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PURPOSE At the preclinical stage, mitozolomide (MTZ) showed exciting preclinical activity but failed later in clinical trial due to toxic side effects. We surmised that by targeting MTZ to epidermal growth factor receptor (EGFR), we may not only alter its toxicity profile, but also enhance its potency in EGFR-overexpressing tumors. To test this hypothesis, we designed JDF12, studied its mechanism of action in human prostate cancer (PCa) cells and determined its potency in vivo. EXPERIMENTAL DESIGN To analyze its mixed EGFR-DNA targeting potential, we performed an enzyme linked immunosorbent assay (ELISA) and western blotting analysis of EGFR phosphorylation in cells stimulated with EGF. DNA damage was analyzed using the comet assay, and apoptosis quantitated by annexin V binding assay. Growth inhibition in vitro was determined by the sulforhodamine B (SRB) assay and in vivo efficacy analyzed in male CD-1 nude mice. RESULTS The results showed that: Under physiological conditions, JDF12 was hydrolyzed to JDF04R and both agents were capable of inhibiting isolated EGFR tyrosine kinase (TK) and EGFR phosphorylation in EGF-stimulated cells. JDF12 significantly damaged DNA, induced apoptosis in DU145 cells and was up to 2–10-fold more potent than equieffective combinations of MTZ and JDF04R or Iressa in a panel that also included LNCaP and its EGFR and ErbB2 transfectants. In vivo, it induced significant antitumor activity in a DU145 xenograft model. CONCLUSIONS The results suggest that the superior cytotoxicity of JDF12 when compared with MTZ and JDF04R may be imputed to its potent EGFR-DNA targeting properties and confirm the ability of this novel strategy to confer EGFR targeting properties to a classical alkylator. Prostate 72:1273–1285, 2012. © 2012 Wiley Periodicals, Inc.

Combi-molecules are agents designed to block receptors on their own and to further degrade to bioactive agents. Here we studied the fate of a novel combi-molecule of triazene class termed “ZRS1” in biological medium using multilayer aggregates and mouse tumour models. ZRS1 is a second generation derivative of RB107, a prodrug designed to release an EGFR inhibitor FD105 plus a methyl diazonium species. RB107 contains an acetoxymethyl function that is hydrolyzed too rapidly to generate BJ2000, a monoalkyltriazene that further degrades to FD105 and DNA alkylating methyldiazonium species. Recently, in order to prevent rapid hydrolysis of the acetoxymethylene function in the absence of cells and to delay the release of BJ2000, we designed ZRS1 that contains a more stable acetoxymethyl carbamate function. The results showed that ZRS1 was more stable than RB107 in cell culture medium supplemented with serum, with a rather long half life ( > 2 h). However, in an experiment where it was allowed to degrade in multilayer aggregates of ovarian cancer cells OV90, it rapidly released BJ2000 and its corresponding metabolite FD105, both in the medium and the multilayer aggregates. Interestingly, the intact ZRS1 could be detected in the multilayer aggregates with a Tmax around 10 min. Studies in vivo, in human DU145 prostate cancer xenograft model, revealed that ZRS1 blocked tumour growth and released FD105 and its acetylated metabolite FD105Ac, the latter being the major metabolite. Likewise, time course analysis in 4T1 mouse syngeneic breast cancer model showed a rapid release of FD105 and FD105Ac in the plasma and in the tumours. In summary, ZRS1 appeared as a good prodrug of the stable EGFR inhibitory metabolites FD105 and FD105Ac. Its ability to generate high concentrations of FD105Ac, a more potent EGFR inhibitor as is its major metabolite, is significant over previous methylating combi-molecules. Furthermore, this study showed that multilayer OV90 aggregates could be developed as an effective model to predict the stability and degradation of ZRS1 in vivo.

Previous strategies for stabilizing combi-triazenes were based on masking the 1,2,3-triazene chain with a 3-acetoxymethylene group. The half-lives of the latter molecules were only ca 5 min longer than those of their parent 1,2,3-triazenes. The novel combi-molecules described herein contain a hydrolysable carbamate group that modulates their kinetics of degradation. Their half-lives were prolonged by ca 20-55 min when compared with their acetoxymethyltriazene counterparts. While they decomposed slowly in serum-containing medium, their intracellular decomposition was extremely rapid. They blocked EGFR tyrosine kinase in an isolated enzyme assay and in MDA-MB-468 breast cancer cells. Similarly, they all induced a dose-dependent DNA damage and G2/M cell cycle arrest in MDA-MB-468 cells, except the most stable compound ZRL2 (a 3-vinyl carbamate). ZRL4 (a chloromethyl carbamate) was the most potent and ZRL2 was the least active of the series against MDA-MB-468 cells. In selectivity assay with NIH-3T3 and NIH-3T3/HER-14, all compounds selectively blocked proliferation of NIH-3T3/HER-14. ZRS1 exerted the strongest growth inhibitory potency of the series. The results in toto suggest that ZRL2, despite being the most stable compound, could not hydrolyze at a rate that permitted the generation of DNA damaging species, thereby behaving primarily as an EGFR inhibitor. Thus the study permitted the definition of an optimized combi-molecule as one that decomposes at a rate that is slower than that of acetoxymethyltriazenes, but rapid enough to generate strong EGFR-DNA targeting potential and growth inhibition. Based on the latter criteria, ZRS1 and ZRL4 were tested in vivo and ZRS1 has proven the more effective.

To enhance the potency of "combi-molecules", we designed 6a-d and 18 to release an inhibitor of EGFR TK and a bifunctional alkylator. The combi-molecules blocked EGFR TK with potency increasing with the basicity of the mustard moiety. They selectively killed cells transfected with EGFR and were potent against the DU145 prostate cancer cells. Combi-molecule 6a blocked EGFR phosphorylation in an irreversible manner, induced DNA-cross-links, and arrested the cells in mid-S.

ZR2003 is a type II of combi-molecule designed to target DNA and the epidermal growth factor receptor (EGFR) without requirement for hydrolysis. In human tumour cell lines cultured as monolayers, it showed 6.5–35 fold greater activity than Iressa. Further evaluation in 3D organ-like multilayer aggregates showed that it could block proliferation at submicromolar level. However, despite the superior potency of ZR2003 over Iressa in vitro, its activity xenograft models was not significantly different from that of Iressa. To rationalize these results, we determined the tumour concentration of both ZR2003 and Iressa in vivo and more importantly in vitro in multicellular aggregates. The results showed that in A431 and 4T1 xenografts, the level of ZR2003 absorbed in the tumours were consistently 2-fold less than those generated by Iressa. Likewise, in the multicellular aggregates model, the penetration of ZR2003 was consistently lower than Iressa. In serum containing media, the level of extractable or free ZR2003 was also inferior to those of Iressa. The results from this bioanalytical study, suggest that the discrepancy between the in vitro and in vivo potency of ZR2003 when compared with Iressa, may be imputed to its significantly lower tumour concentration.

Combi-molecules are novel agents designed to be hydrolyzed into two bioactive species: an epidermal growth factor receptor (EGFR) tyrosine kinase (TK) inhibitor + a DNA alkylating agent. With the purpose of enhancing the tumour concentration of the bioactive species, we synthesized and compared the activities of RB107, a quinazolinotriazene designed to generate the bioactive BJ2000 upon hydrolysis, ZRDM and RB107ZR that require metabolic activation to generate BJ2000. The results showed that RB107 released the highest level of BJ2000 and its degradation product FD105 in vivo and high levels of the DNA alkylating methyl diazonium ion in the brain, kidney, liver and the DU145 tumours as confirmed by (14)C-labeling. The results in toto suggest that RB107 was stable enough to deliver the bioactive species to the tumour site and for optimal tumour distribution of the bioactive species, combi-molecules of the triazene class must be designed to be primarily degraded by hydrolytic cleavage and not by metabolic activation.

A novel type of 3,3-disubstituted bis-triazenes containing an ethylaminoethyl linker flanked by two identical anilinoquinazoline ring was synthesized. These model molecules contained an N-ethylaminomorpholine moiety designed to enhance water solubility. Despite their significant bulkiness, they blocked epidermal growth factor receptor (EGFR) tyrosine kinase in a dose-dependent manner with IC(50) values in low micromolar range. Molecular modeling to predict the interactions of the molecule with the ATP binding site of EGFR suggests that the N-ethylaminomorpholine side chain plays a binding role.

Purpose: JDA58 (NSC 741282), a “combi-molecule” optimized in the context of the “combi-targeting concept,” is a nitrosourea moiety tethered to an anilinoquinazoline. Here, we sought to show its binary epidermal growth factor receptor (EGFR)/DNA targeting property and to study its fragmentation in vitro and in vivo. Experimental Design: The fragmentation of JDA58 was detected in cells in vitro and in vivo by fluorescence microscopy and tandem mass spectrometry. EGFR phosphorylation and DNA damage were determined by Western blotting and comet assay, respectively. Tumor data were examined for statistical significance using the Student's t test. Results: JDA58 inhibited EGFR tyrosine kinase (IC50, 0.2 μmol/L) and blocked EGFR phosphorylation in human DU145 prostate cancer cells. It induced significant levels of DNA damage in DU145 cells in vitro or in vivo and showed potent antiproliferative activity both in vitro and in a DU145 xenograft model. In cell-free medium, JDA58 was hydrolyzed to JDA35, a fluorescent amine that could be observed in tumor cells both in vitro and in vivo. In tumor cells in vitro or in vivo, or in plasma collected from mice, the denitrosated species JDA41 was the predominant metabolite. However, mass spectrometric analysis revealed detectable levels of the hydrolytic product JDA35 in tumor cells both in vitro and in vivo. Conclusions: The results in toto suggest that growth inhibition in vitro and in vivo may be sustained by the intact combi-molecule plus JDA35 plus JDA41, three inhibitors of EGFR, and the concomitantly released DNA-damaging species. This leads to a model wherein a single molecule carries a complex multitargeted-multidrug combination.

With the purpose of developing drugs that can block multiple targets in tumor cells, molecules termed combi-molecules or TZ-I have been designed to be hydrolyzed in vitro to TZ + I, where TZ is a DNA-damaging species and I is an inhibitor of the epidermal growth factor receptor (EGFR). Using HPLC and liquid chromatographymass spectrometry (LC-MS), we investigated the mechanism of in vivo degradation of a prototype of one such combi-molecule, ZRBA1, which when administered i.p. rapidly degraded into FD105 (C max = 50 μmol/l, after 30 min), a 6-aminoquinazoline that was N-acetylated to give FD105Ac (IAc) (C max =18 μmol/l, after 4 h). A similar rate of acetylation was observed when independently synthesized FD105 was administered i.p. More importantly, the EGFR binding affinity of IAc was 3-fold greater than that of I, indicating that the latter is converted in vivo into an even more potent EGFR inhibitor. The results in toto suggest that while in vitro TZ-I is only hydrolyzed to I + TZ, further acetylation of I in vivo leads to a third component - a highly potent EGFR inhibitor with a delayed C max .

Recently, with the purpose of enhancing the potency of epidermal growth factor receptor (EGFR)-based therapies, we designed a novel strategy termed 'Cascade-release targeting' that seeks to develop molecules capable of degrading to multiple tyrosine kinase (TK) inhibitors and highly reactive electrophiles, in a stepwise fashion. Here we report on the first prototype of this model, RB24, a masked methyltriazene, that in addition to being an inhibitor on its own was designed to degrade to RB14, ZR08, RB10+a DNA alkylating methyldiazonium species. The cascade degradation of RB24 requires the generation of two reactive electrophiles: (a) an iminium ion and (b) a methyldiazonium ion. Thus, we surmise that these species could alkylate the active site of EGFR, thereby irreversibly blocking its action and that DNA damage could be induced by the methyldiazonium. Using the EGFR-overexpressing human epidermoid carcinoma of the vulva cell line, A431, we demonstrate herein that (a) RB24 and its derived species (e.g. RB14, ZR08) irreversibly inhibit EGFR autophosphorylation, (b) RB24 induced significant levels of DNA strand breaks, (c) sustained inhibition of EGFR by RB24 was associated with blockade of MAPK activation and c-fos gene expression, (d) RB24 induced irreversible cell growth inhibition with a 100-fold greater potency than Temodaltrade mark, a clinical methyltriazene. The pronounced growth inhibitory potency of RB24 was attributed to its ability to simultaneously damage DNA and irreversibly block EGFR TK activity.

BACKGROUND FD137, a nitrosourea appended to a quinazoline ring, was designed to simultaneously block epidermal growth factor receptor (EGFR)-mediated signaling and damage genomic DNA in refractory EGF-dependent prostate tumors. METHODS The mixed inhibition of cell signaling and DNA damage by FD137 were determined by Western blotting, RT-PCR, flow cytometry, sulforhodamine B (SRB), and comet assay. RESULTS FD137 and its metabolite FD110 induced a dose-dependent increase in inhibition of EGF-stimulated EGFR autophosphorylation and this translated into blockade of c-fos gene expression in DU145 cells. FD137 induced significant levels of DNA damage and showed 150-fold greater anti-proliferative activity than BCNU, a classical nitrosourea. In contrast to BCNU, complete inhibition of EGF-induced cell transition to S-phase was observed at concentrations of FD137 as low as 3 μM. CONCLUSION FD137 could not only damage DNA, but also significantly block downstream EGFR-mediated signaling. The superior activity of FD137 may be imputable to the combined effect of its mixed EGFR/DNA targeting properties. This novel strategy may well represent a new approach to target nitrosoureas to EGFR-overexpressing carcinomas of the prostate. © 2004 Wiley-Liss, Inc.