Proteasome inhibitors have shown relevant clinical activity in several hematological malignancies, namely in multiple myeloma and mantle cell lymphoma, improving patient outcomes such as survival and quality of life, when compared with other therapies. However, initial response to the therapy is a challenge as most patients show an innate resistance to proteasome inhibitors, and those that respond to the therapy usually develop late relapses suggesting the development of acquired resistance. The mechanisms of resistance to proteasome inhibition are still controversial and scarce in the literature. In this review, we discuss the development of proteasome inhibitors and the mechanisms of innate and acquired resistance to their activity—a major challenge in preclinical and clinical therapeutics. An improved understanding of these mechanisms is crucial to guiding the design of new and more effective drugs to tackle these devastating diseases. In addition, we provide a comprehensive overview of proteasome inhibitors used in combination with other chemotherapeutic agents, as this is a key strategy to combat resistance.

Programmed cell death protein 1 (PD-1) and PD-ligand 1 (PD-L1) interaction plays an important role in cancer immunotherapy. Several PD-1/PD-L1 inhibitors have been approved with remarkable impact on overall patient survival rates. Inhibitors in clinical practice are presently limited to monoclonal antibodies. However, their severe shortcomings expose the need for a new generation of PD-L1 inhibitors. Understanding the tumor microenvironment, identifying specific biomarkers and X-ray crystalline structures of PD-1/PD-L1 complexes, including molecular and genomic signature studies are essential to determine the success for the development of PD-1/PD-L1 inhibitors into safer and efficient cancer immunotherapeutics. Currently, the development of immune-modulatory small molecules is being explored due to their benefits over recombinant protein approaches. Nevertheless, their development is hampered in part due to lack of structural information. The current study builds on PD-L1 small-molecule inhibitor structural information and provides insights into the design of new inhibitors. To this end, a comprehensive analysis of crystallographic structures and benchmarking studies were performed, showing the specific structure model and software best suited to study PD-L1. The use of in silico methodologies can give a deeper insight to guide the design of novel PD-L1 small-molecule inhibitors.