An unbiased lncRNAs dropout CRISPR-Cas9 screen reveals RP11-350G8.5 as a novel therapeutic target for Multiple Myeloma

Multiple Myeloma (MM) is an incurable malignancy characterised by altered expression of coding and non-coding genes promoting tumour growth and drug resistance. Although the crucial role of long non-coding RNAs (lncRNAs) in MM is clearly established, the function of the non-coding RNAome, which might allow the design of novel therapeutics, is largely unknown. We performed an unbiased CRISPR-Cas9 loss-of-function screen of 671 lncRNAs in MM cells and their Bortezomib (BZB)-resistant derivative. To rank functionally and clinically relevant candidates, we designed and used a bioinformatic prioritisation pipeline combining functional data from cellular screens with prognostic and transcriptional data from MM patients. With this approach, we unveiled and prioritised 8 onco-lncRNAs essential for MM cell fitness, associated with high expression and poor prognosis in MM patients. The previously uncharacterised RP11-350G8.5 emerged as the most promising target, irrespective of BZB resistance. We i) demonstrated the anti-tumoral effect obtained by RP11-350G8.5 inhibition in vitro and in vivo; ii) highlighted a modulation of the unfolded protein response and the induction of immunogenic cell death triggered by the RP11-350G8.5 knock-out, via RNA-sequencing and molecular studies; iii) characterised its cytoplasmic homing through RNA-FISH; iv) predicted its 2D structure and identified 2 G-quadruplex and 3 hairpin-forming regions by biophysical assays, including Thioflavin T, 1H-NMR and circular dichroism to pave the way to the development of novel targeted therapeutics. Overall we provided innovative insights about unexplored lncRNAs in MM and identified RP11-350G8.5 as an oncogenic target for treatment-naïve and BZB-resistant MM patients.