The strategy and clinical relevance of in vitro models of MAP resistance in osteosarcoma: a systematic review.

Over the last 40 years osteosarcoma (OS) survival has stagnated with patients commonly resistant to neoadjuvant MAP chemotherapy involving high dose methotrexate, adriamycin (doxorubicin) and platinum (cisplatin). Due to the rarity of OS, the generation of relevant cell models as tools for drug discovery is paramount to tackling this issue. Four literature databases were systematically searched using pre-determined search terms to identify MAP resistant OS cell lines and patients. Drug exposure strategies used to develop cell models of resistance and the impact of these on the differential expression of resistance associated genes, proteins and non-coding RNAs are reported. A comparison to clinical studies in relation to chemotherapy response, relapse and metastasis was then made. The search retrieved 1891 papers of which 52 were relevant. Commonly, cell lines were derived from Caucasian patients with epithelial or fibroblastic subtypes. The strategy for model development varied with most opting for continuous over pulsed chemotherapy exposure. A diverse resistance level was observed between models (2.2-338 fold) with 63% of models exceeding clinically reported resistance levels which may affect the expression of chemoresistance factors. In vitro p-glycoprotein overexpression is a key resistance mechanism; however, from the available literature to date this does not translate to innate resistance in patients. The selection of models with a lower fold resistance may better reflect the clinical situation. A comparison of standardised strategies in models and variants should be performed to determine their impact on resistance markers. Clinical studies are required to determine the impact of resistance markers identified in vitro in poor responders to MAP treatment, specifically with respect to innate and acquired resistance. A shift from seeking disputed and undruggable mechanisms to clinically relevant resistance mechanisms may identify key resistance markers that can be targeted for patient benefit after a 40-year wait.

YBX1-interacting small RNAs and RUNX2 can be blocked in primary bone cancer using CADD522.

Primary bone cancer (PBC) comprises several subtypes each underpinned by distinctive genetic drivers. This driver diversity produces novel morphological features and clinical behaviour that serendipitously makes PBC an excellent metastasis model. Here, we report that some transfer RNA-derived small RNAs termed tRNA fragments (tRFs) perform as a constitutive tumour suppressor mechanism by blunting a potential pro-metastatic protein-RNA interaction. This mechanism is reduced in PBC progression with a gradual loss of tRNAGlyTCC cleavage into 5' end tRF-GlyTCC when comparing low-grade, intermediate-grade and high-grade patient tumours. We detected recurrent activation of miR-140 leading to upregulated RUNX2 expression in high-grade patient tumours. Both tRF-GlyTCC and RUNX2 share a sequence motif in their 3' ends that matches the YBX1 recognition site known to stabilise pro-metastatic mRNAs. Investigating some aspects of this interaction network, gain- and loss-of-function experiments using small RNA mimics and antisense LNAs, respectively, showed that ectopic tRF-GlyTCC reduced RUNX2 expression and dispersed 3D micromass architecture in vitro. iCLIP sequencing revealed YBX1 physical binding to the 3' UTR of RUNX2. The interaction between YBX1, tRF-GlyTCC and RUNX2 led to the development of the RUNX2 inhibitor CADD522 as a PBC treatment. CADD522 assessment in vitro revealed significant effects on PBC cell behaviour. In xenograft mouse models, CADD522 as a single agent without surgery significantly reduced tumour volume, increased overall and metastasis-free survival and reduced cancer-induced bone disease. Our results provide insight into PBC molecular abnormalities that have led to the identification of new targets and a new therapeutic.

A Systematic Review of the Expression, Signalling and Function of P2 Receptors in Primary Bone Cancer.

Primary bone cancers are rare malignant diseases with significant morbidity and mortality. The treatment regimen relies on a combination of surgery (often involving amputation), chemotherapy and radiotherapy with outcomes dependent on localization of the tumour, grade, size and response to chemotherapy. Both treatment options and survival statistics have remained constant over the past 40 years and alternative therapies need to be explored. Purinergic signalling involving the interaction of extracellular nucleotides with P2 receptors has been investigated in numerous cancers with activation or inhibition a topic of debate. To assess whether purinergic signalling could be a viable target in primary bone cancer a systematic review for relevant primary literature published in PubMed, MEDLINE and Web of Science was performed. Search terms were formulated around three separate distinct topics; expression of P2 receptors in primary bone cancer models, P2 receptor signalling pathways involved and the functional consequences of P2 receptor signalling. Searching identified 30 primary articles after screening and eligibility assessments. This review highlights the diverse expression, signalling pathways and functional roles associated with different P2 receptors in primary bone cancers and provides a systematic summary of which P2 receptors are exciting targets to treat primary bone cancer and its associated symptoms.