Compositions and methods for treating cancer

1. A nucleic acid construct system comprising:

first nucleic acid constructs (NA1) encoding a bacterial-derived toxin operatively linked to a first constitutive promoter and at least one Ras responsive enhancer element comprising at least one element selected from the group consisting of an Ets binding site, an Ap-1 binding site and a PY2 sequence; and

(ii) second nucleic acid constructs (NA2) encoding a bacterial-derived anti-toxin operatively linked to a second constitutive promoter and 17 copies of a p53 wild type responsive element, wherein said 17 copies of said p53 wild type responsive element are set forth in SEQ ID NO:15;

wherein said first and second constitutive promoters have the same ability to direct transcription; wherein said bacterial-derived toxin and said bacterial-derived anti-toxin are a bacterial type II toxin anti-toxin pair selected from the toxin-antitoxin pairs CcdB-CcdA, ParE-ParD, MazF-MazE, yafO-yafN, HicA-HicB, Kid-Kis, and Zeta-Epsilon; and wherein a greater number of said first nucleic acid constructs are provided than said second nucleic acid constructs, wherein said greater number comprises NA1 and NA2 provided at a ratio of between NA1:NA2=1:0.5 and NA1:NA2=1:0.1.

2. The nucleic acid construct system of claim 1 , wherein said second constitutive promoter comprises CMV and said first promoter comprises SV40.

3. The nucleic acid construct system of claim 1 , wherein said first nucleic acid construct, said second nucleic acid construct or both is adeno-virus based.

4. The nucleic acid construct system of claim 1 , wherein said first nucleic acid construct, said second nucleic acid construct or both is Lenti -virus based.

5. The nucleic acid construct system of claim 1 , wherein said Ras-responsive element comprises a PY2 sequence.

6. The nucleic acid construct system of claim 1 , wherein said Ras responsive enhancer element is a K-Ras responsive enhancer element.

7. The nucleic acid construct system of claim 1 , wherein said first nucleic acid construct comprises four repeats of the PY2 sequence set forth by SEQ ID NO:2 being upstream and operably linked to the SV40 minimal promoter region set forth by SEQ ID NO:4, a toxin coding sequence being downstream of and transcriptionally regulated by said SV40 minimal promoter region, an IRES sequence set forth by SEQ ID NO:7 being downstream and operably linked to said toxin coding sequence, and a Tetracycline repressor set forth by SEQ ID NO: 8 being downstream of and operably linked to said IRES sequence.

8. The nucleic acid construct system of claim 1 , wherein said second nucleic acid construct comprises a CMV minimal promoter which comprises two repeats of a tetracycline operator as set forth by SEQ ID NO:9 and an antitoxin coding sequence being downstream of and operably linked to said CMV minimal promoter.

9. The nucleic acid construct system of claim 1 , wherein said first promoter and said second promoter are identical.

10. The nucleic acid construct system of claim 1 , wherein said first promoter and said second promoter are different.

11. The nucleic acid construct system of claim 1 , wherein said toxin is mazF and said antitoxin is mazE.

12. The nucleic acid construct system of claim 1 , wherein said first nucleic acid construct further comprises a repressor of a bacterial repressor-operator system, said repressor being under a transcriptional regulation of said Ras responsive enhancer element, and wherein said second nucleic acid construct comprises an operator of said bacterial repressor-operator system, such that expression of said repressor inhibits expression of said antitoxin.

13. The nucleic acid construct system of claim 12 , wherein said repressor comprises the Tetracycline repressor (Tet-R) sequence, and wherein said operator comprises the tetracycline operator sequence.

14. The nucleic acid construct system of claim 12 , wherein said operator comprises at least two repeats of the sequence tetracycline operator sequence.

15. A nucleic acid construct system comprising:

(i) first nucleic acid constructs (NA1) encoding a mazF operatively linked to a first constitutive promoter and at least one Ras responsive enhancer element comprising at least one element selected from an Ets binding site, Ap-1 binding site and a PY2 sequence; and

(ii) second nucleic acid constructs (NA2) encoding mazE operatively linked to a second constitutive promoter and 17 copies of a p53 wild type responsive element, wherein said 17 copies of said p53 wild type responsive element are set forth in SEQ ID NO:15;

wherein said first and second constitutive promoters have the same ability to direct transcription; and wherein a greater number of said first nucleic acid constructs are provided than said second nucleic acid constructs, wherein said greater number comprises NA1 and NA2 provided at a ratio of between NA1:NA2=1:0.5 and NA1:NA2=1:0.1.

16. A nucleic acid construct system comprising:

(i) first nucleic acid constructs (NA1) encoding a mazF operatively linked to a first constitutive promoter and at least one Ras responsive enhancer element comprising at least one element selected from an Ets binding site, Ap-1 binding site and a PY2 sequence; and

(ii) second nucleic acid constructs (NA2) encoding mazE operatively linked to a second constitutive promoter and 17 copies of a p53 wild type responsive element, wherein said 17 copies of said p53 wild type responsive element are set forth in SEQ ID NO:15;

wherein said first and second constitutive promoters are identical; and wherein a greater number of said first nucleic acid constructs are provided than said second nucleic acid constructs, wherein said greater number comprises NA1 and NA2 provided at a ratio of between NA1:NA2=1:0.5 and NA1:NA2=1:0.1.

17. A pharmaceutical composition for treatment of a tumor overexpressing Ras, said pharmaceutical composition comprising: (a) the nucleic acid construct system of claim 1 , wherein said nucleic acid construct system is adeno-associated virus based and (b) a pharmaceutically acceptable vehicle.

18. A method for treating a tumor overexpressing Ras in a patient in need thereof, said method comprising introducing into the tumor cells an effective amount of the pharmaceutical composition of claim 17 , wherein said tumor cells are characterized by a hyperactive RAS pathway as compared to non-tumor cells of the same tissue, thereby inhibiting tumor growth.