Canine squamous cell carcinoma cell lines with high expression of survivin are sensitive to survivin inhibitor YM155

Commitment toward cell death by activation of autophagy with survivin inhibitor YM155 in two canine squamous cell carcinoma cell lines with high expression of survivin

Canine squamous cell carcinoma (SCC) is difficult to treat if local therapy is not feasible. Recently, survivin inhibitor YM155 was shown to have growth inhibitory activity on high-survivin-expressing canine SCC cell lines HAPPY and SQ4. Here, the mechanisms underlying the effect of YM155 on these cell lines were investigated. YM155 induced cleavage of poly(ADP-ribose) polymerase (PARP) in HAPPY, but not in SQ4 cells. Analyzing two autophagy markers, the level of microtubule-associated protein 1 light chain 3 (LC3)-II and the LC3-II/LC3-I ratio, indicated that YM155 activates autophagy in both cell lines, and this activation occurs prior to PARP cleavage in HAPPY cells. Moreover, inhibition of autophagic flux by chloroquine almost completely prevented the toxic effect of YM155 in both cell lines. Although there are differences in their eventual cell death type, both cell lines may be committed to cell death by activation of autophagy with YM155. Activation of autophagy is likely to be a key mechanism in the growth-inhibitory effects of YM155 in these lines. These data provide new insights into the cytotoxic mechanism of YM155 in canine SCC cells.

Foxp3+ Regulatory T Cells Associated With CCL17/CCR4 Expression in Carcinomas of Dogs

Regulatory T cells (Tregs) can be targeted in cancer immunotherapy. A previous study has shown that the chemokine CCL17 and the receptor CCR4 play a role in Treg recruitment in canine urothelial carcinoma. Here, we describe the association of tumor-infiltrating Tregs with CCL17/CCR4 expression in dogs with other carcinomas. In this study, we investigated 23 dogs with mammary carcinoma, 14 dogs with oral squamous cell carcinoma, 16 dogs with pulmonary adenocarcinoma, and 8 healthy control dogs. Immunohistochemistry showed that Foxp3⁺ Tregs and CCR4⁺ cells were increased in the tumor tissues of mammary carcinoma, squamous cell carcinoma, and pulmonary adenocarcinoma, when compared with the healthy tissues. The number of CCR4⁺ cells was associated with that of Foxp3⁺ Tregs. Double immunofluorescence labeling confirmed that most tumor-infiltrating Foxp3⁺ Tregs expressed CCR4. In vitro, canine carcinoma cell lines expressed CCL17 mRNA. Quantitative RT-PCR (reverse transcriptase-polymerase chain reaction) showed that CCL17 mRNA expression in canine carcinomas was increased approximately 10- to 25-fold relative to that of healthy tissues. These results suggest that the CCL17/CCR4 axis may drive Treg recruitment in a variety of canine carcinomas. CCR4 blockade may be a potential therapeutic option for tumor eradication through Treg depletion.