Discovery of GDC-0077 (Inavolisib), a Highly Selective Inhibitor and Degrader of Mutant PI3Kα.

Small molecule inhibitors that target the phosphatidylinositol 3-kinase (PI3K) signaling pathway have received significant interest for the treatment of cancers. The class I isoform PI3Kα is most commonly associated with solid tumors via gene amplification or activating mutations. However, inhibitors demonstrating both PI3K isoform and mutant specificity have remained elusive. Herein, we describe the optimization and characterization of a series of benzoxazepin-oxazolidinone ATP-competitive inhibitors of PI3Kα which also induce the selective degradation of the mutant p110α protein, the catalytic subunit of PI3Kα. Structure-based design informed isoform-specific interactions within the binding site, leading to potent inhibitors with greater than 300-fold selectivity over the other Class I PI3K isoforms. Further optimization of pharmacokinetic properties led to excellent in vivo exposure and efficacy and the identification of clinical candidate GDC-0077 (inavolisib, 32), which is now under evaluation in a Phase III clinical trial as a treatment for patients with PIK3CA-mutant breast cancer.

Minimal Rectal Toxicity in the Setting of Comorbid Crohn's Disease Following Prostate Cancer Radiotherapy with a Hydrogel Rectal Spacer.

We present one of the first cases of a prostate cancer (PCa) patient with inflammatory bowel disease (IBD) treated with intensity-modulated radiotherapy (IMRT) and a hydrogel rectal spacer. A 73-year-old male with a past medical history significant for Crohn's disease (CD) and the recent diagnosis of T1cN0M0 high-risk PCa was referred for definitive radiotherapy. Given the patient's history of CD and the possible increased risk of gastrointestinal (GI) toxicity and disease exacerbation, prior to IMRT, a hydrogel spacer was placed between the prostate and the anterior rectal wall to further minimize irradiation to the rectum. The patient then received IMRT (78 Gy/2 Gy fractions at a 100 percent isodose line). Over the course of treatment, Radiation Therapy Oncology Group (RTOG) Grade 1 GI toxicities of mild diarrhea were noted during the fifth and sixth weeks of treatment as well as an RTOG Grade 1 genitourinary (GU) toxicity of a decrease in the urinary stream that resolved with tamsulosin. At the 3, 6, 9, and 12-month follow-ups, bowel movements and urinary stream were reported to be at baseline with prostate-specific antigen (PSA) levels of 0.18 ng/mL and 0.03 ng/mL at the three and nine-month follow-ups, respectively. As such, this case report suggests that IBD patients with localized PCa may be viable candidates for radiotherapy given the promising results of hydrogel spacers in combination with IMRT in limiting rectal toxicity.

Discovery of a Noncovalent, Mutant-Selective Epidermal Growth Factor Receptor Inhibitor.

Inhibitors targeting the activating mutants of the epidermal growth factor receptor (EGFR) have found success in the treatment of EGFR mutant positive non-small-cell lung cancer. A secondary point mutation (T790M) in the inhibitor binding site has been linked to the acquired resistance against those first generation therapeutics. Herein, we describe the lead optimization of a series of reversible, pan-mutant (L858R, del746-750, T790M/L858R, and T790M/del746-750) EGFR inhibitors. By use of a noncovalent double mutant (T790M/L858R and T790M/del746-750) selective EGFR inhibitor (2) as a starting point, activities against the single mutants (L858R and del746-750) were introduced through a series of structure-guided modifications. The in vitro ADME-PK properties of the lead molecules were further optimized through a number of rational structural changes. The resulting inhibitor (21) exhibited excellent cellular activity against both the single and double mutants of EGFR, demonstrating target engagement in vivo and ADME-PK properties that are suitable for further evaluation. The reversible, noncovalent inhibitors described complement the covalent pan-mutant EGFR inhibitors that have shown encouraging results in recent clinical trials.

The Rational Design of Selective Benzoxazepin Inhibitors of the α-Isoform of Phosphoinositide 3-Kinase Culminating in the Identification of (S)-2-((2-(1-Isopropyl-1H-1,2,4-triazol-5-yl)-5,6-dihydrobenzo[f]imidazo[1,2-d][1,4]oxazepin-9-yl)oxy)propanamide (GDC-0326).

Inhibitors of the class I phosphoinositide 3-kinase (PI3K) isoform PI3Kα have received substantial attention for their potential use in cancer therapy. Despite the particular attraction of targeting PI3Kα, achieving selectivity for the inhibition of this isoform has proved challenging. Herein we report the discovery of inhibitors of PI3Kα that have selectivity over the other class I isoforms and all other kinases tested. In GDC-0032 (3, taselisib), we previously minimized inhibition of PI3Kß relative to the other class I insoforms. Subsequently, we extended our efforts to identify PI3Kα-specific inhibitors using PI3Kα crystal structures to inform the design of benzoxazepin inhibitors with selectivity for PI3Kα through interactions with a nonconserved residue. Several molecules selective for PI3Kα relative to the other class I isoforms, as well as other kinases, were identified. Optimization of properties related to drug metabolism then culminated in the identification of the clinical candidate GDC-0326 (4).

Discovery of selective and noncovalent diaminopyrimidine-based inhibitors of epidermal growth factor receptor containing the T790M resistance mutation.

Activating mutations within the epidermal growth factor receptor (EGFR) kinase domain, commonly L858R or deletions within exon 19, increase EGFR-driven cell proliferation and survival and are correlated with impressive responses to the EGFR inhibitors erlotinib and gefitinib in nonsmall cell lung cancer patients. Approximately 60% of acquired resistance to these agents is driven by a single secondary mutation within the EGFR kinase domain, specifically substitution of the gatekeeper residue threonine-790 with methionine (T790M). Due to dose-limiting toxicities associated with inhibition of wild-type EGFR (wtEGFR), we sought inhibitors of T790M-containing EGFR mutants with selectivity over wtEGFR. We describe the evolution of HTS hits derived from Jak2/Tyk2 inhibitors into selective EGFR inhibitors. X-ray crystal structures revealed two distinct binding modes and enabled the design of a selective series of novel diaminopyrimidine-based inhibitors with good potency against T790M-containing mutants of EGFR, high selectivity over wtEGFR, broad kinase selectivity, and desirable physicochemical properties.

Antagonists of the human A(2A) receptor. Part 6: Further optimization of pyrimidine-4-carboxamides.

Antagonists of the human A(2A) receptor have been reported to have potential therapeutic benefit in the alleviation of the symptoms associated with neurodegenerative movement disorders such as Parkinson's disease. As part of our efforts to discover potent and selective antagonists of this receptor, we herein describe the detailed optimization and structure-activity relationships of a series of pyrimidine-4-carboxamides. These optimized derivatives display desirable physiochemical and pharmacokinetic profiles, which have led to promising oral activity in clinically relevant models of Parkinson's disease.

Transient treatment with CDK inhibitors eliminates proliferative potential even when their abilities to evoke apoptosis and DNA damage are blocked.

Transient treatment with small molecule CDK inhibitors is toxic to cancer cells and leads to depletion of anti-apoptotic proteins and Chk1, coupled with DNA damage and induction of apoptosis. Here we have examined, which of these phenomena are necessary for CDK inhibitors to have an anti-proliferative effect. We find that 24 hours treatment with either a primarily CDK2-specific, or a primarily CDK7/9-specific, antagonist eliminates proliferative potential even if apoptosis is blocked and the tendency of CDK inhibition to result in DNA damage is overcome by expression of recombinant Chk1. Loss of proliferative potential is correlated with irreversible suppression of biomarkers of cell cycle progression. CDK inhibitors dramatically reduced levels of the anti-apoptotic proteins, Mcl-1 and XIAP, but siRNA-mediated suppression of Mcl-1 and XIAP did not induce cell death in the osteosarcoma cells used in this study. Finally, we found that many literature CDK inhibitors do not effectively suppress the CDK/cyclin complexes responsible for cell cycle progression at the minimum doses required to block proliferation: some are only effective after a substantial delay and may act via inhibition of CDK7.

Discovery of a potent CDK2 inhibitor with a novel binding mode, using virtual screening and initial, structure-guided lead scoping.

Virtual screening against a pCDK2/cyclin A crystal structure led to the identification of a potent and novel CDK2 inhibitor, which exhibited an unusual mode of interaction with the kinase binding motif. With the aid of X-ray crystallography and modelling, a medicinal chemistry strategy was implemented to probe the interactions seen in the crystal structure and to establish SAR. A fragment-based approach was also considered but a different, more conventional, binding mode was observed. Compound selectivity against GSK-3beta was improved using a rational design strategy, with crystallographic verification of the CDK2 binding mode.

Structure-guided design of pyrazolo[1,5-a]pyrimidines as inhibitors of human cyclin-dependent kinase 2.

The protein structure guided design of a series of pyrazolo[1,5-a]pyrimidines with high potency for human cyclin-dependent kinase 2 (CDK2) is described. Some examples were shown to inhibit the growth of human colon tumour cells, were equipotent for CDK1 and were selective against GSK-3beta and other kinases.

Multi-step application of immobilized reagents and scavengers: a total synthesis of epothilone C.

The total synthesis of the cytotoxic antitumour natural product epothilone C has provided a stage for the exploitation and further development of immobilized reagent methods. A stereoselective convergent synthetic strategy was applied, incorporating polymer-supported reagents, catalysts, scavengers and catch-and-release techniques to avoid frequent aqueous work-up and chromatographic purification.