The cytokine receptor CD30 was identified as an attractive anticancer target more than 30 years ago
This figure illustrates the classical activation of the NF-κB pathway in Hodgkin lymphoma, in which CD30 is among the receptors (top row) that help promote events leading to the survival of cancerous cells.
Adapted from Horton TH, Sheehan AM, López-Terrada D, et al. Analysis of NFκ-B pathway proteins in pediatric Hodgkin lymphoma: correlations with EBV status and clinical outcome—a Children’s Oncology Group Study. Lymphoma. 2012;article ID 341629. http://dx.doi.org/10.1155/2012/341629.
The cytokine receptor CD30 was identified as an attractive anticancer target more than 30 years ago. Initial clinical trials using naked monoclonal antibodies (mAbs) directed against CD30 were disappointing, even when the antibodies were engineered to have enhanced activity. Conjugating CD30 mAbs to a cytotoxic agent resulted in the development of brentuximab vedotin (Adcetris), which has demonstrated remarkable responses in patients with relapsed and refractory Hodgkin lymphoma (HL) and anaplastic large cell lymphoma (ALCL), for which it has now been approved in the United States and Europe.
Today, exploration of the CD30 pathway revolves around a substantial development program for brentuximab vedotin in HL, ALCL, and a number of other CD30-positive malignancies, in some cases in the front-line setting, both as monotherapy and in combination regimens.
Several experimental strategies for using genetically engineered T cells in CD30-positive lymphomas also are being explored.
The CD30 protein is a member of the tumor necrosis factor (TNF) receptor superfamily of cytokine receptors. Although predominantly expressed as a type I transmembrane protein, it also is shed in a soluble form (sCD30).
In healthy individuals, CD30 is found mainly on activated B, T, and NK cells of the immune system and its expression elsewhere is limited. While its exact function is poorly understood, it has been shown to regulate a diverse range of important biological processes in these cells, including activation of mitogen-activated protein (MAP) kinases and nuclear factor-kappa B (NFκB). The outcome of CD30 signaling is context-dependent and can lead to promotion of cell proliferation and survival or, conversely, antiproliferative responses and cell death. A number of other functions for CD30 have been proposed, including regulation of memory cells, B-cell proliferation, and enhancement of immunoglobulin (Ig) production.
CD30 is highly expressed on malignant cells, particularly such lymphoid malignancies as HL and ALCL, which are defined by the presence of CD30 and show CD30 expression on all of the constituent cells of the tumor. It regulates the growth of these malignant lymphomas by promoting NFκB activation and driving cancer cell survival. sCD30 is also observed at elevated levels in patients with HL and ALCL, and has been shown to correlate with poor prognosis.
Given its limited expression in normal cells, high levels of expression in malignant cells, and its important role in driving the development of lymphomas and other malignancies, researchers set their sights on targeting CD30. Although most of the investigations have focused on T-cell and B-cell malignancies, researchers also have explored CD30 expression in testicular embryonal carcinomas.
Antibody-based cancer therapies that target specific antigens expressed on the cancer cell surface have shown remarkable activity in a variety of different tumor types and, in fact, the three top-selling cancer drugs in 2012 were mAbs. Unsurprisingly, therefore, the first CD30-targeting agents to be advanced into clinical trials were mAbs, including cAC10 (SGN-30), a chimeric antibody constructed from the mouse mAb AC10 and the human gamma 1 heavy chain and kappa light chain constant regions, and MDX-060, a fully human IgG1 mAb. However, these agents displayed only limited efficacy when administered as single agents, with low response rates and high production of nontherapeutic antibodies.
Researchers suspected these early failures might result from poor antigen binding properties of the mAbs, ineffective activation of immune effector cells, and neutralization of the mAb as it circulated in the blood by high levels of sCD30. Thus, two modified mAbs were developed with improved antigen binding and increased affinity and specificity for the Fcg receptor (FcgR) on immune effector cells. MDX-1401 is derived from MDX-060 and has a non-fucosylated Fc region that increases its binding affinity for the FcgRIIIa and stimulates more effective antibody-dependent cellular cytotoxicity (ADCC), a major mechanism of anticancer action. XmAb2513 is a humanized version of cAC10 with an engineered Fc region that improves binding to both CD30 and the FcgRIIIa. No response data have been reported for MDX-1401; however, an abstract presented at the 2009 American Association of Cancer Research Annual Meeting indicated that stable disease was achieved in 8 out of 12 patients treated with escalating doses of MDX-1401, and among these patients tumor burden was reduced by ≥40% in 2. Response data for the other agents were disappointing and spurred the development of a third generation of CD30-targeting agents.
The concept of conjugating a mAb to a cytotoxic agent in order to create a kind of targeted chemotherapy has borne significant fruit in the treatment of CD30-positive malignancies.
Antibody-drug conjugates (ADCs) consist of three parts: a mAb, a cytotoxic agent, and a linker (Figure). They were designed to overcome some of the limitations associated with the use of naked antibodies. These include poor penetration of the tumor mass, which can be overcome to some extent by the increased potency of ADCs; inability to overcome immune evasion mechanisms employed by the cancer, which ADCs may achieve since their antitumor activity is independent of the immune system; and high levels of systemic toxicity, which is reduced with ADCs since they exert their cytotoxic activity only after internalization into a target cancer cell.
Reference: Carter PJ et al. Cancer J. 2008;14(3):154-169. Source: Antibody-drug conjugates (ADCs): empowering monoclonal antibodies to fight cancer. Seattle Genetics website. http://www.seagen.com. Published June 2011. Accessed May 29, 2012. Reprinted with permission.
In the case of brentuximab vedotin, the chimeric CD30-targeting mAb cAC10 (also known as brentuximab) is conjugated to the antitubulin agent monomethyl auristatin E (MMAE) via a highly stable valine-citrulline dipeptide linker. Once the mAb binds to CD30 on the surface of cancer cells, the ADC is taken up into cells and the linker is broken down by lysosomal degradation, which releases the cytotoxic agent MMAE that inhibits microtubule polymerization and causes cell cycle arrest and eventual cell death. Pharmacokinetic studies with brentuximab vedotin indicated that only 2% of MMAE was released into human plasma after a 10-day incubation, which suggested that the linker is very stable. This is an extremely important consideration for ADCs as it prevents premature release of the cytotoxic agent and collateral damage to normal tissue.
Brentuximab vedotin may have other antitumor effects besides the direct cytotoxic activity of MMAE. For example, blocking CD30-mediated activation of NFκB can further sensitize cancer cells to chemotherapy, and MMAE may exert “bystander” activity by diffusing out of the target cell and affecting neighboring cells, even those that do not express CD30.
The level of CD30 expression varies across different types of lymphomas and there is no consensus for what defines CD30-positivity. While HL and ALCL express CD30 on all cells that make up the tumor, types of non-Hodgkin lymphoma (NHL) express CD30 on only a subset of cells. This has implications for the design of clinical trials in NHL, which use different cutoffs for CD30-positivity; while some enroll patients with any degree of CD30 expression, others, such as the ECHELON-2 trial, have specific values that define CD30-positivity, in this case as >10% of cells expressing CD30.
CD30 expression is an important diagnostic marker for lymphomas; for example, the diagnostic accuracy of ALCL can be increased to 85% by immunostaining for CD30. The National Comprehensive Cancer Network guidelines recommend that immunohistochemical staining for CD30 be included in the diagnostic workup for both HL and NHL.
The role of CD30 as a biomarker of prognosis is less clear. ALCL, which is CD30-positive, is generally associated with a better prognosis than other T-cell lymphomas, yet in patients with peripheral T-cell lymphoma, the 5-year survival rate is reduced from 32% to just 19% when ≥80% of the cells are CD30-positive.
Questions also have been raised as to the importance of CD30 expression in guiding response to CD30-targeted agents, such as brentuximab vedotin. With trials of this agent being expanded into NHL populations with lower CD30 expression levels, in several cases investigators are finding that there is no statistical correlation between CD30 expression and response rate. This has raised questions as to the role of CD30 expression as a biomarker of response.
In an interview with OncologyLive, Alison J. Moskowitz, MD, an oncologist at Memorial Sloan- Kettering Cancer Center in New York who has been heavily involved in clinical trials of brentuximab vedotin, commented on the role of CD30-positivity in predicting response to brentuximab vedotin. “It is surprising that the degree of positivity does not seem to correlate with response to brentuximab vedotin,” said Moskowitz. “It is not clear if this is because of how we are staining for CD30, if this represents off- target effects of brentuximab vedotin, or if very minimal CD30 positivity is all that is needed for efficacy.”
Brentuximab vedotin has achieved particular success in patients with HL and ALCL. Current first-line treatment for these patients is multiagent chemotherapy and the majority of patients respond; however, many of these patients will ultimately relapse or become refractory to treatment. A significant proportion of relapsed patients have a particularly grim prognosis and it is these patients who may benefit most from a novel treatment paradigm like brentuximab vedotin.
In August 2011, the FDA granted accelerated approval for brentuximab vedotin as a single agent for the third-line treatment of patients with HL, following autologous stem cell transplantation (ASCT), or in patients who are not candidates for ASCT and did not respond to at least two multi- agent chemotherapy regimens, and as second-line treatment of patients with systemic ALCL who did not respond to at least one multiagent chemotherapy regimen.
Approval was based on two pivotal, phase II clinical trials in these patient populations, which demonstrated overall response rates of 75% in HL and 86% in ALCL. The most common adverse events of any grade included nausea, diarrhea, fatigue, and peripheral sensory neuropathy, with grade 3 peripheral neuropathy in 17% of patients.
Recently, the FDA announced the addition of a Boxed Warning for brentuximab vedotin detailing the risk of progressive multifocal leukoencephalopathy. In addition, research presented at the 2013 American Society of Hematology (ASH) Annual Meeting and Exposition this month raised previously unrecognized concerns about pancreatitis as a serious adverse event (Abstract 4380). Investigators from Northwestern University in Chicago, Illinois, reported 8 cases, 2 of which were fatal, although the mechanisms underlying the development of pancreatitis remain unclear.
The agent continues to be developed jointly by Seattle Genetics and Millennium Pharmaceuticals and is currently being evaluated in more than 30 ongoing clinical trials, including several late-stage trials (Table). Since the initial approval was based primarily on response rates, the main focus of research is to further analyze the efficacy of brentuximab vedotin in patients with HL and ALCL in phase III trials to determine if it demonstrates a survival advantage in these patients.
Meanwhile, results from earlier-stage clinical trials of brentuximab vedotin in other CD30-positive malignancies have been reported at conferences this year. At the 2013 ASH Annual Meeting, Nancy L. Bartlett, MD, a professor at the Washington University School of Medicine in St Louis, Missouri, and colleagues reported on a phase II trial of brentuximab vedotin in patients with diffuse large B-cell lymphoma with variable levels of CD30 expression (0-100%) (Abstract 848). The response rate was 40%, with 16% complete remission (CR), among 43 patients, and the safety profile was consistent with that of brentuximab vedotin in other patients. As discussed above, in this study there was no correlation between CD30 expression and response rate.
Number of Participants (estimated enrollment)
High risk of residual HL after ASCTa (NCT01100502)
Brentuximab vs placebo
IV every 21 days
Treatment-naïve, advanced classical HL (NCT01712490)
Brentuximab+AVD vs ABVD
IV on days 1 and 15 of each 28-day cycle
Newly diagnosed CD30+ mature T-cell lymphomas (ECHELON-2) (NCT01777152)
Brentuximab+CHP vs CHOP
Every 3 weeks for 6-8 cycles
CD30+ Primary cutaneous ALCL after prior radiation/at least 1 systemic therapy; MF after at least 1 systemic therapy (NCT01578499)
Brentuximab vs physician’s choice
Relapsed/refractory systemic ALCL after at least 1 multiagent chemotherapy regimen (NCT01909934)
Relapsed/refractory/classical CD30+ HL with no prior SCT or not candidate for SCT (NCT01990534)c
aOngoing but not recruiting participants
ABVD indicates doxorubicin, bleomycin, vinblastine, dacarbazine; ALCL, anaplastic large cell lymphoma; ASCT, autologous stem cell transplant; AVD, doxorubicin, vinblastine, dacarbazine; CHP, cyclophosphamide, doxorubicin, prednisone; CHOP, cyclophosphamide, doxorubicin, vincristine, prednisone; HL, Hodgkin lymphoma; IV, intravenous; MF, mycosis fungoides; SCT, stem cell transplant.
Source: NIH Clinical Trials Registry, www.ClinicalTrials.gov
Data also were presented at ASH from a phase II trial of brentuximab vedotin in patients with cutaneous T-cell lymphomas and other lymphoproliferative disorders (Abstract 367). This latest update in this patient population demonstrated response rates of more than 70% (34 of 48 patients), with 35% CR (17 of 48 patients). Also of note, a response rate of 50% was observed in patients with mycosis fungoides (14 of 28 patients), irrespective of CD30 expression levels.
In the solid tumor realm, researchers reported at the 2013 American Society of Clinical Oncology Annual Meeting in June, that 3 heavily pretreated patients with testicular cancer experienced clinical benefit from brentuximab vedotin and that the therapy was well tolerated (Abstract 327).
Other approaches to targeting CD30 for the treatment of cancer are being evaluated in early-stage clinical trials and preclinical testing. Genetically engineered T cells that express a chimeric T-cell receptor conjugated to a CD30 mAb, known as CD30 chimeric receptor-activated T cells (CARTCD30), are undergoing several phase I clinical trials (NCT01316146, NCT01645293). Typically, the patient’s own T cells are used; however, one clinical trial is under way that is examining the administration of CART-CD30 in Epstein-Barr virus- specific cytotoxic T lymphocytes as these cells may be present in the bloodstream for longer, giving them more time to have antitumor effects (NCT01192464).
Several CD30-targeted immunoRNases have also been developed. ImmunoRNases are antibody-targeted ribonuclease (RNase) fusion proteins; RNases of the superfamily A have been shown to have potent anticancer activity, while lacking immunogenicity and nonspecific toxicity. In order to capitalize on their potential as anticancer agents, RNases are being conjugated to tumor-specific mAbs, such as those targeting CD30. The production of these agents has proved to be challenging and they remain in the preclinical stage of development.
Jane de Lartigue, PhD, is a freelance medical writer and editor based in Davis, California.
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