Targeting the tumor microenvironment by immunotherapy: part 2

Cancer therapy was traditionally centered on the neoplastic cells. This included mainly surgery, radiation, and chemotherapy, in some cases hormone therapy and to a lesser extent immunotherapy – all traditionally targeted to the highly proliferating mutated tumor cells. In view of our present understanding of the powerfull influence of the tumor microenvironment (TME) on cancer behavior and response – and lack of response – to treatment, this previously ignored constituent of cancer now has to be considered as an important, even indispensable target for therapy. The TME may be targeted both to its immune and to its nonimmune components. The various immune evasion elements of the TME should be targeted as well.

Ipilimumab experience in heavily pretreated patients with melanoma in an expanded access program at the University Hospital of Siena (Italy)

AIM OF STUDY

To evaluate the feasibility of ipilimumab treatment for metastatic melanoma outside the boundaries of clinical trials, in a setting similar to that of daily practice.

METHODS

Ipilimumab was available upon physician request in the Expanded Access Programme for patients with life-threatening, unresectable stage III/IV melanoma who failed or did not tolerate previous treatments and for whom no therapeutic option was available. Induction treatment with ipilimumab 10 mg/kg was administered intravenously every 3 weeks, for a total of 4 doses, with maintenance doses every 12 weeks based on physicians' discretion and clinical judgment. Tumors were assessed at baseline, Week 12, and every 12 weeks thereafter per mWHO response criteria, and clinical response was scored as complete response (CR), partial response (PR), stable disease (SD), or progressive disease. Durable disease control (DC) was defined as SD at least 24 weeks from the first dose, CR, or PR.

RESULTS

Disease control rate at 24 and 60 weeks was 29.6% and 15%, respectively. Median overall survival at a median follow-up of 8.5 months was 9 months. The 1- and 2-year survival rates were 34.8% and 23.5%, respectively. Changes in lymphocyte count slope and absolute number during ipilimumab treatment appear to correlate with clinical response and survival, respectively. Adverse events were predominantly immune related, manageable, and generally reversible. One patient died from pancytopenia, considered possibly treatment related.

CONCLUSION

Ipilimumab was a feasible treatment for malignant melanoma in heavily pretreated, progressing patients. A sizeable proportion of patients experienced durable DC, including benefits to long-term survival.

Complete regression of a previously untreated melanoma brain metastasis with ipilimumab

Anecdotal cases of partial or complete responses have been reported after ipilimumab therapy for stage IV melanoma with brain metastasis treated earlier by surgery or radiosurgery. We report the first case of ipilimumab monotherapy resulting in durable complete remission of untreated, progressive brain metastases in a patient with stage IV melanoma. This case and earlier reports provide support for the further evaluation of ipilimumab in melanoma patients with brain metastasis.

Continuous systemic corticosteroids do not affect the ongoing regression of metastatic melanoma for more than two years following ipilimumab therapy

Malignant melanoma is an aggressive skin cancer with no effective therapies currently approved for advanced disease. In the case presented, a 55-year-old female patient diagnosed with widespread disease from amelanotic desmoplastic melanoma was treated with 10 mg/kg ipilimumab as part of a phase II clinical trial (CA184-008). Prior to ipilimumab, three chemotherapeutic regimens had failed. Ipilimumab acts as a T-cell potentiator via blockade of cytotoxic T-lymphocyte antigen-4, a negative regulator of T-cell activation. Response to ipilimumab treatment was rapid, with a substantial drop in tumor volume within 12 weeks of treatment initiation. Based on the appearance of a new subcutaneous lesion, reinduction with ipilimumab was performed at Week 30. Following reinduction, the appearance of another small new lesion made the patient ineligible, as per protocol, for further dosing despite stabilization of her remaining lesions. Ipilimumab-associated immune-related adverse events were manageable with the use of treatment guidelines. It is of remarkable immunotherapeutic importance that no new lesions emerged and gradual tumor regression is still ongoing more than 2 years following the last dose of ipilimumab, despite daily administration of systemic corticosteroids to manage drug-induced AEs. The ongoing clinical response is maintained without any further antineoplastic treatment.

Novel immunotherapies as potential therapeutic partners for traditional or targeted agents: cytotoxic T-lymphocyte antigen-4 blockade in advanced melanoma

The successful management of advanced melanoma remains an unmet need because of a resolutely poor prognosis and therapeutic options with limited effectiveness. Dacarbazine and fotemustine are the only approved chemotherapeutic agents for advanced melanoma, yet neither alone or in combination regimens has been shown to extend survival in randomized clinical trials. The only agent to be approved for advanced melanoma in the US in more than 30 years is high-dose bolus interleukin-2, but its use is associated with high toxicity and cost, and it has also failed to show a survival benefit. Our expanding knowledge of the complex factors and pathways regulating immune function has led to the advent of novel immunotherapeutic agents. Among these are ipilimumab and tremelimumab - fully human, monoclonal antibodies directed against cytotoxic T-lymphocyte antigen-4 (CTLA-4). The pivotal role of CTLA-4 in regulating T-cell function is established, and a series of preclinical studies provided proof-of-concept evidence of the antitumor activity of anti-CLTA-4 antibodies in combination with vaccines or chemotherapy. Subsequently, anti-CTLA-4 antibodies have shown encouraging results in clinical trials in advanced melanoma. Recent progress in the understanding of melanoma genetics and tumorigenesis has led to potential new therapeutic targets. Molecular targeted agents that inhibit the proliferation and survival of metastatic melanoma cells offer potential partners for anti-CTLA-4 antibodies in combined modality regimens. Novel combinations are reviewed in the context of creating an immunosupportive environment in the host.

Targeting cytotoxic T-lymphocyte antigen 4 in immunotherapies for melanoma and other cancers

The immune system can simultaneously protect against tumor growth and sculpt resistant tumor strains. By a variety of mechanisms, anti-cytotoxic T-lymphocyte antigen (CTLA)-4 therapy may shift such opposing forces towards tumor elimination. In recent clinical trials, anti-CTLA-4 therapy induces durable responses that correlate with markers of immune activity, such as antigen-specific CD4+ or CD8+ cytokine release, antitumor antibody formation or cellular phenotype differentiation. However, some patients exhibit atypical responses to anti-CTLA-4 therapy, demonstrating transient/delayed responses or heterogeneity by lesion site. Such atypical responses may offer insight into the mechanism of anti-CTLA-4 therapy. The immunogram – a newly described graphical synthesis of treatment data and immune correlates in individual patients – may help us to confirm, reject or formulate new hypotheses regarding the mechanism of anti-CTLA-4 activity.

Modulation of CTLA-4 and GITR for cancer immunotherapy

The rational manipulation of antigen-specific T cells to reignite a tumor-specific immune response in cancer patients is a challenge for cancer immunotherapy. Targeting coinhibitory and costimulatory T cell receptors with specific antibodies in cancer patients is an emerging approach to T cell manipulation, namely "immune modulation." Cytotoxic T-lymphocyte antigen-4 (CTLA-4) and glucocorticoid-induced tumor necrosis factor family receptor (GITR) are potential targets for immune modulation through anti-CTLA-4 blocking antibodies and anti-GITR agonistic antibodies, respectively. In this review, we first discuss preclinical findings key to the understanding of the mechanisms of action of these immunomodulatory antibodies and the preclinical evidence of antitumor activity which preceded translation into the clinic. We next describe the outcomes and immune related adverse effects associated with anti-CTLA-4 based clinical trials with particular emphasis on specific biomarkers used to elucidate the mechanisms of tumor immunity in patients. The experience with anti-CTLA-4 therapy and the durable clinical benefit observed provide proof of principle to effective antitumor immune modulation and the promise of future clinical immune modulatory antibodies.