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.

Heat Shock Proteins (HSPs): A Novel Target for Cancer Metastasis Prevention

Background:

Heat shock proteins (HSPs) are predominant molecular chaperones which are actively involved in the protein folding; which is essential in protecting the structure and functioning of proteins during various stress conditions. Though HSPs have important physiological roles, they have been well known for their roles in various pathogenic conditions such as carcinogenesis; however, limited literature has consolidated its potential as an anti-metastatic drug target.

Objectives:

The present review outlines the role of different HSPs on cancer progression and metastasis; possible role of HSP inhibitors as anti-neoplastic agents is also discussed.

Methods:

The data were collected from PubMed/Medline and other reputed journal databases. The literature that was too old and had no significant role to the review was then omitted.

Results:

Despite their strong physiological functions, HSPs are considered as good markers for cancer prognosis and diagnosis. They have control over survival, proliferation and progression events of cancer including drug resistance, metastasis, and angiogenesis. Since, neoplastic cells are more dependent on HSPs for survival and proliferation, the selectivity and specificity of HSP-targeted cancer drugs remain high. This has made various HSPs potential clinical and experimental targets for cancer prevention. An array of HSP inhibitors has been in trials and many others are in experimental conditions as anticancer and anti-metastatic agents. Several natural products are also being investigated for their efficacy for anticancer and anti-metastatic agents by modulating HSPs.

Conclusion:

Apart from their role as an anticancer drug target, HSPs have shown to be promising targets for the prevention of cancer progression. Extensive studies are required for the use of these molecules as anti-metastatic agents. Further studies in this line may yield specific and effective antimetastatic agents.

Borealis-1: a randomized, first-line, placebo-controlled, phase II study evaluating apatorsen and chemotherapy for patients with advanced urothelial cancer

Background

Five-year survival of patients with inoperable, advanced urothelial carcinoma treated with the first-line chemotherapy is 5%-15%. We assessed whether the Hsp27 inhibitor apatorsen combined with gemcitabine plus cisplatin (GC) could improve overall survival (OS) in these patients.

Patients and methods

This placebo-controlled, double-blind, phase II trial randomized 183 untreated urothelial carcinoma patients (North America and Europe) to receive GC plus either placebo (N = 62), 600 mg apatorsen (N = 60), or 1000 mg apatorsen (N = 61). In the experimental arm, treatment included loading doses of apatorsen followed by up to six cycles of apatorsen plus GC. Patients receiving at least four cycles could continue apatorsen monotherapy as maintenance until progression or unacceptable toxicity. The primary end point was OS.

Results

OS was not significantly improved in the single or combined 600- or 1000-mg apatorsen arms versus placebo [hazard ratio (HR), 0.86 and 0.90, respectively]. Exploratory study of specific statistical modeling showed a trend for improved survival in patients with baseline poor prognostic features treated with 600 mg apatorsen compared with placebo (HR = 0.72). Landmark analysis of serum Hsp27 (sHsp27) levels showed a trend toward survival benefit for poor-prognosis patients in 600- and 1000-mg apatorsen arms who achieved lower area under the curve sHsp27 levels, compared with the placebo arm (HR = 0.45 and 0.62, respectively). Higher baseline circulating tumor cells (≥5 cells/7.5 ml) was observed in patients with poor prognosis in correlation with poor survival. Treatment-emergent adverse events were manageable and more common in both apatorsen-treatment arms.

Conclusions

Even though apatorsen combined with standard chemotherapy did not demonstrate a survival benefit in the overall study population, patients with poor prognostic features might benefit from this combination. Serum Hsp27 levels may act as a biomarker to predict treatment outcome. Further exploration of apatorsen in poor-risk patients is warranted.

A randomized phase 2 study of a HSP27 targeting antisense, apatorsen with prednisone versus prednisone alone, in patients with metastatic castration resistant prostate cancer

Purpose Heat shock protein 27 (Hsp27) is implicated in prostate cancer progression. Apatorsen is a second generation phosphorothioate antisense inhibitor of Hsp27 expression. We evaluated apatorsen in patients with metastatic castration resistant prostate cancer (mCRPC). Experimental design Eligible patients were randomized 1:1 to receive intravenous apatorsen (3 loading doses of 600 mg within 5-9 days followed by weekly doses of 1000 mg) with oral prednisone 5 mg twice daily or prednisone alone. The primary endpoint was disease progression at 12 weeks. Crossover from prednisone alone was allowed after radiographic progression. Results 74 patients received apatorsen + prednisone (n = 36) or prednisone alone (n = 38). Twenty-five patients crossed-over to receive apatorsen + prednisone. Apatorsen treated patients received a median of 19 infusions. 50% of apatorsen + prednisone patients (95% CI: 32.9%, 67.1%) compared with 42% of prednisone patients (95% CI: 26.3%, 59.2%) did not have disease progression at week 12 (P = 0.33). A PSA decline of ≥50% was observed in 47% of apatorsen + prednisone and 24% of prednisone patients (P = 0.04), with a median duration of response of 24.1 weeks (95% CI: 12.0, 52) and 14.0 weeks (95% CI: 4.0, 44.4), respectively. A PSA decline of ≥50% was observed in 5 patients (20%) that received cross-over apatorsen. Infusion reactions were the most commonly reported adverse event occurring in 77% of apatorsen-treated patients. Conclusions Apatorsen + prednisone did not change the proportion of CRPC patients without disease progression at 12 weeks compared to prednisone but was associated with significant PSA declines. Further evaluation of Hsp27 targeting in prostate cancer is warranted.

Management of Muscle-Invasive Urothelial Cancer and the Emerging Role of Immunotherapy in Advanced Urothelial Cancer

The incidence of bladder cancer has increased in the past decade, and mortality from bladder cancer remains a substantial public health burden. After 3 decades of minimal progress in the treatment of advanced-stage disease, recent advances in the genomic characterization of urothelial cancer and breakthroughs in bladder cancer therapeutics have rejuvenated the field. This review highlights the landmark clinical trials of chemotherapy in both the neoadjuvant and advanced or metastatic urothelial carcinoma settings. We describe treatment paradigms for multimodal treatment of locally advanced bladder cancer, including discussion on bladder preservation strategies. Lastly, we discuss novel immunomodulatory, targeted, and combination therapies in development for the treatment of advanced urothelial carcinoma.