Innovative targeted therapies for chemorefractory B-cell non-Hodgkin lymphomas

Lymphomas are a heterogeneous group of tumors characterized by the proliferation of lymphocytes predominantly in lymphoid structures but also in extranodal tissues. More than 90% of patients are afflicted by lymphomas of B-cell origin. The current World Health Organization (WHO) classification of hematopoietic and lymphoid tumors categorizes B-cell neoplasms in more than 40 distinct disease entities, according to a combination of the morphology, immunophenotype, genetic, molecular and clinical features. Each entity has its own clinical course and requires specific treatments. The characterization of activated signaling pathways involved in survival and proliferation, together with the development of a wide pharmacological armamentarium against cancer, have facilitated the bench-to-bedside translation of new targeted therapies in B-cell non-Hodgkin lymphomas (B-NHL). These novel therapies include two of the most relevant drugs lately approved: the anti-apoptotic agent venetoclax and the BTK inhibitor ibrutinib. One major hurdle to their successful application is the rise of drug resistance. Resistance to therapy is observed in many cases of B-cell malignancies. This phenomenon significantly limits the utility of the current therapeutic strategies, and remains a substantial challenge for the clinical management of patients with advanced cancers. Resistance comes in two flavors: intrinsic resistance (also known as innate or de novo resistance) and acquired resistance, resulting from the clonal evolution of resistant variants. With this concept in mind, in this thesis we have explored new approaches to overcome the development of drug resistance. Venetoclax (ABT-199) is a first-in-class BH3 mimetic, FDA-approved for use in patients with R/R del17p chronic lymphocytic leukemia. In the clinical setting, it has demonstrated high response rates and good toxicity profiles in other subtypes of relapsed/refractory non-Hodgkin lymphoma. We proposed a model of double hit lymphoma (DHL) resistance to ABT-199 in which the capacity of CPI203 to regulate the transcriptome of the cells could help to circumvent this problem. In ABT-199 sensitive cells, the BH3 mimetic acts by displacing BIM from BCL-2 complexes, allowing the de-repression and/or direct activation of BAX and leading to an activation of mitochondrial outer membrane permeabilization. In DHL cells, a compensatory upregulation of BFL-1 would bind and inactivate the pool of BIM proteins released from BCL-2 by ABT-199, avoiding MOMP and preserving cell survival. CPI203 primes cells to death by decreasing BFL-1 and increasing BIM protein levels, and its combination with ABT-199 allows to tip the balance between pro- and anti-apoptotic signaling toward induction of cell death. This concept provides a new insight in the proposed mechanisms of resistance to BH3- mimetics in NHL cell lines, where MCL-1 and BCL-XL have been proposed as the major determinants of drug sensitivity and acquired resistance. On the other hand, ibrutinib is a BTK inhibitor approved for first-line therapy in patients with chronic lymphocytic leukemia, as well as for the treatment of some relapsed/refractory B-NHL. Despite its high level of clinical activity, acquiring of mutations or re-wiring of the BCR pathway to retain the downstream signaling appears to be a common mechanism of resistance. The inhibition of more than one BCR kinase might be useful in B-NHL cases that are resistant to the sole inhibition of BTK. We describe the compound IQS019 as a new BCR kinase inhibitor able to counteract both constitutive and ligand-dependent activation of the BCR pathway. Its capacity to inhibit the three upstream BCR kinases, BTK, SYK and LYN, confer an advantage over the inhibition of BTK alone by ibrutinib, in in vitro and in vivo models of B-NHL, being of special importance for the treatment of those patients with non-canonical NF-κB activation, who are low responders to ibrutinib. Therefore, the development of innovative therapeutic approaches that permit to overcome drug resistance opens a window to important therapeutic advances in the treatment of B-NHL.Las neoplasias linfoides de célula B constituyen un grupo heterogéneo de tumores caracterizados por la proliferación de linfocitos B. Cada entidad clínica posee unas características particulares y requiere de un tratamiento específico. A pesar de los importantes avances terapéuticos, la supervivencia a largo plazo sigue siendo baja y precisa de un desarrollo constante de nuevas aproximaciones terapéuticas. Uno de los mayores problemas asociados a la respuesta a fármacos son las resistencias. En muchos casos estas resistencias se deben a cambios en proteínas diana o a la modulación compensatoria de otras proteínas o vías de señalización. El conocimiento de estos cambios será de gran importancia para poder encontrar aproximaciones terapéuticas que permitan eliminar estas resistencias. El linfoma doble-hit es un linfoma agresivo caracterizado por su baja respuesta a la quimioterapia estándar. Entre los múltiples agentes terapéuticos específicos actualmente en desarrollo encontramos el inhibidor de BCL-2, venetoclax. El venetoclax ha demostrado ser efectivo en varios subtipos de linfoma pero su uso conlleva el problema de la aparición de resistencias. Varios estudios han destacado el papel de proteínas de la familia BCL-2 en este proceso. Nuestros resultados indican que la regulación positiva de BFL-1 es uno de los factores clave en el desarrollo de resistencias al fármaco. Su regulación mediante el CPI203, un modulador epigenético, resulta en una sensibilización al venetoclax, tanto in vitro como in vivo. Por otro lado, la señalización de los receptores de células B (BCR) contribuye a la patogénesis de las neoplasias malignas de células B y ha surgido como una nueva diana terapéutica en varios tipos de linfoma. Así, los inhibidores de quinasas de la vía del BCR constituyen una estrategia terapéutica prometedora. Dentro de este grupo de fármacos destaca el inhibidor de Btk ibrutinib, que ha conseguido esperanzadoras tasas de respuesta pero que también se ve afectado por la aparición de resistencias. Nuestro trabajo muestra que el compuesto IQS019, inhibidor de varias quinasas de la vía del BCR (Btk, Syk y Lyn), posee un potente efecto antitumoral y permite escapar a las resistencias observadas al ibrutinib. Así, supone un buen tratamiento para varios subtipos de linfomas de células B, incluyendo aquellos poco sensibles a los inhibidores de quinasa de BCR actuales