Yucheng Xu

Telomerase is a reverse transcriptase capable of utilizing an integrated RNA component as a template to add protective tandem telomeric single strand DNA repeats, TTAGGG, to the ends of chromosomes. Telomere dysfunction and telomerase reactivation are observed in approximately 90% of human cancers; hence, telomerase activation plays a unique role as a nearly universal step on the path to malignancy. In the past two decades, multiple telomerase targeting therapeutic strategies have been pursued, including direct telomerase inhibition, telomerase interference, hTERT or hTERC promoter driven therapy, telomere-based approaches, and telomerase vaccines. Many of these strategies have entered clinical development, and some have now advanced to phase III clinical trials. In the coming years, one or more of these new telomerase-targeting drugs may be expected to enter the pharmacopeia of standard care. Here, we briefly review the molecular functions of telomerase in cancer and provide an update about the preclinical and clinical development of telomerase targeting therapeutics.

11516 Background: Novel hormonal therapies recently approved for metastatic castration resistant prostate cancer (mCRPC) are now being tested in hormone sensitive disease (mHSPC), prompting evaluation of new biomarkers to guide therapy in this earlier disease state. We are conducting CTC enumeration, sequencing, and gene expression studies in S1216, a SWOG-sponsored North American Intergroup phase 3 trial of androgen deprivation in combination with bicalutamide or orteronel, a CYP17,20 lyase inhibitor. Baseline CTC enumeration data are presented for 225 patients evaluated to date. Methods: Four 7.5mL tubes of blood are collected for CTC analysis (enumeration, sequencing, gene expression) at study entry and at progression to mCRPC. Specimens are logged in the SWOG online specimen tracking system and sent overnight at room temperature to a central site (Goldkorn Lab) for analysis. One of the 4 tubes is a CellSave tube used for CTC enumeration on the FDA-cleared CellSearch platform (Janssen/J&J). CellSearch CTC counts are transmitted to SWOG Statistical Center for analysis and correlation with clinical data. Results: From 11/2014 - 10/2015, CTCs were detected in 78 of 211 evaluable samples (37%), and detection was impacted by whether patients had already initiated therapy at the time of sample collection (29% detection in treated vs. 46% in treatment naïve, p=0.01). Median CTC count for patients with detectable CTCs was 2/7.5 ml blood (1^st quartile =1, 3^rdquartile =9), and median for the entire cohort was 0 (range 0-4000). Presence of baseline CTCs was associated with higher PSA (p=0.03), bony metastases (p=0.05), presence of extensive disease (p1/3 of patients and nearly half of patients who had not yet initiated therapy. Presence of CTCs wasassociated with known baseline prognostic factors and therefore may predict clinical outcome with continued follow-up. Further CTC enumeration, sequencing and gene expression are ongoing in S1216 to maximize the prognostic and predictive benefit of CTC analysis in mHSPC. Clinical trial information: NCT01809691.

This paper reports a novel Magnesium-embedded cell filter for Circulating Tumor Cell (CTC) capture, release and isolation. The new and novel feature is the use of thin-film Mg to release the captured CTCs based on the fact that any Cl- containing culture medium can readily etch Mg away [1]. The releasing and the isolation of each individual CTC are demonstrated here. After filtration process, the filter is submerged in PBS to facilitate Mg etching. The top PA-C filter pieces break apart from the bottom after Mg completely dissolves, enabling captured CTC cells to detach from the filter. The released CTC can then be easily aspirated into a micropipette, and then for further, such as, DNA mutation analysis.

Telomerase plays a key role in cell fate: loss of telomerase in normal differentiated cells heralds senescence and limits cell division, whereas reactivation of telomerase sustains proliferation and potentiates mutagenesis and transformation. Given this pivotal role, telomerase has been the subject of intense investigation in the field of developmental cancer therapeutics. To date, a broad spectrum of therapeutic strategies has been developed, ranging from direct targeting or reprogramming of the enzyme, to immune or virus-mediated targeting of cells expressing telomerase, to strategies focusing on the telomeres themselves. The recent discovery and growing interest in cancer stem cells has thrust telomerase therapy into new relief as an approach that may be uniquely suited to neutralizing this treatment-resistant subpopulation of cancer cells. Here we will review the mechanistic rationale and preclinical and clinical state of development of the various telomerase-based therapeutic approaches, with emphasis on the role of telomerase in cancer stem cell biology and its implications for therapeutic efforts.