STAT3 inhibitor TTI-101 effectively intercepts bladder cancer in a carcinogen-induced rat bladder tumor model

Bladder cancer (BC) is the 9th most common cancer worldwide. Most bladder tumors are detected and treated at the non-muscle invasive (NMIBC) stage. However, tumors recur frequently, many progress to MIBC and metastasize contributing to significant mortality. Rising incidence and mortality in BC underscore the need to develop new regimen for its management. Transcriptional factor Signal transducer and activator of transcription 3 (STAT3) regulates cell proliferation through inflammation and immune responses. Its activation is highly regulated in normal cells but in cancers including BC, it is constitutively active. Expression of dominant-negative STAT3 was shown to inhibit tumor formation in nude mice. Earlier we and others reported that STAT3 inhibitors reduces BC cell survival and proliferation. In the present study, we determined pharmacodynamic pSTAT3 inhibitory effect of STAT3 inhibiting small molecules (GLG-302, SH5-07, TTI-101) in-vitro BC cells and in-vivo rat tumors. TTI-101 was further evaluated for its potential to intercept BC in a N-butyl-N-(4-hydroxyl)-nitrosamine (BBN)-rat BC model. Female F344 rats were randomized into a placebo, STAT3 (n=24) and Sulindac (n=18) intervention groups. Eight-weeks of age, rats were given BBN by oral gavage (150mg/dose; 2x/week for 8 weeks). Drug treatment was initiated at papilloma stage i.e., ~10 weeks after last BBN. Rats in intervention groups received TTI-101 at 25 or 75mg/kg body weight by oral gavage (5x/week) for 20 weeks. Sulindac was administered at 10mg/kg BW as a comparator. All drugs were formulated using 60% labrasol:40% PEG400. Bladder tumors were assessed at ~45 weeks of age. TTI-101 did not cause any overt-toxicities. BBN-induced bladder tumors in all rats, resulting in larger bladders in placebo group (0.31±0.06g; Mean±SEM). Importantly, bladder weights in TT1-101 25mg/kg and 75mg/kg groups were 0.21±0.06mg (32% inhibition; p>0.05) and 0.13±0.01g (58% inhibition; p<0.01) when compared to the placebo. Sulindac treatment had non-significant 46% inhibition (0.17±0.02g; p=0.07). In the placebo group, about half of all rats developed large bladder tumors (>200mg; 50% incidence). Interestingly, significantly fewer rats developed such tumors with TTI-101 25-mg/kg (17% incidence; p<0.05) and at 75mg/kg BW dose (8% incidence; p<0.005) in a dose dependent manner (67%-83% less respectively). Thus, STAT3 inhibition with TTI-101 resulted in a dose dependent inhibition of bladder tumors growth. Biomarker and gene expression analysis suggested modulation of critical tumor promoting pathways with decrease in pSTAT3 expression. Collectively, our study demonstrated that STAT3 inhibition using TTI-101 can intercept bladder tumor growth and warrants further investigation in clinical trials. (Project funded in whole with Federal funds from the NCI-NIH, DHHS, under Contract No. 75N91019D00020-75N91020F00005).