Gene regulation in cancer gene therapy strategies.

Gene regulation in cancer gene therapy strategies. Regulation of expression in gene therapy is considered to be a very desirable goal, preventing toxic effects and improving biological efficacy. A variety of systems have been reported in an ever widening range of applications, this paper describes these systems with specific reference to cancer gene therapy

Self-immolative nitrogen mustards prodrugs cleavable by carboxypeptidase G2 (CPG2) showing large cytotoxicity differentials in GDEPT.

Self-immolative nitrogen mustards prodrugs cleavable by carboxypeptidase G2 (CPG2) showing large cytotoxicity differentials in GDEPT. Nineteen novel potential self-immolative prodrugs and their corresponding drugs have been synthesized for gene-directed enzyme prodrug therapy (GDEPT) with carboxypeptidase G2 (CPG2) as the activating enzyme. The compounds are derived from o- and p-amino and p-methylamino aniline nitrogen mustards. Their aqueous stability, kinetics of drug release by CPG2, and cytotoxicity in the colon carcinoma cell line WiDr, expressing either surface-tethered CPG2 (stCPG2(Q)3) or control beta- galactosidase, are assessed. The effect of various structural features on stability, kinetics of activation, and biological activity is discussed. The p-methylamino prodrugs are the most stable compounds from this series, with the largest cytotoxicity differentials between CPG2-expressing and nonexpressing cells. The most potent compounds in all series are prodrugs of bis-iodo nitrogen mustards. 4-{N-[4'-Bis(2"- iodoethyl)aminophenyll-N'- methylcarbamoyloxymethyl}phenylcarbamoyl-L-glutamic acid, compound 39b, is 124-fold more cytotoxic to WiDr cells expressing CPG2 than to cells expressing beta-galactosidase. An additional six compounds show better cytotoxicity differential than the published N-{4-[(2-chloroethyl)(2- mesyloxyethyl)amino]benzoyl}-L-glutamic acid (CMDA) prodrug

Attenuated Salmonella targets prodrug activating enzyme carboxypeptidase G2 to mouse melanoma and human breast and colon carcinomas for effective suicide gene therapy.

Purpose: We engineered the oncolytic Salmonella typhimurium-derived bacterium VNP20009 as a vector to target delivery to tumors of the prod rug-activating enzyme carboxypepticlase G2 (CPG 2) and to show enhanced antitumor efficacy on administration of different prodrugs. Experimental Design: We characterized CPG2 expression in vectors by immunoblotting, immunofluorescence, and enzyme activity. We assessed prodrug activation by high-performance liquid chromatography. Target human turnorcell and bacterial vector cell cytotoxicity was measured by flow cytometry and colony-forming assays. Therapy was shown in two human tumor xenografts and one mouse allograft with postmortem analysis of bacterial and CPG2 concentration in the tumors. Results: CPG2 is expressed within the bacterial periplasm. It activates prodrugs and induces cytotoxicity in human tumor cells but not in host bacteria. Following systemic administration, bacteria multiply within xenografts reaching 2 x 10(7)/g to 2 x 10(8)/g at 40 days postinoculation. The concentration of CPG2 in these tumors increases steadily to therapeutic levels of 1 to 6 units/g. The bacteria alone reduce the growth of the tumors. Subsequent administration of prodrugs further reduces significantly the growth of the xenografts. Conclusions: The bacteria multiply within tumors, resulting in a selective expression of CPG2. The CPG2-expressing bacteria alone reduce the growth of tumors. However, in the presence of prodrugs activated by CPG2, this oncolytic effect is greatly increased. We conclude that bacterial oncolytic therapy, combined with CPG2-mediated prodrug activation, has great potential in the treatment of a range of cancers