A phase II study of the antisense oligonucleotide GTI-2040 plus docetaxel and prednisone as first-line treatment in castration-resistant prostate cancer

Advancing cancer treatments: The role of oligonucleotide-based therapies in driving progress

Although recent advancements in cancer immunology have resulted in the approval of numerous immunotherapies, minimal progress has been observed in addressing hard-to-treat cancers. In this context, therapeutic oligonucleotides, including interfering RNAs, antisense oligonucleotides, aptamers, and DNAzymes, have gained a central role in cancer therapeutic approaches due to their capacity to regulate gene expression and protein function with reduced toxicity compared with conventional chemotherapeutics. Nevertheless, systemic administration of naked oligonucleotides faces many extra- and intracellular challenges that can be overcome by using effective delivery systems. Thus, viral and non-viral carriers can improve oligonucleotide stability and intracellular uptake, enhance tumor accumulation, and increase the probability of endosomal escape while minimizing other adverse effects. Therefore, gaining more insight into fundamental mechanisms of actions of various oligonucleotides and the challenges posed by naked oligonucleotide administration, this article provides a comprehensive review of the recent progress on oligonucleotide delivery systems and an overview of completed and ongoing cancer clinical trials that can shape future oncological treatments.

Synthesis and evaluation of antisense oligonucleotides prodrug with G-quadruplex assembly and lysosome escape capabilities for oncotherapy

The applications of antisense oligonucleotides (ASOs) in rare or common diseases treatment have garnered great attention in recent years. Nevertheless, challenges associated with stability and bioavailability still persist, hampering the efficiency of ASOs. This work presents an ASO prodrug with parallel G-quadruplex assembly and lysosome escape capabilities for oncotherapy. Our findings revealed that the end-assembled quadruplex structure effectively shielded the ASO from enzymatic degradation. Meanwhile, the conjugation of maleimide within the quadruplex enhanced cellular uptake, potentially offering an alternative cell entry mechanism that circumvents lysosome involvement. Notably, an optimized molecule, Mal2-G4-ASO, exhibited remarkable therapeutic effects both in vitro and in vivo. This work presents a promising avenue for enhancing the activity of nucleic acid drugs in oncotherapy and potentially other disease contexts.

Antitumoral RNA-targeted oligonucleotide therapeutics: the third pillar after small molecule inhibitors and antibodies

Oligonucleotide therapeutics, drugs consisting of 10–50 nucleotide‐long single‐ or double‐stranded DNA or RNA molecules that can bind to specific DNA or RNA sequences or proteins, include antisense oligonucleotides (ASOs), small interfering RNAs (siRNAs), microRNAs (miRNAs), aptamers, and decoys. These oligonucleotide therapeutics could potentially become the third pillar of drug development. In particular, ASOs and siRNAs are advanced tools that are widely used to silence gene expression. They are used in clinical trials, as they have high specificity for target mRNAs and non‐coding RNAs and limited toxicity. However, their clinical application remains challenging. Although chemotherapy has benefits, it has severe adverse effects in many patients. Therefore, new modalities for targeted molecular therapy against tumors, including oligonucleotide therapeutics, are required, and they should be compatible with diagnosis using next‐generation sequencing. This review provides an overview of the therapeutic uses of ASOs, siRNAs, and miRNAs in clinical studies on malignant tumors. Understanding previous research and development will help in developing novel oligonucleotide therapeutics against malignant tumors.

Antisense Oligonucleotide-Mediated Splice Switching: Potential Therapeutic Approach for Cancer Mitigation

Splicing is an essential process wherein precursor messenger RNA (pre-mRNA) is reshaped into mature mRNA. In alternative splicing, exons of any pre-mRNA get rearranged to form mRNA variants and subsequently protein isoforms, which are distinct both by structure and function. On the other hand, aberrant splicing is the cause of many disorders, including cancer. In the past few decades, developments in the understanding of the underlying biological basis for cancer progression and therapeutic resistance have identified many oncogenes as well as carcinogenic splice variants of essential genes. These transcripts are involved in various cellular processes, such as apoptosis, cell signaling and proliferation. Strategies to inhibit these carcinogenic isoforms at the mRNA level are promising. Antisense oligonucleotides (AOs) have been developed to inhibit the production of alternatively spliced carcinogenic isoforms through splice modulation or mRNA degradation. AOs can also be used to induce splice switching, where the expression of an oncogenic protein can be inhibited by the induction of a premature stop codon. In general, AOs are modified chemically to increase their stability and binding affinity. One of the major concerns with AOs is efficient delivery. Strategies for the delivery of AOs are constantly being evolved to facilitate the entry of AOs into cells. In this review, the different chemical modifications employed and delivery strategies applied are discussed. In addition to that various AOs in clinical trials and their efficacy are discussed herein with a focus on six distinct studies that use AO-mediated exon skipping as a therapeutic strategy to combat cancer.

Inhibiting RRM2 to enhance the anticancer activity of chemotherapy

RRM2, the small subunit of ribonucleotide reductase, is identified as a tumor promotor and therapeutic target. It is common to see the overexpression of RRM2 in chemo-resistant cancer cells and patients. RRM2 mediates the resistance of many chemotherapeutic drugs and could become the predictor for chemosensitivity and prognosis. Therefore, inhibition of RRM2 may be an effective means to enhance the anticancer activity of chemotherapy. This review tries to discuss the mechanisms of RRM2 overexpression and the role of RRM2 in resistance to chemotherapy. Additionally, we compile the studies on small interfering RNA targets RRM2, RRM2 inhibitors, kinase inhibitors, and other ways that could overcome the resistance of chemotherapy or exert synergistic anticancer activity with chemotherapy through the expression inhibition or the enzyme inactivation of RRM2.

A phase I pharmacokinetic and pharmacodynamic study of GTI-2040 in combination with gemcitabine in patients with solid tumors

PURPOSE

GTI-2040 is a novel antisense oligonucleotide inhibitor of the R2 subunit of ribonucleotide reductase. This phase I study assessed safety and maximum tolerated dose (MTD) of GTI-2040 in combination with weekly gemcitabine in patients with advanced solid tumors.

METHODS

GTI-2040 was given as a 14-day continuous intravenous infusion, while gemcitabine was administered on days 1, 8, and 15. This combination was repeated every 4 weeks and study followed a modified 3 + 3 Fibonacci schema. Incidence, severity of adverse events, pharmacokinetics (PK), and pharmacodynamics (PD) was assessed. Responses were assessed using RECIST criteria version 1.0 with CT scans performed after every other cycle.

RESULTS

A total of 16 patients received at least one dose of GTI-2040/gemcitabine and were included in the safety analysis. The MTD of this regimen is 100 mg/m²/day of GTI-2040 over 14 days combined with 400 mg/m²/day of gemcitabine administered weekly on days 1, 8, and 15. The dose-limiting toxicities (DLTs) included grade 3 fatigue and thrombocytopenia with hematemesis (both at 100/600 mg/m²/day). The most common adverse events were grade 1/2 fatigue, nausea, vomiting, diarrhea, and anorexia. There was no evidence of alteration in gemcitabine PKs. PD modulation of R2mRNA expression in peripheral blood mononuclear cells was observed. No objective tumor response was observed although stable disease was seen in 25% patients.

CONCLUSIONS

The combination of GTI-2040 and gemcitabine has an acceptable safety profile in a heavily pre-treated patient population with advanced solid tumors. No clear signal of anti-tumor activity was observed; however, several patients had prolonged stable disease.

Anticancer activity of the intraperitoneal-delivered DFP-10825, the cationic liposome-conjugated RNAi molecule targeting thymidylate synthase, on peritoneal disseminated ovarian cancer xenograft model

Introduction

Peritoneal disseminated ovarian cancer is one of the most difficult cancers to treat with conventional anti-cancer drugs and the treatment options are very limited, although an intraperitoneal (ip) paclitaxel has shown some clinical benefit. Therefore, treatment of peritoneal disseminated ovarian cancer is a highly unmet medical need and it is urgent to develop a new ip delivered drug regulating the fast DNA synthesis.

Methods

We developed a unique RNAi molecule consisting of shRNA against the thymidylate synthase (TS) and a cationic liposome (DFP-10825) and tested its antitumor activity and PK profile in peritoneally disseminated human ovarian cancer ascites models by the luciferase gene-transfected SCID mice. DFP-10825 alone, paclitaxel alone or combination with DFP-10825 and paclitaxel were administered in an ip route to the tumor-bearing mice. The TS expression level was measured by conventional RT-PCR. The anti-tumor activity and host survival benefit by DFP-10825 treatment on tumor-bearing mice were observed as resulting from the specific TS mRNA knock-down in tumors.

Results

DFP-10825 alone significantly suppressed the growth of SKOV3-luc tumore ascites cells and further extended the survival time of these tumor-bearing mice. Combination with the ip paclitaxel augmented the antitumor efficacy of DFP-10825 and significantly prolonged the survival time in the tumor-bearing mice. Short-hairpin RNA for TS (TS shRNA) levels derived from DFP-10825 in the ascetic fluid were maintained at a nM range across 24 hours but not detected in the plasma, suggesting that TS shRNA is relatively stable in the peritoneal cavity, to be able to exert its anti-tumor activity, but not in blood stream, indicating little or no systemic effect.

Conclusion

Collectively, the ip delivery of DFP-10825, TS shRNA conjugated with cationic liposome, shows a favorable antitumor activity without systemic adverse events via the stable localization of TS shRNA for a sufficient time and concentration in the peritoneal cavity of the peritoneally disseminated human ovarian cancer-bearing mice.

Clinical pharmacology and clinical trials of ribonucleotide reductase inhibitors: is it a viable cancer therapy?

PURPOSE

Ribonucleotide reductase (RR) enzymes (RR1 and RR2) play an important role in the reduction of ribonucleotides to deoxyribonucleotides which is involved in DNA replication and repair. Augmented RR activity has been ascribed to uncontrolled cell growth and tumorigenic transformation.

METHODS

This review mainly focuses on several biological and chemical RR inhibitors (e.g., siRNA, GTI-2040, GTI-2501, triapine, gemcitabine, and clofarabine) that have been evaluated in clinical trials with promising anticancer activity from 1960's till 2016. A summary on whether their monotherapy or combination is still effective for further use is discussed.

RESULTS

Among the RR2 inhibitors evaluated, GTI-2040, siRNA, gallium nitrate and didox were more efficacious as a monotherapy, whereas triapine was found to be more efficacious as combination agent. Hydroxyurea is currently used more in combination therapy, even though it is efficacious as a monotherapy. Gallium nitrate showed mixed results in combination therapy, while the combination activity of didox is yet to be evaluated. RR1 inhibitors that have long been used in chemotherapy such as gemcitabine, cladribine, fludarabine and clofarabine are currently used mostly as a combination therapy, but are equally efficacious as a monotherapy, except tezacitabine which did not progress beyond phase I trials.

CONCLUSIONS

Based on the results of clinical trials, we conclude that RR inhibitors are viable treatment options, either as a monotherapy or as a combination in cancer chemotherapy. With the recent advances made in cancer biology, further development of RR inhibitors with improved efficacy and reduced toxicity is possible for treatment of variety of cancers.

RNA-targeted therapeutics in cancer clinical trials: Current status and future directions

Recent advances in RNA delivery and target selection provide unprecedented opportunities for cancer treatment, especially for cancers that are particularly hard to treat with existing drugs. Small interfering RNAs, microRNAs, and antisense oligonucleotides are the most widely used strategies for silencing gene expression. In this review, we summarize how these approaches were used to develop drugs targeting RNA in human cells. Then, we review the current state of clinical trials of these agents for different types of cancer and outcomes from published data. Finally, we discuss lessons learned from completed studies and future directions for this class of drugs.

A ribonucleotide reductase inhibitor with deoxyribonucleoside-reversible cytotoxicity

Ribonucleotide Reductase (RNR) is the sole enzyme that catalyzes the reduction of ribonucleotides into deoxyribonucleotides. Even though RNR is a recognized target for antiproliferative molecules, and the main target of the approved drug hydroxyurea, few new leads targeted to this enzyme have been developed. We have evaluated a recently identified set of RNR inhibitors with respect to inhibition of the human enzyme and cellular toxicity. One compound, NSC73735, is particularly interesting; it is specific for leukemia cells and is the first identified compound that hinders oligomerization of the mammalian large RNR subunit. Similar to hydroxyurea, it caused a disruption of the cell cycle distribution of cultured HL-60 cells. In contrast to hydroxyurea, the disruption was reversible, indicating higher specificity. NSC73735 thus defines a potential lead candidate for RNR-targeted anticancer drugs, as well as a chemical probe with better selectivity for RNR inhibition than hydroxyurea.

A phase I pharmacodynamic study of GTI-2040, an antisense oligonucleotide against ribonuclotide reductase, in acute leukemias: a California Cancer Consortium study

We performed a phase I study of GTI-2040, an antisense oligonucleotide against ribonucleotide reductase mRNA, on a novel dosing schedule of days 1-4 and 15-18 by continuous infusion to examine efficacy and tolerability in patients with leukemia. A dose of 11 mg/kg/d was safely reached. Dose-limiting toxicities (DLTs) at the higher levels included elevated troponin I and liver function enzymes. There were no objective responses to GTI-2040 in this study; 7/24 patients were able to complete the predetermined three infusion cycles. Pharmacokinetic and pharmacodynamic studies were performed, indicating a trend towards increasing intracellular drug levels and decreasing RRM2 gene expression with increasing doses. This dose schedule may be considered if appropriate combinations are identified in preclinical studies.

Effect of NF-κB p65 antisense oligodeoxynucleotide on transdifferentiation of normal human lens epithelial cells induced by transforming growth factor-β2

AIM

To study the inhibition of nuclear factor kappa-B p65 (NF-κB p65) antisense oligodeoxynucleotide (ASODN) on transdifferentiation of normal human lens epithelial cells induced by transforming growth factor-β2 (TGF-β2) in vitro.

METHODS

NF-κB p65 ASODN and NF-κB p65 missense oligodeoxynucleotide (MSODN) were designed and synthesized. Human lens epithelial cell line (HLE B-3) cells were prepared for study and divided into 7 groups. Control group was HLE B-3 cells cultured in vitro in dulbecco's modified eagle medium (DMEM). T1, T2, and T3 group were HLE B-3 cells cultured in vitro in DMEM with 10 ng/mL TGF-β2 for 6h, 12h, 24h respectively. A+T group was HLE B-3 cells cultured with 10 ng/mL TGF-β2 for 24h after transfected by NF-κB p65 ASODN for 24h. M+T group was HLE B-3 cells cultured with 10 ng/mL TGF-β2 for 24h after transfected by NF-κB p65 MSODN for 24h. The negative control group was HLE B-3 cells cultured with 10 ng/mL TGF-β2 for 24h after cultured with transfer agent (HiPerFect) for 24h. Cell morphology was observed at different time points using an inverted microscope. The expression of NF-κB p65 mRNA was detected with reverse transcription-polymerase chain reaction (RT-PCR), and the expression of α-smooth muscle actin (α-SMA) protein was assayed with ELISA.

RESULTS

With the TGF-β2 stimulation prolongation, the expression of NF-κB p65 mRNA and α-SMA protein increased in T1, T2, T3 groups compared with the control group, and the difference was statistically significant (P<0.05). NF-κB p65 ASODN lowered the expression of NF-κB p65 mRNA and α-SMA protein induced by TGF-β2. NF-κB p65 MSODN and HiPerFect did not lower the expression of NF-κB p65 mRNA and α-SMA protein induced by TGF-β2. The difference between control group and A+T group was not statistically significant (P>0.05), but the difference among A+T group and other groups was statistically significant (P<0.05).

CONCLUSION

NF-κB p65 ASODN could lower the expression of NF-κB p65 mRNA and α-SMA protein induced by TGF-β2, and antagonized TGF-β2-induced transdifferentiation of HLE B-3 in vitro. NF-κB p65 ASODN could be used as a new biological therapeutic target of posterior capsular opacification.

Oligonucleotide-Based Drug Development: Considerations for Clinical Pharmacology and Immunogenicity

The field of oligonucleotide (OGN)-based therapeutics has been growing dramatically in the past decade, providing innovative platforms to develop agents for the treatment of a wide variety of clinical conditions. OGN agents have unique physicochemical properties and pharmacokinetic/pharmacodynamic characteristics. This review considers findings from the literature and information on new molecular entities submitted to the US Food and Drug Administration as OGN-based therapeutics. In addition, the article discusses several challenging issues from the perspective of clinical pharmacology, emphasizing the potential of immunogenicity, the effect of renal impairment on OGN exposure, drug-drug interactions, and the utility of pharmacokinetic/pharmacodynamic modeling. The field of OGN-based therapeutics is in evolution and will benefit from further studies as well as clinical experience to formulate guidelines and promote the development of this class of agents.

Nucleotide metabolism, oncogene-induced senescence and cancer

Senescence is defined as a stable cell growth arrest. Oncogene-induced senescence (OIS) occurs when an activated oncogene is expressed in a normal cell. OIS acts as a bona fide tumor suppressor mechanism by driving stable growth arrest of cancer progenitor cells harboring the initial oncogenic hit. OIS is often characterized by aberrant DNA replication and the associated DNA damage response. Nucleotides, in particular deoxyribonucleotide triphosphates (dNTPs), are necessary for both DNA replication and repair. Imbalanced dNTP pools play a role in a number of human diseases, including during the early stages of cancer development. This review will highlight what is currently known about the role of decreased nucleotide metabolism in OIS, how nucleotide metabolism leads to transformation and tumor progression, and how this pathway can be targeted as a cancer therapeutic by inducing senescence of cancer cells.

Translating clinical trials to clinical practice: outcomes of men with metastatic castration resistant prostate cancer treated with docetaxel and prednisone in and out of clinical trials

BACKGROUND

Multiple factors can influence outcomes of patients receiving identical interventions in clinical trials and in routine practice. Here, we compare outcomes of men with metastatic castrate-resistant prostate cancer (mCRPC) treated with docetaxel and prednisone in routine practice and in clinical trials.

PATIENTS AND METHODS

We reviewed patients with mCRPC treated with docetaxel at Princess Margaret Cancer Centre. Primary outcomes were overall survival and PSA response rate. Secondary outcomes were reasons for discontinuation and febrile neutropenia. Outcomes were compared for men treated in routine practice and in clinical trials, and with data from the TAX 327 study.

RESULTS

From 2001 to 2011, 438 men were treated, of whom 357 received 3-weekly docetaxel as first-line chemotherapy: 314 in routine practice and 43 in clinical trials. Trial patients were younger and had better performance status. Median survival was 13.6 months [95% confidence interval (95% CI) 12.1-15.1 months] in routine practice and 20.4 months (95% CI 17.4-23.4 months, P = 0.007) within clinical trials, compared with 19.3 months (95% CI 17.6-21.3 months, P < 0.001) in the TAX 327 study. PSA response rates were 45%, 54%, and 53%, respectively (P = NS). Reasons for treatment discontinuation were similar although trial patients received more cycles (median: 6 versus 8 versus 9.5, P < 0.001). Rates of febrile neutropenia were 9.6, 0, and 3% (P < 0.001) while rates of death within 30 days of last dose were 4%, 0%, and 3%, respectively (P = NS).

CONCLUSIONS

Survival of patients with mCRPC treated with docetaxel in routine practice is shorter than for men included in trials and is associated with more toxicity.

Targeting ribonucleotide reductase for cancer therapy

INTRODUCTION

Ribonucleotide reductase (RR) is a unique enzyme, because it is responsible for reducing ribonucleotides to their corresponding deoxyribonucleotides, which are the building blocks required for DNA replication and repair. Dysregulated RR activity is associated with genomic instability, malignant transformation and cancer development. The use of RR inhibitors, either as a single agent or combined with other therapies, has proven to be a promising approach for treating solid tumors and hematological malignancies.

AREAS COVERED

This review covers recent publications in the area of RR, which include: i) the structure, function and regulation of RR; ii) the roles of RR in cancer development; iii) the classification, mechanisms and clinical application of RR inhibitors for cancer therapy and iv) strategies for developing novel RR inhibitors in the future.

EXPERT OPINION

Exploring the possible nonenzymatic roles of RR subunit proteins in carcinogenesis may lead to new rationales for developing novel anticancer drugs. Updated information about the structure and holoenzyme models of RR will help in identifying potential sites in the protein that could be targets for novel RR inhibitors. Determining RR activity and subunit levels in clinical samples will provide a rational platform for developing personalized cancer therapies that use RR inhibitors.

Target mRNA inhibition by oligonucleotide drugs in man

Oligonucleotide delivery in vivo is commonly seen as the principal hurdle to the successful development of oligonucleotide drugs. In an analysis of 26 oligonucleotide drugs recently evaluated in late-stage clinical trials we found that to date at least half have demonstrated suppression of the target mRNA and/or protein levels in the relevant cell types in man, including those present in liver, muscle, bone marrow, lung, blood and solid tumors. Overall, this strongly implies that the drugs are being delivered to the appropriate disease tissues. Strikingly we also found that the majority of the drug targets of the oligonucleotides lie outside of the drugable genome and represent new mechanisms of action not previously investigated in a clinical setting. Despite the high risk of failure of novel mechanisms of action in the clinic, a subset of the targets has been validated by the drugs. While not wishing to downplay the technical challenges of oligonucleotide delivery in vivo, here we demonstrate that target selection and validation are of equal importance for the success of this field.

Current treatment of metastatic bladder cancer and future directions

Metastatic urothelial carcinoma portends a very poor long-term prognosis, with 5-year survival at approximately 5%. The overall survival of metastatic bladder cancer has not improved over the last 20 years. The first-line therapy is cisplatin-based chemotherapy with the response rate approximately 50%. Approximately 30-50% of the patients are unsuitable for cisplatin, and there is no standard of care for this patient population. There is no standard second-line treatment. Several signaling pathways are activated in bladder urothelial carcinoma, but no targeted therapy, either alone or in combination with conventional cytotoxic chemotherapy, has been shown to significantly improve the treatment outcomes. The future of metastatic urothelial carcinoma treatment lies in the ability to deliver personalized therapy. This area remains an active research field today.

Effect of antisense oligodeoxynucleotide targeted against NF-κB/P65 on cell proliferation and tumorigenesis of gastric cancer

To study the inhibitory effect of nuclear transcription factor-kappa B(NF-κB) antisense oligodeoxynucleotide(ASODN) on the growth and tumorgenesis of human gastric cancer. We synthesized and transfected the ASODN of NF-κB/P65 to gastric cancer cell line. The effect of ASODN of NF-κB/P65 on the proliferation of gastric cancer cells was measured by MTT method. The subcutaneous xenograft model of human gastric cancer was established in nude mice, and the tumor growth curve was observed. The cell proliferation was significantly inhibited in P65 ASODN-transfected group in vitro (P<0.05). In vivo, tumor formation test showed that the tumor volume in nude mice in ASODN group was obviously smaller than in other groups (P<0.05); the apoptosis index (AI) was significantly higher (P<0.001). Simultaneously, MVD in ASODN group was markedly lower than in other groups (P<0.01). NF-κB could be used as a new biological therapeutic target of gastric cancer.

A phase 1 dose escalation, pharmacokinetic, and pharmacodynamic evaluation of eIF-4E antisense oligonucleotide LY2275796 in patients with advanced cancer

PURPOSE

The antisense oligonucleotide LY2275796 blocks expression of cap-binding protein eukaryotic initiation factor 4E (eIF-4E), an mRNA translation regulator upregulated in tumors. This phase I study sought an appropriate LY2275796 dose in patients with advanced tumors.

EXPERIMENTAL DESIGN

A 3-day loading dose, then weekly maintenance doses, were given to 1 to 3 patient cohorts, beginning with 100 mg and escalating. Plasma samples were collected to determine LY2275796 concentrations and tumor biopsies to quantify eIF-4E mRNA/protein.

RESULTS

Thirty patients with stage 4 disease received 1 or more LY2275796 dose. A dose-limiting toxicity was observed at 1,200 mg, with 1,000 mg the maximum-tolerated dose. Across all dose levels, most patients (87%) had only grade 1 to 2 toxicities. LY2275796 pharmacokinetics supported the dosing regimen. Comparison of pre- and postdose biopsies showed eIF-4E decreased in most patients. Fifteen patients had progressive disease, and 7 patients achieved stable disease (minimum of 6 weeks) as best response, with 2 patients on therapy for more than 3 months (one with melanoma, one with cystadenocarcinoma of the head/neck).

CONCLUSIONS

LY2275796 was well tolerated up to 1,000 mg. Because tumor eIF-4E expression was decreased, but no tumor response observed, LY2275796 should be studied combined with other treatment modalities.