Discovery of Oral Anticancer 1,2-Bis(hydroxymethyl)benzo[g]pyrrolo[2,1-a]phthalazine Hybrids That Inhibit Angiogenesis and Induce DNA Cross-Links.

Designing hybrid molecules with dual functions is one approach to improve the therapeutic efficacy of combination treatment. We have previously conjugated phthalazine and bis(hydroxymethyl)pyrrole pharmacophores to form hybrids bearing antiangiogenesis and DNA interstrand cross-linking activities. To improve the bioavailability, we adopted a benzology approach to design and synthesize a new series of 1,2-bis(hydroxymethyl)benzo[g]pyrrolo[2,1-a]phthalazines. These new hybrids retained the dual functions and could be formulated into vehicles for intravenous and oral administration. Among them, we demonstrated that compound 19a with dimethylamine at the C6 position markedly suppressed the tumor growth of human small cell lung cancer cell line H526, squamous lung cancer cell line H520, and renal cancer cell line 786-O in nude mice, implying that compound 19a is a broad-spectrum anticancer agent. Our results implicated that the conjugation of antiangiogenic and DNA cross-linking is likely to be a helpful approach to improving the efficacy of combination therapy.

Design, synthesis and antitumour evaluation of pyrrolo[1,2-f]-phenanthridine and dibenzo[f,h]pyrrolo[1,2-b]isoquinoline derivatives.

A series of 1,2-bis(hydroxymethyl)pyrrolo[1,2-f]phenanthridine derivatives and their alkyl (ethyl and isopropyl) carbamates and 12,13-bis(hydroxymethyl)-9,14-dihydro-dibenzo[f,h]pyrrolo[1,2-b]isoquinoline derivatives were synthesized for antiproliferative evaluation. The preliminary antitumour studies revealed that these two types of bis(hydroxymethyl) derivatives showed significant antitumour activities and were able to inhibit the growth of various human tumour cell lines in vitro. Several of the derivatives were demonstrated to cause DNA interstrand cross-links by an alkaline agarose gel shifting assay. These conjugates were cytotoxic to a variety of cancer cell lines by inducing DNA damage, delaying cell cycle progression in the G2/M phase and triggering apoptosis. Compound 21a, dissolved in a vehicle suitable for intravenous administration, was selected for antitumour studies in animal models. We demonstrated that at a dose that did not cause body weight loss in mice, compound 21a could significantly suppress the growth of tumour xenografts of human lung cancer H460 and colorectal cancer HCT-116 cells in nude mice. Our present results confirm the antitumour activities of these conjugates.

Design and Synthesis of 1,2-Bis(hydroxymethyl)pyrrolo[2,1- a]phthalazine Hybrids as Potent Anticancer Agents that Inhibit Angiogenesis and Induce DNA Interstrand Cross-links.

Hybrid molecules are composed of two pharmacophores with different biological activities. Here, we conjugated phthalazine moieties (antiangiogenetic pharmacophore) and bis(hydroxymethyl)pyrrole moieties (DNA cross-linking agent) to form a series of bis(hydroxymethyl)pyrrolo[2,1- a]phthalazine hybrids. These conjugates were cytotoxic to a variety of cancer cell lines by inducing DNA damage, arresting cell cycle progression at the G2/M phase, triggering apoptosis, and inhibiting vascular endothelial growth factor receptor 2 (VEGFR-2) in endothelial cells. Among them, compound 29d encapsulated in a liposomal formulation (e.g., 29dL) significantly suppressed the growth of small-cell lung cancer cell (H526) xenografts in mice. Based on immunohistochemical staining, the tumor xenografts in mice treated with 29dL showed time-dependent decreases in the intensity of CD31, a marker of blood vessels, whereas the intensity of γ-H2AX, a marker of DNA damage, increased. The present data revealed that the conjugation of antiangiogenic and DNA-damaging agents can generate potential hybrid agents for cancer treatment.

A Low-Toxicity DNA-Alkylating N-Mustard-Quinoline Conjugate with Preferential Sequence Specificity Exerts Potent Antitumor Activity Against Colorectal Cancer.

Efficacy and safety are fundamental prerequisites for anticancer drug development. In the present study, we explored the anti-colorectal cancer (CRC) activity of SL-1, a DNA-directed N-mustard-quinoline conjugate. The N-mustard moiety in SL-1 induced DNA strand breaks, interstrand cross-links (ICLs), G2/M arrest, and apoptosis, whereas its quinoline moiety preferentially directed SL-1 to target the selective guanine sequence 5'-G-G/C-N-G-C/T-3'. Notably, SL-1 was highly cytotoxic to various CRC cell lines. Experiments using xenograft models revealed that SL-1 was more potent than 5-fluorouracil (5-FU) and oxaliplatin for suppressing the growth of RKO and RKO-E6 (oxaliplatin-resistant subline) cells as well as metastatic SW620 cells. In addition, SL-1 combined with 5-FU was more effective than oxaliplatin and 5-FU for suppressing RKO or SW620 cell growth in mice. Significantly, compared with cisplatin, oxaliplatin, or 5-FU, SL-1 alone or in combination with 5-FU did not cause obvious kidney or liver toxicity in ICR mice. In summary, SL-1, a DNA-directed alkylating agent, is established as an anti-CRC agent with high efficacy and low toxicity and thus warrants further development for the treatment of CRC patients.

Novel N-mustard-benzimidazoles/benzothiazoles Hybrids, Synthesis and Anticancer Evaluation.

BACKGROUND: Bendamustine, an N-mustard-benzoimidazole hybrid conjugate, was recently approved for the treatment of chronic lymphocytic leukemia. However, the short half-life of bendamustine may limit its clinical applications. OBJECTIVE: The purpose of this study is to design and synthesize compounds with a more favorable pharmacokinetic profile. METHODS: We synthesized a series of hybrid molecules comprising a phenyl N-mustard moiety and benzothiazole or benzimidazole scaffold linked via a urea linker and evaluated their antitumor activity and plasma stability. RESULTS: We revealed that these agents exhibited significant cytotoxicity against a panel of human lymphoblastic leukemia and human solid tumor cells in culture. Human lymphoblastic leukemia CCRM-CEM cells were the most sensitive to the tested compounds. In general, the new hybrids were as potent as cisplatin, but significantly more cytotoxic than bendamustine. Phenyl N-mustard-benzothiazole compound 27d and phenyl N-mustardbenzimidaloe compound 32b possessed significant cytotoxicity and led to apoptotic death in the treated tumor cells. These two agents were able to induce DNA interstrand cross-linking and arrested cell cycle progression at the G2/M phase. Furthermore, we showed that these new hybrids were more chemically stable than bendamustine in rat plasma. CONCLUSION: Our results suggest that conjugation of phenyl N-mustard pharmacophore at C6 of benzimidazole or at C8 of the benzothiazole ring via a urea linker is likely an approach to increase the chemical stability and bioavailability. Highlights ⇒ Series of benzimidazoles and benzothiazoles linked to N-mustard were synthesized. ⇒ The newly synthesized derivatives induced DNA interstrand cross-links. ⇒ These derivatives induced cell cycle arrest in the G2/M phase and triggered apoptosis in H460 cells. ⇒ The new compounds are more cytotoxic than bendamustine. ⇒ The new compounds were chemically more stable than bendamustine in rat plasma.

P-glycoprotein attenuates DNA repair activity in multidrug-resistant cells by acting through the Cbp-Csk-Src cascade.

Recent studies have demonstrated that P-glycoprotein (P-gp) expression impairs DNA interstrand cross-linking agent-induced DNA repair efficiency in multidrug-resistant (MDR) cells. To date, the detailed molecular mechanisms underlying how P-gp interferes with Src activation and subsequent DNA repair activity remain unclear. In this study, we determined that the C-terminal Src kinase-binding protein (Cbp) signaling pathway involved in the negative control of Src activation is enhanced in MDR cells. We also demonstrated that cells that ectopically express P-gp exhibit reduced activation of DNA damage response regulators, such as ATM, Chk2, Braca1 and Nbs1 and hence attenuated DNA double-strand break repair capacity and become more susceptible than vector control cells to DNA interstrand cross-linking (ICL) agents. Moreover, we demonstrated that P-gp can not only interact with Cbp and Src but also enhance the formation of inhibitory C-terminal Src kinase (Csk)-Cbp complexes that reduce phosphorylation of the Src activation residue Y416 and increase phosphorylation of the Src negative regulatory residue Y527. Notably, suppression of Cbp expression in MDR cells restores cisplatin-induced Src activation, improves DNA repair capacity, and increases resistance to ICL agents. Ectopic expression of Cbp attenuates cisplatin-induced Src activation and increases the susceptibility of cells to ICL agents. Together, the current results indicate that P-gp inhibits DNA repair activity by modulating Src activation via Cbp-Csk-Src cascade. These results suggest that DNA ICL agents are likely to have therapeutic potential against MDR cells with P-gp-overexpression.

Novel indolizino[8,7-b]indole hybrids as anti-small cell lung cancer agents: Regioselective modulation of topoisomerase II inhibitory and DNA crosslinking activities.

A novel series of bis(hydroxymethyl)indolizino[8,7-b]indole hybrids composed of ß-carboline (topoisomerase I/II inhibition) and bis(hydroxymethyl)pyrrole (DNA cross-linking) are synthesized for antitumor evaluation. Of tumor cell lines tested, small cell lung cancer (SCLC) cell lines are the most sensitive to the newly synthesized compounds. These hybrids induce cell cycle arrest at the G2/M phase, trigger tumor cell apoptotic death, and display diverse mechanisms of action involving topoisomerase II (Topo II) inhibition and induction of DNA cross-linking. Intriguingly, the substituent at N11 (H or Me) plays a critical role in modulating Topo II inhibition and DNA cross-linking activities. N11-Me derivatives predispose to induce DNA crosslinks, whereas N11-H derivatives potently inhibit Topo II. Computational analysis implicates that N11-Me restrict the torsion angles of the two adjacent OH on pyrrole resulting in a favorable of DNA cross-linking. Among these hybrids, compound 17a with N11-H is more effective than cisplatin and etoposide, but as potent as irinotecan, against the growth of SCLC H526 cells in xenograft model.

BO-1055, a novel DNA cross-linking agent with remarkable low myelotoxicity shows potent activity in sarcoma models.

DNA damaging agents cause rapid shrinkage of tumors and form the basis of chemotherapy for sarcomas despite significant toxicities. Drugs having superior efficacy and wider therapeutic windows are needed to improve patient outcomes. We used cell proliferation and apoptosis assays in sarcoma cell lines and benign cells; γ-H2AX expression, comet assay, immunoblot analyses and drug combination studies in vitro and in patient derived xenograft (PDX) models. BO-1055 caused apoptosis and cell death in a concentration and time dependent manner in sarcoma cell lines. BO-1055 had potent activity (submicromolar IC50) against Ewing sarcoma and rhabdomyosarcoma, intermediate activity in DSRCT (IC50 = 2-3µM) and very weak activity in osteosarcoma (IC50 >10µM) cell lines. BO-1055 exhibited a wide therapeutic window compared to other DNA damaging drugs. BO-1055 induced more DNA double strand breaks and γH2AX expression in cancer cells compared to benign cells. BO-1055 showed inhibition of tumor growth in A673 xenografts and caused tumor regression in cyclophosphamide resistant patient-derived Ewing sarcoma xenografts and A204 xenografts. Combination of BO-1055 and irinotecan demonstrated synergism in Ewing sarcoma PDX models. Potent activity on sarcoma cells and its relative lack of toxicity presents a strong rationale for further development of BO-1055 as a therapeutic agent.

Derivatives of 6-cinnamamido-quinoline-4-carboxamide impair lysosome function and induce apoptosis.

Autophagy is a lysosomal degradative process that protects cancer cells from multiple types of stress. In this study, we synthesized a series of derivatives of 6-cinnamamido-quinoline-4-carboxamide (CiQ), and investigated their effects on the proliferation and autophagy of cancer cells in vitro. These derivatives effectively inhibited the proliferation of a broad spectrum of cancer cell lines. Further study revealed that CiQ derivatives may induce autophagy and result in disruption of autophagy propagation. Consequently, these derivatives triggered massive apoptosis, as evidenced by caspase-9 activation and PARP cleavage. Blockage of autophagy by depletion of autophagy related gene ATG5 or BECN1 considerably alleviated CiQ-induced cell death, indicating that autophagy may mediate CiQ-induced cell death. Furthermore, treatment with CiQ derivatives increased lysosome membrane permeability (LMP) and enhanced accumulation of ubiquitinated proteins, which collectively indicate impaired lysosome function. In addition, treatment of cells with CiQ derivatives activated extracellular signal-regulated kinase (ERK); abrogation of ERK activation, either by treating cells with U0126, an inhibitor of mitogen-activated protein/ERK kinase 1 (MEK1), or by ectopically overexpressing a dominant-negative MEK1, significantly reduced CiQ derivative-induced LMP, LC3 and p62 accumulation, and cytotoxicity. These results indicate that CiQ derivatives activate ERK and disrupt lysosome function, thereby altering autophagic flux and resulting in apoptotic cell death.

A Potent Derivative of Indolizino[6,7-b]Indole for Treatment of Human Non-Small Cell Lung Cancer Cells.

The therapeutic effect in non-small cell lung cancer (NSCLC) patients is limited because of intrinsic and acquired resistance. Thus, an unmet need exists for the development of new drugs to improve the therapeutic efficacy in NSCLC patients. In this study, the novel small molecule indolizino[6,7-b]indole derivative BO-1978 was selected to evaluate its therapeutic effects on NSCLC and its preclinical toxicity in animal models. An in vitro cytotoxicity assay revealed that BO-1978 significantly suppressed the growth of various NSCLC cell lines with or without mutations in epidermal growth factor receptor (EGFR). Mechanistically, we demonstrated that BO-1978 exhibited multiple modes of action, including inhibition of topoisomerase I/II and induction of DNA cross-linking. Treatment of NSCLC cells with BO-1978 caused DNA damage, disturbed cell cycle progression, and triggered apoptotic cell death. Furthermore, BO-1978 significantly suppressed the growth of EGFR wild-type and mutant NSCLC tumors in xenograft tumor and orthotopic lung tumor models with negligible body weight loss. The combination of BO-1978 with gefitinib further suppressed EGFR mutant NSCLC cell growth in xenograft tumor and orthotopic lung tumor models. Preclinical toxicity studies showed that BO-1978 administration did not cause apparent toxicity in mice. Based on its significant therapeutic efficacy and low drug toxicity, BO-1978 is a potential therapeutic agent for treatment of NSCLC.

Repairing of N-mustard derivative BO-1055 induced DNA damage requires NER, HR, and MGMT-dependent DNA repair mechanisms.

Alkylating agents are frequently used as first-line chemotherapeutics for various newly diagnosed cancers. Disruption of genome integrity by such agents can lead to cell lethality if DNA lesions are not removed. Several DNA repair mechanisms participate in the recovery of mono- or bi-functional DNA alkylation. Thus, DNA repair capacity is correlated with the therapeutic response. Here, we assessed the function of novel water-soluble N-mustard BO-1055 (ureidomustin) in DNA damage response and repair mechanisms. As expected, BO-1055 induces ATM and ATR-mediated DNA damage response cascades, including downstream Chk1/Chk2 phosphorylation, S/G2 cell-cycle arrest, and cell death. Further investigation revealed that cell survival sensitivity to BO-1055 is comparable to that of mitomycin C. Both compounds require nucleotide excision repair and homologous recombination, but not non-homologous end-joining, to repair conventional cross-linking DNA damage. Interestingly and unlike mitomycin C and melphalan, MGMT activity was also observed in BO-1055 damage repair systems, which reflects the occurrence of O-alkyl DNA lesions. Combined treatment with ATM/ATR kinase inhibitors significantly increases BO-1055 sensitivity. Our study pinpoints that BO-1055 can be used for treating tumors that with deficient NER, HR, and MGMT DNA repair genes, or for synergistic therapy in tumors that DNA damage response have been suppressed.

The synthesis and biological evaluation of new DNA-directed alkylating agents, phenyl N-mustard-4-anilinoquinoline conjugates containing a urea linker.

We synthesized a series of phenyl N-mustard-4-anilinoquinoline conjugates to study their antitumorigenic effects. These agents were prepared by the condensation of 4-[N,N-bis(2-chloroethyl)amino]phenyl isocyanate with 6-amino-4-methylamino or 4-anilinoquinolines. The structure-activity relationship (SAR) studies revealed that the C2-methylquinoline derivatives (18a-o) were generally more cytotoxic than the C2-phenylquinoline conjugates (23a-d) in inhibiting the cell growth of various human tumor cell lines in vitro. However, the methylamino or aniline substituents at C4 of quinoline did not influence the cytotoxic effects. The title conjugates were capable of inducing DNA cross-linking and promoting cell-cycle arrest at the G2/M phase. This study demonstrates that phenyl N-mustard-4-anilinoquinoline conjugates are generally more potent than phenyl N-mustard-4-anilinoquinazoline conjugates against the cell growth of various tumor cell-lines.

PI3K Inhibition Augments the Therapeutic Efficacy of a 3a-aza-Cyclopenta[α]indene Derivative in Lung Cancer Cells.

The synergistic targeting of DNA damage and DNA repair is a promising strategy for the development of new chemotherapeutic agents for human lung cancer. The DNA interstrand cross-linking agent BO-1509, a derivative of 3a-aza-cyclopenta[α]indene, was synthesized and combined with the phosphoinositide 3-kinase (PI3K) inhibitor LY294002 to treat human lung cancer cells. Our results showed that the BO-1509 and LY294002 combination synergistically killed lung cancer cells in culture and also suppressed the growth of lung cancer xenografts in mice, including those derived from gefitinib-resistant cells. We also found that LY294002 suppressed the induction of several DNA repair proteins by BO-1509 and inhibited the nuclear translocation of Rad51. On the basis of the results of the γH2AX foci formation assays, LY294002 apparently inhibited the repair of DNA damage that was induced by BO-1509. According to the complete blood profile, biochemical enzyme analysis, and histopathologic analysis of major organs, no apparent toxicity was observed in mice treated with BO-1509 alone or in combination with LY294002. Our results suggest that the combination of a DNA cross-linking agent with a PI3K inhibitor is a feasible strategy for the treatment of patients with lung cancer.

Inhibition of autophagy enhances DNA damage-induced apoptosis by disrupting CHK1-dependent S phase arrest.

DNA damage has been shown to induce autophagy, but the role of autophagy in the DNA damage response and cell fate is not fully understood. BO-1012, a bifunctional alkylating derivative of 3a-aza-cyclopenta[a]indene, is a potent DNA interstrand cross-linking agent with anticancer activity. In this study, BO-1012 was found to reduce DNA synthesis, inhibit S phase progression, and induce phosphorylation of histone H2AX on serine 139 (γH2AX) exclusively in S phase cells. Both CHK1 and CHK2 were phosphorylated in response to BO-1012 treatment, but only depletion of CHK1, but not CHK2, impaired BO-1012-induced S phase arrest and facilitated the entry of γH2AX-positive cells into G2 phase. CHK1 depletion also significantly enhanced BO-1012-induced cell death and apoptosis. These results indicate that BO-1012-induced S phase arrest is a CHK1-dependent pro-survival response. BO-1012 also resulted in marked induction of acidic vesicular organelle (AVO) formation and microtubule-associated protein 1 light chain 3 (LC3) processing and redistribution, features characteristic of autophagy. Depletion of ATG7 or co-treatment of cells with BO-1012 and either 3-methyladenine or bafilomycin A1, two inhibitors of autophagy, not only reduced CHK1 phosphorylation and disrupted S phase arrest, but also increased cleavage of caspase-9 and PARP, and cell death. These results suggest that cells initiate S phase arrest and autophagy as pro-survival responses to BO-1012-induced DNA damage, and that suppression of autophagy enhances BO-1012-induced apoptosis via disruption of CHK1-dependent S phase arrest.

Design and synthesis of potent antitumor water-soluble phenyl N-mustard-benzenealkylamide conjugates via a bioisostere approach.

A series of new, water-soluble phenyl N-mustard-benzenealkylamide conjugates containing hydrophilic ω-dialkylaminoalkylamide or ω-cyclic aminoalkylamide moieties were synthesized via a bioisostere approach. These compounds have a broad spectrum of antitumor activity against a panel of human tumor cell lines. Of these derivatives, compound 18b effectively suppressed the growth of colon cancer (HCT-116), prostate cancer (PC3), and lung cancer (H460) xenografts. The growth of HCT-116 xenografts was almost completely suppressed when co-treated with compound 18b and 5-fluorouracil. Furthermore, compound 18b can induce DNA cross-linking and cell-cycle arrest at the G2/M phase. Early preclinical studies, including pharmacokinetics in rats, inhibition of the hERG, and 14 days of acute intravenous injection toxicity, suggest that compound 18b is a promising candidate for further preclinical studies.

The development of bis(hydroxymethyl)pyrrole analogs as bifunctional DNA cross-linking agents and their chemotherapeutic potential.

Bifunctional DNA cross-linking agents are widely used as chemotherapeutic agents in clinics. The advance in the development of these agents as potential antitumor agents has generated various types of bis(hydroxymethyl)pyrrole analogs. In order to develop highly effective anticancer agents, it is necessary to understand the chemophysical properties, structure-activity relationships, therapeutic potency, toxicity/safety, and pharmacokinetics of these DNA cross-linking agents. This review presents an overview of the recent advances in developing various types of bis(hydroxymethyl)pyrrole analogs with potential antitumor activity to provide more information for future drug design and strategies for combination chemotherapy. The rational drug design, chemical syntheses, antitumor activity, mechanism of action, and development of combined chemotherapy regimens, including a DNA repair inhibitor, are discussed.

Novel antitumor indolizino[6,7-b]indoles with multiple modes of action: DNA cross-linking and topoisomerase I and II inhibition.

A series of bis(hydroxymethyl)indolizino[6,7-b]indoles and their bis(alkylcarbamates) were synthesized for antitumor studies. These agents were designed as hybrid molecules of ß-carboline (topoisomerase inhibition moiety) and bis(hydroxymethyl)pyrrole (DNA cross-linking moiety). The preliminary antitumor studies indicated that these agents exhibited significant cytotoxicity against a variety of human tumor cells in vitro. Treatment of human breast carcinoma MX-1 xenograft-bearing nude mice with compounds 18b and 28c achieved more than 99% tumor remission. We also observed that 18a displayed potent therapeutic efficacy against human lung adenocarcinoma A549 and colon cancer HT-29 xenografts. These results revealed that compound 18a was more potent than irinotecan against HT-29 cells and was as potent as irinotecan against A549 cells in xenograft models. Furthermore, we demonstrated that these derivatives possess multiple modes of action, such as induction of DNA cross-linking, inhibition of topoisomerase I and II, and cell-cycle arrest at the S-phase.

Determination of tissue distribution of potent antitumor agent ureidomustin (BO-1055) by HPLC and its pharmacokinetic application in rats.

Ureidomustin hydrochloride (BO-1055) was designed as a water-soluble nitrogen-mustard, which exhibited potent anticancer activity and was selected as a candidate for preclinical studies. However, up to date, there is rarely an easy and economic method to quantize ureidomustin in the biological samples. The aim of this study is to develop a simple yet valid quantization method to tackle this challenge. Here we present a combined high-performance liquid chromatography with photodiode array (HPLC-PDA) method in quantizing the ureidomustin in the plasma and various organs of Sprague-Dawley rats. The method was validated in terms of precision, accuracy, and extraction recovery. Furthermore, the established method was applied to study pharmacokinetics of ureidomustin in the rat's plasma and verified via a liquid chromatography tandem mass spectrometry (LC-MS/MS) method. Calibration curves of the plasma and organ samples were falling at the range between 0.5-50µg/mL and 0.1-50µg/mL (r(2)≥0.999 and CV≤±15%), respectively. The limits of detection (LOD) were 0.1µg/mL for plasma samples and 0.05µg/mL for organ samples, while the detection limits of quantification (LOQ) were 0.5µg/mL for plasma samples and 0.1µg/mL for organ samples. The average recovery of ureidomustin was about 83%. These results demonstrated a linear pharmacokinetic pattern at dosages of 10 and 30mg/kg. The pharmacokinetic data revealed that ureidomustin was best fitted to a two-compartment model with a rapid distribution phase and a slow elimination phase. Besides, after a short intravenous administration time at the dose of 10mg/kg, ureidomustin was found to be quickly distributed to all organs in rats, accumulated mainly in the kidney, and only a limited amount was detected in the brain.