We have tested TAI 1 with the hERG assay, which as sesses the most common mechanism involved in drug induced prolongation of QT interval, which increases the risk of ventricular tachyarrhythmia through the in hibition of potassium ion flow and may lead to sudden cardiac death. The hERG channel assay revealed a competition IC50 1000 times that of cancer cell GI50, suggesting that this compound has little po tential of cardiac toxicity through the hERG channel at the therapeutic doses. In summary, TAI 1 exhibits high specificity to cancer cells and to target and shows no cardiac toxicity by hERG. TAI 1 is synergistic with some commonly used cytotoxic drugs Synergy with currently available anti cancer drugs dem onstrates possibility of a compound to be utilized in combinatorial treatment approach.

To determine Cyclobenzaprine ic50 pos sible synergistic combinations, the effects of TAI 1 in combination with various cytotoxic drugs were evalu ated. TAI 1 sensitive cancer cells were treated with an appropriate ratio of doses of cytotoxic agents to TAI 1 determined by corresponding drug GI50, as shown in Table 3 and MTS assay used to determine cellular proliferation. Combination index was calculated from the GI50s obtained to represent additive, synergistic or antagonistic effects. TAI 1 was synergistic with doxorubicin, topotecan, and paclitaxel, but not synergistic with sorafenib and the novel src inhibitor KX 01. Role of RB and P53 in TAI 1 cellular sensitivity TAI 1 is active on a wide spectrum of cancer cell lines, however, 5 cell lines were resistant to TAI 1.

To explore possible resistance mechanisms of TAI 1, we evaluated the role of retinoblastoma protein RB, and P53, another oncogene in the same category as RB, which might provide a cellular escape mechanism. The RB and P53 tumor suppressors are both critical players in DNA damage checkpoint. buy Etizolam A cross tabulation comparison of the RB and P53 gene status versus sensitivity to TAI 1 revealed an interesting pattern of response to Hec1 inhibitor TAI 1. To quantitate Hec1 protein expression levels, we ana lyzed the expression levels of the Hec1 protein by west ern blotting and quantitated protein levels using HeLa as standard, and high expression determined as 50% HeLa expression levels. As shown in Figure 6, cell lines showing a good cellular proliferative response to TAI 1 had a much higher level of expression of Hec1 compared with resistant cell lines.

Table 4 shows the relation ship between the expression of Hec1 and the status of the markers. High level expression of Hec1 was associ ated with a better response to the Hec1 inhibitor TAI 1. In the same analysis, a higher proportion of wild type P53 cell lines showed more resistance to Hec1 inhibitor TAI 1 compared with those with mutant P53. When the Hec1 expression level was combined with the P53 gene status, the correlation was more tight statistically.