First-in-human Study of AZD5153, A Small-molecule Inhibitor of Bromodomain Protein 4, in Patients with Relapsed/Refractory Malignant Solid Tumors and Lymphoma

AZD5153, a reversible, bivalent inhibitor of the bromodomain and extraterminal family protein BRD4, has preclinical activity in multiple tumors. This first-in-human, phase I study investigated AZD5153 alone or with olaparib in patients with relapsed/refractory solid tumors or lymphoma. Adults with relapsed tumors intolerant of, or refractory to, prior therapies received escalating doses of oral AZD5153 once daily or twice daily continuously (21-day cycles), or AZD5153 once daily/twice daily continuously or intermittently plus olaparib 300 mg twice daily, until disease progression or unacceptable toxicity. Between June 30, 2017 and April 19, 2021, 34 patients received monotherapy and 15 received combination therapy. Dose-limiting toxicities were thrombocytopenia/platelet count decreased (n = 4/n = 2) and diarrhea (n = 1). The recommended phase II doses (RP2D) were AZD5153 30 mg once daily or 15 mg twice daily (monotherapy) and 10 mg once daily (intermittent schedule) with olaparib. With AZD5153 monotherapy, common treatment-emergent adverse events (TEAE) included fatigue (38.2%), thrombocytopenia, and diarrhea (each 32.4%); common grade ≥ 3 TEAEs were thrombocytopenia (14.7%) and anemia (8.8%). With the combination, common TEAEs included nausea (66.7%) and fatigue (53.3%); the most common grade ≥ 3 TEAE was thrombocytopenia (26.7%). AZD5153 had dose-dependent pharmacokinetics, with minimal accumulation, and demonstrated dose-dependent modulation of peripheral biomarkers, including upregulation of HEXIM1. One patient with metastatic pancreatic cancer receiving combination treatment had a partial response lasting 4.2 months. These results show AZD5153 was tolerable as monotherapy and in combination at the RP2Ds; common toxicities were fatigue, hematologic AEs, and gastrointestinal AEs. Strong evidence of peripheral target engagement was observed.

Phase Ia/b, Open-Label, Multicenter Study of AZD4635 (an Adenosine A2A Receptor Antagonist) as Monotherapy or Combined with Durvalumab, in Patients with Solid Tumors

PURPOSE

To evaluate AZD4635, an adenosine A2A receptor antagonist, as monotherapy or in combination with durvalumab in patients with advanced solid tumors.

PATIENTS AND METHODS

In phase Ia (dose escalation), patients had relapsed/refractory solid tumors; in phase Ib (dose expansion), patients had checkpoint inhibitor-naïve metastatic castration-resistant prostate cancer (mCRPC) or colorectal carcinoma, non-small cell lung cancer with prior anti-PD-1/PD-L1 exposure, or other solid tumors (checkpoint-naïve or prior anti-PD-1/PD-L1 exposure). Patients received AZD4635 monotherapy (75-200 mg once daily or 125 mg twice daily) or in combination with durvalumab (AZD4635 75 or 100 mg once daily). The primary objective was safety; secondary objectives included antitumor activity and pharmacokinetics; exploratory objectives included evaluation of an adenosine gene signature in patients with mCRPC.

RESULTS

As of September 8, 2020, 250 patients were treated (AZD4635, n = 161; AZD4635+durvalumab, n = 89). In phase Ia, DLTs were observed with monotherapy (125 mg twice daily; n = 2) and with combination treatment (75 mg; n = 1) in patients receiving nanosuspension. The most common treatment-related adverse events included nausea, fatigue, vomiting, decreased appetite, dizziness, and diarrhea. The RP2D of the AZD4635 capsule formulation was 75 mg once daily, as monotherapy or in combination with durvalumab. The pharmacokinetic profile was dose-proportional, and exposure was adequate to cover target with 100 mg nanosuspension or 75 mg capsule once daily. In patients with mCRPC receiving monotherapy or combination treatment, tumor responses (2/39 and 6/37, respectively) and prostate-specific antigen responses (3/60 and 10/45, respectively) were observed. High versus low blood-based adenosine signature was associated with median progression-free survival of 21 weeks versus 8.7 weeks.

CONCLUSIONS

AZD4635 monotherapy or combination therapy was well tolerated. Objective responses support additional phase II combination studies in patients with mCRPC.

Fanconi-BRCA pathway mutations in childhood T-cell acute lymphoblastic leukemia

BRCA2 (also known as FANCD1) is a core component of the Fanconi pathway and suppresses transformation of immature T-cells in mice. However, the contribution of Fanconi-BRCA pathway deficiency to human T-cell acute lymphoblastic leukemia (T-ALL) remains undefined. We identified point mutations in 9 (23%) of 40 human T-ALL cases analyzed, with variant allele fractions consistent with heterozygous mutations early in tumor evolution. Two of these mutations were present in remission bone marrow specimens, suggesting germline alterations. BRCA2 was the most commonly mutated gene. The identified Fanconi-BRCA mutations encode hypomorphic or null alleles, as evidenced by their inability to fully rescue Fanconi-deficient cells from chromosome breakage, cytotoxicity and/or G2/M arrest upon treatment with DNA cross-linking agents. Disabling the tumor suppressor activity of the Fanconi-BRCA pathway is generally thought to require biallelic gene mutations. However, all mutations identified were monoallelic, and most cases appeared to retain expression of the wild-type allele. Using isogenic T-ALL cells, we found that BRCA2 haploinsufficiency induces selective hypersensitivity to ATR inhibition, in vitro and in vivo. These findings implicate Fanconi-BRCA pathway haploinsufficiency in the molecular pathogenesis of T-ALL, and provide a therapeutic rationale for inhibition of ATR or other druggable effectors of homologous recombination.

Demethylated HSATII DNA and HSATII RNA Foci Sequester PRC1 and MeCP2 into Cancer-Specific Nuclear Bodies

This study reveals that high-copy satellite II (HSATII) sequences in the human genome can bind and impact distribution of chromatin regulatory proteins and that this goes awry in cancer. In many cancers, master regulatory proteins form two types of cancer-specific nuclear bodies, caused by locus-specific deregulation of HSATII. DNA demethylation at the 1q12 mega-satellite, common in cancer, causes PRC1 aggregation into prominent Cancer-Associated Polycomb (CAP) bodies. These loci remain silent, whereas HSATII loci with reduced PRC1 become derepressed, reflecting imbalanced distribution of UbH2A on these and other PcG-regulated loci. Large nuclear foci of HSATII RNA form and sequester copious MeCP2 into Cancer-Associated Satellite Transcript (CAST) bodies. Hence, HSATII DNA and RNA have an exceptional capacity to act as molecular sponges and sequester chromatin regulatory proteins into abnormal nuclear bodies in cancer. The compartmentalization of regulatory proteins within nuclear structure, triggered by demethylation of "junk" repeats, raises the possibility that this contributes to further compromise of the epigenome and neoplastic progression.