BLOCKADE OF CTLA-4 AND PD-1 ENHANCED TUMOR REGRESSION IN MELANOMA

One of the primary roles of the immune system is the specific identification and elimination of tumor cells on the basis of their expression of tumor-specific antigens or molecules induced by cellular stress. This process is referred to as tumor immune surveillance. In this process the immune system recognizes malignant and/or pre-malignant cells and removes them. However, tumor cells do escape from tumor immune surveillance, and therefore, therapies targeted to enhance antitumor immunity is currently in development.

Blockade of immune checkpoints  is the most promising approach to activate therapeutic antitumour immunity. Immune checkpoints refer to a group of inhibitory pathways connected into the immune system that are important for maintaining self-tolerance. In peripheral tissues immune surveillance also modulates the duration and amplitude of physiological immune responses in order to minimize collateral tissue damage. Studies have suggested that tumor cells adopt many immune-checkpoint pathways as a major mechanism of immune resistance. Immune checkpoint receptors cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4, also known as CD152) and programmed death 1 (PD-1) receptor appear to play important roles in antitumor immunity and have been most actively studied in the context of clinical cancer immunotherapy.

monoclonal3CTLA-4 is expressed on T cells and down modulates the amplitude of T cell activation. Several preclinical studies demonstrated significant antitumor responses following blockade of CTL4-A with limited immune toxicities. This led to the development of two fully humanized  CTLA-4 antibodies ipilimumab and tremelimumab. In clinical trials, ipilimumab demonstrated survival benefits for patients with metastatic melanoma, and was approved by the US Food and Drug Administration (FDA) for the treatment of advanced melanoma in 2010.

On the other hand, PD-1limits T cell effector functions within tissues. Tumor  cells block antitumor immune responses in the tumor microenvironment by upregulating ligands (PDL1 and PDL2) for PD1. Several studies detected increased PD1 expression by tumor infiltrating lymphocytes and the increased expression of PD1 ligands in melanoma, ovarian, lung, renal-cell cancers and in lymphomas. This provided an important rationale to target PD1 in order to enhance antitumor immunity. The fully human antibody nivolumab was found to produce durable objective responses in patients with melanoma, renal-cell cancer, and non-small-cell lung cancer.

Even though individual blocking of CTLA-4 and PD-1 have shown substantial clinical antitumor activity, studies suggest that blocking a single inhibitory receptor only leads to up-regulation of the unblocked pathway. Therefore, in order  to enhance antitumor immunity within the tumor microenvironment it appears to require simultaneous blockade of multiple negative co-stimulatory receptors. In preclinical studies, concurrent inhibition of CTLA-4 and PD-1 resulted in more pronounced antitumor activity than blockade of either pathway alone. On the basis of these observations, a phase I study was conducted to investigate the safety and efficacy of combined inhibition of CTLA-4 and PD-1in advanced melanoma patients and published recently in The New England Journal of Medicine (July 11, 2013). In their study, Wolchok and collagues (2013) treated 53 patients concurrently, and 33 patients sequentially with nivolumab and ipilimumab. Rapid responses were observed in concurrent-regimen cohorts as compared with sequential-regimen cohorts. The objective response rate in the concurrent-regimen cohorts was 40% along with 53% patients exhibited tumor regression of 80% or more. The objective response rate in the sequenced-regimen cohorts was 20% and 13% patients had tumor regression of 80% or more. In both groups, treatment related adverse events were managed with the use of immunosuppressants.

Collectively this study suggested that combined blockade of CTLA-4 and PD-1 would be more effective to enhance antitumor immunity compared to single inhibition of either CTLA-4 or PD-1.

References:

1.  Swann, J.B. and M.J. Smyth, Immune surveillance of tumors. J Clin Invest, 2007. 117(5): p. 1137-46.

2.   Pardoll, D.M., The blockade of immune checkpoints in cancer immunotherapy. Nat Rev Cancer, 2012. 12(4): p. 252-64.

3.   Topalian, S.L., et al., Safety, activity, and immune correlates of anti-PD-1 antibody in cancer. N Engl J Med, 2012. 366(26): p. 2443-54.

4.   Wolchok, J.D., et al., Nivolumab plus ipilimumab in advanced melanoma. N Engl J Med, 2013. 369(2): p. 122-33.

Tumor Immunotherapies Combine Big for Synergy in Phase I Trials

There are currently two immune cell targeting cancer_immunotherapyimmunotherapeutic agents that have received FDA approval for treatment of various malignancies.  The first approved in 2010 was the autologous dendritic cell vaccine Provenge (Sipuleucel-T) by Dendreon Corporation, for hormone refractory metastatic prostate cancer.  A second immunotherapeutic gaining FDA approval in 2011 for late stage melanoma, was an antibody called Ipilimumab, which inhibits CTLA-4, a major negative regulator of T cell activation.  Antagonists to PD-1 such as Nivolumab and/or PD-L1, another receptor/ligand pair of T cell negative regulators, are expected to join this crowd by 2015.  However, early results from combinatorial immunotherapeutics trials have demonstrated that significant synergy may be achieved by combining several immunotherapeutic modalities. A report in the June edition of The New England Journal of Medicine by Wolchok et al., demonstrates impressive synergistic results with combination therapy of Ipilimumab and Nivolumab in achieving deep and durable tumor regression in patients with advanced metastatic melanoma.

CTLA-4 and PD-1 are negative regulatory immune checkpoint inhibitors expressed on activated T cells and share homology with the TCR co-stimulatory receptor CD28.  CTLA-4 strongly competes with CD28 for binding to CD80 (B7-1) and CD86 (B7-2) on antigen presenting cells thereby limiting CD28-activation signals, and furthermore recruits inhibitory molecules into the TCR signaling synapse.  PD-1 interacts with ligands homologous with the B7 family, PD-L1 (B7H1) and PD-L2 (B7-DC), which are upregulated on tumor and stromal cells and activated antigen presenting cells.  PD-1 interaction with its ligands leads to recruitment of SHP1 and SHP2 phosphatases to the immune synapse, resulting in inhibition of TCR-mediated signaling.  PD-1 and CTLA-4 are considered non-redundant in their functions, and thus blocking both of these has been proposed to have a synergistic effect on T cell function in cancer, which was previously demonstrated in murine tumor models.

In previous clinical trials, Bristol-Myers Squibb’s Ipilimumab (MDX-010, Yervoy, IgG1) with or without a gp100 peptide vaccine extended overall survival of previously treated metastatic melanoma patients by almost 4 months versus gp100 peptide alone.  In a second study, Ipilimumab plus darcarbazine versus darcarbazine alone was tested in previously untreated metastatic melanoma patients.  The addition of Ipilimumab to the darcarbazine regimen extended overall survival by approximately two months, and lent to significantly higher survival rates at 1, 2, and 3 years later.  Bristol-Myers Squibb’s PD-1 blocking antibody (BMS-936558, IgG4) showed significant clinical efficiency in metastatic or advanced non–small-cell lung cancer, melanoma, and renal-cell cancer.

In this dose-escalation phase I trial reported on by Wolchok et al., 53 patients with advanced melanoma were concurrently treated with Ipilimumab and Nivolumab, and 33 patients received sequenced treatment.  Although the primary goal of a phase I trial is to evaluate safety, the clinical responses of the concurrently treated patients were exciting enough to garner much attention.  In the concurrent regimen, 40% of patients had an objective response (modified WHO criteria), and 16 patients had a reduction in their tumor burden by 80% or more at 12 weeks, 5 being complete responses. Not only were responses faster and more pronounced than the previous clinical trials evaluating these inhibitors alone, but in the responding patients, the reduction in tumor burden was quite durable over the course of the study.  Thus, results from phase III clinical trials comparing the combination to the inhibitors alone will be eagerly awaited.  As an interesting note, tumor expression of PD-L1 has been proposed to be an indication of efficacy for Nivolumab.  However, even in patients with PD-L1-negative tumors, responses to this combination regimen were observed.

Despite the strong promise of these inhibitors in combination, adverse events were notably higher than the inhibitors had exhibited alone in previous trials.  Although no treatment-related deaths were reported, 72% of patients exhibited grade 3 or 4 adverse events, 53% of patients exhibited treatment-related grade 3 or 4 adverse events, and 21% of patients discontinued therapy due to treatment-related adverse events.  Adverse events were however manageable with either immunosuppressant or hormone-replacement therapies.

Many different cancer immunotherapeutics are now being tested in clinical trials, including a number of therapies combining immunotherapeutic modalities in the hopes to achieve synergy.  The results from the current trial indicate that anti-tumor T cells are not only present in tumor-bearing patients, but when uninhibited, can lend significantly to tumor-killing.  This is truly an exciting time for cancer immunology.

Further Reading:

Nivolumab plus Ipilimumab in Advanced Melanoma.  Wolchok JD, Kluger H, Callahan MK, Postow MA, Rizvi NA, Lesokhin AM, Segal NH, Ariyan CE, Gordon RA, Reed K, Burke MM, Caldwell A, Kronenberg SA, Agunwamba BU, Zhang X, Lowy I, Inzunza HD, Feely W, Horak CE, Hong Q, Korman AJ, Wigginton JM, Gupta A, Sznol M. N Engl J Med. 2013 Jun 2.

Safety, Activity, and Immune Correlates of Anti–PD-1 Antibody in Cancer. Topalian, S.L. et al. N. Engl. J. Med. 366, 2443–2454 (2012).

Improved Survival with Ipilimumab in Patients with Metastatic Melanoma.  Hodi, F.S. et al. N. Engl. J. Med. 363, 711–723 (2010).

Ipilimumab plus dacarbazine for previously untreated metastatic melanoma.  Robert C, Thomas L, Bondarenko I, O’Day S, M D JW, Garbe C, Lebbe C, Baurain JF, Testori A, Grob JJ, Davidson N, Richards J, Maio M, Hauschild A, Miller WH Jr, Gascon P, Lotem M, Harmankaya K, Ibrahim R, Francis S, Chen TT, Humphrey R, Hoos A, Wolchok JD. N Engl J Med. 2011 Jun 30;364(26):2517-26.

Ipilimumab: an anti-CTLA-4 antibody for metastatic melanoma.  Lipson EJ, Drake CG. Clin Cancer Res. 2011 Nov 15;17(22):6958-62.