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Targeted Products Yield Most Promising Results

Jennifer Klem, PhD; Stanton R. Mehr; and Marj Pestil Zimmerman, BSPharm
A New Era in Targeted Treatment Has Begun
Melanoma is one of the most frequent cancers; more than 2 million Americans are treated for skin cancer annually. However, in its earlier stages, it can be easily cured by removal of the skin lesion.1 “Melanoma is on the surface of the skin and therefore easily visible to patients, doctors, and other health professionals without the use of x-rays or invasive procedures,” said Lynn Schuchter, MD, professor of medicine, University of Pennsylvania School of Medicine, Philadelphia. “Therefore, early detection is highly feasible. Most melanomas are cured with surgery because the melanoma is detected at an early stage of disease, before melanoma cells have the potential to metastasize.” Schuchter explained, “Once melanoma metastasizes to distant sites, it is highly resistant to therapy.” It caused an estimated 8700 deaths in 2010.1

Chemotherapy for advanced disease has yielded poor 5-year survivals for patients with metastatic disease—16% of those with metastatic melanoma survive 5 years post-diagnosis.2 Dacarbazine is the only drug approved by the US Food and Drug Administration (FDA) for treating metastatic melanoma, and it is often ineffective.3 In other words, the prognosis for patients whose melanoma has spread is generally poor, and very few therapies existed before 2011 that could make more than a marginal difference. Only recently have investigational products emerged that, alone or in combination, seem to yield positive responses in some patients.

Taking Advantage of the Body’s Immune Response

Melanoma is one of the few cancers that trigger the body’s immune response naturally. 4 The problem is that the response is easily overwhelmed by the malignancy. Ipilimumab, which was approved in March 2011 by the FDA, works by spurring the body’s immune system to attack the tumor. The melanoma pipeline comprises several examples of investigational agents that seek to enhance the immune response, including therapeutic vaccines.

Vaccines

OncoVEXGM-CSF. The therapeutic vaccine that is perhaps furthest along the pipeline is OncoVEXGM-CSF, which is customized to the patient by using their own tumor antigens. This viral vaccine invades both healthy cells and melanoma cells, but it does not harm the healthy cells, only replicating within the malignant cells, according to the manufacturer, Biovex, which was acquired by Amgen in March 2011.5 The virus produces granulocyte- macrophage colony-stimulating factor (GM-CSF), which gathers dendritic cells, causing the rupture of the tumor cell. This releases GM-CSF and tumor-cell peptides into the local area. The dendritic cells collect the tumor-cell peptides, allowing the immune system to recognize and attack them.

In 2009, phase II testing of the vaccine in 50 patients with metastatic melanoma revealed overall survival at 2 years of 52%, and an objective response rate was 26% (stable disease rate of 20%).6 Phase III testing is currently under way, and this OPTiM trial is expected to be completed in June 2012 (ClinicalTrials.gov, NCT00769704). The OPTiM trial compares the vaccine with the use of GM-CSF administered subcutaneously in patients with stage III (b-c) and stage IV (M1a-c) disease.

Prophage (vitaspen). Not all autologous vaccine-based therapies entering phase III trials have met with success. This vaccine (formerly known as Oncophage), which is developed using gp96 and other peptides from the patient’s own tumor, was found to not improve survival in patients with stage IV melanoma compared with any other choice of therapy by the physician. In this phase III trial, only patients with better prognostic characteristics who were injected with vitaspen seemed to improve.7

MVax. In the case of MVax, from Avax Technologies, the phase II clinical trial results were encouraging, yet the phase III study was halted in 2010, not for safety reasons or poor outcomes, but because of a lack of capital. It is unclear as to when or if this phase III trial may be continued, or if an interim analysis of the study results will take place as planned.

Similarly, in 2005, CancerVax Corphalted its phase III trial of the vaccine Canavaxini for late-stage melanoma not because of safety reasons but because it had not shown any benefit over placebo.8

Schuchter commented that overall, “Current approaches to vaccine development are still a major challenge. Unless there is a whole new approach to melanoma vaccines, I am not optimistic about the future of vaccines for patients with melanoma.”

Allovectin-7. A plasmid that contains the genetic sequences for HLA-B7 and β2- microglobulin, Allovectin-7 is a receptor that activates T cells to provoke an immune response.9 This immunomodulator can be injected directly into the tumor lesion, which may help T-cell recognition of the malignancy and specific attacks on these specific tumor cells.9 In phase II studies, Allovectin-7 injection in patients with recurrent or refractory advanced melanoma produced a 12% response rate, with a median duration of response of 13.8 months.10 The phase III AIMM trial was begun in 2007 and compares Allovectin- 7 with dacarbazine or temozolomide in patients who had not been previously treated with chemotherapy (ClinicalTrials .gov, NCT00395070). This trial is scheduled for completion in the third quarter of 2012.

GSK2132231A. GSK2132231A is a recombinant fusion protein with potential immunostimulatory and antineoplastic properties that is derived from the melanoma antigen MAGE-3 and protein D from Hemophilus influenzae (it is also referred to as a MAGE-3 + AS02B by the manufacturer). No clinical trial data using this agent have yet been made public, but a phase III trial called DERMA is currently enrolling patients to examine the use of GSK2132231A as adjuvant therapy for patients with resected melanoma (ClinicalTrials.gov, NCT00796445). Thirteen hundred patients will be enrolled, and the study is expected to be completed in December 2016.

Tremelimumab. This product, a fully human IgG2 monoclonal antibody targeted to CTLA-4, like ipilimumab, may summarize the key learning of research on melanoma to date: The shotgun approach to drug development in metastatic melanoma works poorly. In a previous phase III trial, tremelimumab failed to demonstrate a significant improvement in overall survival compared with temozolomide or dacarbazine in a cohort of patients without prior systemic treatment for their metastatic melanoma.11 However, Pfizer came to an agreement with Switzerland’s Debiopharm to revive plans for a clinical trial of tremelimumab in patients with a biomarker indicating it would most likely be effective. Under this arrangement, Debiopharm would be responsible for funding and running the phase III trial (not yet under way).12 In October 2011, Pfizer granted global rights to the product to MedImmune, a subsidiary of AstraZeneca, for development of this product for other indications.13

Ipilimumab. Approved in March 2011 for use in non-resectable or metastatic (untreated) melanoma, its manufacturer, Bristol-Myers Squibb, is conducting additional trials to determine if ipilimumab is also effective in untreated metastatic disease when combined with dacarbazine (ClinicalTrials.gov, NCT00324155) and if it is effective as adjuvant therapy in patients with high-risk stage III disease (ClinicalTrials.gov, NCT00636168). Randomized phase II data have demonstrated 65% 1-year survival and 23% 3-year survival for the ipilimumab + dacarbazine combination in patients with chemotherapy-naïve advanced disease.14

Ipilimumab is a fully human monoclonal antibody targeted to CTLA-4, a molecule known to negatively regulate the immune system.15 By inhibiting CTLA-4, ipilimumab can enhance the immune system’s T-cell response to tumor cells. In its pivotal 3-arm trial, another BMS agent, gp100 peptide vaccine, which was dubbed MDX-1379, was used as the active control, despite the fact that no standard of care exists for this patient population. Patients were randomized to receive ipilimumab and gp100, gp100 and placebo, or ipilimumab and placebo. Compared with the median overall survival (OS) of the gp100 arm (6.4 months), both ipilimumab- containing arms produced significant improvements, with a median OS of 10.0 months in the combination therapy arm (P <.001) and 10.1 months in the monotherapy arm (P =.003). In addition to these promising data, ipilimumab is also in phase III testing as an addition to dacarbazine chemotherapy for patients with untreated advanced melanoma (ClinicalTrials. gov, NCT00324155). Clinical trials have identified potential toxic liver effects.

There is no evidence that BMS is proceeding with the developmental program for MDX-1379.

Focusing on Melanoma Cell Targets

Much research in metastatic melanoma has involved testing of agents on specific melanoma cell targets or biomarkers. The targeted medication that has received the most attention, vemurafenib, was approved along with its companion diagnostic test in August 2011 to treat patients with metastatic (late-stage) or unresected (inoperable) melanoma in patients whose tumors express the BRAF gene’s V600E mutation, a driver of tumor growth. Other targets include c-kit, MEK, and Bcl-2 inhibitors. However, successful targeting is difficult, as demonstrated by Genta, which in May 2011 terminated its Phase III trial and development program for the Bcl-2 inhibitor oblimersen (Gentasense) for the treatment of melanoma.16 On the other hand, GlaxoSmithKline’s GSK2118436, a BRAF inhibitor, has entered Phase III testing (the first Phase III study is scheduled to be completed in June 2012), which if successful in clinical trials won’t reach the market for some time (2014 at the earliest).

GSK1120212. Another targeted agent, GSK1120212, is an inhibitor of the MEK1 and MEK2 (MEK1/2) enzymes, preventing Raf-dependent MEK phosphorylation, resulting in antitumor effects in early-stage trials.17 This GlaxoSmithKline product is the subject of multiple clinical trials for different oncology indications. For melanoma, it is being tested in an open-label, randomized Phase III study comparing GSK1120212 with chemotherapy (eitherdacarbazine or paclitaxel) in up to 297 patients with stage IIIc or stage IV malignant cutaneous melanoma (all having a BRAF mutation–positive tumor). This trial is not scheduled for completion until September 2012 (ClinicalTrials.gov Trial Number NCT01245062).

Vemurafenib. Developed by Plexxicon and Roche, this BRAF V600E inhibitor seems to be effective18—in some cases, dramatically effective—for patients with this mutation, though its effects seem to wane after a period of time.19

In previous studies, vemurafenib had induced response rates of 50% and more in patients with metastatic melanoma who have the BRAF V600E mutation. In the phase III BRIM3 study, this oral agent (960 mg bid) was compared with intravenous dacarbazine (1000 mg/m2 of body surface area) every 3 weeks as monotherapy in 675 previously untreated patients with stage IIIC or IV melanoma.

 
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