KT‐413, A NOVEL IRAKIMID DEGRADER OF IRAK4 AND IMID SUBSTRATES, HAS A DIFFERENTIATED MOA THAT LEADS TO SINGLE‐AGENT AND COMBINATION REGRESSIONS IN MYD88 MT LYMPHOMA MODELS

Second-line treatment of diffuse large B-cell lymphoma: Evolution of options

In the era of immunochemotherapy, approximately 60%-70% of diffuse large B-cell lymphoma (DLBCL) patients achieve remission with first-line rituximab-based chemoimmunotherapy. However, 30%-40% relapse after initial response to first-line therapy and, out of them, 20%-50% are refractory or experience early relapse. The second-line therapy algorithm for DLBCL has recently evolved, thanks to the recent approval of new therapeutic agents or their combinations. The new guidelines suggest a stratification of relapsed/refractory (R/R) DLBCL based on the time to relapse. For transplant-eligible patients, autologous stem cell transplant remains the preferred option when the patient relapses after 12 months from diagnosis, while anti-CD19 CART-cell therapy is the current preferred choice for high-risk DLBCL, defined as primary refractory or relapse ≤12 months. For transplant-ineligible or CAR T-cell therapy-ineligible patients, the therapeutic arsenal historically lacked effective options. However, new therapeutic options, including polatuzumab vedotin combined with bendamustine-rituximab and tafasitamab with lenalidomide, have been recently approved, and novel agents such as loncastuximab tesirine, selinexor, anti-CD19 CAR T-cell therapy, and bispecific antibodies have shown promising efficacy and manageable safety in this setting offering new hope to patients in this challenging scenario.

Clinical Translation of Targeted Protein Degraders

Targeted protein degradation (TPD) has emerged as a potentially transformational therapeutic modality with considerable promise. Molecular glue degraders remodel the surface of E3 ligases inducing interactions with neosubstrates resulting in their polyubiquitination and proteasomal degradation. Molecular glues are clinically precedented and have demonstrated the ability to degrade proteins-of-interest (POIs) previously deemed undruggable due to the absence of a traditional small molecule binding pocket. Heterobifunctional proteolysis targeting chimeras (PROTACs) possess ligands for an E3 complex and the POIs, which are chemically linked together, and similarly hijack the ubiquitin machinery to deplete the target. There has been a recent surge in the number of degraders entering clinical trials, particularly directed toward cancer. Nearly all utilize CRL4CRBN as the E3 ligase, and a relatively limited diversity of POIs are currently targeted. In this review, we provide an overview of the degraders in clinical trials and provide a perspective on the lessons learned from their development and emerging human data that will be broadly useful to those working in the TPD field.

Novel agents in relapsed/refractory diffuse large B-cell lymphoma

Patients with relapsed or refractory (R/R) diffuse large B-cell lymphoma (DLBCL), ineligible for or relapsing after autologous stem-cell transplant or chimeric antigen-receptor T-cell therapies have poor outcomes. Several novel agents, polatuzumab vedotin, tafasitamab, loncastuximab tesirine, and selinexor, have been approved and offer new opportunities for this difficult to treat population. Studies are evaluating combination of these agents with chemotherapy and other emerging therapies. Additionally, advances in our understanding of DLBCL biology, genetics, and immune microenvironment have allowed for the identification of new therapeutic targets like Ikaros and Aiolos, IRAK4, MALT1, and CD47 with several agents in ongoing clinical trials. In this chapter we review updated data supporting the use of the approved agents and discuss other emerging novel therapies for patients with R/R DLBCL.

Targeting cereblon in hematologic malignancies

The protein cereblon (CRBN) is a substrate receptor of the cullin 4-really interesting new gene (RING) E3 ubiquitin ligase complex CRL4^CRBN. Targeting CRBN mediates selective protein ubiquitination and subsequent degradation via the proteasome. This review describes novel thalidomide analogs, immunomodulatory drugs, also known as CRBN E3 ubiquitin ligase modulators or molecular glues (avadomide, iberdomide, CC-885, CC-90009, BTX-1188, CC-92480, CC-99282, CFT7455, and CC-91633), and CRBN-based proteolysis targeting chimeras (PROTACs) with increased efficacy and potent activity for application in hematologic malignancies. Both types of CRBN-binding drugs, molecular glues, and PROTACs stimulate the interaction between CRBN and its neosubstrates, recruiting target disease-promoting proteins and the E3 ubiquitin ligase CRL4^CRBN. Proteins that are traditionally difficult to target (transcription factors and oncoproteins) can be polyubiquitinated and degraded in this way. The competition of CRBN neosubstrates with endogenous CRBN-interacting proteins and the pharmacology and rational combination therapies of and mechanisms of resistance to CRL4^CRBN modulators or CRBN-based PROTACs are described.

Enriching Proteolysis Targeting Chimeras with a Second Modality: When Two Are Better Than One

Proteolysis targeting chimera (PROTAC)-mediated protein degradation has prompted a radical rethink and is at a crucial stage in driving a drug discovery transition. To fully harness the potential of this technology, a growing paradigm toward enriching PROTACs with other therapeutic modalities has been proposed. Could researchers successfully combine two modalities to yield multifunctional PROTACs with an expanded profile? In this Perspective, we try to answer this question. We discuss how this possibility encompasses different approaches, leading to multitarget PROTACs, light-controllable PROTACs, PROTAC conjugates, and macrocycle- and oligonucleotide-based PROTACs. This possibility promises to further enhance PROTAC efficacy and selectivity, minimize side effects, and hit undruggable targets. While PROTACs have reached the clinical investigation stage, additional steps must be taken toward the translational development of multifunctional PROTACs. A deeper and detailed understanding of the most critical challenges is required to fully exploit these opportunities and decisively enrich the PROTAC toolbox.