A phase 1 dose-escalation study of veliparib with bimonthly FOLFIRI in patients with advanced solid tumours. Br J Cancer. 2018;118:938-946. [PMID: 29527010 PMCID: PMC5933261 DOI: 10.1038/s41416-018-0003-3]

PARP Inhibitors in Colorectal Malignancies: A 2023 Update

BACKGROUND

Colorectal carcinoma (CRC) is one of the most common malignancies in the Western world, and metastatic disease is associated with a dismal prognosis. Poly-ADpribose polymerase (PARP) inhibitors gain increasing attention in the field of medical oncology, as they lead to synthetic lethality in malignancies with preexisting alterations in the DNA damage repair (DDR) pathway. As those alterations are frequently seen in CRC, a targeted approach through PARP inhibitors is expected to benefit these patients, both alone and in combination with other agents like chemotherapy, immunotherapy, antiangiogenics, and radiation.

OBJECTIVE

This review article aims to better clarify the role of PARP inhibitors as a treatment option in patients with metastatic CRC with alterations in the DDR pathway.

METHODS

We used the PubMed database to retrieve journal articles and the inclusion criteria were all human studies that illustrated the effective role of PARP inhibitors in patients with metastatic CRC with homologous repair deficiency (HRD) and the correct line of therapy.

RESULTS

Current evidence supports the utilization of PARP inhibitors in CRC subgroups, as monotherapy and in combination with other agents. Up to now, data are insufficient to support a formal indication, and further research is needed.

CONCLUSION

Efforts to precisely define the homologous repair deficiency (HRD) in CRC - and eventually the subgroup of patients that are expected to benefit the most - are also underway.

Case Report: Progressive disease of BRCA2-mutant colon adenocarcinoma following talazoparib therapy

Colorectal cancer (CRC) is currently one of the most common tumor types diagnosed worldwide. In the early stages, the disease responds well to surgical and chemotherapeutic treatment, but in the later stages when therapeutic options are exhausted, comprehensive genomic profiling can guide further treatment decisions. We present the case of a 46-year-old man of Ashkenazi Jewish ancestry who was diagnosed with KRAS-mutated metastatic colorectal cancer. After surgery and progression on standard FOLFOX/FOLFIRI + bevacizumab therapy, as well as on Trifluridine/Tipiracil, comprehensive genomic profiling was performed with the hope of expanding therapeutic options. Following comprehensive tumor molecular profiling via NGS, a discussion of the case was discussed at the local molecular tumor board in order to determine further treatment strategy. An activating variant of KRAS and PIK3CA, FLT3 and SRC amplification and damaging TP53 and APC variants were discarded by MTB as potential targetable biomarkers. The BRCA2 p.S1415fs*4 founder frameshift variant was of interest and the patient was included in the clinical trial investigating the efficacy of a PARP inhibitor talazoparib. Unfortunately, the disease progression was detected within one month of talazoparib treatment and the patient died during the 8th cycle of FOLFIRI + bevacizumab therapy rechallenge.

Potential agnostic role of BRCA alterations in patients with several solid tumors: One for all, all for one?

Germline BRCA1/2 alterations in the Homologous Recombination (HR) pathway are considered as main susceptibility biomarkers to Hereditary Breast and Ovarian Cancers (HBOC). The modern molecular biology technologies allowed to characterize germline and somatic BRCA1/2 alterations in several malignancies, broadening the landscape of BRCA1/2-alterated tumors. In the last years, BRCA genetic testing, beyond the preventive value, also assumed a predictive and prognostic significance for patient management. The approval of molecules with agnostic indication is leading to a new clinical model, defined "mutational". Among these drugs, the Poly (ADP)-Ribose Polymerase inhibitors (PARPi) for BRCA1/2-deficient tumors were widely studied leading to increasing therapeutic implications. In this Review we provided an overview of the main clinical studies describing the association between BRCA-mutated tumors and PARPi response, focusing on the controversial evidence about the potential agnostic indication based on BRCA1/2 alterations in several solid tumors.

Enhancing the anti-tumor response by combining DNA damage repair inhibitors in the treatment of solid tumors

The anti-cancer efficacy of anti-malignancy therapies is related to DNA damage. However, DNA damage-response mechanisms can repair DNA damage, failing anti-tumor therapy. The resistance to chemotherapy, radiotherapy, and immunotherapy remains a clinical challenge. Thus, new strategies to overcome these therapeutic resistance mechanisms are needed. DNA damage repair inhibitors (DDRis) continue to be investigated, with polyadenosine diphosphate ribose polymerase inhibitors being the most studied inhibitors. Evidence of their clinical benefits and therapeutic potential in preclinical studies is growing. In addition to their potential as a monotherapy, DDRis may play an important synergistic role with other anti-cancer therapies or in reversing acquired treatment resistance. Here we review the impact of DDRis on solid tumors and the potential value of combinations of different treatment modalities with DDRis for solid tumors.

NCI 7977: A Phase I Dose-Escalation Study of Intermittent Oral ABT-888 (Veliparib) plus Intravenous Irinotecan Administered in Patients with Advanced Solid Tumors

Purpose

Veliparib is a PARP inhibitor (PARPi) with activity in BRCA 1/2/PALB2-deficient tumors. Preclinical observations reveal topoisomerase inhibitors like irinotecan are synergistic with PARPi irrespective of homologous recombination deficiency (HRD), potentially expanding the role for PARPi.

Experimental Design

NCI 7977 was a multicohort phase I clinical trial evaluating the safety and efficacy of multiple dose schedules of veliparib with irinotecan for solid tumors. In the intermittent veliparib cohort, escalating doses of veliparib were given twice daily at dose level (DL) 1 (50 mg) and DL 2 (100 mg) days 1-4 and 8-11 with irinotecan 100 mg/m2 days 3 and 10 in 21-day cycles.

Results

Fifteen patients enrolled, 8 of 15 (53%) received ≥4 prior systemic treatments. At DL1, 1 of 6 patients experienced a dose-limiting toxicity (DLT) of diarrhea. At DL2, 9 patients were treated, with 3 unevaluable for DLT, and 2 of 6 evaluable patients experienced a DLT of grade 3 neutropenia. Irinotecan 100 mg/m2 and veliparib 50 mg twice daily was the MTD. No objective responses were observed, although 4 patients had progression-free survival >6 months.

Conclusions

The MTD of intermittent veliparib is 50 mg twice daily days 1-4 and 8-11 with weekly irinotecan 100 mg/m2 days 3 and 10 every 21 days. Multiple patients experienced prolonged stable disease irrespective of HRD and prior irinotecan. However, due to the toxicities with higher dose intermittent veliparib and irinotecan, this schedule was determined too toxic for further development and the arm was closed prematurely.

Significance

The combination of intermittent veliparib with weekly irinotecan was deemed too toxic for further development. Future PARPi combinations should focus on agents with nonoverlapping toxicities to improve tolerability. The treatment combination showed limited efficacy with prolonged stable disease observed in multiple heavily pretreated patients, but no objective responses were seen.

Hereditary Gastric Cancer: Single-Gene or Multigene Panel Testing? A Mono-Institutional Experience

Gastric cancer (GC) has long been a 'Cinderella' among hereditary cancers. Until recently, single-gene testing (SGT) was the only approach to identify high-risk individuals. With the spread of multigene panel testing (MGPT), a debate arose on the involvement of other genes, particularly those pertaining to homologous recombination (HR) repair. We report our mono-institutional experience in genetic counseling and SGT for 54 GC patients, with the detection of nine pathogenic variants (PVs) (9/54:16.7%). Seven out of fifty (14%) patients who underwent SGT for unknown mutations were carriers of a PV in CDH1 (n = 3), BRCA2 (n = 2), BRCA1 (n = 1), and MSH2 (n = 1), while one patient (2%) carried two variants of unknown significance (VUSs). CDH1 and MSH2 emerged as genes involved in early-onset diffuse and later-onset intestinal GCs, respectively. We additionally conducted MGPT on 37 patients, identifying five PVs (13.5%), including three (3/5:60%) in an HR gene (BRCA2, ATM, RAD51D) and at least one VUS in 13 patients (35.1%). Comparing PV carriers and non-carriers, we observed a statistically significant difference in PVs between patients with and without family history of GC (p-value: 0.045) or Lynch-related tumors (p-value: 0.036). Genetic counseling remains central to GC risk assessment. MGPT appeared advantageous in patients with unspecific phenotypes, although it led to challenging results.

Update on Emerging Therapies for Advanced Colorectal Cancer

Colorectal cancer (CRC) is the third most common malignancy worldwide. It is projected to increase by 3.2 million new cases and account for 1.6 million deaths by 2040. Mortality is largely due to limited treatment options for patients who present with advanced disease. Thus, the development of effective and tolerable therapies is crucial. Chemotherapy has been the backbone of systemic treatment of advanced CRC, but utility has been limited because of invariable resistance to therapy, narrow mechanisms of action, and unfavorable toxicity profile. Tumors that are mismatch repair-deficient have demonstrated remarkable response to immune checkpoint inhibitor therapy. However, most CRC tumors are mismatch repair-proficient and represent an unmet medical need. Although ERBB2 amplification occurs only in a few cases, it is associated with left-sided tumors and a higher incidence of brain metastasis. Numerous combinations of HER2 inhibitors have demonstrated efficacy, and antibody-drug conjugates against HER2 represent innovative strategies in this area. The KRAS protein has been classically considered undruggable. Fortunately, new agents targeting KRAS G12C mutation represent a paradigm shift in the management of affected patients and could lead the advancement in drug development for the more common KRAS mutations. Furthermore, aberrant DNA damage response is present in 15%-20% of CRCs, and emerging innovative combinations with poly (ADP-ribose) polymerase (PARP) inhibitors could improve the current therapeutic landscape. Multiple novel biomarker-driven approaches in the management of patients with advanced CRC tumors are reviewed in this article.

Blocking PARP activity with the inhibitor veliparib enhances radiotherapy sensitivity in endometrial carcinoma

OBJECTIVE

Our study aimed to investigate the potential clinical utility of a poly(ADP-ribose) polymerase (PARP) inhibitor, veliparib (ABT-888), as a radiosensitizer in the medication of endometrial carcinoma (EC).

METHODS

Human Ishikawa endometrial adenocarcinoma cells were treated with veliparib, radiotherapy (RT), or combination treatment. The viabilities, radiosensitivity enhancement ratio (sensitizer enhancement ratio (SER), and apoptosis of Ishikawa cells were, respectively, evaluated by Cell Counting Kit-8 (CCK-8), colony formation experiment, and flow cytometry. The tumor growth was assessed by xenograft mice models. Western blot assay investigated the expression of DNA damage and apoptosis-related proteins in vivo and in vitro.

RESULTS

Cell Counting Kit-8 revealed that the 10% inhibition concentration (IC₁₀ ) and 50% inhibition concentration (IC₅₀ ) values of veliparib-treated Ishikawa cells were 1.7 and 133.5 µM, respectively. The SER of veliparib combined with RT was 1.229 in vitro. Flow cytometry analysis results indicated that the apoptosis rate of the veliparib + RT group was markedly higher than that of the RT group in vitro (p < 0.05). Furthermore, in vivo data revealed that veliparib + RT treatment significantly decreased tumor growth compared with single treatments of veliparib or RT and with the control group (p < 0.05). Then western blot confirmed the levels of anti-phospho-histone (γH2AX), caspase-3, and B-cell lymphoma 2 (Bcl-2) associated protein X (Bax) were significantly higher in the veliparib + RT group, while the level of Bcl-2 was lower compared with that of the RT group (p < 0.05), both in vivo and in vitro.

CONCLUSION

Our results indicate that veliparib in combination with RT markedly improved the therapeutic efficiency in human endometrial carcinoma.

Associations with response to Poly(ADP-ribose) Polymerase (PARP) inhibitors in patients with metastatic breast cancer

PARP inhibitors (PARPi) have modest antitumor activity in patients with advanced breast cancer and mutation in BRCA. It is unclear whether some subgroups derive greater benefit from treatment. MEDLINE and EMBASE were searched from inception to March 2021 to identify trials of PARPi in patients with metastatic breast cancer. Objective response rate (ORR) and clinical benefit rate (CBR) to PARPi were extracted and pooled in a meta-analysis using the Mantel Haenszel random effects model. Meta-regression explored the influence of patient and tumor characteristics on ORR and CBR. For randomized trials, hazard ratio comparing PARPi to control therapy were pooled using inverse variance and random effects. Analysis included 43 studies comprising 2409 patients. Among these, 1798 (75%) patients had BRCA mutations and 1146 (48%) were triple negative. In 10 studies (28%; n = 680 patients), the PARPi was given in combination with platinum-based chemotherapy. Weighted mean ORR was 45%; 64% when combined with platinum vs 37% with PARPi monotherapy (p < 0.001). Previous platinum-based chemotherapy was associated with lower ORR (p = 0.02). Compared to standard chemotherapy, progression-free survival was improved (HR 0.64, p < 0.001), but there was no difference in overall survival (HR 0.87, p = 0.06). There were no differences in ORR or CBR between BRCA1 and BRCA2 mutations. PARPi are more active in combination with platinum than as monotherapy, with lower response if given as monotherapy after platinum exposure. Significant improvements in ORR translated to modest improvement in progression-free, but not overall survival. There was no association between ORR and BRCA mutations.

Targeting the DNA Damage Response Pathway as a Novel Therapeutic Strategy in Colorectal Cancer

Simple Summary

Defective DNA damage response (DDR) is a hallmark of cancer leading to genomic instability. Up to 15–20% of colorectal cancers carry alterations in DDR. However, the role of DDR alterations as a prognostic factor and as a therapeutic target must be elucidated. To date, disappointing results have been obtained in different clinical trials mainly due to poor molecular selection of patients. Several challenges must be overcome before these compounds may have an impact on colorectal cancer. For instance, although some preclinical evidence showed the vulnerability of a subset of CRCs to PARP inhibitors, no specific clinical or molecular biomarkers have been validated to select patients. Moreover, different DDR alterations may not equally confer platinum sensitivity in CRC patients. Further efforts are needed in both preclinical and clinical settings to exploit DDR alterations as therapeutic targets and to eventually discover PARP or other DDR inhibitors (e.g., Wee1) with clinical benefit on colorectal cancer patients.

Abstract

Major advances have been made in CRC treatment in recent years, especially in molecularly driven therapies and immunotherapy. Despite this, a large number of advanced colorectal cancer patients do not benefit from these treatments and their prognosis remains poor. The landscape of DNA damage response (DDR) alterations is emerging as a novel target for treatment in different cancer types. PARP inhibitors have been approved for the treatment of ovarian, breast, pancreatic, and prostate cancers carrying deleterious BRCA1/2 pathogenic variants or homologous recombination repair (HRR) deficiency (HRD). Recent research reported on the emerging role of HRD in CRC and showed that alterations in these genes, either germline or somatic, are carried by up to 15–20% of CRCs. However, the role of HRD is still widely unknown, and few data about their clinical impact are available, especially in CRC patients. In this review, we report preclinical and clinical data currently available on DDR inhibitors in CRC. We also emphasize the predictive role of DDR mutations in response to platinum-based chemotherapy and the potential clinical role of DDR inhibitors. More preclinical and clinical trials are required to better understand the impact of DDR alterations in CRC patients and the therapeutic opportunities with novel DDR inhibitors.

Fanconi Anemia Pathway in Colorectal Cancer: A Novel Opportunity for Diagnosis, Prognosis and Therapy

Colorectal cancer (CRC) is the third most commonly diagnosed malignancy and has the second highest mortality rate globally. Thanks to the advent of next-generation sequencing technologies, several novel candidate genes have been proposed for CRC susceptibility. Germline biallelic mutations in one or more of the 22 currently recognized Fanconi anemia (FA) genes have been associated with Fanconi anemia disease, while germline monoallelic mutations, somatic mutations, or the promoter hypermethylation of some FANC genes increases the risk of cancer development, including CRC. The FA pathway is a substantial part of the DNA damage response system that participates in the repair of DNA inter-strand crosslinks through homologous recombination (HR) and protects genome stability via replication fork stabilization, respectively. Recent studies revealed associations between FA gene/protein tumor expression levels (i.e., FANC genes) and CRC progression and drug resistance. Moreover, the FA pathway represents a potential target in the CRC treatment. In fact, FANC gene characteristics may contribute to chemosensitize tumor cells to DNA crosslinking agents such as oxaliplatin and cisplatin besides exploiting the synthetic lethal approach for selective targeting of tumor cells. Hence, this review summarizes the current knowledge on the function of the FA pathway in DNA repair and genomic integrity with a focus on the FANC genes as potential predisposition factors to CRC. We then introduce recent literature that highlights the importance of FANC genes in CRC as promising prognostic and predictive biomarkers for disease management and treatment. Finally, we represent a brief overview of the current knowledge around the FANC genes as synthetic lethal therapeutic targets for precision cancer medicine.

A phase I study of veliparib with cyclophosphamide and veliparib combined with doxorubicin and cyclophosphamide in advanced malignancies

PURPOSE

Veliparib (V), an oral poly(ADP-ribose) polymerase (PARP) inhibitor, potentiates effects of alkylating agents and topoisomerase inhibitors in preclinical tumor models. We conducted a phase I trial of V with iv cyclophosphamide (C) and V plus iv doxorubicin (A) and C.

METHODS

Objectives were to establish the maximum tolerated dose (MTD) of the combinations, characterize V pharmacokinetics (PK) in the presence and absence of C, measure PAR in peripheral blood mononuclear cells (PBMCs) and γH2AX in circulating tumor cells (CTCs). In Group 1, dose escalations of V from 10 to 50 mg every 12 h Days 1-4 plus C 450 to 750 mg/m² Day 3 in 21-day cycles were evaluated. In Group 2, V doses ranged from 50 to 150 mg every 12 h Days 1-4 with AC (60/600 mg/m²) Day 3 in 21-day cycles. In Group 3, patients received AC Day 1 plus V Days 1-7, and in Group 4, AC Day 1 plus V Days 1-14 was given in 21-day cycles to evaluate effects on γH2AX foci.

RESULTS

Eighty patients were enrolled. MTD was not reached for V and C. MTD for V and AC was V 100 mg every 12 h Days 1-4 with AC (60/600 mg/m2) Day 3 every 21 days. V PK appears to be dose-dependent and has no effect on the PK of C. Overall, neutropenia and anemia were the most common adverse events. Objective response in V and AC treated groups was 22% (11/49). Overall clinical benefit rate was 31% (25/80). PAR decreased in PBMCs. Percentage of γH2AX-positive CTCs increased after treatment with V and AC.

CONCLUSION

V and AC can be safely combined. Activity was observed in patients with metastatic breast cancer.

Randomized Phase II Study of PARP Inhibitor ABT-888 (Veliparib) with Modified FOLFIRI versus FOLFIRI as Second-line Treatment of Metastatic Pancreatic Cancer: SWOG S1513

PURPOSE

PARP inhibitors synergize with topoisomerase inhibitors, and veliparib plus modified (m) FOLFIRI (no 5-FU bolus) had preliminary activity in metastatic pancreatic cancers. This study evaluated the safety and efficacy of second-line treatment with veliparib and mFOLFIRI versus FOLFIRI (control) for metastatic pancreatic cancer.

PATIENTS AND METHODS

This randomized phase II clinical trial led by the SWOG Cancer Research Network enrolled patients between September 1, 2016 and December 13, 2017. The median follow-up was 9 months (IQR 1-27). BRCA1/2 and homologous recombination DNA damage repair (HR-DDR) genetic defects were tested in blood and tumor biopsies. Patients received veliparib 200 mg twice daily, days 1-7 with mFOLFIRI days 3-5, or FOLFIRI in 14-day cycles.

RESULTS

After 123 of planned 143 patients were accrued, an interim futility analysis indicated that the veliparib arm was unlikely to be superior to control, and the study was halted. Median overall survival (OS) was 5.4 versus 6.5 months (HR, 1.23; P = 0.28), and median progression-free survival (PFS) was 2.1 versus 2.9 months (HR, 1.39; P = 0.09) with veliparib versus control. Grade 3/4 toxicities were more common with veliparib (69% vs. 58%, P = 0.23). For cancers with HR-DDR defects versus wild-type, median PFS and OS were 7.3 versus 2.5 months (P = 0.05) and 10.1 versus 5.9 months (P = 0.17), respectively, with FOLFIRI, and 2.0 versus 2.1 months (P = 0.62) and 7.4 versus 5.1 months (P = 0.10), respectively, with veliparib plus mFOLFIRI.

CONCLUSIONS

Veliparib plus mFOLFIRI did not improve survival for metastatic pancreatic cancer. FOLFIRI should be further studied in pancreatic cancers with HR-DDR defects.

Veliparib and nivolumab in combination with platinum doublet chemotherapy in patients with metastatic or advanced non-small cell lung cancer: A phase 1 dose escalation study

OBJECTIVES

Both combinations of the PARP inhibitor veliparib plus platinum doublet chemotherapy (CT), and the programmed death receptor-1 (PD-1) inhibitor nivolumab plus CT have demonstrated encouraging efficacy for treatment of non-small cell lung cancer (NSCLC). This phase 1 dose-escalation study (NCT02944396) evaluated the quadruple combination of veliparib with nivolumab and doublet CT in patients with unresectable advanced/metastatic NSCLC.

MATERIALS AND METHODS

Patients were enrolled into five dosing cohorts: patients received veliparib 120 mg twice daily (BID) combined with nivolumab 360 mg, carboplatin AUC 6 mg/mL∙min, and paclitaxel 200 mg/m² (C/PAC) or veliparib 80/120/200/240 mg BID in combination with nivolumab 360 mg, carboplatin AUC 6 mg/mL∙min, and pemetrexed 500 mg/m² (C/PEM). Primary objective was to identify the recommended phase 2 dose (RP2D) of veliparib + nivolumab + CT. Safety, tolerability, and efficacy of this combination were also assessed.

RESULTS

Twenty-five patients were enrolled: 6 patients received veliparib 120 mg BID + nivolumab + C/PAC and 19 received veliparib (80-240 mg BID) + nivolumab + C/PEM. No dose-limiting toxicities were reported, and the RP2Ds were veliparib 120 mg BID + nivolumab + C/PAC, and veliparib 240 mg BID + nivolumab + C/PEM. The most common any-grade adverse events (AEs) were fatigue (56%), nausea (52%), and anemia (48%). Grade 3/4 AEs included anemia (32%) and neutropenia (24%), and the most frequent serious AE was malignant neoplasm progression (12%). Veliparib exhibited approximately dose proportional kinetics in the dose range 80-240 mg BID combined with nivolumab and C/PEM, with no effects on pemetrexed pharmacokinetics. Overall, the confirmed objective response rate was 40%, and best overall response was 64%.

CONCLUSION

Veliparib combined with nivolumab and platinum doublet CT was tolerated in patients with advanced/metastatic NSCLC, and no evidence of drug-drug interaction was observed. Although preliminary, this quadruple therapy may have promising antitumor activity.

Treatment opportunities and future perspectives for pancreatic cancer patients with germline BRCA1-2 pathogenic variants

Personalized treatments and predictive biomarkers of pancreatic cancer (PDAC) are still lacking. Recently germline mutations in BRCA 1 and 2 genes, leading to homologous repair deficiency, have emerged as new targets for more specific and effective therapies, exploiting the increased susceptibility to platinum salts and PARP inhibitors. In addition to BRCA, pathogenic variants in PALB2 and in other genes involved in the DNA damage response pathway (DDR) represent potential targets, as well as their respective somatic alterations. This enlarged molecularly-selected population sharing the BRCAness phenotype, is expected to show a higher sensibility to a number of DNA damaging agents and DDR inhibitors. However, the possibility of new therapeutic opportunities for DDR defective PDAC patients has to face the lack of solid evidence about the proper type and timing of targeted-treatments, the potential combination strategies and most importantly, the lack of informations on the functional impact of each specific pathogenic variant on the DDR pathway. This review summarizes the current and near-future options for the clinical management of PDAC patients harboring a DDR deficiency, analyzing the state of the art of the indications of platinum salts and other cytotoxic agents in the advanced and early stage PDAC, the development of PARP inhibitors and the rational for new combinations with immunotherapy and cycle checkpoint inhibitors, as well as the strategy to overcome the development of resistance over treatments.

Therapeutic Potential of PARP Inhibitors in the Treatment of Gastrointestinal Cancers

Gastrointestinal (GI) malignancies are a major global health burden, with high mortality rates. The identification of novel therapeutic strategies is crucial to improve treatment and survival of patients. The poly (ADP-ribose) polymerase (PARP) enzymes involved in the DNA damage response (DDR) play major roles in the development, progression and treatment response of cancer, with PARP inhibitors (PARPi) currently used in the clinic for breast, ovarian, fallopian, primary peritoneal, pancreatic and prostate cancers with deficiencies in homologous recombination (HR) DNA repair. This article examines the current evidence for the role of the DDR PARP enzymes (PARP1, 2, 3 and 4) in the development, progression and treatment response of GI cancers. Furthermore, we discuss the role of HR status as a predictive biomarker of PARPi efficacy in GI cancer patients and examine the pre-clinical and clinical evidence for PARPi and cytotoxic therapy combination strategies in GI cancer. We also include an analysis of the genomic and transcriptomic landscape of the DDR PARP genes and key HR genes (BRCA1, BRCA2, ATM, RAD51, MRE11, PALB2) in GI patient tumours (n = 1744) using publicly available datasets to identify patients that may benefit from PARPi therapeutic approaches.

PARP inhibitors in gastric cancer: beacon of hope

Defects in the DNA damage response (DDR) can lead to genome instability, producing mutations or aberrations that promote the development and progression of cancer. But it also confers such cells vulnerable to cell death when they inhibit DNA damage repair. Poly (ADP-ribose) polymerase (PARP) plays a central role in many cellular processes, including DNA repair, replication, and transcription. PARP induces the occurrence of poly (ADP-ribosylation) (PARylation) when DNA single strand breaks (SSB) occur. PARP and various proteins can interact directly or indirectly through PARylation to regulate DNA repair. Inhibitors that directly target PARP have been found to block the SSB repair pathway, triggering homologous recombination deficiency (HRD) cancers to form synthetic lethal concepts that represent an anticancer strategy. It has therefore been investigated in many cancer types for more effective anti-cancer strategies, including gastric cancer (GC). This review describes the antitumor mechanisms of PARP inhibitors (PARPis), and the preclinical and clinical progress of PARPis as monotherapy and combination therapy in GC.

Poly(ADP-ribose) polymerase inhibition in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is a lethal disease with limited treatment options. Recently, the poly(ADP-ribose) polymerase inhibitor (PARPi) olaparib has been approved for maintenance therapy after successful platinum-based chemotherapy in patients with germline mutations in BRCA1 and BRCA2. Approval was based on the POLO study that has shown a significant improvement in progression-free survival for patients with metastatic PDAC after at least 4 months of platinum-based chemotherapy. Hopefully, this first biomarker-directed targeted therapy for a relevant subgroup of pancreatic cancer patients is only the beginning of an era of personalized therapy for pancreatic cancer. The potential role for PARPi in improving survival in patients with pancreatic cancer containing somatic tumor mutations has yet to be established. Multiple studies investigating whether PARPi therapy might benefit a larger group of pancreatic cancer patients with homologous recombination repair deficiency and whether combinations with chemotherapy, immunotherapy, or small molecules can improve efficacy are currently underway. We here review the molecular basis for PARPi therapy in PDAC patients and recent developments in clinical studies.

The DNA damage response pathway as a land of therapeutic opportunities for colorectal cancer

BACKGROUND

Colorectal cancer (CRC) represents a major cause of cancer deaths worldwide. Although significant progress has been made by molecular and immune therapeutic approaches, prognosis of advanced stage disease is still dismal. Alterations in the DNA damage response (DDR) pathways are emerging as novel targets for treatment across different cancer types. However, even though preclinical studies have shown the potential exploitation of DDR alterations in CRC, systematic and comprehensive testing is lagging and clinical development is based on analogies with other solid tumors according to a tissue-agnostic paradigm. Recently, functional evidence from patient-derived xenografts and organoids have suggested that maintenance with PARP inhibitors might represent a therapeutic opportunity in CRC patients previously responsive to platinum-based treatment.

DESIGN AND RESULTS

In this review, we highlight the most promising preclinical data and systematically summarize published clinical trials in which DDR inhibitors have been used for CRC and provide evidence that disappointing results have been mainly due to a lack of clinical and molecular selection.

CONCLUSIONS

Future preclinical and translational research will help in better understanding the role of DDR alterations in CRC and pave the way to novel strategies that might have a transformative impact on treatment by identifying new therapeutic options including tailored use of standard chemotherapy.

Precision medicine in gastric cancer

Gastric cancer (GC) is a complex disease linked to a series of environmental factors and unhealthy lifestyle habits, and especially to genetic alterations. GC represents the second leading cause of cancer-related deaths worldwide. Its onset is subtle, and the majority of patients are diagnosed once the cancer is already advanced. In recent years, there have been innovations in the management of advanced GC including the introduction of new classifications based on its molecular characteristics. Thanks to new technologies such as next-generation sequencing and microarray, the Cancer Genome Atlas and Asian Cancer Research Group classifications have also paved the way for precision medicine in GC, making it possible to integrate diagnostic and therapeutic methods. Among the objectives of the subdivision of GC into subtypes is to select patients in whom molecular targeted drugs can achieve the best results; many lines of research have been initiated to this end. After phase III clinical trials, trastuzumab, anti-Erb-B2 receptor tyrosine kinase 2 (commonly known as ERBB2) and ramucirumab, anti-vascular endothelial growth factor receptor 2 (commonly known as VEGFR2) monoclonal antibodies, were approved and introduced into first- and second-line therapies for patients with advanced/metastatic GC. However, the heterogeneity of this neoplasia makes the practical application of such approaches difficult. Unfortunately, scientific progress has not been matched by progress in clinical practice in terms of significant improvements in prognosis. Survival continues to be low in contrast to the reduction in deaths from many common cancers such as colorectal, lung, breast, and prostate cancers. Although several target molecules have been identified on which targeted drugs can act and novel products have been introduced into experimental therapeutic protocols, the overall approach to treating advanced stage GC has not substantially changed. Currently, surgical resection with adjuvant or neoadjuvant radiotherapy and chemotherapy are the most effective treatments for this disease. Future research should not underestimate the heterogeneity of GC when developing diagnostic and therapeutic strategies aimed toward improving patient survival.

Highlights in Resistance Mechanism Pathways for Combination Therapy

Combination chemotherapy has been a mainstay in cancer treatment for the last 60 years. Although the mechanisms of action and signaling pathways affected by most treatments with single antineoplastic agents might be relatively well understood, most combinations remain poorly understood. This review presents the most common alterations of signaling pathways in response to cytotoxic and targeted anticancer drug treatments, with a discussion of how the knowledge of signaling pathways might support and orient the development of innovative strategies for anticancer combination therapy. The ultimate goal is to highlight possible strategies of chemotherapy combinations based on the signaling pathways associated with the resistance mechanisms against anticancer drugs to maximize the selective induction of cancer cell death. We consider this review an extensive compilation of updated known information on chemotherapy resistance mechanisms to promote new combination therapies to be to discussed and tested.

Veliparib: a new therapeutic option in ovarian cancer?

The role of poly ADP ribose polymerase inhibitors in ovarian cancer is rapidly evolving. Three different poly ADP ribose polymerase inhibitors (olaparib, niraparib and rucaparib) have been already approved as maintenance after response to platinum-based chemotherapy; two of them (olaparib and rucaparib) also as single agents. Veliparib, a novel PARPI, showed promising results in preclinical and early clinical settings. The aim of this review is to discuss veliparib’s mechanisms of action, to provide a clinical update on its safety and activity in ovarian cancer, and to highlight future perspectives for its optimal use. Veliparib favorable toxicity profile encourages its use either as monotherapy or in combination. Its peculiar neuroprotective and radio-sensitizing effect warrant further investigation.

Exploiting DNA repair defects in colorectal cancer

Colorectal cancer (CRC) is the third leading cause of cancer-related deaths worldwide. Therapies that take advantage of defects in DNA repair pathways have been explored in the context of breast, ovarian, and other tumor types, but not yet systematically in CRC. At present, only immune checkpoint blockade therapies have been FDA approved for use in mismatch repair-deficient colorectal tumors. Here, we discuss how systematic identification of alterations in DNA repair genes could provide new therapeutic opportunities for CRCs. Analysis of The Cancer Genome Atlas Colon Adenocarcinoma (TCGA-COAD) and Rectal Adenocarcinoma (TCGA-READ) PanCancer Atlas datasets identified 141 (out of 528) cases with putative driver mutations in 29 genes associated with DNA damage response and repair, including the mismatch repair and homologous recombination pathways. Genetic defects in these pathways might confer repair-deficient characteristics, such as genomic instability in the absence of homologous recombination, which can be exploited. For example, inhibitors of poly(ADP)-ribose polymerase are effectively used to treat cancers that carry mutations in BRCA1 and/or BRCA2 and have shown promising results in CRC preclinical studies. HR deficiency can also occur in cells with no detectable BRCA1/BRCA2 mutations but exhibiting BRCA-like phenotypes. DNA repair-targeting therapies, such as ATR and CHK1 inhibitors (which are most effective against cancers carrying ATM mutations), can be used in combination with current genotoxic chemotherapies in CRCs to further improve therapy response. Finally, therapies that target alternative DNA repair mechanisms, such as thiopurines, also have the potential to confer increased sensitivity to current chemotherapy regimens, thus expanding the spectrum of therapy options and potentially improving clinical outcomes for CRC patients.

A phase 2 randomised study of veliparib plus FOLFIRI±bevacizumab versus placebo plus FOLFIRI±bevacizumab in metastatic colorectal cancer

Background

Metastatic colorectal cancer (mCRC) has low survival rates. We assessed if addition of veliparib, concurrent to FOLFIRI, improves survival in patients with previously untreated mCRC.

Methods

This study compared veliparib (200 mg BID for 7 days of each 14-day cycle) to placebo, each with FOLFIRI. Bevacizumab was allowed in both arms. The primary endpoint was progression-free survival (PFS).

Results

Patients were randomised to receive veliparib (n = 65) or placebo (n = 65) in combination with FOLFIRI. Median PFS was 12 vs 11 months (veliparib vs placebo) [HR = 0.94 (95% CI: 0.60, 1.48)]. Median OS was 25 vs 27 months [HR = 1.26 (95% CI: 0.74, 2.16)]. Response rate was 57% vs 62%. Median DOR was 11 vs 9 months [HR = 0.73 (95% CI: 0.38, 1.40)]. AEs with significantly higher frequency (p < 0.05) in the veliparib group were anaemia (39% vs 19%, p = 0.019) and neutropenia (66% vs 37%, p = 0.001) for common AEs (≥20%); neutropenia (59% vs 22%, p < 0.001) for common Grade 3/4 AEs (≥5%); none in serious AEs. Haematopoietic cytopenias were more common with veliparib (79% vs 52%, p = 0.003). Fourteen percent of patients on veliparib and 15% on placebo discontinued treatment due to AEs.

Conclusion

Veliparib added to FOLFIRI ± bevacizumab demonstrated similar efficacy as FOLFIRI ± bevacizumab in frontline mCRC patients. No unexpected safety concerns occurred.

Genomic instability in pancreatic adenocarcinoma: a new step towards precision medicine and novel therapeutic approaches

Pancreatic cancer is one of the most challenging cancers. Whole genome sequencing studies have been conducted to elucidate the underlying fundamentals underscoring disease behavior. Studies have identified a subgroup of pancreatic cancer patients with distinct molecular and clinical features. Genetic fingerprinting of these tumors is consistent with an unstable genome and defective DNA repair pathways, which creates unique susceptibility to agents inducing DNA damage. BRCA1/2 mutations, both germline and somatic, which lead to impaired DNA repair, are found to be important biomarkers of genomic instability as well as of response to DNA damaging agents. Recent studies have elucidated that PARP inhibitors and platinum agents may be effective to induce tumor regression in solid tumors bearing an unstable genome including pancreatic cancer. In this review we discuss the characteristics of genomic instability in pancreatic cancer along with its clinical implications and the utility of DNA targeting agents particularly PARP inhibitors as a novel treatment approach.

Pancreatic cancer: optimizing treatment options, new, and emerging targeted therapies

Pancreatic cancer is the fourth leading cause of cancer death in the US and is expected to become the second leading cause of cancer-related deaths in the next decade. Despite 5-fluorouracil/leucovorin with irinotecan and oxaliplatin (FOLFIRINOX) and gemcitabine/nab-paclitaxel significantly improving outcomes for metastatic cancer, refractory disease still poses significant challenges. Difficulties with early detection and the inherent chemo- and radio-resistant nature of this malignancy led to attempts to define the sequential biology of pancreatic cancer in order to improve survival outcomes. Pancreatic adenocarcinoma is characterized by several germline or acquired genetic mutations, the most common being KRAS (90%), CDK2NA (90%), TP53 (75%-90%), DPC4/SMAD4 (50%). In addition, the tumor microenvironment, chemoresistant cancer stem cells, and the desmoplastic stroma have been the target of some promising clinical investigations. Among the core pathways reproducibly shown to lead the development and progression of this disease, DNA repair, apoptosis, G1/S cell cycle transition, KRAS, Wnt, Notch, Hedgehog, TGF-beta, and other cell invasion pathways, have been the target of "precision therapeutics". No single molecularly targeted therapeutic though has been uniformly successful, probably due to the tumor heterogeneity, but biomarker research is evolving and it hopes to select more patients likely to benefit. Recent reports note activity with immunotherapies such as CD40 agonists, CCR2 inhibitors, cancer vaccines, and novel combinations against the immunosuppressive tumor milieu are ongoing. While many obstacles still exist, clearly we are making progress in deciphering the heterogeneity within pancreatic cancers. Integrating conventional and immunological targeting will be the key to effective treatment of this deadly disease.