An in silico docking study and competitive protein chip assay revealed that the SDV sequence of P11 is able to create a stable inhibitory complex onto the vitronectin-binding site of integrin alpha v beta 3. The Arg-Gly-Asp (RGD)-binding site recognition
by P 11 was site specific because the P 11 was inactive for the complex formation of a denatured form of integrin-vitronectin. P 11 showed a strong antagonism against alpha v beta 3-GRGDSP in teraction with an IC(50) value of 25.72 +/- 3.34 nM, whereas the value of GRGDSP peptide was 1968.73 +/- 444.32 nM. The binding-free energies calculated from the docking simulations for each P11 and RGD peptide were -3.99 and -3.10 kcal/mol, respectively. The free energy difference between P11 and RGD corresponds to approximately a 4.5-fold lower K(i) value for the P11 than the RGD peptide. The 4-Hydroxytamoxifen mw 5-Fluoracil in vitro binding orientation of the docked P11 was similar
to the crystal structure of the RGD in alpha v beta 3. The analyzed docked poses suggest that a divalent metal-ion coordination was a common driving force for the formation of both SDV/alpha v beta 3 and RGD/alpha v beta 3 complexes. This is the first report on the specific recognition of the RGD-binding site of alpha v beta 3 by a non-RGD containing peptide using a computer-assisted proteomic approach.”
“Introduction: In spite of recently approved B-RAF inhibitors and immunomodulating antibodies, metastatic melanoma has poor prognosis and novel treatments are needed. Melanoma stem cells (MSC) have been implicated in the resistance of this tumor to chemotherapy. Recently we demonstrated in a Phase I CB-839 supplier clinical trial in patients with metastatic melanoma that radioimmunotherapy (RIT) with 188-Rhenium(Re-188)-6D2 antibody to melanin was a safe and effective modality. Here we investigated the interaction of MSC with RIT as a possible mechanism for RIT efficacy.
Methods: Mice bearing A2058 melanoma xenografts were treated with either 1.5 mCi Re-188-6D2 antibody, saline, unlabeled 6D2 antibody or Re-188-labeled non-specific IgM.
Results: On Day 28 post-treatment the tumor size in
the RIT group was 4-times less than in controls (P<0.001). The tumors were analyzed by immunohistochemistry and FACS for two MSC markers – chemoresistance mediator ABCB5 and H3K4 demethylase JARID1B. There were no significant differences between RIT and control groups in percentage of ABCB5 or JARID1B-positive cells in the tumor population. Our results demonstrate that unlike chemotherapy, which kills tumor cells but leaves behind MSC leading to recurrence, RIT kills MSC at the same rate as the rest of tumor cells.
Conclusions: These results have two main implications for melanoma treatment and possibly other cancers. First, the susceptibility of ABCB5 + and JARID1B + cells to RIT in melanoma might be indicative of their susceptibility to antibody-targeted radiation in other cancers where they are present as well.