apr-246 and Melanoma

Intrinsic and acquired resistance of metastatic melanoma to (V600E/K)BRAF and/or MEK inhibitors, which is often caused by activation of the PI3K/AKT survival pathway, represents a major clinical challenge. Given that p53 is capable of antagonising PI3K/AKT activation we hypothesised that pharmacological restoration of p53 activity may increase the sensitivity of BRAF-mutant melanoma to MAPK-targeted therapy and eventually delay and/or prevent acquisition of drug resistance. To test this possibility we exposed a panel of vemurafenib-sensitive and resistant (innate and acquired) (V600E/K)BRAF melanomas to a (V600E/K)BRAF inhibitor (vemurafenib) alone or in combination with a direct p53 activator (PRIMA-1(Met)/APR-246). Strikingly, PRIMA-1(Met) synergised with vemurafenib to induce apoptosis and suppress proliferation of (V600E/K)BRAF melanoma cells in vitro and to inhibit tumour growth in vivo. Importantly, this drug combination decreased the viability of both vemurafenib-sensitive and resistant melanoma cells irrespectively of the TP53 status. Notably, p53 reactivation was invariably accompanied by PI3K/AKT pathway inhibition, the activity of which was found as a dominant resistance mechanism to BRAF inhibition in our lines. From all various combinatorial modalities tested, targeting the MAPK and PI3K signalling pathways through p53 reactivation or not, the PRIMA-1(Met)/vemurafenib combination was the most cytotoxic. We conclude that PRIMA-1(Met) through its ability to directly reactivate p53 regardless of the mechanism causing its deactivation, and thereby dampen PI3K signalling, sensitises (V600E/K)BRAF-positive melanoma to BRAF inhibitors.

Topics: Animals; Antineoplastic Combined Chemotherapy Protocols; Apoptosis; Cell Line, Tumor; Cell Proliferation; Dose-Response Relationship, Drug; Drug Resistance, Neoplasm; Drug Synergism; Genetic Predisposition to Disease; Humans; Indoles; Male; Melanoma; Mice, Nude; Molecular Targeted Therapy; Mutation; Phosphatidylinositol 3-Kinase; Protein Kinase Inhibitors; Proto-Oncogene Proteins B-raf; Proto-Oncogene Proteins c-akt; Quinuclidines; Signal Transduction; Skin Neoplasms; Sulfonamides; Time Factors; Tumor Suppressor Protein p53; Vemurafenib; Xenograft Model Antitumor Assays

Disseminating malignant melanoma is a lethal disease highly resistant to radio- and chemotherapy. Therefore, the development of new treatment strategies is strongly needed. Tumor suppressor p53-mediated apoptosis is essential for the response to radio- and chemotherapy. Although p53 is not frequently mutated in melanoma, it is inactivated by integrin αv-mediated signaling, as we previously demonstrated 1, which may account, at least partially, for increased apoptosis resistance of malignant melanoma. In this study we addressed the question whether functional restoration of p53 by APR-246 (PRIMA-1Met), which can reactivate mutant p53 and induce massive apoptosis in cancer cells, is able to restore the function of inactive p53 in melanoma. Using a three-dimensional collagen gel (3D-collagen) to culture melanoma cells carrying wild-type p53, we found that APR-246 treatment resulted in activation of p53, leading to increased expression of p53 pro-apoptotic targets Apaf1 and PUMA and activation of caspase- 9 and -3. Moreover, APR-246 triggered melanoma cell apoptosis that was mediated by p53 and caspase 9. Importantly, APR-246 treatment also suppressed human melanoma xenograft tumors in vivo in a p53-dependent manner. Thus, wild-type p53 reactivation may provide a novel approach for malignant melanoma treatment, with APR-246 as a candidate drug for such a development.

Topics: Animals; Antineoplastic Agents; Apoptosis; Apoptosis Regulatory Proteins; Apoptotic Protease-Activating Factor 1; Caspase 3; Caspase 9; Cell Culture Techniques; Cell Line, Tumor; Humans; Melanoma; Mice; Mice, Nude; Proto-Oncogene Proteins; Quinuclidines; RNA Interference; RNA, Small Interfering; Transplantation, Heterologous; Tumor Suppressor Protein p53

Topics: Antineoplastic Agents; Apoptosis; Cell Line, Tumor; Humans; Melanoma; Protein Folding; Quinuclidines; Tumor Suppressor Protein p53