PD-1 and PD-L1 inhibitors


PD-1 inhibitors and PD-L1 inhibitors are a group of checkpoint inhibitor anticancer drugs that block the activity of PD-1 and PDL1 immune checkpoint proteins present on the surface of cells. Immune checkpoint inhibitors are emerging as a front-line treatment for several types of cancer.
PD-1 and PD-L1 inhibitors act to inhibit the association of the programmed death-ligand 1 with its receptor, programmed cell death protein 1. The interaction of these cell surface proteins is involved in the suppression of the immune system and occurs following infection to limit the killing of bystander host cells and prevent autoimmune disease. This immune checkpoint is also active in pregnancy, following tissue allografts, and in different types of cancer.
NameTargetApproved
NivolumabPD-12014
PembrolizumabPD-12014
AtezolizumabPD-L12016
AvelumabPD-L12017
DurvalumabPD-L12017
CemiplimabPD-12018

History

The concept of blocking PD-1 and PD-L1 for the treatment of cancer was first published in 2001. Pharmaceutical companies began attempting to develop drugs to block these molecules, and the first clinical trial was launched in 2006, evaluating nivolumab. As of 2017, more than 500 clinical trials involving PD-1 and PD-L1 inhibitors have been conducted in more than 20,000 patients. By the end of 2017, PD-1/PD-L1 inhibitors had been approved for the treatment of nine forms of cancer.

Cancer immunotherapy

In the cancer disease state, the interaction of PD-L1 on the tumor cells with PD-1 on a T-cell reduces T-cell function signals to prevent the immune system from attacking the tumor cells. Use of an inhibitor that blocks the interaction of PD-L1 with the PD-1 receptor can prevent the cancer from evading the immune system in this way. Several PD-1 and PD-L1 inhibitors are being trialled within the clinic for use in advanced melanoma, non-small cell lung cancer, renal cell carcinoma, bladder cancer and Hodgkin lymphoma, amongst other cancer types.
Immunotherapy with these immune checkpoint inhibitors appears to shrink tumours in a higher number of patients across a wider range of tumour types and is associated with lower toxicity levels than other immunotherapies, with durable responses. However, de-novo and acquired resistance is still seen in a large proportion of patients. Hence PD-L1 inhibitors are considered to be the most promising drug category for many different cancers.
Not all patients respond to PD-1/PD-L1 inhibitors. The FDA has approved several assays to measure the level of PD-L1 expressed by tumor cells, in order to predict the likelihood of response to an inhibitor. PD-L1 levels have been found to be highly predictive of response. Higher mutation burden is also predictive of response to anti-PD-1/PD-L1 agents.
PD-1 and PD-L1 inhibitors are closely related to CTLA4 inhibitors, such as ipilimumab. PD-1 and CTLA-4 are both expressed on activated T cells, but at different phases of immune response.
Current clinical trials are evaluating anti-PD-1 and PD-L1 drugs in combination with other immunotherapy drugs blocking LAG3, B7-H3, KIR, OX40, PARP, CD27, and ICOS.
Goldkuhle et al. conducted Cochrane review in 2018 with prospectively planned and uncontrolled trials to measure the harms and benefits of nivolumab given to adults with a Hodgkin's lymphoma. The exact inclusion and exclusion criteria and information regarding the dose can be found in the original Cochrane review. In the included trials, most participants had a disease stage of III or higher. The authors of the review conducted an analysis to compared nivolumab to no treatment: The evidence is very uncertain about the effect of nivolumab on the overall survival, the quality of life, the progression-free survival, the response-rate, the adverse events with grade 3 or 4 and the serious adverse events. The follow-up had a range of 6 to 27 months and varied between the outcomes.

Therapeutics

PD-1

Pembrolizumab was developed by Merck and first approved by the Food and Drug Administration in 2014 for the treatment of melanoma. It was later approved for metastatic non-small cell lung cancer and head and neck squamous cell carcinoma. In 2017, it became the first immunotherapy drug approved for use based on the genetic mutations of the tumor rather than the site of the tumor. It was shown, that patients with higher non-synonymous mutation burden in their tumors respond better to the treatment. Both their objective response rate and progression-free survival was shown to be higher than in patients with low non-synonymous mutation burden.
Nivolumab was developed by Bristol-Myers Squibb and first approved by the FDA in 2014 for the treatment of melanoma. It was later approved for squamous cell lung cancer, renal cell carcinoma, and Hodgkin's lymphoma.
Cemiplimab was developed by Regeneron Pharmaceuticals and first approved by the FDA in 2018 for the treatment of cutaneous squamous cell carcinoma or locally advanced CSCC who are not candidates for curative surgery or curative radiation.

Experimental

Currently, many PD-1 inhibitors are under development:
Atezolizumab is a fully humanised IgG1 antibody developed by Roche Genentech. In 2016, the FDA approved atezolizumab for urothelial carcinoma and non-small cell lung cancer.
Avelumab is a fully human IgG1 antibody developed by Merck Serono and Pfizer. Avelumab is FDA approved for the treatment of metastatic merkel-cell carcinoma. It failed phase III clinical trials for gastric cancer.
Durvalumab is a fully human IgG1 antibody developed by AstraZeneca. Durvalumab is FDA approved for the treatment of urothelial carcinoma and unresectable non-small cell lung cancer after chemoradiation.

Experimental

At least two PD-L1 inhibitors are in the experimental phase of development.
Immunotherapies as a group have off-target effects and toxicities common to them. Some of these include interstitial pneumonitis, colitis, skin reactions, low levels of platelets and white blood cells, inflammation of the brain or spinal cord, neuromuscular adverse events including myositis, Guillain-Barré syndrome, myasthenia gravis; myocarditis and cardiac insufficiency, acute adrenal insufficiency, and nephritis. The most common kidney related changes are acute interstitial nephritis, followed by glomerular diseases and then tubular damage. The detailed mechanism of these adverse effects are not fully elucidated
When compared with standard chemotherapeutic agents, PD-1/PD-L1 inhibitors had a lower reported incidence of fatigue, sensory neuropathy, diarrhea, bone marrow suppression, loss of appetite, nausea, and constipation.