Subcellular distribution of a fluorescence-labeled combi-molecule designed to block epidermal growth factor receptor tyrosine kinase and damage DNA with a green fluorescent species

Molecular Analysis of the Superior Efficacy of a Dual Epidermal Growth Factor Receptor (EGFR)-DNA-Targeting Combi-Molecule in Comparison with Its Putative Prodrugs 6-Mono-Alkylamino- and 6,6-Dialkylaminoquinazoline in a Human Osteosarcoma Xenograft Model

Background: ZR2002 is a dual EGFR-DNA-targeting combi-molecule that carries a chloroethyl group at the six-position of the quinazoline ring designed to alkylate DNA. Despite its good pharmacokinetics, ZR2002 is metabolized in vivo into dechlorinated metabolites, losing the DNA-alkylating function required to damage DNA. To increase the DNA damage activity in tumor cells in vivo, we compared ZR2002 with two of its 6-N,N-disubstituted analogs: "JS61", with a nitrogen mustard function at the six-position of the quinazoline ring, and "JS84", with an N-methyl group. Methods: Tumor xenografts were performed with the human Saos-2 osteosarcoma cell line expressing EGFR. Mice were treated with ZR2002, JS84 or JS61, and the tumor burden was measured with a caliper and CT/PET imaging. Drug metabolism was analyzed with LC-MS. EGFR and ɣ-H2AX phosphorylation were quantified via Western blot analysis and immunohistochemistry. Results: In vivo analysis showed that significant tumor growth inhibition was only achieved when ZR2002 was administered in its naked form. The metabolic dealkylation of JS61 and JS84 did not release sufficient concentrations of ZR2002 for the intratumoral inhibition of P-EGFR or enhanced levels of P-H2AX. Conclusions: The results in toto suggest that intratumoral concentrations of intact ZR2002 are correlated with the highest inhibition of P-EGFR and induction of DNA damage in vivo. ZR2002 may well represent a good drug candidate for the treatment of EGFR-expressing osteosarcoma.

Quantitative Analysis of the Potency of Equimolar Two-Drug Combinations and Combi-Molecules Involving Kinase Inhibitors In Vitro: The Concept of Balanced Targeting

The median-effect principle proposed by Chou and Talalay is the most effective approach to parameterize interactions between several agents in combination. However, this method cannot be used to evaluate the effectiveness of equimolar drug combinations, which are comparative references for dual-targeting molecular design. Here, using data acquired through the development of “combi-molecules” blocking two kinases (e.g., EGFR-c-Src and EGFR-c-Met), we established potency indices for equimolar and dual-targeted inhibitors. If the fold difference (κ) between the IC50 of the two individual kinase inhibitors was >6, the IC50 of their equimolar combination resembled that of the more potent inhibitor. Hence, the “combi-targeting” of the two kinases was considered “imbalanced” and the combination ineffective. However, if κ ≤ 6, the IC50 of the combination fell below that of each individual drug and the combi-targeting was considered “balanced” and the combination effective. We also showed that combi-molecules should be compared with equimolar combinations only under balanced conditions and propose a new parameter Ω for validating their effectiveness. A multi-targeted drug is effective if Ω < 1, where Ω is defined as the IC50 of the drug divided by that of the corresponding equimolar combination. Our study provides a methodology to determine the in vitro potency of equimolar two-drug combinations as well as combi-/hybrid molecules inhibiting two different kinase targets.

Design and Mechanism of Action of a New Prototype of Combi-Molecule "Programed" to Release Bioactive Species at a pH Range Akin to That of the Tumor Microenvironment

The clinical use of cytotoxic agents is plagued by systemic toxicity. We report a novel approach that seeks to design a “combi-molecule” to behave as an alkylating agent on its own and to undergo acid-catalyzed conversion to two bioactive species at a pH range akin to that of a tumor microenvironment: an AL530 prototype was synthesized and we studied its ability to release a chlorambucil analogue (CBL-A) plus a potent mitogen-activated protein/extracellular signal-regulated kinase kinase (MEK) inhibitor (PD98059) at different pHs in buffered solutions, plasma and tumors. Its potency was compared in vitro with CBL+PD98059 (SRB assay) and in vivo in a xenograft model. Its target modulation was studied by western blotting and immunohistochemistry. AL530 released PD98059+CBL-A at mild acidic pH and in vitro was fivefold more potent than CBL and three-to-fivefold more potent than CBL+PD98059. In vivo it released high levels of PD98059 in tumors with a tumor/plasma ratio of five. It induced γ-H2AX phosphorylation and blocked pErk1,2, indirectly indicating its ability to damage DNA and modulate MEK. It induced significant tumor delay and less toxicity at unachievable doses for CBL and CBL+PD98059. We demonstrated the feasibility of a pH-labile combi-molecule capable of delivering high MEK inhibitor concentration in tumors, damaging DNA therein, and inducing tumor growth delay.

Subcellular distribution and mechanism of action of AL906, a novel and potent EGFR inhibitor rationally designed to be green fluorescent

To enhance the potency of EGFR inhibitors, we developed a novel strategy that seeks to conjugate EGFR to a bioactive moiety leading to a molecule termed "combi-molecule". In order to mimic the penetration of this type of molecules, based upon previously reported structure activity relationship studies, we designed a new molecule containing a quinazoline moiety tethered to a p-nitrobenzoxadiazole (NBD) moiety [molecular weight (MW) 700]. Despite its size, AL906 growth inhibitory activity was superior to that of the clinical drug gefitinib. Furthermore, AL906 retained significant EGFR inhibitory activity and good cellular penetration with abundant distribution in the perinuclear region of the cells. In an isogenic NIH3T3 transfected cell panel, it selectively inhibited the growth  of the NIH3T3-EGFR and HER2 transfectants. Confocal microscopy analysis revealed that it was capable of penetrating multilayer aggregates although to a lesser extent than FD105, a small inhibitor of EGFR inhibitor of the same class (MW 300). Its ability to inhibit EGFR auto-phosphorylation in monolayer culture was stronger than in the aggregates. The results suggest that our strategy did not negatively affect EGFR inhibitory potency, EGFR selectivity and growth inhibition. However, its molecular size may account for its decreased aggregate penetration when compared with a smaller EGFR inhibitor of the quinazoline class.

Design and Synthesis of a Trifunctional Molecular System "Programmed" to Block Epidermal Growth Factor Receptor Tyrosine Kinase, Induce High Levels of DNA Damage, and Inhibit the DNA Repair Enzyme (Poly(ADP-ribose) Polymerase) in Prostate Cancer Cells

Resistance to chemotherapy in advanced cancers can be mediated by different factors such as epidermal growth factor receptor (EGFR) overexpression and DNA repair enzymes. Therefore, current standards of care usually involve combinations of multiple treatments. Here, to reduce the adverse effects of multiple drug combinations and improve outcome, we proposed a single drug approach to block multiple overlapping effects that characterize chemoresistance. Thus, we designed a new linker that allows assembly of multiple functions (e.g., inhibition of EGFR phosphorylation, induction of DNA lesions, and blockade of their repair) into a single molecule. This led to the successful synthesis of a novel and potent combi-molecule JS230. Here, we demonstrated that in resistant prostate cancer cells overexpressing EGFR, it was capable of (a) inhibiting EGFR in a dose-dependent manner, (b) damaging DNA, and (c) sustaining the damage by inhibiting the DNA repair protein poly(ADP-ribose) polymerase (PARP). The triple mechanism of action of JS230 cumulated into growth inhibitory potency superior to that of classical two- or three-drug combinations.

Molecular analysis of the dual targeting of the epidermal growth factor receptor and the O6-methylguanine-DNA methyltransferase with a double arm hybrid molecule

Disordered expression of the epidermal growth factor receptor (EGFR) has been associated with induction of DNA repair genes (e.g. XRCC1, ERCC1) and resistance to radiation and genotoxic drugs. However, our previous work showed that EGFR inhibition did not affect O⁶-methylguanine-DNA methyltransferase (MGMT)-mediated resistance. In order to block uncoupled events associated with EGFR and MGMT, we designed MR30, a single molecule termed “combi-molecule” that contains a quinazoline arm targeted to EGFR and an O⁶-benzylguanine (O⁶-BG) moiety to block MGMT. Molecular analysis of the mechanism of action of its two arms showed that: (a) it could block EGFR phosphorylation, (b) down-regulate the RAF-MAPK and the PI3K-AKT pathways, and (c) covalently modify MGMT through S-benzylation, as confirmed by MALDI analysis of a direct binding assay with isolated MGMT, (d) it induced a dose-dependent down-regulation of MGMT in lung and melanoma cells. The pleiotropic mechanism of action of MR30 culminated into strong growth inhibition (IC₅₀: 0.018-6.02 μM), with superior activity when compared with an equimolar combination of gefitinib (a clinical EGFR inhibitor) and O⁶-BG (a known MGMT inhibitor). Pulse exposure experiments were required to attenuate the contribution of EGFR inhibition to the strong potency of MR30, thereby allowing to achieve the dose level required to sensitize cells to temozolomide (TMZ). Indeed, MR30 significantly sensitized EGFR-MGMT co-expressing cells to TMZ (p<0.05-0.0001). The results in toto suggest that MR30 is the first prototype of agents that may be used against tumours addicted to EGFR and to sensitize resistant tumours co-expressing EGFR and MGMT to TMZ.

Polyamine-Targeting Gefitinib Prodrug and its Near-Infrared Fluorescent Theranostic Derivative for Monitoring Drug Delivery and Lung Cancer Therapy

The therapy of non-small-cell lung cancer (NSCLC) is challenging because of poor prognosis. There are urgent demands for targeting anti-tumor drugs with reliable efficacy and clear pharmacokinetics.

Methods: We designed and synthesized an active tumor-targeting prodrug for the precision therapy of NSCLC. The prodrug polyamine analog Gefitinib (PPG) was derived from the conjugation between a tumor-targeting ligand polyamine analog (PA) and an epidermal growth factor receptor tyrosine kinase inhibitor Gefitinib via a cleavable disulfide linker. Furthermore, the integration of the near-infrared azo-BODIPY fluorophore into the structure of the prodrug PPG yielded an activatable fluorescent theranostics (TPG), which could be used to monitor the in real-time delivery of prodrug PPG and initiate precise medicine in vivo.

Results: PPG efficiently delivered the anti-tumor drug to cancer cells and reduced the serious side effects of the drug to normal cells, thereby increasing the potent of the anti-tumor drug. PPG was not only efficacious for killing Gefitinib-sensitive PC9 cells, but also for inhibiting the growth of Gefitinib-resistant H1650 cells. We provided a new evidence that the tumor-targeting PA ligand could inhibit the Akt pathway in H1650 cells, and had a synergistic effect with Gefitinib for anticancer efficacy. The in vivo results on nude mice bearing tumors of NSCLC cell lines demonstrated that PPG could target tumor lesions and had the expected therapeutic effects. Finally, we used TPG for fluorescent labeling of transbronchial lung biopsy (TBLB) specimens. The results indicated that TPG could provide rapid diagnosis for lung cancer within 4 h.

Conclusion: Our work had identified that PPG could be effectively used for the treatment of Gefitinib-resistance NSCLC in cells and in mice models. The theranostic TPG emerged as a promising fluorescent imaging tool for the application in the therapy and diagnosis of NSCLC.

A type I combi-targeting approach for the design of molecules with enhanced potency against BRCA1/2 mutant- and O6-methylguanine-DNA methyltransferase (mgmt)- expressing tumour cells

BACKGROUND

Mutations of the DNA repair proteins BRCA1/2 are synthetically lethal with the DNA repair enzyme poly(ADP-ribose) polymerase (PARP), which when inhibited, leads to cell death due to the absence of compensatory DNA repair mechanism. The potency of PARP inhibitors has now been clinically proven. However, disappointingly, acquired resistance mediated by the reactivation of wild type BRCA1/2 has been reported. In order to improve their efficacy, trials are ongoing to explore their combinations with temozolomide (TMZ). Here, in order to enhance potency in BRCA1/2-mutant cells, we report on the design of single molecules termed "combi-molecules" capable of not only inhibiting PARP but also damaging DNA like TMZ, which is known to induce a large number of DNA adducts. The majority of these lesions are processed through PARP-dependent base-excision repair machinery. Paradoxically, the least abundant lesion, the O6-methylguanine adduct is the most cytotoxic. Its repair by the O6-methylguanine DNA methyl transferase (MGMT) confers robust resistance to TMZ. Thus, we surmise that a combi-molecule designed to generate the same DNA adducts as TMZ, with an additional ability to block PARP, could induce BRCA1/2 mutant selective potency and a growth inhibitory profile independent of MGMT status.

METHODS

The hydrolysis of EG22 and its stabilized form ZSM02 was analyzed by HPLC and fluorescence spectroscopy. Growth inhibitory potency was determined by SRB assay. PARP inhibition was determined by an enzyme assay and DNA damage by the comet assay. Subcellular distribution was visualized by confocal microscopy.

RESULTS

Studies on EG22 showed that: (a) it inflicted anomalously higher levels of DNA damage than TMZ (b) it induced PARP inhibitory potency in the same range as ANI, a known PARP inhibitor (IC50 = 0.10 μM) (c) it showed strong potency in both BRCA1/2 wild type and mutated cells with 6-fold selectivity for the mutants and it was 65-303-fold more potent than TMZ and 4-63-fold than ANI alone and 3-47-fold than their corresponding equimolar combinations and (d) its potency was independent of MGMT expression.

CONCLUSION

The results in toto suggest that a combi-molecular approach directed at blocking PARP and damaging DNA can lead to single molecules with selective and enhanced potency against BRCA1/2 mutant and with activity independent of MGMT, the major predictive biomarker for resistance to TMZ.

The potential of combi-molecules with DNA-damaging function as anticancer agents

DNA-damaging agents, such as methylating agents, chloroethylating agents and platinum-based agents, have been extensively used as anticancer drugs. However, the side effects, high toxicity, lack of selectivity and resistance severely limit their clinical applications. In recent years, a strategy combining a DNA-damaging agent with a bioactive molecule (e.g., enzyme inhibitors) or carrier (e.g., steroid hormone and DNA intercalators) to produce a new 'combi-molecule' with improved efficacy or selectivity has been attempted to overcome these drawbacks. The combi-molecule simultaneously acts on two targets and is expected to possess better potency than the parent compounds. Many studies have shown DNA-damaging combi-molecules exhibiting excellent anticancer activity in vitro and in vivo. This review focuses on the development of combi-molecules, which possess increased DNA-damaging potency, anticancer efficacy and tumor selectivity and reduced side reactions than the parent compounds. The future opportunities and challenges in the discovery of combi-molecules were also discussed.

Target modulation by a kinase inhibitor engineered to induce a tandem blockade of the epidermal growth factor receptor (EGFR) and c-Src: the concept of type III combi-targeting

Cancer cells are characterized by a complex network of interrelated and compensatory signaling driven by multiple kinases that reduce their sensitivity to targeted therapy. Therefore, strategies directed at inhibiting two or more kinases are required to robustly block the growth of refractory tumour cells. Here we report on a novel strategy to promote sustained inhibition of two oncogenic kinases (Kin-1 and Kin-2) by designing a molecule K1-K2, termed "combi-molecule", to induce a tandem blockade of Kin-1 and Kin-2, as an intact structure and to be further hydrolyzed to two inhibitors K1 and K2 directed at Kin-1 and Kin-2, respectively. We chose to target EGFR (Kin-1) and c-Src (Kin-2), two tyrosine kinases known to synergize to promote tumour growth and progression. Variation of K1-K2 linkers led to AL776, our first optimized EGFR-c-Src targeting prototype. Here we showed that: (a) AL776 blocked EGFR and c-Src as an intact structure using an in vitro kinase assay (IC50 EGFR = 0.12 μM and IC50 c-Src = 3 nM), (b) it could release K1 (AL621, a nanomolar EGFR inhibitor) and K2 (dasatinib, a clinically approved Abl/c-Src inhibitor) by hydrolytic cleavage both in vitro and in vivo, (c) it could robustly inhibit phosphorylation of EGFR and c-Src (0.25-1 μM) in cells, (d) it induced 2-4 fold stronger growth inhibition than gefitinib or dasatinib and apoptosis at concentrations as low as 1 μM, and, (e) blocked motility and invasion at sub-micromolar doses in the highly invasive 4T1 and MDA-MB-231 cells. Despite its size (MW = 1032), AL776 blocked phosphorylation of EGFR and c-Src in 4T1 tumours in vivo. We now term this new targeting model consisting of designing a kinase inhibitor K1-K2 to target Kin-1 and Kin-2, and to further release two inhibitors K1 and K2 of the latter kinases, "type III combi-targeting".

"Combi-targeting" mitozolomide: conferring novel signaling inhibitory properties to an abandoned DNA alkylating agent in the treatment of advanced prostate cancer

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.

Synthesis and studies on three-compartment flavone-containing combi-molecules designed to target EGFR, DNA, and MEK

In order to induce a tandem targeting of EGFR, DNA, and MEK, we built complex combi-molecules containing an EGFR targeting quinazoline and an aminoethyltriazene moiety linking the entire molecule to PD98059. Two complex molecules were synthesized: one with a short aminoethyl spacer, AL232, and the other AL414 with a longer aminoethylaminoethyl spacer. AL414 was a more potent inhibitor of EGFR tyrosine kinase than AL232. Both combi-molecules blocked EGFR phosphorylation in whole cells and downregulated extracellular signaling-regulated kinases (ERK1,2). However, only AL414 was capable of inducing DNA damage. Thus, it was taken in vivo for metabolic analysis. The results showed that 3 h after injection, AL414 was hydrolyzed to an EGFR inhibitor FD105, which was further acetylated to FD105Ac, a more potent inhibitor of EGFR. The detected flavone derivative was PD98059 linked to the hydroxyalkyl moiety resulting from the decomposition of the alkyldiazonium species. Independent synthesis of the latter metabolite and further in vitro analysis showed that it was deprived of antiproliferative activity. The results in toto suggest that while AL414 is a three-compartment combi-molecule, only the EGFR and DNA targeting species can be released and the cleavage to the intact MEK inhibitor PD98059 was mitigated by the stability of the carbamate.

The combi-targeting concept: selective targeting of the epidermal growth factor receptor- and Her2-expressing cancer cells by the complex combi-molecule RB24

Within the context of a new tumor-targeting strategy termed "combi-targeting," we designed RB24 to inhibit epidermal growth factor receptor (EGFR) or Her2 phosphorylation and to further degrade upon hydrolysis to 4-(3'-bromophenylamino)-6-aminoquinazoline (RB10; another EGFR/Her2 inhibitor) plus a strong DNA-alkylating species. 6-(3-Acetoxymethyl-3-methyltriazenyl)-4-(3'-bromophenylamino)quinazoline (RB24) showed significant antiproliferative activity against human breast cancer cells, and transfection of one such cell line, MDA-MB-435, with ErbB1 or ErbB2 (Her2) dramatically enhanced cell death by apoptosis. RB24 was capable of releasing 2- to 3-fold higher levels of RB10 in the transfectants than in their wild-type counterparts. More importantly, RB10 was abundantly distributed in the perinuclear region of the cells, and its elevated levels in the ErbB transfectants were concomitant with increased levels of DNA lesions in the latter cells. This selectivity could be abolished by coincubation of the cells with exogenous RB10, suggesting that the entire combi-molecule may bind primarily to its cognate perinuclear sites before degradation. This localization may exert a bystander effect, allowing the alkylating species to be abundantly propagated into the nucleus. Cell response to this novel targeting mechanism was mediated by 1) activation of c-Jun NH(2)-terminal kinase in response to DNA damage and 2) down-regulation of Bad through blockade of EGFR tyrosine kinase activity: two events that cooperatively converged into enhancement of apoptosis in the oncogene-transfected cells.