Q000378:metabolism*; D004337:Drug Carriers; D004789:Enzyme Activation; D008114:Liver Neoplasms, Experimental / Q000188:drug therapy / Q000201:enzymology / Q000378:metabolism; D008543:Melanins / Q000378:metabolism*; D008546:Melanoma, Experimental / Q000188:drug therapy* / Q000201:enzymology / Q000378:metabolism*; D051379:Mice; D014442:Monophenol Monooxygenase / Q000378:metabolism*
D018906:Antineoplastic Agents, Alkylating; D001549:Benzamides; D004337:Drug Carriers; D008543:Melanins; D002699:Chlorambucil; D004247:DNA; D014442:Monophenol Monooxygenase