Nucleotides for the treatment of cancer

A compound according to Formula I:

• or a pharmaceutically acceptable salt thereof, wherein:
• Base is a nucleobase:
• X is O or S;
• V is hydrogen, halogen or amino;
• Z1 is halogen;
• Z2 is halogen;
• R1 and R2 together with the two oxygen atoms to which they are attached form the ring:
• R8 is C1-10alkylcarbonylthioC1-10alkoxy,
• R9 is C1-10alkyl, C3-10cycloalkyl, aryl or arylC1-6alkyl;
• R10 is C1-10alkyl or COOR9;
• R11 is C1-10alkylcarbonyloxyC1-10alkyl, C3-10cycloalkylcarbonyoxy, aryl, aryloxy, C1-10alkylaryl, arylC1-10alkyl, heteroaryl, heteroarylC1-10alkyl or C1-10alkylheteroaryl;
• Rz is C2-11alkenyl, C2-11alkynyl, C1-10alkoxycarbonylC1-10alkyl, C1-10alkylcarbonylthioC1-10alkyl, C1-10alkyldisulfideC1-6alkyl, aryl or heteroarylC1-10alkyl, wherein alkyl is optionally substituted by one, two or three substituents independently selected from halogen and hydroxy, and heteroaryl is substituted by one or two substituents selected from C1-10 alkyl and nitro;
• and
• W is O or S.