Pixantrone: novel mode of action and clinical readouts

Topoisomerase II-targeting anticancer clinical candidates and drugs: A critical analysis, unravelling molecular medicinal insights and promising research roadmap

In recent years, the USFDA-approved drug molecules are being frequently analyzed to provide perspectives and strategies for novel therapeutic discovery and development. Some of the remarkable analyses include physicochemical properties of drugs relevant to oral bioavailability, frequent presence of drug relevant-structural motifs, natural products as sources of new drugs, and synthetic approaches to new drugs. In this review article, for the first time, we present a structure-function analysis of human topoisomerase II (hTopo II) inhibitors those are currently clinically used or under clinical trials for anticancer treatment. The case studies and a critical molecular medicinal insight for their therapeutic development have been presented. The review illustrates various key aspects: the hTopo II inhibitors' molecular modulations, common pharmacophores, interactions at molecular level crucial for inhibition of enzyme at its various stages of catalytic function, and network polypharmacology of Topo II with different targets. Numerous toxicophore motifs have been identified, which provide important alerts while designing and discovering novel therapeutic agents. A range of innovative approaches including property-focused strategies, ADCs, and Click Activated Protodrugs Against Cancer (CAPAC) that have addressed challenges faced in the hTopo II-based therapeutic development have been discussed. The analysis with perspectives represents a valuable educational and research resource that will encourage hTopo II-inhibition and its network polypharmacology based drug discovery studies.

The mitochondrial calcium uniporter: Balancing tumourigenic and anti-tumourigenic responses

Increased malignancy and poor treatability associated with solid tumour cancers have commonly been attributed to mitochondrial calcium (Ca2+) dysregulation. The mitochondrial Ca2+ uniporter complex (mtCU) is the predominant mode of Ca2+ uptake into the mitochondrial matrix. The main components of mtCU are the pore-forming mitochondrial Ca2+ uniporter (MCU) subunit, MCU dominant-negative beta (MCUb) subunit, essential MCU regulator (EMRE) and the gatekeeping mitochondrial Ca2+ uptake 1 and 2 (MICU1 and MICU2) proteins. In this review, we describe mtCU-mediated mitochondrial Ca2+ dysregulation in solid tumour cancer types, finding enhanced mtCU activity observed in colorectal cancer, breast cancer, oral squamous cell carcinoma, pancreatic cancer, hepatocellular carcinoma and embryonal rhabdomyosarcoma. By contrast, decreased mtCU activity is associated with melanoma, whereas the nature of mtCU dysregulation remains unclear in glioblastoma. Furthermore, we show that numerous polymorphisms associated with cancer may alter phosphorylation sites on the pore forming MCU and MCUb subunits, which cluster at interfaces with EMRE. We highlight downstream/upstream biomolecular modulators of MCU and MCUb that alter mtCU-mediated mitochondrial Ca2+ uptake and may be used as biomarkers or to aid in the development of novel cancer therapeutics. Additionally, we provide an overview of the current small molecule inhibitors of mtCU that interact with the Asp residue of the critical Asp-Ile-Met-Glu motif or through other allosteric regulatory mechanisms to block Ca2+ permeation. Finally, we describe the relationship between MCU- and MCUb-mediating microRNAs and mitochondrial Ca2+ uptake that should be considered in the discovery of new treatment approaches for cancer.

Pixantrone confers radiosensitization in KRAS mutated cancer cells by suppression of radiation-induced prosurvival pathways

Radioresistance towards radiation therapy has generated the need for the development of radiosensitizers as a potential drug. KRAS mutation brings radioresistance in tumor cells. The present work proves sensitization of cancer cells towards radiotherapy through inhibition of KRAS activation. Acquiring a drug repurposing approach, the in-silico screening revealed that pixantrone, an antineoplastic drug, possesses a high affinity towards KRAS G12C and G12D subtypes. The SPR study suggests that maximum affinity of pixantrone was observed with KRAS G12C>WT>G12D and G12S. Pixantrone potentially inhibited the KRAS activation in stable transfectants G12C and G12D cell lines and radiosensitized distinct KRAS mutant subtype cells. The combination of pixantrone with radiation causes enhanced dsDNA breaks along with enhanced ATM expression, and increased late apoptosis. The preclinical studies on NCr-fox1^nu xenograft mice showed potent inhibition of tumor progression and prolonged survival of mcie due to the radiosensitizing effect of pixantrone. Radiation-induced activation of key effector proteins of RAS downstream pathways, like MAPK and PI3K/Akt/mTOR pathways, were downregulated in tumor cells upon combination treatment. Interestingly, a robust upregulation of senescence marker p21 was observed in the tumor cells in combination treatment. These findings reveal a convergence between KRAS signaling, pixantrone treatment, and radiation conferring tumor cell death.

Heterocyclic ring expansion yields anthraquinone derivatives potent against multidrug resistant tumor cells

Chemical modifications of anthraquiones are aimed at novel derivatives with improved antitumor properties. Emergence of multidrug resistance (MDR) due to overexpression of transmembrane ATP binding cassette transporters, in particular, MDR1/P-glycoprotein (Pgp), can limit the use of anthraquinone based drugs. Previously we have demonstrated that annelation of modified five-membered heterocyclic rings with the anthraquinone core yielded a series of compounds with optimized antitumor properties. In the present study we synthesized a series of anthraquinone derivatives with six-membered heterocycles. Selected new compounds showed the ability to kill parental and MDR tumor cell lines at low micromolar concentrations. Molecular docking into the human Pgp model revealed a stronger interaction of 2-methylnaphtho[2,3-g]quinoline-3-carboxamide 17 compared to naphtho[2,3-f]indole-3-carboxamide 3. The time course of intracellular accumulation of compound 17 in parental K562 leukemia cells and in Pgp-positive K562/4 subline was similar. In contrast, compound 3 was readily effluxed from K562/4 cells and was significantly less potent for this subline than for K562 cells. Together with reported strategies of drug optimization of the anthracycline core, these results add ring expansion to the list of perspective modifications of heteroarene-fused anthraquinones.

Effectiveness and Safety of Pixantrone for the Treatment of Relapsed or Refractory Diffuse Large B-Cell Lymphoma in Every-Day Clinical Practice: The Italian Cohort of the PIXA Registry

INTRODUCTION

Treatment of relapsed/refractory (R/R) diffuse large B-cell lymphoma (DLBCL) represents a challenge for clinicians due to the lack of therapeutic options. DLBCL is not a rare disease in Italy. Pixantrone is an aza-anthracenedione, which, when compared to anthracyclines and anthracenediones, has a significantly reduced cardiotoxicity while maintaining good anti-tumor activity. However, the evidence on the use of pixantrone in the context of daily clinical practice is scarce.

METHODS

We focused on the Italian patient subset of a larger European retrospective study (the PIXA Registry) to assess the efficacy and safety of pixantrone in a real-life DLBCL population. The molecular profile of the disease and its impact on drug efficacy were also assessed.

RESULTS

Fifteen heavily pretreated DLBCL patients (13 males and 2 females) underwent treatment with pixantrone for a median of 2 cycles (range 1-6). Eight patients were bcl2 positive, 7 bcl6 positive, and 4 myc positive; 4 patients were diagnosed as double-hit, and 2 as triple-hit DLBCL. The overall response rate was 26.7% with a best response rate of 46.7%. Three patients had grade IV adverse events, which caused drug discontinuation. Four patients had 5 cases of grade III toxicities (1 thrombocytopenia, 1 stomatitis, and 3 neutropenia). One mild cardiac toxicity (sinus tachycardia for which no action was required) was possibly related to the study drug.

CONCLUSION

Our data documented drug efficacy that is satisfactory for this high-risk subset of patients with an acceptable toxicity profile. Results indicate that pixantrone could be a significant treatment option in patients with R/R aggressive DLBCL treated in everyday clinical practice.

Copper Complexes as Anticancer Agents Targeting Topoisomerases I and II

Organometallics, such as copper compounds, are cancer chemotherapeutics used alone or in combination with other drugs. One small group of copper complexes exerts an effective inhibitory action on topoisomerases, which participate in the regulation of DNA topology. Copper complexes inhibitors of topoisomerases 1 and 2 work by different molecular mechanisms, analyzed herein. They allow genesis of DNA breaks after the formation of a ternary complex, or act in a catalytic mode, often display DNA intercalative properties and ROS production, and sometimes display dual effects. These amplified actions have repercussions on the cell cycle checkpoints and death effectors. Copper complexes of topoisomerase inhibitors are analyzed in a broader synthetic view and in the context of cancer cell mutations. Finally, new emerging treatment aspects are depicted to encourage the expansion of this family of highly active anticancer drugs and to expend their use in clinical trials and future cancer therapy.

Efficacy and safety of pixantrone for the treatment of multiply relapsed or refractory aggressive non-Hodgkin B-cell lymphomas

BACKGROUND AND OBJECTIVE

Few treatment options exist for patients with relapsed/refractory (R/R) B-cell non-Hodgkin lymphoma (NHL) who fail first- and second-line therapies. Pixantrone is a novel aza-anthracenedione agent with reduced potential for cardiotoxicity but maintained anti-tumour activity relative to anthracyclines. The current retrospective, observational, real-life study was undertaken in 79 patients who received pixantrone monotherapy for multiply R/R aggressive B-cell NHL in Spain and Italy.

RESULTS

Before pixantrone, patients had received a median of 3 prior therapies and 84.6% of them were refractory to the last regimen. Median progression-free survival (mPFS) was 2.8 months (95% confidence interval [CI] 2.1-3.6) and median overall survival (mOS) was 4.0 months (95%CI 5.6-7.9), with an objective response rate (ORR) of 29% (complete remission [CR]: 13.2%, partial remission [PR]: 15.2%). Patients receiving ≥2 cycles of pixantrone showed mPFS and mOS of 3.1 and 6.0 months, respectively, and an ORR of 36.8% (CR: 17.5%, PR: 19.3%). Overall, 63.3% of patients reported ≥1 adverse event (AE), most commonly haematological AEs. One patient developed grade 2 sinus tachycardia.

CONCLUSION

Pixantrone was effective and well tolerated in a real-world population of multiply R/R patients with aggressive B-cell NHL, many of whom had very poor prognostic factors.

Pixantrone anticancer drug as a DNA ligand: Depicting the mechanism of action at single molecule level

In this work we use single molecule force spectroscopy performed with optical tweezers in order to characterize the complexes formed between the anticancer drug Pixantrone (PIX) and the DNA molecule, at two very different ionic strengths. Firstly, the changes of the mechanical properties of the DNA-PIX complexes were studied as a function of the drug concentration in the sample. Then, a quenched-disorder statistical model of ligand binding was used in order to determine the physicochemical (binding) parameters of the DNA-PIX interaction. In particular, we have found that the PIX molecular mechanism of action involves intercalation into the double helix, followed by a significant compaction of the DNA molecule due to partial neutralization of the phosphate backbone. Finally, this scenario of interaction was quantitatively compared to that found for the related drug Mitoxantrone (MTX), which binds to DNA with a considerably higher equilibrium binding constant and promotes a much stronger DNA compaction. The comparison performed between the two drugs can bring clues to the development of new (and more efficient) related compounds.