Vitamin-mitomycin conjugates

1. A conjugate of the general formula

B-L-X

wherein the group B is folate, or an analog or a derivative thereof, that binds to a surface accessible folate receptor that is uniquely expressed, overexpressed, or preferentially expressed by a population of pathogenic cells;

wherein the group L comprises a cleavable linker and wherein the cleavable linker is a disulfide group; and

wherein the group X comprises a mitomycin compound, or an analog or a derivative thereof.

2. The conjugate of claim 1 wherein the linker is cleaved under reducing conditions.

3. The conjugate of claim 1 wherein the mitomycin is selected from the group consisting of mitomycin A, mitomycin B, mitomycin C, mitomycin D, mitomycin E, mitomycin F, and porfiromycin.

4. A method of selectively eliminating a population of pathogenic cells in a host animal harboring said population of cells wherein the members of said cell population have a surface accessible binding site for folate, or an analog or derivative thereof, said method comprising the steps of:

administering to said host a conjugate of the general formula

B-L-X

wherein the group B is folate, or an analog or a derivative thereof, that binds to a surface accessible folate receptor that is uniquely expressed, overexpressed, or preferentially expressed by the population of pathogenic cells;

wherein the group L comprises a cleavable linker and wherein the cleavable linker is a disulfide group; and

wherein the group X comprises a mitomycin compound, or an analog or a derivative thereof; and

selectively eliminating said population of pathogenic cells.

5. The method of claim 4 wherein the linker is cleaved under reducing conditions.

6. The method of claim 4 wherein the mitomycin is selected from the group consisting of mitomycin A, mitomycin B, mitomycin C, mitomycin D, mitomycin E, mitomycin F, and porfiromycin.

7. The method of claim 4 wherein the population of pathogenic cells is a cancer cell population.

8. The method of claim 4 further comprising the step of administering to said host a therapeutic factor selected from the group consisting of a cell killing agent, a tumor penetration enhancer, a chemotherapeutic agent, a cytotoxic immune cell, and a compound capable of stimulating an endogenous immune response.

9. The method of claim 8 wherein the therapeutic factor is a chemotherapeutic agent.

10. The method of claim 9 wherein the chemotherapeutic agent is paclitaxel.

11. A pharmaceutical composition comprising a conjugate of the general formula

B-L-X

wherein the group B is folate, or an analog or a derivative thereof, that binds to a surface accessible folate receptor that is uniquely expressed, overexpressed, or preferentially expressed by a population of pathogenic cells;

wherein the group L comprises a cleavable linker and wherein the cleavable linker is a disulfide group; and

wherein the group X comprises a mitomycin compound, or an analog or a derivative thereof; and

a pharmaceutically acceptable carrier therefor.

12. The composition of claim 11 wherein the linker is cleaved under reducing conditions.

13. The composition of claim 11 wherein the mitomycin is selected from the group consisting of mitomycin A, mitomycin B, mitomycin C, mitomycin D, mitomycin E, mitomycin F, and porfiromycin.

14. The composition of claim 11 further comprising a therapeutic factor selected from the group consisting of a cell killing agent, a tumor penetration enhancer, a chemotherapeutic agent, and a compound capable of stimulating an endogenous immune response.

15. The composition of claim 14 wherein the therapeutic factor is a chemotherapeutic agent.

16. The composition of claim 15 wherein the chemotherapeutic agent is paclitaxel.

17. A method of preparing a biologically active conjugate of the formula

B-L-X

wherein B is folate or a folate-receptor-binding analog or derivative thereof;

X comprises a mitomycin compound or an analog or derivative thereof;

and L is a divalent linker comprising a disulfide bond, said method comprising the steps of forming a thiosulfonate intermediate of the formula B-(L″)nSSO2R or an intermediate of the formula X-(L′)nSSO2R

and reacting said thiosulfonate intermediate with a compound of the formula X-(L′)n′-SH or B-(L″)n′-SH, respectively, wherein L′ and L″ are, independently, divalent linkers through which the thiol group SH is covalently bonded to B and X, respectively;

n and n′ are 1 or 0; and

R is alkyl, substituted alkyl, aryl, heteroaryl or substituted aryl or heteroaryl.

18. A conjugate comprising folate, or an analog or derivative thereof, linked by a cleavable linker to a mitomycin compound, or an analog or derivative thereof, wherein the cleavable linker is a disulfide group, wherein the folate binds to a surface accessible folate receptor that is uniquely expressed, overexpressed, or preferentially expressed by a population of pathogenic cells.

19. A method of selectively eliminating a population of pathogenic cells in a host animal harboring said population of cells wherein the members of said cell population have a surface accessible binding site for folate, or an analog or derivative thereof, said method comprising the steps of:

administering to said host a conjugate comprising folate, or an analog or derivative thereof, linked by a cleavable linker to a mitomycin compound, or an analog or derivative thereof, wherein the cleavable linker is a disulfide group, wherein the folate binds to a surface accessible folate receptor that is uniquely expressed, overexpressed, or preferentially expressed by a population of pathogenic cells; and

selectively eliminating said population of pathogenic cells.