Pralatrexate Pharmacology and Clinical Development

Cellular Genome-Scale Metabolic Modeling Identifies New Potential Drug Targets Against Hepatocellular Carcinoma

Genome-scale metabolic modeling (GEM) is one of the key approaches to unpack cancer metabolism and for discovery of new drug targets. In this study, we report the Transcriptional Regulated Flux Balance Analysis-CORE (TRFBA-), an algorithm for GEM using key growth-correlated reactions using hepatocellular carcinoma (HCC), an important global health burden, as a case study. We generated a HepG2 cell-specific GEM by integrating this cell line transcriptomic data with a generic human metabolic model to forecast potential drug targets for HCC. A total of 108 essential genes for growth were predicted by the TRFBA-CORE. These genes were enriched for metabolic pathways involved in cholesterol, sterol, and steroid biosynthesis. Furthermore, we silenced a predicted essential gene, 11-beta dehydrogenase hydroxysteroid type 2 (HSD11B2), in HepG2 cells resulting in a reduction in cell viability. To further identify novel potential drug targets in HCC, we examined the effect of nine drugs targeting the essential genes, and observed that most drugs inhibited the growth of HepG2 cells. Some of these drugs in this model performed better than Sorafenib, the first-line therapeutic against HCC. A HepG2 cell-specific GEM highlights sterol metabolism to be essential for cell growth. HSD11B2 downregulation results in lower cell growth. Most of the compounds, selected by drug repurposing approach, show a significant inhibitory effect on cell growth in a wide range of concentrations. These findings offer new molecular leads for drug discovery for hepatic cancer while also illustrating the importance of GEM and drug repurposing in cancer therapeutics innovation.

Naturally occurring, natural product inspired and synthetic heterocyclic anti-cancer drugs

This chapter describes the importance and activity of a huge number of commercially available naturally occurring, natural product derived or synthetic heterocyclic anti-cancer drugs.

Multidrug resistance proteins (MRPs): Structure, function and the overcoming of cancer multidrug resistance

ATP-binding cassette (ABC) transporters mediate the ATP-driven translocation of structurally and mechanistically distinct substrates against steep concentration gradients. Among the seven human ABC subfamilies namely ABCA-ABCG, ABCC is the largest subfamily with 13 members. In this respect, 9 of the ABCC members are termed "multidrug resistance proteins" (MRPs1-9) due to their ability to mediate cancer multidrug resistance (MDR) by extruding various chemotherapeutic agents or their metabolites from tumor cells. Furthermore, MRPs are also responsible for the ATP-driven efflux of physiologically important organic anions such as leukotriene C₄, folic acid, bile acids and cAMP. Thus, MRPs are involved in important regulatory pathways. Blocking the anticancer drug efflux function of MRPs has shown promising results in overcoming cancer MDR. As a result, many novel MRP modulators have been developed in the past decade. In the current review, we summarize the structure, tissue distribution, biological and pharmacological functions as well as clinical insights of MRPs. Furthermore, recent updates in MRP modulators and their therapeutic applications in clinical trials are also discussed.

Schedule-Dependent Synergy Between the Histone Deacetylase Inhibitor Belinostat and the Dihydrofolate Reductase Inhibitor Pralatrexate in T-and B-cell Lymphoma Cells in vitro

Pralatrexate (Folotyn; PLX) and belinostat (Beleodaq; BLS) are registered for the treatment of patients with peripheral T-cell lymphoma (PTCL) and are being considered for other lymphomas. In this study we investigated whether BLS had the ability to potentiate the cytotoxicity of PLX. A panel of lymphoma cell lines was used for the combination studies: the B-cell SUDHL-4, SUDHL-5, HT, Jeko-1 and T-cell Karpas-299 and Hut-78. Uptake of PLX was mediated by the reduced folate carrier (RFC). PLX showed a 6-fold better RFC substrate affinity compared to methotrexate, and 2-fold better than levoleucovorin (l-LV). Sensitivity expressed as the concentration that resulted in 50% growth inhibition (IC50) after 72 hr exposure to PLX varied from 2.8 to 20 nM and for BLS from 72 to 233 nM, independent of the background of the cell lines. The interaction between BLS and PLX was studied using the median-drug effect analysis. At a fixed molar ratio between the drugs based on the IC50 concentration the average combination index (CI) for all cell lines showed additivity (CI: around 1.0). In three selected cell lines (SUDHL-4, SUDHL-5, and HT) sequential exposure (24 h pretreatment with BLS, followed by 48 h to PLX + BLS), did not improve interaction (CI: 0.9–1.4). As an alternative approach a non-fixed ratio was used by exposing SUDHL-4, SUDHL-5, and HT cells to IC25 concentrations of either BLS or PLX in combination with the other drug. Exposure to IC25 of PLX did not decrease the IC50 for BLS (CI from 0.6–1.2), but exposure to IC25 of BLS markedly increased PLX sensitivity (low CIs from 0.40 to 0.66). Mechanistic studies focused on induction of apoptosis, and showed cleavage of predominantly caspase-9 in HT and SUDHL-4 cells for both drugs at their IC50s, being similar in the combination setting. Moreover, at these concentrations, the drugs were shown to confer an S-phase arrest. In conclusion, the combination of PLX and BLS showed additivity in various lymphoma cell lines, with a schedule-dependent synergism in B-cell lymphoma. Based on these data, proficient inhibition of HDAC activity by BLS holds promise in sensitization of tumor cells to PLX.

Pralatrexate injection for the treatment of patients with relapsed or refractory peripheral T-cell lymphoma

INTRODUCTION

Peripheral T cell lymphomas (PTCL) are a heterogenous group of lymphoproliferative disorders which are generally not curable with conventional chemotherapy and associated with inferior outcomes. Pralatrexate is a novel folate analog, the first FDA approved drug) for the treatment of relapsed/refractory (R/R) PTCL.

AREAS COVERED

This paper provides a comprehensive review of PubMed literature describing the use of pralatrexate in R/R peripheral T-cell lymphoma. Pharmacokinetics and mechanism of action of pralatrexate are discussed as well as its clinical efficacy and safety in comparison to other agents available in R/R PTCL.

EXPERT OPINION

Pralatrexate is an active agent in relapsed/refractory PTCL with lower response rates seen in patients with angioimmunoblastic T cell lymphomas. Mucositis is the most frequently observed adverse event and this can be mitigated by the use of leucovorin along with cyanocobalamin and folic acid.

Pralatrexate in Chinese Patients with Relapsed or Refractory Peripheral T-cell Lymphoma: A Single-arm, Multicenter Study

BACKGROUND

Peripheral T-cell lymphoma (PTCL) is associated with poor prognosis, particularly in patients with relapsed/refractory (R/R) disease. Pralatrexate, a folate analogue inhibitor, was the first drug approved to treat R/R PTCL.

OBJECTIVE

As the distribution of PTCL subtypes differs between populations and few patients in the pivotal trial of pralatrexate were Asian, this study investigated the safety and efficacy of pralatrexate as monotherapy in Chinese patients with R/R PTCL.

PATIENTS AND METHODS

In this single-arm, open-label, multicenter study, 71 patients with R/R PTCL (median [range] 2 [1-14] prior systemic treatments) were recruited from 15 centers in China and received pralatrexate IV 30 mg/m²/week for 6 weeks in 7-week cycles (with vitamin B₁₂/folate). The primary endpoint was objective response rate (ORR) per central review (null hypothesis: ORR < 15%).

RESULTS

The study's primary objective was met: ORR (95% CI) was 52% (40-64%) (p < 0.001) and responses were observed across pre-specified patient subgroups. Median (95% CI) duration of response was 8.7 (3.3-14.1) months and first response was observed in Cycle 1 for most (84%) patients. Median (95% CI) progression-free survival and overall survival was 4.8 (3.1-8.1) months and 18.0 (10.4-NA) months, respectively. The most common treatment-emergent adverse events were stomatitis (68% [Grade 3/4: 20%]), anemia (49% [Grade 3/4: 24%]) and alanine aminotransferase increase (41% [Grade 3/4: 4%]).

CONCLUSIONS

These results demonstrate that pralatrexate may represent a promising treatment option for Chinese patients with R/R PTCL. The ORR of 52% compared favorably with prior studies of pralatrexate in other populations and there were no unanticipated side effects.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT03349333.

Clinical efficacy and mechanism of Pralatrexate combined with Palbociclib Isethionate in treatment of bladder cancer patients

The clinical efficacy and mechanism of Pralatrexate (PTX) combined with Palbociclib Isethionate (PAL) in the treatment of bladder cancer patients was investigated. A retrospective analysis of medical records of 82 bladder cancer patients admitted to Shengjing Hospital of China Medical University from February 2015 to February 2018 was performed. Patients treated with PTX combined with PAL served as study group (42 cases) and patients with conventional GC (gemcitabine plus cisplatin) chemotherapy regimen were the control group (40 cases). Changes in liver function indexes before and after treatment were observed, including alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), and total bilirubin (TBil). RT-qPCR was used for detection of relative expression levels of serum dihydrofolate reductase (DHFR) and vascular endothelial growth factor (VEGF) before and after treatment in the two groups. The clinical efficacy after treatment and adverse reactions during treatment were observed in the two groups. There was no significant difference in the clinical remission rate (RR) nor in the serum ALT, AST, ALP and TBil levels between the study and the control groups (P>0.05). Concentrations of serum ALT, AST, ALP and TBil were significantly higher than those before treatment in both groups (P<0.05). Serum ALT, AST, ALP and TBil concentrations in study group were significantly lower than those in control group (P<0.05). There was no significant difference in the incidence of thrombocytopenia and leukopenia between the two groups (P>0.05). There was no significant difference in relative expression levels of serum DHFR mRNA and VEGF mRNA before treatment between the study and control groups (P>0.05). Those after treatment were significantly lower than those before treatment in both groups (P<0.05), and those after treatment in study group were significantly lower than those in control group (P<0.05). PTX combined with PAL can reduce adverse reactions of nausea and vomiting and liver function impairment during treatment and suppress tumor neovascularization. This is achieved possibly by inhibiting expression levels of DHFR and VEGF, thereby killing cancer cells. PTX combined with PAL may become a new method for the treatment of bladder cancer patients. DHFR and VEGF are expected to become novel therapeutic targets for the treatment of bladder cancer.

Therapeutic potential of pteridine derivatives: A comprehensive review

Pteridines are aromatic compounds formed by fused pyrazine and pyrimidine rings. Many living organisms synthesize pteridines, where they act as pigments, enzymatic cofactors, or immune system activation molecules. This variety of biological functions has motivated the synthesis of a huge number of pteridine derivatives with the aim of studying their therapeutic potential. This review gathers the state-of-the-art of pteridine derivatives, describing their biological activities and molecular targets. The antitumor activity of pteridine-based compounds is one of the most studied and advanced therapeutic potentials, for which several molecular targets have been identified. Nevertheless, pteridines are also considered as very promising therapeutics for the treatment of chronic inflammation-related diseases. On the other hand, many pteridine derivatives have been tested for antimicrobial activities but, although some of them resulted to be active in preliminary assays, a deeper research is needed in this area. Moreover, pteridines may be of use in the treatment of many other diseases, such as diabetes, osteoporosis, ischemia, or neurodegeneration, among others. Thus, the diversity of the biological activities shown by these compounds highlights the promising therapeutic use of pteridine derivatives. Indeed, methotrexate, pralatrexate, and triamterene are Food and Drug Administration approved pteridines, while many others are currently under study in clinical trials.

Therapeutic Options for Aggressive T-Cell Lymphomas

T-cell lymphomas (TCL) are a rare, heterogeneous group of non-Hodgkin lymphomas associated with very poor prognosis with standard cytotoxic chemotherapy. Epigenetic-based therapy, such as with histone deacetylase inhibitors, was initially discovered to be efficacious in TCL. In recent years, our understanding of the mechanisms driving T-cell lymphomagenesis has validated the use of epigenetic-based drugs and has also led to the development of novel agents with promising efficacy in pre-clinical and early clinical trials. These new treatments play upon the prominent existence of epigenetic and immune dysfunction present in T-cell lymphomas. With these advances, novel therapeutic regimens combining traditional chemotherapy as well as epigenetic and/or immunotherapy serve as promising future treatment options for TCL. In this review, we discuss the traditional methods of treatment for TCL as well as novel agents and combinations that will likely change the treatment paradigms resulting in better clinical outcomes.

Recent advances in understanding and managing T-cell lymphoma

Owing to the rarity of peripheral T-cell lymphoma (PTCL) and the heterogeneity of subtypes, there are no compelling data to guide the therapeutic approaches for such patients. Over the years, there have been remarkable advances in molecular subtyping and treatment of PTCL, although there are still many areas to be explored. In this review, we summarize recent updates on the evolution of understanding and treatment for PTCL.

Phase I/II study of pralatrexate in Japanese patients with relapsed or refractory peripheral T-cell lymphoma

Pralatrexate is a novel antifolate approved in the USA for the treatment of relapsed or refractory peripheral T‐cell lymphoma. To assess its safety, efficacy, and pharmacokinetics in Japanese patients with this disease, we undertook a phase I/II study. Pralatrexate was given i.v. weekly for 6 weeks of a 7‐week cycle. All patients received concurrent vitamin B₁₂ and folic acid. In phase I, three patients received pralatrexate 30 mg/m² and none experienced a dose‐limiting toxicity. In phase II, we treated 22 additional patients with that dose. The median number of treatment cycles was 1 (range, 1–9). Nine of 20 evaluable patients (45%) achieved an objective response by central review, including two complete responses. All responses occurred within the first treatment cycle. At the time of data cut‐off, median progression‐free survival was 150 days. Median overall survival was not reached. In the total population, the most commonly reported adverse events included mucositis (88%), thrombocytopenia (68%), liver function test abnormality (64%), anemia (60%), and lymphopenia (56%). Grade 3/4 adverse events included lymphopenia (52%), thrombocytopenia (40%), leukopenia (28%), neutropenia (24%), anemia (20%), and mucositis (20%). The pharmacokinetic profile showed no drug accumulation with repeat dosing. These results indicate that pralatrexate is generally well tolerated and effective in Japanese patients with relapsed or refractory peripheral T‐cell lymphoma. This trial was registered with ClinicalTrials.gov (NCT02013362).

T-cell lymphomas, a challenging disease: types, treatments, and future

T-cell lymphomas are rare and aggressive malignancies associated with poor outcome, often because of the development of resistance in the lymphoma against chemotherapy as well as intolerance in patients to the established and toxic chemotherapy regimens. In this review article, we discuss the epidemiology, pathophysiology, current standard of care, and future treatments of common types of T-cell lymphomas, including adult T-cell leukemia/lymphoma, angioimmunoblastic T-cell lymphoma, anaplastic large-cell lymphoma, aggressive NK/T-cell lymphoma, and cutaneous T-cell lymphoma.

Folylpoly-γ-glutamate synthetase: A key determinant of folate homeostasis and antifolate resistance in cancer

Mammalians are devoid of autonomous biosynthesis of folates and hence must obtain them from the diet. Reduced folate cofactors are B9-vitamins which play a key role as donors of one-carbon units in the biosynthesis of purine nucleotides, thymidylate and amino acids as well as in a multitude of methylation reactions including DNA, RNA, histone and non-histone proteins, phospholipids, as well as intermediate metabolites. The products of these S-adenosylmethionine (SAM)-dependent methylations are involved in the regulation of key biological processes including transcription, translation and intracellular signaling. Folate-dependent one-carbon metabolism occurs in several subcellular compartments including the cytoplasm, mitochondria, and nucleus. Since folates are essential for DNA replication, intracellular folate cofactors play a central role in cancer biology and inflammatory autoimmune disorders. In this respect, various folate-dependent enzymes catalyzing nucleotide biosynthesis have been targeted by specific folate antagonists known as antifolates. Currently, antifolates are used in drug treatment of multiple human cancers, non-malignant chronic inflammatory disorders as well as bacterial and parasitic infections. An obligatory key component of intracellular folate retention and intracellular homeostasis is (anti)folate polyglutamylation, mediated by the unique enzyme folylpoly-γ-glutamate synthetase (FPGS), which resides in both the cytoplasm and mitochondria. Consistently, knockout of the FPGS gene in mice results in embryonic lethality. FPGS catalyzes the addition of a long polyglutamate chain to folates and antifolates, hence rendering them polyanions which are efficiently retained in the cell and are now bound with enhanced affinity by various folate-dependent enzymes. The current review highlights the crucial role that FPGS plays in maintenance of folate homeostasis under physiological conditions and delineates the plethora of the molecular mechanisms underlying loss of FPGS function and consequent antifolate resistance in cancer.

Pralatrexate in Combination with Bortezomib for Relapsed or Refractory Peripheral T Cell Lymphoma in 5 Elderly Patients

Peripheral T cell lymphoma (PTCL) is a heterogeneous group of aggressive lymphomas with poor prognosis. Elderly (age ≥ 65years) patients generally have impaired bone marrow function, altered drug metabolism, comorbidities, and poor functional status. Thus, treatment of elderly patients with relapsed or refractory PTCL remains a challenge for clinicians. A recent study disclosed that pralatrexate has a synergistic effect in combination with bortezomib. Weekly pralatrexate and bortezomib were administered intravenously for 3 weeks in a 4-week cycle. Of 5 patients, one achieved complete response after 4 cycles which has lasted 12 months until now. Another patient attained partial response after 2 cycles. Only 1 patient experienced grade 3 thrombocytopenia and neutropenia. Two patients suffered from grade 3 mucositis. Combination therapy with pralatrexate and bortezomib may be used as a salvage therapy for relapsed or refractory PTCL in the elderly with a favorable safety profile.

Inside the biochemical pathways of thymidylate synthase perturbed by anticancer drugs: Novel strategies to overcome cancer chemoresistance

Our current understanding of the mechanisms of action of antitumor agents and the precise mechanisms underlying drug resistance is that these two processes are directly linked. Moreover, it is often possible to delineate chemoresistance mechanisms based on the specific mechanism of action of a given anticancer drug. A more holistic approach to the chemoresistance problem suggests that entire metabolic pathways, rather than single enzyme targets may better explain and educate us about the complexity of the cellular responses upon cytotoxic drug administration. Drugs, which target thymidylate synthase and folate-dependent enzymes, represent an important therapeutic arm in the treatment of various human malignancies. However, prolonged patient treatment often provokes drug resistance phenomena that render the chemotherapeutic treatment highly ineffective. Hence, strategies to overcome drug resistance are primarily designed to achieve either enhanced intracellular drug accumulation, to avoid the upregulation of folate-dependent enzymes, and to circumvent the impairment of DNA repair enzymes which are also responsible for cross-resistance to various anticancer drugs. The current clinical practice based on drug combination therapeutic regimens represents the most effective approach to counteract drug resistance. In the current paper, we review the molecular aspects of the activity of TS-targeting drugs and describe how such mechanisms are related to the emergence of clinical drug resistance. We also discuss the current possibilities to overcome drug resistance by using a molecular mechanistic approach based on medicinal chemistry methods focusing on rational structural modifications of novel antitumor agents. This paper also focuses on the importance of the modulation of metabolic pathways upon drug administration, their analysis and the assessment of their putative roles in the networks involved using a meta-analysis approach. The present review describes the main pathways that are modulated by TS-targeting anticancer drugs starting from the description of the normal functioning of the folate metabolic pathway, through the protein modulation occurring upon drug delivery to cultured tumor cells as well as cancer patients, finally describing how the pathways are modulated by drug resistance development. The data collected are then analyzed using network/netwire connecting methods in order to provide a wider view of the pathways involved and of the importance of such information in identifying additional proteins that could serve as novel druggable targets for efficacious cancer therapy.

Acetylenic antifolates as anticancer agents

Folates are crucial cofactors involved in the de novo generation of purine and deoxythymidine monophosphate, which are essential for DNA synthesis. Antifolates are structural analogues of folate derivatives that act as inhibitors of folate-dependent enzymes and constitute the oldest antimetabolite class of anticancer agents. This review focuses on antifolates with remarkable anticancer activities that include a terminal alkyne function in their molecular structure. The properties of CB3717, a tremendous inhibitor of thymidylate synthase, are described, and the development of raltitrexed and pralatrexate, a dihydrofolate reductase inhibitor approved by the U.S. Food and Drug Administration (FDA) as the first drug for the treatment of relapsed and refractory peripheral T cell lymphoma are presented.

Leucovorin rescue allows effective high-dose pralatrexate treatment and an increase in therapeutic index in mesothelioma xenografts

Purpose

To investigate the ability of leucovorin (LV) to abrogate dose-limiting toxicities of pralatrexate (PDX) while maintaining efficacy, in vivo.

Methods

H2052 mesothelioma cells were treated with the antifolates methotrexate (MTX), PDX and pemetrexed, with and without LV rescue 24 h later. Cell killing was evaluated 48 h later. Female nude mice bearing H2052 xenografts were treated with varying doses and schedules of the antifolate PDX and LV.

Results

In vitro, H2052 cells were more sensitive to PDX as compared to MTX and pemetrexed. Administration of LV 24 h after antifolate treatment reduced efficacy of antifolates MTX and pemetrexed, but not PDX. In vivo, LV was found to reduce toxicity of PDX at the maximum tolerated dose without sacrificing efficacy. Lethal doses of PDX were rescued by LV, and mice bearing the H2052 tumor demonstrated prolonged and enhanced tumor regression.

Conclusions

High-dose PDX with subsequent LV rescue may be a viable treatment strategy in mesothelioma and other cancers. The inclusion of LV rescue into new and existing PDX treatment protocols should be explored as a way to expand the tolerability and effectiveness of PDX in the clinic.

Standing the test of time: targeting thymidylate biosynthesis in cancer therapy

Over the past 60 years, chemotherapeutic agents that target thymidylate biosynthesis and the enzyme thymidylate synthase (TS) have remained among the most-successful drugs used in the treatment of cancer. Fluoropyrimidines, such as 5-fluorouracil and capecitabine, and antifolates, such as methotrexate and pemetrexed, induce a state of thymidylate deficiency and imbalances in the nucleotide pool that impair DNA replication and repair. TS-targeted agents are used to treat numerous solid and haematological malignancies, either alone or as foundational therapeutics in combination treatment regimens. We overview the pivotal discoveries that led to the rational development of thymidylate biosynthesis as a chemotherapeutic target, and highlight the crucial contribution of these advances to driving and accelerating drug development in the earliest era of cancer chemotherapy. The function of TS as well as the mechanisms and consequences of inhibition of this enzyme by structurally diverse classes of drugs with distinct mechanisms of action are also discussed. In addition, breakthroughs relating to TS-targeted therapies that transformed the clinical landscape in some of the most-difficult-to-treat cancers, such as pancreatic, colorectal and non-small-cell lung cancer, are highlighted. Finally, new therapeutic agents and novel mechanism-based strategies that promise to further exploit the vulnerabilities and target resistance mechanisms within the thymidylate biosynthesis pathway are reviewed.

The major facilitative folate transporters solute carrier 19A1 and solute carrier 46A1: biology and role in antifolate chemotherapy of cancer

This review summarizes the biology of the major facilitative membrane transporters, the reduced folate carrier (RFC) (Solute Carrier 19A1) and the proton-coupled folate transporter (PCFT) (Solute Carrier 46A1). Folates are essential vitamins, and folate deficiency contributes to a variety of health disorders. RFC is ubiquitously expressed and is the major folate transporter in mammalian cells and tissues. PCFT mediates the intestinal absorption of dietary folates and appears to be important for transport of folates into the central nervous system. Clinically relevant antifolates for cancer, such as methotrexate and pralatrexate, are transported by RFC, and loss of RFC transport is an important mechanism of methotrexate resistance in cancer cell lines and in patients. PCFT is expressed in human tumors, and is active at pH conditions associated with the tumor microenvironment. Pemetrexed is an excellent substrate for both RFC and PCFT. Novel tumor-targeted antifolates related to pemetrexed with selective membrane transport by PCFT over RFC are being developed. In recent years, there have been major advances in understanding the structural and functional properties and the regulation of RFC and PCFT. The molecular bases for methotrexate resistance associated with loss of RFC transport and for hereditary folate malabsorption, attributable to mutant PCFT, were determined. Future studies should continue to translate molecular insights from basic studies of RFC and PCFT biology into new therapeutic strategies for cancer and other diseases.