Abstract 1644: VX-970, the first-in-class inhibitor of the DNA damage repair enzyme ATR

Proficient repair of DNA damage is important for cancer cell survival and is a leading cause for the poor response many patients experience when treated with DNA-damaging drugs or ionizing radiation. The protein kinase ataxia telangiectasia mutated and Rad3 related (ATR) regulates an important DNA damage response pathway that is most commonly activated by replication stress (RS). RS arises during S-phase when the cell's DNA replication machinery attempts to copy through an unresolved damage lesion. Such events are common after cells are treated with DNA-damaging agents. Unresolved RS often leads to double strand breaks, which in turn may cause DNA mutations, chromosomal rearrangements or cell death. Pre-clinical data suggests a reliance on ATR for survival is a common feature in cancer cells. This may occur when there are defects in other DNA damage repair pathways or high levels of background RS.

VX-970 is the first potent (Ki <0.3nM) and highly selective ATR inhibitor to enter clinical trials (EUDRACT: 2012-003126-250). In pre-clinical studies, it markedly increases the cytotoxic activity of multiple DNA damaging agents across large panels of cancer cell lines. In contrast, normal cells tolerate inhibition of ATR by activating compensatory repair signaling for example the pathway mediated by ATM. Defects in this ATM pathway, most notably as a result of mutations in the TP53 gene that encodes p53 (a principle substrate for ATM) is found to be a predictive marker for cell sensitivity in cancer cell lines. In mouse xenograft models VX-970 strongly potentiates the anti-cancer activity of DNA damaging drugs that include cisplatin, carboplatin, irinotecan and gemcitabine. Combinations are generally well tolerated and have been shown to provide better anti-cancer activity than the cytotoxic alone at its MTD. In addition, VX-970 has marked cytotoxic activity when combined with inhibitors of PARP (base excision repair protein) in multiple cancer cell lines, but is well tolerated by normal cells. Emerging data suggests that the cancer cell specificity for this combination may again be associated, at least in part, with defective ATM-p53 pathway signaling. Finally, VX-970 has potential as a monotherapy since potent single agent cytotoxic activity is observed in certain cancer cell lines. The basis for sensitivity to monotherapy may require both defects in alternative repair pathways and high background replication stress levels.

VX-970 is currently in Phase 1 clinical studies as monotherapy and in combination with gemcitabine, cisplatin and carboplatin.

Note: This abstract was not presented at the meeting.

Citation Format: John Pollard, Philip Reaper, Julie Jones, Christopher Barnes, Scott Gladwell, Stuart Hughes, Adele Peak, Hakim Djeha, Amy Hall, David Newsome, Yuxin Wang, Diane Boucher, Brenda Eustace, Yong Gu, Brian Hare, Mac Johnson, Sean Milton, Cheryl Murphy, Darin Takemoto, Crystal Tolman, Mark Wood, Brinley Furey, Marina Penney, Howard Li, Christopher Defranco, Mohammed Asmal, Scott Fields. VX-970, the first-in-class inhibitor of the DNA damage repair enzyme ATR. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1644. doi:10.1158/1538-7445.AM2015-1644

Abstract 2614: Anti-tumor efficacy and pharmacokinetics of the novel aptamer AS1411 in a continuous infusion nude rat xenograft model

AS1411 is a novel DNA aptamer that binds to the multi-functional protein nucleolin and induces cell death. AS1411 has shown activity at two different doses in combination with cytarabine in a phase II study of patients with AML.

We have previously shown that AS1411 has activity against a range of solid and hematological cancer cell lines, with IC50 values between 1 and 10 μM, when cells are exposed to AS1411 continuously for more than 3 days. We have also demonstrated efficacy in vivo in both lung (A549) and renal (A498) mouse xenografts. However, it has been challenging to provide optimal continuous dosing of AS1411 in mice; use of osmotic pumps or intraperitoneal bolus injection have been associated with low drug exposure. In the current study, we optimized the continuous infusion model by using nude, athymic rats with a surgically implanted catheter in a two-cycle xenograft study. Plasma and tumor samples were collected for PK determination, allowing a correlation of PK with efficacy.

The colorectal cell line HT29, which is sensitive to AS1411 in vitro, was used in this study. Cells (5×106) were implanted subcutaneously in the flank of female nude rats and tumors were allowed to grow to approximately 200 − 300 mm3 before surgical cannulation of the femoral vein. Following recovery, animals received AS1411 at 40, 80 or 180 mg/kg/day for two 7 day cycles of continuous infusion, 7 days apart. A vehicle control group received saline.

Animals in the 80 and 180 mg/kg/day groups exhibited a significant (p<0.01) reduction in tumor volume compared to control animals at day 33 and at day 22 (interim analysis); this was not observed for animals in the 40mg/kg/day group (40mg kg/day in this model does not directly correlate to the clinical dose of the same name). AS1411 was well-tolerated by all animals in all dose groups.

Plasma levels of AS1411 were measured at the three dose levels after one cycle of treatment. Mean AS1411 plasma concentrations were 0.7, 2.5 and 5.0 μM, for rats treated at 40, 80 and 180 mg/kg/day, respectively. The plasma concentrations in the two higher dose groups are within the range of the in vitro IC50 concentrations of a panel of cell lines.

We conclude that AS1411 shows activity in vivo in the HT29 nude rat xenograft model. Doses associated with significant reductions in tumor volume were those that produced plasma concentrations close to the IC50 level for AS1411. This correlation has been used in planning further clinical development of AS1411, including a phase IIb study of patients with AML.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2614.

An oncolytic adenovirus vector combining enhanced cell-to-cell spreading, mediated by the ADP cytolytic protein, with selective replication in cancer cells with deregulated wnt signaling

We have constructed a novel oncolytic adenovirus (Ad) vector named VRX-009 that combines enhanced cell spread with tumor-specific replication. Enhanced spread, which could significantly increase antitumor efficacy, is mediated by overexpression of the Ad cytolytic protein named ADP (also known as E3-11.6K). Replication of VRX-009 is restricted to cells with a deregulated wnt signal transduction pathway by replacement of the wild-type Ad E4 promoter with a synthetic promoter consisting of five consensus binding sites for the T-cell factor transcription factor. Tumor-selective replication is indicated by several lines of evidence. VRX-009 expresses E4ORF3, a representative Ad E4 protein, only in colon cancer cell lines. Furthermore, VRX-009 replicates preferentially in colon cancer cell lines as evidenced by virus productivity 2 orders of magnitude higher in SW480 colon cancer cells than in A549 lung cancer cells. Replication in primary human bronchial epithelial cells and human umbilical vein endothelial cells was also significantly lower than in SW480 cells. When tested in human tumor xenografts in nude mice, VRX-009 effectively suppressed the growth of SW480 colon tumors but not of A549 lung tumors. VRX-009 may provide greater level of antitumor efficacy than standard oncolytic Ad vectors in tumors in which a defect in wnt signaling increases the level of nuclear beta-catenin.