FDA Approval Summary: Rucaparib for the Treatment of Patients with Deleterious BRCA-Mutated Metastatic Castrate-Resistant Prostate Cancer

Lost opportunities: the underutilization of castrate-resistant prostate cancer treatment in real-world settings

Background

Various treatment regimens are now available for metastatic castrate-resistant prostate cancer (CRPC). This work evaluates the real-world prescription patterns of CRPC in a large tertiary care center and the factors influencing them.

Methods

Health records of 330 patients with de novo metastatic hormone-sensitive prostate cancer (HSPC), treated and progressed to CRPC between 2016 and 2020, were reviewed from a prospective uro-oncological database. We studied their demographics, medical co-morbidities, treatment utilization patterns before and after progression to CRPC, and survival outcomes.

Results

The median age was 74 years [interquartile range (IQR), 67-80 years] at diagnosis of CRPC. At CRPC, beyond androgen deprivation therapy (ADT) monotherapy, 70.3% (n=232) of patients received at least one additional line, 21.5% (n=71) received two lines, and 5.5% (n=18) received three lines of systemic treatments. As first-line treatment, novel hormonal agents (NHAs) were the most prescribed at 57.6% (n=190). The likelihood of receiving treatment was associated with age <65 years [odds ratio (OR) 2.08, P=0.01, 95% confidence interval (CI): 1.22-3.57] and lower Charlson Comorbidity Index (CCI) score (OR: 2.62, P=0.04, 95% CI: 1.07-6.45), treatment intensification for HSPC (OR 2.45, P=0.04, 95% CI: 1.07-5.62) and primary physician being an oncologist (OR 1.59, P=0.04, 95% CI: 1.04-2.48). Patients who received additional treatment lines at CRPC had longer survival (median: 23 vs. 17 months, OR 1.72, P<0.01, 95% CI: 1.23-2.38).

Conclusions

More than one in four patients do not receive any additional treatment line beyond ADT monotherapy and have worse survival outcomes. Health status, prescribing physician, and treatment at HSPC appear to affect prescription patterns at the CRPC stage.

Combination of PARP Inhibitors and Androgen Receptor Pathway Inhibitors in Metastatic Castration-Resistant Prostate Cancer

Despite recent advances in the treatment of metastatic prostate cancer, progression to a castration-resistant state remains inevitable for most and prognosis is limited. Genetic testing for homologous recombination repair pathway alterations is recommended for all patients with advanced prostate cancer given that a mutation is present in up to 25% of cases. Poly(ADP-ribose) polymerase (PARPis) are now approved for use in patients with metastatic castration-resistant prostate cancer who have progressed on an androgen receptor pathway inhibitor (ARPI) and harbour a germline or somatic homologous recombination repair mutation. Preclinical data support a synergistic effect with an ARPI and PARPi, and various ARPI-PARPi combinations have therefore been explored in phase III clinical trials. Despite heterogeneous findings, a clear hierarchy of benefit is evident, with patients harbouring a BRCA mutation deriving the greatest magnitude of benefit, followed by any homologous recombination repair mutation. The benefit in homologous recombination repair-proficient cohort is less clear, and questions remain about whether ARPI-PARPi combination therapy should be offered to patients without a homologous recombination repair mutation. With ARPIs now considered standard-of-care for metastatic hormone-sensitive prostate cancer, ARPI-PARPi combination therapy is currently being explored earlier in the treatment paradigm. The purpose of this review is to discuss the rationale behind ARPI-PARPi combination therapy, summarise the results of key clinical trials, and discuss clinical considerations and future perspectives.

Targeted Nanocarrier-Based Drug Delivery Strategies for Improving the Therapeutic Efficacy of PARP Inhibitors against Ovarian Cancer

The current focus of ovarian cancer (OC) research is the improvement of treatment options through maximising drug effectiveness. OC remains the fifth leading cause of cancer-induced mortality in women worldwide. In recent years, nanotechnology has revolutionised drug delivery systems. Nanoparticles may be utilised as carriers in gene therapy or to overcome the problem of drug resistance in tumours by limiting the number of free drugs in circulation and thereby minimising undesired adverse effects. Cell surface receptors, such as human epidermal growth factor 2 (HER2), folic acid (FA) receptors, CD44 (also referred to as homing cell adhesion molecule, HCAM), and vascular endothelial growth factor (VEGF) are highly expressed in ovarian cancer cells. Generation of active targeting nanoparticles involves modification with ligands that recognise cell surface receptors and thereby promote internalisation by cancer cells. Several poly(ADP-ribose) polymerase (PARP) inhibitors (PARPi) are currently used for the treatment of high-grade serous ovarian carcinomas (HGSOC) or platinum-sensitive relapsed OC. However, PARP resistance and poor drug bioavailability are common challenges, highlighting the urgent need to develop novel, effective strategies for ovarian cancer treatment. This review evaluates the utility of nanoparticles in ovarian cancer therapy, with a specific focus on targeted approaches and the use of PARPi nanocarriers to optimise treatment outcomes.

Dual inhibition of ATR and DNA-PKcs radiosensitizes ATM-mutant prostate cancer

In advanced castration resistant prostate cancer (CRPC), mutations in the DNA damage response (DDR) gene ataxia telangiectasia mutated ( ATM ) are common. While poly(ADP-ribose) polymerase inhibitors are approved in this context, their clinical efficacy remains limited. Thus, there is a compelling need to identify alternative therapeutic avenues for ATM mutant prostate cancer patients. Here, we generated matched ATM-proficient and ATM-deficient CRPC lines to elucidate the impact of ATM loss on DDR in response to DNA damage via irradiation. Through unbiased phosphoproteomic screening, we unveiled that ATM-deficient CRPC lines maintain dependence on downstream ATM targets through activation of ATR and DNA-PKcs kinases. Dual inhibition of ATR and DNA-PKcs effectively inhibited downstream γH2AX foci formation in response to irradiation and radiosensitized ATM-deficient lines to a greater extent than either ATM-proficient controls or single drug treatment. Further, dual inhibition abrogated residual downstream ATM pathway signaling and impaired replication fork dynamics. To circumvent potential toxicity, we leveraged the RUVBL1/2 ATPase inhibitor Compound B, which leads to the degradation of both ATR and DNA-PKcs kinases. Compound B effectively radiosensitized ATM-deficient CRPC in vitro and in vivo , and impacted replication fork dynamics. Overall, dual targeting of both ATR and DNA-PKcs is necessary to block DDR in ATM-deficient CRPC, and Compound B could be utilized as a novel therapy in combination with irradiation in these patients.

Preparation and Evaluation of a Novel 99mTc-Labeled Niraparib Isonitrile Complex as a Potential PARP-1 Imaging Agent

Poly ADP-ribose polymerase (PARP) plays an important role in the DNA repair process and has become an attractive target for cancer therapy in recent years. Given that niraparib has good clinical efficacy as a PARP inhibitor, this study aimed to develop radiolabeled niraparib derivatives for tumor imaging to detect PARP expression and improve the accuracy of stratified patient therapy. The niraparib isonitrile derivative (CNPN) was designed, synthesized, and radiolabeled to obtain the [99mTc]Tc-CNPN complex with high radiochemical purity (>95%). It was lipophilic and stable in vitro. In HeLa cell experiments, the uptake of [99mTc]Tc-CNPN was effectively inhibited by the ligand CNPN, indicating the binding affinity for PARP. According to the biodistribution studies of HeLa tumor-bearing mice, [99mTc]Tc-CNPN has moderate tumor uptake and can be effectively inhibited, demonstrating its specificity for targeting PARP. The SPECT imaging results showed that [99mTc]Tc-CNPN had tumor uptake at 2 h postinjection. All of the results of this study indicated that [99mTc]Tc-CNPN is a promising tumor imaging agent that targets PARP.

Circulating Tumor DNA in Genitourinary Cancers: Detection, Prognostics, and Therapeutic Implications

CtDNA is emerging as a non-invasive clinical detection method for several cancers, including genitourinary (GU) cancers such as prostate cancer, bladder cancer, and renal cell carcinoma (RCC). CtDNA assays have shown promise in early detection of GU cancers, providing prognostic information, assessing real-time treatment response, and detecting residual disease and relapse. The ease of obtaining a "liquid biopsy" from blood or urine in GU cancers enhances its potential to be used as a biomarker. Interrogating these "liquid biopsies" for ctDNA can then be used to detect common cancer mutations, novel genomic alterations, or epigenetic modifications. CtDNA has undergone investigation in numerous clinical trials, which could address clinical needs in GU cancers, for instance, earlier detection in RCC, therapeutic response prediction in castration-resistant prostate cancer, and monitoring for recurrence in bladder cancers. The utilization of liquid biopsy for ctDNA analysis provides a promising method of advancing precision medicine within the field of GU cancers.

Homologous Recombination Repair Gene Mutations in Prostate Cancer: Prevalence and Clinical Value

Despite advances in our understanding of the molecular landscape of prostate cancer and the development of novel biomarker-driven therapies, the prognosis of patients with metastatic prostate cancer that is resistant to conventional hormonal therapy remains poor. Data suggest that a significant proportion of patients with metastatic castration-resistant prostate cancer (mCRPC) have mutations in homologous recombination repair (HRR) genes and may benefit from poly(ADP-ribose) polymerase (PARP) inhibitors. However, the adoption of HRR gene mutation testing in prostate cancer remains low, meaning there is a missed opportunity to identify patients who may benefit from targeted therapy with PARP inhibition, with or without novel hormonal agents. Here, we review the current knowledge regarding the clinical significance of HRR gene mutations in prostate cancer and discuss the efficacy of PARP inhibition in patients with mCRPC. This comprehensive overview aims to increase the clinical implementation of HRR gene mutation testing and inform future efforts in personalized treatment of prostate cancer.

Therapeutic biomarkers in metastatic castration-resistant prostate cancer: does the state matter?

The treatment of metastatic castration-resistant prostate cancer (mCRPC) has been fundamentally transformed by our greater understanding of its complex biological mechanisms and its entrance into the era of precision oncology. A broad aim is to use the extreme heterogeneity of mCRPC by matching already approved or new targeted therapies to the correct tumor genotype. To achieve this, tumor DNA must be obtained, sequenced, and correctly interpreted, with individual aberrations explored for their druggability, taking into account the hierarchy of driving molecular pathways. Although tumor tissue sequencing is the gold standard, tumor tissue can be challenging to obtain, and a biopsy from one metastatic site or primary tumor may not provide an accurate representation of the current genetic underpinning. Sequencing of circulating tumor DNA (ctDNA) might catalyze precision oncology in mCRPC, as it enables real-time observation of genomic changes in tumors and allows for monitoring of treatment response and identification of resistance mechanisms. Moreover, ctDNA can be used to identify mutations that may not be detected in solitary metastatic lesions and can provide a more in-depth understanding of inter- and intra-tumor heterogeneity. Finally, ctDNA abundance can serve as a prognostic biomarker in patients with mCRPC.The androgen receptor (AR)-axis is a well-established therapeutical target for prostate cancer, and through ctDNA sequencing, insights have been obtained in (temporal) resistance mechanisms that develop through castration resistance. New third-generation AR-axis inhibitors are being developed to overcome some of these resistance mechanisms. The druggability of defects in the DNA damage repair machinery has impacted the treatment landscape of mCRPC in recent years. For patients with deleterious gene aberrations in genes linked to homologous recombination, particularly BRCA1 or BRCA2, PARP inhibitors have shown efficacy compared to the standard of care armamentarium, but platinum-based chemotherapy may be equally effective. A hierarchy exists in genes associated with homologous recombination, where, besides the canonical genes in this pathway, not every other gene aberration predicts the same likelihood of response. Moreover, evidence is emerging on cross-resistance between therapies such as PARP inhibitors, platinum-based chemotherapy and even radioligand therapy that target this genotype. Mismatch repair-deficient patients can experience a beneficial response to immune checkpoint inhibitors. Activation of other cellular signaling pathways such as PI3K, cell cycle, and MAPK have shown limited success with monotherapy, but there is potential in co-targeting these pathways with combination therapy, either already witnessed or anticipated. This review outlines precision medicine in mCRPC, zooming in on the role of ctDNA, to identify genomic biomarkers that may be used to tailor molecularly targeted therapies. The most common druggable pathways and outcomes of therapies matched to these pathways are discussed.

Pharmacodynamic effects of the PARP inhibitor talazoparib (MDV3800, BMN 673) in patients with BRCA-mutated advanced solid tumors

PURPOSE

Talazoparib is an inhibitor of the poly (ADP-ribose) polymerase (PARP) family of enzymes and is FDA-approved for patients with (suspected) deleterious germline BRCA1/2-mutated, HER2‑negative, locally advanced or metastatic breast cancer. Because knowledge of the pharmacodynamic (PD) effects of talazoparib in patients has been limited to studies of PARP enzymatic activity (PARylation) in peripheral blood mononuclear cells, we developed a study to assess tumoral PD response to talazoparib treatment (NCT01989546).

METHODS

We administered single-agent talazoparib (1 mg/day) orally in 28-day cycles to adult patients with advanced solid tumors harboring (suspected) deleterious BRCA1 or BRCA2 mutations. The primary objective was to examine the PD effects of talazoparib; the secondary objective was to determine overall response rate (ORR). Tumor biopsies were mandatory at baseline and post-treatment on day 8 (optional at disease progression). Biopsies were analyzed for PARylation, DNA damage response (γH2AX), and epithelial‒mesenchymal transition.

RESULTS

Nine patients enrolled in this trial. Four of six patients (67%) evaluable for the primary PD endpoint exhibited a nuclear γH2AX response on day 8 of treatment, and five of six (83%) also exhibited strong suppression of PARylation. A transition towards a more mesenchymal phenotype was seen in 4 of 6 carcinoma patients, but this biological change did not affect γH2AX or PAR responses. The ORR was 55% with the five partial responses lasting a median of six cycles.

CONCLUSION

Intra-tumoral DNA damage response and inhibition of PARP enzymatic activity were confirmed in patients with advanced solid tumors harboring BRCA1/2 mutations after 8 days of talazoparib treatment.

Platinum-based chemotherapy in metastatic prostate cancer: what possibilities?

Metastatic prostate cancer is a major health burden worldwide, necessitating the continuous development of effective treatment strategies. Androgen deprivation therapy remains the cornerstone of prostate cancer treatment, but novel approaches are needed for metastatic castration-resistant prostate cancer (mCRPC). Recent studies have highlighted the prevalence of mutations in DNA repair genes, including BRCA1 and BRCA2, in mCRPC patients, rendering them more susceptible to platinum-based chemotherapy and Poly (ADP-ribose) polymerase (PARP) inhibitors. Platinum-based chemotherapy, particularly in combination with taxanes, has demonstrated encouraging activity in mCRPC, as well as homologous recombination gene alterations have shown increased sensitivity to platinum compounds in these patients. The combination of platinum-based chemotherapy with PARP inhibitors represents a novel and potentially effective therapeutic strategy for this subgroup of patients. However, the optimal sequence of administering these agents and the potential for cross-resistance and cross-toxicities remain areas requiring further investigation. Prospective randomized studies are essential to elucidate the most effective treatment approach for this challenging patient population. This review aims to explore the potential of platinum-based chemotherapy in the context of prostate cancer, and more in detail in homologous recombination repair (HRR) mutated patients. We discuss the synergistic effects of combining platinum compounds with PARP inhibitors and the potential benefits of adopting specific therapeutic sequences.

Synthesis and clinical application of small-molecule drugs approved to treat prostatic cancer

Prostate cancer is a prevalent form of cancer that primarily affects men, with a high incidence and mortality rate. It is the second most common cancer among males, following lung cancer. Typically occurring in individuals aged 50 and above, this malignant tumor originates from abnormal cells in the prostate tissue. If left untreated, it can spread to nearby tissues, lymph nodes, and even bones. Current treatment methods include surgery, radiotherapy, and chemotherapy. However, these treatments have certain limitations and side effects. Therefore, researching and developing new small-molecule drugs to treat prostate cancer is of great significance. In recent years, many small-molecule drugs have been proven to have therapeutic effects on prostate cancer. The purpose of this review is to give a comprehensive look at the clinical uses and synthetic methods of various significant small-molecule drugs that have been approved to treat prostate cancer, to facilitate the development of more powerful and innovative drugs for the effective control of prostate cancer.

Discovery of novel 2,3,4,5-tetrahydrospiro[benzo[c]azepine-1,1'-cyclohexan]-5-ol derivatives as PARP-1 inhibitors

As an essential marker of cancer treatment, PARP-1 inhibitors could effectively kill tumor cells through a mechanism known as synthetic lethality and are used to treat a variety of cancers. In order to explore novel PARP-1 inhibitors, a series of 22 novel erythrina derivatives were reported and preliminarily explored their mechanism of action. The antitumor activities against four human cancer cell lines including A549, OVCAR-3, HCT-116, and MCF-7 were evaluated, and the preliminary SARs were summarized. Among them, compound 11b exhibited better anti-proliferative effects against A549 cells (IC50 = 1.95 µM). The SI results showed that compound 11b had low toxicity. Moreover, compound 11b displayed excellent PARP-1 inhibitory activities with IC50 values of 19.24 nM. In addition, molecular docking studies provided the rational binding modes of compound 11b in complexes with PARP-1. The flow cytometry assays revealed that compound 11b could induce apoptosis of A549 cells (P < 0.001). Simultaneously, compound 11b could effectively reduce the formation of PAR (P < 0.001). The ADMET prediction results indicated compound 11b had similar properties to rucaparib. Collectively, compound 11b has potential research value for further investigation.

The function and regulation of ADP-ribosylation in the DNA damage response

ADP-ribosylation is a post-translational modification involved in DNA damage response (DDR). In higher organisms it is synthesised by PARP 1-3, DNA strand break sensors. Recent advances have identified serine residues as the most common targets for ADP-ribosylation during DDR. To ADP-ribosylate serine, PARPs require an accessory factor, HPF1 which completes the catalytic domain. Through ADP-ribosylation, PARPs recruit a variety of factors to the break site and control their activities. However, the timely removal of ADP-ribosylation is also key for genome stability and is mostly performed by two hydrolases: PARG and ARH3. Here, we describe the key writers, readers and erasers of ADP-ribosylation and their contribution to the mounting of the DDR. We also discuss the use of PARP inhibitors in cancer therapy and the ways to tackle PARPi treatment resistance.

Therapeutic Targeting of DNA Replication Stress in Cancer

This article reviews the currently used therapeutic strategies to target DNA replication stress for cancer treatment in the clinic, highlighting their effectiveness and limitations due to toxicity and drug resistance. Cancer cells experience enhanced spontaneous DNA damage due to compromised DNA replication machinery, elevated levels of reactive oxygen species, loss of tumor suppressor genes, and/or constitutive activation of oncogenes. Consequently, these cells are addicted to DNA damage response signaling pathways and repair machinery to maintain genome stability and support survival and proliferation. Chemotherapeutic drugs exploit this genetic instability by inducing additional DNA damage to overwhelm the repair system in cancer cells. However, the clinical use of DNA-damaging agents is limited by their toxicity and drug resistance often arises. To address these issues, the article discusses a potential strategy to target the cancer-associated isoform of proliferating cell nuclear antigen (caPCNA), which plays a central role in the DNA replication and damage response network. Small molecule and peptide agents that specifically target caPCNA can selectively target cancer cells without significant toxicity to normal cells or experimental animals.

Small Molecules Targeting DNA Polymerase Theta (POLθ) as Promising Synthetic Lethal Agents for Precision Cancer Therapy

Synthetic lethality (SL) is an innovative strategy in targeted anticancer therapy that exploits tumor genetic vulnerabilities. This topic has come to the forefront in recent years, as witnessed by the increased number of publications since 2007. The first proof of concept for the effectiveness of SL was provided by the approval of poly(ADP-ribose)polymerase inhibitors, which exploit a SL interaction in BRCA-deficient cells, although their use is limited by resistance. Searching for additional SL interactions involving BRCA mutations, the DNA polymerase theta (POLθ) emerged as an exciting target. This review summarizes, for the first time, the POLθ polymerase and helicase inhibitors reported to date. Compounds are described focusing on chemical structure and biological activity. With the aim to enable further drug discovery efforts in interrogating POLθ as a target, we propose a plausible pharmacophore model for POLθ-pol inhibitors and provide a structural analysis of the known POLθ ligand binding sites.

Management of Advanced Prostate Cancer in the Precision Oncology Era

Prostate cancer (PC) is the second leading cause of cancer death in men in the United States. While diversified and improved treatment options for aggressive PC have improved patient outcomes, metastatic castration-resistant prostate cancer (mCRPC) remains incurable and an area of investigative therapeutic interest. This review will cover the seminal clinical data supporting the indication of new precision oncology-based therapeutics and explore their limitations, present utility, and potential in the treatment of PC. Systemic therapies for high-risk and advanced PC have experienced significant development over the past ten years. Biomarker-driven therapies have brought the field closer to the goal of being able to implement precision oncology therapy for every patient. The tumor agnostic approval of pembrolizumab (a PD-1 inhibitor) marked an important advancement in this direction. There are also several PARP inhibitors indicated for patients with DNA damage repair deficiencies. Additionally, theranostic agents for both imaging and treatment have further revolutionized the treatment landscape for PC and represent another advancement in precision medicine. Radiolabeled prostate-specific membrane antigen (PSMA) PET/CT is rapidly becoming a standard of care for diagnosis, and PSMA-targeted radioligand therapies have gained recent FDA approval for metastatic prostate cancer. These advances in precision-based oncology are detailed in this review.

Frequency of Germline and Somatic BRCA1 and BRCA2 Mutations in Prostate Cancer: An Updated Systematic Review and Meta-Analysis

In prostate cancer (PC), the presence of BRCA somatic and/or germline mutation provides prognostic and predictive information. Meta-analysis aims to estimate the frequency of BRCA mutations in patients with PC (PCp). In November 2022, we reviewed literature searching for all articles testing the proportion of BRCA mutations in PCp, without explicit enrichment for familiar risk. The frequency of germline and somatic BRCA1 and/or BRCA2 mutations was described in three stage disease populations (any/metastatic/metastatic castration-resistant PC, mCRPC). Out of 2253 identified articles, 40 were eligible. Here, 0.73% and 1.20% of any stage PCp, 0.94% and 1.10% of metastatic PCp, and 1.21% and 1.10% of mCRPC patients carried germline and somatic BRCA1 mutation, respectively; 3.25% and 6.29% of any stage PCp, 4.51% and 10.26% of metastatic PCp, and 3.90% and 10.52% of mCRPC patients carried germline and somatic BRCA2 mutation, respectively; and 4.47% and 7.18% of any stage PCp, 5.84% and 10.94% of metastatic PCp, and 5.26% and 11.26% of mCRPC patients carried germline and somatic BRCA1/2 mutation, respectively. Somatic mutations are more common than germline and BRCA2 are more common than BRCA1 mutations; the frequency of mutations is higher in the metastatic setting. Despite that BRCA testing in PC is now standard in clinical practice, several open questions remain.

Tumor testing and treatment patterns in veterans with metastatic castration-resistant prostate cancer

INTRODUCTION

In 2016, the Department of Veterans Affairs (VA) and Prostate Cancer Foundation (PCF) began a partnership to improve access to testing. The primary objective of this analysis was to describe the use of tumor testing and treatment patterns in Veterans who progressed to metastatic castration-resistant prostate cancer (mCRPC) from 2016 to 2021. Secondary objectives including identifying factors associated with receipt of tumor testing, and reporting HRR mutation results among a subset who were tested.

METHODS AND MATERIALS

Natural language processing algorithms were applied to VA electronic health record data to identify a nationwide cohort of veterans with mCRPC. Tumor testing over time and by region were reported, alongside first-, second-, and third-line treatment patterns. Factors associated with receipt of tumor testing were identified using generalized linear mixed models with binomial distributions and logit links to account for clustering by VA facility.

RESULTS

Of the 9,852 veterans analyzed, 1,972 (20%) received tumor testing, with 73% of testing occurring in 2020-2021. Factors associated with tumor testing included younger age, later diagnosis year, being treated in the Midwest, or Puerto Rico or other compared to the South, and being treated at a PCF-VA Center of Excellence. Fifteen percent of tests were positive for a pathogenic HRR mutation. Seventy-six percent of the study cohort received first-line treatment, and among those, a subsequent 52% received second-line treatment. A subsequent 46% received third-line treatment.

CONCLUSION

After the VA-PCF partnership, one-fifth of veterans with mCRPC received tumor testing, with most tests occurring in 2020-2021.

Cancer stem cell in prostate cancer progression, metastasis and therapy resistance

Prostate cancer (PCa) is the most diagnosed malignancy in the men worldwide. Cancer stem cells (CSCs) are the sub-population of cells present in the tumor which possess unique properties of self-renewal and multilineage differentiation thus thought to be major cause of therapy resistance, disease relapse, and mortality in several malignancies including PCa. CSCs have also been shown positive for the common stem cells markers such as ALDH EZH2, OCT4, SOX2, c-MYC, Nanog etc. Therefore, isolation and characterization of CSCs specific markers which may discriminate CSCs and normal stem cells are critical to selectively eliminate CSCs. Rapid advances in the field offers a theoretical explanation for many of the enduring uncertainties encompassing the etiology and an optimism for the identification of new stem-cell targets, development of reliable and efficient therapies in the future. The emerging reports have also provided unprecedented insights into CSCs plasticity, quiescence, renewal, and therapeutic response. In this review, we discuss the identification of PCa stem cells, their unique properties, stemness-driving pathways, new diagnostics, and therapeutic interventions.

A PARP inhibitor, rucaparib, improves cardiac dysfunction in ADP-ribose-acceptor hydrolase 3 ( Arh3 ) deficiency

Aims

Patients with ADP-ribose-acceptor hydrolase 3 ( ARH3 ) deficiency exhibit stress-induced childhood-onset neurodegeneration with ataxia and seizures (CONDSIAS). ARH3 degrades protein-linked poly(ADP- ribose) (PAR) synthesized by poly(ADP-ribose)polymerase (PARP)-1 during oxidative stress, leading to cleavage of the ADP-ribose linked to protein. ARH3 deficiency leads to excess accumulation of PAR, resulting in PAR-dependent cell death or parthanatos. Approximately one-third of patients with homozygous mutant ARH3 die from cardiac arrest, which has been described as neurogenic, suggesting that ARH3 may play an important role in maintaining myocardial function. To address this question, cardiac function was monitored in Arh3 -knockout (KO) and - heterozygous (HT) mice.

Methods and results

Arh3 -KO male mice displayed cardiac hypertrophy by histopathology and decreased cardiac contractility assessed by MRI. In addition, both genders of Arh3 -KO and -HT mice showed decreased cardiac contractility by dobutamine stress test assessed by echocardiography. A direct role of ARH3 on myocardial function was seen with a Langendorff-perfused isolated heart model . Arh3 -KO male mouse hearts showed decreased post-ischemic rate pressure products, increased size of ischemia-reperfusion (IR) infarcts, and elevated PAR levels. Consistently, in vivo IR injury showed enhanced infarct size in Arh3 -KO mice in both genders. In addition, Arh3 -HT male mice showed increased size of in vivo IR infarcts. Treatment with an FDA-approved PARP inhibitor, rucaparib, improved cardiac contractility during dobutamine-induced stress and exhibited reduced size of in vivo IR infarcts. To understand better the role of ARH3, CRISPR-Cas9 was used to generate different Arh3 genotypes of myoblasts and myotubes. Incubation with H2O2 decreased viability of Arh3 -KO and -HT myoblasts and myotubes, resulting in PAR-dependent cell death that was reduced by PARP inhibitors or by transfection with the Arh3 gene.

Conclusion

ARH3 regulates PAR homeostasis in myocardium to preserve function and protect against oxidative stress; PARP inhibitors reduce the myocardial dysfunction seen with Arh3 mutations.

Analysis of BRCA2 Copy Number Loss and Genomic Instability in Circulating Tumor Cells from Patients with Metastatic Castration-resistant Prostate Cancer

BACKGROUND

BRCA2 alterations predict for a response to poly-ADP-ribose polymerase inhibition in metastatic castration-resistant prostate cancer (mCRPC). However, detection is hindered by insufficient tumor tissue and low sensitivity of cell-free DNA for detecting copy number loss.

OBJECTIVE

To evaluate the BRCA2 loss detection using single-cell, shallow whole-genome sequencing (sWGS) of circulating tumor cells (CTCs) in patients with mCRPC.

DESIGN, SETTING, AND PARTICIPANTS

We analyzed CTC samples collected concurrently with tumor biopsies intended for clinical sequencing in patients with progressing mCRPC.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Differences in proportions were evaluated using the chi-square test. Correlations between assays were analyzed in linear regression models. Associations between alterations and genomic instability were assessed on the single-cell level using mixed-effect negative binomial models.

RESULTS AND LIMITATIONS

We identified 138 patients with concurrent CTC and biopsy samples. CTC sWGS generated copy number profiles in a similar proportion of patients to biopsy samples (83% vs 78%, p = 0.23), but was more effective than bone biopsies (79% vs 50%; p = 0.009). CTC sWGS detected BRCA2 loss in more patients than tissue at the ≥1 (42% vs 16%; p < 0.001) and ≥2 (27% vs 16%; p = 0.028) CTC thresholds. The overall prevalence of BRCA2 loss was not increased in CTCs using sample-level composite z scores (p = 0.4), but was significantly increased compared with a lower-than-expected prevalence in bone samples (21% vs 3%, p = 0.014). Positive/negative predictive values for CTC BRCA2 loss were 89%/96% using the ≥1 CTC threshold and 67%/92% using the composite z score. CTC BRCA2 loss was associated with higher genomic instability in univariate (1.4-fold large-scale transition difference, 95% confidence interval [CI]: 1.2-1.6; p < 0.001) and multivariable analysis (1.4-fold difference, 95% CI: 1.2-1.6; p < 0.001).

CONCLUSIONS

Copy number profiles can reliably be generated using CTC sWGS, which detected a majority of tissue-confirmed BRCA2 loss and "CTC-only" losses. BRCA2 losses were supported by increases in genomic instability.

PATIENT SUMMARY

Current testing strategies have limitations in their ability to detect BRCA2 loss, a relatively common alteration in prostate cancer that is used to identify patients who may benefit from targeted therapy. In this paper, we evaluated whether we could detect BRCA2 loss in individual tumor cells isolated from patient blood samples and found this method to be suitable for further analysis.

Combining Poly (ADP-Ribose) Polymerase (PARP) Inhibitors with Chemotherapeutic Agents: Promise and Challenges

Better understanding of molecular drivers and dysregulated pathways has furthered the concept of precision oncology and rational drug development. The role of DNA damage response (DDR) pathways has been extensively studied in carcinogenesis and as potential therapeutic targets to improve response to chemotherapy or overcome resistance. Treatment with small molecule inhibitors of PARP has resulted in clinical response and conferred survival benefit to patients with ovarian cancer, BRCA-mutant breast cancer, HRD-deficient prostate cancer and BRCA-mutant pancreatic cancer, leading to US Food and Drug Administration (FDA) approvals. However, the observed clinical benefit with single agent PARP inhibitors is limited to few tumor types within the relevant genetic context. Since DDR pathways are essential for repair of damage caused by cytotoxic agents, PARP inhibitors have been evaluated in combination with various chemotherapeutic agents to broaden the therapeutic application of this class of drugs. In this chapter, we discuss the combination of PARP inhibitors with different chemotherapeutics agents, clinical experience to date, lessons learnt, and future directions for this approach.

What is the most effective way to ensure that patients successfully undergo germline testing for prostate cancer?

INTRODUCTION

We sought to identify the most effective way to refer patients with prostate cancer to germline testing.

METHODS

After IRB approval, we queried the electronic medical records (EMR) to identify patients (ages 18-89) with prostate cancer who were referred for or offered germline testing for prostate cancer from May 1, 2019 to February 24, 2021 through either telephone referral, EMR referral or in-office testing. The 3 cohorts were compared on receipt of testing and time to testing. Multivariate logistic regression and Cox regression evaluated the influence of referral cohort and reason for testing on receipt of testing and time to testing, respectively.

RESULTS

A total of 184 patients met study inclusion criteria; 47 were referred for germline testing via telephone, 70 were referred through the EMR and 67 were offered testing in the office. No significant demographic or clinical differences were observed. Telephone referral yielded the lowest response (17%; P < 0.001) with the longest time interval between referral and testing (103 days; P < 0.001); in-office testing yielded the highest response (66%). More patients were referred because of both family history and high risk characteristics in the EMR and in-office testing cohorts (21.4% and 25.4% respectively). Referral method was significantly (P < 0.001) associated with receipt of test, while reason for testing was not. Referral method was also independently related to time to testing (P < 0.001) while reason for referral was not.

CONCLUSIONS

Urologists should offer germline testing in the office for the most effective and expedient results.

Targeting the BRCA1/2 deficient cancer with PARP inhibitors: Clinical outcomes and mechanistic insights

BRCA1 and BRCA2 play a critical role in a variety of molecular processes related to DNA metabolism, including homologous recombination and mediating the replication stress response. Individuals with mutations in the BRCA1 and BRCA2 (BRCA1/2) genes have a significantly higher risk of developing various types of cancers, especially cancers of the breast, ovary, pancreas, and prostate. Currently, the Food and Drug Administration (FDA) has approved four PARP inhibitors (PARPi) to treat cancers with BRCA1/2 mutations. In this review, we will first summarize the clinical outcomes of the four FDA-approved PARPi in treating BRCA1/2 deficient cancers. We will then discuss evidence supporting the hypothesis that the cytotoxic effect of PARPi is likely due to inducing excessive replication stress at the difficult-to-replicate (DTR) genomic regions in BRCA1/2 mutated tumors. Finally, we will discuss the ongoing preclinical and clinical studies on how to combine the PARPi with immuno-oncology drugs to further improve clinical outcomes.

Human PARP1 substrates and regulators of its catalytic activity: An updated overview

Poly (ADP-ribose) polymerase 1 (PARP1) is a key DNA damage sensor that is recruited to damaged sites after DNA strand breaks to initiate DNA repair. This is achieved by catalyzing attachment of ADP-ribose moieties, which are donated from NAD⁺, on the amino acid residues of itself or other acceptor proteins. PARP inhibitors (PARPi) that inhibit PARP catalytic activity and induce PARP trapping are commonly used for treating BRCA1/2-deficient breast and ovarian cancers through synergistic lethality. Unfortunately, resistance to PARPi frequently occurs. In this review, we present the novel substrates and regulators of the PARP1-catalyzed poly (ADP-ribosyl)ation (PARylatison) that have been identified in the last 3 years. The overall aim is the presentation of protein interactions of potential therapeutic intervention for overcoming the resistance to PARPi.

CRISPR screens guide the way for PARP and ATR inhibitor biomarker discovery

DNA repair pathways are heavily studied for their role in cancer initiation and progression. Due to the large amount of inherent DNA damage in cancer cells, tumor cells profoundly rely on proper DNA repair for efficient cell cycle progression. Several current chemotherapeutics promote excessive DNA damage in cancer cells, thus leading to cell death during cell cycle progression. However, if the tumor has efficient DNA repair mechanisms, DNA-damaging therapeutics may not be as effective. Therefore, directly inhibiting DNA repair pathways alone and in combination with chemotherapeutics that cause DNA damage may result in improved clinical outcomes. Nevertheless, tumors can acquire resistance to DNA repair inhibitors. It is essential to understand the genetic mechanisms underlying this resistance. Genome-wide CRISPR screening has emerged as a powerful tool to identify biomarkers of resistance or sensitivity to DNA repair inhibitors. CRISPR knockout and CRISPR activation screens can be designed to investigate how the loss or overexpression of any human gene impacts resistance or sensitivity to specific inhibitors. This review will address the role of CRISPR screening in identifying biomarkers of resistance and sensitivity to DNA repair pathway inhibitors. We will focus on inhibitors targeting the PARP1 and ATR enzymes, and how the biomarkers identified from CRISPR screens can help inform the treatment plan for cancer patients.

Small molecule inhibitors targeting the cancers

Compared with traditional therapies, targeted therapy has merits in selectivity, efficacy, and tolerability. Small molecule inhibitors are one of the primary targeted therapies for cancer. Due to their advantages in a wide range of targets, convenient medication, and the ability to penetrate into the central nervous system, many efforts have been devoted to developing more small molecule inhibitors. To date, 88 small molecule inhibitors have been approved by the United States Food and Drug Administration to treat cancers. Despite remarkable progress, small molecule inhibitors in cancer treatment still face many obstacles, such as low response rate, short duration of response, toxicity, biomarkers, and resistance. To better promote the development of small molecule inhibitors targeting cancers, we comprehensively reviewed small molecule inhibitors involved in all the approved agents and pivotal drug candidates in clinical trials arranged by the signaling pathways and the classification of small molecule inhibitors. We discussed lessons learned from the development of these agents, the proper strategies to overcome resistance arising from different mechanisms, and combination therapies concerned with small molecule inhibitors. Through our review, we hoped to provide insights and perspectives for the research and development of small molecule inhibitors in cancer treatment.

Role of Rucaparib in the Treatment of Prostate Cancer: Clinical Perspectives and Considerations

Prostate cancer is one of the most common types of cancer worldwide and has strong genetic associations. This is important for the development of therapeutics for the condition, as metastatic castrate-resistant prostate cancer (mCRPC) is resistant to standard androgen deprivation therapy (ADT) and has a relatively poor prognosis. We conducted a literature review on rucaparib, a poly(adenosine diphosphate-ribose) polymerase (PARP) inhibitor that is currently indicated for the treatment of patients with mCRPC who harbor mutations in BRCA1/2 (homologous recombination repair [HRR] genes) and who have already tried androgen receptor-axis-targeted therapies (ARAT) and a taxane chemotherapy. We describe rucaparib's FDA approval, which was based on the results of the single-arm, open-label, Phase II TRITON2 clinical trial, which found an objective response rate (ORR) of 43.5%, a duration of response (DOR) of over six months in length and an acceptable safety profile. Rucaparib's dosage and clinical considerations for use were also discussed. We also compared rucaparib's use and safety profile with Olaparib, niraparib and talazoparib, three other PARP inhibitors tested for the treatment of mCRPC. Overall, initial results show that the safety profile of all four drugs in mCRPC was relatively similar, and further testing is currently indicated for all four. Differences in their metabolism, however, also warrant further research. The clinical validity of rucaparib will be tested by the follow-up TRITON3 clinical trial, which is comparing the effect of rucaparib compared to standard therapies for mCRPC harboring BRCA1/2 or ATM mutations. Other than TRITON3, other clinical trials are testing rucaparib's ability against other cancers (prostate or otherwise) with HRR mutations, and also the efficacy of combination therapies involving rucaparib. Finally, more research is needed to elucidate rucaparib's effect on HRR mutations other than BRCA1/2. Advancements in understanding the genetic landscape of mCRPC will also assist in understanding rucaparib's full therapeutic potential.

Identification of phenocopies improves prediction of targeted therapy response over DNA mutations alone

DNA mutations in specific genes can confer preferential benefit from drugs targeting those genes. However, other molecular perturbations can “phenocopy” pathogenic mutations, but would not be identified using standard clinical sequencing, leading to missed opportunities for other patients to benefit from targeted treatments. We hypothesized that RNA phenocopy signatures of key cancer driver gene mutations could improve our ability to predict response to targeted therapies, despite not being directly trained on drug response. To test this, we built gene expression signatures in tissue samples for specific mutations and found that phenocopy signatures broadly increased accuracy of drug response predictions in-vitro compared to DNA mutation alone, and identified additional cancer cell lines that respond well with a positive/negative predictive value on par or better than DNA mutations. We further validated our results across four clinical cohorts. Our results suggest that routine RNA sequencing of tumors to identify phenocopies in addition to standard targeted DNA sequencing would improve our ability to accurately select patients for targeted therapies in the clinic.

Talazoparib, a Poly(ADP-ribose) Polymerase Inhibitor, for Metastatic Castration-resistant Prostate Cancer and DNA Damage Response Alterations: TALAPRO-1 Safety Analyses

BACKGROUND

The phase II TALAPRO-1 study (NCT03148795) demonstrated durable antitumor activity in men with heavily pretreated metastatic castration-resistant prostate cancer (mCRPC). Here, we detail the safety profile of talazoparib.

PATIENTS AND METHODS

Men received talazoparib 1 mg/day (moderate renal impairment 0.75 mg/day) orally until radiographic progression, unacceptable toxicity, investigator decision, consent withdrawal, or death. Adverse events (AEs) were evaluated: incidence, severity, timing, duration, potential overlap of selected AEs, dose modifications/discontinuations due to AEs, and new clinically significant changes in laboratory values and vital signs.

RESULTS

In the safety population (N = 127; median age 69.0 years), 95.3% (121/127) experienced all-cause treatment-emergent adverse events (TEAEs). Most common were anemia (48.8% [62/127]), nausea (33.1% [42/127]), decreased appetite (28.3% [36/127]), and asthenia (23.6% [30/127]). Nonhematologic TEAEs were generally grades 1 and 2. No grade 5 TEAEs or deaths were treatment-related. Hematologic TEAEs typically occurred during the first 4-5 months of treatment. The median duration of grade 3-4 anemia, neutropenia, and thrombocytopenia was limited to 7-12 days. No grade 4 events of anemia or neutropenia occurred. Neither BRCA status nor alteration origin significantly impacted the safety profile. The median (range) treatment duration was 6.1 (0.4-24.9) months; treatment duration did not impact the incidence of anemia. Only 3 of the 15 (11.8% [15/127]) permanent treatment discontinuations were due to hematologic TEAEs (thrombocytopenia 1.6% [2/127]; leukopenia 0.8% [1/127]).

CONCLUSION

Common TEAEs associated with talazoparib could be managed through dose modifications/supportive care. Demonstrated efficacy and a manageable safety profile support continued evaluation of talazoparib in mCRPC.

CLINICALTRIALS.GOV IDENTIFIER

NCT03148795.

Upregulation of PARG in prostate cancer cells suppresses their malignant behavior and downregulates tumor-promoting genes

Post-translational modification of nuclear proteins through the addition of poly(ADP-ribose) (pADPr) moieties is upregulated in many metastatic cancers, where the high levels of pADPr have often been associated with poor cancer prognosis. Although the inhibitors of poly(ADP-ribose) polymerases (PARPs) have been utilized as potent anti-cancer agents, their efficacy in clinical trials varied among patient groups and has often been unpredictable. Such outcome cannot be interpreted solely by the inability to keep PARP-driven DNA repair in check. The focus of studies on PARP-driven tumorigenesis have recently been shifted toward PARP-dependent regulation of transcription. Here we utilized the controlled overexpression of poly(ADP-ribose) glycohydrolase (PARG), a sole pADPr-degrading enzyme, to investigate pADPr-dependent gene regulation in prostate cancer PC-3 cells. We demonstrated that PARG upregulation reduces pADPr levels and inhibits the expression of genes in key tumor-promoted pathways, including TNFα/NF-kB, IL6/STAT3, MYC, and KRAS signaling, the genes involved in inflammation response, especially chemokines, and endothelial-mesenchymal transition. The observed effect of PARG on transcription was consistent across all tested prostate cancer cell lines and correlates with PARG-induced reduction of clonogenic potential of PC-3 cells in vitro and a significant growth inhibition of PC-3-derived tumors in nude mice in vivo.

Current status and progress in using radiolabelled PARP-1 inhibitors for imaging PARP-1 expression in tumours

Poly(ADP-ribose) polymerase-1 (PARP-1) is a key enzyme in the DNA repair process, and the overexpression of PARP-1 in several tumours makes this enzyme a promising molecular target. Recently, several PARP-1 inhibitors, such as olaparib, rucaparib, niraparib and talazoparib, have been clinically approved as anticancer drugs. Several of these inhibitors have been radiolabelled for noninvasive imaging of PARP-1 expression in several types of tumours. In this review, the background and progress for using various radiolabelled PARP-1 inhibitors for cancer diagnosis are discussed and future development directions are proposed.

PARP Inhibitors: Clinical Limitations and Recent Attempts to Overcome Them

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

A cyanide-catalyzed imino-Stetter reaction enables the concise total syntheses of rucaparib

Two routes toward the synthesis of rucaparib, an FDA-approved drug used for the treatment of ovarian and prostate cancers, have been developed from commercially available starting materials utilizing the cyanide-catalyzed imino-Stetter reaction as the key step for the construction of the indole motif bearing all the desired substituents in their correct positions. In the first-generation synthesis, meta-fluorobenzoate, the starting material currently used in the process chemistry route of rucaparib, was converted into 4,6-disubstituted 2-aminocinnamic acid derivatives (ester or amide). The cyanide-catalyzed imino-Stetter reaction of aldimines derived from the resulting 2-aminocinnamic acid derivatives and a commercially available aldehyde afforded the desired indole-3-acetic acid derivatives. The final azepinone formation completed the total synthesis of rucaparib in 27% overall yield. To resolve the issues raised in the first-generation synthesis, we further developed a second-generation synthesis of rucaparib. The Heck reaction of a commercially available ortho-iodoaniline derivative with acrylonitrile provided 4,6-disubstituted 2-aminocinnamonitrile, which was subjected to the imino-Stetter reaction with the same aldehyde to provide the desired indole-3-acetonitrile product. Subsequent construction of the azepinone scaffold completed the total synthesis of rucaparib in 59% overall yield over three separation operations. The synthetic strategy reported herein can provide a highly practical route to access rucaparib from commercially available starting materials (5.2% overall yield in the current process chemistry route vs. 59% overall yield in the second-generation synthesis).

Drug resistance in metastatic castration-resistant prostate cancer: an update on the status quo

Prostate cancer (PCa) is a leading cause of cancer-related morbidity and mortality in men globally. Despite improvements in the diagnosis and treatment of PCa, a significant proportion of patients with high-risk localized disease and all patients with advanced disease at diagnosis will experience progression to metastatic castration-resistant prostate cancer (mCRPC). Multiple drugs are now approved as the standard of care treatments for patients with mCRPC that have been shown to prolong survival. Although the majority of patients will respond initially, primary and secondary resistance to these therapies make mCRPC an incurable disease. Several molecular mechanisms underlie the development of mCRPC, with the androgen receptor (AR) axis being the main driver as well as the key drug target. Understanding resistance mechanisms is crucial for discovering novel therapeutic strategies to delay or reverse the progression of the disease. In this review, we address the diverse mechanisms of drug resistance in mCRPC. In addition, we shed light on emerging targeted therapies currently being tested in clinical trials with promising potential to overcome mCRPC-drug resistance.

A Case Study of Clinical Response to Rucaparib in a Patient with Metastatic Castration-Resistant Prostate Cancer and a RAD51B Alteration

PARP inhibitors, such as rucaparib, have been well characterized in metastatic castration-resistant prostate cancer (mCRPC) associated with BRCA alterations, and the clinical activity of these agents has also been evaluated in patients with mCRPC associated with alterations in other non-BRCA DNA damage repair (DDR) genes, including RAD51B. There is likely a differential sensitivity to PARP inhibition based on the specific DDR gene altered, but research in this area is limited because of the low frequency of alterations in these genes. Here, we describe a mCRPC patient with a truncating rearrangement of RAD51B who had a radiographic and PSA response when treated with the PARP inhibitor rucaparib within the TRITON2 trial. We investigated the patients’ response parameters, circulating tumor DNA (ctDNA) fraction and tumor genomics longitudinally, using next-generation sequencing (NGS) of tissue and plasma. ctDNA fraction correlates with radiographic and PSA response and is lower during times of response. NGS did not reveal any potential genomic mechanism of acquired drug resistance. This case shows evidence for rucaparib activity in a rare patient with mCRPC and a RAD51B truncation.

Small cell lung cancer: novel treatments beyond immunotherapy

Small cell lung cancer (SCLC) arises in peribronchial locations and infiltrates the bronchial submucosa, including about 15% of lung cancer cases. Despite decades of research, the prognosis for SCLC patients remains poor because this tumor is characterized by an exceptionally high proliferative rate, strong tendency for early widespread metastasis and acquired chemoresistance. Omics profiling revealed that SCLC harbor extensive chromosomal rearrangements and a very high mutation burden. This led to the development of immune-checkpoint inhibitors as single agents or in combination with chemotherapy, which however resulted in a prolonged benefit only for a small subset of patients. Thus, the present review discusses the rationale and limitations of immunotherapeutic approaches, presenting the current biological understanding of aberrant signaling pathways that might be exploited with new potential treatments. In particular, new agents targeting DNA damage repair, cell cycle checkpoint, and apoptosis pathways showed several promising results in different preclinical models. Epigenetic alterations, gene amplifications and mutations can act as biomarkers in this context. Future research and improved clinical outcome for SCLC patients will depend on the integration between these omics and pharmacological studies with clinical translational research, in order to identify specific predictive biomarkers that will be hopefully validated using clinical trials with biomarker-selected targeted treatments.

Preclinical In Vivo Validation of the RAD51 Test for Identification of Homologous Recombination-Deficient Tumors and Patient Stratification

PARP inhibitors (PARPi) are approved drugs for platinum-sensitive, high-grade serous ovarian cancer (HGSOC) and for breast, prostate, and pancreatic cancers (PaC) harboring genetic alterations impairing homologous recombination repair (HRR). Detection of nuclear RAD51 foci in tumor cells is a marker of HRR functionality, and we previously established a test to detect RAD51 nuclear foci. Here, we aimed to validate the RAD51 score cut off and compare the performance of this test to other HRR deficiency (HRD) detection methods. Laboratory models from BRCA1/BRCA2-associated breast cancer, HGSOC, and PaC were developed and evaluated for their response to PARPi and cisplatin. HRD in these models and patient samples was evaluated by DNA sequencing of HRR genes, genomic HRD tests, and RAD51 foci detection. We established patient-derived xenograft models from breast cancer (n = 103), HGSOC (n = 4), and PaC (n = 2) that recapitulated patient HRD status and treatment response. The RAD51 test showed higher accuracy than HRR gene mutations and genomic HRD analysis for predicting PARPi response (95%, 67%, and 71%, respectively). RAD51 detection captured dynamic changes in HRR status upon acquisition of PARPi resistance. The accuracy of the RAD51 test was similar to HRR gene mutations for predicting platinum response. The predefined RAD51 score cut off was validated, and the high predictive value of the RAD51 test in preclinical models was confirmed. These results collectively support pursuing clinical assessment of the RAD51 test in patient samples from randomized trials testing PARPi or platinum-based therapies.

SIGNIFICANCE

This work demonstrates the high accuracy of a histopathology-based test based on the detection of RAD51 nuclear foci in predicting response to PARPi and cisplatin.

Total Synthesis of Rucaparib

A concise total synthesis of rucaparib, an FDA-approved drug for ovarian and prostate cancers, is reported. The Heck reaction of the commercially available aryl iodide with acrylonitrile provided the desired (E)-2-aminocinnamonitrile derivative. A subsequent imino-Stetter reaction of the aldimine derived from 2-aminocinnamonitrile and aldehyde furnished indole-3-acetonitrile bearing the desired substituents at appropriate positions. The construction of the final azepinone scaffold via reduction of the nitrile group followed by seven-membered lactamization afforded rucaparib. Notably, the synthesis of rucaparib is achieved using commercially available starting materials in only three separation operations with 54% overall yield.

Evaluation of phototoxicity induced by the anticancer drug rucaparib

Rucaparib (RCP) is a potent selective inhibitor of both PARP-1 and PARP-2 enzymes that induces synthetic lethality in cancer cells. It is used for the treatment of breast and ovarian tumors harboring deleterious germline or somatic cancer susceptibility genes mutations. Although RCP has an indole chromophore in its structure, it displays a bathochromic shift of the absorption band towards the UVA region of sunlight, thus extending the active fraction of solar light able to produce photosensitivity reactions. In this context, it is highly interesting to study the photo(geno)toxicity disorders associated with this drug, bearing in mind that, for dermatologists it is crucial to understand the toxicity mechanism to improve clinical management. In the present work, RCP has shown to be potentially phototoxic, as observed in the neutral red uptake phototoxicity test. Moreover, this significant phototoxicity is attributed to both proteins and genomic DNA, as revealed in the protein photooxidation and comet assays. The results obtained are highly relevant concerning RCP photosafety and become clinically important in the context of identification of the cutaneous adverse events that can be associated with the targeted therapies. Interestingly, this is the first example of a PARP inhibitor able to induce photosensitized damage to biomolecules.

Guidelines for Management of Treatment-Emergent Adverse Events During Rucaparib Treatment of Patients with Metastatic Castration-Resistant Prostate Cancer

Purpose

The US Food and Drug Administration has recently granted accelerated approval of the poly(ADP-ribose) polymerase (PARP) inhibitor rucaparib as treatment for men with metastatic castration-resistant prostate cancer (mCRPC) associated with a deleterious germline or somatic BRCA1 or BRCA2 (BRCA) alteration. As the safety profile of this new addition to the mCRPC treatment landscape may be unfamiliar to clinicians and patients, we summarize the data from the literature and provide practical guidelines for the management of treatment-emergent adverse events (TEAEs) that may occur during rucaparib treatment.

Materials and Methods

Safety data were identified from PubMed and congress publications of trials involving men with mCRPC treated with oral rucaparib monotherapy (600 mg twice daily). Management guidelines for TEAEs were developed based on trial protocols, prescribing information, oncology association guidance, and the authors’ clinical experience.

Results

In clinical trials of men with mCRPC who received rucaparib (n = 193), TEAEs observed were consistent with that of other PARP inhibitors. The most frequent any-grade TEAEs included gastrointestinal events, asthenia/fatigue, anemia, increased alanine/aspartate aminotransferase, rash, and thrombocytopenia; the most frequent grade ≥3 TEAE was anemia. The majority of TEAEs were self-limiting and did not require treatment modification or interruption. Here, we provide recommendations on management of the most common TEAEs reported with rucaparib as well as other TEAEs of interest.

Conclusion

Rucaparib’s recent approval for treatment of BRCA-mutant mCRPC is practice changing. Proper management of TEAEs will allow maximum treatment benefit for patients receiving rucaparib.

Precision Medicine in Oncology: A Review of Multi-Tumor Actionable Molecular Targets with an Emphasis on Non-Small Cell Lung Cancer

Precision medicine is essential for the modern care of a patient with cancer. Comprehensive molecular profiling of the tumor itself is necessary to determine the presence or absence of certain targetable abnormalities or biomarkers. In particular, lung cancer is a disease for which targetable genomic alterations will soon guide therapy in the majority of cases. In this comprehensive review of solid tumor-based biomarkers, we describe the genomic alterations for which targeted agents have been approved by the United States Food and Drug Administration (FDA). While focusing on alterations leading to approvals in a tumor-agnostic fashion (MSI-h, TMB-h, NTRK) and on those alterations with approvals in multiple malignancies (BRAF, ERBB2, RET, BRCA, PD-L1), we also describe several biomarkers or indications that are likely to lead to an approved drug in the near future (e.g., KRAS G12C, PD-L1 amplification, HER2 overexpression in colon cancer, HER2 mutations in lung cancer). Finally, we detail the current landscape of additional actionable alterations (EGFR, ALK, ROS1, MET) in lung cancer, a biomarker-rich malignancy that has greatly benefitted from the precision oncology revolution.

Tankyrase inhibitors as antitumor agents: a patent update (2013 - 2020)

INTRODUCTION

Tankyrase inhibitors gained significant attention as therapeutic targets in oncology because of their potency. Their primary role in inhibiting the Wnt signaling pathway makes them an important class of compounds with the potential to be used as a combination therapy in future treatments of colorectal cancer.

AREAS COVERED

This review describes pertinent work in the development of tankyrase inhibitors with a great emphasis on the recently patented TNKS inhibitors published from 2013 to 2020. This article also highlights a couple of promising candidates having tankyrase inhibitory effects and are currently undergoing clinical trials.

EXPERT OPINION

Following the successful clinical applications of PARP inhibitors, tankyrase inhibition has gained significant attention in the research community as a target with high therapeutic potential. The ubiquitous role of tankyrase in cellular homeostasis and Wnt-dependent tumor proliferation brought difficulties for researchers to strike the right balance between potency and on-target toxicity. The need for novel tankyrase inhibitors with a better ADMET profile can introduce an additional regimen in treating various malignancies in monotherapy or adjuvant therapy. The development of combination therapies, including tankyrase inhibitors with or without PARP inhibitory properties, can potentially benefit the larger population of patients with unmet medical needs.