Slow-release conjugates of sn-38

A conjugate of formula (I)

• wherein
• PEG is linear or branched and, when q is 2-8, multi-armed, polyethylene glycol;
• X is O, NH, (CH2)m, OC(═O)(CH2)m, or NHC(═O)(CH2)m wherein m=1-6;
• L is (CH2)r or (CH2CH2O)p(CH2)r, wherein r=1-10 and p=1-10;
• R1 is CN or SO2NR22, wherein each R2 is independently alkyl, aryl, heteroaryl, alkylalkenyl, alkylaryl, or alkylheteroaryl, each optionally substituted, or two R2 taken together can form a ring;
• Y is COR3 or SO2R3, wherein R3═OH, alkoxy, or NR42, wherein each R4 is independently alkyl, substituted alkyl, or two R4 taken together can form a ring;
• and
• q is 1-8.