Treatment of advanced HCC- current approaches, recent advancements, emerging therapies

Immunotherapy 

There are many surgical treatment options for the treatment of HCC. However, resection or transplantation has limited effectiveness due to a low classification rate for surgery and a high 5-year recurrence rate ranging up to 70% after surgery. [30] This is related to the late diagnosis of HCC, which in most patients is at an advanced stage. Treatment is then based on a combination of targeted therapy, chemotherapy, or radiotherapy. Recently, immunotherapy has also been included in the treatment of HCC.  

Continuous exposure of the liver to bacterial components and dietary antigens from the gastrointestinal tract led to the creation of an immune microenvironment consisting of Kupffer cells, hepatic stellate cells, sinusoidal hepatic endothelial cells, natural killer (NK) cells, gamma-delta T cells, and dendritic cells. [31] When the liver is damaged or infected, the protective response is initiated by cytokines, growth factors, chemokines, and interactions with the immune microenvironment of the liver, the incorrect regulation of which could result in the development of cancer. [32] Zhang et al. in their study found that hypoxia- and inflammation-related hypoxia-inducible factor 1α (HIF-1α) can stimulate the excessive expression of IL-1β in tumor-associated macrophages (TAMs), which, thanks to positive feedback, can induce the production of HIF-1α and facilitates the process of epithelial-mesenchymal transition (EMT) leading to metastatic progression. [33] Other important cytokines involved in the pathogenesis of HCC are IL-6, IL-11, and lncRNA activated by TGF-β (lncRNA-ATB). [32] Patients with HCC usually have an increased number of Tregs, which can inhibit the function of CD8 + T cells and thus the elimination of tumor cells. [34] Additionally, continuous antigen stimulation leads to the exhaustion of T cells and thus an increase in the expression of co-inhibitory signaling molecules such as cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), programmed cell death protein 1 (PD-1) and lymphocyte-activation gene 3 (LAG-3). [35] 

The study of immune checkpoint inhibitors, i.e. monoclonal antibodies directed against extracellular ligands involved in suppressing the antitumor immune response, allowed the recognition on the basis of clinical trials of three categories of molecular targets, PD-1, CTLA-4, and LAG-3, which are intended to restore the antitumor capacity of lymphocytes T. [36] Compared to ICI (immune checkpoint inhibitor) monotherapy, combination therapy targeting several immune checkpoints is associated with better treatment outcomes, but the increased efficacy is associated with potential increase in immune-related adverse events. [32] 

Nivolumab is a human anti-PD-1 IgG4 monoclonal antibody directed against PD-1. [37] It is used as a second-line therapy in the treatment of HCC after approval by the FDA in 2017. The CheckMate 040 (NCT01658878) study evaluated nivolumab in combination with ipilimumab in patients treated with sorafenib as a first-line therapy in the treatment of advanced HCC, while the CheckMate 459 study (NCT02576509) compared nivolumab with sorafenib. The results from the first study led to FDA approval in 2020 of this regimen for the treatment of patients with advanced HCC who were previously treated with sorafenib. The results of the second study showed that there was no significant difference in OS, but the use of immunotherapy showed a lower incidence of grade 3 to 4 adverse effects, and improvement in patients’ quality of life, so nivolumab may be an alternative treatment option for patients who cannot undergo therapy with tyrosine kinase inhibitors or antiangiogenic therapy. [38]. Currently, the monoclonal antibody atezolizumab is known, which binds to the PD-L1 protein (programmed death-ligand 1), blocking the binding site of PD-1. The IMbrave150 study (NCT03434379) compared atezolizumab therapy in combination with the antiangiogenic bevacizumab with a group of patients treated with sorafenib. This study showed statistically significantly better OS and PFS with monoclonal antibody immunotherapy compared to sorafenib. [39, 40] Another known monoclonal antibody is pembrolizumab. The phase II KEYNOTE-224 study (NCT02702414) tested the effectiveness of pembrolizumab monotherapy in patients with HCC previously treated with sorafenib (cohort 1) and with no prior systemic therapy (cohort 2), and the results in the study groups were better in terms of safety profile and OS. [41, 42] Similar effectiveness and safety were demonstrated by pembrolizumab in combination with the best supportive care (BCS) in the phase III KEYNOTE-394 study (NCT03062358), where the study group included Asian patients previously treated with sorafenib or oxaliplatin-based chemotherapy. Compared to the placebo plus BCS group, pembrolizumab showed statistically significant improvement in OS and PFS, as well as in the objective response rate (ORR). The findings of these studies demonstrated a consistent clinical benefit for pembrolizumab monotherapy in advanced HCC. The phase 3 KEYNOTE-937 study (NCT03867084), where pembrolizumab is being tested as adjuvant therapy is undergoing. [43] 

The CTLA-4 protein, a CD28 homolog, prevents the binding of CD28 to CD80 and CD86, which is necessary for optimal T-cell activation. Moreover, it reduces the activity of helper T cells, increasing Treg activity, which leads to suppression of the immune response. A phase I/II study (NCT02519348) compared tremelimumab, a monoclonal antibody against CTLA-4, in combination with durvalumab (T300+D) with tremelimumab or durvalumab monotherapy. The results showed that combination therapy was associated with overall treatment benefits and the most encouraging benefit-risk profile due to unique pharmacodynamic activity. [44] In the phase III HIMALAYA study (NCT03298451) the T300 + D regimen and durvalumab monotherapy were evaluated versus sorafenib. T300 + D, which a single dose is known as STRIDE (Single Tremelimumab Regular Interval Durvalumab) displayed efficacy and a favorable benefit-risk profile versus sorafenib. [45] The regimen of two ICIs that block CTLA-4 and PD-L1 is the first-line treatment for adults with advanced or unresectable HCC in the EU. [46] 

LAG-3 present in CD8+ T cells binds to MHC class II molecules, and its increased expression correlates with dysfunction of T cells. [32] Zhou et al. showed that after using antibodies against PD-L1, TIM-3 (mucin domain containing-3), or LAG-3 (lymphocyte-activation gene 3), T lymphocytes respond to HCC antigens. [47] TIM-3 is present in TAM cells, and its increased expression correlates with poor prognosis of HCC patients. [48] The effectiveness of TIM-3-targeted therapies remains uncertain, but studies are currently underway using the anti-TIM-3 antibody, Colbolimab, LY3321367, or sabatolimab. [49]  

Due to the role of TGF-β in creating a tumor microenvironment conducive to growth and metastasis, as well as by hindering the infiltration of T lymphocytes into the tumor center, blocking the action of this cytokine has become another therapeutic target. [32] The discovery of the synergism of the effect of TGF-β blockade and anti-PD-L1 antibodies allowed the consideration in a clinical trial (NCT02423343) of the combination of galunisertib with nivolumab in the treatment of recurrent or refractory non-small cell lung cancer (NSCLC) or hepatocellular carcinoma (HCC). The results showed that the combination is well tolerated. [50] The ongoing phase III CheckMate 9DX study (NCT03383458) is investigating if nivolumab will improve recurrence-free survival (RFS) compared to placebo in HCC patients who have undergone resection or local ablation but are at high risk of recurrence. A bifunctional inhibitor bintrafusp (M7824) targeting PD-L1 and the extracellular domain of TGFβR2 was also created, which have been tested in studies: NCT02517398, NCT02699515, NCT03840915, and NCT04246489. The recurring bleeding adverse events were reported, so the dose reduction was chosen. Further investigation is needed to evaluate the effectiveness of bintrafusp. [51] 

ICIs can be combined not only with each other, but also with radiotherapy, FGFR inhibitors, tyrosine kinase inhibitors (TKI), SBRT, TACE, or chemotherapy. The combination of ICI + TKI in the first-line setting of metastatic disease is being investigated in several phase III trials, such as, the LEAP-002 trial (NCT03713593) evaluating lenvatinib plus pembrolizumab compared with placebo, and the trial NCT03764293 with evaluation of camrelizumab (SHR-1210) plus apatinib vs. sorafenib. [32, 52] The ORIENT-32 trial (NCT03794440) evaluated the combination of sintilimab (a PD-1 inhibitor) plus IBI305, a bevacizumab biosimilar, versus sorafenib. The results showed that the combination has significantly greater OS and PFS than sorafenib which could provide a novel treatment option for patients with unresectable, HBV-associated HCC patients. [53] 

In a phase II study (NCT03092895), previously untreated patients with advanced primary HCC received a combination of camrelizumab (anti-PD-1) plus FOLFOX4 (fluorouracil + calcium folinate + oxaliplatin) or GEMOX (gemcitabine and oxaliplatin). The results showed tolerability and preliminary antitumor activity. [54] The aim of the phase III study (NCT03605706) is to demonstrate the effectiveness of the combination of camrelizumab with FOLFOX4 compared to placebo with FOLFOX4 in the treatment of HCC. [36] ICI can also be used in combination with TACE, whose safety and effectiveness are being investigated in the phase II/III TACE-3 study (NCT04268888), IMMUTACE study (NCT03572582), TRIPLET study (NCT04191889) and LEAP-012 study (NCT04246177). [36] The combination of radiotherapy (SBRT) and ICI (Atezolizumab/Bevacizumab) is being explored in clinical trial NCT04857684. The evaluation of this therapy is being investigated in the other clinical trial NCT05137899 in HCC patients with the presence of portal vein tumour thrombus (PVTT). [55] (Table ) 

Thanks to CRISPR-Cas9 technology, there has been a revolution in CAR-T immunotherapy. The treatment involves genetic modification of T lymphocytes using retroviruses or lentiviruses, which causes proliferation when a specific antigen is recognized, and when the appropriate number is reached, the lymphocytes are injected into the patient to kill cancer cells. The action is hindered by inhibitory receptors on the surface of T cells such as PD-1, CTLA-4, and LAG-3, which may lower the effectiveness of CAR-T. [32] CRISPR-Cas9, by disrupting the expression of genes encoding these surface receptors, can significantly increase the effectiveness of CAR-T. [56, 57] Due to the fact that interleukins such as IL-12, IL-15, IL-18, and IL-7 are overexpressed through retrovirus or lentivirus, which may lead to T cell exhaustion by producing too many cytokines, CRISPR/Cas9 can be used to knock out the TRAC gene. Without this gene, cytokine production will be inhibited. [58] CAR-T therapy is an opportunity for patients with strong anti-cancer properties, as well as a great opportunity to identify new checkpoints of the immune system. [32] Currently, more than 20 phase I/II CAR-T cell clinical trials for HCC are ongoing. [59]