Purpose: The oral prodrug of gemcitabine LY2334737 is cleaved systemically to gemcitabine; the mechanism responsible for hydrolysis is unknown. LY2334737 cytotoxicity was tested in the NCI-60 panel; mining of microarray expression data identified carboxylesterase (CES) as a top hydrolase candidate. Studies examined whether CES is responsible for hydrolysis and whether cellular CES expression confers prodrug sensitivity.Experimental Design: Human recombinant CES isozymes were assayed for LY2334737 hydrolysis. Stable CES-overexpressing HCT-116 transfectants and a SK-OV-3 knockdown were prepared. Cell lines were tested for drug sensitivity and CES expression by quantitative real time-PCR (qRT-PCR), Western blotting, and immunohistochemical staining. Bystander cytotoxicity studies were conducted with GFP-tagged PC-3 cells as the reporter cell line. Therapeutic response of the HCT-116 transfectants was evaluated in xenografts.Results: Of 3 human CES isozymes tested, only CES2 hydrolyzed LY2334737. Five cell lines that express CES2 responded to LY2334737 treatment. LY2334737 was less cytotoxic to a SK-OV-3 CES2 knockdown than parental cells. The drug response of CES2-transfected HCT-116 cells correlated with CES2 expression level. Bystander studies showed statistically greater PC-3-GFP growth inhibition by LY2334737 when cells were cocultured with CES2 and not mock transfectants. Oral treatment of xenograft models with 3.2 mg/kg LY2334737 once a day for 21 days showed greater tumor growth inhibition of CES2 transfectant than the mock transfectant (P 0.001).Conclusions: CES2 is responsible for the slow hydrolysis of LY2334737. Because intact prodrug circulates at high plasma levels after oral LY2334737 administration, improved response rates may be observed by tailoring LY2334737 treatment to patients with CES2 tumor expression.

LY2334737, an oral prodrug of gemcitabine, is cleaved in vivo, releasing gemcitabine and valproic acid. Oral dosing of mice results in absorption of intact prodrug with slow systemic hydrolysis yielding higher plasma levels of LY2334737 than gemcitabine and prolonged gemcitabine exposure. Antitumor activity was evaluated in human colon and lung tumor xenograft models. The dose response for efficacy was examined using 3 metronomic schedules, once-a-day dosing for 14 doses, every other day for 7 doses, and once a day for 7 doses, 7 days rest, followed by an additional 7 days of once-a-day dosing. These schedules gave significant antitumor activity and were well tolerated. Oral gavage of 6 mg/kg LY2334737 daily for 21 days gave equivalent activity to i.v. 240 mg/kg gemcitabine. HCl administered once a week for 3 weeks to mice bearing a patient mesothelioma tumor PXF 1118 or a non-small cell lung cancer tumor LXFE 937. The LXFE 397 tumor possessed elevated expression of the equilibrative nucleoside transporter-1 (ENT1) important for gemcitabine uptake but not prodrug uptake and responded significantly better to treatment with LY2334737 than gemcitabine (P 0.001). In 3 colon xenografts, antitumor activity of LY2334737 plus a maximally tolerated dose of capecitabine, an oral prodrug of 5-fluorouracil, was significantly greater than either monotherapy. During treatment, the expression of carboxylesterase 2 (CES2) and concentrative nucleoside transporter-3 was induced in HCT-116 tumors; both are needed for the activity of the prodrugs. Thus, metronomic oral low-dose LY2334737 is efficacious, well tolerated, and easily combined with capecitabine for improved efficacy. Elevated CES2 or ENT1 expression may enhance LY2334737 tumor response.

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3004 Background: The highly potent MDM2–p53 antagonist BI 907828 showed antitumor efficacy in vivo, particularly in TP53 wild-type, MDM2-amplified de-differentiated LPS (DDLPS) patient-derived xenografts and syngeneic models. This phase I study (NCT03449381) is assessing BI 907828 monotherapy in patients with advanced solid tumors, including LPS. In Part A (dose escalation), patients received one of two BI 907828 dosing schedules: Arm A, day 1 of 21-day cycles (q3w); Arm B, days 1 and 8 of 28-day cycles. Based on previously reported results from Part A (LoRusso ASCO 2021), the MTD was 60 mg q3w and the recommended dose for expansion (RDE) was selected as 45 mg q3w. Methods: In Part B (dose expansion), patients received BI 907828 45 mg q3w. The primary endpoint was PFS. Secondary endpoints/objectives included objective response rate, overall survival, the number of patients with grade ≥3 treatment-related AEs, and PK parameters. Here, we report overall safety data and efficacy data in the subgroup of patients with advanced LPS. Results: As of January 10, 2022, 90 patients had been enrolled; 49 (54.4%) were male, 55 (61.1%)/34 (37.8%) were ECOG PS 0/1, the median number of prior systemic therapies was 2 (range, 0–11), 44 had advanced LPS (28 DDLPS, 16 well-differentiated LPS [WDLPS]). At data cut-off, 31/90 patients (34.4%) had received treatment for ≥6 months. In the 41 evaluable patients with advanced LPS, best response of PR or SD was observed in 24/27 patients with DDLPS (88.9%) and 13/14 patients with WDLPS (92.9%). Two DDLPS and 4 WDLPS patients achieved a PR; all had MDM2-amplified disease. In Part A, 5/11 DDLPS patients and 4/8 WDLPS patients have achieved PFS ≥10.5 months. In the 42 patients who received the RDE of 45 mg q3w, 18 patients (42.9%) had grade ≥3 AEs; the most common grade ≥3 AEs were neutropenia (23.8%), thrombocytopenia (21.4%), and anemia (11.9%). Seven patients (16.7%) had SAEs; the most common were thrombocytopenia (4.8%) and pyrexia (4.8%). PK analysis showed that mean plasma exposures (Cmax and AUC0-inf) increased with dose and showed no significant deviation from linearity in the dose range 10–60 mg. A correlation was observed between exposure and GDF-15 levels in plasma, as a target engagement marker. Conclusions: BI 907828 showed a manageable safety profile, high plasma exposure, target engagement and encouraging signs of antitumor activity in patients with advanced DDLPS and WDLPS. The Part B dose expansion is ongoing. Clinical trial information: NCT03449381.

Chk1 is a key component of the cellular response to DNA damage resulting from exposure to various genotoxic agents. When damaged DNA is present, Chk1 maintains genomic integrity by stalling cell cycle progression thereby providing time for the appropriate repair to occur. Inhibition of Chk1 kinase activity leads to a loss in the regulation of this damage response and results in abrogation of cell cycle arrest and ultimately to cell death as cells with damaged DNA proceed inappropriately into mitosis. Thus first generation small molecule inhibitors of Chk1 kinase were developed to act as companion compounds that would be used together with established standard -of-care (SoC) cancer treatments that target DNA to enhance the effectiveness of such treatments. As a second generation inhibitor, LY2606368 distinguishes itself from other molecules in this class in that it has been shown to inhibit tumor growth when used either as monotherapy or in combination with SoC agents. The single agent activity of LY2606368 is likely related to the ability of this molecule to potently inhibit Chk1 thereby effectively interfering with its function to support normal DNA replication via regulation of origin firing and/or aspects of chromosomal dynamics during mitosis which are thought to be dependent upon Chk1 kinase activity. The studies presented here have evaluated the potential of LY2606368 to inhibit ovarian tumor growth both as monotherapy and in combination with cisplatin or paclitaxel. Treatment of tumor-bearing animals on a BID X 3 schedule with LY2606368 alone resulted in profound growth inhibition such that greater than 80% inhibition was observed at doses of 12mg/kg in both subcutaneous and orthotopic models. Moreover, the studies in the orthotopic SKOV3 model demonstrated that treatment with LY2606368 not only robustly inhibited growth of the primary tumor but also significantly reduced the incidence of metastases and accumulation of ascites fluid. Subsequent studies in SKOV3 subcutaneous xenografts revealed that significant growth inhibition could be achieved with various combination strategies which include agents that are commonly used in the treatment of ovarian cancer. In particular, the extent of growth inhibition that could be achieved with cisplatin or paclitaxel alone was augmented by combining these agents with LY2606368. Overall these animal studies indicate the potential therapeutic benefit in ovarian cancer that could be achieved with LY2606368 either as monotherapy or in combination with SoC agents. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr A108.