Our mission at BellBrook Labs is to accelerate drug discovery by producing truly enabling high throughput screening tools for protein targets and phenotypic cellular assays. Like our customers, we’re driven by a desire to make a real impact on improving human health.
We’re proud of our products and the innovative work our customers are doing with them, and we want to share their successes with the biotech community. Each month we’ll feature a BellBrook customer who’s had success using our products. We’ll talk about the scientists themselves, the work they do, and how they benefited from using BellBrook’s tools. Our hope is to inform you, inspire you, and ultimately, accelerate drug discovery. Because at the end of the day, that’s what really drives us all.
This month we feature David Whalley, a scientist in the Assay Development and Screening Group at MRC Technology in London. David spends his time outside of the lab being as active as possible, enjoying both yoga and cycling. He is also an avid runner and is hoping to attempt a half marathon later this year.
When he is in the lab, David works primarily within the field of biochemical assay development, focusing specifically on kinases. His main focus is developing primary HTS assays and downstream assays for the characterization of hit compounds and mechanistic studies. While much of David’s eight years at MRCT has been focused targeting malarial kinases, in this case his focus was on breast cancer. David used Bellbrook’s Transcreener ADP assay in order to identify inhibitors of PAICS, a key enzyme in the de novo purine biosynthesis pathway that has been suggested as an attractive drug target for cancer.
Recently our Director of Scientific Sales, Karen Kleman, caught up with David and discussed the project in question, the challenges he encountered and his experience working with Bellbrook.
Why are you interested in the target? What is the therapeutic rationale?
Our interest in this target was based on work by Daniel Peeper and his colleagues at the Netherlands Cancer Institute. The molecule being targeted is the product of the gene PAICS (phosphoribosylaminoimidazole carboxylase, phosphoribosylaminoimidazole succinocarboxamide synthetase), which encodes a bifunctional enzyme that catalyzes two consecutive steps of the de novo purine biosynthesis pathway.
PAICS has been suggested to be an attractive drug target for cancer since rapidly dividing cancer cells may be more dependent on de novo purine biosynthesis than normal cells. Moreover, PAICS expression has been associated with several malignancies. We observed that PAICS is frequently overexpressed in human breast cancer cell lines as compared to non-tumorigenic mammary epithelial cells. Downregulation of PAICS expression in highly metastatic human breast cancer cells using two independent sh-RNAs almost completely abolished the ability of these cells to form metastases to the lungs when injected intravenously into immunocompromised mice. Inhibition of PAICS expression also strongly impaired the primary tumour growth when breast cancer cells were injected orthotopically in the mammary fat pad of mice. We therefore propose that a small molecule inhibitor of this enzyme could be particularly effective for therapeutic intervention in metastatic breast cancers. Moreover, we observed that expression of this gene is higher in poor-prognosis breast cancer patients than those with good-prognosis. Of note, this gene is part of a highly predictive gene-expression signature that we identified and which has a similar prognostic power in breast cancer patients as the gene-expression signatures, MammaPrint® or OncotypeDX®, currently used in clinic. Therefore, small molecule inhibitors of PAICS could be used in combination with this gene expression signature to identify those patients with poor-prognosis that show high levels of PAICS expression and which could respond to PAICS inhibition.
What challenges did you encounter in the process of screening?
In vitro, the first step of the reaction, i.e. the carboxylation of AIR to CAIR, exists as an equilibrium which lies in favor of the reverse non-physiologic direction. The main challenge was to overcome the AIR/CAIR equilibrium and derive conditions to force the equilibrium in the forward direction in order to allow us to focus on the second step of the reaction, i.e. the ATP-dependent aspartylation of CAIR to SAICAR, mediated by the synthetase domain of PAICS. BellBrook’s Transcreener ADP assay allowed us to work with very low [E] and generate an excellent assay window typically with only ~5% ATP conversion (1.5 µM ADP).
What were the results and where do you plan to take the project from here? Is there anything you want to say about working with BellBrook, positive or negative?
The screen yielded a number of series. Representatives of each are currently being characterized both biochemically and biophysically in order to determine mechanism. So far there is one “stand out” series which shows good binding characteristics in the Biacore assay. We’re now in the process of generating SAR for this series.
Working with BellBrook Labs has been a good experience. Impressive, competitive quotes were provided for the HTS and technical issues/queries have always been addressed promptly and effectively.