Tadalafil augments tumor specific immunity in patients with head and neck squamous cell carcinoma

Abstract

Purpose: To determine if phosphodiesterase 5 (PDE5) inhibitors can augment immune function in patients with head and neck cancer through inhibition of myeloid-derived suppressor cells (MDSC).

Experimental design: We performed a randomized, prospective, double blinded, placebo controlled, phase II clinical trial to determine the in vivo effects of systemic PDE5 inhibition on immune function in patients with head and neck squamous cell carcinoma (HNSCC).

Results: Tadalafil augmented immune response, increasing ex vivo T-cell expansion to a mean 2.4-fold increase compared with 1.1-fold in control patients (P = 0.01), reducing peripheral MDSC numbers to mean 0.81-fold change compared with a 1.26-fold change in control patients (P = 0.001), and increasing general immunity as measured by delayed type hypersensitivity response (P = 0.002). Tumor-specific immunity in response to HNSCC tumor lysate was augmented in tadalafil-treated patients (P = 0.04).

Conclusions: These findings demonstrate that tadalafil augments general and tumor-specific immunity in patients with HNSCC and has therapeutic potential in HNSCC. Evasion of immune surveillance and suppression of systemic and tumor-specific immunity is a significant feature of head and neck cancer development. This study demonstrates that a PDE5 inhibitor, tadalafil, can reverse tumor-specific immune suppression in patients with head and neck cancer, with potential for therapeutic application.

Figure 1

A. Schematic Representation of PDE5 Blockade on MDSC Function: PDE inhibition increases cGMP which results in destabilization of the iNOS mRNA, reduced synthesis of iNOS and ultimately less production of NO. It is also able to down-regulate the expression of IL4Rα resulting in a reduction of arginase-1 expression. Taken together, these effects lead to a reversal of the immunosuppressive properties of MDSCs. B. Tadalafil reduces MDSC function: Quantitative RT-PCR was performed on CD15 isolated peripheral blood cells. Tadalafil treatment resulted in: a decrease in Arg-1 production. Mean fold change pre- vs post-treatment for placebo 1.0, tadalafil 0.83 (p=0.004); a decrease in iNOS, mean placebo 1.02, tadalafil 0.66. (p=0.003); a decrease in Treg, mean placebo1.79, tadalafil 0.84, (p=0.0006); and a decrease in MDSC, mean placebo 1.28, tadalafil 0.81, (p<0.0001). The length of the box is the inter-quartile range and represents the middle 50% of the data. The horizontal line inside the box shows the median. The lower and upper hinges of the box represent the 25th and 75th percentiles, respectively. The vertical dashed lines extend from the box to the upper and lower 1.5 inter-quartile values from the upper and lower hinges. The filled circles represent the actual values of the fold change where potential outliers are indicated by open circles.

Figure 2. Tadalafil augments immune function

Fold increase in T cell expansion was determined following anti-CD3/CD28 stimulation. Expansion was significantly greater in tadalafil-treated arm 2.4 fold vs placebo 1.1 fold (p=0.003). Systemic immune responsiveness as measured by fold change in area of induration from a DTH response to Candida with an increase in response in tadalafil treated patients (p=0.002), Change in activated T cells as assessed by CD69 expression: peripheral CD4⁺ cells, and peripheral CD8⁺ cells. Two outliers with a large fold change in DTH area suppressed, these are included in Supplementary Figure 5. Figures reflect data points as in Figure 2.

Figure 3. Tadalafil increases HNSCC specific immunity

CFSE-labeled T cells obtained pre- and post-treatment were added to dendritic cells pulsed with the indicated tumor lysate of either a mixture of HPV+ and HPV- HNSCC cell lines or myeloma cell lines (U266, H929). Tumor specificity was determined after a 7-day co-culture by flow cytometry as CFSE^low/ IFNγ⁺ CD3 cells. Shown is the change in tumor specificity in the CD4⁺ T cells in the placebo or tadalafil treated groups (p=0.04). No significant changes in tumor specificity were observed in the CD8⁺ T cells.