A Phase I Study of Topotecan, Carboplatin and the PARP Inhibitor Veliparib in Acute Leukemias, Aggressive Myeloproliferative Neoplasms, and Chronic Myelomonocytic Leukemia

PARP inhibition leads to synthetic lethality with key splicing-factor mutations in myelodysplastic syndromes

BACKGROUND

Splicing factors are frequently mutated in patients with myelodysplastic syndromes and acute myeloid leukaemia. Recent studies have revealed convergent molecular defects caused by splicing factor mutations, among which R-loop dysregulation and resultant genome instability are suggested as contributing factors to disease progression. On the other hand, understanding how mutant cells survive upon aberrant R-loop formation and genome instability is essential for developing novel therapeutics.

METHODS

The immunoprecipitation was performed to identify R-loops in association with PARP1/poly-ADP-ribosylation. The western blot, immunofluorescence, and flow cytometry assays were used to test the cell viability, cell cycle arrest, apoptosis, and ATM activation in mutant cells following the treatment of the PARP inhibitor. The Srsf2(P95H) knock-in murine hematopoietic cells and MLL-AF9 transformed leukaemia model were generated to investigate the potential of the PARP inhibitor as a therapy for haematological malignancies.

RESULTS

The disease-causing mutations in SRSF2 activate PARP and elevate the overall poly-ADP-ribosylation levels of proteins in response to R-loop dysregulation. In accordance, mutant cells are more vulnerable to the PARP inhibitors in comparison to the wild-type counterpart. Notably, the synthetic lethality was further validated in the Srsf2(P95H) knock-in murine hematopoietic cell and MLL-AF9 leukaemia model.

CONCLUSIONS

Our findings suggest that mutant cells antagonise the genome threat caused by R-loop disruption by PARP activation, thus making PARP targeting a promising therapeutic strategy for myeloid cancers with mutations in SRSF2.

DNA damage response defects in hematologic malignancies: mechanistic insights and therapeutic strategies

ABSTRACT

The DNA damage response (DDR) encompasses the detection and repair of DNA lesions and is fundamental to the maintenance of genome integrity. Germ line DDR alterations underlie hereditary chromosome instability syndromes by promoting the acquisition of pathogenic structural variants in hematopoietic cells, resulting in increased predisposition to hematologic malignancies. Also frequent in hematologic malignancies are somatic mutations of DDR genes, typically arising from replication stress triggered by oncogene activation or deregulated tumor proliferation that provides a selective pressure for DDR loss. These defects impair homology-directed DNA repair or replication stress response, leading to an excessive reliance on error-prone DNA repair mechanisms that results in genomic instability and tumor progression. In hematologic malignancies, loss-of-function DDR alterations confer clonal growth advantage and adverse prognostic impact but may also provide therapeutic opportunities. Selective targeting of functional dependencies arising from these defects could achieve synthetic lethality, a therapeutic concept exemplified by inhibition of poly-(adenosine 5'-diphosphate ribose) polymerase or the ataxia telangiectasia and Rad 3 related-CHK1-WEE1 axis in malignancies harboring the BRCAness phenotype or genetic defects that increase replication stress. Furthermore, the role of DDR defects as a source of tumor immunogenicity, as well as their impact on the cross talk between DDR, inflammation, and tumor immunity are increasingly recognized, thus providing rationale for combining DDR modulation with immune modulation. The nature of the DDR-immune interface and the cellular vulnerabilities conferred by DDR defects may nonetheless be disease-specific and remain incompletely understood in many hematologic malignancies. Their comprehensive elucidation will be critical for optimizing therapeutic strategies to target DDR defects in these diseases.

Definitions, Biology, and Current Therapeutic Landscape of Myelodysplastic/Myeloproliferative Neoplasms

Myelodysplastic/myeloproliferative neoplasms (MDS/MPN) are hematological disorders characterized by both proliferative and dysplastic features. According to the 2022 International Consensus Classification (ICC), MDS/MPN consists of clonal monocytosis of undetermined significance (CMUS), chronic myelomonocytic leukemia (CMML), atypical chronic myeloid leukemia (aCML), MDS/MPN with SF3B1 mutation (MDS/MPN-T-SF3B1), MDS/MPN with ring sideroblasts and thrombocytosis not otherwise specified (MDS/MPN-RS-T-NOS), and MDS/MPN-NOS. These disorders exhibit a diverse range of genetic alterations involving various transcription factors (e.g., RUNX1), signaling molecules (e.g., NRAS, JAK2), splicing factors (e.g., SF3B, SRSF2), and epigenetic regulators (e.g., TET2, ASXL1, DNMT3A), as well as specific cytogenetic abnormalities (e.g., 8 trisomies, 7 deletions/monosomies). Clinical studies exploring therapeutic options for higher-risk MDS/MPN overlap syndromes mostly involve hypomethylating agents, but other treatments such as lenalidomide and targeted agents such as JAK inhibitors and inhibitors targeting PARP, histone deacetylases, and the Ras pathway are under investigation. While these treatment modalities can provide partial disease control, allogeneic bone marrow transplantation (allo-BMT) is the only potentially curative option for patients. Important prognostic factors correlating with outcomes after allo-BMT include comorbidities, splenomegaly, karyotype alterations, and the bone marrow blasts percentage at the time of transplantation. Future research is imperative to optimizing therapeutic strategies and enhancing patient outcomes in MDS/MPN neoplasms. In this review, we summarize MDS/MPN diagnostic criteria, biology, and current and future treatment options, including bone marrow transplantation.

Oxidative DNA Damage-induced PARP-1-mediated Autophagic Flux Disruption Contributes to Bupivacaine-induced Neurotoxicity During Pregnancy

OBJECTIVE

Severe neurologic complications after spinal anesthesia are rare but highly distressing, especially in pregnant women. Bupivacaine is widely used in spinal anesthesia, but its neurotoxic effects have gained attention.

METHODS

Furthermore, the etiology of bupivacaine-mediated neurotoxicity in obstetric patients remains unclear. Female C57BL/6 mice were intrathecally injected with 0.75% bupivacaine on the 18th day of pregnancy. We used immunohistochemistry to examine DNA damage after bupivacaine treatment in pregnant mice and measured γ-H2AX (Ser139) and 8-OHdG in the spinal cord. A PARP-1 inhibitor (PJ34) and autophagy inhibitor (3-MA) were administered with bupivacaine in pregnant mice. Parp-1flox/flox mice were crossed with Nes-Cre transgenic mice to obtain neuronal conditional knockdown mice. Then, LC3B and P62 staining were performed to evaluate autophagic flux in the spinal cords of pregnant wild-type (WT) and Parp-1-/- mice. We performed transmission electron microscopy (TEM) to evaluate autophagosomes.

RESULTS

The present study showed that oxidative stress-mediated DNA damage and neuronal injury were increased after bupivacaine treatment in the spinal cords of pregnant mice. Moreover, PARP-1 was significantly activated, and autophagic flux was disrupted. Further studies revealed that PARP-1 knockdown and autophagy inhibitors could alleviate bupivacaine-mediated neurotoxicity in pregnant mice.

CONCLUSION

Bupivacaine may cause neuronal DNA damage and PARP-1 activation in pregnant mice. PARP-1 further obstructed autophagic flux and ultimately led to neurotoxicity.

Synergistic effect of combined PI3 kinase inhibitor and PARP inhibitor treatment on BCR/ABL1-positive acute lymphoblastic leukemia cells

Poly (ADP-ribose) polymerase (PARP) inhibitors (PARPi) function by inhibiting base excision repair and inducing synthetic lethality in homologous recombination repair-deficient cells, such as BRCA1/2-mutated cancer cells. The BCR/ABL1 fusion protein causes dysregulated cell proliferation and is responsible for chronic myelogenous leukemia and Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph⁺ALL). BCR/ABL1 also induces genomic instability by downregulating BRCA1. We investigated the effect of the PARPi, olaparib, against Ph⁺ALL cell lines and found that they show variable sensitivity, presumably due to cancer-associated genetic alterations other than BCR/ABL1. To investigate the reasons for the variable responses of Ph⁺ALL cells to PARPi treatment, we analyzed the transcriptomes of olaparib-sensitive and -resistant Ph⁺ALL cell lines, which revealed that activation of the phosphatidylinositol 3-kinase (PI3K) pathway was a hallmark of PARPi resistance. Based on these findings, we examined the effects of adding a PI3K inhibitor (PI3Ki) to PARPi treatment to overcome PARPi insensitivity in Ph⁺ALL cell lines. Combination with PI3Ki increased PARPi cytotoxicity in PARPi-resistant Ph⁺ALL cell lines. Tyrosine kinase inhibitor (TKI) therapy is the gold standard for Ph⁺ALL, and, based on our findings, we propose that PARPi combined with TKI and PI3K inhibition could be a novel therapeutic strategy for Ph⁺ALL.

Pre-Existing and Acquired Resistance to PARP Inhibitor-Induced Synthetic Lethality

The advanced development of synthetic lethality has opened the doors for specific anti-cancer medications of personalized medicine and efficient therapies against cancers. One of the most popular approaches being investigated is targeting DNA repair pathways as the implementation of the PARP inhibitor (PARPi) into individual or combinational therapeutic schemes. Such treatment has been effectively employed against homologous recombination-defective solid tumors as well as hematopoietic malignancies. However, the resistance to PARPi has been observed in both preclinical research and clinical treatment. Therefore, elucidating the mechanisms responsible for the resistance to PARPi is pivotal for the further success of this intervention. Apart from mechanisms of acquired resistance, the bone marrow microenvironment provides a pre-existing mechanism to induce the inefficiency of PARPi in leukemic cells. Here, we describe the pre-existing and acquired mechanisms of the resistance to PARPi-induced synthetic lethality. We also discuss the potential rationales for developing effective therapies to prevent/repress the PARPi resistance in cancer cells.

Role of PARP Inhibitors in Cancer Immunotherapy: Potential Friends to Immune Activating Molecules and Foes to Immune Checkpoints

Poly (ADP-ribose) polymerase (PARP) inhibitors (PARPi) induce cytotoxic effects as single agents in tumors characterized by defective repair of DNA double-strand breaks deriving from BRCA1/2 mutations or other abnormalities in genes associated with homologous recombination. Preclinical studies have shown that PARPi-induced DNA damage may affect the tumor immune microenvironment and immune-mediated anti-tumor response through several mechanisms. In particular, increased DNA damage has been shown to induce the activation of type I interferon pathway and up-regulation of PD-L1 expression in cancer cells, which can both enhance sensitivity to Immune Checkpoint Inhibitors (ICIs). Despite the recent approval of ICIs for a number of advanced cancer types based on their ability to reinvigorate T-cell-mediated antitumor immune responses, a consistent percentage of treated patients fail to respond, strongly encouraging the identification of combination therapies to overcome resistance. In the present review, we analyzed both established and unexplored mechanisms that may be elicited by PARPi, supporting immune reactivation and their potential synergism with currently used ICIs. This analysis may indicate novel and possibly patient-specific immune features that might represent new pharmacological targets of PARPi, potentially leading to the identification of predictive biomarkers of response to their combination with ICIs.

Synthesis of Morpholine-, Piperidine-, and N-Substituted Piperazine-Coupled 2-(Benzimidazol-2-yl)-3-arylquinoxalines as Novel Potent Antitumor Agents

A novel series of 2-(benzimidazol-2-yl)quinoxalines with three types of pharmacophore groups, namely, piperazine, piperidine, and morpholine moieties, which are part of known antitumor drugs, was designed and synthesized. The compounds have been characterized by NMR and IR spectroscopy, high- and low-resolution mass spectrometry, and X-ray crystallography. 2-(Benzimidazol-2-yl)quinoxalines with N-methylpiperazine substituents showed promising activity against a wide range of cancer lines, without causing hemolysis and showing little cytotoxicity against normal human Wi-38 cells (human fetal lung). A mixture of regioisomers 2-(benzimidazol-2-yl)-3-(4-fluorophenyl)-6(and 7)-(4-methylpiperazin-1-yl)quinoxalines (mri BIQ 13da/14da) showed a highly selective cytotoxic effect against human lung adenocarcinoma (cell line A549) with a half-maximal inhibitory concentration at the level of doxorubicin with a selectivity index of 12. The data obtained by flow cytometry, fluorescence microscopy, and multiparametric fluorescence analysis suggested that the mechanism of the cytotoxic effect of the mri BIQ 13da/14da on A549 cells may be associated with the stopping of the cell cycle in phase S and inhibition of DNA synthesis as well as with the induction of mithochondrial apoptosis. Thus, mri BIQ 13da/14da can be considered as a leading compound deserving further study, optimization, and development as a new anticancer agent.

Positive Feedback Regulation of Poly(ADP-ribose) Polymerase 1 and the DNA-PK Catalytic Subunit Affects the Sensitivity of Nasopharyngeal Carcinoma to Etoposide

Etoposide (VP-16) is used for the treatment of various cancers, including nasopharyngeal carcinoma (NPC); however, cancers develop resistance to this agent by promoting DNA repair. The DNA-PK (DNA-PKcs) catalytic subunit and poly(ADP-ribose) polymerase 1 (PARP1) mediate acquired resistance and poor survival in NPC cells exposed to DNA damaging agents. DNA repair can alter the sensitivity of NPC cells to DNA damaging agents, and these two enzymes function concomitantly in response to DNA damage in vivo. Therefore, we explored the relationship between DNA-PKcs and PARP1, which may affect NPC cell survival by regulating DNA repair after VP-16 treatment. We performed quantitative real-time polymerase chain reaction, western blotting, and enzyme-linked immunoassays and found that DNA-PKcs knockdown downregulated the PARP1 and PAR expression. Conversely, PARP1 knockdown reduced DNA-PKcs activity, indicating the mutual regulation between DNA-PKcs and PARP1 in VP-16-induced DNA repair. Moreover, a combination treatment with olaparib (a PARP1 inhibitor) and NU7441 (a DNA-PKcs inhibitor) sensitized NPC cells to VP-16 in vitro and in vivo, suggesting that the combined treatment of olaparib, NU7441, and a DNA-damaging agent may be a successful treatment regimen in patients with NPC.

Targeting PARP proteins in acute leukemia: DNA damage response inhibition and therapeutic strategies

The members of the Poly(ADP‐ribose) polymerase (PARP) superfamily are involved in several biological processes and, in particular, in the DNA damage response (DDR). The most studied members, PARP1, PARP2 and PARP3, act as sensors of DNA damages, in order to activate different intracellular repair pathways, including single-strand repair, homologous recombination, conventional and alternative non-homologous end joining. This review recapitulates the functional role of PARPs in the DDR pathways, also in relationship with the cell cycle phases, which drives our knowledge of the mechanisms of action of PARP inhibitors (PARPi), encompassing inhibition of single-strand breaks and base excision repair, PARP trapping and sensitization to antileukemia immune responses. Several studies have demonstrated a preclinical activity of the current available PARPi, olaparib, rucaparib, niraparib, veliparib and talazoparib, as single agent and/or in combination with cytotoxic, hypomethylating or targeted drugs in acute leukemia, thus encouraging the development of clinical trials. We here summarize the most recent preclinical and clinical findings and discuss the synthetic lethal interactions of PARPi in acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL). Despite the low frequency of genomic alterations of PARP and other DDR-related genes in acute leukemia, selective vulnerabilities have been reported in several disease subgroups, along with a “BRCAness phenotype.” AML carrying the RUNX1-RUNX1T1 or PML-RARA fusion genes or mutations in signaling genes (FLT3-ITD in combination with TET2 or TET2 and DNMT3A deficiency), cohesin complex members (STAG2), TP53 and BCOR as co-occurring lesions, IDH1/2 and ALL cases expressing the TCF3-HLF chimera or TET1 was highly sensitive to PARPi in preclinical studies. These data, along with the warning coming from the observation of cases of therapy-related myeloid malignancies among patients receiving PARPi for solid tumors treatment, indicate that PARPi represents a promising strategy in a personalized medicine setting. The characterization of the clonal and subclonal genetic background and of the DDR functionality is crucial to select acute leukemia patients that will likely benefit of PARPi-based therapeutic regimens.

PARP Inhibitors and Myeloid Neoplasms: A Double-Edged Sword

Simple Summary

Poly(ADP-ribose) polymerase (PARP) inhibitors, which are medications approved to treat various solid tumors, including breast, prostate, ovarian, and prostate cancers, are being examined in hematological malignancies. This review summarizes the potential role of PARP inhibitors in the treatment of myeloid diseases, particularly acute myeloid leukemia (AML). We review ongoing clinical studies investigating the safety and efficacy of PARP inhibitors in the treatment of AML, focusing on specific molecular and genetic AML subgroups that could be particularly sensitive to PARP inhibitor treatment. We also discuss reports describing an increased risk of treatment-related myeloid neoplasms in patients receiving PARP inhibitors for solid tumors.

Abstract

Despite recent discoveries and therapeutic advances in aggressive myeloid neoplasms, there remains a pressing need for improved therapies. For instance, in acute myeloid leukemia (AML), while most patients achieve a complete remission with conventional chemotherapy or the combination of a hypomethylating agent and venetoclax, de novo or acquired drug resistance often presents an insurmountable challenge, especially in older patients. Poly(ADP-ribose) polymerase (PARP) enzymes, PARP1 and PARP2, are involved in detecting DNA damage and repairing it through multiple pathways, including base excision repair, single-strand break repair, and double-strand break repair. In the context of AML, PARP inhibitors (PARPi) could potentially exploit the frequently dysfunctional DNA repair pathways that, similar to deficiencies in homologous recombination in BRCA-mutant disease, set the stage for cell killing. PARPi appear to be especially effective in AML with certain gene rearrangements and molecular characteristics (RUNX1-RUNX1T1 and PML-RARA fusions, FLT3- and IDH1-mutated). In addition, PARPi can enhance the efficacy of other agents, particularly alkylating agents, TOP1 poisons, and hypomethylating agents, that induce lesions ordinarily repaired via PARP1-dependent mechanisms. Conversely, emerging reports suggest that long-term treatment with PARPi for solid tumors is associated with an increased incidence of myelodysplastic syndrome (MDS) and AML. Here, we (i) review the pre-clinical and clinical data on the role of PARPi, specifically olaparib, talazoparib, and veliparib, in aggressive myeloid neoplasms and (ii) discuss the reported risk of MDS/AML with PARPi, especially as the indications for PARPi use expand to include patients with potentially curable cancer.

Involvement of classic and alternative non-homologous end joining pathways in hematologic malignancies: targeting strategies for treatment

Chromosomal translocations are the main etiological factor of hematologic malignancies. These translocations are generally the consequence of aberrant DNA double-strand break (DSB) repair. DSBs arise either exogenously or endogenously in cells and are repaired by major pathways, including non-homologous end-joining (NHEJ), homologous recombination (HR), and other minor pathways such as alternative end-joining (A-EJ). Therefore, defective NHEJ, HR, or A-EJ pathways force hematopoietic cells toward tumorigenesis. As some components of these repair pathways are overactivated in various tumor entities, targeting these pathways in cancer cells can sensitize them, especially resistant clones, to radiation or chemotherapy agents. However, targeted therapy-based studies are currently underway in this area, and furtherly there are some biological pitfalls, clinical issues, and limitations related to these targeted therapies, which need to be considered. This review aimed to investigate the alteration of DNA repair elements of C-NHEJ and A-EJ in hematologic malignancies and evaluate the potential targeted therapies against these pathways.

PARP Inhibitors and Haematological Malignancies-Friend or Foe?

Simple Summary

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

Abstract

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

Secondary AML Emerging After Therapy with Hypomethylating Agents: Outcomes, Prognostic Factors, and Treatment Options

PURPOSE OF REVIEW

Secondary AML (s-AML) encompasses a distinct subgroup of AML with either therapy-related AML or AML arising from preexisting myeloid neoplasms. Despite recent advances in the treatment armamentarium of AML, outcomes remain poor in s-AML. The purpose of this review is to highlight distinct characteristics, prognostic factors, and treatment options for patients with s-AML. Further, we focus on a distinctly poor-risk subgroup of s-AML with previous exposure to hypomethylating agents (HMAs) and describe ongoing clinical trials in this patient population.

RECENT FINDINGS

CPX-351 (liposomal daunorubicin and cytarabine) is the first drug approved for s-AML and represents an advancement in the management of fit patients with this subtype of AML. Despite incremental improvement in remission rates and survival, long-term survival remains poor. Patients who have received prior HMAs for antecedent MDS rarely benefit from CPX-351 or other cytotoxic chemotherapy regimens. The approval of venetoclax in combination with azacitidine has led to a paradigm shift in the management of newly diagnosed older unfit AML patients; however, patients with s-AML and prior HMA therapy were excluded from the landmark randomized phase 3 study. Several early phase clinical trials with both low- and high-intensity therapies are ongoing for s-AML patients, though prior HMA exposure limits inclusion in many of these studies that include HMAs. Patients with s-AML previously treated with an HMA have dismal outcomes with standard therapeutic options and are under-represented in clinical trials. Trials investigating novel therapeutic options in this population are critically needed.

DNA repair pathways as guardians of the genome: Therapeutic potential and possible prognostic role in hematologic neoplasms

DNA repair pathways, which are also identified as guardians of the genome, protect cells from frequent damage that can lead to DNA breaks. The most deleterious types of damage are double-strand breaks (DSBs), which are repaired by homologous recombination (HR) and non-homologous end joining (NHEJ). Single strand breaks (SSBs) can be corrected through base excision repair (BER), nucleotide excision repair (NER), and mismatch repair (MMR). Failure to restore DNA lesions or inappropriately repaired DNA damage culminates in genomic instability and changes in the regulation of cellular functions. Intriguingly, particular mutations and translocations are accompanied by special types of leukemia. Besides, expression patterns of certain repair genes are altered in different hematologic malignancies. Moreover, analysis of mutations in key mediators of DNA damage repair (DDR) pathways, as well as investigation of their expression and function, may provide us with emerging biomarkers of response/resistance to treatment. Therefore, defective DDR pathways can offer a rational starting point for developing DNA repair-targeted drugs. In this review, we address genetic alterations and gene/protein expression changes, as well as provide an overview of DNA repair pathways.

Synthesis of 2,3-dihydrobenzo[b][1,4]dioxine-5-carboxamide and 3-oxo-3,4-dihydrobenzo[b][1,4]oxazine-8-carboxamide derivatives as PARP1 inhibitors

Poly(ADP-ribose) polymerase 1 (PARP1), a widely explored anticancer drug target, plays an important role in single-strand DNA break repair processes. High-throughput virtual screening (HTVS) of a Maybridge small molecule library using the PARP1-benzimidazole-4-carboxamide co-crystal structure and pharmacophore model led to the identification of eleven compounds. These compounds were evaluated using recombinant PARP1 enzyme assay that resulted in the acquisition of three PARP1 inhibitors: 3 (IC₅₀ = 12 μM), 4 (IC₅₀ = 5.8 μM), and 10 (IC₅₀ = 0.88 μM). Compound 4 (2,3-dihydro-1,4-benzodioxine-5-carboxamide) was selected as a lead and was subjected to further chemical modifications, involving analogue synthesis and scaffold hopping. These efforts led to the identification of (Z)-2-(4-hydroxybenzylidene)-3-oxo-3,4-dihydro-2H-benzo[b][1,4]oxazine-8-carboxamide (49, IC₅₀ = 0.082 μM) as the most potent inhibitor of PARP1 from the series.

PARP goes the weasel! Emerging role of PARP inhibitors in acute leukemias

Poly (ADP-ribose) polymerase (PARP) inhibitors, which induce synthetic lethality of BRCA mutant breast and ovarian cancers, are now under active exploration for treatment of acute leukemias, specifically acute myeloid leukemia (AML). Experimental data has revealed that DNA repair deficiencies similar to those found in BRCA mutant solid tumors function in malignant hematopoietic cells to enhance cell survival and promote therapy resistance. Preclinical studies have demonstrated that inhibition of PARP with a variety of agents can dramatically enhance the efficacy of other therapeutic approaches including cytotoxic and epigenetic chemotherapy, small molecule inhibitors (IDH and FLT3 inhibitors) and antibody drug conjugates. This has led to early stage clinical trials of multiple PARP inhibitors (PARPi) for AML patients. Despite small patient numbers, evidence of modest clinical efficacy and tolerability in combinatorial regimens support the further development of PARP inhibition as a novel therapeutic strategy for AML, particularly in select molecular subsets (MLL rearranged, FLT3 and IDH1 mutant disease.

PARP1 V762A polymorphism affects the prognosis of myelodysplastic syndromes

OBJECTIVE

Myelodysplastic syndromes (MDS), caused by various genetic mutations in hematopoietic stem cells, are associated with highly variable outcomes. Poly (ADP-ribose) polymerase-1 (PARP1) plays an important role in DNA damage repair and contributes to the progression of several types of cancer. Here, we investigated the impact of PARP1 V762A polymorphism on the susceptibility to and prognosis of MDS.

METHODS

Samples collected from 105 MDS patients and 202 race-matched healthy controls were subjected to polymerase chain reaction-restriction fragment length polymorphism for genotyping.

RESULTS

The allele and genotype frequencies of PARP1 V762A did not differ between MDS patients and the control group. However, MDS patients with the PARP1 V762A non-AA genotype, which is associated with high gene activity, had shorter overall survival rates (P = .01) than those with the AA genotype. Multivariate analysis of overall survival also revealed PARP1 V762A non-AA genotype as a poor prognostic factor (P = .02). When patients were analyzed according to treatment history, the PARP1 V762A non-AA genotype was only associated with poor survival in patients who had received treatment (P = .02).

CONCLUSION

PARP1 V762A polymorphism may be an independent prognostic factor for MDS, and a predictive biomarker for MDS treatment.

Recent Advances in Use of Topoisomerase Inhibitors in Combination Cancer Therapy

Inhibitors targeting human topoisomerase I and topoisomerase II alpha have provided a useful chemotherapy option for the treatment of many patients suffering from a variety of cancers. While the treatment can be effective in many patient cases, use of these human topoisomerase inhibitors is limited by side-effects that can be severe. A strategy of employing the topoisomerase inhibitors in combination with other treatments can potentially sensitize the cancer to increase the therapeutic efficacy and reduce resistance or adverse side effects. The combination strategies reviewed here include inhibitors of DNA repair, epigenetic modifications, signaling modulators and immunotherapy. The ongoing investigations on cellular response to topoisomerase inhibitors and newly initiated clinical trials may lead to adoption of novel cancer therapy regimens that can effectively stop the proliferation of cancer cells while limiting the development of resistance.

Targeting ADP-ribosylation by PARP inhibitors in acute myeloid leukaemia and related disorders

Acute myeloid leukaemia (AML) is a highly heterogeneous disease characterized by uncontrolled proliferation, block in myeloid differentiation and recurrent genetic abnormalities. In the search of new effective therapies, identification of synthetic lethal partners of AML genetic alterations might represent a suitable approach to tailor patient treatment. Genetic mutations directly affecting DNA repair genes are not commonly present in AML. Nevertheless, several studies indicate that AML cells show high levels of DNA lesions and genomic instability. Leukaemia-driving oncogenes (e.g., RUNX1-RUNXT1, PML-RARA, TCF3-HLF, IDH1/2, TET2) or treatment with targeted agents directed against aberrant kinases (e.g., JAK1/2 and FLT3 inhibitors) have been associated with reduced DNA repair gene expression/activity that would render leukaemia blasts selectively sensitive to synthetic lethality induced by poly(ADP-ribose) polymerase inhibitors (PARPi). Thus, specific oncogenic chimeric proteins or gene mutations, rare or typically distinctive of certain leukaemia subtypes, may allow tagging cancer cells for destruction by PARPi. In this review, we will discuss the rationale for using PARPi in AML subtypes characterized by a specific genetic background and summarize the preclinical and clinical evidence reported so far on their activity when used as single agents or in combination with classical cytotoxic chemotherapy or with agents targeting AML-associated mutated proteins.

New Concepts of Treatment for Patients with Myelofibrosis

OPINION STATEMENT

Seven years after the approval of the Janus kinase 1/2 (JAK1/2) inhibitor ruxolitinib, it remains the only drug licensed for the treatment of myelofibrosis. Patients who discontinue ruxolitinib have a dismal outcome, and this is, therefore, an area of significant unmet need. Given the central role that JAK-signal transducer and activator of transcription (STAT) activation plays in disease pathogenesis, there have been many other JAK inhibitors tested, but most have been abandoned, for a variety of reasons. The JAK2-selective inhibitor fedratinib has recently been resurrected, and there has been a resurgence of interest in the failed JAK1/2 inhibitor momelotinib, which possibly improves anemia. Pacritinib, a non-myelosuppressive JAK2-selective inhibitor, is currently in a dose-ranging study mandated by regulatory authorities. A plethora of other targeted agents, most backed by preclinical data, are in various stages of investigation. These include epigenetic and immune therapies, agents targeting cellular survival, metabolic and apoptotic pathways, the cell cycle, DNA repair, and protein folding and degradation, among others. However, at this time, none of these is close to registration or even in a pivotal trial, illustrating the difficulties in recapitulating the clinical disease in preclinical models. Most current clinical trials are testing the addition of a novel agent to ruxolitinib, either in the frontline setting or in the context of an insufficient response to ruxolitinib, or attempting to study new drugs in the second-line, "ruxolitinib failure" setting. Emerging data supports the addition of azacitidine to ruxolitinib in some patients. Other strategies have focused on improving cytopenias, through amelioration of bone marrow fibrosis or other mechanisms. This is important, because cytopenias are the commonest reason for ruxolitinib interruption and/or dose reduction, and dose optimization of ruxolitinib is tied to its survival benefit. The activin receptor ligand trap, sotatercept, and the anti-fibrotic agent, PRM-151, have shown promise in this regard.

The leukemia strikes back: a review of pathogenesis and treatment of secondary AML

Secondary AML is associated with a disproportionately poor prognosis, consistently shown to exhibit inferior response rates, event-free survival, and overall survival in comparison with de novo AML. Secondary AML may arise from the evolution of an antecedent hematologic disorder, or it may arise as a complication of prior cytotoxic chemotherapy or radiation therapy in the case of therapy-related AML. Because of the high frequency of poor-risk cytogenetics and high-risk molecular features, such as alterations in TP53, leukemic clones are often inherently chemoresistant. Standard of care induction had long remained conventional 7 + 3 until its reformulation as CPX-351, recently FDA approved specifically for secondary AML. However, recent data also suggests relatively favorable outcomes with regimens based on high-dose cytarabine or hypomethylating agents. With several investigational agents being studied, the therapeutic landscape becomes even more complex, and the treatment approach involves patient-specific, disease-specific, and therapy-specific considerations.

Synergistic Cytotoxic Effect of Busulfan and the PARP Inhibitor Veliparib in Myeloproliferative Neoplasms

Patients with high-risk myeloproliferative neoplasms (MPNs), and in particular myelofibrosis (MF), can be cured only with allogeneic hematopoietic stem cell transplantation (HSCT). Because MPNs and JAK2^V617F-mutated cells show genomic instability, stalled replication forks, and baseline DNA double-strand breaks, DNA repair inhibition with poly(ADP-ribose) polymerase-1 (PARP-1) inhibitors represents a potential novel therapy. Because the alkylating agent busulfan is integral in conditioning regimens for HSCT and leads to stalled replication forks through DNA strand cross-linking, we hypothesized that PARP inhibition with veliparib in combination with busulfan may lead to synergistic cytotoxicity in MPN cells. We first treated 2 MPN cell lines harboring the JAK2^V617F mutation (SET2 and HEL) with veliparib at increasing concentrations and measured cell proliferation. SET2 and HEL cells were relatively sensitive to veliparib (IC₅₀ of 11.3 μM and 74.2 μM, respectively). We next treated cells with increasing doses of busulfan in combination with 4 μM veliparib and found that the busulfan IC₅₀ decreased from 27 μM to 4 μM in SET2 cells and from 45.1 μM to 28.1 μM in HEL cells. The mean combination index was .55 for SET2 cells and .40 for HEL cells. Combination treatment of SET2 cells caused G2M arrest in 53% of cells, compared with 30% with veliparib alone and 35% with busulfan alone. G2M arrest was associated with activation of the ATR-Chk1 pathway, as shown by an immunofluorescence assay for phosphorylated Chk1 (p-Chk1). We then tested in vivo the effect of combined low doses of busulfan and veliparib in a JAK2^V617F MPN-AML xenotransplant model. Vehicle- and veliparib-treated mice had similar median survival of 39 and 40 days, respectively. Combination treatment increased median survival from 47 days (busulfan alone) to 50 days (P = .02). Finally, we tested the combined effect of busulfan and veliparib on CD34⁺ cells obtained from the bone marrow or peripheral blood of 5 patients with JAK2^V617F-mutated and 2 patients with CALR-mutated MF. MF cells treated with the combination of veliparib and busulfan showed reduced colony formation compared with busulfan alone (87% versus 68%; P = .001). In contrast, treatment of normal CD34⁺ cells with veliparib did not affect colony growth. Here we show that in vivo confirmation that treatment with the PARP-1 inhibitor veliparib and busulfan results in synergistic cytotoxicity in MPN cells. Our data provide the rationale for testing novel pretransplantation conditioning regimens with combinations of PARP-1 inhibition and reduced doses of alkylators, such as busulfan and melphalan, for high-risk MPNs or MPN-derived acute myelogenous leukemia.

Novel Therapeutics for Ovarian Cancer: The 11th Biennial Rivkin Center Ovarian Cancer Research Symposium

OBJECTIVE

The aim of this study was to summarize developments in novel therapeutics for ovarian cancer presented at the Ovarian Cancer Research Symposium held at the University of Washington.

METHODS

A symposium of the leaders in ovarian cancer research was convened to present and discuss current advances and future directions in ovarian cancer research.

RESULTS

The fourth session was held on September 13, 2016, and focused on Novel Therapeutics for Ovarian Cancer. The session featured a keynote presentation on Novel Immunotherapeutics for Ovarian Cancer from Nora Disis and an invited oral presentation from Scott Kaufmann that discussed poly (ADP-ribose) polymerase (PARP) Inhibitor Combinations for the Treatment of Ovarian Cancer. Eight additional oral presentations were selected from abstract submissions. Thirty-eight abstracts were presented as posters highlighting recent advances in tumor immunology, PARP inhibition, chemoresistance, and novel targets for ovarian cancer therapy.

CONCLUSIONS

PARP inhibitors, immunotherapies, and targeted therapies are but some of the expanding number of treatment options for ovarian cancer patients. Identification of the subsets of patients who will benefit most from these treatments remains the subject of intense preclinical and clinical research. Evidence presented at this symposium suggests that non-BRCA patients also benefit from PARP inhibitor therapies. Improved understanding of the mechanisms of chemoresistance and encouraging preclinical data presented for combinatorial approaches may soon yield new therapies for ovarian cancers that are resistant and refractory to standard treatments.

Advantages of evaluating γH2AX induction in non-clinical drug development

γH2AX, the phosphorylated form of a histone variant H2AX at Ser 139, is already widely used as a biomarker to research the fundamental biology of DNA damage and repair and to assess the risk of environmental chemicals, pollutants, radiation, and so on. It is also beginning to be used in the early non-clinical stage of pharmaceutical drug development as an in vitro tool for screening and for mechanistic studies on genotoxicity. Here, we review the available information on γH2AX-based test systems that can be used to develop drugs and present our own experience of practically applying these systems during the non-clinical phase of drug development. Furthermore, the potential application of γH2AX as a tool for in vivo non-clinical safety studies is also discussed.

Combination of a hypomethylating agent and inhibitors of PARP and HDAC traps PARP1 and DNMT1 to chromatin, acetylates DNA repair proteins, down-regulates NuRD and induces apoptosis in human leukemia and lymphoma cells

Combination of drugs that target different aspects of aberrant cellular processes is an efficacious treatment for hematological malignancies. Hypomethylating agents (HMAs) and inhibitors of poly(ADP-ribose) polymerases (PARPis) and histone deacetylases (HDACis) are clinically active anti-tumor drugs. We hypothesized that their combination would be synergistically cytotoxic to leukemia and lymphoma cells. Exposure of AML and lymphoma cell lines to the combination of the PARPi niraparib (Npb), the HMA decitabine (DAC) and the HDACi romidepsin (Rom) or panobinostat (Pano) synergistically inhibited cell proliferation by up to 70% via activation of the ATM pathway, increased production of reactive oxygen species, decreased mitochondrial membrane potential, and activated apoptosis. Addition of the DNA alkylating agents busulfan (Bu) and/or melphalan enhanced the anti-proliferative/cytotoxic effects of the triple-drug combination. [Npb+DAC+Rom] significantly increased the level of chromatin-bound PARP1 and DNMT1 and caused acetylation of DNA repair proteins, including Ku70, Ku80, PARP1, DDB1, ERCC1 and XPF/ERCC4. This three-drug combination down-regulated the components of the nucleosome-remodeling deacetylase (NuRD) complex, which is involved in DNA-damage repair. Addition of Bu to this combination further enhanced these effects on NuRD. The trapping of PARP1 and DNMT1 to chromatin, acetylation of DNA repair proteins, and down-regulation of NuRD may all have increased double-strand DNA break (DSB) formation as suggested by activation of the DNA-damage response, concomitantly resulting in tumor cell death. Similar synergistic cytotoxicity was observed in blood mononuclear cells isolated from patients with AML and lymphoma. Our results provide a rationale for the development of [Npb+DAC+Rom/Pano] combination therapies for leukemia and lymphoma patients.

Exposure-Response of Veliparib to Inform Phase II Trial Design in Refractory or Relapsed Patients with Hematological Malignancies

Purpose: A phase I trial of veliparib in combination with topotecan plus carboplatin (T+C) demonstrated a 33% objective response rate in patients with hematological malignancies. The objective is to perform exposure-response analysis to inform the phase II trial design.Experimental Design: Pharmacokinetic, efficacy, and safety data from 95 patients, who were administered 10 to 100 mg b.i.d. doses of veliparib for either 8, 14, or 21 days with T+C, were utilized for exposure-efficacy (objective response and overall survival) and exposure-safety (≥grade 3 mucositis) analysis. Multivariate cox proportional hazards and logistic regression analyses were conducted. The covariates evaluated were disease status, duration of treatment, and number of prior therapies.Results: The odds of having objective response were 1.08-fold with 1,000 ng/hr/mL increase in AUC, 1.8-fold with >8 days treatment, 2.8-fold in patients with myeloproliferative neoplasms (MPN), and 0.5-fold with ≥2 prior therapies. Based on analysis of overall survival, hazard of death decreased by 1.5% for 1,000 ng/hr/mL increase in AUC, 39% with >8 days treatment, 44% in patients with MPN, while increased by 19% with ≥2 prior therapies. The odds of having ≥grade 3 mucositis increased by 29% with 1,000 ng.h/mL increase in AUC.Conclusions: Despite shallow exposure-efficacy relationship, doses lower than 80 mg do not exceed veliparib single agent preclinical IC50 Shallow exposure-mucositis relationship also supports the 80-mg dose. Based on benefit/risk assessment, veliparib at a dose of 80 mg b.i.d. for at least 14 days in combination with T+C is recommended to be studied in MPN patients. Clin Cancer Res; 23(21); 6421-9. ©2017 AACR.

Therapeutic options for leukemic transformation in patients with myeloproliferative neoplasms

Approximately 5-10% of patients with Philadelphia chromosome negative myeloproliferative neoplasms (MPN) comprising of essential thrombocythemia, polycythemia vera and primary myelofibrosis) experience transformation to acute myeloid leukemia (AML, ≥20% blasts). Treatment options for post-MPN AML patients are limited, as conventional approaches like standard chemotherapy, fail to offer long-term benefit. Median survival for secondary AML is ∼2.4 months. Post-MPN AML therefore represents an area of urgent clinical need. At present, allogeneic stem cell transplant (ASCT) following induction therapy is the best therapeutic option. Patients ineligible for ASCT are treated with hypomethylating agents. New agents under investigation include histone deacetylase inhibitors, JAKinhibitors and agents targeting the BRD4 protein. Combined treatment strategies involving these novel agents are being tested. In this review we present the current evidence regarding treatment options for post-MPN AML patients.

Myelodysplastic and myeloproliferative neoplasms: updates on the overlap syndromes

Myelodysplastic and myeloproliferative neoplasms (MDS/MPN) is a rare and distinct group of myeloid neoplasms with overlapping MDS and MPN features. Next generation sequencing studies have led to an improved understanding of MDS/MPN disease biology by identifying recurrent somatic mutations. Combining the molecular findings to patho-morphologic features has improved the precision of diagnosis and prognostic models in MDS/MPN. We discuss and highlight these updates in MDS/MPN nomenclature and diagnostic criteria per revised 2016 WHO classification of myeloid neoplasms in this article. There is an ongoing effort for data integration allowing for comprehensive genomic characterization, development of improved prognostic tools, and investigation for novel therapies using an international front specific for MDS/MPN. In this article, we discuss updates in prognostic models and current state of treatment for MDS/MPN.

Drugging the Cancers Addicted to DNA Repair

Defects in DNA repair can result in oncogenic genomic instability. Cancers occurring from DNA repair defects were once thought to be limited to rare inherited mutations (such as BRCA1 or 2). It now appears that a clinically significant fraction of cancers have acquired DNA repair defects. DNA repair pathways operate in related networks, and cancers arising from loss of one DNA repair component typically become addicted to other repair pathways to survive and proliferate. Drug inhibition of the rescue repair pathway prevents the repair-deficient cancer cell from replicating, causing apoptosis (termed synthetic lethality). However, the selective pressure of inhibiting the rescue repair pathway can generate further mutations that confer resistance to the synthetic lethal drugs. Many such drugs currently in clinical use inhibit PARP1, a repair component to which cancers arising from inherited BRCA1 or 2 mutations become addicted. It is now clear that drugs inducing synthetic lethality may also be therapeutic in cancers with acquired DNA repair defects, which would markedly broaden their applicability beyond treatment of cancers with inherited DNA repair defects. Here we review how each DNA repair pathway can be attacked therapeutically and evaluate DNA repair components as potential drug targets to induce synthetic lethality. Clinical use of drugs targeting DNA repair will markedly increase when functional and genetic loss of repair components are consistently identified. In addition, future therapies will exploit artificial synthetic lethality, where complementary DNA repair pathways are targeted simultaneously in cancers without DNA repair defects.

Population pharmacokinetics and site of action exposures of veliparib with topotecan plus carboplatin in patients with haematological malignancies

AIMS

Veliparib is a potent inhibitor of poly(ADP-ribose) polymerase (PARP) enzyme. The objectives of the analysis were to evaluate the effect of baseline covariates and co-administration of topotecan plus carboplatin (T + C) on pharmacokinetics of veliparib in patients with refractory acute leukaemia, and compare veliparib concentration in various biological matrices.

METHODS

A population pharmacokinetic model was developed and effect of age, body size indices, sex, creatinine clearance (CrCL) and co-administration of T + C on the pharmacokinetics of veliparib were evaluated. The final model was qualified using bootstrap and quantitative predictive check. Linear regression was conducted to correlate concentrations of veliparib in various biological matrices.

RESULTS

A two compartment model with first-order absorption with T_lag described veliparib pharmacokinetics. The apparent clearance (CL/F) and volume (V_c /F) were 16.5 l h^-1 and 122.7 l, respectively. The concomitant administration of T + C was not found to affect veliparib CL/F. CrCL and lean body mass (LBM) were significant covariates on CL/F and Vc/F, respectively. While a strong positive relationship was observed between veliparib concentrations in plasma and bone marrow supernatant, no correlation was observed between plasma and peripheral blood or bone marrow blasts.

CONCLUSIONS

Consistent with veliparib's physiochemical properties and its elimination mechanism, LBM and CrCL were found to affect pharmacokinetics of veliparib while concomitant administration of T + C did not affect veliparib's CL/F. Plasma concentrations were found to be a reasonable surrogate for veliparib concentrations in peripheral blood and bone marrow supernatant but not blasts. The current model will be utilized to conduct exposure-response analysis to support dosing recommendations.

Genomic instability is a principle pathologic feature of FLT3 ITD kinase activity in acute myeloid leukemia leading to clonal evolution and disease progression

Acute Myeloid Leukemia with FLT3 ITD mutations are associated with a poor prognosis characterized by a higher relapse rate, shorter relapse free survival, and decreased likelihood of response to therapy at relapse. FLT3 ITD signaling drives cell proliferation and survival. FLT3 ITD AML disease progression is associated with cytogenetic evolution and acquired tyrosine kinase inhibitor (TKI) resistance suggesting a potential role of genomic instability. There is growing evidence demonstrating a relationship between FLT3 signaling and increased DNA damage, specifically through increased reactive oxygen species (ROS) resulting in double-strand breaks (DSB), as well as impaired DNA repair, involving deficiencies in the non-homologous end joining (NHEJ), alternative non-homologous end joining (ALT NHEJ) and homologous recombination (HR) pathways. The role of genomic instability in the pathogenesis of FLT3 ITD AML warrants further examination as it offers potential therapeutic targets.