Poly(ADP-ribose) polymerase inhibitors in cancer treatment: a clinical perspective

An insight into recent developments in imidazole based heterocyclic compounds as anticancer agents: Synthesis, SARs, and mechanism of actions

Among all non-communicable diseases, cancer is ranked as the second most common cause of death and is rising constantly. While cancer treatments mainly include radiation therapy, chemotherapy, and surgery; chemotherapy is considered the most commonly employed and effective treatment. Most of the chemotherapeutic agents are azoles based compounds and imidazole is one such insightful azole. The anticancer properties of imidazole-based compounds have been thoroughly explored in recent years and all monosubstituted, disubstituted, trisubstituted, and tetrasubstituted imidazoles have been explored for their anticancer activities. Along with these compounds, other imidazole-based compounds like 1,3-dihydro-2H-imidazole-2-thiones, imidazolones, and poly imidazole compounds have also been explored for their anticancer activities. The activities of these compounds are heavily influenced by their structural resemblance to combretastatin 4A and ABI (2-aryl-4-benzoyl-imidazole). The lead compounds were highly active on breast, gastric, colon, ovarian, cervical, bone marrow, melanoma, prostate, lung, leukemic, neuroblastoma, liver, Ehrlich, melanoma, and pancreatic cancers. The targets of these leads like tubulin, heme oxygenases, VEGF, tyrosine kinases, EGFR, and others have also been explored. The exploration of the anticancer potential of substituted imidazole compounds is the main topic of this review including synthesis, SAR, and mechanism.

Pyrrole-containing hybrids as potential anticancer agents: An insight into current developments and structure-activity relationships

Cancer poses a significant threat to human health. Therefore, it is urgent to develop potent anti-cancer drugs with excellent inhibitory activity and no toxic side effects. Pyrrole and its derivatives are privileged heterocyclic compounds with significant diverse pharmacological effects. These compounds can target various aspects of cancer cells and have been applied in clinical settings or are undergoing clinical trials. As a result, pyrrole has emerged as a promising drug scaffold and has been further probed to get novel entities for the treatment of cancer. This article reviews recent research progress on anti-cancer drugs containing pyrrole. It focuses on the mechanism of action, biological activity, and structure-activity relationships of pyrrole derivatives, aiming to assist in designing and synthesizing innovative pyrrole-based anti-cancer compounds.

Combination Therapy with Trastuzumab and Niraparib: Quantifying Early Proliferative Alterations in HER2+ Breast Cancer Models

HER2-targeted treatments have improved survival rates in HER2+ breast cancer patients, yet poor responsiveness remains a major clinical obstacle. Recently, HER2+ breast cancer cells, both resistant and responsive to HER2-targeted therapies, have demonstrated sensitivity to poly-(ADP-ribose) polymerase (PARP) inhibition, independent of DNA repair deficiencies. This study seeks to describe biological factors that precede cell viability changes in response to the combination of trastuzumab and PARP inhibition. Treatment response was evaluated in HER2+ and HER2- breast cancer cells. Further, we evaluated the utility of 3'-Deoxy-3'-[18F]-fluorothymidine positron emission tomography ([18F]FLT-PET) imaging for early response assessment in a HER2+ patient derived xenograft (PDX) model of breast cancer. In vitro, we observed decreased cell viability. In vivo, we observed decreased inhibition in tumor growth in combination therapies, compared to vehicle and monotherapy-treated cohorts. Early assessment of cellular proliferation corresponds to endpoint cell viability. Standard summary statistics of [18F]FLT uptake from PET were insensitive to early proliferative changes. Meanwhile, histogram analysis of [18F]FLT uptake indicated the potential translatability of imaging proliferation biomarkers. This study highlights the potential of combined trastuzumab and PARP inhibition in HER2+ breast cancer, while demonstrating a need for optimization of [18F]FLT-PET quantification in heterogeneous models of HER2+ breast cancer.

Unveiling the mechanistic roles of chlorine substituted phthalazinone-based compounds containing chlorophenyl moiety towards the differential inhibition of poly (ADP-ribose) polymerase-1 in the treatment of lung cancer

PARP-1 has become an attractive target in cancer treatment owing to its significant role in breast and ovarian cancers. The design of highly selective and effective poly (ADP ribose) polymerase-1 inhibitors has significant therapeutic advantages and has remained the core of several PARP-1-based drug discovery research. The pharmacophoric relevance of a chlorine substituent in a recent study led to the design of compounds 11c (meta-chlorophenyl) and 11d (para-chlorophenyl). In this study, we resolved the mechanistic effects of the changes in chlorine positional orientation, which underlie the inhibitory potencies and selectivity exhibited disparately by 11c and 11d. Compared to 11d, among other multiple higher-affinity complementary interactions with key site residues, the meta-Cl positioning in 11c facilitated its optimal motion and orientation towards conserved residues Arg878 and Asp766 with consistent pi-cation and pi-anion interactions, respectively, thereby favoring the stability of the ligand towards PARP-1. These could account for the higher inhibitory potency exhibited by 11c relative to 11d against PARP-1. The thermodynamics calculation revealed that 11c had a relatively higher total binding energy (ΔGbind) than 11d. We also observed that 11d displayed high deviations, compared to 11c, indicative of its unstable binding orientation. Furthermore, we reported in this study that the high involvement of electrostatic and van der Waal effects potentiated the binding affinity and strength of 11c (ΔE_vdW = -50.58 and ΔE_ele = -27.20) relative to 11d (ΔE_vdW = -49.46 and ΔE_ele = -19.96) at PARP-1 binding pocket. We believe the findings in this current study would provide valuable insights into the design of selective PARP-1 inhibitors containing chlorine substituent for cancer treatment, including lung cancer.Communicated by Ramaswamy H. Sarma.

Synthesis and in vitro biological evaluation of 3-ethyl-1,5-naphthyridin-2(1H)-one derivatives as potent PARP-1 selective inhibitors and PARP-1 DNA trappers

Inhibition of poly (ADP-ribose) polymerase (PARP) has been applied with great success in the clinical treatment of homologous recombination-deficient malignancy. Recent study demonstrated that not only PARP-1 inhibition but also DNA trapping contributes to the efficacy in BRCA mutant tumors and the toxicities results from the poor selectivity of PARP-1 over PARP-2 as well as their DNA trapping. Herein, a series of 3-ethyl-1,5-naphthyridin-2(1H)-one derivatives (7a-7l, 8a-8n) were synthesized and identified as PARP-1 selective inhibitors and PARP-1 DNA trappers. Among them, compound 8m was found to be highly potent and selective. It inhibited PARP-1 activity and BRCA mutant DLD-1 cell activity with IC₅₀ values of 0.49 nM and 4.82 nM, and the in vitro DNA trapping efficacy of compound 8m was 1.85 nM. Compared with AZD5305, compound 8m significantly improved the selectivity of PARP-1 over PARP-2 as well. Compound 8m was>1000-fold selective for PARP-1 DNA trapping over PARP-2.

CXCR4 inhibitor, AMD3100, down-regulates PARP1 expression and Synergizes with olaparib causing severe DNA damage in BRCA-proficient triple-negative breast cancer

Poly ADP-ribose polymerase inhibitor (PARPi) treatment is effective in triple-negative breast cancer (TNBC) with BRCA mutation. However, its efficacy in BRCA-proficient TNBC remains unexplored. It is, therefore, an exciting proposition to broaden the indication of PARPi for BRCA-proficient TNBC patients. Chemokine receptor (CXCR4) is a transmembrane G protein-coupled receptor, which is involved in cell migration, proliferation, apoptosis, and damage repair, and it initiates many signalling pathways. Although administration of CXCR4 inhibitor alone is not ideal as a target drug, it can play a strong synergistic role in combination with other drugs. We explored the effect of CXCR4 and PARP1 on tumour cell proliferation, migration, metastasis, and apoptosis in vitro and in vivo and found that a CXCR4 inhibitor, AMD3100, enhanced the anti-tumour effect of PARP1 inhibitor, olaparib, on BRCA-proficient TNBC. When CXCR4 was inhibited and silenced, DNA damage repair and DNA replication fork activity were suppressed by up-regulating caspase-3-mediated increase in PARP1 cleavage; in combination with the inhibition of PARP1, AMD3100 resulted in the accumulation of fatal DNA damage and induction of apoptosis. This combination regimen can be effective against BRCA-proficient TNBC.

PARP Inhibitors: Clinical Limitations and Recent Attempts to Overcome Them

PARP inhibitors are the first clinically approved drugs that were developed based on synthetic lethality. PARP inhibitors have shown promising outcomes since their clinical applications and have recently been approved as maintenance treatment for cancer patients with BRCA mutations. PARP inhibitors also exhibit positive results even in patients without homologous recombination (HR) deficiency. Therapeutic effects were successfully achieved; however, the development of resistance was unavoidable. Approximately 40–70% of patients are likely to develop resistance. Here, we describe the mechanisms of action of PARP inhibitors, the causes of resistance, and the various efforts to overcome resistance. Particularly, we determined the survival probability of cancer patients according to the expression patterns of genes associated with HR restoration, which are critical for the development of PARP inhibitor resistance. Furthermore, we discuss the innovative attempts to degrade PARP proteins by chemically modifying PARP inhibitors. These efforts would enhance the efficacy of PARP inhibitors or expand the scope of their usage.

Investigating the Mechanistic Inhibitory Discrepancies of Novel Halogen and Alkyl Di-Substituted Oxadiazole-Based Dibenzo-Azepine-Dione Derivatives on Poly (ADP-Ribose) Polymerase-1

Numerous studies have established the involvement of Poly (ADP-ribose) Polymerase-1 (PARP-1) in cancer presenting it as an important therapeutic target over recent years. Although homology among the PARP protein family makes selective targeting difficult, two compounds [d11 (0.939 μM) and d21 (0.047 μM)] with disparate inhibitory potencies against PARP-1 were recently identified. In this study, free energy calculations and molecular simulations were used to decipher underlying mechanisms of differential PARP-1 inhibition exhibited by the two compounds. The thermodynamics calculation revealed that compound d21 had a relatively higher ΔG_bind than d11. High involvement of van der Waal and electrostatic effects potentiated the affinity of d21 at PARP-1 active site. More so, incorporated methyl moiety in d11 accounted for steric hindrance which, in turn, prevented complementary interactions of key site residues such as TYR889, MET890, TYR896, TYR907. Conformational studies also revealed that d21 is more stabilized for interactions in the active site compared to d11. We believe that findings from this study would provide an important avenue for the development of selective PARP-1 inhibitors.

Phase I study of continuous olaparib capsule dosing in combination with carboplatin and/or paclitaxel (Part 1)

Background The PARP inhibitor olaparib has shown acceptable toxicity at doses of up to 400 mg twice daily (bid; capsule formulation) with encouraging signs of antitumor activity. Based on its mode of action, olaparib may sensitize tumor cells to DNA-damaging agents. This Phase I trial (NCT00516724) evaluated the safety, pharmacokinetics (PK) and preliminary efficacy of olaparib combined with carboplatin and/or paclitaxel. Methods Patients with advanced solid tumors received olaparib (capsule bid) plus carboplatin (Part A), carboplatin and paclitaxel (Part B), or paclitaxel (Part C). In each part of the study, different drug doses were given to define the most appropriate dose/drug combination to use in further studies. Safety assessments included evaluation of dose-limiting toxicities (DLTs; cycle 1 only), adverse events (AEs) and physical examinations. PK assessments of olaparib, carboplatin and paclitaxel were performed. Tumor responses (RECIST) were assessed every two cycles. Results Fifty-seven patients received treatment. DLTs were reported in two patients (both receiving olaparib 100 mg bid and carboplatin AUC 4; Part A, cohort 2): grade 1 thrombocytopenia with grade 2 neutropenia lasting for 16 days, and grade 2 neutropenia lasting for 7 days. Non-hematologic AEs were predominantly grade 1-2 and included fatigue (70%) and nausea (40%). Bone marrow suppression, mainly neutropenia (51%) and thrombocytopenia (25%), frequently led to dose modifications. Conclusions Olaparib in combination with carboplatin and/or paclitaxel resulted in increased hematologic toxicities, making it challenging to establish a dosing regimen that could be tolerated for multiple cycles without dose modifications.

Sensitization of chondrosarcoma cells with PARP inhibitor and high-LET radiation

Chondrosarcoma is a malignant tumor that arises from cartilaginous tissue and is radioresistant and chemoresistant to conventional treatments. The preferred treatment consists of surgical resection, which might cause severe disabilities for the patient; in addition, this procedure might be impossible for inoperable locations, such as the skull base. Carbon ion irradiation (hadron therapy) has been proposed as an alternative treatment, primarily due to its greater biological effectiveness and improved ballistic properties compared with conventional radiotherapy with X-rays. The goal of this study was to characterize the genetic mutations of a grade III chondrosarcoma cell line (CH2879) and examine the cellular responses to conventional radiotherapy (X-rays) and hadron therapy (proton and carbon ions) in the presence of the PARP inhibitor Olaparib. To better understand PARP inhibition, we first analyzed the formation of poly-ADP ribose chains by western blot; we observed an increase in its signal after irradiation, which disappeared on addition of the PARP inhibitor. PARPi enhanced ratio of approximately 1.3, 1.8, and 1.5 following irradiation of cells with X-rays, protons, and C-ions, respectively, as detected by clonogenic assay. The decrease in cell survival was confirmed by proliferation assay. The radiosensitivity of CH2879 cells was associated with mutations in homologous recombination repair genes, such as RAD50, SMARCA2 and NBN. This study demonstrates the capacity of the PARP inhibitor Olaparib to radiosensitize mutated chondrosarcoma cells to conventional photon irradiation, proton and carbon ion irradiation.

Cationic liposome codelivering PI3K pathway regulator improves the response of BRCA1-deficient breast cancer cells to PARP1 inhibition

Although some progresses have been made in breast cancer therapy, effective treatment for BRCA1-deficient breast cancer remains to be a great challenge. It has been demonstrated that the PI3K pathway is inappropriately activated in BRCA1-deficient breast cancers which can be downregulated by microRNA 451 (miR-451). In addition, although PARP1 inhibitors showed relatively positive results in both preclinical and clinical studies, additional efforts to decrease drug resistance as well as reduce systematic toxicity need to be addressed. To this end, by encapsulating the miR-451 mimic and PARP1 inhibitor in the same cationic liposome, we examined the potential of enhancing the response of PARP1 inhibition on BRCA1-deficient breast cancer by regulating the PI3K pathway. Our results revealed that in BRCA1-deficient human breast cancer cell line, PARP1 inhibition resulted in DNA damage with viability decrease, G2/M arrest as well as apoptosis. In contrast, single PI3K inhibition induced G1 arrest along with retarded cell proliferation. However, it was noted that combination of PARP inhibitor and PI3K regulator could exert synergetic function to evidently decrease cell proliferation compared with PARP inhibition alone, which was also confirmed by in vivo antitumor assay using xenograft tumor models. Collectively, our results offer an alternative but superior strategy for the therapy of BRCA1-deficient human breast cancers which may benefit the clinical applications.

Potential role of poly (ADP-ribose) polymerase in delayed cerebral vasospasm following subarachnoid hemorrhage in rats

Poly (ADP-ribose) polymerase (PARP) serves a key role in several neurological disorders, however, the specific role of PARP in delayed cerebral vasospasm (DCVS) following subarachnoid hemorrhage (SAH) remains unclear. The present study was conducted to clarify the possible mechanism of PARP in DCVS with the treatment of 3-aminobenzamide (3-AB), a PARP inhibitor. In the preliminary experiment, an internal carotid artery puncture SAH model, a cisterna magna double injection SAH model and prechiasmatic cistern single injection SAH model were compared with respect to mortality and neurobehavioral test results. The prechiasmatic cistern single injection SAH model was chosen to induce DCVS in the formal experiment. In the formal experiment, a total of 96 Sprague Dawley rats were randomly allocated into the sham group, the SAH group and the SAH+3-AB group and then each group was further subdivided into days 3, 5, 7 and 14 post-SAH subgroups (n=8 for each subgroup). The prechiasmatic cistern single injection SAH model was established to induce DCVS. Neurobehavioral testing and HE staining were conducted to evaluate the degree of cerebral vasospasm. PARP activity was assessed by ELISA and immunohistochemistry. An electrophoretic mobility shift assay was used to detect nuclear factor (NF)-κB DNA-binding activity. The expression of monocyte chemotactic protein 1 (MCP-1) and C-reactive protein (CRP) were measured by western blotting. Cerebral vasospasm occurred following SAH and became most severe on around day 7 post-SAH. NF-κB activity, PARP activity, the expression of MCP-1 and CRP exhibited a similar time course to cerebral vasospasm. Treatment with 3-AB alleviated the degree of cerebral vasospasm. NF-κB activity, PARP activity and the expression of MCP-1 and CRP were also suppressed by 3-AB treatment. In conclusion, PARP may serve an important role in regulating the inflammatory response and ultimately contribute to DCVS. Therefore 3-AB may be a potential therapeutic agent for DCVS.

Phase 1 trial evaluating cisplatin, gemcitabine, and veliparib in 2 patient cohorts: Germline BRCA mutation carriers and wild-type BRCA pancreatic ductal adenocarcinoma

BACKGROUND

A phase 1 trial was used to evaluate a combination of cisplatin, gemcitabine, and escalating doses of veliparib in patients with untreated advanced pancreatic ductal adenocarcinoma (PDAC) in 2 cohorts: a germline BRCA1/2-mutated (BRCA+) cohort and a wild-type BRCA (BRCA-) cohort. The aims were to determine the safety, dose-limiting toxicities (DLTs), maximum tolerated dose, and recommended phase 2 dose (RP2D) of veliparib combined with cisplatin and gemcitabine and to assess the antitumor efficacy (Response Evaluation Criteria in Solid Tumors, version 1.1) and overall survival.

METHODS

Gemcitabine and cisplatin were dosed at 600 and 25 mg/m2 , respectively, over 30 minutes on days 3 and 10 of a 21-day cycle. Four dose levels of veliparib were evaluated: 20 (dose level 0), 40 (dose level 1), and 80 mg (dose level 2) given orally twice daily on days 1 to 12 and 80 mg given twice daily on days 1 to 21 (dose level 2A [DL2A]).

RESULTS

Seventeen patients were enrolled: 9 BRCA+ patients, 7 BRCA- patients, and 1 patient with an unknown status. DLTs were reached at DL2A (80 mg twice daily on days 1 to 21). Two of the 5 patients in this cohort (40%) experienced grade 4 neutropenia and thrombocytopenia. Two grade 5 events occurred on protocol. The objective response rate in the BRCA+ cohort was 7 of 9 (77.8%). The median overall survival for BRCA+ patients was 23.3 months (95% confidence interval [CI], 3.8-30.2 months). The median overall survival for BRCA- patients was 11 months (95% CI, 1.5-12.1 months).

CONCLUSIONS

The RP2D of veliparib was 80 mg by mouth twice daily on days 1 to 12 in combination with cisplatin and gemcitabine; the DLT was myelosuppression. Substantial antitumor activity was seen in BRCA+ PDAC. A randomized phase 2 trial is currently evaluating cisplatin and gemcitabine with and without veliparib for BRCA+ PDAC (NCT01585805). Cancer 2018;124:1374-82. © 2018 American Cancer Society.

Discovery of potent 2,4-difluoro-linker poly(ADP-ribose) polymerase 1 inhibitors with enhanced water solubility and in vivo anticancer efficacy

Poly (ADP-ribose) polymerase 1 (PARP1) is overexpressed in a variety of cancers, especially in breast and ovarian cancers; tumor cells that are deficient in breast cancer gene 1/2 (BRCA1/2) are highly sensitive to PARP1 inhibition. In this study, we identified a series of 2,4-difluorophenyl-linker analogs (15-55) derived from olaparib as novel PARP1 inhibitors. Four potent analogs 17, 43, 47, and 50 (IC₅₀=2.2-4.4 nmol/L) effectively inhibited the proliferation of Chinese hamster lung fibroblast V-C8 cells (IC₅₀=3.2-37.6 nmol/L) in vitro, and showed specificity toward BRCA-deficient cells (SI=40-510). The corresponding hydrochloride salts 56 and 57 (based on 43 and 47) were highly water soluble in pH=1.0 buffered salt solutions (1628.2 μg/mL, 2652.5 μg/mL). In a BRCA1-mutated xenograft model, oral administration of compound 56 (30 mg·kg^-1·d^-1, for 21 d) exhibited more prominent tumor growth inhibition (96.6%) compared with the same dose of olaparib (56.3%); in a BRCA2-mutated xenograft model, oral administration of analog 43 (10 mg·kg^-1·d^-1, for 28 d) significantly inhibited tumor growth (69.0%) and had no negative effects on the body weights. Additionally, compound 56 exhibited good oral bioavailability (F=32.2%), similar to that of olaparib (F=45.4%). Furthermore, the free base 43 of the hydrochloride salt 56 exhibited minimal hERG inhibition activity (IC₅₀=6.64 μmol/L). Collectively, these data demonstrate that compound 56 may be an excellent drug candidate for the treatment of cancer, particularly BRCA-deficient tumors.

Genome stability of programmed stem cell products

Inherited and acquired genomic abnormalities are known to cause genetic diseases and contribute to cancer formation. Recent studies demonstrated a substantial mutational load in mouse and human embryonic and induced pluripotent stem cells (ESCs and iPSCs). Single nucleotide variants, copy number variations, and larger chromosomal abnormalities may influence the differentiation capacity of pluripotent stem cells and the functionality of their derivatives in disease modeling and drug screening, and are considered a serious risk for cellular therapies based on ESC or iPSC derivatives. This review discusses the types and origins of different genetic abnormalities in pluripotent stem cells, methods for their detection, and the mechanisms of development and enrichment during reprogramming and culture expansion.

Parent-Metabolite Pharmacokinetic Modeling and Pharmacodynamics of Veliparib (ABT-888), a PARP Inhibitor, in Patients With BRCA 1/2-Mutated Cancer or PARP-Sensitive Tumor Types

Veliparib (ABT-888) is a novel oral poly-ADP-ribose polymerase (PARP) inhibitor that is being developed for the treatment of hematologic malignancies and solid tumors. Although the pharmacokinetics of veliparib have been studied in combination with cytotoxic agents, limited information exists regarding the pharmacokinetics (PK) of chronically dosed single-agent veliparib in patients with either BRCA 1/2-mutated cancer or PARP-sensitive tumors. The objectives of the current analysis were to characterize the population pharmacokinetics of veliparib and its primary, active metabolite, M8, and to evaluate the relationship between veliparib and M8 concentrations and poly-ADP-ribose (PAR) level observed in peripheral blood mononuclear cells (PBMCs). Seventy-one subjects contributed with veliparib plasma concentrations, M8 plasma concentrations, and PAR levels in PBMCs. Veliparib and M8 concentrations were modeled simultaneously using a population PK approach. A 2-compartment model with delayed first-order absorption and the elimination parameterized as renal (CLR /F) and nonrenal clearance (CLNR /F) adequately described veliparib pharmacokinetics. The pharmacokinetics of the M8 metabolite was described with a 2-compartment model. Creatinine clearance(CLCR ) and lean body mass (LBM) were identified as significant predictors of veliparib CLR /F and central volume of distribution, respectively. For a typical subject (LBM, 48 kg; CLCR , 95 mL/min), total clearance (CLR /F + CLNR /F), and central and peripheral volume of distribution for veliparib were estimated as 17.3 L/h, 98.7 L, and 48.3 L, respectively. At least 50% inhibition of PAR levels in PBMCs was observed at dose levels ranging from 50 to 500 mg.

Nup153 and Nup50 promote recruitment of 53BP1 to DNA repair foci by antagonizing BRCA1-dependent events

DNA double strand breaks are typically repaired through either the high-fidelity process of homologous recombination (HR), in which BRCA1 plays a key role, or the more error-prone process of non-homologous end joining (NHEJ), which relies on 53BP1. The balance between NHEJ and HR depends, in part, on whether 53BP1 predominates in binding to damage sites, where it protects the DNA ends from resection. The nucleoporin Nup153 has been implicated in the DNA damage response, attributed to a role in promoting nuclear import of 53BP1. Here, we define a distinct requirement for Nup153 in 53BP1 intranuclear targeting to damage foci and report that Nup153 likely facilitates the role of another nucleoporin, Nup50, in 53BP1 targeting. The requirement for Nup153 and Nup50 in promoting 53BP1 recruitment to damage foci induced by either etoposide or olaparib is abrogated in cells deficient for BRCA1 or its partner BARD1, but not in cells deficient for BRCA2. Together, our results further highlight the antagonistic relationship between 53BP1 and BRCA1 and place Nup153 and Nup50 in a molecular pathway that regulates 53BP1 function by counteracting BRCA1-mediated events.

Sensitization strategies in lung cancer

The commonly used treatment avenues employed by cancer physicians include surgery, radiotherapy (RT) and chemotherapy in addition to rapid developmental and confirmatory studies on the efficacy of targeted therapies. However, the success rate in these commonly used treatments remains relatively low due to associated side effects, such as normal cell targeting/toxicity and resistance. In addition, investigators are continuing their efforts to enhance the efficacy of RT and chemotherapy to prevent associated side effects and improve the survival rate of the affected patient in order to increase patient survival. In the present study, we have reviewed the sensitization approaches used to improve chemotherapy and RT sensitivity in tumors.

Olaparib, Monotherapy or with Ionizing Radiation, Exacerbates DNA Damage in Normal Tissues: Insights from a New p21 Reporter Mouse

Many drugs targeting the DNA damage response are being developed as anticancer therapies, either as single agents or in combination with ionizing radiation (IR) or other cytotoxic agents. Numerous clinical trials in this area are either in progress or planned. However, concerns remain about the potential of such treatments to increase toxicity to normal tissues. In order to address this issue, a novel reporter mouse line was created through the simultaneous incorporation of multiple reporters, β-galactosidase, and firefly luciferase, into the DNA damage-inducible p21 (CDKN1A) locus. The data demonstrate that in situ β-galactosidase staining facilitates high fidelity mapping of p21 expression across multiple organs and tissues at single-cell resolution, whereas the luciferase reporter permits noninvasive bioluminescent imaging of p21 expression. This model was used to determine the capacity of a number of DNA-damaging agents, including IR, cisplatin, and etoposide to induce p21 expression in normal tissues. In addition, the PARP inhibitor olaparib was examined alone or in combination with IR as well as cisplatin. A single exposure to olaparib alone caused DNA damage to cells in the mucosal layer lining mouse large intestine. It also exacerbated DNA damage induced in this organ and the kidney by coadministered IR. These studies suggest that olaparib has carcinogenic potential and illustrate the power of this new model to evaluate the safety of new therapeutic regimens involving combination therapies.

IMPLICATIONS

Olaparib causes DNA damage to normal tissues and might be a carcinogen. Mol Cancer Res; 14(12); 1195-203. ©2016 AACR.

Use of poly ADP-ribose polymerase [PARP] inhibitors in cancer cells bearing DDR defects: the rationale for their inclusion in the clinic

BACKGROUND

DNA damage response (DDR) defects imply genomic instability and favor tumor progression but make the cells vulnerable to the pharmacological inhibition of the DNA repairing enzymes. Targeting cellular proteins like PARPs, which cooperate and complement molecular defects of the DDR process, induces a specific lethality in DDR defective cancer cells and represents an anti-cancer strategy. Normal cells can tolerate the DNA damage generated by PARP inhibition because of an efficient homologous recombination mechanism (HR); in contrast, cancer cells with a deficient HR are unable to manage the DSBs and appear especially sensitive to the PARP inhibitors (PARPi) effects.

MAIN BODY

In this review we discuss the proof of concept for the use of PARPi in different cancer types and the success and failure of their inclusion in clinical trials. The PARP inhibitor Olaparib [AZD2281] has been approved by the FDA for use in pretreated ovarian cancer patients with defective BRCA1/2 genes, and by the EMEA for maintenance therapy in platinum sensitive ovarian cancer patients with defective BRCA1/2 genes. BRCA mutations are now recognised as the molecular targets for PARPi sensitivity in several tumors. However, it is noteworthy that the use of PARPi has shown its efficacy also in non-BRCA related tumors. Several trials are ongoing to test different PARPi in different cancer types. Here we review the concept of BRCAness and the functional loss of proteins involved in DDR/HR mechanisms in cancer, including additional molecules that can influence the cancer cells sensitivity to PARPi. Given the complexity of the existing crosstalk between different DNA repair pathways, it is likely that a single biomarker may not be sufficient to predict the benefit of PARP inhibitors therapies. Novel general assays able to predict the DDR/HR proficiency in cancer cells and the PARPi sensitivity represent a challenge for a personalized therapy.

CONCLUSIONS

PARP inhibition is a potentially important strategy for managing a significant subset of tumors. The discovery of both germline and somatic DNA repair deficiencies in different cancer patients, together with the development of new PARP inhibitors that can kill selectively cancer cells is a potent example of targeting therapy to molecularly defined tumor subtypes.

Pancreatic ductal adenocarcinoma in BRCA2 mutation carriers

Germline BRCA2 mutations are the first known cause of inherited (familial) pancreatic ductal adenocarcinoma (PDAC). This tumor is the third most frequent cancer in carriers of germline BRCA2 mutations, as it occurs in around 10% of BRCA2 families. PDAC is known as one of the most highly lethal cancers, mainly because of its chemoresistance and frequently late diagnosis. Based on recent developments in molecular biology, a subgroup of BRCA2-associated PDAC has been created, allowing screening, early surgical treatment and personalized systemic treatment. BRCA2 germline mutation carriers who have ≥1 first-degree relative, or ≥2 blood relatives with PDAC, should undergo screening and regular follow-up based on magnetic resonance imaging and endoscopic ultrasound. The goal of screening is to detect early invasive PDAC and advanced precancerous lesions suitable for a stepwise surgical complete (R0) resection. Increasing evidence on the molecular role of the BRCA2 protein in the homologous recombination of DNA damages suggest that BRCA2-related PDAC are sensitive to agents causing DNA cross-linking damage, such as platinum salts, and treatments targeting rescue DNA repair pathways, such as poly(ADP-ribose) polymerase inhibitors that are currently under investigation.

Novel tricyclic poly (ADP-ribose) polymerase-1/2 inhibitors with potent anticancer chemopotentiating activity: Design, synthesis and biological evaluation

8,9-Dihydro-2,4,7,9a-tetraazabenzo[cd]azulen-6(7H)-ones were designed and synthesized as a new class of PARP-1/2 inhibitors. The compounds displayed a variable pattern of PARP-1/2 enzymes inhibition profile that, in part, paralleled the antiproliferative activity in cell lines. Among them, compound 9e exhibited not only the significant IC50 value of 28nM in the PARP-1 and 7.7nM in PARP-2 enzyme assay, but also a profound synergic efficacy combined with temozolomide with PF50 values of 2.6, 2.5, and 6.5 against MDA-MB-468, SW-620 and A549 and cell line, respectively.

Randomized phase II trial of cyclophosphamide and the oral poly (ADP-ribose) polymerase inhibitor veliparib in patients with recurrent, advanced triple-negative breast cancer

Background In tumors carrying BRCA mutations, DNA damage caused by standard cytotoxic chemotherapy can be potentiated by poly [ADP-ribose] polymerase (PARP) inhibitors, leading to increased cell death through synthetic lethality. Individuals carrying mutations in BRCA have an increased incidence of triple negative breast cancer (TNBC). In order to assess the role of PARP inhibition in the treatment of TNBC, we conducted a randomized phase II trial of the combination of veliparib, a small molecule PARP inhibitor, with the cytotoxic agent cyclophosphamide versus cyclophosphamide alone in patients with refractory TNBC. Methods Adult patients with TNBC were randomized to receive oral cyclophosphamide 50 mg once daily with or without oral veliparib at 60 mg daily in 21-day cycles. Patients on the cyclophosphamide arm could crossover to the combination arm at disease progression. Results Forty-five patients were enrolled; 18 received cyclophosphamide alone and 21 received the combination as their initial treatment regimen. Lymphopenia was the most common grade 3/4 toxicity noted in both arms. One patient in the cyclophosphamide alone arm, and 2 in the combination arm had objective responses. Response rates and median progression free survival did not significantly differ between both treatment arms. Conclusion The addition of veliparib to cyclophosphamide, at the dose and schedule evaluated, did not improve the response rate over cyclophosphamide treatment alone in patients with heavily pre-treated triple-negative breast cancer.

Xeroderma Pigmentosum Group A Promotes Autophagy to Facilitate Cisplatin Resistance in Melanoma Cells through the Activation of PARP1

Xeroderma pigmentosum group A (XPA), a key protein in the nucleotide excision repair pathway, has been shown to promote the resistance of tumor cells to chemotherapeutic drugs by facilitating the DNA repair process. However, the role of XPA in the resistance of melanoma to platinum-based drugs like cisplatin is largely unknown. In this study, we initially found that XPA was expressed at higher levels in cisplatin-resistant melanoma cells than in cisplatin-sensitive ones. Furthermore, the knockdown of XPA not only increased cellular apoptosis but also inhibited cisplatin-induced autophagy, which rendered the melanoma cells more sensitive to cisplatin. Moreover, we discovered that the increased XPA in resistant melanoma cells promoted poly(adenosine diphosphate-ribose) polymerase 1 (PARP1) activation and that the inhibition of PARP1 could attenuate the cisplatin-induced autophagy. Finally, we proved that the inhibition of PARP1 and the autophagy process made resistant melanoma cells more susceptible to cisplatin treatment. Our study shows that XPA can promote cell-protective autophagy in a DNA repair-independent manner by enhancing the activation of PARP1 in melanoma cells resistant to cisplatin and that the XPA-PARP1-mediated autophagy process can be targeted to overcome cisplatin resistance in melanoma chemotherapy.

Consequence of the tumor-associated conversion to cyclin D1b

Clinical evidence suggests that cyclin D1b, a variant of cyclin D1, is associated with tumor progression and poor outcome. However, the underlying molecular basis was unknown. Here, novel models were created to generate a genetic switch from cyclin D1 to cyclin D1b. Extensive analyses uncovered overlapping but non-redundant functions of cyclin D1b compared to cyclin D1 on developmental phenotypes, and illustrated the importance of the transcriptional regulatory functions of cyclin D1b in vivo. Data obtained identify cyclin D1b as an oncogene, wherein cyclin D1b expression under the endogenous promoter induced cellular transformation and further cooperated with known oncogenes to promote tumor growth in vivo. Further molecular interrogation uncovered unexpected links between cyclin D1b and the DNA damage/PARP1 regulatory networks, which could be exploited to suppress cyclin D1b-driven tumors. Collectively, these data are the first to define the consequence of cyclin D1b expression on normal cellular function, present evidence for cyclin D1b as an oncogene, and provide pre-clinical evidence of effective methods to thwart growth of cells dependent upon this oncogenic variant.

Chromatin to Clinic: The Molecular Rationale for PARP1 Inhibitor Function

Poly(ADP-ribose) polymerase 1 (PARP1) inhibitors were recently shown to have potential clinical impact in a number of disease settings, particularly as related to cancer therapy, treatment for cardiovascular dysfunction, and suppression of inflammation. The molecular basis for PARP1 inhibitor function is complex, and appears to depend on the dual roles of PARP1 in DNA damage repair and transcriptional regulation. Here, the mechanisms by which PARP-1 inhibitors elicit clinical response are discussed, and strategies for translating the preclinical elucidation of PARP-1 function into advances in disease management are reviewed.

Long-term safety and anti-tumour activity of olaparib monotherapy after combination with carboplatin and paclitaxel in patients with advanced breast, ovarian or fallopian tube cancer

BACKGROUND

Olaparib (AZD2281), a PARP-1/2 inhibitor, has been extensively investigated in clinical trials. However, limited clinical data are available about its long-term safety and anti-tumour activity.

METHODS

Patients had first participated in a phase I study of olaparib combined with carboplatin and/or paclitaxel. They continued with olaparib monotherapy in their best interest if they failed to tolerate the combination due to the treatment-related adverse events (TRAEs). Safety data were collected by physical examination and regular laboratory evaluations. Disease evaluations were performed by CT scan.

RESULTS

At data cutoff, 21 patients were included; 10 with breast, 9 with ovarian and 2 with fallopian tube cancer of whom 16 patients had a BRCA mutation (13 BRCA1; 3 BRCA2). TRAEs were mostly haematological and most prominent shortly after switching from combination to monotherapy, probably due to carry-over effects of chemotherapy. Over time, both severity and frequency of TRAEs decreased. Responses to olaparib were durable with a median treatment duration of 52 (range 7-183) weeks. In total, nine (43%) patients were still on study at data cutoff.

CONCLUSION

Continued long-term daily olaparib was found to be safe and tolerable. Encouragingly, patients who showed a favourable response on earlier combination therapy maintained this response on olaparib monotherapy.

Niraparib (MK-4827), a novel poly(ADP-Ribose) polymerase inhibitor, radiosensitizes human lung and breast cancer cells

The aim of this study was to assess niraparib (MK-4827), a novel poly(ADP-Ribose) polymerase (PARP) inhibitor, for its ability to radiosensitize human tumor cells. Human tumor cells derived from lung, breast and prostate cancers were tested for radiosensitization by niraparib using clonogenic survival assays. Both p53 wild-type and p53-defective lines were included. The ability of niraparib to alter the repair of radiation-induced DNA double strand breaks (DSBs) was determined using detection of γ-H₂AX foci and RAD51 foci. Clonogenic survival analyses indicated that micromolar concentrations of niraparib radiosensitized tumor cell lines derived from lung, breast, and prostate cancers independently of their p53 status but not cell lines derived from normal tissues. Niraparib also sensitized tumor cells to H₂O₂ and converted H₂O₂-induced single strand breaks (SSBs) into DSBs during DNA replication. These results indicate that human tumor cells are significantly radiosensitized by the potent and selective PARP-1 inhibitor, niraparib, in the in vitro setting. The mechanism of this effect appears to involve a conversion of sublethal SSBs into lethal DSBs during DNA replication due to the inhibition of base excision repair by the drug. Taken together, our findings strongly support the clinical evaluation of niraparib in combination with radiation.

Genomic profiling guides the choice of molecular targeted therapy of pancreatic cancer

Pancreatic cancer has the worst five-year survival rate of all malignancies due to its aggressive progression and resistance to therapy. Current therapies are limited to gemcitabine-based chemotherapeutics, surgery, and radiation. The current trend toward "personalized genomic medicine" has the potential to improve the treatment options for pancreatic cancer. Gene identification and genetic alterations like single nucleotide polymorphisms and mutations will allow physicians to predict the efficacy and toxicity of drugs, which could help diagnose pancreatic cancer, guide neoadjuvant or adjuvant treatment, and evaluate patients' prognosis. This article reviews the multifaceted roles of genomics and pharmacogenomics in pancreatic cancer.

Randomized Trial of Oral Cyclophosphamide and Veliparib in High-Grade Serous Ovarian, Primary Peritoneal, or Fallopian Tube Cancers, or BRCA-Mutant Ovarian Cancer

PURPOSE

Veliparib, a PARP inhibitor, demonstrated clinical activity in combination with oral cyclophosphamide in patients with BRCA-mutant solid tumors in a phase I trial. To define the relative contribution of PARP inhibition to the observed clinical activity, we conducted a randomized phase II trial to determine the response rate of veliparib in combination with cyclophosphamide compared with cyclophosphamide alone in patients with pretreated BRCA-mutant ovarian cancer or in patients with pretreated primary peritoneal, fallopian tube, or high-grade serous ovarian cancers (HGSOC).

EXPERIMENTAL DESIGN

Adult patients were randomized to receive cyclophosphamide alone (50 mg orally once daily) or with veliparib (60 mg orally once daily) in 21-day cycles. Crossover to the combination was allowed at disease progression.

RESULTS

Seventy-five patients were enrolled and 72 were evaluable for response; 38 received cyclophosphamide alone and 37 the combination as their initial treatment regimen. Treatment was well tolerated. One complete response was observed in each arm, with three partial responses (PR) in the combination arm and six PRs in the cyclophosphamide alone arm. Genetic sequence and expression analyses were performed for 211 genes involved in DNA repair; none of the detected genetic alterations were significantly associated with treatment benefit.

CONCLUSION

This is the first trial that evaluated single-agent, low-dose cyclophosphamide in HGSOC, peritoneal, fallopian tube, and BRCA-mutant ovarian cancers. It was well tolerated and clinical activity was observed; the addition of veliparib at 60 mg daily did not improve either the response rate or the median progression-free survival.

S-benzyl-cysteine-mediated cell cycle arrest and apoptosis involving activation of mitochondrial-dependent caspase cascade through the p53 pathway in human gastric cancer SGC-7901 cells

S-benzyl-cysteine (SBC) is a structural analog of S-allylcysteine (SAC), which is one of the major water- soluble compounds in aged garlic extract. In this study, anticancer activities and the underlying mechanisms of SBC action were investigated and compared these with those of SAC using human gastric cancer SGC-7901 cells. SBC significantly suppressed the survival rate of SGC-7901 cells in a concentration- and time-dependent manner, and the inhibitory activities of SBC were stronger than those of SAC. Flow cytometry revealed that SBC induced G2-phase arrest and apoptosis in SGC-7901 cells. Typical apoptotic morphological changes were observed by Hoechst 33258 dye assay. SBC-treatment dramatically induced the dissipation of mitochondrial membrane potential (Δψm), and enhanced the enzymatic activities of caspase-9 and caspase-3 whilst hardly affecting caspase-8 activity. Furthermore, Western blotting indicated that SBC-induced apoptosis was accompanied by up-regulation of the expression of p53, Bax and the down-regulation of Bcl-2. Taken together, this study suggested that SBC exerts cytotoxic activity involving activation of mitochondrial-dependent apoptosis through p53 and Bax/Bcl-2 pathways in human gastric cancer SGC-7901 cells.

Current medical treatment of glioblastoma

Glioblastoma is the most common adult malignant primary brain tumor. Despite the advances in therapeutic options, survival of patients with glioblastoma remains dismal at 15-18 months. Current standard of care for newly diagnosed glioblastoma is maximal possible safe resection consistent with the preservation of neurologic function followed by concurrent temozolomide with radiation and adjuvant. Treatment options at recurrence include surgical resection with or without the placement of carmustine wafers, re-irradiation and chemotherapeutics such as nitrosoureas (lomustine, carmustine) or bevacizumab, a monoclonal antibody targeting vascular endothelial growth factor (VEGF).

Mutational landscape of candidate genes in familial prostate cancer

BACKGROUND

Family history is a major risk factor for prostate cancer (PCa), suggesting a genetic component to the disease. However, traditional linkage and association studies have failed to fully elucidate the underlying genetic basis of familial PCa.

METHODS

Here, we use a candidate gene approach to identify potential PCa susceptibility variants in whole exome sequencing data from familial PCa cases. Six hundred ninety-seven candidate genes were identified based on function, location near a known chromosome 17 linkage signal, and/or previous association with prostate or other cancers. Single nucleotide variants (SNVs) in these candidate genes were identified in whole exome sequence data from 33 PCa cases from 11 multiplex PCa families (3 cases/family).

RESULTS

Overall, 4,856 candidate gene SNVs were identified, including 1,052 missense and 10 nonsense variants. Twenty missense variants were shared by all three family members in each family in which they were observed. Additionally, 15 missense variants were shared by two of three family members and predicted to be deleterious by five different algorithms. Four missense variants, BLM Gln123Arg, PARP2 Arg283Gln, LRCC46 Ala295Thr and KIF2B Pro91Leu, and one nonsense variant, CYP3A43 Arg441Ter, showed complete co-segregation with PCa status. Twelve additional variants displayed partial co-segregation with PCa.

CONCLUSIONS

Forty-three nonsense and shared, missense variants were identified in our candidate genes. Further research is needed to determine the contribution of these variants to PCa susceptibility.

Evaluation of the Dutch BRCA1/2 clinical genetic center referral criteria in an unselected early breast cancer population

In this study, we evaluated the diagnostic value of the Dutch Clinical Genetic Center (CGC) referral guidelines for BRCA1/2 mutation testing in 903 early breast cancer patients, unselected for family history, diagnosed in a cancer hospital before the age of 50 years in 1974-2002; most prevalent Dutch pathogenic BRCA1/2 mutations had been analyzed on coded DNA in a research setting. Forty-nine (5.4%) of the patients were proven to be BRCA1/2 mutation carriers. We found that 78% and 69% of BRCA1 and BRCA2 mutation carriers identified met the criteria for referral to the CGC based on age, family history and synchronous multiple tumors; reflected by a combined sensitivity of 75.5% and specificity of 63.2%. More than half of the BRCA1 mutation carriers, that is, 58% had a triple-negative tumor. The highest AUC was obtained by shifting the age at diagnosis threshold criterion from 40 to 35 years and by adding a 'triple-negative breast cancer' criterion with an age threshold of 45 years; the specificity increased to 71.2%, whereas the sensitivity remained the same; that is, a referral of fewer patients will lead to the identification of at least the same number of BRCA1/2 mutation carriers. Two-thirds of the BRCA1/2 mutation carriers identified in this research setting had been referred for counseling and testing. Our results indicate that, awaiting a possibly more extended mutation screening of all breast cancer patients, the triple-negative status of a breast cancer should be added to the CGC referral criteria.

Poly (ADP) ribose polymerase enzyme inhibitor, veliparib, potentiates chemotherapy and radiation in vitro and in vivo in small cell lung cancer

Poly (ADP) ribose polymerase (PARP) plays a key role in DNA repair and is highly expressed in small cell lung cancer (SCLC). We investigated the therapeutic impact of PARP inhibition in SCLC. In vitro cytotoxicity of veliparib, cisplatin, carboplatin, and etoposide singly and combined was determined by MTS in 9 SCLC cell lines (H69, H128, H146, H526, H187, H209, DMS53, DMS153, and DMS114). Subcutaneous xenografts in athymic nu/nu mice of H146 and H128 cells with relatively high and low platinum sensitivity, respectively, were employed for in vivo testing. Mechanisms of differential sensitivity of SCLC cell lines to PARP inhibition were investigated by comparing protein and gene expression profiles of the platinum sensitive and the less sensitive cell lines. Veliparib showed limited single-agent cytotoxicity but selectively potentiated (≥50% reduction in IC₅₀) cisplatin, carboplatin, and etoposide in vitro in five of nine SCLC cell lines. Veliparib with cisplatin or etoposide or with both cisplatin and etoposide showed greater delay in tumor growth than chemotherapy alone in H146 but not H128 xenografts. The potentiating effect of veliparib was associated with in vitro cell line sensitivity to cisplatin (CC = 0.672; P = 0.048) and DNA-PKcs protein modulation. Gene expression profiling identified differential expression of a 5-gene panel (GLS, UBEC2, HACL1, MSI2, and LOC100129585) in cell lines with relatively greater sensitivity to platinum and veliparib combination. Veliparib potentiates standard cytotoxic agents against SCLC in a cell-specific manner. This potentiation correlates with platinum sensitivity, DNA-PKcs expression and a 5-gene expression profile.

Inhibition of poly(ADP-ribosyl)ation in cancer: old and new paradigms revisited

Inhibitors of poly(ADP-ribose) polymerases actualized the biological concept of synthetic lethality in the clinical practice, yielding a paradigmatic example of translational medicine. The profound sensitivity of tumors with germline BRCA mutations to PARP1/2 blockade owes to inherent defects of the BRCA-dependent homologous recombination machinery, which are unleashed by interruption of PARP DNA repair activity and lead to DNA damage overload and cell death. Conversely, aspirant BRCA-like tumors harboring somatic DNA repair dysfunctions (a vast entity of genetic and epigenetic defects known as "BRCAness") not always align with the familial counterpart and appear not to be equally sensitive to PARP inhibition. The acquisition of secondary resistance in initially responsive patients and the lack of standardized biomarkers to identify "BRCAness" pose serious threats to the clinical advance of PARP inhibitors; a feeling is also emerging that a BRCA-centered perspective might have missed the influence of additional, not negligible and DNA repair-independent PARP contributions onto therapy outcome. While regulatory approval for PARP1/2 inhibitors is still pending, novel therapeutic opportunities are sprouting from different branches of the PARP family, although they remain immature for clinical extrapolation. This review is an endeavor to provide a comprehensive appraisal of the multifaceted biology of PARPs and their evolving impact on cancer therapeutics.

Medical therapy of gliomas

Medical therapies are an important part of adjunctive therapy for gliomas. In this chapter we will review the chemotherapeutic and targeted agents that have been evaluated in clinical trials in grade II-IV gliomas in the last decade. A number of randomized phase III trials were completed and reported. There has been a clear success in oligodendroglial tumors and low grade glioma. Although some progress has been made in glioblastoma, considerable work involving the multidisciplinary collaboration of basic science, translational and clinical investigators needs to be done to improve the outcome of patients with anaplastic astrocytoma and glioblastoma. In addition, tailoring treatment based on molecular cytogenetic characteristics is a major focus of research into precision based medicine for glioma.

PARP-1 inhibitors and radiotherapy sensitivity: future prospects for therapy?

SUMMARY 

Despite the efficacy of multimodality treatment for women with breast cancer, sustained locoregional control remains a significant issue. Efforts to identify effective targeted therapies for treatment of these patients have intensified in recent years. The PARP family of proteins represents one potential target. PARP-1 is a DNA repair enzyme that plays a critical role in base excision repair, homologous recombination, nonhomologous end joining and transcriptional regulation. In this review, we discuss the rationale for using PARP-1 inhibitors clinically, the role of PARP-1 in DNA damage repair and the potential clinical utility of using PARP-1 inhibitors as a radiosensitization strategy. We will also review the most relevant clinical trials using various PARP-1 inhibitors and the future of biomarker development to predict response to PARP-1 inhibition.

Disaccharide pyrimidine nucleosides and their derivatives: a novel group of cell-penetrating inhibitors of poly(ADP-ribose) polymerase 1

Nearly 30 synthetic nucleosides were tested with human recombinant poly(ADP-ribose) polymerase 1 as potential inhibitors of this enzyme. The most active compounds were some disaccharide analogues of thymidine: 3'-O-β-D-ribofuranosyl-5-iodo-dUrd (2d; IC₅₀ = 45 μM), 3'-O-β-D-ribofuranosyl-2'-deoxythymidine (2e; IC₅₀ = 38 μM), and 3'-O-β-D-ribofuranosyl-2'-deoxythymidine oxidized (4; IC₅₀ = 25 μM). These compounds also reduced H₂O₂-induced synthesis of poly(ADP-ribose) in cultured human ovarian carcinoma (SKOV-3) cells in a dose-dependent manner. Furthermore, compounds 2d or 2e until a concentration of 1 mM did not affect growth of SKOV-3 cells, whereas dialdehyde compound 4, as well as thymidine, exhibited a significant cytotoxicity.

Appraising iniparib, the PARP inhibitor that never was--what must we learn?

Several drugs targeting poly(ADP-ribose) polymerase (PARP) enzymes are under development. Responses have been observed in patients with germline mutations in BRCA1 and BRCA2, with further data supporting antitumour activity of PARP inhibitors in sporadic ovarian cancer. Strategies to identify other predictive biomarkers remain under investigation. Iniparib was purported to be a PARP inhibitor that showed promising results in randomized phase II trials in patients with triple-negative breast cancer. Negative results from a phase III study in this disease setting, however, tempered enthusiasm for this agent. Recently, data from in vitro experiments suggest that iniparib is not only structurally distinct from other described PARP inhibitors, but is also a poor inhibitor of PARP activity. In this context, the negative iniparib phase III data might have erroneously promulgated the notion that PARP inhibition is not an effective therapeutic strategy. Here, we scrutinize the development of iniparib from preclinical studies to registration trials, and identify and discuss the pitfalls in the development of anticancer drugs to prevent future late-stage trial failures.

Increased expression of biological markers as potential therapeutic targets in Saudi women with triple-negative breast cancer

Aims and background

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer that lacks the expression of hormone receptors and human epidermal growth factor receptor 2 (HER2). Although TNBC represents only 15% of all types of breast cancer, it accounts for a large number of metastatic cases and deaths. Because of the high metastatic rate and both local and systemic recurrence associated with TNBC, extensive research efforts are actively looking for target therapies to effectively treat this aggressive disease. Accordingly, this study has been initiated to investigate the differential expression of biological markers in TNBC and non-TNBC Saudi women that might be utilized as potential targeted therapy and/or predict the sensitivity to currently available therapeutic regimens.

Methods and study design

Two hundred formalin-fixed, paraffin-embedded (FFPE) breast cancer tissues were selected and divided into 3 groups: benign breast tissues (20), TNBC tissues (80) and non-TNBC tissues (100). Expression of mRNA in FFPE tissues was analyzed using real-time polymerase chain reaction (RT-PCR) for the following genes: poly (ADP-ribose) polymerase 1 (PARP-1), topoisomerase 2A (TOPO-2A), vascular endothelial growth factor (VEGF), C-MYC, basic fibroblast growth factor (bFGF), matrix metalloproteinases (MMP-2 and MMP-9), human epidermal growth factor 1 (HER1) and multidrug resistance (MDR) genes.

Results

In the TNBC group, expression of PARP-1, TOPO-2A, HER1, C-MYC, VEGF, bFGF and MMP-2 showed a highly significant increase compared to the non-TNBC group.

Conclusions

The results of this study suggest that (1) TNBC patients will benefit more from TOPO-2A inhibitors as well as antiangiogenic and antimetastatic therapies; (2) inhibition of these target genes is emerging as one of the most exciting and promising targeted therapeutic strategies to treat TNBC in which the intended targets are DNA repair, tumor angiogenesis and metastasis.

Molecular biology of adenocarcinoma of the pancreatic duct, current state and future therapeutic avenues

Pancreatic adenocarcinoma is a lethal disease; currently surgery offers five years survival of less than 5%. Any improvement in the outcome is likely to be through novel therapeutic agents that will target the genetic machinery of the cell. Knowledge of genetic alterations in the process of carcinogenesis is expanding rapidly, the targeted therapy, however, is progressing slowly. Pancreatic adenocarcinoma displays a variety of molecular changes that evolve exponentially with time and lend the cancer cells their ability not only to survive, but also to invade the surrounding tissues and metastasise to distant sites. These changes involve genetic alteration in oncogenes, cancer suppressor genes, changes in cell cycle, pathways of apoptosis and also changes in epithelial to mesenchymal transition. Monotherapeutic targeted agents seem(s) to have limited effect on cancer cells. The near future is likely to show an improvement in the treatment outcome, which is likely to be a result of the combination of targeted agents with surgery and chemotherapy.

p63 involvement in poly(ADP-ribose) polymerase 1 signaling of topoisomerase I-dependent DNA damage in carcinoma cells

Poly(ADP-ribose)polymerase 1 (PARP-1) inhibitors are thought as breakthrough for cancer treatment in solid tumors such as breast cancer through their effects on PARP's enzymatic activity. Our previous findings showed that the hydrophilic PARP inhibitor PJ34 enhances the sensitivity of p53 proficient MCF7 breast carcinoma cells to topotecan, a DNA Topoisomerase I (TOP 1) inhibitor. In the present study, we combine the classical TOP 1 poison camptothecin or its water-soluble derivative topotecan with PJ34 to investigate the potentiation of chemotherapeutic efficiency in MCF7 (p53(WT)), MDA-MB231 (p53(mut)) breast carcinoma cells and SCC022 (p53(null)) squamous carcinoma cells. We show that, following TPT-PJ34 combined treatment, MCF7 cells exhibit apoptotic death while MDA-MB231 and SCC022 cells are more resistant to these agents. Specifically, in MCF7, (i) PJ34 in combination with TPT causes a G2/M cell cycle arrest followed by massive apoptosis; (ii) PJ34 addition reverts TPT-dependent PARP-1 automodification and triggers caspase-dependent PARP-1 proteolysis; (iii) TPT, used as a single agent, stimulates p53 expression while in combination with PJ34 increases p53, TAp63α and TAp63γ protein levels with a concomitant reduction of MDM2 protein. The identification of p63 proteins as new players involved in the cancer cell response to TPT-PJ34 is relevant for a better understanding of the PARP1-dependent signaling of DNA damage. Furthermore, our data indicate that, in response to TPT-PJ34 combined chemotherapy, a functional cooperation between p53 and TAp63 proteins may occur and be essential to trigger apoptotic cell death.

3-Nitro-naphthalimide and nitrogen mustard conjugate NNM-25 induces hepatocellular carcinoma apoptosis via PARP-1/p53 pathway

Hepatocellular carcinoma (HCC) is one of the main causes of death in cancer. Some naphthalimide derivatives exert high anti-proliferative effects on HCC. In this study, it is confirmed that 3-nitro-naphthalimide and nitrogen mustard conjugate (NNM-25), a novel compound conjugated by NNM-25, displayed more potent therapeutic action on HCC, both in vivo and in vitro, than amonafide, a naphthalimide drug in clinical trials. More importantly, preliminary toxicological evaluation also supported that NNM-25 exhibited less systemic toxicity than amonafide at the therapeutic dose. The antitumor mechanism of conjugates of naphthalimides with nitrogen mustard remains poorly understood up to now. Here, we first reported that apoptosis might be the terminal fate of cancer cells treated with NNM-25. Inhibition of p53 by siRNA resulted in a significant decrease of NNM-25-induced apoptosis, which corroborated that p53 played a vital role in the cell apoptosis triggered by NNM-25. NNM-25 inhibited the PARP-1 activity, AKT phosphorylation, up-regulated the protein expression of p53, Bad, and mTOR as well as down-regulating the protein expression of Bcl-2 and decreasing mitochondrial membrane potential. It also facilitated cytochrome c release from mitochondria to cytoplasm, activated caspase 8, caspase 9, and caspase 3 in HepG2 cells in vitro, as also authenticated in H22 tumor-bearing mice in vivo. Collectively, the conjugation of naphthalimides with nitrogen mustard provides favorable biological activity and thus is a valuable strategy for future drug design in HCC therapy.

Modulation of farnesoid X receptor results in post-translational modification of poly (ADP-ribose) polymerase 1 in the liver

The farnesoid X receptor (FXR) is a bile acid-activated transcription factor belonging to the nuclear receptor superfamily. FXR deficiency in mice results in cholestasis, metabolic disorders, and tumorigenesis in liver and intestine. FXR is known to contribute to pathogenesis by regulating gene transcription; however, changes in the post-transcriptional modification of proteins associated with FXR modulation have not been determined. In the current study, proteomic analysis of the livers of wild-type (WT) and FXR knockout (FXR-KO) mice treated with a FXR synthetic ligand or vehicle was performed. The results identified five proteins as novel FXR targets. Since FXR deficiency in mice leads to liver tumorigenesis, poly (ADP-ribose) polymerase family, member 1 (Parp1) that is important for DNA repair, was validated in the current study by quantitative real-time PCR, and 1- and 2-dimensional gel electrophoresis/western blot. The results showed that Parp1 mRNA levels were not altered by FXR genetic status or by agonist treatment. However, total Parp1 protein levels were increased in FXR-KO mice as early as 3 month old. Interestingly, total Parp1 protein levels were increased in WT mice in an age-dependent manner (from 3 to 18 months), but not in FXR-KO mice. Finally, activation of FXR in WT mice resulted in reduction of phosporylated Parp1 protein in the liver without affecting total Parp1 protein levels. In conclusion, this study reveals that FXR genetic status and agonist treatment affects basal levels and phosphorylation state of Parp1, respectively. These alterations, in turn, may be associated with the hepatobiliary alterations observed in FXR-KO mice and participate in FXR agonist-induced protection in the liver.