Shock block for improved immunotherapy

HSP90 Inhibition Enhances Cancer Immunotherapy by Modulating the Surface Expression of Multiple Immune Checkpoint Proteins

Cancer immunotherapies, including immune checkpoint blockade, have the potential to significantly impact treatments for diverse tumor types. At present, response failures and immune-related adverse events remain significant issues, which could be addressed using optimized combination therapies. Through a cell-based chemical screen of ∼200,000 compounds, we identified that HSP90 inhibitors robustly decrease PD-L1 surface expression, through a mechanism that appears to involve the regulation of master transcriptional regulators (i.e., STAT-3 and c-Myc). Interestingly, HSP90 inhibitors were found to also modulate the surface expression of additional checkpoint proteins (i.e., PD-L2). In the MC-38 syngeneic mouse tumor model, HSP90 inhibition was found to dramatically reduce PD-L1 surface expression on isolated live tumor cells and, consistent with recent findings, was found to increase the number of activated CD8+ T cells within the tumor microenvironment. These findings provide further rationale to explore HSP90 inhibitors as part of combination immunotherapies for the treatment of cancer.

Design, synthesis and molecular mechanisms of novel dual inhibitors of heat shock protein 90/phosphoinositide 3-kinase alpha (Hsp90/PI3Kα) against cutaneous melanoma

Overexpression of heat shock protein 90 (Hsp90) is common in various types of cancer. In cutaneous melanoma, a cancer with one of the high levels of Hsp90 overexpression, such expression was correlated with a panel of protein kinases, thus offering an opportunity to identify Hsp90-based multi-kinase inhibitors for novel cancer therapies. Towards this goal, we utilized a 2,4-dihydroxy-5-isopropylbenzate-based Hsp90 inhibitor scaffold and thieno[2,3-d]pyrimidine-based kinase inhibitor scaffold to develop a Hsp90-inhibiting compound library. Our inhibitory compound named 8m inhibited Hsp90 and PI3Kα with an IC₅₀ value of 38.6 nM and 48.4 nM, respectively; it displayed improved cellular activity which could effectively induce cell cycle arrest and apoptosis in melanoma cells and lead to the inhibition of cell proliferation, colony formation, migration and invasion. Our results demonstrated 8m to be a promising lead compound for further therapeutic potential assessment of Hsp90/PI3Kα dual inhibitors in melanoma targeted therapy.

Trial Watch: Proteasomal inhibitors for anticancer therapy

The so-called "ubiquitin-proteasome system" (UPS) is a multicomponent molecular apparatus that catalyzes the covalent attachment of several copies of the small protein ubiquitin to other proteins that are generally (but not always) destined to proteasomal degradation. This enzymatic cascade is crucial for the maintenance of intracellular protein homeostasis (both in physiological conditions and in the course of adaptive stress responses), and regulates a wide array of signaling pathways. In line with this notion, defects in the UPS have been associated with aging as well as with several pathological conditions including cardiac, neurodegenerative, and neoplastic disorders. As transformed cells often experience a constant state of stress (as a result of the hyperactivation of oncogenic signaling pathways and/or adverse microenvironmental conditions), their survival and proliferation are highly dependent on the integrity of the UPS. This rationale has driven an intense wave of preclinical and clinical investigation culminating in 2003 with the approval of the proteasomal inhibitor bortezomib by the US Food and Drug Administration for use in multiple myeloma patients. Another proteasomal inhibitor, carfilzomib, is now licensed by international regulatory agencies for use in multiple myeloma patients, and the approved indications for bortezomib have been extended to mantle cell lymphoma. This said, the clinical activity of bortezomib and carfilzomib is often limited by off-target effects, innate/acquired resistance, and the absence of validated predictive biomarkers. Moreover, the antineoplastic activity of proteasome inhibitors against solid tumors is poor. In this Trial Watch we discuss the contribution of the UPS to oncogenesis and tumor progression and summarize the design and/or results of recent clinical studies evaluating the therapeutic profile of proteasome inhibitors in cancer patients.