A naphthalenesulfonic acid or quinolinesulfonic acid of formula (I), wherein A is N or a CR8 formula group, where R8 is H, OH, NR10R11, independently from one another, where R10 and R11 represent H or C1-C6 alkyl or a group of formula NH—CO—R12, where R12 is C1-C6 alkyl or C6-C10 aryl; R1 and R2 represent H or SO3R9, independently from one another, where R9 is H, ammonium or a cation of an alkali or alkaline-earth metal; R3 is H or OH; and R4, R5, R6 and R7 represent H, an NR10R11 or NH—CO—R12 group, independently from one another; on the condition that (i) at least one of R1 or R2 is SO3R9, and (ii) at least one of R4, R5, R6 or R7 is an NR10R11 or NH—CO—R12 group, or their pharmaceutically acceptable salts; and a pharmaceutically acceptable excipient.