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Elevated expression of the anti-apoptotic factor Bcl-2 is believed to be one of the contributing factors to an increased relapse rate associated with multiple cisplatin-resistant cancers. DNA damage-binding protein complex subunit 2 (DDB2) has recently been revealed to play an important role in sensitizing human ovarian cancer cells to cisplatin-induced apoptosis through the down-regulation of Bcl-2, but the underlying molecular mechanism remains poorly defined. Here, we report that DDB2 functions as a transcriptional repressor for Bcl-2 in combination with DDB1. Quantitative ChIP and EMSA analysis revealed that DDB2 binds to a specific cis-acting element at the 5′-end of bcl-2 P1 promoter. Overexpression of DDB2 resulted in marked losses of histone H3K9,14 acetylation along the bcl-2 promoter and enhancer regions, concomitant with a local enrichment of HDAC1 to the bcl-2 P1 core promoter in ovarian cancer cells. Co-immunoprecipitation analysis and in vitro binding assay identified a physical interaction between DDB1 and HDAC1, while downregulation of HDAC1 significantly enhanced bcl-2 promoter activity. Finally, in comparison to wild-type DDB2, mutated DDB2, which is unable to repress Bcl-2 transcription, mediates a compromised apoptosis upon cisplatin treatment. Taken together, our data support a model wherein DDB1 and DDB2 cooperate with each other to repress bcl-2 transcription. DDB2 recognizes and binds to the bcl-2 P1 promoter, and HDAC1 is recruited through the DDB1 subunit associated with DDB2, to deacetylate histone H3K9,14 across bcl-2 regulatory regions, resulting in suppressed bcl-2 transcription. Thus, increasing the expression of DDB complex may provide a molecular strategy for cancer therapy.

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3003 Background: PTEN is a tumor suppressor gene and mutations in PTEN causing loss of protein expression/function may play a significant role in the pathogenesis of EC. Loss of PTEN protein expression has been reported in 26–80% of EC and leads to deregulated PI3K/Akt/mTOR signalling which may give neoplastic cells a survival advantage by enhancing angiogenesis, protein translation and cell cycle progression. Inhibition of mTOR, a protein kinase downstream of the PI3K/Akt pathway and target of rapamycins, inhibits proliferation of EC cell lines and formation of EC in PTEN−/+ heterozygous mice. We have evaluated temsirolimus (T) an ester derivative of rapamycin that inhibits mTOR given the frequent loss of PTEN in human EC. Methods: A two stage, phase II study has been conducted to evaluate single agent activity of T in women with recurrent or metastatic EC (chemotherapy naïve, upto 1 prior line of hormonal therapy). Treatment was 25mg i.v. weekly. One cycle is defined as 4 weeks of therapy. Thirty one patients (pts) have been registered; 23 are evaluable for toxicity and 19 for response. Results: Preliminary results have demonstrated encouraging activity and the trial fulfilled predefined criteria for activity. Of 19 pts evaluable for response, 5 have had a confirmed partial response (PR) (26%) and 12 have stable disease (SD) as best response (63%). Two pts had progressive disease (PD) (11%). PTEN, phosphorylated (p) mTOR and p-S6 protein (immunohistochemistry) results are available on 9 pts to date. The preliminary results indicate that responses and stable disease are seen in pts irrespective of PTEN status. Loss of p-mTOR was evident in tumor cells from all pts (range 75–99% loss) and did not correlate with response. Phosphorylated S6 was low in tumor cells in the one pt who had PD (5%), and levels were higher in pts with PR and SD (mean and median 30%). Conclusions: We conclude that Temsirolimus has encouraging single agent activity for in recurrent and metastatic EC, and the findings indicate this is irrespective of PTEN status. We are currently evaluating activity of T in pts previously treated with chemotherapy and molecular correlates in additional specimens. No significant financial relationships to disclose.

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3558 Background: Temsirolimus (T) has encouraging activity in many malignancies, including endometrial cancer and a combination with carboplatin and paclitaxel would logical regimen for further development. This trial was designed to assess the safety and tolerability of this combination and expand experience at the recommended dose in pts with endometrial and ovarian cancers. Methods: A 3+3 dose escalation Phase I study has been conducted in pts with advanced solid malignancies suitable for carboplatin and paclitaxel chemotherapy who had not received more than 2 prior lines of chemotherapy. To date, 31 eligible pts with a median age of 59 have been treated and 27 are evaluable for toxicity. Pts were entered in 6 dose levels, with the first two levels administering T on Days 8 and 15 and the next 4 levels switching to a D1, 8 administration. Eighteen had received prior chemotherapy and 15 prior radiation. Results: Day 8, 15 administration of T was not feasible due to myelosuppression on day 15. The combination of carboplatin and paclitaxel on day 1 with T on D1 and 8 has been well tolerated, and patients have received a median of 5 cycles of therapy. At dose level 6 (T 25 mg D1 and 8, paclitaxel 175 mg/m2 D1, carboplatin AUC 6 D1) dose limiting toxicity (DLT) was seen in one of 6 pts treated to date (Gr 4 thrombocytopenia) and a second pt had a possible DLT ( Gr 3 fatigue in presence of baseline fatigue). This dose level is being expanded in 4 endometrial and ovarian cancer pts. The regimen is active: of the 26 patients with follow-up data, there have been 10 with partial response (38.5%; med. duration 7.1 mo [1.0–12.7]) and 12 with stable disease (46%; med. duration 6.9 mo [1.3- 7.8]). One patient had progressive disease and three were inevaluable. Conclusions: The results indicate this combination is well tolerated and requires additional assessment in a Phase II setting. The recommended Phase II dose will be dose level 6 provided no further DLTs are observed in the additional 4 patients entered. [Table: see text] No significant financial relationships to disclose.