Discovery of Reversible Covalent Bruton's Tyrosine Kinase Inhibitors PRN473 and PRN1008 (Rilzabrutinib)

Bruton's tyrosine kinase (BTK), a Tec family tyrosine kinase, is critical in immune pathways as an essential intracellular signaling element, participating in both adaptive and immune responses. Currently approved BTK inhibitors are irreversible covalent inhibitors and limited to oncology indications. Herein, we describe the design of covalent reversible BTK inhibitors and the discoveries of PRN473 (11) and rilzabrutinib (PRN1008, 12). These compounds have exhibited potent and durable inhibition of BTK, in vivo efficacy in rodent arthritis models, and clinical efficacy in canine pemphigus foliaceus. Compound 11 has completed phase 1 trials as a topical agent, and 12 is in phase 3 trials for pemphigus vulgaris and immune thrombocytopenia.

Single-cell transcriptomics of the naked mole-rat reveals unexpected features of mammalian immunity

The immune system comprises a complex network of specialized cells that protects against infection, eliminates cancerous cells, and regulates tissue repair, thus serving a critical role in homeostasis, health span, and life span. The subterranean-dwelling naked mole-rat (NM-R; Heterocephalus glaber) exhibits prolonged life span relative to its body size, is unusually cancer resistant, and manifests few physiological or molecular changes with advancing age. We therefore hypothesized that the immune system of NM-Rs evolved unique features that confer enhanced cancer immunosurveillance and prevent the age-associated decline in homeostasis. Using single-cell RNA-sequencing (scRNA-seq) we mapped the immune system of the NM-R and compared it to that of the short-lived, cancer-prone mouse. In contrast to the mouse, we find that the NM-R immune system is characterized by a high myeloid-to-lymphoid cell ratio that includes a novel, lipopolysaccharide (LPS)-responsive, granulocyte cell subset. Surprisingly, we also find that NM-Rs lack canonical natural killer (NK) cells. Our comparative genomics analyses support this finding, showing that the NM-R genome lacks an expanded gene family that controls NK cell function in several other species. Furthermore, we reconstructed the evolutionary history that likely led to this genomic state. The NM-R thus challenges our current understanding of mammalian immunity, favoring an atypical, myeloid-biased mode of innate immunosurveillance, which may contribute to its remarkable health span.

Prolonged and tunable residence time using reversible covalent kinase inhibitors

Drugs with prolonged, on-target residence time often show superior efficacy, yet general strategies for optimizing drug-target residence time are lacking. Here, we demonstrate progress toward this elusive goal by targeting a noncatalytic cysteine in Bruton's tyrosine kinase (BTK) with reversible covalent inhibitors. Utilizing an inverted orientation of the cysteine-reactive cyanoacrylamide electrophile, we identified potent and selective BTK inhibitors that demonstrate biochemical residence times spanning from minutes to 7 days. An inverted cyanoacrylamide with prolonged residence time in vivo remained bound to BTK more than 18 hours after clearance from the circulation. The inverted cyanoacrylamide strategy was further utilized to discover fibroblast growth factor receptor (FGFR) kinase inhibitors with residence times of several days, demonstrating generalizability of the approach. Targeting noncatalytic cysteines with inverted cyanoacrylamides may serve as a broadly applicable platform that facilitates “residence time by design”, the ability to modulate and improve the duration of target engagement in vivo.

Efficacy in collagen induced arthritis models with a selective, reversible covalent Bruton’s tyrosine kinase inhibitor PRN473 is driven by durable target occupancy rather than extended plasma exposure (THER5P.904)

Bruton’s Tyrosine Kinase (BTK) is an essential signaling element downstream of the B-cell receptor (BCR). Inhibition of BTK activity in B cells produces phenotypic changes consistent with blockade of the BCR, including inhibition of cell proliferation, differentiation, maturation, and survival. A selective BTK inhibitor has the potential to treat diseases involving inflammation and autoimmunity. Using Principia Biopharma’s proprietary Tailored Covalency™ technology, we discovered PRN473, a reversible covalent BTK inhibitor that selectively binds BTK with a slow off-rate as assessed in biochemical and cell based assays. A slow off-rate molecule with rapid systemic clearance may lead to a long duration of action and high efficacy, while reducing the potential for off target toxicities. The duration of binding of PRN473 was measured in vivo, with prolonged BTK occupancy confirmed after drug was cleared from plasma. In mouse and rat collagen-induced arthritis (CIA) models, PRN473 when dosed therapeutically demonstrated dose-dependent inhibition, reversal of arthritis, with almost complete abrogation of clinical scores and preservation of joint integrity and histology. BTK occupancy in splenocytes was found to be a robust measure of BTK inhibition and correlated with efficacy in the CIA models. These data in combination with GLP toxicology studies, where no organ specific toxicities were observed, validate using a reversible covalent BTK inhibitor to treat autoimmune diseases.

Differential drug class-specific metastatic effects following treatment with a panel of angiogenesis inhibitors

Inhibiting angiogenesis has become an important therapeutic strategy for cancer treatment but, like other current targeted therapies, benefits experienced for late-stage cancers can be curtailed by inherent refractoriness or by acquired drug resistance, requiring a need for better mechanistic understanding of such effects. Numerous preclinical studies have demonstrated that VEGF pathway inhibitors suppress primary tumour growth and metastasis. However, it has been recently reported that short-term VEGF and VEGFR inhibition can paradoxically accelerate tumour invasiveness and metastasis in certain models. Here we comprehensively compare the effects of both antibody and small molecule receptor tyrosine kinase (RTK) inhibitors targeting the VEGF-VEGFR pathway, using short-term therapy in various mouse models of metastasis. Our findings demonstrate that antibody inhibition of VEGF pathway molecules does not promote metastasis, in contrast to selected small molecule RTK inhibitors at elevated-therapeutic drug dosages. In particular, a multi-targeted RTK inhibitor, sunitinib, which most profoundly potentiated metastasis, also increased lung vascular permeability and promoted tumour cell extravasation. Mechanistically, sunitinib, but not anti-VEGF treatment, attenuated endothelial barrier function in culture and caused a global inhibition of protein tyrosine phosphorylation, including molecules important for maintaining endothelial cell-cell junctions. Together these findings indicate that, rather than a specific consequence of inhibiting the VEGF signalling pathway, pharmacological inhibitors of the VEGF pathway can have dose- and drug class-dependent side-effects on the host vasculature. These findings also advocate for the continued identification of mechanisms of resistance to anti-angiogenics and for therapy development to overcome it.

Therapeutic antibody targeting of individual Notch receptors

The four receptors of the Notch family are widely expressed transmembrane proteins that function as key conduits through which mammalian cells communicate to regulate cell fate and growth. Ligand binding triggers a conformational change in the receptor negative regulatory region (NRR) that enables ADAM protease cleavage at a juxtamembrane site that otherwise lies buried within the quiescent NRR. Subsequent intramembrane proteolysis catalysed by the gamma-secretase complex liberates the intracellular domain (ICD) to initiate the downstream Notch transcriptional program. Aberrant signalling through each receptor has been linked to numerous diseases, particularly cancer, making the Notch pathway a compelling target for new drugs. Although gamma-secretase inhibitors (GSIs) have progressed into the clinic, GSIs fail to distinguish individual Notch receptors, inhibit other signalling pathways and cause intestinal toxicity, attributed to dual inhibition of Notch1 and 2 (ref. 11). To elucidate the discrete functions of Notch1 and Notch2 and develop clinically relevant inhibitors that reduce intestinal toxicity, we used phage display technology to generate highly specialized antibodies that specifically antagonize each receptor paralogue and yet cross-react with the human and mouse sequences, enabling the discrimination of Notch1 versus Notch2 function in human patients and rodent models. Our co-crystal structure shows that the inhibitory mechanism relies on stabilizing NRR quiescence. Selective blocking of Notch1 inhibits tumour growth in pre-clinical models through two mechanisms: inhibition of cancer cell growth and deregulation of angiogenesis. Whereas inhibition of Notch1 plus Notch2 causes severe intestinal toxicity, inhibition of either receptor alone reduces or avoids this effect, demonstrating a clear advantage over pan-Notch inhibitors. Our studies emphasize the value of paralogue-specific antagonists in dissecting the contributions of distinct Notch receptors to differentiation and disease and reveal the therapeutic promise in targeting Notch1 and Notch2 independently.

HER2-targeted therapy reduces incidence and progression of midlife mammary tumors in female murine mammary tumor virus huHER2-transgenic mice

PURPOSE

This study examined the effectiveness of early and prolonged mu4D5 (the murine form of trastuzumab/Herceptin) treatment in transgenic mice that overexpress human HER2 (huHER2), under the murine mammary tumor virus promoter, as a model of huHER2-overexpressing breast cancer.

EXPERIMENTAL DESIGN

Mice were randomly assigned to one of three treatment groups and received i.p. injections from 17 weeks of age until either 52 weeks of age or morbidity. Fourteen mice received 100 mg/kg mu4D5, 14 mice received 100 mg/kg antiherpes simplex virus glycoprotein D control antibody, and 11 mice received a diluent control.

RESULTS

High levels of huHER2 expression were detectable in mammary glands of young virgin founder mice. Mammary adenocarcinomas were frequently found in female founders and progeny at an average age of 28 weeks, with some progressing to metastatic disease. The incidence of mammary tumors was significantly reduced, and tumor growth inhibition was observed in mice receiving mu4D5 compared with control mice. In addition, Harderian gland neoplasms, highly associated with overexpression of huHER2 in this transgenic line, were entirely absent in the mu4D5 treatment group, indicating down-regulation of huHER2 in vivo activity.

CONCLUSIONS

Early intervention with mu4D5 was of benefit in our transgenic mice at high risk for developing huHER2-overexpressing breast cancer. This study suggests a potential benefit of early treatment with Herceptin in HER2-positive primary breast cancer.

In vivo effects of cardiotrophin-1

Cardiotrophin-1 (CT-1) is a recently discovered cytokine that was isolated based on its ability to induce cardiac myocyte hypertrophy in vitro. In this study, the effects of chronic administration of CT-1 to mice (0.5 or 2 microg by intraperitoneal injection, twice a day for 14 days) were determined. A dose-dependent increase in both the heart weight and ventricular weight to body ratios was observed in the treated groups. The body weights of the animals were unaffected. These results indicate that CT-1 can induce cardiac hypertrophy in vivo. CT-1 was not specific for the heart, however. It stimulated the growth of the liver, kidney, and spleen, and caused atrophy of the thymus. CT-1 administration also increased the platelet counts by 70%, with no change in mean platelet volume. Red blood cell counts were increased in the treated animals, and there was a concomitant increase in haemoglobin concentration. Thus, CT-1 has a broad spectrum of biological activities in vivo. This observation is consistent with previous in-vitro findings showing that the mRNA for CT-1 is expressed in several tissues, and that CT-1 can function through binding to the leukaemia inhibitory factor (LIF) receptor and signalling through the gp130 pathway.

Buffered hydrochloric acid: a modern method of treating metabolic alkalosis

Twenty-one patients with metabolic alkalosis were treated successfully with intravenous hydrochloric acid (HCl) buffered in an amino acid solution (TPN). No complications of HCl were seen. TPN was used to meet energy needs and provide a buffering effect through the interaction of HCl and amino acids. Buffered HCl therapy should be considered as the initial treatment in patients with metabolic alkalosis associated with congestive heart failure, renal failure, hepatic failure, cerebral edema, or refractory metabolic alkalosis.