Immunohistochemical detection of poly(ADP-ribose) polymerase inhibition by ABT-888 in patients with refractory solid tumors and lymphomas

PARP Inhibitors and Haematological Malignancies-Friend or Foe?

Simple Summary

PARP inhibitors are a class of orally active drugs that kill a range of cancer types by inducing synthetic lethality. The usefulness of PARP inhibitors for the treatment of haematological malignancies has begun to be explored in a variety of both pre-clinical models and human clinical trials. Despite being largely considered safe and well tolerated, secondary haematological malignancies have arisen in patients following treatment with PARP inhibitors, raising concerns about their use. In this review, we discuss the potential benefits and risks for using PARP inhibitors as treatments for haematological malignancies.

Abstract

Since their introduction several years ago, poly (ADP-ribose) polymerase (PARP) inhibitors (PARPi) have become the standard of care for breast and gynaecological cancers with BRCA gene mutations. Given that PARPi act by exploiting defective DNA repair mechanisms within tumour cells, they should be ideally suited to combatting haematological malignancies where these pathways are notoriously defective, even though BRCA mutations are rare. To date, despite promising results in vitro, few clinical trials in humans for haematological malignancies have been performed, and additional investigation is required. Paradoxically, secondary haematological malignancies have arisen in patients after treatment with PARPi, raising concerns about their potential use as therapies for any blood or bone marrow-related disorders. Here, we provide a comprehensive review of the biological, pre-clinical, and clinical evidence for and against treating individual haematological malignancies with approved and experimental PARPi. We conclude that the promise of effective treatment still exists, but remains limited by the lack of investigation into useful biomarkers unique to these malignancies.

Discovery of the PARP (poly ADP-ribose polymerase) inhibitor 2-(1-(4,4-difluorocyclohexyl)piperidin-4-yl)-1H-benzo[d]imidazole-4-carboxamide for the treatment of cancer

In this work, two series of cyclic amine-containing benzimidazole carboxamide derivatives were designed and synthesized as potent anticancer agents. PARP1/2 inhibitory activity assays indicated that most of the compounds showed significant activity. The in vitro antiproliferative activity of these compounds was investigated against four human cancer cell lines (MDA-MB-436, MDA-MB-231, MCF-7 and CAPAN-1), and several compounds exhibited strong cytotoxicity to tumor cells. Among them, 2-(1-(4,4-difluorocyclohexyl)piperidin-4-yl)-1H-benzo[d]imidazole-4-carboxamide (17d) was found to be effective PARP1/2 inhibitors (IC50 = 4.30 and 1.58 nM, respectively). In addition, 17d possessed obvious selective antineoplastic activity and noteworthy microsomal metabolic stability. What's more, further studies revealed that 17d was endowed with an excellent ADME profile. These combined results indicated that 17d could be a promising candidate for the treatment of cancer.

Radiosynthesis of 3 H- and 14 C-labeled Veliparib

Veliparib, a potent PARP inhibitor used against multiple cancerous cells such as metastatic melanoma, breast, non-small cell lung cancer (NSCLC) and prostatic cancer, is required for absorption, distribution, metabolism and excretion (ADME) and environmental toxicology assessments studies. Tritium-labeled Veliparib was prepared via the tritiodebromination using tritium gas (T2 ) in two steps. [14 C]Veliparib was achieved through an asymmetric synthetic route in seven radioactive steps starting from [14 C] (S)-benzyl 2-aminopropanoate.

ADP-Ribosylation Levels and Patterns Correlate with Gene Expression and Clinical Outcomes in Ovarian Cancers

Inhibitors of nuclear PARP enzymes (e.g., PARP-1) have improved clinical outcomes in ovarian cancer, especially in patients with BRCA1/2 gene mutations or additional homologous recombination (HR) DNA repair pathway deficiencies. These defects serve as biomarkers for response to PARP inhibitors (PARPi). We sought to identify an additional biomarker that could predict responses to both conventional chemotherapy and PARPi in ovarian cancers. We focused on cellular ADP-ribosylation (ADPRylation), which is catalyzed by PARP enzymes and detected by detection reagents we developed previously. We determined molecular phenotypes of 34 high-grade serous ovarian cancers and associated them with clinical outcomes. We used the levels and patterns of ADPRylation and PARP-1 to distribute ovarian cancers into distinct molecular phenotypes, which exhibit dramatically different gene expression profiles. In addition, the levels and patterns of ADPRylation, PARP-1 protein, and gene expression correlated with clinical outcomes in response to platinum-based chemotherapy, with cancers exhibiting the highest levels of ADPRylation having the best outcomes independent of BRCA1/2 status. Finally, in cell culture-based assays using patient-derived ovarian cancer cell lines, ADPRylation levels correlated with sensitivity to the PARPi, Olaparib, with cell lines exhibiting high levels of ADPRylation having greater sensitivity to Olaparib. Collectively, our study demonstrates that ovarian cancers exhibit a wide range of ADPRylation levels, which correlate with therapeutic responses and clinical outcomes. These results suggest ADPRylation may be a useful biomarker for PARPi sensitivity in ovarian cancers, independent of BRCA1/2 or homologous recombination deficiency status.

PET of Poly (ADP-Ribose) Polymerase Activity in Cancer: Preclinical Assessment and First In-Human Studies

Purpose To demonstrate that positron emission tomography (PET) with fluorine 18 (¹⁸F) fluorthanatrace (FTT) depicts activated poly (adenosine diphosphate-ribose)polymerase (PARP) expression and is feasible for clinical trial evaluation. Materials and Methods All studies were conducted prospectively from February 2012 through July 2015 under protocols approved by the local animal studies committee and institutional review board. The area under the receiver operating characteristic curve (AUC, in g/mL· min) for ¹⁸F-FTT was assessed in normal mouse organs before and after treatment with olaparib (n = 14), a PARP inhibitor, or iniparib (n = 11), which has no PARP inhibitory activity. Murine biodistribution studies were performed to support human translational studies. Eight human subjects with cancer and eight healthy volunteers underwent imaging to verify the human radiation dosimetry of ¹⁸F-FTT. The Wilcoxon signed rank test was used to assess for differences among treatment groups for the mouse studies. Results In mice, olaparib, but not iniparib, significantly reduced the ¹⁸F-FTT AUC in the spine (median difference before and after treatment and interquartile range [IQR]: -17 g/mL· min and 10 g/mL · min, respectively [P = .0001], for olaparib and -3 g/mL · min and 13 g/mL · min [P = .70] for iniparib) and in nodes (median difference and interquartile range [IQR] before and after treatment: -23 g/mL · min and 13 g/mL · min [P = .0001] for olaparib; -9 g/mL · min and 17 g/mL · min [P = .05] for iniparib). The effective dose was estimated at 6.9 mSv for a 370-MBq ¹⁸F-FTT dose in humans. In humans, the organs with the highest uptake on images were the spleen and pancreas. Among five subjects with measurable tumors, increased ¹⁸F-FTT uptake was seen in one subject with pancreatic adenocarcinoma and another with liver cancer. Conclusion The results suggest that ¹⁸F-FTT uptake reflects PARP expression and that its radiation dosimetry profile is compatible with those of agents currently in clinical use. ^© RSNA, 2016 Online supplemental material is available for this article.

Notch1 phenotype and clinical stage progression in non-small cell lung cancer

Background

Notch1 transmembrane receptor is activated through ligand-binding- triggered proteolytic cleavages and, upon release, the intracellular domain (N1-ICD) translocates into the nucleus and modulates target gene transcriptions. Notch activation has been implicated in tumorigenesis in an increasing number of human malignancies including non-small cell lung cancer (NSCLC). However, Notch1 in distinct expression patterns and activation status with tumor progression remains to be defined in NSCLC.

Methods

Notch1 and activated Notch1, N1-ICD, were examined by immunohistochemistry in 58 cases of stage I to IV NSCLC tumors. Association between Notch1 or N1-ICD expression and clinicopathological factors was assessed via correlation coefficient r statistics. P-values are two-sided.

Results

Detectable tumor Notch1, predominantly localized to the membrane and cytoplasm, was observed in 29 cases (50%, 95% Blyth-Still-Casella confidence interval 37 – 63%). It was negatively associated with stage (r = - 0.43, P < 0.001) and nodal status (r = - 0.33, P = 0.01), but not tumor size. In contrast, nuclear N1-ICD expression level was low and found in 12% of NSCLC patients, neither significantly associated with stage nor nodal status. Upon Notch1 activation in vitro, a mostly extra-nuclear staining was substantially turned into the nuclear signal in cancer cells.

Conclusions

Notch1 in the largely inactivated phenotype is inversely associated with clinical stage progression in NSCLC. Notch1, rather than activated N1-ICD, may be a context-dependent restrictive factor to nodal metastasis.

Standard of care and promising new agents for triple negative metastatic breast cancer

Triple negative breast cancer (TNBC) is a cluster of heterogeneous diseases, all of them sharing the lack of expression of estrogen and progesterone receptors and HER2 protein. They are characterized by different biological, molecular and clinical features, including a poor prognosis despite the increased sensitivity to the current cytotoxic therapies. Several studies have identified important molecular features which enable further subdivision of this type of tumor. We are drawing from genomics, transcription and translation analysis at different levels, to improve our knowledge of the molecular alterations along the pathways which are activated during carcinogenesis and tumor progression. How this information should be used for the rational selection of therapy is an ongoing challenge and the subject of numerous research studies in progress. Currently, the vascular endothelial growth factor (VEGF), poly (ADP-ribose) polymerase (PARP), HSP90 and Aurora inhibitors are most used as targeting agents in metastatic setting clinical trials. In this paper we will review the current knowledge about the genetic subtypes of TNBC and their different responses to conventional therapeutic strategies, as well as to some new promising molecular target agents, aimed to achieve more tailored therapies.

Doubling down on the PI3K-AKT-mTOR pathway enhances the antitumor efficacy of PARP inhibitor in triple negative breast cancer model beyond BRCA-ness

Phosphoinositide 3-kinase (PI3K) pathway, in addition to its pro-proliferative and antiapoptotic effects on tumor cells, contributes to DNA damage repair (DDR). We hypothesized that GDC-0980, a dual PI3K-mammalian target of rapamycin (mTOR) inhibitor, would induce an efficient antitumor effect in BRCA-competent triple negative breast cancer (TNBC) model when combined with ABT888 and carboplatin. Mechanism-based in vitro studies demonstrated that GDC-0980 treatment alone or in combination led to DNA damage (increased pγH2AX(S139); Western blot, immunofluorescence), gain in poly ADP-ribose (PAR), and a subsequent sensitization of BRCA-competent TNBC cells to ABT888 plus carboplatin with a time-dependent 1) decrease in proliferation signals (pAKTT308/S473, pP70S6KT421/S424, pS6RPS235/236), PAR/poly(ADP-ribose) polymerase (PARP) ratios, PAR/pγH2AX ratios, live/dead cell ratios, cell cycle progression, and three-dimensional clonogenic growths and 2) increase in apoptosis markers (cleaved caspases 3 and 9, a pro-apoptotic BH3-only of Bcl-2 family (BIM), cleaved PARP, annexin V). The combination was effective in vitro in BRCA-wild-type PIK3CA-H1047R-mutated BT20 and PTEN-null HCC70 cells. The combination blocked the growth of established xenograft tumors by 80% to 90% with a concomitant decrease in tumor Ki67, CD31, phosphorylated vascular endothelial growth factor receptor, pS6RPS235/236, and p4EBP1T37/46 as well as an increase in cleaved caspase 3 immunohistochemistry (IHC) levels. Interestingly, a combination with GDC-0941, a pan-PI3K inhibitor, failed to block the tumor growth in MDA-MB231. Results demonstrate that the dual inhibition of PI3K and mTOR regulates DDR. In a BRCA-competent model, GDC-0980 enhanced the antitumor activity of ABT888 plus carboplatin by inhibiting both tumor cell proliferation and tumor-induced angiogenesis along with an increase in the tumor cell apoptosis. This is the first mechanism-based study to demonstrate the integral role of the PI3K-AKT-mTOR pathway in DDR-mediated antitumor action of PARP inhibitor in TNBC.

The VEGF inhibitor axitinib has limited effectiveness as a therapy for adrenocortical cancer

CONTEXT

Adrenocortical carcinoma (ACC) is a rare malignancy with a poor prognosis in need of more effective treatment options. Published evidence indicates many ACCs express the vascular endothelial growth factor receptor (VEGFR), suggesting inhibiting vascular endothelial growth factor signaling could potentially impact tumor growth.

OBJECTIVE

The objective of the study was to determine the antitumor efficacy of axitinib (AG-013736), a potent, selective inhibitor of VEGFR1, -2, and -3.

DESIGN

This was a phase II, open-label trial using a two-stage design.

PATIENTS

Thirteen patients with metastatic ACC previously treated with at least one chemotherapy regimen with or without mitotane participated in the study.

INTERVENTION

Starting axitinib dose was 5 mg orally twice daily. Dose escalations were permitted if the administered dose was tolerable.

RESULTS

Thirteen patients were enrolled. Dose escalation was possible in seven patients, but the majority could not tolerate a dose higher than the starting 5 mg, twice-daily dose for prolonged periods of time. All patients experienced known grade 1/2 toxicities, and 10 of 13 patients had at least one grade 3/4 adverse event. No patient tumor could be scored as a Response Evaluation Criteria in Solid Tumors response, although the growth rate on therapy compared with that prior to starting axitinib was reduced in 4 of the 13 patients. The median progression-free survival was 5.48 months, and the median overall survival was longer than 13.7 months.

CONCLUSION

Axitinib has limited effectiveness in ACC. Together with 48 patients previously reported who received either sorafenib or sunitinib, a total of 61 ACC patients have now been treated with a VEGFR tyrosine kinase inhibitor without an objective Response Evaluation Criteria in Solid Tumors response. Future trials in ACC should look to other targets for possible active agents.

Perspective: Opportunities in recalcitrant, rare and neglected tumors

The ‘Recalcitrant Cancer Research Act of 2012’ defines recalcitrant cancers as having a 5-year survival rate of <20% and estimated to cause the death of at least 30,000 individuals in the US each year. Cancers specifically mentioned in the act are lung and pancreatic cancers. In addition to recalcitrant tumors, rare tumors are often neglected in the drug discovery arena. Sarcomas are ~1% of cancers. The NCI Specialized Programs of Research Excellence (SPOREs) provide disease-focused cancer center grants specifically to accelerate the impact of laboratory research on the treatment of patients. There are 3 SPOREs focused on pancreatic cancer, 7 SPOREs focused on lung cancer and 1 SPORE focused on sarcoma. Through the Developmental Therapeutics Program (DTP), NCI maintains the infrastructure and expertise for the operation of cell-free and cell-based high-, medium- and low-throughput assays. The current effort is on sarcoma, SCLC and pancreatic lines. The DTP functional genomics laboratory provides molecular analyses including gene expression microarrays, exon arrays, microRNA arrays, multiplexing gene assays, plus others as tools to identify potential drug targets and to determine the role of selected genes in the mechanism(s) of drug action and cellular responses to stressors. The DTP tumor microenvironment laboratory focuses on the discovery of targets and the development of therapeutic strategies targeting the tumor microenvironment and physiological abnormalities of tumors resulting from environmental factors or alterations in metabolic enzymes. The DTP maintains a group focused on determining the mechanism(s) of action and identifying potential surrogate markers of activity for select compounds integrating proteomics, transcriptomics and molecular biology platforms. In conclusion, the NCI has active SPORE programs and an internal effort focused on recalcitrant, rare and neglected cancers which are generating data toward improving treatment of these difficult diseases.

Treating breast cancer in the 21st century: emerging biological therapies

For many years, the medical treatment of breast cancer was reliant solely on cytotoxic chemotherapy. However, over the past twenty years, treatment has evolved to a more target-directed approach. We now employ tailored therapy based on the presence or absence of receptors for estrogen, progesterone, and human epidermal growth factor 2 (HER2). We expect this trend to continue, as agents that use novel approaches to target HER2, as well as targeting different portions of the HER signaling pathway, are in various stages of development. Notably, pertuzumab, a humanized monoclonal antibody that binds to a different domain of the extracellular portion of the HER2 receptor than trastuzumab, was recently approved for use, as was lapatinib, a small-molecule tyrosine kinase inhibitor. Patients with triple negative breast cancer, particularly those with the BRCA mutation, have more limited treatment options and carry a worse prognosis than those who are hormone receptor positive. However, recent data has shown that PARP inhibitors may have significant anti-tumor effect in those with this subtype of breast cancer. Novel agents that inhibit mTOR, PI3K, the insulin-like growth factor, heat shock protein 90, and histone deacetylase have shown promise in phase I-III trials and offer exciting new possibilities for the treatment of this often fatal disease. As we are presented with an ever increasing number of treatment options, the timing and combinations of therapeutic agents used becomes ever more complex in the age of personalized care, but we are hopeful that ultimately this will lead to improved patient outcomes.

Enhanced killing of cancer cells by poly(ADP-ribose) polymerase inhibitors and topoisomerase I inhibitors reflects poisoning of both enzymes

Poly(ADP-ribose) polymerase-1 (PARP1) plays critical roles in the regulation of DNA repair. Accordingly, small molecule inhibitors of PARP are being developed as agents that could modulate the activity of genotoxic chemotherapy, such as topoisomerase I poisons. In this study we evaluated the ability of the PARP inhibitor veliparib to enhance the cytotoxicity of the topoisomerase I poisons topotecan and camptothecin (CPT). Veliparib increased the cell cycle and cytotoxic effects of topotecan in multiple cell line models. Importantly, this sensitization occurred at veliparib concentrations far below those required to substantially inhibit poly(ADP-ribose) polymer synthesis and at least an order of magnitude lower than those involved in selective killing of homologous recombination-deficient cells. Further studies demonstrated that veliparib enhanced the effects of CPT in wild-type mouse embryonic fibroblasts (MEFs) but not Parp1(-/-) MEFs, confirming that PARP1 is the critical target for this sensitization. Importantly, parental and Parp1(-/-) MEFs had indistinguishable CPT sensitivities, ruling out models in which PARP1 catalytic activity plays a role in protecting cells from topoisomerase I poisons. To the contrary, cells were sensitized to CPT in a veliparib-independent manner upon transfection with PARP1 E988K, which lacks catalytic activity, or the isolated PARP1 DNA binding domain. These results are consistent with a model in which small molecule inhibitors convert PARP1 into a protein that potentiates the effects of topoisomerase I poisons by binding to damaged DNA and preventing its normal repair.

Poly(ADP-ribose) polymerase inhibition enhances p53-dependent and -independent DNA damage responses induced by DNA damaging agent

Targeting DNA repair with poly(ADP-ribose) polymerase (PARP) inhibitors has shown a broad range of anti-tumor activity in patients with advanced malignancies with and without BRCA deficiency. It remains unclear what role p53 plays in response to PARP inhibition in BRCA-proficient cancer cells treated with DNA damaging agents. Using gene expression microarray analysis, we find that DNA damage response (DDR) pathways elicited by veliparib (ABT-888), a PARP inhibitor, plus topotecan comprise the G1/S checkpoint, ATM, and p53 signaling pathways in p53-wildtype cancer cell lines and BRCA1, BRCA2 and ATR pathway in p53-mutant lines. In contrast, topotecan alone induces the G1/S checkpoint pathway in p53-wildtype lines and not in p53-mutant cells. These responses are coupled with G2/G1 checkpoint effectors p21(CDKN1A) upregulation, and Chk1 and Chk2 activation. The drug combination enhances G2 cell cycle arrest, apoptosis and a marked increase in cell death relative to topotecan alone in p53-wildtype and p53-mutant or -null cells. We also show that the checkpoint kinase inhibitor UCN-01 abolishes the G2 arrest induced by the veliparib and topotecan combination and further increases cell death in both p53-wildtype and -mutant cells. Collectively, PARP inhibition by veliparib enhances DDR and cell death in BRCA-proficient cancer cells in a p53-dependent and -independent fashion. Abrogating the cell-cycle arrest induced by PARP inhibition plus chemotherapeutics may be a strategy in the treatment of BRCA-proficient cancer.

Current Status of Poly(ADP-ribose) Polymerase Inhibitors as Novel Therapeutic Agents for Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is an aggressive type of breast cancer that is clinically defined as lacking estrogen and progesterone receptors, as well as being ERBB2 (HER-2) negative. Without specific therapeutic targets, TNBC carries a worse prognosis than other types of breast cancer in the absence of therapy. Research has now further differentiated breast cancer into subtypes based on genetic expression patterns. One of these subtypes, basal-like, frequently overlaps with the clinical picture of TNBC. Additionally, both TNBC and basal-like breast cancer link to BRCA mutations. Recent pharmaceutical advances have created a class of drugs, poly(ADP-ribose) polymerase (PARP) inhibitors, which are showing potential to effectively treat these patients. The aim of this paper is to summarize the basis behind PARP inhibitors and update the current status of their development in clinical trials for the treatment of TNBC.

Poly(ADP-ribosyl)ation polymerases: mechanism and new target of anticancer therapy

Poly(ADP-ribose)polymerase (PARP) is a ubiquitously present nuclear enzyme that is not only involved in many important cellular pathways but also contributes to chromosomal structure and genomic stability. The development of highly selective and potent PARP inhibitors has become of increasing clinical interest because of their promising efficacy in patients with breast or ovarian cancer. Furthermore, recent Phase I and Phase II trials have demonstrated that PARP inhibitors have low toxicity rates. In particular patients with either deficiency or dysfunction of BRCA, which is involved in DNA double strand break repair, appear to benefit from PARP inhibition. This article summarizes the present knowledge regarding the physiological function of PARP and ([poly]ADP-ribose) PAR, the functional product of PARP, the development of PARP inhibitors, the recent clinical data of PARP inhibitors in cancer treatment and the selection of patients who may benefit from PARP inhibition.

Histone gammaH2AX and poly(ADP-ribose) as clinical pharmacodynamic biomarkers

Tumor cells are often deficient in DNA damage response (DDR) pathways, and anticancer therapies are commonly based on genotoxic treatments using radiation and/or drugs that damage DNA directly or interfere with DNA metabolism, leading to the formation of DNA double-strand breaks (DSB), and ultimately to cell death. Because DSBs induce the phosphorylation of histone H2AX (γH2AX) in the chromatin flanking the break site, an antibody directed against γH2AX can be employed to measure DNA damage levels before and after patient treatment. Poly(ADP-ribose) polymerases (PARP1 and PARP2) are also activated by DNA damage, and PARP inhibitors show promising activity in cancers with defective homologous recombination (HR) pathways for DSB repair. Ongoing clinical trials are testing combinations of PARP inhibitors with DNA damaging agents. Poly(ADP-ribosylation), abbreviated as PAR, can be measured in clinical samples and used to determine the efficiency of PARP inhibitors. This review summarizes the roles of γH2AX and PAR in the DDR, and their use as biomarkers to monitor drug response and guide clinical trials, especially phase 0 clinical trials. We also discuss the choices of relevant samples for γH2AX and PAR analyses.