This observation prompted our further exploration of markers for TAI 1 response, which may have clinical implications for personalized therapy. A number of known cellular factors were assessed for their impact on the cellular response to TAI 1. The expression of Hec1, its interacting partner RB, and P53, a tumor suppressor like RB, were evaluated based on possible crosstalk of pathways. The profile in Table 1 shows a possible association of the sta tus of the tumor suppressors with cellular sensitivity to TAI 1. Analysis of the three factors indicate that the participation of RB is nominal, however, the in vitro siRNA studies show that RB may play a role in TAI 1 sensitivity. The impact of RB remains to be clarified in future biomarker studies.

In contrast, the combined markers Hec1 and P53 showed a signifi cant impact on cellular sensitivity to TAI 1. In addition, the role of P53 is further supported by the in vitro siRNA knockdown studies. Although these are very interesting findings, a larger study to allow multivariate analysis additional resources will be necessary for more accurate evaluation, but such study is beyond the scope of the current study. Nevertheless, these findings provide a rationale for the building of the parameters for re sponse into future clinical studies for Hec1 inhibitors, in particular TAI 1, and analogues of TAI 1. In contrast to in vitro cell line studies, the in vivo models demonstrated efficacy but doesnt reflect the po tency from in vitro studies.

Administration L-Mimosine c-Met inhibitor of drug to animal models, in comparison to cell lines in culture, adds another level of complexity due to possible variabil ity in drug absorption levels due to barriers encountered during oral administration, such as enzymatic degrad ation, pH sensitivity, drug pumps in the gastrointestinal tract, etc, hence, the efficacy values between the in vivo models and in vitro models cannot be directly compar able. It is therefore only appropriate to use these prelim inary xenograft models to determine efficacy but not to efficacy doses directly to in vitro GI50. Furthermore, bet ter comparison of the efficacy doses between xenograft models should be designed so absorption levels are con trolled and formulation of the vehicle for administration is optimized. Note that we are the first to evaluate the oral efficacy of Hec1 targeted inhibitors as an anticancer agent and demonstrate efficacy of the improved Hec1 targeted compound in human liver, colon and breast in vivo tumor models.

Even though the great leap in in vitro potency doesnt correlate well with the in vivo efficacy, this study provides a basis for the pharmaceut ical development of a Hec1 targeted small molecule based on the significant improvement in in vitro efficacy, which translates to a clinically applicable oral dosage.