**16. Combination immunotherapy and targeted therapy**

and treated with binimetinib. The objective response rate was 21% and the progression-free survival was 3.7 months. Further study in this patient population will be necessary to confirm its clinical activity in comparison to other standard therapies. While prospective data with trametinib in NRAS mutant melanoma patients is not available, early retrospective data from ongoing clinical studies suggests that trametinib may have activity in a subset of NRAS

Therapy with a MEK inhibitor in combination with a BRAF inhibitor is more effective and less toxic than treatment with a BRAF inhibitor alone, and has become the standard of care for patients with BRAF-mutated melanoma. Trametinib, the first MEK inhibitor was approved for the treatment of BRAF-mutated metastatic melanoma not previously treated with BRAF inhibitors, and is also approved in combination with the BRAF inhibitor dabrafenib [68].

The clinical study about combination dabrafenib and trametinib versus dabrafenib monotherapy in BRAF V600E/K–mutant metastatic melanoma demonstrated improved progression-free survival and overall survival. Phase III clinical study enrolled previously untreated patients with BRAF V600E/K–mutant unresectable stage IIIC or stage IV melanoma. Patients were randomized to receive dabrafenib, 150 mg twice daily, plus trametinib, 2 mg once daily, or dabrafenib plus placebo. The primary endpoint was progression-free survival; secondary endpoints were overall response, duration of response, pharmacokinetics and safety. Results showed that 423 of 947 screened patients were randomly assigned to receive dabrafenib plus trametinib (n = 211) or dabrafenib monotherapy (n = 212). At data cutoff, outcomes remained superior with the combination: 3-year progression-free was 22% with dabrafenib plus trametinib versus 12% with monotherapy, and 3-year overall response was 44 versus 32%, respectively. Twenty-five patients receiving monotherapy crossed over to combination therapy, with continued follow-up under the monotherapy arm. Of combination-arm patients alive at 3 years, 58% remained on dabrafenib plus trametinib. Three-year overall response with the combination reached 62% in the most favorable subgroup (normal lactate dehydrogenase) versus only 25% in the unfavorable subgroup (elevated lactate dehydrogenase). The dabrafenib plus trametinib safety profile was consistent with previous clinical trial observations, and no new safety signals were detected with long-term use. These data demonstrate that durable survival is achievable with dabrafenib plus trametinib in patients with BRAF V600–mutant metastatic

The optimal timing and sequence of combination therapy (in particular targeted therapy in combination with immunotherapy) is currently in progress and cannot be precisely predicted for all patients with melanoma. Due to the existence of many potential targets in the immune system many critical questions arise, e.g. which therapy combinations should move forward

in development and which patients will benefit from these treatments [70].

mutant melanoma patients [67].

melanoma [69].

**15. BRAF plus MEK inhibitors**

122 Human Skin Cancers - Pathways, Mechanisms, Targets and Treatments

Studies about combinations of anti-PD-1/PD-L1 agents with other immunotherapeutic agents are currently conducted in treatment of multiple tumor types. Targeting immune checkpoints such as PD-1, PDL-1 and CTLA-4 has achieved remarkable benefit in multiple cancers by blocking immunoinhibitory signals and enabling patients to produce an effective antitumor response. Inhibitors of CTLA-4, PD-1 or PDL-1 administered as single agents have resulted in durable tumor regression in some patients, and combinations of PD-1 and CTLA-4 inhibitors may even enhance antitumor benefit [70]. The combination of ipilimumab and nivolumab was studied in a phase I trial of 86 patients with pretreated malignant melanoma and demonstrated a 40% objective response rate [71]. In Phase II [72] and III studies [73] of this combination used in the treatment of advanced melanoma response rates were quite impressive, but toxicity was notably increased. Almost 83–89% of patients required either topical or oral immunosuppressive therapy for immune-related adverse events (irAE), which led to treatment discontinuation in 36–47% of all patients [72, 73]. However, almost all of the patients (80–100%) treated with immunosuppressive agents had their irAE completely resolved [74].

Recent study by Kim et al. suggests that the addition of MEK inhibitors to targeted and immunotherapy combinations may be associated with increased toxicity; several patients treated by dabrafenib (BRAF inhibitor), trametinib (MEK inhibitor), and ipilimumab (CTLA-4 inhibitor) developed adverse events related to colonic perforation. This condition found in several patients increases the need to further understand the immunomodulatory effects of trametinib [75].

Promising results have been presented in a Phase I study in BRAF-mutant advanced melanoma patients receiving atezolizumab (anti PD-L1) combined with vemurafenib (BRAF inhibitor) and cobimetinib (MEK inhibitor), with a response rate of 83%; currently a Phase III study is on-going [76].

*Atezolizumab* (Tecentriq, Genentech Oncology) is PD-L1 blocking antibody that previously received FDA accelerated approval for the treatment of locally advanced or metastatic urothelial carcinoma that has progressed after platinum-containing chemotherapy. Atezolizumab was granted FDA approval on October 18, 2016 for the treatment of patients with metastatic non-small cell lung cancer whose disease progressed during or following platinum-containing chemotherapy. Also the combination of atezolizumab with trametinib in patients with BRAF-wild type melanoma demonstrated encouraging results in an early phase study—a Phase III study is planned [77]. Patients with advanced melanoma and high serum lactate dehydrogenase activity present very poor prognosis, regardless of the systemic treatment used [78]. Current research should be focused on understanding the relationship between high serum lactate dehydrogenase activity and the lack of treatment efficacy with immunotherapy and targeted therapy. Probably novel treatment strategies should be developed in this patient population [42].

#### **17. Future direction in targeted therapy**

Despite extensive new approaches in the treatment of advanced stage melanoma, i.e. chemotherapy, targeted therapy and immunotherapy, response rate is rarely higher than 20%. Especially in the treatment with BRAF inhibitors the drug resistance is very common [79]. Due to this reason there is an urgent need to invent other alternatives and targeted therapies. Preclinical studies looking at least this main drug association strategies seems to be very promising: targeting of either MEK or phosphatidylinositol-3 kinase (PI3K)/mammalian target of rapamycin (mTOR); strategies aimed at blocking anti-apoptotic proteins belonging to B-cell lymphoma (BCL-2) or inhibitors of apoptosis (IAP) families associated with MEK/ BRAF/p38 inhibition; co-inhibition of other molecules important for survival (proteasome, histone deacetylase and signal transducers and activators of transcription) [80]. *PI3K-AKTmammalian target* of rapamycin signaling pathway is important for melanoma initiation and progression so the preclinical investigation of a novel and highly potent PI3K-mTOR dual inhibitor *VS-5584* was realized. VS-5584 induced caspase-dependent apoptotic death in melanoma cells, and its cytotoxicity was alleviated by the caspase inhibitors [81]. Whereas the main aim of inhibiting MAPK signaling pathway is to prevent cancer cell proliferation, apoptosis is controlled by the availability of anti-apoptotic *BCL-2 proteins* (e.g. BCL-2), which reside at the outer mitochondrial membrane. BCL-2 supports neoplastic growth by blocking cell death and this target may be future direction in the treatment of various types of cancers [82]. Development of small molecule inhibitors specific for antiapoptotic BCL-2 proteins is a novel approach not only for therapy of chronic lymphocytic leukemia [83] but is very promising in therapy of advanced melanoma [84]. This new targeted approach could by more successful when the combination with retinoid derivative is used [85]. *Venetoclax (ABT-199)* (**Figure 4**) is the first orally bioavailable selective inhibitor of BCL-2 protein often over-expressed in chronic lymphotic leukemia (CLL) and other types of B-cell related cancers developed by AbbVie in partnership with Roche. It is currently being evaluated in Phase II and Phase III studies for CLL and in Phase I and II studies for several other blood cancers and can be one of the next molecules used in the treatment of melanoma in the near future [86].

In the field of other genetic abnormalities such as *CDKN2A* also known as cyclin-dependent kinase inhibitor 2A, EGF (epidermal growth factor, which plays a role in skin cell growth), *Fas gene*, tumor suppressor gene *PTEN* (phosphatase and tensin homolog), there is a challenge in the research of new therapeutic targets and development of new anti-melanoma drugs in the future that can eventually lead to therapeutic benefit. Recent study by Hodis et al. describes six novel melanoma genes (PPP6C, RAC1, SNX31, TACC1, STK19, and ARID2), three of which RAC1, PPP6C, and STK19 harbored recurrent and potentially targetable mutations [87]. The prevalence of BRAFV600 and KIT mutations were significantly associated with melanoma subtypes and BRAFV600 and TP53 mutations were significantly associated with cutaneous primary tumor location. These results enrich understanding of the patterns and clinical associations of oncogenic mutations in melanoma, which could be the goal of future direction of melanoma therapy [88].

Possibilities for the Therapy of Melanoma: Current Knowledge and Future Directions

http://dx.doi.org/10.5772/intechopen.70368

125

The development of drugs in the treatment of melanoma has never been as intense as at present. Single-agent chemotherapy is considered to have rather palliative effect on patients with melanoma; it is usually well tolerated but is associated with lower response rate. Detailed knowledge of protein structures and the understanding of their role in key signaling pathways in melanoma development lead to the designation of new targets for treatment of melanoma. Targeted therapy for patients whose tumors harbor the BRAF mutation achieves high response rates and OS benefit with combination BRAF/MEK inhibition. No other therapy in melanoma has shown a better response rate in late-phase clinical trials than combined BRAF and MEK inhibitors. The rapid kinetics of response to BRAF plus MEK targeted therapies represents the ideal frontline treatment for symptomatic, BRAF-mutant advanced melanoma patients. Although the concept of a combination of immunotherapeutic and targeted agents appears to be crucial in the treatment of melanoma, the synergy between these two approaches in melanoma treatment remains controversial due to the potential increased toxicity. Recently enormous progress in cancer therapy has been achieved by the use of immune checkpoint inhibitors. Activating the body's own immune system has added a novel and powerful therapeutic option for the treatment of melanoma. The potential use of immunotherapy is being extensively explored also in other malignancies. In the future, it is necessary to conduct further clinical trials and collect more data about overall survival, response rates, appropriate timing and sequence of combination therapy to manage the complexity of melanoma treatment.

Marcela Valko-Rokytovská\*, Jana Šimková, Mária Milkovičová and Zuzana Kostecká

Department of Chemistry, Biochemistry and Biophysics, University of Veterinary Medicine

\*Address all correspondence to: marcela.valko.rokytovska@gmail.com

and Pharmacy in Košice, Košice, Slovak Republic

**18. Conclusion**

**Author details**

**Figure 4.** Chemical structure of venetoclax.

In the field of other genetic abnormalities such as *CDKN2A* also known as cyclin-dependent kinase inhibitor 2A, EGF (epidermal growth factor, which plays a role in skin cell growth), *Fas gene*, tumor suppressor gene *PTEN* (phosphatase and tensin homolog), there is a challenge in the research of new therapeutic targets and development of new anti-melanoma drugs in the future that can eventually lead to therapeutic benefit. Recent study by Hodis et al. describes six novel melanoma genes (PPP6C, RAC1, SNX31, TACC1, STK19, and ARID2), three of which RAC1, PPP6C, and STK19 harbored recurrent and potentially targetable mutations [87]. The prevalence of BRAFV600 and KIT mutations were significantly associated with melanoma subtypes and BRAFV600 and TP53 mutations were significantly associated with cutaneous primary tumor location. These results enrich understanding of the patterns and clinical associations of oncogenic mutations in melanoma, which could be the goal of future direction of melanoma therapy [88].
