Abstract P6-21-07: The stapled peptide ALRN-6924, a dual inhibitor of MDMX and MDM2, and the CDK4/6 inhibitors palbociclib or abemaciclib synergistically enhance each other's in vitro and in vivo anticancer activity

Background ALRN-6924 is a cell-penetrating α-helical stapled peptide that disrupts the interaction of the p53 tumor suppressor protein and its inhibitors, MDMX and MDM2. Reactivation of p53 with ALRN-6924 in TP53-wild-type tumors triggers cell cycle arrest and apoptosis resulting in antitumor efficacy. CDK4/6 inhibitors induce apoptosis, senescence, and cell growth arrest via the interrelated Rb pathway, and co-amplification of MDM2 and CDK4 (both on chromosome 12q13) is a known oncogenic driver, suggesting that combinations of ALRN-6924 and CDK4/6i's may be synergistic. This study evaluates the antitumor efficacy and pharmacodynamics (PD) of ALRN-6924 combined with palbociclib or abemaciclib.

Methods ALRN-6924 was tested in combination with palbociclib or abemaciclib in MCF-7 breast cancer cell lines and MDM2- and CDK4-co-amplified SJSA-1 sarcoma cell lines using WST-1 cell viability assays. Synergy was quantified by the Chou-Talalay combination index method. Single agents and combinations were evaluated in cell culture using assays for apoptosis (Caspase 3/7 cleavage), proliferation (BrdU), senescence (ß-Galactosidase), colony growth (Giemsa), and Western blot analysis of p53, p21, Rb, phospho-Rb, FOXM1, and phospho-FOXM1; and E2F1 mRNA. In vivo combinations were tested in athymic nude mouse MCF-7 and SJSA-1 xenograft models, with cell cycle assays (EdU) measured in tumor samples by flow cytometry.

Results ALRN-6924 combinations with palbociclib or abemaciclib display synergistic in vitro anti-proliferative activity in MCF-7 and SJSA-1 cells. ALRN-6924 induces senescence in vitro as a monotherapy and in combination with CDK4/6i's. Western blot assays show that ALRN-6924/palbociclib combinations trigger sustained on-mechanism biomarker activation, vs. transient activation with single agents. Phospho-Rb and phospho-FOXM1 down-regulation, p53 and p21 up-regulation, and repression of E2F1 mRNA are sustained after wash-out in combination, but not in single agent-treated cells. MCF-7 and SJSA-1 tumor growth inhibition was improved in mice treated with ALRN-6924 combinations with either palbociclib or abemaciclib vs. single agent. EdU assays show that ALRN-6924/palbociclib combinations inhibit SJSA-1 tumor cell proliferation in vivo. Body weights and mortality data show the combination of ALRN-6924 with palbociclib 75 mg/kg/day was well tolerated; the combination with abemaciclib 100 mg/kg/day was tolerated with interruption and dose-reduction. No pharmacokinetic (PK) drug-drug interactions were noted in nude mice due to different modes of metabolism for ALRN-6924 (proteolysis) and palbociclib (CYP3A).

Conclusions This study demonstrates that ALRN-6924 and CDK4/6i combinations show synergistic activity. PD biomarkers indicate on-mechanism in vitro activity that is sustained after wash-out. In vivo efficacy, biomarker, PK, and tolerability results, plus clinical evidence that the most frequent and concerning safety issues for CDK4/6i's (neutropenia, leukopenia, infections) do not overlap with ALRN-6924's reported safety profile (Meric-Bernstam et al., ASCO 2017) support the development of combination regimens for breast cancer and other malignancies.

Citation Format: Annis A, Carvajal LA, Ren J-G, Sutton D, Santiago S, Narasimhan N, Guerlavais V, Aivado M. The stapled peptide ALRN-6924, a dual inhibitor of MDMX and MDM2, and the CDK4/6 inhibitors palbociclib or abemaciclib synergistically enhance each other's in vitro and in vivo anticancer activity [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-21-07.

Abstract P6-20-11: The stapled peptide ALRN-6924, a dual inhibitor of MDMX and MDM2, enhances antitumor efficacy of paclitaxel and Nab-paclitaxel in TP53 wild-type MCF-7 breast cancer models

Background: MDMX and MDM2 are endogenous inhibitors of the p53 tumor suppressor protein. MDMX levels are frequently elevated in luminal breast cancer, which generally expresses wild-type p53. ALRN-6924, an α-helical stapled peptide, is the first and only dual inhibitor of MDMX and MDM2 currently in clinical trials for solid tumors and hematological malignancies. We sought to determine the antitumor efficacy of the combination of ALRN-6924 with taxanes in models of human breast cancer.

Methods: Sulforhodamine B colorimetric assay was used to assess the cytotoxicity of the combination of ALRN-6924 with taxanes in vitro. Athymic nude mice were implanted with MCF-7 tumors and treated for four weeks with ALRN-6924 alone and in combination with paclitaxel in cremaphor (Taxol®, study #1) or a nanoparticle-albumin-bound (nab) formulation (Abraxane®, study #2). In study #1, ALRN-6924 (5, 10 mg/kg) was dosed twice weekly and paclitaxel (10, 15 mg/kg) was dosed weekly, with paclitaxel administered 6 h prior to ALRN-6924. In study #2, ALRN-6924 alone (5 mg/kg) was dosed twice weekly while nab-paclitaxel (15 mg/kg) was administered weekly in combination at -24h, -6h, 0h, +6h, or +24h relative to ALRN-6924 administration.

Results: ALRN-6924 was found to have synergistic activity with paclitaxel in both MCF-7 and ZR-75-1 cell lines in vitro (Combination index: 0.874 and 0.323 respectively). In in vivo study #1, the combination of ALRN-6924 and paclitaxel significantly inhibited MCF-7 tumor growth compared to either agent alone (p<0.005). Paclitaxel 15 mg/kg + ALRN-6924 5 mg/kg resulted in the greatest tumor inhibition with average tumor size decreased by 13% at four weeks versus the starting size.

In study #2, the combination of nab-paclitaxel with ALRN-6924 administered -6h to +24h relative to nab-paclitaxel resulted in improved efficacy over either single agent and a significant increase in the number of tumor regressions (up to 6/10 with 3 consecutive measurements <50% of starting volume) compared to nab-paclitaxel alone (1/10, p<0.005). When ALRN-6924 was administered 24h prior to nab-paclitaxel, there was a marked decrease in efficacy and no tumor regressions were observed.

In both studies, drug treatments were well tolerated with no significant weight loss in mice.

Conclusion: The significant increase in efficacy observed with ALRN-6924 in combination with paclitaxel supports further evaluation in patients with breast cancer.

Citation Format: Pairawan SS, Yuca E, Evans K, Annis A, Narasimhan N, Sutton D, Carvajal LA, Ren J-G, Santiago S, Guerlavais V, Akcakanat A, Tapia C, Illeana Dumbrava EE, Aivado M, Meric-Bernstam F. The stapled peptide ALRN-6924, a dual inhibitor of MDMX and MDM2, enhances antitumor efficacy of paclitaxel and Nab-paclitaxel in TP53 wild-type MCF-7 breast cancer models [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-20-11.

Pharmacologic treatment of chronic alcoholism

Of the many drug therapies mentioned in this review, only the alcohol-sensitizing drugs have current therapeutic applications in primary alcoholics. When alcohol abuse occurs in association with anxiety, depression, or schizophrenia, treatment with the anxiolytic, antidepressant, and neuroleptic drugs, respectively, may facilitate the alcoholic's ability to participate in other programs. Patients should receive drugs that are appropriate to treatment goals as well as to their psychosocial status. Even if a drug therapy is shown to be efficacious under controlled experimental conditions, its effectiveness may be compromised by a large number of factors that include poor compliance by the patient, a lack of a treatment strategy, or failure to optimize the treatment conditions. New pharmacotherapies with actions directed at central neurochemical pathways mediating alcohol consumption are urgently needed. However, even if such agents become available, they too will only be adjuncts to behavioral and social therapies directed at stabilizing all aspects of the alcoholic's life.