REVIEW

Beyond PD-1 Immunotherapy in MalignantMelanoma

Dominika Kwiatkowska . Piotr Kluska . Adam Reich

Received: January 26, 2019 / Published online: March 29, 2019� The Author(s) 2019

ABSTRACT

For many years, the standard therapy formalignant melanoma was based mainly onsurgical resection. Unfortunately, this treat-ment is curative only in the early localized stageof this malignancy. The metastatic stage ofmalignant melanoma still remains a hugetherapeutic challenge. Despite the many newtherapeutic options that have become availableover the last years, there is a constant need forsafer and more effective treatment modalities.There has been a dynamic development of var-ious anti-cancer immunotherapies directedagainst new molecular targets. A number ofclinical trials are currently being conducted toconfirm their effectiveness and safety. In thisreview of the literature, we summarize thecontemporary knowledge on promising newimmunotherapies beyond the currently avail-able treatment options for malignant mela-noma, including oncolytic immunotherapy,

selective inhibitors of indoleamine 2,3-dioxy-genease, anti-PD-(L)1 (programmed deathligand 1) drugs, immune checkpoint proteinLAG-3 antibodies, inhibitors of histonedeacetylase (HDAC) and inhibitors of B7-H3.

Keywords: Atezolizumab; Epacadostat; Immu-notherapy; Indoximod; LAG3 inhibitors; Malig-nant melanoma; Oncolytic immunotherapy;Talimogene laherparepvec

AbbreviationsAE Adverse eventsBRAF B-Raf proto-oncogeneCTLA4 Cytotoxic T-lymphocyte associated

protein 4DLTs Dose-limiting toxicitiesGM-CSF Granulocyte macrophage-colony-

stimulating factorHDAC Inhibitors of histone deacetylaseIDO1 Indoleamine 2,3-dioxygenase 1IDO2 Indoleamine 2,3-dioxygenase 2IFN-c Interferon gammaLAG-3 Lymphocyte activation gene 3MEK Mitogen-activated protein kinaseORR Overall response ratePD1 Programmed cell death protein 1PDL-1 Programmed death ligand 1SAE Serious adverse eventT-VEC Talimogene laherparepvecTregs Tumor-associated regulatory T cells

Enhanced digital features To view enhanced digitalfeatures for this article go to https://doi.org/10.6084/m9.figshare.7857098.

D. Kwiatkowska � A. Reich (&)Department of Dermatology, University of Rzeszow,Rzeszow, Polande-mail: adi_medicalis@go2.pl

P. KluskaWroclaw University of Science and Technology,Wrocław, Poland

Dermatol Ther (Heidelb) (2019) 9:243–257

https://doi.org/10.1007/s13555-019-0292-3

INTRODUCTION

Malignant melanoma is one of the most fatalskin tumors with a consistent increase of inci-dence reported over the last 3 decades [1]. Thedata from the World Health Organization(WHO) show that every year 132,000 new casesof this neoplasm are diagnosed around theworld [2]. For years, prognosis for patients withunresectable stage III–IV tumors was poor.Responses to systemic therapy, with the excep-tion of the small group of patients reacting wellto high doses of interleukin 2 (IL-2), wereunsatisfactory [3, 4]. During the last years, sig-nificant progress has been made in the devel-opment of new targeted therapies andimmunotherapies [5], which has given hope topatients with advanced stage malignant mela-noma and markedly changed the future direc-tions of progress in contemporary oncology.Although new treatments have already beenintroduced with many studies confirming theireffectiveness, other therapeutic options are stillneeded for this group of patients.

In this review, we have presented currenttrends in the development of therapy formalignant melanoma and its future potentialimpact on the survival of patients with thistumor.

METHODS

For the purpose of this report, the PubMed andClinicalTrials.gov database were searched(Fig. 1). Articles were included for analysis ifthey concerned the following malignant mela-noma treatments: oncolytic immunotherapy(e.g., talimogene laherparepvec and otheroncolytic viruses), selective inhibitors of indo-leamine 2,3-dioxygenease (e.g., epacadostat,indoximod), anti-PD-(L)1 (programmed deathligand 1) (e.g., atezolizumab), immune check-point protein LAG-3 (lymphocyte-activationgene 3) antibodies (e.g., relatlimab, eftilagimodalpha, LAG525), selective histone deacetylase(HDAC) inhibitors (e.g., entinostat), B7H3inhibitors (e.g., enoblituzumab) and selectedcombinations of the above-mentioned thera-pies with other medications. The research data

had to be published and available before 31December 2018. Reports were excluded if theycontained a description of current standardtherapy of advanced melanoma, such as:checkpoint inhibitors—anti-PD1 antibodies(nivolumab and pembrolizumab), anti-CTLA-4(cytotoxic T-lymphocyte-associated protein 4)immunoglobulin (ipilimumab) and targetedtherapy (BRAF inhibitor, MEK inhibitor) unlessthese therapies were used in combination withpreviously mentioned drugs. Additional articleswere included manually during investigation ofpapers’ references if they were found relevantfor current review. This article is based on pre-viously conducted studies and does not containany studies with human participants or animalsperformed by any of the authors.

Talimogene Laherparepvec and OtherOncolytic Viruses

The development of oncolytic immunotherapyhas resulted in a promising treatment strategy,which in the future could yield improvement ofthe overall survival of patients with metastaticor unresectable malignant melanoma [6, 7].Oncolytic viruses (OVs) act through selectiveinfection and lysis of tumor cells as well asenhancement of the anti-tumor immuneresponse [8].

Talimogene laherparepvec (T-VEC) is the firstand currently the only oncolytic herpes simplexvirus type 1 (HSV1) used for the treatment ofinoperable stage III and IV malignant mela-noma approved by the FDA (Food and DrugAdministration). To prevent toxicity, which wasuntil recently a significant limitation associatedwith a therapeutic viral infection, HSV1 hasbeen genetically modified to achieve T-VEC.Inactivation of neurovirulence factor ICP34.5resulted in increased replication of the virus intumor cells and reduced pathogenicity throughthe protection of normal cells [9]. This effect isenhanced by simultaneous insertion of theUS11 gene [10]. Further modification by delet-ing the ICP47 gene allows the presentation ofan antigen that has previously been inhibitedby the virus [11]. T-VEC also has the ability toexpress GM-CSF, which potentially augments

244 Dermatol Ther (Heidelb) (2019) 9:243–257

the systemic T-cell immune response of the hostto neoplasm cells [12].

As mentioned above, the T-VEC mode ofaction is defined by two mechanisms: selectiveinfection and termination of tumor cells as wellas the induction of local and distant anti-tumorhost immunity. In studies carried out by Kauf-man et al. in patients with unresectable stageIIIc and IV metastatic melanoma, it was foundthat injected melanoma lesions showed anincrease of MART-1 (melanoma-associatedantigen recognized by T cells) specific CD8? Tcells and a significant decrease of suppressiveimmune cells [13]. It seems that these changesin the tumor microenvironment might be validdeterminants of the therapeutic response.

In the randomized, open-label, phase 3clinical trial (OPTiM), the effectiveness ofT-VEC was compared with GM-CSF on a groupof 436 randomly assigned patients with unre-sected, injectable, stage IIIB–IV malignant mel-anoma [14]. Analysis of the durable responserate (DRR), which includes cases with completeresponse (CR) and partial response (PR) presentfor at least 6 months, showed that DRR inpatients treated with T-VEC was significantlyhigher than in the GM-CSF group (16.3% vs.2.1%, respectively). Based on this study, theFDA approved T-VEC for advanced malignantmelanoma.

There is a possibility of combining OVs withchemotherapy, radiation therapy, targetedtherapy or immunotherapy. Strategies of

Fig. 1 Process of searching the PubMed database (BRAF B-Raf proto-oncogene, MEK mitogen-activated protein kinase,PD1 programmed cell death protein 1, CTLA4 cytotoxic T-lymphocyte associated protein 4)

Dermatol Ther (Heidelb) (2019) 9:243–257 245

combination therapy could potentially revolu-tionize and widen the spectrum of availabletreatment options for patients with advancedmalignant melanoma. The first randomizedstudy with the aim to check the efficacy ofT-VEC with and without an anti-CTLA-4 anti-body, ipilimumab, revealed that the objectiveresponse rate was higher for simultaneoustreatment compared with monotherapy [15].

Furthermore, a multicenter phase 1B study(MASTERKEY-265) investigating the safety andtolerability of T-VEC with pembrolizumab inpatients with stage IIIB–IV malignant mela-noma also showed that combined treatment isassociated with a clinical benefit [16]. The sub-sequent randomized, double-blind phase 3 trial(KEYNOTE-034) evaluating T-VEC (versusT-VEC-placebo) plus pembrolizumab is ongo-ing, and the results are not available yet [17].

There are also attempts to use T-VEC as aneoadjuvant therapy. The phase 2 study aimedto examine 150 patients with stage IIIB–IVM1atumors before resection to evaluate the effec-tiveness of T-VEC treatment combined withsurgical treatment compared with surgeryalone. The results of this analysis have not yetbeen published [18].

Currently, ongoing clinical trials evaluateseveral other OVs in the treatment of malignantmelanoma including adenoviruses, Coxsackieviruses, reoviruses, polio viruses, measles virus,vesicular stomatitis virus, vaccinia virus, Sendaivirus, Newcastle disease virus (NVD) and HSV1[19]. Although the number of the ever-testedOVs is high, in Table 1 we present those thatprobably should gain more clinical attention.

Indoleamine-2,3-dioxygenase (IDO)Inhibitors

Selective inhibitors of indoleamine 2,3-dioxy-genease (IDO) may be effective for the treat-ment of advanced and metastatic melanoma.IDO is a catabolic enzyme responsible for oxi-dation of tryptophan to N-formyl-kynurenine[20]. Overexpression of this rate-limitingenzyme by malignant cells is involved inimmune modulation because of its ability toinhibit T-cell immune responses and

consequent tumor outgrowth. Overexpressionof IDO is usually associated with a worse prog-nosis; thus, IDO is a promising therapeutic tar-get, and the use of its inhibitors couldsignificantly reduce cancer neovascularizationand decrease the prevalence of metastasis. Pre-sently, preclinical and clinical trials are under-way for several IDO inhibitors [21]. In Table 2,we presented selected studies focused on IDOinhibitors as well as their combinations withother treatments for malignant melanoma.

Epacadostat (INCB024360) is a novel selec-tive inhibitor of IDO1 with good oral bioavail-ability. A phase 1 dose-escalation studyinvolving 52 participants with advancedmalignancies was performed to determine thesafety of epacadostat. The most common sideeffects were abdominal pain, fatigue and hypo-kalemia, including grade 3 and 4 adverse events.The study also identified 600 mg epacadostat asthe recommended dose of the drug asmonotherapy [22]. Nevertheless, monotherapywith IDO1 inhibitors did not show markedclinical activity; therefore, further studies areongoing to establish the best combination ofepacadostat with other immunotherapies.

In a phase 1/2 randomized and placebo-controlled study, an attempt was made tocombine epacadostat with ipilimumab. The25-mg dose of epacadostat in combination withthe standard dose of ipilimumab was generallywell tolerated. Adverse effects were reversiblewith corticosteroids and discontinuation oftreatment. This research allowed the conclusionthat epacadostat might enhance clinical activityof ipilimumab [23].

Epacadostat has also been evaluated incombination with pembrolizumab in referenceto patients with advanced melanoma and othersolid tumors. A phase 1/2, multicenter, non-randomized, open-label study showed promis-ing efficacy and durable antitumor activity.Unfortunately, phase 3 study did not meet theprimary end point of improvement in PFScompared with pembrolizumab monotherapy[24, 25]. The reasons for this negative trialremain undetermined [26]. Furthermore, otherattempts were taken to assess the effectivenessof various drugs plus epacadostat, some ofwhich are gathered in Table 2.

246 Dermatol Ther (Heidelb) (2019) 9:243–257

Table 1 Examples of oncolytic viruses tested for malignant melanoma treatment

Oncolyticvirus

Description Researchphase

Researchstatus

Participants Research ID Outcomes

CoxsackievirusA21

Multicenter, open-label, phase 2 studyin patients with stageIIIc and IVmalignant melanoma

Phase 2 Completed 57 NCT01227551 ORR rate was 28.1%

Grade 1 AEs included:fatigue, chills, localinjection sitereactions and fever

No grade 3 or 4 AEswere observed

Phase 2 study inpatients with stageIIIc–IV malignantmelanoma to extenddosing for up to48 weeks

Phase 2 Completed 16 NCT01636882 CVA21 treatmentincreased immunecell infiltrates(CD3? CD8 ) andexpression of PD-L1

SAEs and AEs wereirrespective oftreatment

Adenovirus Phase 1/2, single-armstudy ofintratumoralinjections in patientswith inoperable stageIII–IV melanoma

Phase 1/2 Completed 14 NCT01397708 Treatment was welltolerated andinduced biologic andclinical activity.

AEs included chills(78.6%), pyrexia(78.6%), fatigue(71.4%) and nausea(71.4%)

ECHO 7virus(Rigvir�)

A retrospective studyto determine theefficacy of Rigvir� inpatients with IB–IICmalignant melanoma

Registeredin Latvia

Notapplicable

79 PMC4560272 Rigvir� extendedsurvival in patientswith malignantmelanoma

AEs[ class 2 wereabsent

HF10 Phase 1, open-labelmulticenter study,evaluatingintratumoralinjections of theHF10 in refractoryand superficiallesions (includingmalignantmelanoma)

Phase 1 Completed 28 NCT01017185 Six patients had AEsassociated withHF10, includingchills (two patients)and discolorations atthe injection site,edema and pain,malaise, pruritus andhypotension (onepatient each)

ORR overall response rate, AEs adverse events, SAEs serious adverse events

Dermatol Ther (Heidelb) (2019) 9:243–257 247

Table2

Clin

icaltrialsof

indoleam

ine-2,3-dioxygenase(IDO)inhibitorsin

malignant

melanom

a

Agent

Description

Research

status

Com

bination

with

ResearchID

Outcomes

Epacadostat

Open-labeldose

escalation

studyin

patientswithadvanced

malignancies

Com

pleted

–NCT01195311

Dosesof

C100mgBID

caused

maxim

al

inhibition

ofID

O1activity

Treatment-relatedAEsin[

20%

of

patientsincluded:fatigue,nausea,

decreasedappetite,vom

iting,

constipation

,abdom

inalpain,d

iarrhea,

dyspnea,back

pain

andcough

Phase2trialstudyof

epacadostatand

vaccinetherapyin

treating

patients

withstageIII–IV

malignant

melanom

a

Com

pleted

Vaccine

therapy

NCT01961115

Confirmed

clinicalactivity

andevidence

ofincreasedCD8T-cellinfiltration

DLTsin

2patients:grade

3transaminase

elevation,

grade3syncope

Phase1blindedresearch

ofipilimum

ab

withepacadostat(orplacebo)

in

patientswithinoperableor

metastatic

malignant

melanom

a

Terminated

Ipilimum

abNCT01604889

Sevenpatientsreceived

adoseof

300mg

BID

;fiveof

thesepatientshad

significant

alanineam

inotransferase

activity

elevationafter30–7

6days

Enrollmentwas

prem

aturelystopped

AEswerereversiblewithcorticosteroids.

Enrollmentwasrestartedat25

mgBID

Com

bination

of25

mgepacadostatand

ipilimum

abcouldenhanced

efficacy

comparedwithipilimum

ab

monotherapy

Phase1b

studyevaluating

efficacyof

itacitinib

?epacadostatand/or

icacitinib

?IN

CB050465

in

advanced

ormetastaticsolid

tumors

Active,not

recruiting

Itacitinib

NCT02559492

N/A

248 Dermatol Ther (Heidelb) (2019) 9:243–257

Table2

continued

Agent

Description

Research

status

Com

bination

with

ResearchID

Outcomes

Phase1and2studyevaluating

combination

ofazacitidinewith

pembrolizum

abandepacadostatin

patientswithadvanced

solid

tumors,

includingmelanom

a

Active,not

recruiting

Azacytidine

?pembrolizum

abNCT02959437

N/A

Indoximod

Phase1trialinvestigatingside

effects

anddose

ofindoximod

inpatients

withmetastaticor

unresectablesolid

tumors

Com

pleted

–NCT00567931

Indoximod

was

safe

atdosesup

to

2000

mgBID

.ORRwas

10%,A

Es

were:fatigue(56%

),anem

iaand

anorexia(37.5%

),dyspnea(35.4%

)

cough(33.3%

),nausea

(29%

)

Phase1studyof

usingindoximod

for

refractory

solid

tumorsincluding

malignant

melanom

a

Terminated

–NCT00739609

Lackof

enrollm

ent

Phase1and2studyof

indoximod

in

combination

withcheckpoint

inhibitorsforpatientswithmetastatic

malignant

melanom

a

Active

Checkpointinhibitors

NCT02073123

Com

bination

ofindoximod

and

pembrolizum

abdemonstratesan

ORR

of55.7%,C

R18.6%,com

paredwith

reported

33%

ORRfor

pembrolizum

abalone

Phase2and3assessingtheefficacyof

indoximod

orplacebowith

pembrolizum

abor

nivolumab

in

patientswithinoperable,m

etastatic

malignant

melanom

a

Recruiting

Pembrolizum

ab/N

ivolum

abNCT03301636

N/A

Dermatol Ther (Heidelb) (2019) 9:243–257 249

Table2

continued

Agent

Description

Research

status

Com

bination

with

ResearchID

Outcomes

IDO peptide

vaccine

Phase1research

assessingefficacyof

vaccinationwithpeptides

in

combination

withipilimum

abor

vemurafenib

forpatientswith

unresectablestageIIIor

IVmalignant

melanom

a

Com

pleted

Ipilimum

ab/V

emurafenib

NCT02077114

Vaccine-related

grade1and2AEs:

erythema,edem

aandpruritus

AllAEsweremanageablewith

corticosteroids

NoAEsgrade3or

4

Phase2studyto

exam

inetreatm

ent

withpeptidevaccineand

temozolom

ideformetastatic

melanom

apatients

Terminated

Tem

ozolom

ide

NCT01543464

Trialwas

term

inated

before

full

enrollm

ent

Phase1and2trialof

combination

therapywithnivolumab

andPD

-L1/

IDO

peptidevaccinein

patientswith

metastaticmelanom

a

Recruiting

Nivolum

abNCT03047928

N/A

GDC-0919

Phase1studyevaluating

thesafety,

tolerabilityanddosesof

GDC-0919

forpatientswithmalignant

melanom

a

Com

pleted

–NCT02048709

Navoxim

od(G

DC-0919)

was

well

toleratedat

dosesup

to800mgBID

Grade

C3AEsrelatedto

navoximod

occurred

in9%

ofpatients

HTI-1090

Phase1trialof

HTI-1090

inpatients

withadvanced

solid

tumors

Recruiting

–NCT03208959

N/A

NLG802

Phase1studyexam

iningthesafety,

tolerabilityanddosesof

NLG802in

patientswithadvanced

solid

tumors

Recruiting

–NCT03164603

N/A

BMS-

986205

Phase1studyevaluating

thetreatm

ent

ofsolid

tumorswithdifferent

combinationsof

immun

otherapy

Recruiting

Various

combinationsof

immun

otherapy

NCT03335540

N/A

AEsadverseevents,D

LTsdose-limitingtoxicities,B

IDtwicedaily,N

/Anotapplicable,O

RRoverallresponse

rate

250 Dermatol Ther (Heidelb) (2019) 9:243–257

Indoximod (D-1-methyl-tryptophan) is anorally available, indirect inhibitor of IDO1 andalso a more selective IDO2 inhibitor of theindoleamine 2,3-dioxygenase pathway. Indoxi-mod showed anti-tumor activity and synergisticaction with various chemotherapeutics. Theprimary end point in the phase 1 study was todetermine the maximal well-tolerated dose(MTD) in 48 patients with advanced malignan-cies. The dose ranged from 200 mg once a day to2000 mg twice daily. Unfortunately, MTD hasnot been reached, but no significant increase intoxicity was observed between various doses,and no patients stopped treatment because ofany toxicity. The authors concluded thatindoximod was generally well tolerated [27]. Asin the case of epacadostat, antitumor activity ofmonotherapy with indoximod was unsatisfac-tory, and many combinations with otherimmunotherapies are being investigated(Table 2).

The ineffectiveness of the IDO inhibitor asmonotherapy can be associated with immuneevasion of TRCs that lead to tumor recurrence,drug resistance and formation of metastasis.TRCs are self-renewing cancer cells similar tostem cells with the ability to repopulate tumors.Nonetheless, the combination of IFN-c withIDO1 inhibitors is currently the only therapythat could potentially eliminate TRCs and thusmay improve treatment outcomes. Given theTRC dormancy that was induced by IFN-c andimmunosuppression caused by IDO1, TRCs arevulnerable to attacks by T cells and NK cells,which makes this strategy of immunotherapyvery promising [28].

Anti-PD-(L)1-Programmed Death Ligand 1

Expression of an immune-checkpoint protein-PD-L1 on the surface of tumor cells couldrestrain T-cell function. PD-L1 binds to the PD-1and B7.1 proteins. The PD-1/PD-L signalingpathway is one of the key mechanisms thatcould contribute to the inhibition of the anti-tumor response and thus protect tumor cells.The respective components of the PD-1/PD-Lpathway are targets of immunotherapy withspecific monoclonal antibodies. One of them is

atezolizumab—an engineered humanizedmonoclonal anti-PD-L1 antibody [29].

Monotherapy with atezolizumab will beinvestigated in a phase 1b study(NCT03178851) with the following evaluationcriteria: the efficacy, safety and pharmacoki-netics of this drug in patients with BRAFV600-WT metastatic malignant melanoma who havenot been previously treated. This study will alsoassess the combination of cobimetinib and ate-zolizumab in patients who have worseneddespite anti-PD-1 therapy.

Recent studies have shown that ate-zolizumab can act synergistically with MEKinhibitors, such as cobimetinib [30]. Thus, itmight be a potential therapeutic option forpatients with metastatic malignant melanoma.Unfortunately, this combination has not beenlicensed yet for any indication in the EU. Thephase 3, multicenter, randomized trial(NCT03273153) intended to measure the effi-cacy and safety of cobimetinib plus ate-zolizumab compared with pembrolizumab inpreviously untreated participants withadvanced wild-type BRAFV600 melanoma. Thisstudy is currently in a recruitment phase. Therehave also been attempts to combine ate-zolizumab with cobimetinib and vemurafenib.Updated results confirm the preliminary data,which have shown a manageable safety profile[31, 32]. Continued investigation of this com-bination is justified.

LAG3 inhibitors

Tumors have the ability to escape immunesurveillance, and detailed knowledge of thesemechanisms led to discoveries that signaling viaspecific receptors, such as LAG3 or PD1, couldcause T-cell dysfunction [33]. The first results ofa clinical trial have shown that the concomitantusage of immune checkpoint protein LAG-3antibodies, relatlimab and nivolumab, toincrease the anti-tumor immunity by restoringthe activation of T cells is safe and effective forpatients who have progressed despite targetedimmunotherapy. ORR was 11.5%; one patientachieved a complete response, and six hadpartial responses. In patients with LAG-3

Dermatol Ther (Heidelb) (2019) 9:243–257 251

expression C 1%, ORR was higher. In this study,4.4% of patients had one or more AEs in grade 3or 4 associated with the treatment, and 1.5%had to stop the treatment because of AE [34].

Under investigation is also IMP321-eftilagi-mod alpha, the first class MHC-II agonist thatcould potentially be used with other drugs.Phase 1 study (NCT02676869) of IMP321 incombination with pembrolizumab was per-formed to determine the safety, tolerability andrecommended dose for phase 2 study onpatients with stage III and IV malignantmelanoma.

Moreover, another monoclonal antibody,LAG525, is currently being tested in a phase 1/2clinical trial (NCT02460224). The main purposeof the study is to assess the safety, tolerability,pharmacokinetics (PK), pharmacodynamics(PD) and antitumor activity of LAG525 alone orwith PDR001 (new anti-PD1 compound) inadult patients with solid tumors.

Inhibitors of Histone Deacetylase (HDAC)and B7-H3

Another promising therapy for patients whosuffer from malignant melanoma unequivocallyresistant to prior anti-PD-(L)1 treatment is thesimultaneous administration of a class I selec-tive histone deacetylase (HDAC) inhibitor,entinostat, with pembrolizumab. The purposeof this combination is to reinforce inflamma-tion in the neoplasm microenvironmentrequired for propitiously retreatment with ananti-PD(L)1. In a phase 1b/2 study, the pre-dominant treatment-related AEs were nausea,fatigue, diarrhea and pruritus. Updated resultsconfirm preliminary findings that entinostatplus pembrolizumab have a manageable safetyprofile [35].

Furthermore, patients with B7-H3-expressingmelanoma have been enrolled in a phase 1study whose aim is to evaluate the safety ofenoblituzumab (MGA271) with pem-brolizumab. Enoblituzumab is a monoclonalantibody that has the ability to bind to B7-H3(CD276). B7-H3 overexpression has been shownin many tumors, including melanoma; unfor-tunately, it is also associated with poor

prognosis. On the other hand, B7-H3 showslimited expression in normal tissue, which mayhelp to reduce the risk of AEs associated withautoimmunity. The NCT02475213 trial (a doseescalation, open-label and cohort expansionstudy) focuses on the evaluation of targetingboth receptors, B7-H3 and PD-1, in patientswith advanced B7-H3-expressing cancers [36].

Future Directions

In our article, we have summarized a number ofdifferent treatment strategies currently underdevelopment for malignant melanoma. How-ever, there are many unanswered questions thatneed to be addressed in the near future.

Regarding oncolytic viruses, future studiesshould focus on new potential combinationswith other treatment modalities. Besides clini-cal trials evaluating combination with immuneT-cell checkpoint inhibitors targeting CTLA-4 orPD-1, special attention should be given to acombination of available oncolytic virothera-pies with radiation therapy, BRAF inhibitors,MEK inhibitors or adaptive T-cell therapy.Moreover, further investigations might evaluatethe application of oncolytic viruses not only inmelanoma therapy, but also in other skintumors that are easily accessible for injections,such as Merkle cell tumors, squamous cell car-cinoma or basal cell carcinoma. Studies shouldalso focus on better understanding of themechanisms underlying the anti-cancerimmune response mediated by oncolytic virusesand on the assessment of prognostic biomarkersof therapeutic response; these are crucial for theproper identification of patients who couldbenefit from this type of therapy. This couldalso enable a better selection of patients forclinical trials and might help to reduce unnec-essary expenses while such therapy is beingapproved for use.

Monotherapies do not always bring thedesired results, as in the case of IDO inhibitors.However, combined therapies create theopportunity to widen the therapeutic window.IDO2 inhibitors could limit autoimmune-re-lated adverse events caused by other cancertherapies. There is also quite strong evidence of

252 Dermatol Ther (Heidelb) (2019) 9:243–257

the interaction among CTLA-4, PD-L1 and IDO.Holmgaard et al. have shown that IDO expres-sion has an inhibitory role in both anti-CTLA-4and anti-PD1/PD-L1 therapies [37]. Despite sofar unsuccessful clinical trials, investigation ofthe effect of IDO inhibitors, as part of combi-nation strategies in malignant melanomapatients, is essential and should be furtherstudied.

As in the case of many other immunothera-pies, blockade of PD-L1 presented beneficialeffects only in a subgroup of patients. The lateststudies have shown that the efficacy of PD-L1

therapy could be improved by modulation ofgut microbiota [38]. Increased anti-PD-L1 effi-cacy was observed in mouse models afteradministration of Bifidobacterium [39]. Futurestudies should concentrate on investigations ofthe molecular mechanisms of this action.Finally, the question of whether chronic infec-tion or inflammation could impact the effec-tiveness of the PD-L1 blockade arises.

Furthermore, the current studies did notfully disclose the exact function of LAG-3.Comprehensive understanding of this actionmight have a tremendous impact on the

Fig. 2 Overview of action mechanisms of selected drugsthat are under development for malignant melanomatherapy: (from left to right) relatlimab, a monoclonalantibody, binds to the LAG3 receptor, which is present onthe surface of specialized immune cells, restoring its activityand allowing them to attack cancer cells; atezolizumab, amonoclonal antibody, binds to the PD-L1 on both tumorcells and immune cells, blocking its interactions with PD1and B7.1 receptors and restoring T-cell activity; T-VECpresents a dual mechanism of action—selective viralreplication results in lysis of tumor cells and productionof GM-CSF by tumor cells upon T-VEC further leads toproliferation of CD4? and CD8? T-cell and IFN-cexpression; indoximod downregulates the IDO pathway,resulting in the immunostimulatory effect of CD4 ? and

CD8 ? T cells and a decrease of Tregs; epacadostatinhibits the IDO1 enzyme, which leads to the restorationof CD8? T-cell and CD4? T-cell proliferation and areduction of Tregs; entinostat works through the epige-netic mechanism of action involving histone acetylationand simultaneous acetylation of non-histone proteins—this dual mechanism causes an increase of the immuneresponse and melanoma cell apoptosis (T-VEC talimogenelaherparepvec, LAG-3 lymphocyte activation gene 3, PDL-1 programmed death ligand 1, PD1 programmed cell deathprotein 1, GM-CSF granulocyte macrophage-colony-stim-ulating factor, IDO1 indoleamine 2,3-dioxygenase 1, IDO2indoleamine 2,3-dioxygenase 2, IFN-c interferon gamma;Tregs tumor-associated regulatory T cells)

Dermatol Ther (Heidelb) (2019) 9:243–257 253

Table 3 Summary of different immunotherapies being currently developed

Drug Mechanism of action Comments References

Atezolizumab Binding to the PD-L1 and further

blocking its interaction with PD1 and

B7.1

Restoring T-cell activity

Atezolizumab can act synergistically with

MEK inhibitors

Continued investigation of this drug in

combination with other

immunotherapies is required

[29–32]

Enoblituzumab Direct binding to B7-H3 over-expressed

on tumor cells and cancer stem-like cells

The drug is currently being tested in

combination with pembrolizumab for

patients with B7-H3-expressing

melanoma

NCT02475213

trial

Entinostat Histone and non-histone acetylation.

Increase of immune response and

apoptosis

Entinostat plus pembrolizumab achieved

manageable safety profile

Reinforcing of inflammation in the

neoplasm microenvironment could

improve retreatment with an anti-PD-

L1 in patients with malignant melanoma

[35]

Epacadostat Selective inhibition of IDO1 resulting in

restoration of CD8 ? T cells,

proliferation of CD4 ? T cells and

reduction of Tregs

Epacadostat was generally well tolerated

and might enhance activity of

ipilimumab

Monotherapy with epacadostat did not

show marked clinical activity

The attempt of simultaneous usage of

epacadostat and pembrolizumab did not

meet the primary end point

Combinations with other

immunotherapies are currently under

investigation

[22–26]

IMP321—

eftilagimod

alpha

Stimulation of antigen-presenting cells

and induction of sustained immune

responses

The addition of eftilagimod alpha might

improve the objective response rates as

compared with PD1 inhibitor

monotherapy

Clinical trials for patients with malignant

melanoma are still ongoing

NCT02676869

trial

Indoximod Indirect suppression of IDO1 and more

selective inhibition of IDO2 resulting in

an increased number of CD8? T cells,

CD4? T cells and a decrease of Tregs

Indoximod was generally well tolerated

Antitumor activity as monotherapy was

unsatisfactory

Further investigations of combination of

indoximod with other immunotherapies

are pending

[27]

254 Dermatol Ther (Heidelb) (2019) 9:243–257

indication of new therapeutic regimens. Theheightened interest should not only concerncombinatorial PD1 immunotherapy and LAG-3,but also other first-line treatment options withLAG-3 inhibitors.

CONCLUSIONS

In recent years, poor efficacy of the treatment ofmalignant melanoma has led to the continua-tion of research to better understand how tostimulate the anti-cancer immune response. Asstated before, many clinical trials are stillongoing. The simplified action mechanisms ofdrugs that were considered in this review arepresented in the Fig. 2 below, and the summaryof the discussed drugs is shown in Table 3.

We hope that novel treatment modalities foradvanced malignant melanoma can lead tomarked changes in this neoplasm therapy andsignificant improvement of the survival rate ofpatients with malignant melanoma.

ACKNOWLEDGEMENTS

Funding. No funding or sponsorship wasreceived for this study or publication of thisarticle.

Authorship. All named authors meet theInternational Committee of Medical JournalEditors (ICMJE) criteria for authorship for thisarticle, take responsibility for the integrity ofthe work as a whole, and have given theirapproval for this version to be published.

Disclosures. Adam Reich has worked as aConsultant or Speaker for AbbVie, Bioderma,Celgene, Chema Elektromet, Eli Lilly, Gal-derma, Janssen, Leo Pharma, Medac, MenloTherapeutics, Novartis, Pierre-Fabre and Treviand participated as Principal Investigator orSubinvestigator in clinical trials sponsored byAbbVie, Drug Delivery Solutions Ltd, Galderma,Janssen, Kymab Limited, Leo Pharma, Menlo

Table 3 continued

Drug Mechanism of action Comments References

LAG525 Antibody-dependent cell cytotoxicity and

T-cell stimulation

This monoclonal antibody is currently

being tested to assess its safety and

efficacy

LAG525 has potential to change the

tumor microenvironment to be more

favorable for immune response

NCT02460224

trial

Relatlimab Binding to the LAG3 receptor and

restoring T-cell activity

Simultaneous administration of relatlimab

and nivolumab was well tolerated and

effective

Safety profile was similar to nivolumab

monotherapy

[34]

T-VEC Selective infection and lysis of tumor cells,

increase of GM-CSF production as well

as induction of local and distant tumor

specific immune response

T-VEC has a favorable safety profile and

good efficacy in patients with

unresectable malignant melanoma

without distant metastases

T-VEC can also be successfully combined

with other immunotherapies to improve

their efficacy

[9–16]

Dermatol Ther (Heidelb) (2019) 9:243–257 255

Therapeutics, MetrioPharm, MSD, Novartis andTrevi. Piotr Kluska and Dominika Kwiatkowskahave nothing to disclose.

Compliance with Ethics Guidelines. Thisarticle is based on previously conducted studiesand does not contain any studies with humanparticipants or animals performed by any of theauthors.

Data Availability. Data sharing is notapplicable to this article as no data sets weregenerated or analyzed during the current study.

Open Access. This article is distributedunder the terms of the Creative CommonsAttribution-NonCommercial 4.0 InternationalLicense (http://creativecommons.org/licenses/by-nc/4.0/), which permits any noncommer-cial use, distribution, and reproduction in anymedium, provided you give appropriate creditto the original author(s) and the source, providea link to the Creative Commons license, andindicate if changes were made.

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