E. coli NfsA: an alternative nitroreductase for prodrug activation gene therapy in combination with CB1954

Prodrug activation gene therapy is a developing approach to cancer treatment, whereby prodrug-activating enzymes are expressed in tumour cells. After administration of a non-toxic prodrug, its conversion to cytotoxic metabolites directly kills tumour cells expressing the activating enzyme, whereas the local spread of activated metabolites can kill nearby cells lacking the enzyme (bystander cell killing). One promising combination that has entered clinical trials uses the nitroreductase NfsB from Escherichia coli to activate the prodrug, CB1954, to a potent bifunctional alkylating agent. NfsA, the major E. coli nitroreductase, has greater activity with nitrofuran antibiotics, but it has not been compared in the past with NfsB for the activation of CB1954. We show superior in vitro kinetics of CB1954 activation by NfsA using the NADPH cofactor, and show that the expression of NfsA in bacterial or human cells results in a 3.5- to 8-fold greater sensitivity to CB1954, relative to NfsB. Although NfsB reduces either the 2-NO2 or 4-NO2 positions of CB1954 in an equimolar ratio, we show that NfsA preferentially reduces the 2-NO2 group, which leads to a greater bystander effect with cells expressing NfsA than with NfsB. NfsA is also more effective than NfsB for cell sensitisation to nitrofurans and to a selection of alternative, dinitrobenzamide mustard (DNBM) prodrugs

Explicit hypoxia targeting with tumor suppression by creating an “obligate” anaerobic Salmonella Typhimurium strain

Using bacteria as therapeutic agents against solid tumors is emerging as an area of great potential in the treatment of cancer. Obligate and facultative anaerobic bacteria have been shown to infiltrate the hypoxic regions of solid tumors, thereby reducing their growth rate or causing regression. However, a major challenge for bacterial therapy of cancer with facultative anaerobes is avoiding damage to normal tissues. Consequently the virulence of bacteria must be adequately attenuated for therapeutic use. By placing an essential gene under a hypoxia conditioned promoter, Salmonella Typhimurium strain SL7207 was engineered to survive only in anaerobic conditions (strain YB1) without otherwise affecting its functions. In breast tumor bearing nude mice, YB1 grew within the tumor, retarding its growth, while being rapidly eliminated from normal tissues. YB1 provides a safe bacterial vector for anti-tumor therapies without compromising the other functions or tumor fitness of the bacterium as attenuation methods normally do

Direct Injection of Functional Single-Domain Antibodies from E. coli into Human Cells

Intracellular proteins have a great potential as targets for therapeutic antibodies (Abs) but the plasma membrane prevents access to these antigens. Ab fragments and IgGs are selected and engineered in E. coli and this microorganism may be also an ideal vector for their intracellular delivery. In this work we demonstrate that single-domain Ab (sdAbs) can be engineered to be injected into human cells by E. coli bacteria carrying molecular syringes assembled by a type III protein secretion system (T3SS). The injected sdAbs accumulate in the cytoplasm of HeLa cells at levels ca. 105–106 molecules per cell and their functionality is shown by the isolation of sdAb-antigen complexes. Injection of sdAbs does not require bacterial invasion or the transfer of genetic material. These results are proof-of-principle for the capacity of E. coli bacteria to directly deliver intracellular sdAbs (intrabodies) into human cells for analytical and therapeutic purposes

Caffeine inhibits excision of 7-bromomethylbenz (a) anthracene-DNA adducts from exponentially growing but not from stationary phase Chinese hamster cells.

Excision of 7-bromomethylbenz(a)anthracene (7-BMBA)-DNA adducts from exponentially growing cultures of Chinese hamster V79-379A cells followed logarithmic kinetics with a half of approximately 20 hrs. Post-treatment incubation in the presence of a sub-toxic concentration of caffeine markedly reduced this loss. Caffeine brought about a concomitant increase in overall DNA synthetic rate in treated exponential cultures. Excision in stationary, non-DNA-replicating cultures, was slower and caffeine did not affect this reduced rate of excision. These findings lend support to a previous proposition that the caffeine-induced inhibition of elongation of nascent DNA on a template containing chemical lesions results in an interference with the excision repair mechanism that removes these lesions

Novel fluorinated prodrugs for activation by carboxypeptidase G2 showing good in vivo antitumor activity in gene-directed enzyme prodrug therapy.

Novel fluorinated prodrugs for activation by carboxypeptidase G2 showing good in vivo antitumor activity in gene-directed enzyme prodrug therapy Sixteen novel polyfluorinated benzoic acid mustards have been synthesized for use in gene-directed enzyme prodrug therapy (GDEPT). Eight of these were benzoic acid L-glutamate mustards for evaluation as prodrugs and the other eight were the active drugs formed by the action of the bacterial enzyme carboxypeptidase G2 (CPG2). All of the di- and trifluorinated prodrugs were efficiently cleaved by the enzyme. In contrast, the tetrafluorinated prodrugs were found to be competitive inhibitors of CPG2, the first such inhibitors to have been described. The di- and trifluorinated prodrugs were differentially cytotoxic to human breast carcinoma cells (MDA MB 361) expressing CPG2, compared to control cells that did not express the enzyme. The difluorinated prodrug {4-[bis(2- bromoethyl)amino]-3,5-difluorobenzoyl}-L-glutamic acid and its iodoethylamino analogue were effective substrates for the enzyme and showed excellent therapeutic activity in CPG2- expressing MDA MB 361 xenografts, either curing or greatly inhibiting tumor growth and extending the life of the animals

Activated B-RAF is an Hsp90 client protein that is targeted by the anticancer drug 17-allylamino-17-demethoxygeldanamycin.

Activated B-RAF is an Hsp90 client protein that is targeted by the anticancer drug 17-allylamino-17-demethoxygeldanamycin Hsp90 is a ubiquitously expressed molecular chaperone that folds, stabilizes, and functionally regulates many cellular proteins. The benzoquinone ansamysin 17-allylamino-17demethoxygeldanamycin (17-AAG) is an anticancer drug that disrupts Hsp90 binding to its clients, causing their degradation through the ubiquitin-dependent proteasomal pathway. The protein kinase B-RAF is mutated in similar to 7% of human cancers. The most common mutation (similar to 90%) is B-V600E-RAF, which has constitutively elevated kinase activity, stimulates cancer cell proliferation, and promotes survival. Here, we show that B-V600E-RAF is an Hsp90 client protein that requires Hsp90 for its folding and stability. (V600E)BRAF is more sensitive to degradation by 17-AAG treatment than B-WT-RAF and we show that the majority of the other mutant forms of B-RAF are also sensitive to 17-AAG-mediated proteasomal degradation. Our data show that B-RAF is an important target for 17-AAG in human cancer. (Cancer Res 2005; 65(23): 10686-91)

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

Significant differences in biological parameters between prodrugs cleavable by carboxypeptidase G2 that generate 3,5-difluoro-phenol and -aniline nitrogen mustards in gene-directed enzyme prodrug therapy systems.

Nine new nitrogen mustard compounds derived from 2,6-difluoro-4-hydroxy- (3a-e) and 2,6-difluoro-4-amino- (4a-d) aniline were synthesized as potential prodrugs. They were designed to be activated to their corresponding 3,5-difluorophenol and -aniline (4)-nitrogen mustards by the enzyme carboxypeptidase G2 (CPG2) in gene-directed enzyme prodrug therapy (GDEPT) models. The compounds were tested for cytotoxicity in the MDA MB-361 breast adenocarcinoma. The cell line was engineered to express stably either CPG2 tethered to the cell surface stCPG2-(Q)3 or beta-galactosidase (beta-Gal) as control. The cytotoxicity differentials were calculated between CPG 2-expressing and -nonexpressing cells and yielded different results for the two series of prodrugs despite their structural similarities. While the phenol compounds are ineffective as prodrugs, their aniline counterparts exhibit outstanding activity in the tumor cell lines expressing CPG2. [3,5-Difluoro-4-[bis(2-chloroethyl)amino]phenyl]carbamoyl-l-glutamic acid gave a differential of >227 in MDA MB361 cells as compared with 19 exhibited by 4-[(2-chloroethyl)(2-mesyloxyethyl)amino]benzoyl-l-glutamic acid, 1a, which has been in clinical trials