Reprogramming of cellular metabolism towards de novo serine production fuels the growth of cancer cells, providing essential precursors such as amino acids and nucleotides and controlling the ...antioxidant and methylation capacities of the cell. The enzyme serine hydroxymethyltransferase (SHMT) has a key role in this metabolic shift, and directs serine carbons to one-carbon units metabolism and thymidilate synthesis. While the mitochondrial isoform of SHMT (SHMT2) has recently been identified as an important player in the control of cell proliferation in several cancer types and as a hot target for anticancer therapies, the role of the cytoplasmic isoform (SHMT1) in cancerogenesis is currently less defined. In this paper we show that SHMT1 is overexpressed in tissue samples from lung cancer patients and lung cancer cell lines, suggesting that, in this widespread type of tumor, SHMT1 plays a relevant role. We show that SHMT1 knockdown in lung cancer cells leads to cell cycle arrest and, more importantly, to p53-dependent apoptosis. Our data demonstrate that the induction of apoptosis does not depend on serine or glycine starvation, but is because of the increased uracil accumulation during DNA replication.
The phosphatidylinositol 3-kinase (PI3K) pathway plays a central role in cell proliferation and survival in human cancer. Mutations in PIK3CA, the gene coding the p110α catalytic subunit of PI3K, are ...frequent in cancer and result in PI3K pathway activation. About 25% of HER2-positive breast cancers also carry PIK3CA mutations, known to confer resistance to anti-HER2 therapy. Here we report the preclinical characterization of MEN1611, a potent and selective orally available PI3K inhibitor, showing high activity against p110α mutant isoforms and sparing the δ isoform.
In vivo efficacy studies were evaluated through Tumour Volume Inhibition % (TVI%) and mRECIST criteria using cancer cell lines and patient-derived xenograft (PDX) models. Pathway activation and protein degradation analyses were performed by western blot and capillary electrophoresis immunoassay. Immune modulation was evaluated using murine macrophages differentiated in vitro.
Consistent with its mechanism of action, MEN1611 down-modulates the PI3K/AKT signaling as well as selected downstream targets, both in vitro and in vivo. MEN1611 acts synergistically when combined with trastuzumab in several HER2-positive PIK3CA-mutated breast cancer cell lines and patient-derived xenograft models. The in vivo efficacy in trastuzumab-resistant models is supported by a long-lasting antitumor activity, paralleled by mechanistic down-regulation of pharmacodynamic biomarkers. Moreover, MEN1611 showed the ability to induce a dose-dependent alpha-isoform depletion, and to modulate the macrophage polarization towards a pro-inflammatory phenotype, consistent with its capability to co-inhibit P110γ.
Overall, these preclinical data support the progression in the development of MEN1611 in breast cancer and pave the way to the B-Precise-01 clinical study, a multicentre phase Ib study.
NCT03767335.
Menarini Ricerche S.p.A.
Menarini Ricerche S.p.A.
A. Fiascarelli: Full / Part-time employment: Menarini RIcerche S.p.A. G. Merlino: Full / Part-time employment: Menarini Ricerche S.p.A. S. Capano: Full / Part-time employment: Menarini Ricerche S.p.A. A. Paoli: Full / Part-time employment: Menarini Ricerche S.p.A.. A. Bressan: Full / Part-time employment: Menarini Ricerche. M. Bigioni: Full / Part-time employment: Menarini Ricerche S.p.A.. M. Scaltriti: Advisory / Consultancy: Memorial Sloan-Kettering Cancer Center. J. Arribas: Advisory / Consultancy: Vall d’Hebron Institute of Oncology. C. Bernadó Morales: Advisory / Consultancy: Vall d’Hebron Institute of Oncology. A. Pellacani: Leadership role, Full / Part-time employment: Menarini Ricerche S.p.A.. M. Salerno: Leadership role, Full / Part-time employment: Menarini Ricerche. M. Binaschi: Leadership role, Full / Part-time employment: Menarini Ricerche S.p.A.
Abstract
Background
The phosphatidylinositol 3-kinase (PI3K) pathway plays a central role in cell proliferation and survival in human cancer. Mutations in PIK3CA, the gene coding the p110α catalytic ...subunit of PI3K, are frequent in cancer and result in PI3K pathway activation. About 25% of HER2-positive breast cancers also carry PIK3CA mutations, known to confer resistance to anti-HER2 therapy. Here we report the preclinical characterization of MEN1611, a potent and selective orally available PI3K inhibitor, showing high activity against p110α mutant isoforms and sparing the δ isoform.
Methods
In vivo efficacy studies were evaluated through Tumour Volume Inhibition % (TVI%) and mRECIST criteria using cancer cell lines and patient-derived xenograft (PDX) models. Pathway activation and protein degradation analyses were performed by western blot and capillary electrophoresis immunoassay. Immune modulation was evaluated using murine macrophages differentiated in vitro.
Results
Consistent with its mechanism of action, MEN1611 down-modulates the PI3K/AKT signaling as well as selected downstream targets, both in vitro and in vivo. MEN1611 acts synergistically when combined with trastuzumab in several HER2-positive PIK3CA-mutated breast cancer cell lines and patient-derived xenograft models. The in vivo efficacy in trastuzumab-resistant models is supported by a long-lasting antitumor activity, paralleled by mechanistic down-regulation of pharmacodynamic biomarkers. Moreover, MEN1611 showed the ability to induce a dose-dependent alpha-isoform depletion, and to modulate the macrophage polarization towards a pro-inflammatory phenotype, consistent with its capability to co-inhibit P110γ.
Conclusions
Overall, these preclinical data support the progression in the development of MEN1611 in breast cancer and pave the way to the B-Precise-01 clinical study, a multicentre phase Ib study.
Clinical trial identification
NCT03767335.
Legal entity responsible for the study
Menarini Ricerche S.p.A.
Funding
Menarini Ricerche S.p.A.
Disclosure
A. Fiascarelli: Full / Part-time employment: Menarini RIcerche S.p.A. G. Merlino: Full / Part-time employment: Menarini Ricerche S.p.A. S. Capano: Full / Part-time employment: Menarini Ricerche S.p.A. A. Paoli: Full / Part-time employment: Menarini Ricerche S.p.A.. A. Bressan: Full / Part-time employment: Menarini Ricerche. M. Bigioni: Full / Part-time employment: Menarini Ricerche S.p.A.. M. Scaltriti: Advisory / Consultancy: Memorial Sloan-Kettering Cancer Center. J. Arribas: Advisory / Consultancy: Vall d’Hebron Institute of Oncology. C. Bernadó Morales: Advisory / Consultancy: Vall d’Hebron Institute of Oncology. A. Pellacani: Leadership role, Full / Part-time employment: Menarini Ricerche S.p.A.. M. Salerno: Leadership role, Full / Part-time employment: Menarini Ricerche. M. Binaschi: Leadership role, Full / Part-time employment: Menarini Ricerche S.p.A.
Purpose Dysregulation of the PI3K pathway is one of the most common events in breast cancer. Here we investigate the activity of the PI3K inhibitor MEN1611 at both molecular and phenotypic levels by ...dissecting and comparing its profile and efficacy in HER2 + breast cancer models with other PI3K inhibitors. Methods Models with different genetic backgrounds were used to investigate the pharmacological profile of MEN1611 against other PI3K inhibitors. In vitro studies evaluated cell viability, PI3K signaling, and cell death upon treatment with MEN1611. In vivo efficacy of the compound was investigated in cell line- and patient-derived xenografts models. Results Consistent with its biochemical selectivity, MEN1611 demonstrated lower cytotoxic activity in a p110delta-driven cellular model when compared to taselisib, and higher cytotoxic activity in the p110beta-driven cellular model when compared to alpelisib. Moreover, MEN1611 selectively decreased the p110alpha protein levels in PIK3CA mutated breast cancer cells in a concentration- and proteasome-dependent manner. In vivo, MEN1611 monotherapy showed significant and durable antitumor activity in several trastuzumab-resistant PIK3CA-mutant HER2 + PDX models. The combination of trastuzumab and MEN1611 significantly improved the efficacy compared to single agent treatment. Conclusions The profile of MEN1611 and its antitumoral activity suggest an improved profile as compared to pan-inhibitors, which are limited by a less than ideal safety profile, and isoform selective molecules, which may potentially promote development of resistance mechanisms. The compelling antitumor activity in combination with trastuzumab in HER2 + trastuzumab-resistant, PIK3CA mutated breast cancer models is at the basis of the ongoing B-Precise clinical trial (NCT03767335).
MEN1611 is a novel orally bioavailable PI3K inhibitor currently in clinical development for patients with HER2‐positive (HER2+) PI3KCA mutated advanced/metastatic breast cancer (BC) in combination ...with trastuzumab (TZB). In this work, a translational model‐based approach to determine the minimum target exposure of MEN1611 in combination with TZB was applied. First, pharmacokinetic (PK) models for MEN1611 and TZB in mice were developed. Then, in vivo tumor growth inhibition (TGI) data from seven combination studies in mice xenograft models representative of the human HER2+ BC non‐responsive to TZB (alterations of the PI3K/AkT/mTOR pathway) were analyzed using a PK‐pharmacodynamic (PD) TGI model for co‐administration of MEN1611 and TZB. The established PK‐PD relationship was used to quantify the minimum effective MEN1611 concentration, as a function of TZB concentration, needed for tumor eradication in xenograft mice. Finally, a range of minimum effective exposures for MEN1611 were extrapolated to patients with BC, considering the typical steady‐state TZB plasma levels in patients with BC following three alternative regimens (i.v. 4 mg/kg loading dose +2 mg/kg q1w, i.v. 8 mg/kg loading dose +6 mg/kg q3w or s.c. 600 mg q3w). A threshold of about 2000 ng·h/ml for MEN1611 exposure associated with a high likelihood of effective antitumor activity in a large majority of patients was identified for the 3‐weekly and the weekly i.v. schedule for TZB. A slightly lower exposure (i.e., 25% lower) was found for the 3‐weekly s.c. schedule. This important outcome confirmed the adequacy of the therapeutic dose administered in the ongoing phase 1b B‐PRECISE‐01 study in patients with HER2+ PI3KCA mutated advanced/metastatic BC.
Adaptive metabolic reprogramming gives cancer cells a proliferative advantage. Tumour cells extensively use glycolysis to sustain anabolism and produce serine, which not only refuels the one‐carbon ...units necessary for the synthesis of nucleotide precursors and for DNA methylation, but also affects the cellular redox homeostasis. Given its central role in serine metabolism, serine hydroxymethyltransferase (SHMT), a pyridoxal 5′‐phosphate (PLP)‐dependent enzyme, is an attractive target for tumour chemotherapy. In humans, the cytosolic isoform (SHMT1) and the mitochondrial isoform (SHMT2) have distinct cellular roles, but high sequence identity and comparable catalytic properties, which may complicate development of successful therapeutic strategies. Here, we investigated how binding of the cofactor PLP controls the oligomeric state of the human isoforms. The fact that eukaryotic SHMTs are tetrameric proteins while bacterial SHMTs function as dimers may suggest that the quaternary assembly in eukaryotes provides an advantage to fine‐tune SHMT function and differentially regulate intertwined metabolic fluxes, and may provide a tool to address the specificity problem. We determined the crystal structure of SHMT2, and compared it to the apo‐enzyme structure, showing that PLP binding triggers a disorder‐to‐order transition accompanied by a large rigid‐body movement of the two cofactor‐binding domains. Moreover, we demonstrated that SHMT1 exists in solution as a tetramer, both in the absence and presence of PLP, while SHMT2 undergoes a dimer‐to‐tetramer transition upon PLP binding. These findings indicate an unexpected structural difference between the two human SHMT isoforms, which opens new perspectives for understanding their differing behaviours, roles or regulation mechanisms in response to PLP availability in vivo.
Antibody drug conjugates represent an important class of anti-cancer drugs in both solid tumors and hematological cancers. Here, we report preclinical data on the anti-tumor activity of the ...first-in-class antibody drug conjugate MEN1309/OBT076 targeting CD205. The study included preclinical in vitro activity screening on a large panel of cell lines, both as single agent and in combination and validation experiments on in vivo models. CD205 was first shown frequently expressed in lymphomas, leukemias and multiple myeloma by immunohistochemistry on tissue microarrays. Anti-tumor activity of MEN1309/OBT076 as single agent was then shown across 42 B-cell lymphoma cell lines with a median IC50 of 200 pM and induction of apoptosis in 25/42 (59.5%) of the cases. The activity appeared highly correlated with its target expression. After in vivo validation as the single agent, the antibody drug conjugate synergized with the BCL2 inhibitor venetoclax, and the anti-CD20 monoclonal antibody rituximab. The first-in-class antibody drug targeting CD205, MEN1309/OBT076, demonstrated strong pre-clinical anti-tumor activity in lymphoma, warranting further investigations as a single agent and in combination.
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