X₁ and X₂ represent, independently of each other, H, a halogen atom, a (C₁-C₆)alkoxy, an optionally substituted aryloxy, or —O—(CH₂CH₂O)_rH, provided that X₁ and X₂ do not represent H at the same time;

L₁ represents a group of formula L₁′-(CO—Z′)_z′ with L₁′ being —(CH₂)_n—, —(CH₂CH₂O)_m—CH₂—CH₂—, arylene, heteroarylene, cycloalkanediyl, —(CH₂)_n-arylene-, —(CH₂)_n-heteroarylene-, —(CH₂)_n-cycloalkanediyl-, -arylene-(CH₂)_p—, -heteroarylene-(CH₂)_p—, -cycloalkanediyl-(CH₂)_p—, —(CH₂)_n-arylene-(CH₂)_p—, —(CH₂)_n-heteroarylene-(CH₂)_p—, —(CH₂)_n-cycloalkanediyl-(CH₂)_p—, —(CH₂CH₂O)_m—CH₂—CH₂-arylene-(CH₂)_p—, —(CH₂CH₂O)_m—CH₂—CH₂-heteroarylene-(CH₂)_p—, —(CH₂CH₂O)_m—CH₂—CH₂-cycloalkanediyl-(CH₂)_p—, —(CH₂)_n-arylene-CH₂—CH₂—(OCH₂CH₂)_m—, —(CH₂)_n-heteroarylene-CH₂—CH₂—(OCH₂CH₂)_m—, or —(CH₂)_n-cycloalkanediyl-CH₂—CH₂—(OCH₂CH₂)_m—;

each W independently represents an amino acid unit;

Y is PAB-CO—(Z)_z—, with PAB being

Z is —NR₄—(CH₂)_u—NR₅—, —NR₄—(CH₂)_u—NR₅—CO—, —NR₄—(CH₂)_u—NR₅—CO—(CH₂)_v—, or —NR₄—(CH₂)_u—NR₅—CO—(CH₂)_v—CO—, the NR₄ group being linked to the CO group of PAB-CO;

Z′ is —NR₄—(CH₂)_u—NR₅— or —NR₄—(CH₂)_u—NR₅—CO—(CH₂)_v—, the NR₄ group being linked to the CO group of CO—Z′;

R₄ and R₅ are independently H or a (C₁-C₆)alkyl group;

Q is a residue of an auristatin, an anthracycline, camptothecin, SN-38, a tubulysin, a calicheamicin, a maytansinoid, a duocarmycin, an amanitine, a pyrrolobenzodiazepine, or an activator of immune check point;

c is 0 or 1;

m is an integer from 1 to 15;

n is an integer from 1 to 6;

p is an integer from 1 to 6;

q is 0, 1 or 2;

r is an integer from 1 to 24;

u is an integer from 1 to 6;

v is an integer from 1 to 6;

w is an integer from 0 to 5;

y is 0 or 1;

z is 0 or 1; and

z′ is 0 or 1.