We find that while apoptosis facilitates a more rapid tumor regression, it is dispensable for complete tumor regression. Necrosis is often observed in solid tumor areas where vascularization lags behind tumor tissue growth. cell death, plays a crucial role in the clearance of cells that have potentially harmful genetic mutations. The ability of a cell to evade apoptosis is a crucial step in tumorigenesis (13). Despite the fact that human cancers are defective in their apoptotic pathways, DNA alkylating agents remain among the most effective chemotherapeutic agents used clinically (4), suggesting that alternative cell death pathways are activated. Five main types of cytocidal and cytostatic mechanisms have been described in the context of cancer therapy: apoptosis, necrosis, mitotic catastrophe, senescence, and autophagy (2,57). However, a comprehensive understanding of tumor cell death has been lacking due to the complexity of a tumors response to chemotherapy. Presently, most mechanistic studies of the anti-cancer activities of DNA alkylating agents have been conducted using cultured cells. It is therefore important to develop anin vivosystem to evaluate the contribution of the alternative cell death pathways in anti-cancer therapy. Apoptosis is mainly controlled by two sets of molecules: the Bcl-2 family of proteins, and the caspases. Deletion of the pro-apoptotic Bcl-2 family members Bax and Bak is sufficient to prevent apoptotic events initiated by mitochondrial membrane permeabilization (8). We utilized these cells to address the question as to how conventional chemotherapy induces cancer cell deathin vivo. == Materials and Methods == == Cell lines == Immortalized wild-type andbax/bak/murine embryonic fibroblasts (MEFs) (8) were retrovirally transformed with E1A and K-Ras. The cells were subcutaneously injected into the back of 68 week old male athymic nude mice (Taconic Farms). When tumors formed they were excised from the mice, minced, and digested with trypsin-EDTA (0.05%) and collagenase A (1 mg/mL) to generate stable tumor cell lines. == Antibodies == Bax (Santa Cruz), Bak (Upstate), Caspase 3 (Transducation Lab), cleaved Caspase 3 (Cell Signaling), H2A.X (Cell Signaling), HMGB1 (Abcam), -tubulin (Sigma), IL-1 (R&D systems), F4/80 (Serotec), Neutrophil (Serotec), PE-conjugated anti-Mac-1 (BD Biosciences), NVP-BEP800 Alexa 488-conjugated anti-Mac-1 (BD Biosciences), APC-conjugated anti-F4/80 (eBiosciences), PE-conjugated anti-Gr-1 (BD Biosciences), and Alexa 488-conjugated anti-Gr-1 (Serotec). == Electron microscopy == The tumor samples for TEM were collected immediately after sacrificing the mouse to ensure tissue integrity. TEM was performed according to standard protocol by the Central Microscopy Imaging Center at Stony Brook University. == Xenograft mouse tumor experiments == Tumors were established by injecting 1106tumor cells into the mid flanks of nude mice. When palpable tumors formed, mice were randomly grouped and either left untreated or treated via intraperitoneal injections of 170 mg/kg of cyclophosphamide monohydrate (CP) (Sigma) every 5 days. The tumor length (l) and width (w) were measured every 45 days with electronic calipers. Rabbit Polyclonal to KCNK15 Tumor volume (v) was calculated using the formula: v = (lw2)/2. The animals bearing untreated tumors were sacrificed post tumor inoculation before tumors reached 4 cm3in size in compliance with the Stony Brook University IACUC guidelines. == Statistical analysis == Data are represented as mean S.E.M. (standard error of the mean). Statistical analyses were performed using Microsoft Excel. == Results == == Cyclophosphamide NVP-BEP800 induces tumor regressionin vivoindependent of key apoptosis regulators == In order to study the contribution of different cell death pathways in the anti-tumor activity of chemotherapy, we first established anin vivosystem to compare tumors derived from apoptosis-competent and deficient cells. E1A and K-Ras oncoproteins were used to transform genetically defined MEFs NVP-BEP800 isolated from wild-type andbax/bak/mice (Fig. 1A). Moreover, the anti-apoptotic protein Bcl-xL was expressed in wild-type cells (Fig. 1B). Stable tumor cell lines were generated from these MEFs which maintained their respective genotypes (Fig. NVP-BEP800 1A and 1B). == Figure 1. DNA alkylating agents induce tumor regression independent of apoptosis. == Mouse embryonic fibroblasts (MEFs) were obtained from wild-type andbax/bak/mice and transformed with E1A and K-Ras. Transformed cells were injected into nude mice to generate tumors. The tumors were excised from the mice to generate stable.