Onvansertib in Combination with FOLFIRI and Bevacizumab in Second-Line Treatment of KRAS-Mutant Metastatic Colorectal Cancer: A Phase Ib Clinical Study

PURPOSE

Onvansertib is a highly specific inhibitor of polo-like kinase 1 (PLK1), with demonstrated safety in solid tumors. We evaluated, preclinically and clinically, the potential of onvansertib in combination with chemotherapy as a therapeutic option for KRAS-mutant colorectal cancer.

PATIENTS AND METHODS

Preclinical activity of onvansertib was assessed (i) in vitro in KRAS wild-type and -mutant isogenic colorectal cancer cells and (ii) in vivo, in combination with irinotecan, in a KRAS-mutant xenograft model. Clinically, a phase Ib trial was conducted to investigate onvansertib at doses 12, 15, and 18 mg/m2 (days 1-5 and 14-19 of a 28-day cycle) in combination with FOLFIRI/bevacizumab (days 1 and 15) in patients with KRAS-mutant metastatic colorectal cancer who had prior oxaliplatin exposure. Safety, efficacy, and changes in circulating tumor DNA (ctDNA) were assessed.

RESULTS

In preclinical models, onvansertib displayed superior activity in KRAS-mutant than wild-type isogenic colorectal cancer cells and demonstrated potent antitumor activity in combination with irinotecan in vivo. Eighteen patients enrolled in the phase Ib study. Onvansertib recommended phase II dose was established at 15 mg/m2. Grade 3 and 4 adverse events (AE) represented 15% of all treatment-related AEs, with neutropenia being the most common. Partial responses were observed in 44% of patients, with a median duration of response of 9.5 months. Early ctDNA dynamics were predictive of treatment efficacy.

CONCLUSIONS

Onvansertib combined with FOLIFRI/bevacizumab exhibited manageable safety and promising efficacy in second-line treatment of patients with KRAS-mutant metastatic colorectal cancer. Further exploration of this combination therapy is ongoing. See related commentary by Stebbing and Bullock, p. 2005.

Spliceosome mutations are associated with clinical response in a phase 1b/2 study of the PLK1 inhibitor onvansertib in combination with decitabine in relapsed or refractory acute myeloid leukemia

PLK1 is overexpressed in acute myeloid leukemia (AML). A phase 1b trial of the PLK1 inhibitor onvansertib (ONV) combined with decitabine (DAC) demonstrated initial safety and efficacy in patients with relapsed/refractory (R/R) AML. The current study aimed to identify molecular predictors of response to ONV + DAC in R/R AML patients. A total of 44 R/R AML patients were treated with ONV + DAC and considered evaluable for efficacy. Bone marrow (BM) samples were collected at baseline for genomic and transcriptomic analysis (n = 32). A 10-gene expression signature, predictive of response to ONV + DAC, was derived from the leading-edge genes of gene set enrichment analyses (GSEA). The gene signature was evaluated in independent datasets and used to identify associated mutated genes. Twenty percent of the patients achieved complete remission, with or without hematologic count recovery (CR/CRi), and 32% exhibited a ≥50% reduction in bone marrow blasts. Patients who responded to treatment had elevated mitochondrial function and OXPHOS. The gene signature was not associated with response to DAC alone in an independent dataset. By applying the signature to the BeatAML cohort (n = 399), we identified a positive association between predicted ONV + DAC response and mutations in splicing factors (SF). In the phase 1b/2 trial, patients with SF mutations (SRSF2, SF3B1) had a higher CR/CRi rate (50%) compared to those without SF mutations (9%). PLK1 inhibition with ONV in combination with DAC could be a potential therapy in R/R AML patients, particularly those with high OXPHOS gene expression and SF mutations.

Abstract 4995: Targeting PLK1 effectively suppresses growth of small cell lung cancer

Small cell lung cancer (SCLC) is an aggressive neuroendocrine tumor characterized by rapid disease progression and poor patient survival. Key transcription factors implicated as drivers of unique biological phenotypes of SCLC include ASCL1, NEUROD1, YAP1, and POU2F3. Strategies to exploit these phenotypes for innovative precision medicine approaches will be impactful. Using an unbiased agnostic preclinical drug screen to uncover therapeutic opportunities in SCLC, we identified a strong signal with PLK1 inhibitors (PLK1i) with low nanomolar IC50. We extended the in vitro findings by testing the efficacy of PLK1i in vivo using traditional xenograft of SCLC H526 cell line and patient derived xenografts (PDX). Volasertib achieved significant tumor growth inhibition relative to control in H526 xenografts. Also, onvansertib significantly inhibited growth of platinum-resistant and platinum-sensitive PDXs. The combination of PLK1i with standard chemotherapeutic agents identified promising synergy of the combination of onvansertib and paclitaxel. We further interrogated for predictive biomarkers of PLK1i sensitivity using gene expression profile comparing highly sensitive to less sensitive cell lines. High expression of C-MYC but not PLK1, TP53 or RB was associated with resistance to PLK1i. Conversely, while TP53 expression level did not correlate, TP53 gene mutation status (inactivating disruptive mutations) correlated with cell sensitivity to PLK1i. We queried the publicly available CCLE and the Cancer Therapeutics Response Portal to evaluate whether any of the SCLC subtypes have therapeutic vulnerability to PLK1i. In general, high expression of YAP1 in SCLC cell lines correlated with greater sensitivity to PLK1i. A YAP1 positive cell line, SW1271, with strong TP53 expression was particularly resistant to PLK1i. CRISPR knockout of YAP1 in this cell line enhanced SW1271 sensitivity to PLK1i suggesting that YAP1 expression as a marker of vulnerability to PLK1i could be context dependent especially when co-occurring with TP53 mutations. The mechanism of this interaction will be discussed.

Citation Format: John C. Schmitz, Guojing Zhang, Andrey A. Ivanov, Abbe Pannucci, Maya Ridinger, Taofeek K. Owonikoko. Targeting PLK1 effectively suppresses growth of small cell lung cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4995.

Plk1 Inhibitors and Abiraterone Synergistically Disrupt Mitosis and Kill Cancer Cells of Disparate Origin Independently of Androgen Receptor Signaling

Abiraterone is a standard treatment for metastatic castrate-resistant prostate cancer (mCRPC) that slows disease progression by abrogating androgen synthesis and antagonizing the androgen receptor (AR). Here we report that inhibitors of the mitotic regulator polo-like kinase-1 (Plk1), including the clinically active third-generation Plk1 inhibitor onvansertib, synergizes with abiraterone in vitro and in vivo to kill a subset of cancer cells from a wide variety of tumor types in an androgen-independent manner. Gene-expression analysis identified an AR-independent synergy-specific gene set signature upregulated upon abiraterone treatment that is dominated by pathways related to mitosis and the mitotic spindle. Abiraterone treatment alone caused defects in mitotic spindle orientation, failure of complete chromosome condensation, and improper cell division independently of its effects on AR signaling. These effects, although mild following abiraterone monotherapy, resulted in profound sensitization to the antimitotic effects of Plk1 inhibition, leading to spindle assembly checkpoint-dependent mitotic cancer cell death and entosis. In a murine patient-derived xenograft model of abiraterone-resistant metastatic castration-resistant prostate cancer (mCRPC), combined onvansertib and abiraterone resulted in enhanced mitotic arrest and dramatic inhibition of tumor cell growth compared with either agent alone. Overall, this work establishes a mechanistic basis for the phase II clinical trial (NCT03414034) testing combined onvansertib and abiraterone in mCRPC patients and indicates this combination may have broad utility for cancer treatment.

SIGNIFICANCE

Abiraterone treatment induces mitotic defects that sensitize cancer cells to Plk1 inhibition, revealing an AR-independent mechanism for this synergistic combination that is applicable to a variety of cancer types.

Abstract 1236: Biomarkers of response to abiraterone and the polo-like kinase 1 (PLK1) inhibitor onvansertib in metastatic castration resistant prostate cancer (mCRPC) patients

Background: Abiraterone (abi), a widely-used standard of care for castration-sensitive and castration-resistant prostate cancers, inhibits the androgen receptor signaling pathway. While abi slows disease progression, extended treatment universally results in acquired resistance. PLK1 is a serine/threonine protein kinase, master regulator of the cell cycle. PLK1 is upregulated in prostate cancer following androgen-deprivation therapy and PLK1 inhibition synergizes with abi in CRPC models, providing a potential means to reverse or delay abi resistance. Onvansertib is an oral highly selective PLK1 inhibitor that showed synergistic anti-tumor activity with abi in in-vitro and in-vivo CRPC models. A phase 2 clinical trial (NCT03414034) is ongoing to assess the efficacy of onvansertib in combination with abi in mCRPC patients with early abi resistance. Genomic and transcriptomic analyses were performed to identify response biomarkers for the onvansertib/abi combination.

Methods: Cell-free DNA isolated from patient plasma was analyzed by targeted sequencing using Guardant OMNI® (500-gene panel). RNA expression profiling was performed using archival tissues by Veracyte (formerly Decipher Biosciences). Genomic and transcriptomic profiles of patients who progressed within 12 weeks of treatment (“PD” patients) were compared to patients who had radiographic stable disease at 12 weeks (“SD” patients).

Results: Genomic profiles were successfully obtained from 19 PD patients and 31 SD patients. On average, PD patients had more somatic alterations than SD patients (14 vs 7, p=0.017). SD was positively correlated with the presence of alterations affecting signaling pathways such as MTOR, NF1, PTEN and EGFR, and negatively correlated with gene alterations involved in cell migration and invasion such as APC, KDR, PREX2, NF2 and AKT3. Eight (26%) of the 31 SD patients had alterations either in MTOR (n=5) or PTEN (n=3), that were predicted to have functional impacts on the protein, while only 1 PD patient (5%) had an alteration in either of those 2 genes. Moreover, transcriptomic analyses performed on tissue from 8 patients revealed that SD patients (n=5) exhibited a gene expression signature of “PTEN loss” that was absent in PD patients (n=3) (p=0.016).

Conclusions: Taken together, these data suggest that alterations in PTEN and MTOR, two key genes of the PI3K signaling pathway, are potential biomarkers for sensitivity to onvansertib/abi combination in mCRPC patients with early abi-resistance. Preclinical studies are underway to assess the activity of onvansertib/abi in combination with PI3K-pathway inhibitors.

Citation Format: Maya Ridinger, Errin Samuelsz, Peter J. Croucher, Mark Erlander, Katherine Ruffner, David J. Einstein. Biomarkers of response to abiraterone and the polo-like kinase 1 (PLK1) inhibitor onvansertib in metastatic castration resistant prostate cancer (mCRPC) patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1236.

Abstract 3237: Combining PARP inhibition with the polo-like kinase 1 (PLK1) inhibitor onvansertib overcomes PARP inhibitor resistance

Background: BRCA1/2 mutant tumors cells are deficient for homologous recombination (HR)-mediated DNA repair and are particularly sensitive to PARP inhibitors (PARPi). PARPi have proved efficacy in breast, ovarian, prostate, and pancreatic cancers, particularly in HR-deficient tumors, while their activity is limited in HR-proficient tumors. However, PARPi resistance is inevitable and therapeutic resistance resulting from restoration of HR repair is a pressing clinical problem. Identifying combination treatments to sensitize tumors cells to PARPi and/or overcome PARPi resistance is critical to expand the benefit of these therapies. The Polo-like kinase 1 (PLK1), a serine threonine kinase, is a master regulator of mitosis, overexpressed in many cancers. PLK1 is also involved in the DNA damage response through the promotion of HR-mediated DNA repair and the recovery from the G2/M checkpoint. PLK1 roles in HR repair suggest that PLK1 inhibition may reverse PARPi resistance.

Methods: To test the effect of PLK1 and PARP inhibitors combination, we used onvansertib, a highly selective, ATP-competitor PLK1 inhibitor currently in clinical development and the FDA-approved PARPi olaparib. The antitumor effect of the single and combined drug treatments was tested in 2 BRCA1 mutated high-grade serous ovarian cancer (HGSOC) patient derived (PDX) models resistant to olaparib. Orthotopically PDX transplanted mice were treated for 4 weeks and followed for survival.

Results: The combination of onvansertib and olaparib was well tolerated and showed strong anti-tumor activity in both PDX models. The combination significantly increased mice survival in comparison to vehicle, olaparib and onvansertib, and showed that onvansertib can re-sensitize PARPi-resistant tumors to olaparib. Median survival increased by 2.7-fold and 8.1-fold respectively in the 2 PDX models in the combination group versus vehicle and the Kaplan Meyer survival curves of mice treated with the combination showed a statistically survival advantage versus control and single agent treated mice. Pharmacodynamic analyses showed an increase in mitotic, apoptotic and DNA damage markers in tumors treated with the combination versus vehicle.

Conclusions: The combination of the PLK1 inhibitor onvansertib and the PARPi olaparib showed potent anti-tumor activity in olaparib-resistant BRAC1 mutant HGSOC PDX models. Additional studies are ongoing to further assess the potential of the combination in BRCA wild-type and mutant ovarian, prostate, pancreatic and breast cancer preclinical models.

Citation Format: Michela Chiappa, Federica Guffanti, Alessandra Decio, Alessandro Aliverti, Francesca Ricci, Eugenio Scanziani, Federica Camin, Ilaria Craparotta, Maria Chiara Barbera, Marco Bolis, Maya Ridinger, Giovanna Damia. Combining PARP inhibition with the polo-like kinase 1 (PLK1) inhibitor onvansertib overcomes PARP inhibitor resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3237.

Onvansertib and paclitaxel combined in platinum-resistant ovarian carcinomas

Background

Ovarian carcinoma is extremely sensitive to (platinum-based) chemotherapy; however, most patients will relapse with platinum-resistant disease, badly affecting their prognosis. Effective therapies for relapsing resistant tumors are urgently needed.

Methods

We used patient-derived xenografts (PDXs) of ovarian carcinoma resistant to cisplatin (DDP) to test in vivo the combination of paclitaxel (15 mg/kg i.v. once a week for 3 weeks) and onvansertib, a plk1 inhibitor, (50 mg/kg orally 4 days a week for 3 weeks). The PDX models were subcutaneously (s.c.) or orthotopically transplanted in nude mice and antitumor efficacy was evaluated as tumor growth inhibition and survival advantages of the combination over untreated and single agent treatment.

Results

The combination of onvansertib and paclitaxel was very well tolerated with weight loss no greater than 15% in the combination group compared with the control group. In the orthotopically transplanted PDXs, single onvansertib and paclitaxel treatments prolonged survival; however, the combined treatment was much more active, with median survival from three- to six-fold times that of untreated mice. Findings were similar with the s.c. transplanted PDX, though there was greater heterogeneity in tumor response. Ex vivo tumors treated with the combination showed greater induction of γH2AX, marker of apoptosis and DNA damage, and pSer10H3, a marker of mitotic block.

Conclusion

The efficacy of onvansertib and paclitaxel combination in these preclinical ovarian cancer models supports the clinical translatability of this combination as an effective therapeutic approach for platinum-resistant high-grade ovarian carcinoma.

A novel PLK1 inhibitor onvansertib effectively sensitizes MYC-driven medulloblastoma to radiotherapy

BACKGROUND

Group 3 medulloblastoma (MB) is often accompanied by MYC amplification. PLK1 is an oncogenic kinase that controls cell cycle and proliferation and has been preclinically validated as a cancer therapeutic target. Onvansertib (PCM-075) is a novel, orally available PLK1 inhibitor, which shows tumor growth inhibition in various types of cancer. We aim to explore the effect of onvansertib on MYC-driven medulloblastoma as a monotherapy or in combination with radiation.

METHODS

Crisper-Cas9 screen was used to discover essential genes for MB tumor growth. Microarray and immunohistochemistry on pediatric patient samples were performed to examine the expression of PLK1. The effect of onvansertib in vitro was measure by cell viability, colony-forming assays, extreme limiting dilution assay, and RNA-Seq. ALDH activity, cell-cycle distribution, and apoptosis were analyzed by flow cytometry. DNA damage was assessed by immunofluorescence staining. Medulloblastoma xenografts were generated to explore the monotherapy or radio-sensitizing effect.

RESULTS

PLK1 is overexpressed in Group 3 MB. The IC50 concentrations of onvansertib in Group 3 MB cell lines were in a low nanomolar range. Onvansertib reduced colony formation, cell proliferation, stem cell renewal and induced G2/M arrest in vitro. Moreover, onvansertib in combination with radiation increased DNA damage and apoptosis compared with radiation treatment alone. The combination radiotherapy resulted in marked tumor regression in xenografts.

CONCLUSIONS

These findings demonstrate the efficacy of a novel PLK1 inhibitor onvansertib in vitro and in xenografts of Group 3 MB, which suggests onvansertib is an effective strategy as monotherapy or in combination with radiotherapy in MB.

A phase 2 study of onvansertib in combination with abiraterone and prednisone in patients with metastatic castration-resistant prostate cancer (mCRPC)

TPS219

Background: Metastatic CRPC is a leading cause of cancer death worldwide. Although abiraterone (abi) + prednisone in either castration-sensitive or castration-resistant disease increases survival, resistance is universal and generally occurs within 9-16 months of initiating treatment. Polo-like kinase 1 (PLK1) is a serine/threonine protein kinase that regulates mitotic function and is upregulated in prostate cancer following androgen-deprivation therapy (ADT). Onvansertib is an oral and highly-selective PLK1 inhibitor that demonstrated safety and tolerability as a single agent in a Ph1 trial. Preclinical studies showed that PLK1 inhibition enhanced abi anti-tumor effect in cell line models and in patient-derived tumor xenografts via an AR-independent mechanism. Transcriptomic analyses revealed that abi induced mitosis-related gene sets in cells synergistic for abi + onvansertib, and identified an abi-onvansertib synergy gene signature. Methods: The goal of this phase 2 study (NCT03414034) is to observe the effects of onvansertib + abi on disease control, as assessed by prostate-specific antigen (PSA) decline or stabilization after 12 weeks of study treatment, in subjects with mCRPC and early resistance to abi. Patients are enrolled at time of PSA progression while on standard abi. Prior treatment with enzalutamide or apalutamide is not permitted. Three onvansertib dosing schedules are tested in noncomparative arms: arm A (24 mg/m2 on days 1-5 of a 21-day cycle), arm B (18 mg/m2 on days 1-5 of a 14-day cycle), and arm C (12 mg/m2 on days 1-14 of a 21-day cycle). To-date, 24 patients were enrolled in Arm A, and 20 patients each in Arms B and C. With 32 patients in each arm, there will be 90% power to detect a change in disease-control rate from 10% (null) to 30% (alternative). Based on a Simon’s two-stage optimal design, the study will terminate early if < 2 of the first 13 patients in each arm achieve disease control. Exploratory analyses include evaluation of the presence of the androgen receptor variant 7 (AR-V7) in circulating tumor cells and targeted genomic profiling of circulating tumor DNA to assess associations between genomic alterations and response to treatment. Additionally, transcriptomic analysis of archived tumor tissue will be performed to identify gene expression signatures associated with clinical responses. Clinical trial information: NCT03414034.

A phase 1b/2 trial of the PLK1 inhibitor onvansertib in combination with FOLFIRI-bev in 2L treatment of KRAS-mutated (mKRAS) metastatic colorectal carcinoma (mCRC)

100

Background: CRC is a common cancer world-wide, accounting for ̃10% of cancer cases and mortality. Treatment options are limited, and survival is poor for pts with advanced disease, particularly those with mKRAS. After failure of 1L treatment for mCRC, regardless of KRAS mutation status, the ORR for FOLFIRI-bev is 5-13%, with PFS 4-6 mos, and OS 10-12 mos. Onvansertib is a highly selective, ATP-competitive, orally bioavailable PLK1 inhibitor that is synergistic with irinotecan and with 5FU in xenograft models of mKRAS CRC. We present preliminary safety, efficacy, and biomarker data from an ongoing Ph1b/2 trial of onvansertib + FOLFIRI-bev in pts with mKRAS mCRC progressing after 1L treatment with fluoropyrimidine + oxaliplatin, +/- bev. Methods: Pts with mCRC with a KRAS mutation detected by a CLIA-certified lab were eligible. In the Ph1b portion of the study, onvansertib was given on a 3+3 dose escalation at 12, 15 or 18 mg/m2 on days 1-5 and 15-19 of each 28-day cycle in combination with FOLFIRI-bev. The MTD was 15 mg/m2 and was chosen as the RP2D. The primary endpoint for the Ph2 was ORR, and radiographic response was assessed every 8 wks per RECIST v1.1. Safety was evaluated continuously, and AEs were recorded using CTCAE v5.0. Baseline and post-treatment blood samples were collected for biomarker analyses, including mutant allele frequency (MAF) of the pt’s known KRAS mutation. Results: As of 16Sep2021, a total of 50 pts had been treated: 18 on the Ph1b and 32 on the Ph2, including 35 pts at the RP2D, and median follow up was 4.7 mos (range 0.4-18). Of the 50 pts, 26 remain on treatment, as do 24 of 35 RP2D pts. The combination was well-tolerated: fatigue, neutropenia, and nausea were the most common treatment-emergent adverse events (TEAE) and were generally low-grade. Neutropenia was managed by removing the 5FU bolus from subsequent cycles of FOLFIRI and adding growth factor. Of the 50 pts, 44 were evaluable for efficacy, including 31 of 35 RP2D pts. ORR was 36% for the total group (1CR and 15 PR in 44 pts) and 35% for the RP2D group (1 CR and 10 PR in 31 pts). First responses were seen between 2 and 6 months after the start of therapy. Responses were observed across different KRAS variants. Pts achieving a CR or PR showed the greatest decreases in plasma MAF after the first cycle of therapy. Of the 50 pts, 24 pts have discontinued for the following reasons: progressive disease (13), toxicity (4), patient decision (4), proceeding to potentially curative surgery or other localized therapy (3). Conclusions: The combination of onvansertib with FOLFIRI-bev was well tolerated: observed TEAEs have been generally low-grade and manageable. The combination has demonstrated a promising ORR in 2L treatment of mCRC pts harboring various KRAS mutations, and efficacy was correlated with early changes in plasma mKRAS. Updated safety, efficacy, and biomarker analyses will be presented. Clinical trial information: NCT03829410.

Abstract 425: Expanded access program of the PLK1 inhibitor onvansertib for treatment of patients with KRAS-mutant metastatic colorectal cancer

Introduction: Chemotherapy in combination with targeted agents are standard-of-care options for first and second-line treatment of metastatic colorectal cancer (mCRC) patients. Second-line treatment of KRAS-mutated mCRC confers a dismal patient outcome with response rates of 4% to FOLFIRI (5-fluorouracil (5FU), leucovorin, irinotecan) + bevacizumab and median progression-free survival of 5.5 months (Tournigand et al., JCO 2004). PLK1 is a serine/threonine kinase, master regulator of mitosis and its overexpression is associated with poorer outcomes in CRC (Weichert et al., World J. Gastroenterol. 2005). Onvansertib is an oral and highly selective PLK1 inhibitor with demonstrated efficacy as a single agent and synergistically with irinotecan and 5-FU in CRC preclinical models. Onvansertib was granted Fast Track Designation by the Food and Drug Administration for its clinical development program and is currently being investigated in combination with FOLFIRI + bevacizumab in a phase 1b/2 clinical study for second line treatment of patients with KRAS-mutated mCRC (NCT03829410). Preliminary results indicate that onvansertib in combination with chemotherapy is safe and efficacious and that early changes in plasma KRAS mutant are predictive of clinical response (ESMO 2020, Poster #2969).

Method: An expanded access program (EAP) was initiated to provide access to onvansertib for treatment of patients who do not meet eligibility criteria for enrollment in the clinical trial, and provides an opportunity to collect safety and efficacy data outside of the clinical study. Patients must be at least 18 years old, have confirmed metastatic and unresectable CRC with a KRAS mutation and have failed or progressed on standard of care systemic therapy. Patients are treated with onvansertib (15 mg/m2, Days 1 to 5 of a 14-day cycle) in combination with FOLFIRI + bevacizumab (Day 1 of each cycle). Patients are being monitored for safety, efficacy by radiographic scans, and for changes in KRAS mutant allelic frequency (MAF) in circulating tumor DNA (ctDNA) by liquid biopsy.

Result: The EAP was activated on June 9th 2020. As of November 12th 2020, 19 patients have been treated at 11 clinical sites across the United States. Changes in KRAS MAF after two cycles of therapy was evaluated in 17 patients. Thirteen patients had a KRAS mutation detected in ctDNA at baseline and 8 patients showed a decrease of &gt;50% in KRAS MAF after the first two cycles. Clinical outcomes including efficacy and its correlation with changes in KRAS MAF will be presented at the AACR Annual meeting.

Conclusions: The EAP provides a path for patients who may benefit clinically, but are not eligible for the ongoing clinical trial, to gain access to onvansertib treatment.

Citation Format: Manish R. Sharma, Daniel Isaac, Ryan Ramaekers, Maya Ridinger, Mark Erlander, Lawrence Mendelsohn. Expanded access program of the PLK1 inhibitor onvansertib for treatment of patients with KRAS-mutant metastatic colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 425.

Abstract 973: The selective polo-like kinase (Plk1) inhibitor onvansertib and the antiandrogen abiraterone synergistically kill cancer cells through disruption of mitosis independently of androgen receptor signaling

Abiraterone acetate, a widely-used standard of care for metastatic castrate-resistant prostate cancer (mCRPC), both abrogates androgen synthesis and inhibits the androgen receptor (AR). The AR is a central driver of prostate cancer, and abiraterone slows disease progression in the majority of men, however, extended treatment universally results in acquired resistance. We have observed that Plk1 inhibitors (Plk1i), including the clinically active, highly-selective and orally available Plk1i onvansertib, synergize with abiraterone in models of CRPC, providing a potential means to reverse or delay the onset of abiraterone resistance. Plk1 is a serine/threonine kinase that regulates entry into and progression through mitosis. In contrast to abiraterone, the AR-antagonist enzalutamide does not synergistically kill CRPC cells in combination with Plk1i. Moreover, we have found Plk1i-abiraterone synergy in AR-negative cancer cells demonstrating that this synergy is AR independent. A phase 2 clinical trial (NCT03414034) is currently testing combination of onvansertib and abiraterone in mCRPC patients with nascent abiraterone resistance. Preliminary efficacy, as measured by PSA decline or stabilization, was observed in a subset of patients, including those harboring the AR splice variant 7.

To identify the mechanisms driving Plk1i-abiraterone synergy, prostate cancer cell lines showing, or not showing, synergy between these drugs (referred to as synergistic or non-synergistic cells, respectively), were treated with vehicle, abiraterone, enzalutamide, or onvansertib prior to RNA sequencing and Gene Set Variation Analysis (GSVA).

In synergistic cells, a group of mitosis and mitotic spindle related gene sets were significantly upregulated by both abiraterone and onvansertib. These gene sets were not upregulated in non-synergistic cells, or by enzalutamide, indicating that abiraterone may target mitosis related genes or processes in an AR-independent manner. Live-cell microscopy showed that, while abiraterone does not cause gross mitotic arrest, it does impair mitotic spindle assembly. These mitotic gene sets were also relatively upregulated in untreated synergistic cells, suggesting that synergistic responses reflect baseline differences in molecular pathways.

In summary, we have found that abiraterone impacts spindle assembly and sensitizes some cancer cells to Plk1i resulting in synergistic mitotic arrest and spindle assembly checkpoint dependent cell death. Baseline differences in these processes may predict synergy and be predicative of patient responses to the onvansertib + abiraterone combination. This hypothesis is being evaluated in patients currently enrolled in the clinical study of onvansertib + abiraterone.

Citation Format: Jesse C. Patterson, Peter J. Croucher, Maya Ridinger, David J. Einstein, Andreas Varkaris, Steven P. Balk, Glenn J. Bubley, Mark G. Erlander, Michael B. Yaffe. The selective polo-like kinase (Plk1) inhibitor onvansertib and the antiandrogen abiraterone synergistically kill cancer cells through disruption of mitosis independently of androgen receptor signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 973.

EMBR-30. A NOVEL PLK1 INHIBITOR ONVANSERTIB EFFECTIVELY SENSITIZES GROUP 3 MEDULLOBLASTOMA TO RADIOTHERAPY

Medulloblastoma (MB) is often accompanied by MYC amplification. PLK1 is an oncogenic kinase that controls cell cycle and proliferation, and it has been preclinically validated as a cancer therapeutic target. Onvansertib (PCM-075) is a novel, orally available PLK1 inhibitor, which shows tumor growth inhibition in many types of cancer. We examined the effect of Onvansertib on MYC-driven medulloblastoma as a monotherapy or in combination with radiation. A Crisper-Cas9 screen was used to discover essential genes for MB tumor growth. Microarray and immunohistochemistry on pediatric patient samples were performed to examine the expression of PLK1. The effect of Onvansertib in vitro was measure by cell viability, colony-forming assays, extreme limiting dilution assay, and RNA-Seq. ALDH activity, cell-cycle distribution, and apoptosis were analyzed by flow cytometry. DNA damage was assessed by immunofluorescence staining. Medulloblastoma xenografts were generated to explore the monotherapy or radio-sensitizing effect. PLK1 is overexpressed in Group 3 MB. The IC50 concentrations of Onvansertib in Group 3 MB cell lines were between 4.9 and 6 nM. Onvansertib reduced colony formation, cell proliferation, stem cell renewal, and induced G2/M arrest in vitro. Moreover, Onvansertib in combination with radiation increased DNA damage and apoptosis compared with radiation alone. The combination of Onvansertib with radiotherapy resulted in marked tumor regression in orthotopic xenografts. These findings suggest that Onvansertib is an effective strategy in combination with radiotherapy in MB.

A phase II study of onvansertib in combination with abiraterone and prednisone in patients with metastatic castration-resistant prostate cancer (mCRPC)

TPS186

Background: Metastatic CRPC remains a leading cause of cancer-related deaths worldwide. Although abiraterone + prednisone (abi) in either the castration-sensitive or castration-resistant setting increases survival, resistance is universal and generally occurs within 9-16 months of initiating treatment. Polo-like kinase 1 (PLK1) is a serine/threonine protein kinase that regulates mitotic functions and progression, and it is highly upregulated in prostate cancer following castration. Onvansertib is an oral and highly-selective PLK1 inhibitor that demonstrated safety and tolerability in a Phase 1 trial. Preclinical studies showed that PLK1 inhibition enhanced abi efficacy in cell line models and in patient-derived tumor xenografts via an AR-independent mechanism. Transcriptomic analyses revealed that abi induced mitosis-related gene sets in cells synergistic for abi + onvansertib, and identified an abi-onvansertib synergy gene signature. Methods: The goal of this phase 2 study (NCT03414034) is to observe the effects of onvansertib in combination with abi on disease control, as assessed by prostate-specific antigen (PSA) decline or stabilization after 12 weeks of study treatment, in subjects with mCRPC and early resistance to abi. Patients are enrolled at time of PSA progression while on standard abi. Patients with prior treatment with enzalutamide or apalutamide are excluded. Three onvansertib dosing schedules are tested in noncomparative arms: arm A (24 mg/m2 on days 1-5 of a 21-day cycle), arm B (18 mg/m2 on days 1-5 of a 14-day cycle), and arm C (12 mg/m2 on days 1-14 of a 21-day cycle). The 3 arms have completed their safety-lead phases and expansion phases are ongoing. With 32 patients in each arm, there will be 90% power to detect a change in disease-control rate from 10% (null) to 30% (alternative). Based on a Simon’s two-stage optimal design, the study will terminate early if < 2 of the first 13 patients in each arm achieve disease control. Exploratory analyses include evaluation of the presence of the androgen receptor variant 7 (AR-V7) in circulating tumor cells and targeted genomic profiling of circulating tumor DNA to assess associations between genomic alterations and response to treatment. Additionally, transcriptomic analysis of archived tumor tissue will be performed to determine whether enrichment for gene expression signatures, such as the abi-onv synergy signature identified in preclinical models, could be used to predict clinical response. Clinical trial information: NCT03414034.

A phase Ib/II study of the polo-like kinase 1 (PLK1) inhibitor, onvansertib, in combination with FOLFIRI and bevacizumab for second-line treatment of patients with KRAS-mutated metastatic colorectal Cancer (mCRC)

TPS155

Background: Chemotherapy in combination with targeted agents are standard-of-care options for patients for mCRC with response rates > 50% in first line. In the second line setting, efficacy of chemotherapy and targeted agents are much lower with response rates of 5% for FOLFIRI (5-fluorouracil, leucovorin, irinotecan) + bevacizumab (anti-VEGF). New treatment options are urgently needed in particular for the 50 % of patients harboring a KRAS mutation. PLK1 is a serine/threonine kinase, master regulator of the mitotic checkpoint and cell division. PLK1 is overexpressed in CRC and its overexpression is associated with poor prognostic. A genome wide RNAi screen identified PLK1 as a synthetic lethal target in KRAS mutant CRC cells, inducing cell cycle arrest and apoptosis upon inhibition. Onvansertib is an oral, highly selective PLK1 inhibitor that demonstrates single agent and synergistic activity with irinotecan and 5-FU in preclinical CRC models. Additionally, KRAS mutated versus wild-type cells showed higher sensitivity to onvansertib. PLK1 inhibition is a potential target in KRAS-mutated mCRC, and the combination of onvansertib + FOLFIRI + bevacizumab may provide a new second-line treatment option. Methods: The primary objective of this single-arm Phase 1b/2 study is to assess the safety and preliminary efficacy of onvansertib in combination with FOLFIRI and bevacizumab in the second line setting for KRAS-mutated mCRC patients. For the Phase 1b segment, a standard 3 + 3 dose-escalation design is used to determine the maximum tolerated dose or recommended phase 2 dose (RP2D) of onvansertib. As of September 15th 2020, the first two dose levels have been cleared for safety and the third is enrolling. Efficacy will be determined by objective response rate (ORR) according to RECIST v1.1 (primary endpoint), progression-free survival and reduction in KRAS allelic burden in liquid biopsies (secondary endpoints). Biomarker analyses include genomic profiling of circulating tumor DNA genomic to evaluate altered pathways that correlate with patient clinical response. Based on a one-sided one sample log-rank test with 10% Type I error, there will be at least 90% power to detect an improvement in ORR from 5% to 20% with 32 patients. Clinical trial information: NCT03829410.

Abstract 2019: Oxidative phosphorylation (OXPHOS) dependency predicts response to the Polo-like kinase 1 (PLK1) inhibitor onvansertib in a phase 1b/2 of relapsed/refractory acute myeloid leukemia (R/R AML)

Background: PLK1, a serine-threonine kinase and key regulator of the cell cycle, controls mitotic entry and progression. PLK1 is overexpressed in AML and its inhibition induces G2/M arrest, apoptosis and tumor growth inhibition in AML preclinical models. Onvansertib is the first PLK1-selective inhibitor orally bioavailable to enter the clinic, and has potent anti-tumor activity in AML models, including venetoclax-resistant models. A phase 1b/2 study (NCT03303339) is ongoing to assess the efficacy and safety of onvansertib in combination with decitabine or low-dose cytarabine (LDAC) in R/R AML. Correlative studies aim at identifying biomarkers associated with response to treatment.

Methods: R/R AML patients were dosed for 5 days with onvansertib (12 to 90 mg/m2) in combination with either decitabine (20 mg/m2 IV qd x 5d ) or LDAC (20 mg/m2 SC qd x 10d ) within a 21 to 28-day cycle. PLK1 inhibition is monitored by Western-Blot through changes in phosphorylation of its direct substrate: the translationally controlled tumor protein (TCTP). Target engagement (TE) was defined as ≥ 50% decrease in pTCTP/TCTP in blood samples collected at 3 hours versus pre-dose, in patients with at least 10% circulating blasts (CB). RNA-sequencing is performed on blood samples collected at pre-dose, 3h and 24h post-dose on day 1. To reduce dimensionality, gene counts were transformed into gene set enrichment (GSE) scores using GSVA, and corrected for %CB via ordination. GSE was evaluated for association with clinical response or TE via permutation T-tests and machine learning.

Results: Target engagement (TE) in CB was observed in only 8 (33%) of the 24 evaluable patients. TE was associated with higher response to treatment as measured by decrease in BM %blasts and objective responses (CR/CRi). TE was not dependent on onvansertib dose level, pharmacokinetics, or combination treatment.

At pre-dose, TE patients had a notable upregulation of OXPHOS, DNA repair, and proliferative pathways. Responders (CR/CRi, n=5) versus non-responders (n=25) showed a similar upregulation of OXPHOS plus stress and immune related pathways, and downregulation of glycolysis. Comparison of baseline versus treatment (3h and 24h), TE and responder samples exhibited similar changes, with a strong decrease in metabolic processes, including: OXPHOS, mTORC1 signaling, and glycolysis.

Conclusion: Our analyses identified OXPHOS as an up-regulated pathway at baseline associated with response to onvansertib (TE and CR/CRi) that is subsequently down-regulated post-therapy. OXPHOS driven metabolism is characteristic of leukemic stem cells and chemo-resistant AML, therefore patients resistant to conventional chemo-treatments may benefit from the addition of onvansertib.

Citation Format: Peter JP Croucher, Errin Samuelsz, Latifa Hassaine, Brittany Ross, Marion Luebbermann, Maya Ridinger, Mark Erlander. Oxidative phosphorylation (OXPHOS) dependency predicts response to the Polo-like kinase 1 (PLK1) inhibitor onvansertib in a phase 1b/2 of relapsed/refractory acute myeloid leukemia (R/R AML) [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2019.

Abstract CT235: A phase 1b/2 study of onvansertib (PCM-075) in combination with FOLFIRI and bevacizumab for second line treatment of patients with KRAS-mutated metastatic colorectal cancer (mCRC)

Background: Chemotherapy in combination with targeted agents are standard-of-care options for patients for mCRC with response rates &gt;50% in first line. In the second line setting, efficacy of chemotherapy and targeted agents are much lower with response rates of 5% for FOLFIRI (5-fluorouracil, leucovorin, irinotecan) + bevacizumab (anti-VEGF). New treatment options are urgently needed in particular for the 50 % of patients harboring a KRAS mutation. Polo-like kinase 1 (PLK1) is a serine/threonine kinase, master regulator of the mitotic checkpoint and cell division. PLK1 is overexpressed in CRC and its overexpression is associated with poor prognostic. A genome wide RNAi screen identified PLK1 as a synthetic lethal target in KRAS mutant CRC cells, inducing cell cycle arrest and apoptosis upon inhibition. Onvansertib is an oral, highly selective PLK1 inhibitor that demonstrates single agent and synergistic activity with irinotecan in preclinical CRC models. Additionally, KRAS mutated vs wild-type cells showed higher sensitivity to onvansertib. PLK1 inhibition is a potential target in KRAS-mutated mCRC and onvansertib + FOLFIRI + bevacizumab may provide a new second-line treatment option.

Trial design: The primary objective of this single-arm Phase 1b/2 study is to assess the safety and preliminary efficacy of onvansertib in combination with FOLFIRI and bevacizumab in the second line setting for KRAS-mutated mCRC patients. For the Phase 1b segment, a standard 3 + 3 dose-escalation design is used to determine the maximum tolerated dose or recommended phase 2 dose (RP2D) of onvansertib. As of January 24th 2020, enrollment in the second dose level is ongoing. Efficacy will be determined by objective response rate (ORR) according to RECIST v1.1 (primary endpoint), progression-free survival and reduction in KRAS allelic burden in liquid biopsies (secondary endpoints). In the phase 2, based on a one-sided one sample log-rank test with 10% Type I error, there will be at least 90% power to detect an improvement in ORR from 5% to 20% with 26 patients. Exploratory endpoints include genomic studies of circulating tumor cells and ctDNA to evaluate altered pathways that correlate with patient response. Clinical trial identification NCT03829410.

Citation Format: Afsaneh Barzi, Heinz-Josef Lenz, Errin Samuëlsz, Maya Ridinger, Mark Erlander, Tanios S. Bekaii-Saab, Daniel H. Ahn. A phase 1b/2 study of onvansertib (PCM-075) in combination with FOLFIRI and bevacizumab for second line treatment of patients with KRAS-mutated metastatic colorectal cancer (mCRC) [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr CT235.

Abstract A43: Plasma-derived circulating tumor DNA (ctDNA) as a surrogate biomarker for treatment response with the polo-like kinase 1 (PLK1) inhibitor, onvansertib, in combination with LDAC or decitabine in acute myeloid leukemia (AML)

Background: Cancer cells from solid tumors release ctDNA into the bloodstream, clinically enabling assessment, monitoring tumor mutational heterogeneity, treatment response, minimal residual disease (MRD), and disease progression. However, the clinical utility of ctDNA in AML has yet to be established. In AML, blast cells carrying a driver mutation originate in the bone marrow (BM) and migrate into circulation in peripheral blood (PB). Here, we aimed to determine the potential of ctDNA as a surrogate for response to treatment in the phase 1b/2 study (NCT03303339) testing the efficacy and safety of the PLK1 inhibitor, onvansertib, in combination with either decitabine or LDAC in relapsed or refractory AML (R/R AML).

Methods: R/R AML patients were dosed for 5 days with onvansertib in combination with either decitabine (5 days) or LDAC (10 days) within 21 to 28-day cycle. BM aspirates and blood samples were collected pre-dose, at the end of cycles 1, 2 and every other cycle after. Genomic DNA (gDNA) was extracted from BM and PB mononuclear cells (BMMCs and PBMCs, respectively), while ctDNA was extracted from plasma. Clinically significant mutations were detected in gDNA from PBMCs and BMMCs using a next-generation sequencing panel targeting variants in 75 genes associated with AML. For each patient, a droplet digital PCR (ddPCR) assay was developed to assess mutant allele frequencies (MAF) of a single variant of interest across timepoints and three sample sources (BMMC, PBMC, and Plasma). MAF changes across all 3 sample sources were compared to the clinical response assessed by immunohistochemistry in bone marrow aspirate (BM-IHC).

Results: As of October 16th, 16 patients were evaluated, totaling 33 timepoints with MAF measured in all 3 sources. MAF in plasma highly correlated with BMMCs MAF (R2 = 0.85), more so than PBMCs with BMMCs (R2 = 0.78) and over plasma with PBMCs (R2 = 0.68). Clinically, 4 patients had a complete response (with or without count recovery, CR+CRi) and showed a corresponding drop in ctDNA MAF at or before clinical diagnosis. Similarly, 3 of 4 evaluable patients with progressive disease showed an increase in ctDNA MAF before or at the timepoint when blast percentages rose in BM, with the fourth patient maintaining a stable MAF across timepoints. In 5 patients with stable disease, 2 showed a divergence between ctDNA MAF and BM-IHC, while 3 maintained congruency.

Conclusions: Serial testing of plasma-derived ctDNA was representative of treatment response and relapse in R/R AML patients. The correlation between ctDNA MAF and BMMCs MAF supports the utility of ctDNA as a surrogate biomarker for disease status, and in some cases provides a more immediate diagnostic of response or nonresponse. More patients need to be evaluated to build an objective classification of clinical significance around ctDNA MAF, and, importantly, the biology of R/R AML subclonal heterogeneity and MRD likely necessitate interrogation and monitoring of multiple variants of interest.

Citation Format: Errin Samuelsz, Maya Ridinger, Mark Erlander, Latifa Hassaine, Marion Luebbermann, Brittany Ross. Plasma-derived circulating tumor DNA (ctDNA) as a surrogate biomarker for treatment response with the polo-like kinase 1 (PLK1) inhibitor, onvansertib, in combination with LDAC or decitabine in acute myeloid leukemia (AML) [abstract]. In: Proceedings of the AACR Special Conference on Advances in Liquid Biopsies; Jan 13-16, 2020; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(11_Suppl):Abstract nr A43.

A phase Ib/II study of the polo-like kinase 1 (PLK1) inhibitor, onvansertib, in combination with FOLFIRI and bevacizumab for second-line treatment of patients with KRAS-mutated metastatic colorectal cancer (mCRC)

TPS4116

Background: Chemotherapy in combination with targeted agents are standard-of-care options for patients for mCRC with response rates >50% in first line. In the second line setting, efficacy of chemotherapy and targeted agents are much lower with response rates of 5% for FOLFIRI (5-fluorouracil, leucovorin, irinotecan) + bevacizumab (anti-VEGF). New treatment options are urgently needed in particular for the 50 % of patients harboring a KRAS mutation. PLK1 is a serine/threonine kinase, master regulator of the mitotic checkpoint and cell division. PLK1 is overexpressed in CRC and its overexpression is associated with poor prognostic. A genome wide RNAi screen identified PLK1 as a synthetic lethal target in KRAS mutant CRC cells, inducing cell cycle arrest and apoptosis upon inhibition. Onvansertib is an oral, highly selective PLK1 inhibitor that demonstrates single agent and synergistic activity with irinotecan in preclinical CRC models. Additionally, KRAS mutated vs wild-type cells showed higher sensitivity to onvansertib. PLK1 inhibition is a potential target in KRAS-mutated mCRC, and the combination of onvansertib + FOLFIRI + bevacizumab may provide a new second-line treatment option. Methods: The primary objective of this single-arm Phase 1b/2 study is to assess the safety and preliminary efficacy of onvansertib in combination with FOLFIRI and bevacizumab in the second line setting for KRAS-mutated mCRC patients. For the Phase 1b segment, a standard 3 + 3 dose-escalation design is used to determine the maximum tolerated dose or recommended phase 2 dose (RP2D) of onvansertib. As of January 24, 2020, enrollment in the second dose level is ongoing. Efficacy will be determined by objective response rate (ORR) according to RECIST v1.1 (primary endpoint), progression-free survival and reduction in KRAS allelic burden in liquid biopsies (secondary endpoints). In the phase 2, based on a one-sided one sample log-rank test with 10% Type I error, there will be at least 90% power to detect an improvement in ORR from 5% to 20% with 26 patients. Exploratory endpoints include genomic studies of circulating tumor cells and ctDNA to evaluate altered pathways that correlate with patient clinical response. Clinical trial information: NCT03829410 .

Onvansertib, a polo-like kinase 1 inhibitor, inhibits prostate stromal cell growth and prostate smooth muscle contraction, which is additive to inhibition by α1-blockers

Prostate smooth muscle contraction and prostate enlargement contribute to lower urinary tract symptoms suggestive of benign prostatic hyperplasia. Recent evidence demonstrated that inhibitors for polo-like kinases (PLKs) inhibit smooth muscle contraction of human prostate tissues. However, their additive effects to α1-blockers, and effects on prostate growth are unknown. Here, we examined effects of a novel and highly selective PLK1 inhibitor, onvansertib on prostate smooth muscle contraction alone and in combination with α1-blockers, and on proliferation and viability of prostate stromal cells (WPMY-1). Prostate tissues were obtained from radical prostatectomy. Contractions were studied in an organ bath. Proliferation and viability were assessed by plate colony, EdU, and CCK-8 assay. Electric field stimulation (EFS)-induced contractions of human prostate tissues were inhibited to 34% by 100 nM and 1 μM onvansertib at 32 Hz, and to 48% and 47% by the α1-blockers tamsulosin and silodosin. Combination of onvansertib with tamsulosin or silodosin further reduced EFS-induced contractions in comparison to α1-blockers alone (59% and 61% respectively), and to onvansertib alone (68% for both). Noradrenaline-, phenylephrine-, methoxamine-, endothelin-1-, and ATP-induced contractions were inhibited by onvansertib (100 nM) to similar extent. Viability and proliferation of WPMY-1 cells were reduced in a concentration- and time-dependent manner (24-72 h, 10-100 nM). Onvansertib inhibits neurogenic, adrenergic, and endothelin-1- and ATP-induced contractions of human prostate smooth muscle, and proliferation of stromal cells. Contractions are reduced not more than 50% by α1-blockers. Combination of α1-blockers with onvansertib provides additive inhibition of prostate contractions.

A phase II study of onvansertib in combination with abiraterone and prednisone in patients with metastatic castration-resistant prostate cancer (mCRPC)

TPS266

Background: Metastatic CRPC remains a leading cause of cancer-related deaths worldwide. Although abiraterone (abi) in either the castration-sensitive or castration-resistant setting increases survival, resistance is universal and generally occurs within 9-16 months of initiating treatment. Polo-like kinase 1 (PLK1) is a serine/threonine protein kinase that regulates mitotic functions and progression, and it is highly upregulated in prostate cancer following castration. PLK1 inhibition enhances the efficacy of abi in cell line models and patient-derived tumor xenografts via several mechanisms. Onvansertib (PCM-075; Trovagene, Inc.) is the first orally available PLK1-specific inhibitor. In phase 1 testing, onvansertib demonstrated a manageable safety profile, with transient and reversible hematologic effects. Methods: The goal of this phase 2 study (NCT03414034) is to observe the effects of onvansertib in combination with abi + prednisone on disease control, as assessed by prostate-specific antigen (PSA) decline or stabilization after 12 weeks of study treatment, in subjects with mCRPC and early resistance to abi. Patients will be enrolled at time of PSA progression while on standard abi. A safety lead-in phase has been completed at one dosing schedule (24 mg/m2 on days 1-5 of a 21-day cycle) and is ongoing at a second dosing schedule (18 mg/m2 on days 1-5 of a 14-day cycle). Expansion phases are ongoing on both arms. In addition, a more continuous dosing schedule has been proposed (12 mg/m2 on days 1-14 of a 21-day cycle). With 32 patients in each arm, there will be 90% power to detect a change in disease-control rate from 10% (null) to 30% (alternative). Based on a Simon’s two-stage optimal design, the study will terminate early if <2 of the first 13 patients achieve disease control. Exploratory analyses include evaluation of the presence of the androgen receptor variant 7 (AR-V7) and other genomic alterations in circulating tumor cells and circulating tumor DNA that may be associated with response to treatment. Clinical trial information: NCT03414034.

A phase Ib/II study of onvansertib (PCM-075) in combination with FOLFIRI and bevacizumab for second-line treatment of metastatic colorectal cancer (mCRC) in patients with a KRAS mutation

TPS265

Background: FOLFOX (5-flourouracil, leucovorin, oxaliplatin) and FOLFIRI (fluorouracil, leucovorin, irinotecan) in combination with targeted agents are standard-of-care options for patients for mCRC with response rates >50% in first line. In the second line setting, efficacy of chemotherapy and targeted agents are much lower with response rates of 4% for FOLFIRI + bevacizumab and treatment options are limited in particular for the 50% of patients harboring a RAS mutation. Polo-like kinase 1 (PLK1) is a serine/threonine kinase, master regulator of G2/M cell-cycle progression and genome wide RNAi screens identified PLK1 to be synthetic lethal for KRAS mutated tumor cells inducing cell cycle arrest and apoptosis. Onvansertib is an oral, highly selective PLK1 inhibitor that demonstrated single agent activity and synergistic activity with irinotecan in preclinical CRC models. Additionally, KRAS mutated cells showed higher sensitivity to onvansertib than isogenic KRAS wild-type cells. PLK1 inhibition is a potential target in KRAS-mutated mCRC and onvansertib + FOLFIRI may provide a new second-line treatment option. Methods: The primary objective of this single-arm Phase 1b/2 study (NCT03829410) is to assess the safety and preliminary efficacy of onvansertib in combination with FOLFIRI and bevacizumab in the second line setting for KRAS-mutated mCRC patients. The phase 1b will determine the MTD or RP2D using a traditional 3+3 design, with onvansertib initial dose at 12 mg/m2. The phase 2 will enroll 26 patients at the RP2D to further assess the safety of the combination and to evaluate preliminary anti-tumor activity measured by objective response rate (ORR, RECIST v1.1). Based on a one-sided one sample log-rank test with 10% Type I error, there will be at least 90% power to detect an improvement in ORR from 5% to 20% with 26 patients. Exploratory studies include quantitation of KRAS circulating tumor DNA (ctDNA) and genomic studies of circulating tumor cells and ctDNA to determine altered pathways associated with patient response. Clinical trial information: NCT03829410.

Polo-like kinase 1 (Plk1) inhibition synergizes with taxanes in triple negative breast cancer

Within triple negative breast cancer, several molecular subtypes have been identified, underlying the heterogeneity of such an aggressive disease. The basal-like subtype is characterized by mutations in the TP53 gene, and is associated with a low pathologic complete response rate following neoadjuvant chemotherapy. In a genome-scale short hairpin RNA (shRNA) screen of breast cancer cells, polo-like kinase 1 (Plk1) was a frequent and strong hit in the basal breast cancer cell lines indicating its importance for growth and survival of these breast cancer cells. Plk1 regulates progression of cells through the G2-M phase of the cell cycle. We assessed the activity of two ATP-competitive Plk1 inhibitors, GSK461364 and onvansertib, alone and with a taxane in a set of triple negative breast cancer cell lines and in vivo. GSK461364 showed synergism with docetaxel in SUM149 (Combination Index 0.70) and SUM159 (CI, 0.62). GSK461364 in combination with docetaxel decreased the clonogenic potential (interaction test for SUM149 and SUM159, p<0.001 and p = 0.01, respectively) and the tumorsphere formation of SUM149 and SUM159 (interaction test, p = 0.01 and p< 0.001). In the SUM159 xenograft model, onvansertib plus paclitaxel significantly decreased tumor volume compared to single agent paclitaxel (p<0.0001). Inhibition of Plk1 in combination with taxanes shows promising results in a subset of triple negative breast cancer intrinsically resistant to chemotherapy. Onvansertib showed significant tumor volume shrinkage when combined with paclitaxel in vivo and should be considered in clinical trials for the treatment of triple negative cancers.

Abstract CT161: A Phase II study of the polo-like kinase (PLK1) inhibitor onvansertib in combination with abiraterone (abi) and prednisone in patients with metastatic castration-resistant prostate cancer (mCRPC)

Background: mCRPC remains a leading cause of cancer-related deaths worldwide. Although abi increases survival, resistance is universal and generally occurs within 9-16 months of initiating treatment. PLK1, a serine/threonine kinase, is a master regulator of cell-cycle progression and is highly upregulated in prostate cancer following castration. PLK1 inhibition enhances the efficacy of abi in cell line models and patient-derived tumor xenografts. Onvansertib (PCM-075; Trovagene, Inc.) is the first orally available PLK1-specific inhibitor. In Phase I testing, onvansertib demonstrated a manageable safety profile, with transient hematologic effects as its most prominent, yet reversible, toxicity.

Methods: The goal of this Phase II study (NCT03414034) is to observe the effects of onvansertib in combination with abi + prednisone on disease control, as assessed by prostate-specific antigen (PSA) decline or stabilization after 12 weeks of study treatment, in subjects with mCRPC and early resistance to abi. Patients are enrolled at time of PSA progression while on standard abi and treated with onvansertib (24 mg/m2 orally on days 1-5 of a 21-day cycle) plus abi (administered orally and continuously once daily with prednisone) until time of radiographic or symptomatic progression. The safety lead-in of 3 subjects showed no dose-limiting toxicities or new toxicities from the combination of onvansertib with abi. A 29-patient expansion phase is ongoing, with 11 patients enrolled as of January 2019. With 32 patients, there will be 90% power to detect a change in disease-control rate from 10% (null) to 30% (alternative). Based on a Simon’s two-stage optimal design, the study will terminate early if &lt;2 of the first 13 patients achieve disease control. Toxicity and PSA levels are monitored during treatment. Exploratory analyses include quantification of circulating tumor cells, evaluation of PLK1 inhibition in vivo and evaluation of predictive genomic biomarkers in circulating tumor DNA, such as alterations in oncogenes and tumor suppressors.

Citation Format: David J. Einstein, Atish Choudhury, Philip Saylor, Lillian Werner, Mark Erlander, Maya Ridinger, Glenn Bubley. A Phase II study of the polo-like kinase (PLK1) inhibitor onvansertib in combination with abiraterone (abi) and prednisone in patients with metastatic castration-resistant prostate cancer (mCRPC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr CT161.

Abstract CT102: Phase Ib safety, preliminary anti-leukemic activity and biomarker analysis of the polo-like kinase 1 (PLK1) inhibitor, onvansertib, in combination with low-dose cytarabine or decitabine in patients with relapsed or refractory acute myeloid leukemia

Background: Despite recent advances in the understanding of the biology and development of new agents for patients with acute myeloid leukemia (AML), prognosis remains poor with most patients (pts) succumbing to their disease. PLK1 is a serine/threonine kinase, a master regulator of cell-cycle progression, and is overexpressed in numerous cancer types including AML. Onvansertib is a third generation, orally active and highly selective PLK1 inhibitor with a ~24-hour half-life that demonstrates activity in preclinical AML models both as a single agent and in combination with low-dose cytarabine (LDAC). A Phase I study showed that Onvansertib was well tolerated in pts with solid tumors.

Methods: The goal of this Phase Ib (NCT03303339) study is to test the safety of Onvansertib in combination with either LDAC or Decitabine in relapsed or refractory AML. Efficacy, pharmacokinetics and pharmacodynamics of the combination are secondary endpoints. Pts are treated with Onvasertib for 5 days in combination with either LDAC (20 mg/m2 SC qd x 10d) or Decitabine (20 mg/m2 IV qd x 5d) over a flexible 21 to 28-day cycle, with the next cycle initiated based on recovery of cell counts. Each arm follows a standard dose escalation design with 50% increments in successive cohorts of 3 pts. Dose limiting toxicity (DLT) is evaluated during the 1stcycle. As of January 2, 2019, 21 pts have enrolled. The starting dose of Onvansertib was 12mg/m2 and was escalated to 18, 27 and 40mg/m2 in subsequent cohorts. In both arms, no treatment-related serious adverse events and deaths or DLTs occurred at the first 3 doses and treatment at 40mg/m2 is ongoing. Additional objectives include pharmacokinetics, preliminary anti-leukemic activity and correlative biomarker and pharmacodynamics analyses. Assessment of PLK1 inhibition is being determined in pts by changes in phosphorylation status of the translationally controlled tumor protein (TCTP), which is a PLK1 substrate, and is being evaluated not only in terms of response to treatment, but also as a potentially identifiable marker ex vivo for pts that may be more responsive to therapy. Genomic and gene expression analysis are assessed to identify biomarkers that may also be associated with response to treatment.

Citation Format: Amer M. Zeidan, Pamela Becker, Alexander I. Spira, Prapti A. Patel, Gary J. Schiller, Michaela L. Tsai, Tara L. Lin, Maya Ridinger, Mark Erlander, Sandra L. Silberman, Jorge E. Cortes. Phase Ib safety, preliminary anti-leukemic activity and biomarker analysis of the polo-like kinase 1 (PLK1) inhibitor, onvansertib, in combination with low-dose cytarabine or decitabine in patients with relapsed or refractory acute myeloid leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr CT102.

A phase II study of onvansertib (PCM-075) in combination with abiraterone and prednisone in patients with metastatic castration-resistant prostate cancer

TPS336

Background: Metastatic castration-resistant prostate cancer (mCRPC) remains a leading cause of cancer-related deaths worldwide. Although abiraterone (abi) in either the castration-sensitive or castration-resistant setting increases survival, resistance is universal and limits the efficacy of subsequent hormonal therapies. Polo-like kinase 1 (PLK1) is a serine/threonine protein kinase that regulates mitotic functions and promotes the progression of cells through mitosis, and it is highly upregulated in prostate cancer following castration. PLK1 inhibition enhances the efficacy of abi in cell line models as well as patient-derived tumor xenografts via several mechanisms. Onvansertib (PCM-075; Trovagene, Inc.) is the first orally available PLK1-specific inhibitor. In phase 1 testing, onvansertib demonstrated a manageable safety profile, with transient hematologic effects as its most prominent, yet reversible, toxicity. Methods: The goal of this phase 2 study (NCT03414034) is to observe the effects of onvansertib in combination with abi + prednisone on disease control, as assessed by prostate-specific antigen (PSA) decline or stabilization after 12 weeks of study treatment, in subjects with mCRPC and early resistance to abi. Patients will be enrolled at time of PSA progression while on standard abi. A completed 3-patient safety lead-in phase tested the safety of the combination of onvansertib with abi, and the accruing expansion phase will treat 29 more patients with onvansertib (24 mg/m2 orally on days 1-5 of a 21-day cycle) plus abi (administered orally and continuously once daily with prednisone) until time of radiographic or symptomatic progression. With 32 patients, there will be 90% power to detect a change in disease-control rate from 10% (null) to 30% (alternative). Based on a Simon’s two-stage optimal design, the study will terminate early if < 2 of the first 13 patients achieve disease control. Exploratory analyses include evaluations of predictive genomic biomarkers in circulating tumor cells and circulating tumor DNA, including alterations of oncogenes and tumor suppressors implicated in PLK1 sensitivity within preclinical models. Clinical trial information: NCT03414034.

Abstract 992: Pancreatic tuft cells resolve injury and restrain tumorigenesis

Pancreatic ductal adenocarcinoma (PDA) is the 3rd leading cause of cancer-related deaths in the United States and is predicted to be 2nd by the year 2020. The overall 5-year survival rate is &lt; 9% and median survival is only 4-6 months. Symptoms appear late in disease progression and metastasis has typically occurred by the time of diagnosis, making the study of early events in tumorigenesis essential. Intra-tumoral heterogeneity contributes to metastasis and engenders chemotherapeutic resistance in cancer. We have identified acinar-to-ductal metaplasia (ADM) as a source of heterogeneity in early pancreatic disease progression. ADM is the formation of highly reactive, dedifferentiated ducts from pancreatic acinar cells and is hypothesized to progress to pancreatic intraepithelial neoplasia (PanIN), a proposed precursor to PDA. Interestingly, we have identified phenotypically distinct cell populations in ADM, associated with both pancreatitis and PanIN, including a significant number of tuft cells. Tuft cells are solitary chemosensory cells found throughout the hollow organs of the respiratory and digestive tracts. Simultaneous expression of taste, inflammatory, and neuronal signaling pathways is thought to allow for monitoring of intraluminal content and local control of absorptive and secretory processes, though how they contribute to tissue injury and tumorigenesis remains a critical knowledge gap. Using imaging and sequencing techniques, as well as novel mouse models, we have found that tuft cells accumulate during chronic, caerulein-induced pancreatitis and form during the recovery phase of acute injury. Tuft cell ablation using Pou2f3 knockout mice significantly worsens chronic injury, including greater tissue loss and extracelluar matrix deposition, and impairs recovery. Similarly, tuft cell knockout mice experienced greater transformation and advanced tumorigenesis in a LSL-KrasG12D;Ptf1aCre/+ model of pancreatic tumorigenesis, suggesting that tuft cells abate disease progression. Tuft cell isolation and RNA sequencing revealed expression of several immune modulators including prostaglandin synthase Hpgds. We have found that treatment of primary pancreatic stellate cells and macrophages with Pgd2-family prostaglandins inhibits activation providing one mechanism by which tuft cells contribute to pancreatic disease and a possible therapeutic route to inhibit disease progression. In conclusion, chemosensory tuft cells form following tissue injury and in early pancreatic tumorigenesis and use paracrine signaling mechanisms to quell inflammation and ebb disease progression.

Citation Format: Kathleen E. DelGiorno, Chi-Yeh Chung, Maya Ridinger, Wahida Ali, Crystal Tsui, Cynthia Ramos, Makoto Ohmoto, LinJing Fang, Uri Manor, Ichiro Matsumoto, Geoffrey M. Wahl. Pancreatic tuft cells resolve injury and restrain tumorigenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 992.

Abstract 4833: Pharmacodynamic and tumor biomarker analysis of a PLK1 inhibitor, PCM-075, in a phase 1b/2 trial for acute myeloid leukemia

Acute myeloid leukemia (AML) is an aggressive hematologic disease that is characterized by the accumulation of immature myeloid precursor cells. Treatment options for patients are selected based on factors such as age, comorbidities, and cytogenetics. For patients deemed ineligible for standard intensive induction chemotherapy, treatments include either low-dose cytarabine (LDAC) or hypomethylating agents (e.g., azacitidine and decitabine) but when used as single agents, relapses are inevitable. Polo-like Kinase 1 (PLK1), a serine/threonine kinase that is a master regulator of cell-cycle progression, is overexpressed in a number of cancer types including AML. Depletion of PLK1 preferentially induces cell death in tumor versus normal cells. Inhibition of PLK1 in preclinical AML models results in significant efficacy. PCM-075, a highly selective PLK1 inhibitor, is currently in a phase 1b/2 trial (NCT03303339) in combination with standard-of care (LDAC or decitabine) for AML. Collection and processing of blood and bone marrow samples from patients is being performed pre- and post-treatment to assess 1) the inhibition of PLK1 kinase activity and downstream effects by measurement of pharmacodynamic (PD) and mechanism of action (MOA) biomarkers (blood), and 2) the genomic profile of blast cell population(s) from individual patients (blood and bone marrow). For each patient, blood is collected into CellSave, EDTA, and PAXgene blood RNA tubes at various time points as per the clinical protocol schedule of events. PBMCs isolated from CellSave blood tubes are used to assess the phosphorylation status of PD biomarkers using Western blot and phospho-flow cytometry. DNA extracted from blasts (EDTA tube) is used to detect somatic alterations and RNA extracted from the total cell population (PAXgene) is used to detect fusions and determine gene expression profiles by next-generation sequencing. To identify potential PD biomarkers that would enable assessment of PLK1 inhibition in AML patients treated with PCM-075, nine candidate substrates phosphorylated by PLK1 were screened in the AML cell line MV4-11 by Western blot using selected phospho-antibodies. Of these, phosphorylation of Translational Control Tumor Protein (TCTP) at Ser46 was both time- and dose-dependently inhibited by PCM-075. pTCTP detection by Western blot and phospho-flow cytometry was first optimized in PBMCs isolated from healthy donors and later in blast cells from AML patients resulting in a functional biomarker. Additional downstream MOA biomarkers of PCM-075 activity (DNA content, phospho-histone H3, cleaved caspase 3) and tumor DNA biomarkers that enable categorization of AML molecular subtypes have been validated. We present preliminary patient data from the ongoing phase 1b/2 trial and describe biomarker assays that will be used to evaluate target engagement of PCM-075 in AML patients.

Citation Format: Maya Ridinger, Karena Kosco, Latifa Hassaine, Jeffrey N. Miner, Mark Erlander. Pharmacodynamic and tumor biomarker analysis of a PLK1 inhibitor, PCM-075, in a phase 1b/2 trial for acute myeloid leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4833.

Abstract 1885: Selective Polo-like Kinase 1 (PLK1) inhibitor PCM-075 is highly active alone and shows synergy when combined with FLT3 inhibitors in models of acute myeloid leukemia (AML)

First generation FLT3 inhibitors have been useful in treating AML (sorafenib, midostaurin). Second generation inhibitors with more selectivity are currently in P3 trials in AML (quizartinib, gilteritinib). Despite the advances, resistance to FLT3 inhibitors and disease progression while on FLT3 inhibitors remains an important problem for patient care. We analyzed the activity of a highly-selective PLK1 inhibitor, PCM-075 (formerly NMS-1286937), in models of acute myeloid leukemia (AML) alone and in combination with various chemotherapies and targeted therapeutics including FLT3 inhibitors. PCM-075 is a potent, highly-selective adenosine triphosphate competitive inhibitor of PLK1, a serine/threonine kinase, which is over-expressed in hematologic malignancies and solid tumors such as AML, breast, prostate, ovarian, lung, gastric and colon. PCM-075 is highly active in blocking proliferation and inducing G2/M arrest in multiple AML cell lines. In a therapeutic model, PCM-075 was capable of inducing significant tumor growth inhibition (TGI)1, and increasing survival in an in vivo disseminated leukemia model (AML-NS8 Cells)2. Orally administered PCM-075 is currently in development for multiple tumor types and is in clinical trials for the treatment of AML (NCT03303339). Synergistic interactions between Quizartinib, other FLT3 inhibitors and PCM-075 were examined in cell culture models. In vivo, combination studies in an AML FLT3 mutant 21 day treatment xenograft model (MV4-11) revealed synergistic interactions between Quizartinib and PCM-075. PCM-075 (dosed orally 30 mg/kg, QD for days 1-10 and 12 -21) in combination with Quizartinib (1 mg/kg, QD for 21 days) resulted in 97.3% (96.2-98.4) TGI, compared to 77.9% (70.0-85.8) with Quizartinib and 80.2% (70.4-90.0) with PCM-075 as monotherapy. Body weight in treated mice remained within 20% of controls. To better understand the mechanism of the synergistic activity of PCM-075, we have conducted in vitro RNA-based profiling studies examining the combination of PCM-075 with FLT3 inhibitors for impact on specific gene pathways in AML cell lines and this will be presented. Combination therapy is the mainstay of current oncology treatment regimens and these results suggest that combining PCM-075 with FLT3 inhibitors could be useful in the treatment of AML and a potential next step for patients developing resistance to FLT3 inhibitors. 1 Mol Cancer Ther. 2012 Apr;11(4):1006-162 PLoS One. 2013;8(3):e58424

Citation Format: Karena Kosco, Maya Ridinger, Penn Whitley, Peter Croucher, Jeffrey N. Miner, Mark Erlander. Selective Polo-like Kinase 1 (PLK1) inhibitor PCM-075 is highly active alone and shows synergy when combined with FLT3 inhibitors in models of acute myeloid leukemia (AML) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1885.

Abstract B24: p53 mediates reprograming of cancer-associated fibroblasts in pancreatic cancer

Pancreatic ductal adenocarninoma (PDA) is one of the most aggressive human cancers and is characterized by a uniquely abundant stroma. The stroma, composed of immune and fibroblastic cells, acts both as a resource for soluble factors that sustain tumor cell growth and survival, as well as a barrier to drug delivery. The pancreatic stellate cells (PSCs) are the main fibroblastic cells in the stroma of PDA. During tumor progression, quiescent PSCs evolve into activated and proliferative myofibroblast-like cells that synthesize extracellular matrix proteins to create the desmoplasia characteristic of PDA. Identifying means to reprogram the cancer associated fibroblats (CAF) to quiescence may alter the stroma and thereby reduce PDA progression and improve therapeutic susceptibility.

Our data reveal that the tumor suppressor p53 regulates CAF quiescence/activation. We show that CAFs isolated from PDA patients express wild-type p53 that can be activated by the p53 agonist Nutlin-3a. Nutlin-3a reprogrammed CAFs to a quiescence-like state as shown by accumulation of lipid droplets, decrease of αSMA expression and growth arrest. This process is strictly p53-dependent. We also found that cell cycle arrest induced by a CDK4/6 inhibitor did not induce lipid droplet accumulation and did not decrease αSMA expression. Together, the data support the idea that growth arrest is not sufficient to reprogram CAFs toward quiescence, and that a downstream effects p53 activation are involved.

To gain insights into mechanisms of p53 induced CAF reprogramming, we investigated p53-activation induced lipid droplet accumulation. Nutlin-induced lipid droplet formation does not require lipid uptake from the media, and appears independent of growth factors since it occurs in serum-free de-lipidated medium. This implies that p53 activation may affect intracellular lipid regulation. Lipidomics and RNA-seq analysis were performed using Nutlin 3a or vehicle treated CAFs. These analyses revealed that p53 activation increases different lipid categories such as triacylglycerols, sphyngolipids and cholesterol esthers, and transcriptionaly regulates genes associated with these pathways. Further investitgations are on going to assess the importance of putative pathways identified by RNA-seq for p53-induced lipid accumulation.

RNA-seq analyses also revealed that p53 modulates expression of cytokines, growth factors, and extracellular components involved in fibrosis. Stromal p53 could therefore influence tumor growth, immune cell recruitment and therapeutic responses in vivo. We are currently testing these hypothesis using mouse models of PDA.

Citation Format: Maya Ridinger, Ronald M. Evans, Alan Saghatelian, Andrew M. Lowy, Geoffrey M. Wahl.{Authors}. p53 mediates reprograming of cancer-associated fibroblasts in pancreatic cancer. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr B24.

Abstract B10: Function and therapeutic implications of p53 in the stroma of pancreatic cancer

Pancreatic ductal adenocarninoma (PDA) is one of the most aggressive human cancers and is characterized by a predominant stromal compartment mainly composed of fibroblastic and immune cells. Pancreatic stellate cells (PSCs) are the main fibroblastic cells in the pancreatic tumor microenvironment. During tumor progression, they evolve into activated and proliferative myofibroblast-like cells that synthesize copious amounts of extracellular matrix (ECM) proteins and have diminished lipid storage capacity. They produce a dense fibrous stroma that obstructs intratumoral vasculature to create physical and biological therapeutic barriers. These observations suggest that strategies that normalize the stroma may enhance anti-tumor treatment strategies.

Activated PSCs in pancreatic cancers encode wild type p53, raising the possibilities that p53 activation could prevent their proliferation, and induce other paracrine anti-tumor effects. Nutlin-3a is a small-molecule p53 agonist that blocks the binding of its major negative regulator, Mdm2. As Nutlin derivatives are currently in clinical trials, we tested the consequences of activating p53 by Nutlin-3a in PSCs.

The data to be presented show that Nutlin-3a induces transcriptional regulation of genes that induce multiple changes consistent with quiescence. Using PSCs from patient samples, we show that p53 activation induces lipid droplet formation, decreases expression of αSMA (ACTA2), and produces growth arrest. We also observed that p53 activation inhibits TGFβ-induced transcription of genes involved in PSC activation.

To assess the genome-wide effects of p53, we performed transcriptome analysis of PSCs grown in the presence or absence of Nutlin-3a. This analysis revealed that p53 inhibits the expression of genes associated with the activation of PSCs such as ECM components and induces the expression of genes implicated in lipid metabolism characteristic of the quiescent state. P53 activation also decreased expression of genes with tumor-supporting potential including cytokines, growth factors and signaling molecules.

Ongoing investigations are designed to determine the consequences of stromal p53 activation on cancer cells using in vitro co-culture systems and mouse models of pancreatic cancer.

Citation Format: Maya Ridinger, Annabelle Kraus, Miranda Cox, Mark Wade, Christopher Liddle, Michael Downes, Ron Evans, Geoffrey Wahl. Function and therapeutic implications of p53 in the stroma of pancreatic cancer. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr B10.

Association of functional DBH genetic variants with alcohol dependence risk and related depression and suicide attempt phenotypes: results from a large multicenter association study

OBJECTIVE

Dopamine-beta-hydroxylase (DBH) metabolizes the conversion of dopamine to noradrenaline. DBH, located on chromosome 9q34.2 has variants with potential functional consequences which may be related to alterations of neurotransmitter function and several psychiatric phenotypes, including alcohol dependence (AD), depression (MD) and suicidal behavior (SA). The aim of this association study in a large multicenter sample of alcohol-dependent individuals and controls is to investigate the role of DBH SNPs and haplotypes in AD risk and associated phenotypes (AD with MD or SA).

METHOD

1606 inpatient subjects with DSM-IV AD from four addiction treatment centers and 1866 control subjects were included. Characteristics of AD, MD and SA were obtained using standardized structured interviews. After subjects were genotyped for 4 DBH polymorphisms, single SNP case-control and haplotype analyses were conducted.

RESULTS

rs1611115 (near 5') C-allele and related haplotypes were significantly associated with alcohol dependence in females. This association with female alcohol dependence also accounts for the significant relationship between this variant and comorbid conditions and traits.

CONCLUSIONS

This study presents evidence for a potentially functional DBH variant influencing the risk for alcohol dependence while other comorbid conditions are not independently influenced by this SNP. However, the study also supports the possible role of the dopamine system in the etiology of female alcohol dependence.

[Indicators of course of inpatient therapy in offenders with substance dependency]

The objective of this review is to summarise the recent state of research on intake criteria for forensic psychiatry in Germany. Therefore, a systematic literature review was conducted on the legal basis of paragraph 64 of the German Penal Code for forensic psychiatry. Although the patients were very heterogeneous, relatively robust indicators were identified that may yield an unsuccessful therapy outcome. A younger age, previous delinquency, absence of an educational and vocational qualification, and personality disorders are the most robust indicators adversely affecting therapy in German forensic psychiatric institutions.

No association of alcohol dependence with HOMER 1 and 2 genetic variants

Several lines of evidence indicate that alterations of the central cortico-accumbens glutamate pathway are involved in the development and maintenance of alcohol- and substance-use disorders. The HOMER protein family is encoded by 3 genes HOMER (1-3) which are components of the excitatory postsynaptic density complex and function to modulate synaptic activity by the regulation of glutamate signaling. HOMER 1 and 2 have been reported to contribute to chronic alcohol-induced long-term neurochemical changes in the endogenous reward system. Data from animal models suggest a potential role of the Homer protein family in the development of alcohol and substance use. The aim of this study is to assess potential associations between HOMER 1 and 2 genetic variants in a larger sample of alcohol-dependent individuals and unrelated controls. Five genetic variants of HOMER 1 and 3 of HOMER 2 were genotyped in a multi-site sample of 1,923 German healthy controls and 2,039 alcohol-dependent subjects. Neither single SNP nor haplotype analysis could detect significant associations with alcohol dependence (AD) and related phenotypes. While most of the HOMER 1 and 2 SNPs are in low-to-moderate linkage disequilibrium, three major haplotypes of HOMER 1 and 4 haplotypes of HOMER 2 are present in the majority of alcohol-dependent and control subjects. In conclusion, our results suggest that single SNPs, respectively, haplotypes of the HOMER 1 and 2 genes are unlikely to play a major role in the pathophysiology of AD.

[The impact of attachment styles and ADHD on alcohol dependence]

BACKGROUND

Insecure attachment (IA) and attention-deficit/hyperactivity disorder (ADHD) are discussed as risk factors for increased alcohol intake and the development of alcoholism.

METHODS

Among a sample of 517 consecutively admitted German inpatients with alcohol dependence we investigated the contribution of IA to alcoholism phenotypes, taking into consideration comorbid ADHD.

RESULTS

IA was significantly associated with increased alcohol consumption, increased frequency of withdrawal symptoms, increased frequency of physical or psychological problems that are likely to have been worsened by alcohol, and reduced social activities because of alcohol use. ADHD has no significant effect on these parameters.

CONCLUSIONS

IA developed as a result of social interactions during childhood long before alcohol dependence. The results point to an important effect of IA on the severity and acceleration of alcohol dependence. Therefore, it might be helpful to improve efforts in primary prevention and psychotherapy of alcohol dependence by considering the specific needs of subjects with an IA.

Endothelium-dependent gender differences in the response of the rat aorta

Segments of rat aortic arch were studied to determine the existence of sexual dimorphism. The influence of the endothelium in mediating gender differences in contractility (maximum tension, Tmax) and sensitivity (ED50) to prostaglandin F2 alpha was measured. This was done in both intact and denuded vascular ring preparations which were dissected from adult male and female rats. Group I comprised untreated male and female rats; Groups II and III were treated with testosterone (10 mg/kg i.m.) or 17 beta-estradiol (2.5 mg/kg i.m.), respectively, on days 1, 3 and 6 and sacrificed on day 7. Intact vascular ring preparations from untreated females were significantly less sensitive (P less than .01) and less contractile (P less than .025) than those from the males. After the intimal surface of the aortic arch rings was rubbed the rings from females exhibited a significant increase in Tmax. However, in vessels from males endothelial denudation had no effect on either Tmax or ED50. Testosterone treatment of female rats significantly increased Tmax (P less than .01) and decreased the ED50 (P less than .01) when compared to rings from untreated females. Testosterone treatment did not significantly affect either parameter in vessels from females which had been rubbed. Testosterone treatment also had no significant effect in either intact or rubbed vessels from males. Estrogen treatment significantly increased the Tmax (P less than .05) of intact vessels from females and had no effect on other vessel segments. Thus, the gender difference in Tmax may relate to an attenuating effect of the endothelium on contractility in the rings from females.(ABSTRACT TRUNCATED AT 250 WORDS)