Conjugates useful in the treatment of prostate cancer

A conjugate of the formula I:

• wherein:
• oligopeptide is an oligopeptide which is specifically recognized by the free prostate specific antigen (PSA) and is capable of being proteolytically cleaved by the enzymatic activity of the free prostate specific antigen,
• XL is selected from:
• a bond, —C(O)—(CH2)u—W—(CH2)u—O— and —C(O)—(CH2)u—W—(CH2)u—NH
• R is selected from
• R1 and R2 are independently selected from:
• hydrogen, OH, C1-C6 alkyl, C1-C6 alkoxy, C1-C6 aralkyl and aryl;
• R1a is C1-C6-alkyl, hydroxylated C3-C8-cycloalkyl, polyhydroxylated C3-C8-cycloalkyl, hydroxylated aryl, polyhydroxylated aryl or aryl,
• R9 is hydrogen, (C1-C3 alkyl)-CO, or chlorosubstituted (C1-C3 alkyl)-CO;
• W is selected from a branched or straight chain C1-C6-alkyl, cyclopentyl, cyclohexyl, cycloheptyl or bicyclo[2.2.2]octanyl;
• n is 1, 2, 3 or 4;
• p is zero or an integer between 1 and 100;
• q is 0 or 1, provided that if p is zero, q is 1;
• r is 1, 2 or 3;
• t is 3 or 4;
• u is 0, 1, 2 or 3,
• or a pharmaceutically acceptable salt or optical isomer thereof.