Combination therapy with proteasome inhibitors and TLR agonists enhances tumour cell death and IL-1β production

Abstract

Proteasome inhibitors have emerged as an effective therapy for the treatment of haematological malignancies; however, their efficacy can be limited by the development of tumour resistance mechanisms. Novel combination strategies including the addition of TLR adjuvants to increase cell death and augment immune responses may help enhance their effectiveness. Although generally thought to inhibit inflammatory responses and NF-κB activation, we found that under specific conditions proteasome inhibitors can promote inflammatory responses by mediating IL-1β maturation and secretion after TLR stimulation. This was dependent on the timing of proteasome inhibition relative to TLR stimulation where reversal of treatment order could alternatively increase or inhibit IL-1β secretion (P < 0.001). TLR stimulation combined with proteasome inhibition enhanced cell death in vitro and delayed tumour development in vivo in NOD SCID mice (P < 0.01). However, unlike IL-1β secretion, cell death occurred similarly regardless of treatment order and was only partially caspase dependent, possessing characteristics of both apoptosis and necrosis as indicated by activation of caspase-1, 3, 8 and RIP3 phosphorylation. Although stimulation of various TLRs was capable of driving IL-1β production, TLR4 stimulation was the most effective at increasing cell death in THP-1 and U937 cells. TLR4 stimulation and proteasome inhibition independently activated the RIP3 necroptotic pathway and ultimately reduced the effectiveness of caspase/necroptosis inhibitors in mitigating overall levels of cell death. This strategy of combining TLR stimulation with proteasome inhibition may improve the ability of proteasome inhibitors to generate immunogenic cell death and increase anti-tumour activity.

Biological and therapeutic implications of a unique subtype of NPM1 mutated AML

“…Specifically, the increased activity of the TLR signaling pathway has been associated with hematopoietic and AML differentiation 36 , 37 . Activating TLRs using agonists represents a promising avenue for cancer immunotherapy and there is accumulating evidence supporting a potential role for such agonists in the treatment of AML 38 , 39 . The differential activity of the TLR pathway among the subtypes might present an opportunity for TLR agonist-based therapy.…”

The Human Cytomegalovirus US31 Gene Predicts Favorable Survival and Regulates the Tumor Microenvironment in Gastric Cancer

“…For example, TNF-a is an inflammatory mediator and functions as an anti-tumorigenic factor at high concentrations (35). IL-1b is also reported to mediate anti-tumor responses through T lymphocytes (36,37). Our previous studies found that US31 interacted with NF-kB2 (22), leading to phosphorylated P100 polyubiquitination and activating NF-kB2 (22).…”

Surface Immunogenic Protein of Streptococcus Group B is an Agonist of Toll-Like Receptors 2 and 4 and a Potential Immune Adjuvant

“…To identify whether apoptosed BM-DC cells were associated to caspase-3, BMDCs were pulsed with increased concentrations of rSIP for 12 h. Apoptosis of BM-DCs pulsed with rSIP was not associated to caspase-3 activation (Figure 4H). These results indicate that rSIP is nontoxic at concentrations below 0.1 µg/mL and that rSIP can be associated to BM-DC necroptosis, a form of cell death known to involve inflammasome activation and IL-1β secretion, which proceeds in a caspase-independent manner [15].…”