Harnessing the Epichaperome As a Therapeutic Approach in Multiple Myeloma
Authors: Caldas Lopes Eloisi , Wang Tai , Jayabalan David S , Taldone Tony , Monge Jorge , Contreras Jorge , Winnie Yip , Trujillo Vicenta , Palak Panchal , Lombardi Nicholas , Sahil Sharma , Chander Digwal , Coleman Morton , Chiosis Gabriela , Niesvizky Ruben , Guzman Monica L. 
Published: November 2019

Multiple Myeloma (MM) accounts for approximately 1% of all malignancies and 10-15% of hematologic malignancies. Most MM ultimately becomes refractory to treatment, due in part to a lack of a successful mechanism-based therapy. Novel agents have increased the survival of MM patients; however, high-risk and relapsed/refractory patients remain challenging to treat and their outcome is poor. We have described a new cellular entity termed "epichaperome" that consists of tightly integrated networks that facilitate cancer cell survival (Rodina et al Nature 2016). The epichaperome confers a state of addiction that renders cells vulnerable to therapeutic targeting. We have developed biochemical tools to monitor epichaperome abundance and allows for the monitoring of its modulation with pharmacological interventions in order to identify tumors more likely to respond to PU-H71 (epichaperome inhibitor) and combinatorial therapies to improve tumor eradication, respectively. We implemented these tools to evaluate the potential modulating the epichaperome to target MM cells. First, we determined the epichaperome abundance using capillary-based nano-immunoassay platform in bone marrow (BM) from MM patient. We found high epichaperome abundance in the majority of CD138+ while it was not detected in CD138- fractions. Observations were corroborated by our flow cytometry-based assay (PU-FITC binding). Importantly, epichaperome abundance correlated with high sensitivity to PU-H71. In addition, we tested the epichaperome levels and the effect of PU-H71 on the MM cell lines (N=8) and fount that all displayed more than 50% cell death in 72h of exposition to PU-H71 regardless of their resistance status of bortezomib (BZ) or carfilzomib (CZ). We observed that U266 cells resistant to lenalidomide (U266-LR) presented decreased epichaperome levels, consistent with the expected decreased in sensitivity to PU-H71 (U266 LD50 0.098μM and U266-LR LD50 0.503μM). We hypothesized that restoring epichaperome levels will re-sensitize cells to PU-H71. Finally, we performed a drug screen using agents that could be used in combination with PU-H71 for MM. BZ was among the drugs capable of increasing epichaperome abundance. U266-LR cells were subjected to pharmacological stress, such as treatment with a sub-lethal dose of BZ (0.01μM) and found that epichaperome levels were increased after exposure with BZ as soon as 1h. Importantly, pre-treatment with BZ sensitized cells to PU-H71. The LD50s for PU-H71 in U266-LR were: not pre-treated 0.503μM; pre-treated with 0.01μM of BZ 0.251μM and pre-treated with 0.1μM of BZ 0.023μM (Figure-1). Next, we tested in vivo the combination of BZ plus PU-H71 treatment in NSG mice bearing U266-BLIV (GFP+/Luciferase+) where we observed an improved overall survival. In summary, our results suggest that PU-H71 is a potential candidate for treatment of MM, including relapsed patients with high epichaperome abundance. Importantly, modulating epichaperome levels using epichaperome modulating agents (such as BZ) can result in improved elimination of MM cells. Thus, using the available biochemical tools to measure the epichaperome abundance one can identify patients more likely to respond to PU-H71 and what agents may be optimally combined.

Disclosures
Coleman: Pharmacyclics: Speakers Bureau; Kite Pharmaceuticals: Equity Ownership; Merck: Research Funding; Gilead, Bayer, Celgene: Consultancy, Research Funding, Speakers Bureau. Chiosis:Samus Therapeutics: Equity Ownership, Patents & Royalties: Intellectual rights to the PU-FITC assay. Niesvizky:Takeda, Amgen, BMS, Janssen, Celgene: Consultancy, Research Funding. Guzman:Cellectis: Research Funding; SeqRx: Consultancy; Samus Therapeutics: Patents & Royalties: intellectual rights to the PU-FITC assay.