Initial testing (stage 1) of the PARP inhibitor BMN 673 by the pediatric preclinical testing program: PALB2 mutation predicts exceptional in vivo response to BMN 673

Lessons learned from 20 years of preclinical testing in pediatric cancers

Programs for preclinical testing of targeted cancer agents in murine models of childhood cancers have been supported by the National Cancer Institute (NCI) since 2004. These programs were established to work collaboratively with industry partners to address the paucity of targeted agents for pediatric cancers compared with the large number of agents developed and approved for malignancies primarily affecting adults. The distinctive biology of pediatric cancers and the relatively small numbers of pediatric cancer patients are major challenges for pediatric oncology drug development. These factors are exacerbated by the division of cancers into multiple subtypes that are further sub-classified by their genomic properties. The imbalance between the large number of candidate agents and small patient populations requires careful prioritization of agents developed for adult cancers for clinical evaluation in children with cancer. The NCI-supported preclinical pediatric programs have published positive and negative results of efficacy testing for over 100 agents to aid the pediatric research community in identifying the most promising candidates to move forward for clinical testing in pediatric oncology. Here, we review and summarize lessons learned from two decades of experience with the design and execution of preclinical trials of antineoplastic agents in murine models of childhood cancers.

Star wars against leukemia: attacking the clones

Leukemia, although most likely starts as a monoclonal genetic/epigenetic anomaly, is a polyclonal disease at manifestation. This polyclonal nature results from ongoing evolutionary changes in the genome/epigenome of leukemia cells to promote their survival and proliferation advantages. We discuss here how genetic and/or epigenetic aberrations alter intracellular microenvironment in individual leukemia clones and how extracellular microenvironment selects the best fitted clones. This dynamic polyclonal composition of leukemia makes designing an effective therapy a challenging task especially because individual leukemia clones often display substantial differences in response to treatment. Here, we discuss novel therapeutic approach employing single cell multiomics to identify and eradicate all individual clones in a patient.

Widening the spectrum of players affected by genetic changes in Wilms tumor relapse

Few studies investigated the genetics of relapsed Wilms tumor (WT), suggesting the SIX1 gene, the microRNA processing genes, and the MYCN network as possibly involved in a relevant percentage of relapses. We investigated 28 relapsing WT patients (10 new cases and 18 cases in which the involvement of SIX and miRNAPG had been excluded) with a panel of ∼5000 genes. We identified variants affecting genes involved in DNA damage prevention and repair in 12/28 relapsing patients (42.9%), and affecting genes involved in chromatin modification and regulation in 6/28 relapsing patients (21.4%), widening the spectrum of anomalies detected in relapsed tumors. The disclosure of molecular pathways possibly underlying tumor progression might allow to use molecularly targeted therapies at relapse. Surprisingly, germline anomalies, mostly affecting DNA damage prevention and repair genes, were identified in 13/28 patients (46.4%), raising the issue of performing a genetic testing to all children presenting with a WT.

Olaparib for childhood tumors harboring defects in DNA damage repair genes: arm H of the NCI-COG Pediatric MATCH trial

BACKGROUND

The National Cancer Institute-Children's Oncology Group Pediatric Molecular Analysis for Therapy Choice (MATCH) precision oncology platform trial enrolled children aged 1-21 years with treatment-refractory solid tumors and predefined actionable genetic alterations. Patients with tumors harboring alterations in DNA damage repair (DDR) genes were assigned to receive olaparib.

METHODS

Tumor and blood samples were submitted for centralized molecular testing. Tumor and germline sequencing were conducted in parallel. Olaparib was given twice daily for 28-day cycles starting at a dose 30% lower than the adult recommended phase 2 dose (RP2D). The primary endpoint was the objective response.

RESULTS

Eighteen patients matched (1.5% of those screened) based on the presence of a deleterious gene alteration in BRCA1/2, RAD51C/D, or ATM detected by tumor sequencing without germline subtraction or analysis of loss of heterozygosity (LOH). Eleven (61%) harbored a germline mutation, with only one exhibiting LOH. Six patients enrolled and received the olaparib starting dose of 135 mg/m2/dose. Two participants were fully evaluable; 4 were inevaluable because <85% of the prescribed dose was administered during cycle 1. There were no dose-limiting toxicities or responses. Minimal hematologic toxicity was observed.

CONCLUSION

Most DDR gene alterations detected in Pediatric MATCH were germline, monoallelic, and unlikely to confer homologous recombination deficiency predicting sensitivity to olaparib monotherapy. The study closed due to poor accrual.

CLINICALTRIALS.GOV IDENTIFIER

NCT03233204. IRB approved: initial July 24, 2017.

Synergistic Antitumor Activity of Talazoparib and Temozolomide in Malignant Rhabdoid Tumors

Malignant rhabdoid tumors (MRTs) are among the most aggressive and treatment-resistant malignancies affecting infants, originating in the kidney, brain, liver, and soft tissues. The 5-year event-free survival rate for these cancers is a mere 20%. In nearly all cases of MRT, the SMARCB1 gene (occasionally SMARCA4)-a pivotal component of the SWI/SNF chromatin remodeling complex-is homozygously deleted, although the precise etiology of these tumors remains unknown. While young patients with localized MRT generally show improved outcomes, especially those who are older and have early-stage disease, the overall prognosis remains poor despite optimal standard treatments. This highlights the urgent need for more effective treatment strategies. We investigated the antitumor activity of a PARP1 inhibitor (talazoparib, TLZ) combined with a DNA alkylating agent (temozolomide, TMZ) in MRT xenograft models. PARP1 is a widely targeted molecule in cancer treatment and, beyond its role in DNA repair, it participates in transcriptional regulation by recruiting chromatin remodeling complexes to modulate DNA accessibility for RNA polymerases. To widen the therapeutic window of the drug combination, we employed PEGylated TLZ (PEG~TLZ), which has been reported to reduce systemic toxicity through slow drug release. Remarkably, our findings indicate that five out of six MRT xenografts exhibited an objective response to PEG~TLZ+TMZ therapy. Significantly, the loss of SMARCB1 was found to confer a protective effect, correlating with higher expression levels of DNA damage and repair proteins in SMARCB1-deficient MRT cells. Additionally, we identified MGMT as a potential biomarker indicative of in vivo MRT response to PEG~TLZ+TMZ therapy. Moreover, our analysis revealed alterations in signaling pathways associated with the observed antitumor efficacy. This study presents a novel and efficacious therapeutic approach for MRT, along with a promising candidate biomarker for predicting tumor response.

Therapeutic targeting of DNA damage repair pathways guided by homologous recombination deficiency scoring in ovarian cancers

The susceptibility of cells to DNA damage and their DNA repair ability are crucial for cancer therapy. Homologous recombination is one of the major repairing mechanisms for DNA double-strand breaks. Approximately half of ovarian cancer (OvCa) cells harbor homologous recombination deficiency (HRD). Considering that HRD is a major hallmark of OvCas, scholars proposed HRD scoring to evaluate the HRD degree and guide the choice of therapeutic strategies for OvCas. In the last decade, synthetic lethal strategy by targeting poly (ADP-ribose) polymerase (PARP) in HR-deficient OvCas has attracted considerable attention in view of its favorable clinical effort. We therefore suggested that the uses of other DNA damage/repair-targeted drugs in HR-deficient OvCas might also offer better clinical outcome. Here, we reviewed the current small molecule compounds that targeted DNA damage/repair pathways and discussed the HRD scoring system to guide their clinical uses.

Preclinical Efficacy of a PARP-1 Targeted Auger-Emitting Radionuclide in Prostate Cancer

There is an unmet need for better therapeutic strategies for advanced prostate cancer. Poly (ADP-ribose) polymerase-1 (PARP-1) is a chromatin-binding DNA repair enzyme overexpressed in prostate cancer. This study evaluates whether PARP-1, on account of its proximity to the cell's DNA, would be a good target for delivering high-linear energy transfer Auger radiation to induce lethal DNA damage in prostate cancer cells. We analyzed the correlation between PARP-1 expression and Gleason score in a prostate cancer tissue microarray. A radio-brominated Auger emitting inhibitor ([77Br]Br-WC-DZ) targeting PARP-1 was synthesized. The ability of [77Br]Br-WC-DZ to induce cytotoxicity and DNA damage was assessed in vitro. The antitumor efficacy of [77Br]Br-WC-DZ was investigated in prostate cancer xenograft models. PARP-1 expression was found to be positively correlated with the Gleason score, thus making it an attractive target for Auger therapy in advanced diseases. The Auger emitter, [77Br]Br-WC-DZ, induced DNA damage, G2-M cell cycle phase arrest, and cytotoxicity in PC-3 and IGR-CaP1 prostate cancer cells. A single dose of [77Br]Br-WC-DZ inhibited the growth of prostate cancer xenografts and improved the survival of tumor-bearing mice. Our studies establish the fact that PARP-1 targeting Auger emitters could have therapeutic implications in advanced prostate cancer and provides a strong rationale for future clinical investigation.

Gene of the month: PALB2

The partner and localiser of BRCA2 (PALB2) gene, located on chromosome 16, functions as a tumour suppressor that plays a critical role in homologous recombination repair after DNA double-strand breaks. It encodes proteins involved in the BRCA2 and BRCA1, and RAD51 pathways. Heterozygous germline mutations in PALB2 have been implicated in the development of breast, pancreatic and ovarian cancers. Whereas biallelic mutations of PALB2 have been associated with Fanconi anaaemia. Currently, 604 distinct PALB2 variants have been discovered. However, only 140 variants are thought to be pathogenic and approximately 400 are variants of unknown significance. Further studies are needed before the presence of PLAB2 mutations can be implemented as a routine clinical biomarker.

DNA Damage Response in Cancer Therapy and Resistance: Challenges and Opportunities

Resistance to chemo- and radiotherapy is a common event among cancer patients and a reason why new cancer therapies and therapeutic strategies need to be in continuous investigation and development. DNA damage response (DDR) comprises several pathways that eliminate DNA damage to maintain genomic stability and integrity, but different types of cancers are associated with DDR machinery defects. Many improvements have been made in recent years, providing several drugs and therapeutic strategies for cancer patients, including those targeting the DDR pathways. Currently, poly (ADP-ribose) polymerase inhibitors (PARP inhibitors) are the DDR inhibitors (DDRi) approved for several cancers, including breast, ovarian, pancreatic, and prostate cancer. However, PARPi resistance is a growing issue in clinical settings that increases disease relapse and aggravate patients' prognosis. Additionally, resistance to other DDRi is also being found and investigated. The resistance mechanisms to DDRi include reversion mutations, epigenetic modification, stabilization of the replication fork, and increased drug efflux. This review highlights the DDR pathways in cancer therapy, its role in the resistance to conventional treatments, and its exploitation for anticancer treatment. Biomarkers of treatment response, combination strategies with other anticancer agents, resistance mechanisms, and liabilities of treatment with DDR inhibitors are also discussed.

Review of various NAMPT inhibitors for the treatment of cancer

Nicotinamide phosphoribosyltransferase (NAMPT) is a rate-limiting enzyme in the NAD salvage pathway of mammalian cells and is overexpressed in numerous types of cancers. These include breast cancer, ovarian cancer, prostate cancer, gastric cancer, colorectal cancer, glioma, and b-cell lymphoma. NAMPT is also known to impact the NAD and NADPH pool. Research has demonstrated that NAMPT can be inhibited. NAMPT inhibitors are diverse anticancer medicines with significant anti-tumor efficacy in ex vivo tumor models. A few notable NAMPT specific inhibitors which have been produced include FK866, CHS828, and OT-82. Despite encouraging preclinical evidence of the potential utility of NAMPT inhibitors in cancer models, early clinical trials have yielded only modest results, necessitating the adaptation of additional tactics to boost efficacy. This paper examines a number of cancer treatment methods which target NAMPT, including the usage of individual inhibitors, pharmacological combinations, dual inhibitors, and ADCs, all of which have demonstrated promising experimental or clinical results. We intend to contribute further ideas regarding the usage and development of NAMPT inhibitors in clinical therapy to advance the field of research on this intriguing target.

Novel Targeted Therapeutic Strategies for Ewing Sarcoma

Simple Summary

Ewing sarcoma is an uncommon cancer that arises in mesenchymal tissues and represents the second most widespread malignant bone neoplasm after osteosarcoma in children. Therapy has increased the 5-year survival rate in the last 40 years, although the recurrence rate has remained high. There is an immediate and unmet need for the development of novel Ewing sarcoma therapies. We offer new prospective targets for the therapy of Ewing sarcoma. The EWSR1/FLI1 fusion protein, which is identified in 85–90% of Ewing sarcoma tumors, and its direct targets are given special focus in this study. Experimantal therapy that targets multiple signaling pathways activated during ES progression, alone or in combination with existing regimens, may become the new standard of care for Ewing sarcoma patients, improving patient survival.

Abstract

Ewing sarcoma (ES) is an uncommon cancer that arises in mesenchymal tissues and represents the second most widespread malignant bone neoplasm after osteosarcoma in children. Amplifications in genomic, proteomic, and metabolism are characteristics of sarcoma, and targeting altered cancer cell molecular processes has been proposed as the latest promising strategy to fight cancer. Recent technological advancements have elucidated some of the underlying oncogenic characteristics of Ewing sarcoma. Offering new insights into the physiological basis for this phenomenon, our current review examines the dynamics of ES signaling as it related to both ES and the microenvironment by integrating genomic and proteomic analyses. An extensive survey of the literature was performed to compile the findings. We have also highlighted recent and ongoing studies integrating metabolomics and genomics aimed at better understanding the complex interactions as to how ES adapts to changing biochemical changes within the tumor microenvironment.

Germline sequence variants contributing to cancer susceptibility in South African breast cancer patients of African ancestry

Since the discovery of the breast cancer susceptibility genes, BRCA1 and BRCA2, various other genes conferring an increased risk for breast cancer have been identified. Studies to evaluate sequence variants in cancer predisposition genes among women of African ancestry are limited and mostly focused on BRCA1 and BRCA2. To characterize germline sequence variants in cancer susceptibility genes, we analysed a cohort of 165 South African women of self-identified African ancestry diagnosed with breast cancer, who were unselected for family history of cancer. With the exception of four cases, all others were previously investigated for BRCA1 and BRCA2 deleterious variants, and were negative for pathogenic variants. We utilized the Illumina TruSight cancer panel for targeted sequencing of 94 cancer susceptibility genes. A total of 3.6% of patients carried a pathogenic/likely pathogenic variant in a known breast cancer susceptibility gene: 1.2% in BRCA1, 0.6% in each of BRCA2, ATM, CHEK2 and PALB, none of whom had any family history of breast cancer. The mean age of patients who carried deleterious variant in BRCA1/BRCA2 was 39 years and 8 months compared to 47 years and 3 months among women who carried a deleterious variant in other breast cancer susceptibility genes.

One oncogene, several vulnerabilities: EWS/FLI targeted therapies for Ewing sarcoma

EWS/FLI is the defining mutation of Ewing sarcoma. This oncogene drives malignant transformation and progression and occurs in a genetic background characterized by few other recurrent cooperating mutations. In addition, the tumor is absolutely dependent on the continued expression of EWS/FLI to maintain the malignant phenotype. However, EWS/FLI is a transcription factor and therefore a challenging drug target. The difficulty of directly targeting EWS/FLI stems from unique features of this fusion protein as well as the network of interacting proteins required to execute the transcriptional program. This network includes interacting proteins as well as upstream and downstream effectors that together reprogram the epigenome and transcriptome. While the vast number of proteins involved in this process challenge the development of a highly specific inhibitors, they also yield numerous therapeutic opportunities. In this report, we will review how this vast EWS-FLI transcriptional network has been exploited over the last two decades to identify compounds that directly target EWS/FLI and/or associated vulnerabilities.

Development of the PARP inhibitor talazoparib for the treatment of advanced BRCA1 and BRCA2 mutated breast cancer

INTRODUCTION

BRCA1 and BRCA2 (BRCA1/2) mutation breast cancers constitute an uncommon, but unique group of breast cancers that present at a younger age, and are underscored by genomic instability and accumulation of DNA damage. Talazoparib is a potent poly(ADP-ribose) polymerase (PARP) inhibitor that exploits impaired DNA damage response mechanisms in this population of patients and results in significant efficacy. Based on the results of the EMBRACA trial, talazoparib was approved for the treatment of patients with advanced germline BRCA1/2 mutant breast cancer.

AREAS COVERED

In this review, the authors highlight the relevant clinical trials of talazoparib, as well as, safety, tolerability, and quality of life considerations. They also examine putative response and resistance mechanisms, and rational combinatorial therapeutic strategies under development.

EXPERT OPINION

Talazoparib has been a major advance in the treatment of germline BRCA1/2 mutation breast cancer with both clinical efficacy and improvement in quality of life compared to standard cytotoxic chemotherapy. To date, the optimal sequencing of talazoparib administration in the metastatic setting has not yet been established. A deeper understanding of response and resistance mechanisms, and more broadly, the DNA repair pathway, will lead to additional opportunities in targeting this pathway and open up therapeutic indications to a broader patient population.

Prioritization of Novel Agents for Patients with Rhabdomyosarcoma: A Report from the Children's Oncology Group (COG) New Agents for Rhabdomyosarcoma Task Force

Rhabdomyosarcoma is the most common soft tissue sarcoma diagnosed in children and adolescents. Patients that are diagnosed with advanced or relapsed disease have exceptionally poor outcomes. The Children’s Oncology Group (COG) convened a rhabdomyosarcoma new agent task force in 2020 to systematically evaluate novel agents for inclusion in phase 2 or phase 3 clinical trials for patients diagnosed with rhabdomyosarcoma, following a similar effort for Ewing sarcoma. The task force was comprised of clinicians and basic scientists who collectively identified new agents for evaluation and prioritization in clinical trial testing. Here, we report the work of the task force including the framework upon which the decisions were rendered and review the top classes of agents that were discussed. Representative agents include poly-ADP-ribose polymerase (PARP) inhibitors in combination with cytotoxic agents, mitogen-activated protein kinase (MEK) inhibitors in combination with type 1 insulin-like growth factor receptor (IGFR1) inhibitors, histone deacetylase (HDAC) inhibitors, and novel cytotoxic agents.

A Very Long-Acting PARP Inhibitor Suppresses Cancer Cell Growth in DNA Repair-Deficient Tumor Models

PARP inhibitors are approved for treatment of cancers with BRCA1 or BRCA2 defects. In this study, we prepared and characterized a very long-acting PARP inhibitor. Synthesis of a macromolecular prodrug of talazoparib (TLZ) was achieved by covalent conjugation to a PEG_40kDa carrier via a β-eliminative releasable linker. A single injection of the PEG∼TLZ conjugate was as effective as ∼30 daily oral doses of TLZ in growth suppression of homologous recombination-defective tumors in mouse xenografts. These included the KT-10 Wilms' tumor with a PALB2 mutation, the BRCA1-deficient MX-1 triple-negative breast cancer, and the BRCA2-deficient DLD-1 colon cancer; the prodrug did not inhibit an isogenic DLD-1 tumor with wild-type BRCA2. Although the half-life of PEG∼TLZ and released TLZ in the mouse was only ∼1 day, the exposure of released TLZ from a single safe, effective dose of the prodrug exceeded that of oral TLZ given daily over one month. μPET/CT imaging showed high uptake and prolonged retention of an 89Zr-labeled surrogate of PEG∼TLZ in the MX-1 BRCA1-deficient tumor. These data suggest that the long-lasting antitumor effect of the prodrug is due to a combination of its long t _1/2, the high exposure of TLZ released from the prodrug, increased tumor sensitivity upon continued exposure, and tumor accumulation. Using pharmacokinetic parameters of TLZ in humans, we designed a long-acting PEG∼TLZ for humans that may be superior in efficacy to daily oral TLZ and would be useful for treatment of PARP inhibitor-sensitive cancers in which oral medications are not tolerated. SIGNIFICANCE: These findings demonstrate that a single injection of a long-acting prodrug of the PARP inhibitor talazoparib in murine xenografts provides tumor suppression equivalent to a month of daily dosing of talazoparib.

Frequency and prognostic value of mutations associated with the homologous recombination DNA repair pathway in a large pan cancer cohort

PARP inhibitors have shown remarkable efficacy in the clinical management of several BRCA-mutated tumors. This approach is based on the long-standing hypothesis that PARP inhibition will impair the repair of single stranded breaks, causing synthetic lethality in tumors with loss of high-fidelity double-strand break homologous recombination. While this is now well accepted and has been the basis of several successful clinical trials, emerging evidence strongly suggests that mutation to several additional genes involved in homologous recombination may also have predictive value for PARP inhibitors. While this notion is supported by early clinical evidence, the mutation frequencies of these and other functionally related genes are largely unknown, particularly in cancers not classically associated with homologous recombination deficiency. We therefore evaluated the mutation status of 22 genes associated with the homologous recombination DNA repair pathway or PARP inhibitor sensitivity, first in a pan-cancer cohort of 55,586 patients, followed by a more focused analysis in The Cancer Genome Atlas cohort of 12,153 patients. In both groups we observed high rates of mutations in a variety of HR-associated genes largely unexplored in the setting of PARP inhibition, many of which were associated also with poor clinical outcomes. We then extended our study to determine which mutations have a known oncogenic role, as well as similar to known oncogenic mutations that may have a similar phenotype. Finally, we explored the individual cancer histologies in which these genomic alterations are most frequent. We concluded that the rates of deleterious mutations affecting genes associated with the homologous recombination pathway may be underrepresented in a wide range of human cancers, and several of these genes warrant further and more focused investigation, particularly in the setting of PARP inhibition and HR deficiency.

A therapeutic update on PARP inhibitors: implications in the treatment of glioma

Central nervous system (CNS) cancers are among the most aggressive and devastating. Further, due to unavailability of neuro-oncologists and neurosurgeons, the specialized treatment options of CNS cancers are still not completely available in most parts of the world. Among various strategies of inducing death in cancer cells, inhibition of poly(ADP-ribose) polymerase (PARP) has emerged as a beneficial therapy when combined with other anticancer agents. In this review, we provide a detailed therapeutic update of PARP inhibitors that have shown clinical activity against glioma.

DL, Esteban-Cardeñosa EM, Avila Cobos F, Lastra E, Abella LE, de la Cruz V, Lobatón CD, Claes KB, Durán M, Infante M. Germline Genetic Findings Which May Impact Therapeutic Decisions in Families with a Presumed Predisposition for Hereditary Breast and Ovarian Cancer

In this study, we aim to gain insight in the germline mutation spectrum of ATM, BARD1, BRIP1, ERCC4, PALB2, RAD51C and RAD51D in breast and ovarian cancer families from Spain. We have selected 180 index cases in whom a germline mutation in BRCA1 and BRCA2 was previously ruled out. The importance of disease-causing variants in these genes lies in the fact that they may have possible therapeutic implications according to clinical guidelines. All variants were assessed by combined annotation dependent depletion (CADD) for scoring their deleteriousness. In addition, we used the cancer genome interpreter to explore the implications of some variants in drug response. Finally, we compiled and evaluated the family history to assess whether carrying a pathogenic mutation was associated with age at diagnosis, tumour diversity of the pedigree and total number of cancer cases in the family. Eight unequivocal pathogenic mutations were found and another fourteen were prioritized as possible causal variants. Some of these molecular results could contribute to cancer diagnosis, treatment selection and prevention. We found a statistically significant association between tumour diversity in the family and carrying a variant with a high score predicting pathogenicity (p = 0.0003).

DNA Repair and Ovarian Carcinogenesis: Impact on Risk, Prognosis and Therapy Outcome

There is ample evidence for the essential involvement of DNA repair and DNA damage response in the onset of solid malignancies, including ovarian cancer. Indeed, high-penetrance germline mutations in DNA repair genes are important players in familial cancers: BRCA1, BRCA2 mutations or mismatch repair, and polymerase deficiency in colorectal, breast, and ovarian cancers. Recently, some molecular hallmarks (e.g., TP53, KRAS, BRAF, RAD51C/D or PTEN mutations) of ovarian carcinomas were identified. The manuscript overviews the role of DNA repair machinery in ovarian cancer, its risk, prognosis, and therapy outcome. We have attempted to expose molecular hallmarks of ovarian cancer with a focus on DNA repair system and scrutinized genetic, epigenetic, functional, and protein alterations in individual DNA repair pathways (homologous recombination, non-homologous end-joining, DNA mismatch repair, base- and nucleotide-excision repair, and direct repair). We suggest that lack of knowledge particularly in non-homologous end joining repair pathway and the interplay between DNA repair pathways needs to be confronted. The most important genes of the DNA repair system are emphasized and their targeting in ovarian cancer will deserve further attention. The function of those genes, as well as the functional status of the entire DNA repair pathways, should be investigated in detail in the near future.

A global functional analysis of missense mutations reveals two major hotspots in the PALB2 tumor suppressor

While biallelic mutations in the PALB2 tumor suppressor cause Fanconi anemia subtype FA-N, monoallelic mutations predispose to breast and familial pancreatic cancer. Although hundreds of missense variants in PALB2 have been identified in patients to date, only a few have clear functional and clinical relevance. Herein, we investigate the effects of 44 PALB2 variants of uncertain significance found in breast cancer patients and provide detailed analysis by systematic functional assays. Our comprehensive functional analysis reveals two hotspots for potentially deleterious variations within PALB2, one at each terminus. PALB2 N-terminus variants p.P8L [c.23C>T], p.Y28C [c.83A>G], and p.R37H [c.110G>A] compromised PALB2-mediated homologous recombination. At the C-terminus, PALB2 variants p.L947F [c.2841G>T], p.L947S [c.2840T>C], and most strikingly p.T1030I [c.3089C>T] and p.W1140G [c.3418T>C], stood out with pronounced PARP inhibitor sensitivity and cytoplasmic accumulation in addition to marked defects in recruitment to DNA damage sites, interaction with BRCA2 and homologous recombination. Altogether, our findings show that a combination of functional assays is necessary to assess the impact of germline missense variants on PALB2 function, in order to guide proper classification of their deleteriousness.

Spectrum of PALB2 germline mutations and characteristics of PALB2-related breast cancer: Screening of 16,501 unselected patients with breast cancer and 5890 controls by next-generation sequencing

BACKGROUND

Partner and localizer BRCA2 (PALB2) is a breast cancer predisposition gene, but the clinical relevance of PALB2 germline mutations in Chinese patients with breast cancer remains unknown. This study attempted to investigate the full prevalence and spectrum of PALB2 germline mutations in China and the associations between PALB2 germline mutations and breast cancer risk.

METHODS

A total of 21,216 unselected patients with breast cancer were enrolled from 10 provinces in China, and 5890 Chinese women without cancer were enrolled as healthy controls. PALB2 screening was based on next-generation sequencing.

RESULTS

A total of 16,501 BRCA1/2-negative patients with breast cancer were analyzed. Deleterious PALB2 mutation carriers accounted for 0.97% (n = 160) in the breast cancer cohort and for 0.19% (n = 11) in the healthy control cohort. Forty-one novel PALB2 germline mutations were identified. A high frequency of PALB2 c.751C>T was detected, and it accounted for 10.63% of the PALB2 germline mutations detected (17 of 160). PALB2 mutations were significantly associated with increased breast cancer risk (odds ratio [OR], 5.23; 95% confidence interval [CI], 2.84-9.65; P < .0001), especially among women 30 years old or younger (OR, 10.09; 95% CI, 3.95-25.79; P < .0001). Clinical characteristics, including a family history, bigger tumor size, triple-negative breast cancer, positive lymph nodes, and bilateral breast cancer, were closely related to PALB2 mutations.

CONCLUSIONS

This study revealed a comprehensive spectrum of PALB2 germline mutations and characteristics of PALB2-related breast cancer in China. PALB2 germline mutations confer a moderately increased risk for breast cancer but profoundly increase breast cancer risk for those 30 years old or younger in the Chinese population.

Genomic alterations in breast cancer: level of evidence for actionability according to ESMO Scale for Clinical Actionability of molecular Targets (ESCAT)

Better knowledge of the tumor genomic landscapes has helped to develop more effective targeted drugs. However, there is no tool to interpret targetability of genomic alterations assessed by next-generation sequencing in the context of clinical practice. Our aim is to rank the level of evidence of individual recurrent genomic alterations observed in breast cancer based on the ESMO Scale for Clinical Actionability of molecular Targets (ESCAT) in order to help the clinicians to prioritize treatment. Analyses of databases suggested that there are around 40 recurrent driver alterations in breast cancer. ERBB2 amplification, germline BRCA1/2 mutations, PIK3CA mutations were classified tier of evidence IA based on large randomized trials showing antitumor activity of targeted therapies in patients presenting the alterations. NTRK fusions and microsatellite instability (MSI) were ranked IC. ESR1 mutations and PTEN loss were ranked tier IIA, and ERBB2 mutations and AKT1 mutations tier IIB. Somatic BRCA 1/2 mutations, MDM2 amplifications and ERBB 3 mutations were ranked tier III. Seventeen genes were ranked tier IV based on preclinical evidence. Finally, FGFR1 and CCND1 were ranked tier X alterations because previous studies have shown lack of actionability.

Inhibitors of the Fanconi anaemia pathway as potential antitumour agents for ovarian cancer

The Fanconi anaemia (FA) pathway is an important mechanism for cellular DNA damage repair, which functions to remove toxic DNA interstrand crosslinks. This is particularly relevant in the context of ovarian and other cancers which rely extensively on interstrand cross-link generating platinum chemotherapy as standard of care treatment. These cancers often respond well to initial treatment, but reoccur with resistant disease and upregulation of DNA damage repair pathways. The FA pathway is therefore of great interest as a target for therapies that aim to improve the efficacy of platinum chemotherapies, and reverse tumour resistance to these. In this review, we discuss recent advances in understanding the mechanism of interstrand cross-link repair by the FA pathway, and the potential of the component parts as targets for therapeutic agents. We then focus on the current state of play of inhibitor development, covering both the characterisation of broad spectrum inhibitors and high throughput screening approaches to identify novel small molecule inhibitors. We also consider synthetic lethality between the FA pathway and other DNA damage repair pathways as a therapeutic approach.

Molecular Mechanisms of PALB2 Function and Its Role in Breast Cancer Management

Partner and localizer of BRCA2 (PALB2) is vital for homologous recombination (HR) repair in response to DNA double-strand breaks (DSBs). PALB2 functions as a tumor suppressor and participates in the maintenance of genome integrity. In this review, we summarize the current knowledge of the biological roles of the multifaceted PALB2 protein and of its regulation. Moreover, we describe the link between PALB2 pathogenic variants (PVs) and breast cancer predisposition, aggressive clinicopathological features, and adverse clinical prognosis. We also refer to both the opportunities and challenges that the identification of PALB2 PVs provides in breast cancer genetic counseling and precision medicine.

Therapeutic Application of PARP Inhibitors in Neuro-Oncology

In response to a variety of cellular stresses, poly(ADP-ribose) polymerase 1 (PARP1) has vital roles in orchestrating DNA damage repair and preserving genomic integrity. Clinical activity of PARP inhibitors (PARPis) in BRCA1/2 mutant cancers validated the concept of synthetic lethality between PARP inhibition and deleterious BRCA1/2 mutations, leading to clinical approval of several PARPis. Preclinical and clinical studies aiming to broaden the therapeutic application of PARPis identified sensitivity biomarkers and rationale combination strategies that can target BRCA wild-type and homologous recombination (HR) DNA repair-proficient cancers, including central nervous system (CNS) malignancies. In this review, we summarize recent progress in PARPi therapy in brain tumors, and discuss current opportunities for, and challenges to, the use of PARPis in neuro-oncology.

Nanoformulation of Talazoparib Increases Maximum Tolerated Doses in Combination With Temozolomide for Treatment of Ewing Sarcoma

The Pediatric Preclinical Testing Program previously identified the PARP inhibitor talazoparib (TLZ) as a means to potentiate temozolomide (TMZ) activity for the treatment of Ewing sarcoma. However, the combination of TLZ and TMZ has been toxic in both preclinical and clinical testing, necessitating TMZ dose reduction to ~15% of the single agent maximum tolerated dose. We have synthesized a nanoparticle formulation of talazoparib (NanoTLZ) to be administered intravenously in an effort to modulate the toxicity profile of this combination treatment. Results in Ewing sarcoma xenograft models are presented to demonstrate the utility of this delivery method both alone and in combination with TMZ. NanoTLZ reduced gross toxicity and had a higher maximum tolerated dose than oral TLZ. The dose of TMZ did not have to be reduced when combined with NanoTLZ as was required when combined with oral TLZ. This indicated the NanoTLZ delivery system may be advantageous in decreasing the systemic toxicity associated with the combination of oral TLZ and TMZ.

Novel therapy for pediatric and adolescent kidney cancer

Pediatric and adolescent renal tumors account for approximately 7% of all new cancer diagnoses in the USA each year. The prognosis and treatment are varied based on factors including the underlying histology and tumor stage, with survival rates ranging from greater than 90% in favorable histology Wilms tumor to almost universally fatal in other disease types, including those patients with advanced stage malignant rhabdoid tumor and renal medullary carcinoma. In recent years, our understanding of the underlying genetic drivers of the different types of pediatric kidney cancer has dramatically increased, opening the door to utilization of new targeted biologic agents alone or in combination with conventional chemotherapy to improve outcomes. Several ongoing clinical trials are investigating the use of a variety of targeted agents in pediatric patients with underlying genetic aberrations. In this manuscript, the underlying biology and early phase clinical trials relevant to pediatric renal cancers are reviewed.

Challenges and Opportunities for Childhood Cancer Drug Development

Cancer in children is rare with approximately 15,700 new cases diagnosed in the United States annually. Through use of multimodality therapy (surgery, radiation therapy, and aggressive chemotherapy), 70% of patients will be "cured" of their disease, and 5-year event-free survival exceeds 80%. However, for patients surviving their malignancy, therapy-related long-term adverse effects are severe, with an estimated 50% having chronic life-threatening toxicities related to therapy in their fourth or fifth decade of life. While overall intensive therapy with cytotoxic agents continues to reduce cancer-related mortality, new understanding of the molecular etiology of many childhood cancers offers an opportunity to redirect efforts to develop effective, less genotoxic therapeutic options, including agents that target oncogenic drivers directly, and the potential for use of agents that target the tumor microenvironment and immune-directed therapies. However, for many high-risk cancers, significant challenges remain.

Genome-scale CRISPR knockout screen identifies TIGAR as a modifier of PARP inhibitor sensitivity

Treatment of cancer with poly (ADP-ribose) polymerase (PARP) inhibitors is currently limited to cells defective in the homologous recombination (HR) pathway. Identification of genetic targets that induce or mimic HR deficiencies will extend the clinical utility of PARP inhibitors. Here we perform a CRISPR/Cas9-based genome-scale loss-of-function screen, using the sensitivity of PARP inhibitor olaparib as a surrogate. We identify C12orf5, encoding TP53 induced glycolysis and apoptosis regulator (TIGAR), as a modifier of PARP inhibitor response. We show that TIGAR is amplified in several cancer types, and higher expression of TIGAR associates with poor overall survival in ovarian cancer. TIGAR knockdown enhances sensitivity to olaparib in cancer cells via downregulation of BRCA1 and the Fanconi anemia pathway and increases senescence of these cells by affecting metabolic pathways and increasing the cytotoxic effects of olaparib. Our results indicate TIGAR should be explored as a therapeutic target for treating cancer and extending the use of PARP inhibitors.

Pingping Fang et al. report a CRISPR/Cas9-based genome-scale loss-of-function screen identifying TIGAR as a modifier of response to PARP inhibition. The authors find that knockdown of TIGAR increases intracellular reactive oxygen species levels, enhances more DNA damage after olaparib treatment, and induces a state of “BRCAness”, suggesting that TIGAR is a potential therapeutic target in ovarian cancer patients.

Targeting PARP-1 with Alpha-Particles Is Potently Cytotoxic to Human Neuroblastoma in Preclinical Models

Alpha-emitters can be pharmacologically delivered for irradiation of single cancer cells, but cellular lethality could be further enhanced by targeting alpha-emitters directly to the nucleus. PARP-1 is a druggable protein in the nucleus that is overexpressed in neuroblastoma compared with normal tissues and is associated with decreased survival in high-risk patients. To exploit this, we have functionalized a PARP inhibitor (PARPi) with an alpha-emitter astatine-211. This approach offers enhanced cytotoxicity from conventional PARPis by not requiring enzymatic inhibition of PARP-1 to elicit DNA damage; instead, the alpha-particle directly induces multiple double-strand DNA breaks across the particle track. Here, we explored the efficacy of [²¹¹At]MM4 in multiple cancers and found neuroblastoma to be highly sensitive in vitro and in vivo Furthermore, alpha-particles delivered to neuroblastoma show antitumor effects and durable responses in a neuroblastoma xenograft model, especially when administered in a fractionated regimen. This work provides the preclinical proof of concept for an alpha-emitting drug conjugate that directly targets cancer chromatin as a therapeutic approach for neuroblastoma and perhaps other cancers.

The Tumor Suppressor PALB2: Inside Out

Partner and Localizer of BRCA2 (PALB2) has emerged as an important and versatile player in genome integrity maintenance. Biallelic mutations in PALB2 cause Fanconi anemia (FA) subtype FA-N, whereas monoallelic mutations predispose to breast, and pancreatic familial cancers. Herein, we review recent developments in our understanding of the mechanisms of regulation of the tumor suppressor PALB2 and its functional domains. Regulation of PALB2 functions in DNA damage response and repair occurs on multiple levels, including homodimerization, phosphorylation, and ubiquitylation. With a molecular emphasis, we present PALB2-associated cancer mutations and their detailed analysis by functional assays.

A PALB2 truncating mutation: Implication in cancer prevention and therapy of Hereditary Breast and Ovarian Cancer

Explaining genetic predisposition in Hereditary Breast and Ovarian Cancer (HBOC) families without BRCA mutations is crucial. Germline PALB2 inactivating mutations were associated with an increased risk of HBOC due to its role in DNA repair through cooperation with BRCA proteins. The prevalence and penetrance of PALB2 mutations in Spanish HBOC patients remains unexplained. PALB2 mutation screening has been conducted in 160 high-risk BRCA-negative patients and 320 controls. We evaluated four predicted splicing disruption variants and large genomic rearrangements by multiplex ligation-dependent probe amplification. We have found a frameshift mutation which segregates in an early onset cancer family; and four rare missense variants. None of the variants tested for a predicted splicing disruption showed an aberrant transcript pattern. No large genomic rearrangements were detected. Although PALB2 truncating mutations are rarely identified, segregation analysis and early onset cancer suggest a significant contribution to HBOC susceptibility in the Spanish population. PALB2 screening may improve genetic counselling through prevention measures, pedigree management and PARP inhibitor therapy selection.

The Combination of the PARP Inhibitor Olaparib and the WEE1 Inhibitor AZD1775 as a New Therapeutic Option for Small Cell Lung Cancer

Purpose: Introduced in 1987, platinum-based chemotherapy remains standard of care for small cell lung cancer (SCLC), a most aggressive, recalcitrant tumor. Prominent barriers to progress are paucity of tumor tissue to identify drug targets and patient-relevant models to interrogate novel therapies. Following our development of circulating tumor cell patient-derived explants (CDX) as models that faithfully mirror patient disease, here we exploit CDX to examine new therapeutic options for SCLC.Experimental Design: We investigated the efficacy of the PARP inhibitor olaparib alone or in combination with the WEE1 kinase inhibitor AZD1775 in 10 phenotypically distinct SCLC CDX in vivo and/or ex vivo These CDX represent chemosensitive and chemorefractory disease including the first reported paired CDX generated longitudinally before treatment and upon disease progression.Results: There was a heterogeneous depth and duration of response to olaparib/AZD1775 that diminished when tested at disease progression. However, efficacy of this combination consistently exceeded that of cisplatin/etoposide, with cures in one CDX model. Genomic and protein analyses revealed defects in homologous recombination repair genes and oncogenes that induce replication stress (such as MYC family members), predisposed CDX to combined olaparib/AZD1775 sensitivity, although universal predictors of response were not noted.Conclusions: These preclinical data provide a strong rationale to trial this combination in the clinic informed by prevalent, readily accessed circulating tumor cell-based biomarkers. New therapies will be evaluated in SCLC patients after first-line chemotherapy, and our data suggest that the combination of olaparib/AZD1775 should be used as early as possible and before disease relapse. Clin Cancer Res; 24(20); 5153-64. ©2018 AACR.

Osteosarcoma cells with genetic signatures of BRCAness are susceptible to the PARP inhibitor talazoparib alone or in combination with chemotherapeutics

We recently discovered mutation signatures reminiscent of BRCA deficiency in the vast majority of a set of primary osteosarcomas (OS). In the current study, we therefore investigated the sensitivity of a panel of OS cell lines to the poly(ADP)-ribose polymerase (PARP) inhibitor talazoparib alone and in combination with several chemotherapeutic drugs (i.e. temozolomide (TMZ), SN-38, doxorubicin, cisplatin, methotrexate (MTX), etoposide/carboplatin). Here, we identified an association between homologous recombination (HR) repair deficiency and the response of OS cell lines to talazoparib. All OS cell lines with molecular features characteristic of BRCA1/2 mutant tumors (so-called “BRCAness”), such as disruptive gains in PTEN or FANCD2 and/or losses of ATM, BAP1, BARD1 or CHEK2, were susceptible to talazoparib-induced reduction of cell viability (i.e. MG63, ZK-58,, SaOS-2 and MNNG-HOS). Consistent with their high sensitivity to talazoparib, MG63 and ZK-58 cells scored positive in a DNA-based measure of genomic instability (i.e. homologous recombination deficiency (HRD)-loss of heterozygosity (LOH) score). In contrast, U2OS cells that carry a heterozygous BRCA2 mutation and therefore most likely have one intact BRCA2 allele left proved to be resistant to talazoparib. Furthermore, we identified TMZ as the most potent chemotherapeutic drug together with talazoparib to synergistically reduce cell viability, as confirmed by calculation of combination index (CI) values, and to suppress long-term clonogenic survival. Mechanistically, talazoparib and TMZ cooperated to induce apoptotic cell death, as demonstrated by activation of BAX and BAK, loss of mitochondrial membrane potential (MMP), caspase activation, DNA fragmentation and caspase-dependent cell death. Genetic silencing of BAX and BAK or pharmacological inhibition of caspases by zVAD.fmk significantly rescued OS cells from talazoparib/TMZ-induced apoptosis. These findings have important implications for the development of novel treatment strategies using PARP inhibitors alone or together with chemotherapy in a subset of OS with features of BRCAness.

Targeting DNA repair: the genome as a potential biomarker

Genomic instability and mutations are fundamental aspects of human malignancies, leading to progressive accumulation of the hallmarks of cancer. For some time, it has been clear that key mutations may be used as both prognostic and predictive biomarkers, the best-known examples being the presence of germline BRCA1 or BRCA2 mutations, which are not only associated with improved prognosis in ovarian cancer, but are also predictive of response to poly(ADP-ribose) polymerase (PARP) inhibitors. Although biomarkers as specific and powerful as these are rare in human malignancies, next-generation sequencing and improved bioinformatic analyses are revealing mutational signatures, i.e. broader patterns of alterations in the cancer genome that have the power to reveal information about underlying driver mutational processes. Thus, the cancer genome can act as a stratification factor in clinical trials and, ultimately, will be used to drive personalized treatment decisions. In this review, we use ovarian high-grade serous carcinoma (HGSC) as an example of a disease of extreme genomic complexity that is marked by widespread copy number alterations, but that lacks powerful driver oncogene mutations. Understanding of the genomics of HGSC has led to the routine introduction of germline and somatic BRCA1/2 testing, as well as testing of mutations in other homologous recombination genes, widening the range of patients who may benefit from PARP inhibitors. We will discuss how whole genome-wide analyses, including loss of heterozygosity quantification and whole genome sequencing, may extend this paradigm to allow all patients to benefit from effective targeted therapies. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Synthetic Lethality of PARP Inhibition and Ionizing Radiation is p53-dependent

PARP inhibitors (PARPi) are potentially effective therapeutic agents capable of inducing synthetic lethality in tumors with deficiencies in homologous recombination (HR)-mediated DNA repair such as those carrying BRCA1 mutations. However, BRCA mutations are rare, the majority of tumors are proficient in HR repair, and thus most tumors are resistant to PARPi. Previously, we observed that ionizing radiation (IR) initiates cytoplasmic translocation of BRCA1 leading to suppression of HR-mediated DNA repair and induction of synthetic PARPi lethality in wild-type BRCA1 and HR-proficient tumor cells. The tumor suppressor p53 was identified as a key factor that regulates DNA damage-induced BRCA1 cytoplasmic sequestration following IR. However, the role of p53 in IR-induced PARPi sensitization remains unclear. This study elucidates the role of p53 in IR-induced PARPi cytotoxicity in HR-proficient cancer cells and suggests p53 status may help define a patient population that might benefit from this treatment strategy. Sensitization to PARPi following IR was determined in vitro and in vivo utilizing human breast and glioma tumor cells carrying wild-type BRCA1 and p53, and in associated cells in which p53 function was modified by knockdown or mutation. In breast and glioma cells with proficient HR repair, IR-induced BRCA1 cytoplasmic sequestration, HR repair inhibition, and subsequent PARPi sensitization in vitro and in vivo was dependent upon functional p53.Implications: Implications: p53 status determines PARP inhibitor sensitization by ionizing radiation in multiple BRCA1 and HR-proficient tumor types and may predict which patients are most likely to benefit from combination therapy. Mol Cancer Res; 16(7); 1092-102. ©2018 AACR.

Initial testing (stage 1) of M6620 (formerly VX-970), a novel ATR inhibitor, alone and combined with cisplatin and melphalan, by the Pediatric Preclinical Testing Program

BACKGROUND

M6620 is a novel inhibitor of the DNA damage repair enzyme ATR, and has potentiated the activity of cisplatin and irinotecan in non-small cell lung cancer and colon cancer xenografts, respectively.

PROCEDURES

M6620 was tested in vitro at concentrations ranging from 1.0 nM to 10.0 μM and at 75 nM in combination with cisplatin or melphalan. M6620 was tested against 24 solid tumor xenografts alone and in combination with cisplatin. Cisplatin was administered intraperitoneally on days 1 and 8 at a dose of 5 mg/kg. M6620 was administered intravenously on days 2 and 9 at 20 mg/m2 approximately 16 hr after cisplatin.

RESULTS

The median relative IC50 (rIC50 ) value for M6620 was 0.19 μM (range 0.03-1.38 μM). M6620 reduced the mean IC50 of cisplatin and melphalan by 1.48- and 1.95-fold, respectively. M6620 as a single agent in vivo induced significant differences in event-free survival (EFS) distribution in 5 of 24 (21%) solid tumor xenografts, but induced no objective responses. Cisplatin as a single agent induced significant differences in EFS distribution compared to control in 18 of 24 (75%) solid tumor xenografts. Three objective responses to cisplatin were observed. The M6620 and cisplatin combination induced significant differences in EFS distribution compared to control in 21 of 24 (88%), with four objective responses.

CONCLUSIONS

M6620 showed modest potentiation of cisplatin and melphalan activity for some cell lines. M6620 showed little single-agent activity and the addition of M6620 to cisplatin significantly prolonged time to event for a minority of tested xenografts across several histologies.

Replication Study: Systematic identification of genomic markers of drug sensitivity in cancer cells

In 2016, as part of the Reproducibility Project: Cancer Biology, we published a Registered Report (Vanden Heuvel et al., 2016), that described how we intended to replicate selected experiments from the paper ‘Systematic identification of genomic markers of drug sensitivity in cancer cells’ (Garnett et al., 2012). Here we report the results. We found Ewing’s sarcoma cell lines, overall, were more sensitive to the PARP inhibitor olaparib than osteosarcoma cell lines; however, while the effect was in the same direction as the original study (Figure 4C; Garnett et al., 2012), it was not statistically significant. Further, mouse mesenchymal cells transformed with either the EWS-FLI1 or FUS-CHOP rearrangement displayed similar sensitivities to olaparib, whereas the Ewing’s sarcoma cell line SK-N-MC had increased olaparib sensitivity. In the original study, mouse mesenchymal cells transformed with the EWS-FLI1 rearrangement and SK-N-MC cells were found to have similar sensitivities to olaparib, whereas mesenchymal cells transformed with the FUS-CHOP rearrangement displayed a reduced sensitivity to olaparib (Figure 4E; Garnett et al., 2012). We also studied another Ewing’s sarcoma cell line, A673: A673 cells depleted of EWS-FLI1 or a negative control both displayed similar sensitivities to olaparib, whereas the original study reported a decreased sensitivity to olaparib when EWS-FLI1 was depleted (Figure 4F; Garnett et al., 2012). Differences between the original study and this replication attempt, such as the use of different sarcoma cell lines and level of knockdown efficiency, are factors that might have influenced the outcomes. Finally, where possible, we report meta-analyses for each result.

WD40 repeat domain proteins: a novel target class?

Antagonism of protein-protein interactions (PPIs) with small molecules is becoming more feasible as a therapeutic approach. Successful PPI inhibitors tend to target proteins containing deep peptide-binding grooves or pockets rather than the more common large, flat protein interaction surfaces. Here, we review one of the most abundant PPI domains in the human proteome, the WD40 repeat (WDR) domain, which has a central peptide-binding pocket and is a member of the β-propeller domain-containing protein family. Recently, two WDR domain-containing proteins, WDR5 and EED, as well as other β-propeller domains have been successfully targeted by potent, specific, cell-active, drug-like chemical probes. Could WDR domains be a novel target class for drug discovery? Although the research is at an early stage and therefore not clinically validated, cautious optimism is justified, as WDR domain-containing proteins are involved in multiple disease-associated pathways. The druggability and structural diversity of WDR domain binding pockets suggest that understanding how to target this prevalent domain class will open up areas of disease biology that have so far resisted drug discovery efforts.

Prospective Feasibility Trial for Genomics-Informed Treatment in Recurrent and Progressive Glioblastoma

Purpose: Glioblastoma is an aggressive and molecularly heterogeneous cancer with few effective treatment options. We hypothesized that next-generation sequencing can be used to guide treatment recommendations within a clinically acceptable time frame following surgery for patients with recurrent glioblastoma.Experimental Design: We conducted a prospective genomics-informed feasibility trial in adults with recurrent and progressive glioblastoma. Following surgical resection, genome-wide tumor/normal exome sequencing and tumor RNA sequencing were performed to identify molecular targets for potential matched therapy. A multidisciplinary molecular tumor board issued treatment recommendations based on the genomic results, blood-brain barrier penetration of the indicated therapies, drug-drug interactions, and drug safety profiles. Feasibility of generating genomics-informed treatment recommendations within 35 days of surgery was assessed.Results: Of the 20 patients enrolled in the study, 16 patients had sufficient tumor tissue for analysis. Exome sequencing was completed for all patients, and RNA sequencing was completed for 14 patients. Treatment recommendations were provided within the study's feasibility time frame for 15 of 16 (94%) patients. Seven patients received treatment based on the tumor board recommendations. Two patients reached 12-month progression-free survival, both adhering to treatments based on the molecular profiling results. One patient remained on treatment and progression free 21 months after surgery, 3 times longer than the patient's previous time to progression. Analysis of matched nonenhancing tissue from 12 patients revealed overlapping as well as novel putatively actionable genomic alterations.Conclusions: Use of genome-wide molecular profiling is feasible and can be informative for guiding real-time, central nervous system-penetrant, genomics-informed treatment recommendations for patients with recurrent glioblastoma. Clin Cancer Res; 24(2); 295-305. ©2017 AACRSee related commentary by Wick and Kessler, p. 256.

Matrix Screen Identifies Synergistic Combination of PARP Inhibitors and Nicotinamide Phosphoribosyltransferase (NAMPT) Inhibitors in Ewing Sarcoma

Purpose: Although many cancers are showing remarkable responses to targeted therapies, pediatric sarcomas, including Ewing sarcoma, remain recalcitrant. To broaden the therapeutic landscape, we explored the in vitro response of Ewing sarcoma cell lines against a large collection of investigational and approved drugs to identify candidate combinations.Experimental Design: Drugs displaying activity as single agents were evaluated in combinatorial (matrix) format to identify highly active, synergistic drug combinations, and combinations were subsequently validated in multiple cell lines using various agents from each class. Comprehensive metabolomic and proteomic profiling was performed to better understand the mechanism underlying the synergy. Xenograft experiments were performed to determine efficacy and in vivo mechanism.Results: Several promising candidates emerged, including the combination of small-molecule PARP and nicotinamide phosphoribosyltransferase (NAMPT) inhibitors, a rational combination as NAMPTis block the rate-limiting enzyme in the production of nicotinamide adenine dinucleotide (NAD⁺), a necessary substrate of PARP. Mechanistic drivers of the synergistic cell killing phenotype of these combined drugs included depletion of NMN and NAD⁺, diminished PAR activity, increased DNA damage, and apoptosis. Combination PARPis and NAMPTis in vivo resulted in tumor regression, delayed disease progression, and increased survival.Conclusions: These studies highlight the potential of these drugs as a possible therapeutic option in treating patients with Ewing sarcoma. Clin Cancer Res; 23(23); 7301-11. ©2017 AACR.

Differential Toxicity in Patients with and without DNA Repair Mutations: Phase I Study of Carboplatin and Talazoparib in Advanced Solid Tumors

Purpose: The PARP inhibitor (PARPi) talazoparib may potentiate activity of chemotherapy and toxicity in cells vulnerable to DNA damage.Experimental Design: This phase I study evaluated the safety, tolerability, pharmacokinetics, and efficacy of talazoparib and carboplatin. Pharmacokinetic modeling explored associations between DNA vulnerability and hematologic toxicity.Results: Twenty-four patients (eight males; 16 females) with solid tumors were enrolled in four cohorts at 0.75 and 1 mg daily talazoparib and weekly carboplatin (AUC 1 and 1.5, every 2 weeks or every 3 weeks), including 14 patients (58%) with prior platinum treatment. Dose-limiting toxicities included grade 3 fatigue and grade 4 thrombocytopenia; the MTD was not reached. Grade 3/4 toxicities included fatigue (13%), neutropenia (63%), thrombocytopenia (29%), and anemia (38%). After cycle 2's dose, delays/reductions were required in all patients. One complete and two partial responses occurred in germline BRCA1/2 (gBRCA1/2) patients. Four patients showed stable disease beyond 4 months, three of which had known mutations in DNA repair pathways. Pharmacokinetic toxicity modeling suggests that after three cycles of carboplatin AUC 1.5 every 3 weeks and talazoparib 1 mg daily, neutrophil counts decreased 78% [confidence interval (CI), 87-68] from baseline in gBRCA carriers and 63% (CI, 72-55) in noncarriers (P < 0.001). Pharmacokinetic toxicity modeling suggests an intermittent, pulse dosing schedule of PARP inhibition, differentiated by gBRCA mutation status, may improve the benefit/risk ratio of combination therapy.Conclusions: Carboplatin and talazoparib showed efficacy in DNA damage mutation carriers, but hematologic toxicity was more pronounced in gBRCA carriers. Carboplatin is best combined with intermittent talazoparib dosing differentiated by germline and somatic DNA damage mutation carriers. Clin Cancer Res; 23(21); 6400-10. ©2017 AACR.

Target and Agent Prioritization for the Children's Oncology Group-National Cancer Institute Pediatric MATCH Trial

Over the past decades, outcomes for children with cancer have improved dramatically through serial clinical trials based in large measure on dose intensification of cytotoxic chemotherapy for children with high-risk malignancies. Progress made through such dose intensification, in general, is no longer yielding further improvements in outcome. With the revolution in sequencing technologies and rapid development of drugs that block specific proteins and pathways, there is now an opportunity to improve outcomes for pediatric cancer patients through mutation-based targeted therapeutic strategies. The Children's Oncology Group (COG), in partnership with the National Cancer Institute (NCI), is planning a trial entitled the COG-NCI Pediatric Molecular Analysis for Therapeutic Choice (Pediatric MATCH) protocol utilizing an umbrella design. This protocol will have centralized infrastructure and will consist of a biomarker profiling protocol and multiple single-arm phase II trials of targeted therapies. Pediatric patients with recurrent or refractory solid tumors, lymphomas, or histiocytoses with measurable disease will be eligible. The Pediatric MATCH Target and Agent Prioritization (TAP) committee includes membership representing COG disease committees, the Food and Drug Administration, and the NCI. The TAP Committee systematically reviewed target and agent pairs for inclusion in the Pediatric MATCH trial. Fifteen drug-target pairs were reviewed by the TAP Committee, with seven recommended for further development as initial arms of the Pediatric MATCH trial. The current evidence for availability, efficacy, and safety of targeted agents in children for each class of mutation considered for inclusion in the Pediatric MATCH trial is discussed in this review.

PARP inhibitors as precision medicine for cancer treatment

Personalized or precision medicine is an emerging treatment approach tailored to individuals or certain groups of patients based on their unique characteristics. These types of therapies guided by biomarkers tend to be more effective than traditional approaches, especially in cancer. The inhibitor against poly (ADP-ribose) polymerase (PARP), olaparib (Lynparza, AstraZeneca), which was approved by the US Food and Drug Administration (FDA) in 2014, demonstrated efficacy specifically for ovarian cancer patients harboring mutations in BRCA genes, which encode proteins in DNA double-strand break repairs. However, the response to PARP inhibitors has been less encouraging in other cancer types that also carry defects in the BRCA genes. Thus, furthering our understanding of the underlying mechanism of PARP inhibitors and resistance is critical to improve their efficacy. In this review, we summarize the results of preclinical studies and the clinical application of PARP inhibitors, and discuss the future direction of PARP inhibitors as a potential marker-guided personalized medicine for cancer treatment.

Precision medicine in pediatric oncology: Lessons learned and next steps

The maturation of genomic technologies has enabled new discoveries in disease pathogenesis as well as new approaches to patient care. In pediatric oncology, patients may now receive individualized genomic analysis to identify molecular aberrations of relevance for diagnosis and/or treatment. In this context, several recent clinical studies have begun to explore the feasibility and utility of genomics-driven precision medicine. Here, we review the major developments in this field, discuss current limitations, and explore aspects of the clinical implementation of precision medicine, which lack consensus. Lastly, we discuss ongoing scientific efforts in this arena, which may yield future clinical applications.

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.