Lymphoma Overview - Signaling Pathway. Diagnostics Marker. Targeted Therapy and Clinical Trials.

Fig.1 Lymphoma signaling pathway. Targeted agents (listed in orange boxes) include those in clinical use (colored in green) and those in preclinical or early phase development (colored in red) for the treatment of lymphoma.

An Introduction to Lymphoma

Lymphoma is blood cancer arising from lymphocytes of the lymphatic system. These cells exist in various organs or tissues such as the lymph nodes, bone marrow, thymus, spleen. During the lymphoma process, lymphocytes often show abnormal change and growth. Currently, Lymphomas have many subtypes, such as the anaplastic large cell lymphoma (ALCL), Hodgkin's lymphomas (HL), non-Hodgkin lymphomas (NHL) and diffuse large B-cell lymphoma (DLBCL). HL and NHL represent the two main subtypes of lymphomas, and about 90% of lymphomas are NHL. In most cases, the cause of the lymphomas is unclear. However, some factors are associated with this cancer including age, genders, weak immune system, immune system disease, infection of a virus, exposure to chemicals and treated for cancer with radiation. Signs and symptoms commonly include enlarged lymph nodes, fever, drenching sweats, unintended weight loss, itching, and constantly feeling tired and sweating at night. To date, the main treatment strategies of this cancer often include chemotherapy, radiation therapy, targeted therapy, and surgery.

1 Main Signaling Pathways in Lymphoma Therapy

1.1 B-cell receptor (BCR) signaling cascade

BCR signaling pathways are divided into chronic active BCR signaling, tonic BCR signaling, and autonomous BCR signaling based on their modes of initiation. This first classical antigen-dependent BCR signaling and its downstream signaling involve in numerous cellular functions, including proliferation, survival, apoptosis and differentiation. This pathway is frequently and aberrantly activated in chronic lymphocytic leukemia/ small lymphocytic lymphoma (CLL/SLL) with low level IgM expression, in a subset of active B-cell-like (ABC) DLBCL bearing CD79B and CARD11 mutations, in mucosa-associated lymphoid tissue lymphoma (MALT) with Hp infection, and in splenic marginal zone lymphoma with hepatitis C virus infection. MALT1/API2 fusion and B-cell lymphoma 10 overexpression, PI3K mutation, phosphatase and tensin homolog (PTEN) gene loss of function are associated with the oncogenesis of MALT and DLBCL. The second BCR pathway, tonic BCR signaling exists in normal B-cell function and is commonly observed in Burkitt lymphoma (BL) that bears some distinctly different genetic abnormality, such as in transcription factor 3 (TCF3) and inhibitor of DNA binding 3 (ID3) alterations. Autonomous BCR signaling pathway is the third kind of BCR pathway where the BCR aggregates without external antigen but relies on an interaction between the two neighboring BCRs through CDR3 and FR2 crosslinking.

1.2 Nuclear factor-kappaB (NF-κB) signaling cascade

The NF-κB pathway is one of the most common signaling pathways in normal lymphoid cells and several types of tissues. The constitutively activated NF-κB pathway has been proved involved in oncogenesis of many types of human malignancies including lymphomas. The NF-κB pathway includes canonical and noncanonical pathway, and includes p50, p65 (RelA), RelB, p52, and c-Rel proteins. The constitutively activated canonical and non-canonical NF-κB signaling pathways exist in almost all types of lymphoma. One example, ABC-DLBCL is the type affected by NF-κB through various mechanisms. These oncogenic events can cause a dysregulated upstream chronic active BCR signaling. In addition, other oncogenic events, such as dysregulated upstream of the JAK/STAT pathway, NF-κB target genes alteration, chromosomal translocation, or EBV infection, also can trigger the constitutive activation of the NF-κB pathway in ABC-DLBCL, MALT, BL, HL, or other types of lymphoma.

1.3 PI3K/AKT/mTOR signaling cascade

The PI3K/AKT/mTOR signaling pathway is activated following the BCR pathway, the TNFR pathway, or other upstream pathways. This pathway plays a critical role in cell growth, survival, apoptosis, proliferation, metabolism, and motility processes. The aberrant activation of the PI3K/AKT/mTOR pathway can lead to many types of cancer. Commonly, this oncogenic activation is associated with the PIK3CD mutation in DLBCL, loss of function PTEN in GCB-DLBCL, and PIK3CA copy number increasing in mantle cell lymphoma (MCL). Moreover, the overexpression of p-AKT has been acted as an inferior outcome indicator in DLBCL, MCL, and peripheral T-cell lymphoma. Given the critical status of the PI3K/AKT/mTOR pathway in lymphoma, PI3K, AKT, and mTOR are considered as potential targets to design drugs for the treatment of lymphoma patients.

1.4 JAK/STAT signaling cascade

The JAK/STAT pathway is an important signaling pathway as a key mediator of cytokine signaling. The underlying molecular mechanisms of the JAK/STAT pathway dysregulation in lymphoma still remain unclear. But some main aberrations like JAK2 aberration are companied by Jumonji domain-containing protein 2C (JMJD2C) abnormality, loss-of-function mutation of SOCS1, and protein tyrosine phosphatase non-receptor type 2 (PTPN2) deletion may contribute to the oncogenic JAK/STAT signaling in primary mediastinal B-cell lymphoma (PMBL), classical HL, and ABC-DLBCL. Particularly, aberrations of STAT3, STAT5, and JAK2 have been found to be the most common characterization in these malignancies. Thus, targeting the JAK/STAT pathway is an approach to treat hematologic patients with lymphoma. Some inhibitors against JAKs, STATs, or ILs, and other related biomarkers have been developed or are under investigation, which are promising to treat lymphoma via many rational ways such as inducing growth arrest and inhibiting angiogenesis.

1.5 Apoptosis signaling cascade

Apoptosis is a pathway of programmed cell death that is involved in a variety of important biological process including the normal organism development, biological evolution, internal environmental stability, and abnormal cells clearance. This process is regulated by a series of highly conserve molecules, like the BCL2 family, the caspase family, and the tumor suppressor protein p53. The apoptosis pathway can function through at least two distinct but interconnected pathways, the extrinsic and the intrinsic apoptosis pathways. In the pathologic process, the normal apoptosis signaling pathway is interrupted by oncogenic defects and cells grow unchecked, resulting in the oncogenesis of a wild variety of cancer including the lymphoma. Interfering pathologic apoptosis pathway and restoring its normal function by targeting therapeutic targets, such as BCL2, MYC, and p53 are regarded as potential therapy methods.

1.6 PD-1/PD-Ls signaling cascade

PD-1 and PD-Ls are regulated by the immune system to balance its immune function. Upon binding to its ligands, PD-1 transfers co-inhibitory signals, negatively regulating the functions of T and B cells to maintain the immune balance. However, during tumor process, overexpression of PD-Ls in tumor cells and infiltrating cells due to genetic alteration, virus infection, or other intrinsic and extrinsic factors, can activate PD-1 signaling and cause exhaustion of effector T cells after the interaction of PD-1 and PD-Ls. Such an immune escaping signaling is a primary mechanism resulting in oncogenesis, tumor aggression and metastasis. Agents blocking the immune checkpoint path way is a promising approach and showed encouraging efficacy to treat a broad spectrum of malignancies such as the lymphoma including relapsed/refractory cHL, DLBCL, and follicular lymphoma (FL). More and more of the checkpoint inhibitors especially the monoclonal antibodies have been approved and translated into clinical immunotherapy management.

Lymphoma Diagnosis

Lymphoma targeted therapies target specific biomarkers that are key components of oncogenic pathways or other related molecules in cases of mutation, deletion, translocation, and overexpression. These biomarkers can be used for disease diagnosis, rational drugs design, and to predict treatment outcome of patients who may benefit from the pathway-based therapy management.

2.1 Molecular Markers for Lymphoma

The detection of highly recurrent hot spot mutations, such as MYD88 L265P in lymphoplasmacytic lymphoma (LPL) have helped to refine these entities and added markers to the diagnostic repertoire, which can be evaluated using relatively simple, straightforward techniques such as allele-specific PCR or pyrosequencing. BRAF V600E occurs in rare cases of plasma cell myeloma and nodal marginal zone lymphoma that can be used as a biomarker. Pathogenic mutations in lymphoma are not distributed randomly, but can influence certain pathways linked to lymphocyte biology, often leading to similar biological effects despite targeting different genes. In B-NHL, B-cell receptor and TOLL-like signaling, the NF-kB and NOTCH pathways and epigenetic regulators are commonly affected, whereas in T-cell lymphoma, the TCR and the JAK/STAT signaling pathways are frequently targeted. Both B- and T-cell lymphomas show common mutations of tumor suppressor genes such as TP53. In mature B-NHL, aberrant somatic hypermutation can target a variety of genes, including BCL6, PAX5, PIM1, BTG1/2 IRF4 and MYC, as well as the translocated alleles of BCL2 in cases of FL and DLBCL carrying a t(14; 18) translocation. Another frequent target of mutations in NHL are genes involved in epigenetic regulation of gene expression, including TET2, CREBBP, DNMT3A, EZH2 and others.

2.2 Protein Markers for Lymphoma

A variety of therapeutic biomarkers in lymphoma have been identified. BCL2 is encoded by the BCL2 gene located on chromosome 18q21.3. BCL2 is an apoptosis regulator that can suppress apoptotic death by interacting with caspases and other BCL2 family members. BCL2 is the critical molecule in the apoptosis pathway and involved in cell survival, apoptosis, and proliferation. As a nuclear transcription factor, p53 can regulate the expression of numerous target genes involved in physiological cellular functions. As a tumor suppressor protein, p53 functions as an important mediator in the apoptosis pathways under oncogenic stress, DNA damage, and hypoxia. Inactivation and the dysregulation of p53 signaling pathway contribute to oncogenesis of cancers including in lymphomas. Myc protein is encoded by the proto-oncogene Myc, which is a typical pleiotropic transcription factor and is involved in almost every process of cell biology and oncology by regulating thousands of target genes. In aggressive lymphomas, Myc acts as a driver involving in oncogenesis, malignant transformation, and aggressive clinical features. BTK is a member of the Tec family as a cytoplasmic tyrosine kinase and is mainly expressed in B cells and myeloid cells. In addition to its critical function in B lymphocyte development and differentiation, BTK is an indispensable component for BCR signaling. BTK as a therapeutic biomarker can be targeted by its inhibitors to interrupt BCR signaling and NF-kB signaling. Other protein markers include SYK (a cytoplasmic nonreceptor-type tyrosine kinas), PI3Ks, AKT, mTOR, PTEN, STATs, JAKs, Interleukin 6 (IL-6), MYD88, PD-1 and PD-Ls, etc.

3 Targeted Therapy for Lymphoma

The BCR, NF-κB, PI3K/AKT/mTOR, JAK/STAT, apoptosis and PD-1/PD-Ls signaling pathway plays important roles in malignant transformation, prevention of apoptosis, drug resistance and metastasis. The overexpression of oncogenes and tumor suppressor genes include p-IκBα, PI3K, AKT, mTOR, JAKs, STATs, ILs, BCL2, MYC, and p53 have been used as targets for targeted therapy in lymphoma progress.

We have focused on recently discovered therapeutic targets for lymphoma. Here, we summarize the potential targets and new drugs developed that have been used in recent, ongoing and future clinical trials to try to improve the clinical outcomes of this disease (Table1-25).

3.1 Lymphoma therapy for BCR pathway

Aberrant activation of BCR signaling has been increasingly implicated in oncogenesis of several types of B-cell hematologic malignancies, especially in CLL/SLL and ABC-DLBCL, the inhibitors targeting the BCR pathway provide the patients with B-cell lymphomas an effective option for treatment. Some clinical trials targeting some oncogenic biomarkers in the BCR pathway have been showing promising efficacy to treat the malignant lymphomas with aberrant signaling pathway activation. These BCR pathway inhibitors include Ibrutinib (PCI-32765), BGB-3111, AVL-292 (cc-292), M7583, Acalabrutinib (ACP-196), Fostamatinib (R788) (R406), Cerdulatinib (PRT062070) and Entospletinib (GS-9973).

Table 1 Clinical trials of BTK inhibitor Ibrutinib

Nct id

Status

Lead sponsor

Study first posted

According to statistics, a total of 135 Ibrutinib projects targeting lymphoma BTK are currently in clinical stage, of which 75 are recruiting and 60 are not recruiting.

Table 2 Clinical trials of BTK inhibitor BGB-3111

Nct id

Status

Lead sponsor

Study first posted

According to statistics, a total of 18 BGB-3111 projects targeting lymphoma BTK are currently in clinical stage, of which 9 are recruiting and 9 are not recruiting.

Table 3 Clinical trials of BTK inhibitor M7583

Nct id

Status

Lead sponsor

Study first posted

According to statistics, a total of 1 M7583 project targeting lymphoma BTK is currently in clinical stage and is not recruiting.

Table 4 Clinical trials of BTK inhibitor Acalabrutinib

Nct id

Status

Lead sponsor

Study first posted

According to statistics, a total of 35 Acalabrutinib projects targeting lymphoma BTK are currently in clinical stage, of which 18 are recruiting and 17 are not recruiting.

Table 5 Clinical trials of SYK inhibitor Cerdulatinib

Nct id

Status

Lead sponsor

Study first posted

According to statistics, a total of 1 Cerdulatinib project targeting lymphoma SYK is currently in clinical stage and is not recruiting.

Table 6 Clinical trials of SYK inhibitor Entospletinib

Nct id

Status

Lead sponsor

Study first posted

According to statistics, a total of 1 Entospletinib project targeting lymphoma SYK is currently in clinical stage and is not recruiting.

3.2 Lymphoma therapy for NF-κB pathway

The inhibition of NF-κB pathway can be performed by directly inhibiting NF-κB components or indirectly by inhibiting its upstream pathways. For example, Bortezomib, a proteasome inhibitor targeting p-IκBα is a rational option for treating patients with constitutive NF-κB pathway activities and has shown good efficacy for DLBCL patients in combination with traditional chemotherapy. Another p-IκBα blockade, MLN 4924 has shown obvious anti-tumor activity in mantle cell lymphoma (MCL) and DLBCL.

Table 7 Clinical trials of p-IκBα inhibitor Bortezomib

Nct id

Status

Lead sponsor

Study first posted

According to statistics, a total of 38 Bortezomib projects targeting lymphoma p-IκBα are currently in clinical stage, of which 22 are recruiting and 16 are not recruiting.

Table 8 Clinical trials of p-IκBα inhibitor MLN 4924

Nct id

Status

Lead sponsor

Study first posted

According to statistics, a total of 3 MLN 4924 projects targeting lymphoma p-IκBαis currently in clinical stage and are recruiting

3.3 Lymphoma therapy for PI3K/AKT/mTOR pathway

Idelalisib (CAL-101, GS-1101), a p110δ-selective inhibitor, is the first FDA-approved PI3K inhibitor in treating relapsed FL and SLL. Clinical trials demonstrated that idelalisib was tolerable and had modest single-agent activity in relapsed or refractory HL. Umbralisib (TGR-1202) and parsaclisib (INCB050465) are also p110δ inhibitors with different chemical structures. A phase 1 trial (NCT02268851) of umbralisib and ibrutinib showed an ORR of 67% (CR 19%) in relapsed or refractory MCL. Duvelisib (IPI-145/INK1197), which is an inhibitor of both p110δ and p110γ, showed efficacy in various types of lymphomas, including DLBCL and MCL, in preclinical studies. Temsirolimus (CCI-779) is a derivative of rapamycin, and is assessed in clinical trial. Everolimus (RAD001) is an oral mTOR inhibitor that has been used as a single agent in relapsed or refractory aggressive and indolent NHLs as well as HL. Other PI3K/AKT/mTOR inhibitors include AMG 319, Acalisib (GS-9820) (CAL-120), Buparlisib (BKM120), SAR 245408 (XL147), Perifosine (KRX-0401), MK-2206, GSK690693, Ridaforolimus (AP23573, MK-8669), Rapamycin (Sirolimus) and AZD2014.

Table 9 Clinical trials of PI3Kδ inhibitor Idelalisib

Nct id

Status

Lead sponsor

Study first posted

According to statistics, a total of 17 Idelalisib projects targeting lymphoma PI3Kδ are currently in clinical stage, of which 10 are recruiting and 7 are not recruiting.

Table 10 Clinical trials of PI3Kδ/γ inhibitor Duvelisib

Nct id

Status

Lead sponsor

Study first posted

According to statistics, a total of 13 Duvelisib projects targeting lymphoma PI3Kδ/γ are currently in clinical stage, of which 9 are recruiting and 4 are not recruiting.

Table 11 Clinical trials of PI3Kγ inhibitor Buparlisib

Nct id

Status

Lead sponsor

Study first posted

According to statistics, a total of 2 Buparlisib projects targeting lymphoma PI3Kγ are currently in clinical stage, and are not recruiting.

Table 12 Clinical trials of mTOR inhibitor Temsirolimus

Nct id

Status

Lead sponsor

Study first posted

According to statistics, a total of 29 Temsirolimus projects targeting lymphoma mTOR are currently in clinical stage, of which 18 are recruiting and 11 are not recruiting.

Table 13 Clinical trials of mTOR inhibitor Rapamycin

Nct id

Status

Lead sponsor

Study first posted

According to statistics, a total of 29 Rapamycin projects targeting lymphoma mTOR are currently in clinical stage, of which 17 are recruiting and 12 are not recruiting.

Table 14 Clinical trials of mTOR inhibitor Everolimus

Nct id

Status

Lead sponsor

Study first posted

According to statistics, a total of 10 Everolimus projects targeting lymphoma mTOR are currently in clinical stage, of which 8 are recruiting and 2 are not recruiting.

Table 15 Clinical trials of mTOR inhibitor AZD2014

Nct id

Status

Lead sponsor

Study first posted

According to statistics, a total of 1 AZD2014 project targeting lymphoma mTOR is currently in clinical stage and is not recruiting.

3.4 Lymphoma therapy for JAK/STAT pathway

Ruxolitinib (INCB018424) is a JAK1/2 inhibitor approved by the FDA to treat myelofibrosis, which can significantly promote apoptosis in HL and PMBCL and survival in a lymphoma xenograft murine model. A phase 1 study (NCT03681561) of ruxolitinib in combination with nivolumab in relapsed or refractory HL is currently recruiting patients. itacitinib (INCB039110) is another JAK1 inhibitor can selectively inhibit JAK1, which is expected to better treat lymphomas. A phase 1/2 study (NCT03697408) of itacitinib in combination with everolimus in relapsed or refractory HL is evaluating. Additionally, a phase 1/2 trial (NCT02760485) of itacitinib in combination with ibrutinib in subjects with relapsed or refractory DLBCL is also ongoing. Other JAK/STAT inhibitors include Tofacitinib (CP-690550), Pacritinib (SB1518), Pyrimethamine and IONIS-STAT3Rx (ISIS 481464).

Table 16 Clinical trials of JAK1/2 inhibitor Ruxolitinib

Nct id

Status

Lead sponsor

Study first posted

According to statistics, a total of 16 Ruxolitinib projects targeting lymphoma JAK1/2 are currently in clinical stage, of which 9 are recruiting and 7 are not recruiting.

Table 17 Clinical trials of JAK1 inhibitor itacitinib

Nct id

Status

Lead sponsor

Study first posted

According to statistics, a total of 4 itacitinib projects targeting lymphoma JAK1 are currently in clinical stage, of which 3 are recruiting and 1 is not recruiting.

Table 18 Clinical trials of JAK3 inhibitor Tofacitinib

Nct id

Status

Lead sponsor

Study first posted

According to statistics, a total of 1 Tofacitinib project targeting lymphoma JAK3 is currently in clinical stage and is not recruiting.

Table 19 Clinical trials of JAK2 inhibitor Pacritinib

Nct id

Status

Lead sponsor

Study first posted

According to statistics, a total of 1 Pacritinib project targeting lymphoma JAK2 is currently in clinical stage and is recruiting.

Table 20 Clinical trials of STAT3 inhibitor Pyrimethamine

Nct id

Status

Lead sponsor

Study first posted

According to statistics, a total of 1 Pyrimethamine project targeting lymphoma STAT3 is currently in clinical stage and is recruiting.

3.5 Lymphoma therapy for PD-1/PD-Ls pathway

Nivolumab and pembrolizumab were approved to treat relapsed or refractory HL by the FDA. A variety of clinical trials are assessed the outcome of nivolumab in different lymphoma. Nivolumab combinations with other targeted agents such as lenalidomide in relapsed or refractory lymphoma (NCT03015896), rituximab in FL (NCT03245021), cabiralizumab in PTCL (NCT03927105), and in combination with chemotherapy, such as rituximab, gemcitabine, and oxaliplatin (R-GemOx) in elderly lymphoma patients (NCT03366272), R-CHOP (NCT03704714), and rituximab, dose-adjusted etoposide, prednisone, vincristine, cyclophosphamide, and doxorubicin (DA-R-EPOCH) (NCT03749018) in aggressive NHLs are ongoing. Pembrolizumab, a humanized mAb of PD-1 is investigated in clinical trials for relapsed or refractory HL, transformed DLBCL, relapsed or refractory CLL, relapsed or refractory PMBCL, relapsed or refractory gray-zone lymphoma and PCNSL and B-NHLs treatment. Pembrolizumab in combination with other targeted agents, such as umbralisib (NCT03283137), lenalidomide (NCT02875067), mogamulizumab (NCT03309878), rituximab (NCT03401853), pralatrexate (NCT03598998), CAR-T (tisagenlecleucel, NCT03630159), and radiation (NCT03210662 and NCT03385226), are ongoing. Other PD-1/PD-Ls inhibitors include MEDI0680 (AMP-514), Pidilizumab (CT-011), Durvalumab (MEDI4736), Avelumab (MSB0010718C) and Atezolizumab (MPDL3280A) (RG7446).

Table 21 Clinical trials of PD-1 inhibitor Nivolumab

Nct id

Status

Lead sponsor

Study first posted

According to statistics, a total of 86 Nivolumab projects targeting lymphoma PD-1 are currently in clinical stage, of which 65 are recruiting and 21 are not recruiting.

Table 22 Clinical trials of PD-1 inhibitor pembrolizumab

Nct id

Status

Lead sponsor

Study first posted

According to statistics, a total of 88 pembrolizumab projects targeting lymphoma PD-1 are currently in clinical stage, of which 70 are recruiting and 18 are not recruiting.

Table 23 Clinical trials of PD-L1 inhibitor Durvalumab

Nct id

Status

Lead sponsor

Study first posted

According to statistics, a total of 16 Durvalumab projects targeting lymphoma PD-L1 are currently in clinical stage, of which 11 are recruiting and 5 are not recruiting.

Table 24 Clinical trials of PD-L1 inhibitor Avelumab

Nct id

Status

Lead sponsor

Study first posted

According to statistics, a total of 8 Avelumab projects targeting lymphoma PD-L1 are currently in clinical stage, of which 6 are recruiting and 2 are not recruiting.

Table 25 Clinical trials of PD-L1 inhibitor Atezolizumab

Nct id

Status

Lead sponsor

Study first posted

According to statistics, a total of 18 Atezolizumab projects targeting lymphoma PD-L1 are currently in clinical stage, of which 13 are recruiting and 5 are not recruiting.