Dermatology update: The dawn of targeted treatment
ABSTRACTDuring the past several years, targeted therapies have significantly improved outcomes in advanced basal cell carcinoma, psoriasis, and metastatic melanoma. This article reviews how advances in our understanding of the molecular pathogenesis of these diseases led to the development of targeted therapies and how these therapies are improving outcomes. Research is ongoing to address continuing challenges of drug resistance, adverse effects, and how best to use the new medications.
KEY POINTS
- Vismodegib, an inhibitor of the “hedgehog” pathway, dramatically shrinks basal cell carcinomas, but resistance and adverse effects remain troublesome. Using it to shrink tumors to operable size may be its best future role.
- Th-17 cells and interleukin 17 are now thought to play central roles in the pathogenesis of psoriasis. Clinical trials of new drugs that block interleukin 17 show striking improvement in skin manifestations with few side effects. Benefits in psoriatic arthritis have not yet been shown.
- About half of patients with melanoma harbor BRAF mutations, and new treatments that target this pathway have improved survival rates. For melanoma not involving BRAF mutations, a better understanding of how tumors evade immune control has led to improved immunotherapies. These targeted medications mark the first major advancements in metastatic melanoma treatment in decades.
Arthritis improvement not shown
Where the IL-17 inhibitors eventually settle within algorithms of psoriasis treatment largely depends on their efficacy in treating psoriatic arthritis compared with TNF-alpha inhibitors and IL-12/23 inhibitors. Joint inflammation is typically evaluated with the American College of Rheumatology (ACR) scoring tool, which in simple terms can be thought of as analogous to the PASI scoring tool for the skin. Although the ACR scoring tool was developed to assess joint inflammation in clinical trials for patients with rheumatoid arthritis, it is commonly used to assess improvement of psoriatic arthritis in clinical trials. The ACR tool involves assessing and scoring the number of swollen and tender joints, but also incorporates serologic assessment of acute-phase reactants (erythrocyte sedimentation rate or C-reactive protein level), patient and physician global assessment, pain, and function. ACR 20 implies roughly a 20% improvement in these criteria, whereas ACR 50 indicates 50% improvement, and so on.
Two phase 2 trials of IL-17 inhibitors for psoriatic arthritis have been published, one with secukinumab27 and one with brodalumab.28 Neither had impressive improvement in the ACR score vs TNF inhibitors—39% for ACR 20 at week 12 and less than 10% for ACR 70. Clinical trial design may have played a role, and phase 3 trials are under way for all three IL-17 inhibitors.
Adverse effects of IL-17 inhibitors
For the most part, adverse effects reported with the IL-17 inhibitors have been mild and similar to those reported with available biologic treatments for psoriasis. Adverse effects most commonly reported have been nasopharyngitis, upper respiratory infection, arthralgia, and mild injection-site reactions. In the future, attention will be paid to the rate of infections known to be associated with IL-17, mainly localized infections with Staphylococcus aureus and Candida species. Some patients have developed Candida esophagitis, but this appears to resolve with discontinuation of the drugs. Neutropenia has occurred, but very few patients have developed grade 3 (500–1,000 cells/mm3) or worse. All adverse effects were reversible with discontinuation of treatment.
Approval of secukinumab, and current studies of IL-17 inhibitors
On January 21, 2015, secukinumab was approved by the FDA for treatment of moderate to severe psoriasis vulgaris in adult patients and is now available by prescription.
More trials of IL-17 inhibitors for the treatment of psoriasis and psoriatic arthritis are under way and are at various phases at the time of this writing.23
TARGETED THERAPY FOR ADVANCED MELANOMA
Case 3. A 58-year-old man presents with an irregular pigmented lesion on his back. Biopsy shows malignant melanoma with an intense, chronic inflammatory infiltrate surrounding the tumor (Figure 3). The tumor was surgically excised with standard margins. Two years later, the patient developed multiple pigmented lesions on the face and complained of headache. Magnetic resonance imaging of the brain revealed multiple enhancing lesions consistent with metastatic melanoma (Figure 3). What are this patient’s options?
Melanoma is the fifth most common cancer in humans, with about 132,000 new cases diagnosed worldwide each year and 48,000 deaths from advanced disease. Its incidence has risen rapidly over the last few decades. Advanced disease has a poor prognosis, with the median overall survival less than 1 year and 5-year survival less than 10%.
Despite decades of research, a paucity of FDA-approved medications were available to treat advanced melanoma until recently. The alkylating agent dacarbazine was approved in 1975, interferon alpha in 1995, and high-dose IL-2 in 1998. Although some patients respond, studies have not shown significant improvement in survival with any of these medications.29–31
In 2002, Davies et al32 found that 50% to 65% of metastatic cutaneous melanomas have a mutation in the BRAF gene. Interestingly, 80% of these patients share a single specific mutation: substitution of glutamic acid for valine in codon 600 (BRAF V600E). The second most common mutation is a single substitution of a lysine for that same valine (BRAF V600K). Additionally, NRAS is mutated in about 20% of melanomas. These discoveries implicated a mitogen-activated protein kinase (MAPK) pathway (Figure 4) as playing a critical role in metastatic melanoma for a large percentage of patients.29
Based on this knowledge, several targeted therapies for melanoma have been developed, and some have been approved.
BRAF inhibitors—first success against melanoma
Vemurafenib. In 2010, Flaherty et al33 reported on a phase 1 and phase 2 clinical trial of vemurafenib (960 mg orally twice daily), a potent inhibitor of BRAF with the V600E mutation. They demonstrated a clinical benefit in 80% of patients with stage IV BRAF-mutant melanoma, an unprecedented response that opened the door to changes in the treatment of metastatic melanoma.
The phase 3 BRAF Inhibitor in Melanoma (BRIM)-3 clinical trial,34 published in 2011, randomized 675 previously untreated patients with advanced melanoma to either vemurafenib 960 mg orally twice daily or dacarbazine, the standard of care. The trial was terminated early when an interim analysis showed a significant overall advantage for vemurafenib (median progression-free survival 5.3 months vs 1.6 months for dacarbazine). Based on these results, vemurafenib was FDA-approved in August 2011 for use in patients with BRAF-mutant melanoma.
Dabrafenib. In a phase 3 clinical trial in 2012, Hauschild et al35 randomized 250 patients with BRAF (V600E)-mutated melanoma in a 3:1 ratio to receive either dabrafenib, a more potent second-generation BRAF inhibitor, or dacarbazine. Half of patients responded to dabrafenib, with a significantly improved progression-free survival rate (5.1 vs 2.7 months respectively), leading to FDA approval for its use in BRAF-mutant melanoma in May 2013.
Adverse effects common to vemurafenib and dabrafenib include rash, fatigue, fever, and joint pain. In addition, up to 25% of patients develop multiple secondary cutaneous squamous cell carcinomas and keratoacanthomas, usually within the first few months of therapy, which are believed to be caused by paradoxical activation of the MAPK pathway.
A more important problem with these medications is the development of resistance. Tumors typically progress again after a median progression-free survival of 6 to 7 months.
MEK inhibitors—another line of defense
Inhibitors of MEK—a serine-threonine kinase that is part of the same MAPK pathway involving BRAF—have been developed as well.
Trametinib. In 2012, trametinib, an allosteric MEK inhibitor, was used in an open-label phase 3 trial in 322 patients with advanced melanoma. Progression-free survival was 4.8 months for trametinib-treated patients compared with 1.5 months for the standard chemotherapy group (dacarbazine or paclitaxel).36 These results led to FDA approval of trametinib in May 2013 for treating BRAF-mutant melanoma.29
Cobimetinib is a second MEK inhibitor being evaluated alone and in combination with other targeted treatments for advanced melanoma.
Both MEK inhibitors have adverse effects similar to those seen with the BRAF inhibitors, including diarrhea, rash, fatigue, and edema. They also tend to cause asymptomatic elevated creatine kinase and transient retinopathy, reduced ejection fraction, and ventricular dysfunction. Unlike BRAF inhibitors, they are not associated with development of secondary cutaneous squamous cell carcinomas or keratoacanthomas. However, as with BRAF inhibitors, resistance is a problem with MEK inhibitors, with most patients relapsing less than a year after starting therapy.
Combination therapy improves outcomes
Possible mechanisms underlying resistance to these medications are being studied. A number of important factors appear to drive resistance, including expression of truncated BRAF proteins that do not bind the BRAF inhibitors and still activate downstream signaling, and amplification of BRAF to such a degree that it overwhelms the medications. This has led to the idea of combining BRAF inhibitors and MEK inhibitors to block the MAPK pathway at two points, potentially increasing the response and decreasing resistance.
Two trials have evaluated combinations of BRAF and MEK inhibitors in patients with advanced melanoma. Larkin et al37 conducted a phase 3 study evaluating combined vemurafenib (a BRAF inhibitor) and cobimetinib (a MEK inhibitor) vs combined vemurafenib and placebo. Survival with the combination therapy was 9.9 months vs 6.2 months with the single treatment.
The incidence of serious adverse effects was not significantly increased with the combination therapy, and keratoacanthomas, cutaneous squamous cell carcinomas, alopecia, and arthralgias were reduced compared with the vemurafenib and placebo group.
Another trial38 evaluating combined dabrafenib (a BRAF inhibitor) and trametinib (a MEK inhibitor) vs combined dabrafenib and placebo had similar findings: increased survival in the combined therapy group (9.3 months vs 8.8 months) and lower rates of squamous cell carcinoma (2% vs 9%).
In January 2014, the FDA approved the combination of BRAF and MEK inhibitors for the treatment of BRAF-mutant metastatic melanoma based on improved survival and generally reduced adverse effects.
