Faculty Bibliography

Immunotherapy has revolutionized cancer therapy and has been named the cancer advance of the year for 2016. Checkpoint inhibitors have demonstrated unprecedented rates of durable responses in some of the most difficult-to-treat cancers; however, many treated patients do not respond, and the potential for serious side effects exists. There is a growing need to identify biomarkers that will improve the selection of patients who will best respond to therapy, further elucidate drug mechanisms of action, and help tailor therapy regimens. Biomarkers are being explored at the soluble, cellular, and genomic levels, and examples in immunotherapy include serum proteins, tumor-specific receptor expression patterns, factors in the tumor microenvironment, circulating immune and tumor cells, and host genomic factors. The search for reliable biomarkers is limited by our incomplete understanding of how immunotherapies modify the already complex immune response to cancer, as well as the contribution of immuno-editing to a dynamic and inducible tumor microenvironment and immune milieu. Furthermore, there has been little extension of any candidate assay into large, prospective studies, and the lack of standardization in measurement and interpretation restricts their validity. Both tumor-infiltrating lymphocytes and PD-L1 expression within the tumor microenvironment have been recognized as having both prognostic and predictive value for patients treated with immunotherapy. Alternately, a larger panel of gene signatures, chemokines, and other factors that correlate with response has been proposed. In this article, we will explore the status of current biomarker candidates.

Mucosal melanoma is an exceedingly rare variant of cutaneous melanoma that, due to its rarity, is poorly described and infrequently studied. Primary sites of origin include the head and neck, anorectum and vulvovaginal regions. It is uniquely different from cutaneous melanoma with respect to epidemiology, etiology, pathogenesis and prognosis. The etiology and pathogenesis remain unclear. Unlike cutaneous melanoma, exposure to UV light is not an apparent risk factor. Furthermore, distinct molecular features including a lower incidence of BRAF oncogene mutations but a higher incidence of KIT oncogene mutations suggest divergent genetic etiologies. Mucosal melanomas generally present at a later stage, are more aggressive and carry a worse prognosis regardless of the stage at diagnosis. Establishing standardized treatment guidelines has been challenging due to the rarity of the disease. Early detection provides the best chance at survival but is often difficult due to anatomic location. Surgery remains the primary therapeutic intervention if complete resection is technically feasible given the anatomic location. Radiotherapy may be used to achieve local control when resection is not feasible, or adjuvantly to enhance locoregional control, but most studies have failed to demonstrate an improvement in overall survival. There are no consensus guidelines on the optimal systemic therapy, and regimens are often extrapolated from data based on therapies used to treat advanced cutaneous melanoma. Clinical trials, particularly utilizing newer targeted therapies and immunotherapies, are investigating novel treatment approaches.

Macroautophagy (autophagy hereafter) captures intracellular proteins and organelles and degrades them in lysosomes. The degradation breakdown products are released from lysosomes and recycled into metabolic and biosynthetic pathways. Basal autophagy provides protein and organelle quality control by eliminating damaged cellular components. Starvation-induced autophagy recycles intracellular components into metabolic pathways to sustain mitochondrial metabolic function and energy homeostasis. Recycling by autophagy is essential for yeast and mammals to survive starvation through intracellular nutrient scavenging. Autophagy suppresses degenerative diseases and has a context-dependent role in cancer. In some models, cancer initiation is suppressed by autophagy. By preventing the toxic accumulation of damaged protein and organelles, particularly mitochondria, autophagy limits oxidative stress, chronic tissue damage, and oncogenic signaling, which suppresses cancer initiation. This suggests a role for autophagy stimulation in cancer prevention, although the role of autophagy in the suppression of human cancer is unclear. In contrast, some cancers induce autophagy and are dependent on autophagy for survival. Much in the way that autophagy promotes survival in starvation, cancers can use autophagy-mediated recycling to maintain mitochondrial function and energy homeostasis to meet the elevated metabolic demand of growth and proliferation. Thus, autophagy inhibition may be beneficial for cancer therapy. Moreover, tumors are more autophagy-dependent than normal tissues, suggesting that there is a therapeutic window. Despite these insights, many important unanswered questions remain about the exact mechanisms of autophagy-mediated cancer suppression and promotion, how relevant these observations are to humans, and whether the autophagy pathway can be modulated therapeutically in cancer. See all articles in this CCR Focus section, "Cell Death and Cancer Therapy."

IMPORTANCE/OBJECTIVE:The treatment of multiple brain metastases (MBM) from melanoma is controversial and includes surgical resection, stereotactic radiosurgery (SRS), and whole-brain radiation therapy (WBRT). Several new classes of agents have revolutionized the treatment of metastatic melanoma, allowing some subsets of patients to have long-term survival. Given this, management of MBM from melanoma is continually evolving. OBJECTIVE:To review the current evidence regarding the treatment of MBM from melanoma. EVIDENCE REVIEW/METHODS:The PubMed database was searched using combinations of search terms and synonyms for melanoma, brain metastases, radiation, chemotherapy, immunotherapy, and targeted therapy published between January 1, 1995, and January 1, 2015. Articles were selected for inclusion on the basis of targeted keyword searches, manual review of bibliographies, and whether the article was a clinical trial, large observational study, or retrospective study focusing on melanoma brain metastases. Of 2243 articles initially identified, 110 were selected for full review. Of these, the most pertinent 73 articles were included. FINDINGS/RESULTS:Patients with newly diagnosed MBM can be treated with various modalities, either alone or in combination. Level 1 evidence supports the use of SRS alone, WBRT, and SRS with WBRT. Although the addition of WBRT to SRS improves the overall brain relapse rate, WBRT has no significant impact on overall survival and has detrimental neurocognitive outcomes. Cytotoxic chemotherapy has largely been ineffective; targeted therapies and immunotherapies have been reported to have high response rates and deserve further attention in larger clinical trials. Further studies are needed to fully evaluate the efficacy of these novel regimens in combination with radiation therapy. CONCLUSIONS AND RELEVANCE/CONCLUSIONS:At this time, the standard management for patients with MBM from melanoma includes SRS, WBRT, or a combination of both. Emerging data exist to support the notion that SRS in combination with targeted therapies or immune therapy may obviate the need for WBRT; prospective studies are required to fully evaluate the efficacy of these novel regimens in combination with radiation therapy.

UNLABELLED:Macroautophagy (autophagy hereafter) may promote survival and growth of spontaneous tumors, including melanoma. We utilized a genetically engineered mouse model of melanoma driven by oncogenic BrafV600E and deficiency in the Pten tumor suppressor gene in melanocytes to test the functional consequences of loss of the essential autophagy gene autophagy-related-7, Atg7. Atg7 deficiency prevented melanoma development by BrafV600E and allelic Pten loss, indicating that autophagy is essential for melanomagenesis. Moreover, BrafV600E-mutant, Pten-null, Atg7-deficient melanomas displayed accumulation of autophagy substrates and growth defects, which extended animal survival. Atg7-deleted tumors showed increased oxidative stress and senescence, a known barrier to melanomagenesis. Treatment with the BRAF inhibitor dabrafenib decreased tumor growth and induced senescence that was more pronounced in tumors with Atg7 deficiency. Thus, Atg7 promotes melanoma by limiting oxidative stress and overcoming senescence, and autophagy inhibition may be of therapeutic value by augmenting the antitumor activity of BRAF inhibitors. SIGNIFICANCE/CONCLUSIONS:The essential autophagy gene Atg7 promotes development of BrafV600E-mutant, Pten-null melanomas by overcoming senescence, and deleting Atg7 facilitated senescence induction and antitumor activity of BRAF inhibition. This suggests that combinatorial BRAFV600E and autophagy inhibition may improve therapeutic outcomes in patients whose tumors have BRAFV600E/K mutations, an approach currently being explored in clinical trials.

BACKGROUND:Type 1 insulin-like growth factor receptor (IGF-IR) signaling is often dysregulated in cancer. Cixutumumab, a fully human IgG1 monoclonal antibody, blocks IGF-IR and inhibits downstream signaling. The current study determined the recommended dose, safety, and pharmacokinetic (PK) profile of weekly or every-2-week dosing of cixutumumab. PATIENTS AND METHODS/METHODS:Two open-label, multicenter phase I studies evaluated weekly (3-15 mg/kg) or every-2-weeks (6-15 mg/kg) dosing of cixutumumab in patients with advanced solid tumors. Serial blood samples for PK were collected up to 168-336 h (day 8-15) following the first administration of cixutumumab. Efficacy was evaluated as best overall tumor response. RESULTS:A total of 24 and 16 patients were enrolled in the weekly and every-2-week dosing studies, respectively. Treatment-emergent adverse events (≥10%) included hyperglycemia, fatigue, anemia, nausea, and vomiting. Severe adverse events (AE) were infrequent; one serious AE (grade 3 electrocardiogram QT prolongation) was deemed possibly cixutumumab-related (10 mg/kg every-2-weeks). One death occurred due to disease progression (6 mg/kg weekly cohort). Maximum serum concentrations increased with dose. A maximum tolerated dose was not identified; pre-determined target serum minimum concentrations (60 μg/mL) were achieved with ≥6 mg/kg weekly and ≥10 mg/kg every-2-week dosing. Cixutumumab terminal elimination half-life is approximately a week (individual range, t1/2 = 4.58-9.33 days based upon 10 mg/kg every 2 weeks). Overall, stable disease was achieved in 25% of all patients. CONCLUSIONS:Cixutumumab was associated with favorable safety and PK profiles. A dosing regimen of 10 mg/kg every 2 weeks was recommended for subsequent disease-focused clinical trials.

Melanoma is a type of skin cancer arising from melanocytes and is increasing in incidence. Although complete surgical excision of early stage lesions may be curative, metastatic melanoma continues to be a major therapeutic challenge. Advances in understanding the molecular pathways that promote tumorigenesis and the interactions between melanoma cells and the immune system have resulted in the approval of several newly targeted agents and immunotherapy strategies for the treatment of advanced disease. Oncolytic virus immunotherapy is a new approach that uses native or attenuated live viruses to selectively kill melanoma cells and induce systemic tumor-specific immune responses. A variety of viruses are now in clinical development with the attenuated oncolytic herpesvirus encoding granulocyte-macrophage colony stimulating factor, known as talimogene laherparepvec, recently demonstrating an improvement in durable response rate in patients with advanced melanoma compared with granulocyte-macrophage colony stimulating factor alone. A major advantage of talimogene laherparepvec and related agents is the limited toxicity and ability to use each individual tumor as a source of antigen to generate a highly specific antitumor immune response. These agents are easily administered in the out-patient setting and may be a reasonable option for patients with limited metastatic tumor burden, those with a good performance status and without extensive prior treatment, and in those who cannot tolerate more difficult therapeutic regimens. Further investigation into the impact on overall survival as monotherapy and combination of oncolytic virus immunotherapy with other forms of immunotherapy merit high priority for further clinical application of these novel agents for the treatment of melanoma and perhaps other cancers as well.

Our laboratory previously described the oncogenic properties of metabotropic glutamate receptor 1 (mGluR1) in melanocytes. mGluR1 transformed immortalized mouse melanocytes in vitro and induced vigorous tumor formation in vivo. Subsequently, we observed the activation of PI3K/AKT in mGluR1-mediated melanocytic tumorigenesis in vivo. In particular, we identified AKT2 being the predominant isoform contributing to the activation of AKT. Suppression of Grm1 or AKT2 using an inducible Tet-R siRNA system resulted in a 60 or 30% reduction, respectively, in in vivo tumorigenesis. We show that simultaneous downregulation of Grm1 plus AKT2 results in a reduction of approximately 80% in tumor volumes, suggesting that both mGluR1 and AKT2 contribute to the tumorigenic phenotype in vivo. The discrepancy between the mild in vitro transformation characteristics and the aggressive in vivo tumorigenic phenotypes of these stable mGluR1-melanocytic clones led us to investigate the possible involvement of other growth factors. Here, we highlight a potential crosstalk network between mGluR1 and tyrosine kinase, insulin-like growth factor 1 receptor (IGF-1R).

Glutamate-triggered signal transduction is thought to contribute widely to cancer pathogenesis. In melanoma, overexpression of the metabotropic glutamate receptor (GRM)-1 occurs frequently and its ectopic expression in melanocytes is sufficient for neoplastic transformation. Clinical evaluation of the GRM1 signaling inhibitor riluzole in patients with advanced melanoma has demonstrated tumor regressions that are associated with a suppression of the mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase/protein kinase B (PI3K/AKT) pathways. Together, these results prompted us to investigate the downstream consequences of GRM1 signaling and its disruption in more detail. We found that melanoma cells with enhanced GRM1 expression generated larger tumors in vivo marked by more abundant blood vessels. Media conditioned by these cells in vitro contained relatively higher concentrations of interleukin-8 and VEGF due to GRM1-mediated activation of the AKT-mTOR-HIF1 pathway. In clinical specimens from patients receiving riluzole, we confirmed an inhibition of MAPK and PI3K/AKT activation in posttreatment as compared with pretreatment tumor specimens, which exhibited a decreased density of blood vessels. Together, our results demonstrate that GRM1 activation triggers proangiogenic signaling in melanoma, offering a mechanistic rationale to design treatment strategies for the most suitable combinatorial use of GRM1 inhibitors in patients.