A phase I/II study of GB1275, a first-in-class oral CD11b modulator, alone, and combined with pembrolizumab in specified advanced solid tumors or with chemotherapy in metastatic pancreatic cancer (KEYNOTE-A36)

3085

Background: GB1275 is a first-in-class CD11b modulator that reduced myeloid-derived suppressor cells (MDSCs) and tumor associated macrophages (TAMs) at the tumor site, repolarized M2 immunosuppressive TAMs to an M1 phenotype, and increased tumor infiltration of activated CD8+ T cells in preclinical models. When combined with an anti-PD-1 antibody or chemotherapy, these immunomodulatory effects translated into potent anti-tumor effects and prolonged survival in orthotopic PDAC models [Panni RZ, et al. Sci Transl Med. 2019 Jul 3;11(499)]. This ongoing first-in-human study consists of dose escalation of GB1275 monotherapy (Regimen A), GB1275 + pembrolizumab (Regimen B), and GB1275 + nab-paclitaxel + gemcitabine (Regimen C), followed by Phase 2 expansion in newly diagnosed metastatic pancreatic, MSS colorectal, and PD-L1-positive gastric/GEJ cancers. Here we report interim results of the dose escalation portion of the trial. Methods: The dose escalation phase is based on a standard oncology phase 1, 3+3 design. Cohorts of 3 to 6 patients (pts) with histologically confirmed locally advanced/metastatic pancreatic, esophageal, gastric, MSS colorectal, prostate, or breast cancer were sequentially assigned to ascending dose levels of GB1275 taken orally twice daily (BID) in 1 of 3 regimens: Regimen A was initiated first; Regimen B commenced after completion of the first two cohorts of Regimen A, and Regimen C will be initiated when Regimen A is completed. Dose escalation was based on assessment of safety including dose-limiting toxicity (DLT). Serial blood and tumor samples were collected for pharmacokinetic (PK) and biomarker analyses. Results: As of January 21, 2020, 13 pts were treated, with 3 each in Regimen A (GB1275 100mg, 200 mg and 400 mg BID) dose levels and 4 in Regimen B with GB1275 100 mg BID + pembrolizumab. No DLTs have been reported. GB1275 treatment-related adverse events were reported in 5 pts; all were Grade 1 in severity. Preliminary PK analyses showed a mean elimination half-life of ~7 hours. Reduction in peripheral MDSCs was observed in the majority of pts with serial samples. Biomarker analysis in serial tumor tissue is ongoing. Conclusions: Preliminary data show minimal treatment-related toxicities with the studied regimens. PK data support BID dosing. Dose escalation is ongoing. Updated data will be presented. Clinical trial information: NCT04060342 .

Results from the safety lead-in for a phase II study of pembrolizumab in combination with binimetinib and bevacizumab in patients with refractory metastatic colorectal cancer (mCRC)

4031

Background: The majority of pts with mCRC have microsatellite stable (MSS) tumors with minimal response to PD-L1/PD-1 blockade. MEK inhibition and VEGF inhibition have immunomodulatory effects (upregulation of tumor major histocompatibility complex-I expression, enhanced T-cell infiltration, reduced MDSCs and Tregs in tumors) supporting clinical evaluation of combined MEKi (B), anti–PD-1 (P), and anti-VEGF (BV) in pts with mCRC. We hypothesize that the combination of binimetinib, pembrolizumab, and bevacizumab (BPBV) will result in greater clinical benefit than pembrolizumab alone. Methods: Patients with chemotherapy-refractory mCRC were evaluated (20 planned in the safety lead-in and 50 planned for total accrual). B was dosed at 45mg PO BID, P was administered at 200mg IV Q21 days, and BV was administered at 7.5mg/kg IV Q21 days. Primary objectives were safety, tolerability, and investigator-assessed ORR by RECIST 1.1. Clinical benefit rate (CR+PR+SD) and progression-free survival were secondary endpoints. Descriptive statistics were used to summarize safety and clinical activity. Results: As of January 9, 2020, 21 pts (10 KRAS/NRASmt, 11 RASwt, 21 MSS) were enrolled into the safety lead-in and were evaluable. The median number of prior therapies was 6. The BPBV combination was tolerable. Treatment-related Gr 1-2 and Gr 3-4 AEs occurred at 60% and 38%, respectively. The most frequent related Gr 3-4 AEs were aceniform rash, diarrhea, and hypertension (19%, 14%, 14% respectively). No treatment-related Gr 5 AEs occurred. A total of 17 patients were evaluable for response. Confirmed PR was observed in 2 pts (12%). SD was noted in 14 patients (82%) leading to a clinical benefit rate of 94%. 1 patient had PD as the best response to treatment. Median PFS was 6.4 months (95% CI 4.2-8.9). Molecular determinants, immune biomarkers, and updated tumor assessments of response will be presented. Conclusions: B + P + BV demonstrated a tolerable safety profile and improvements in ORR and clinical benefit rate compared to those reported with SOC in heavily pretreated pts with mCRC. Objective responses observed in pts were durable, suggesting benefit of this novel combination in a patient population refractory to immune therapies. Clinical trial information: NCT03475004 .

A phase I study of ALX148, a CD47 blocker, in combination with standard anticancer antibodies and chemotherapy regimens in patients with advanced malignancy

3056

Background: CD47 is a myeloid checkpoint upregulated by tumor cells to evade the host immune response. ALX148 (A) is a fusion protein comprised of a high affinity CD47 blocker linked to an inactive immunoglobulin Fc region. ALX148 enhances innate and adaptive immune responses against cancer and has previously been shown to be well tolerated in combination with the checkpoint inhibitor (CPI), pembrolizumab (P), and trastuzumab (T) in a range of solid tumors (ASCO 2019 #2514). ALX148 safety and activity in combination with T or P and standard chemotherapy regimens are reported in patients (pts) including head and neck squamous cell cancer (HNSCC) and HER2 positive gastric/gastroesophageal cancer (GC). Methods: Pts with advanced malignancy were administered AP or AT. Patients with ≥2L HNSCC progressed on platinum therapy received AP, while those with untreated advanced disease received AP+5FU (FU)+platinum. Pts with ≥2L GC progressed on T+FU+platinum received AT +/- ramucirumab (ram)+paclitaxel (pac). Safety, response, pharmacokinetic and pharmacodynamic (PD) markers were assessed. Data are reported as of 21, Jan. 2020. Results: Patients received AP (n=52); AP+FU+platinum (n=1); AT (n=30); or AT+ram+pac (n=3) as of data cutoff. Eighty-two pts experienced any adverse event (AE). Fifty-seven pts administered AP or AT regimens reported mostly low grade ALX148 treatment related (TR) AEs, the most common being fatigue (18%), AST increase (11%), platelets decreased (10%), ALT increase (8.5%), anemia (8.5%), and pruritus (8.5%). Pts receiving AP+FU+platinum or AT+ram+pac reported no TRAEs as of data cutoff. Anticancer activity was observed in response-evaluable pts. AP: HNSCC CPI-naïve (n=10) 40% ORR, mPFS 4.6 [95% CI:0.5;7.5], mOS not reached with 14.4m median follow-up; AP: HNSCC CPI-experienced (n=10) 0% ORR, mPFS 2.0 [95% CI:0.9;3.6], mOS 7.4 [95% CI:3.1;NC]; and AT: GC (n=20) 20% ORR, mPFS 2.2 [95% CI:1.9;5.4], mOS 8.1 [95% CI:3.4;12.8]. Full peripheral CD47 target occupancy and increased infiltrating immune cells in tumor biopsies were seen. Exploratory analysis of biomarkers associated with response is ongoing. Conclusions: Initial data suggests ALX148 demonstrates excellent tolerability in combination with anti cancer antibodies and standard chemotherapy. Clinical activity in pts with advanced CPI naïve HNSCC (including PD-L1 negative) and GC compares favorably with historic controls. Final data from AP and AT cohorts and initial data from chemotherapy combination cohorts will be presented. Clinical trial information: NCT03013218 .

Bgb-A425, an investigational anti-TIM-3 monoclonal antibody, in combination with tislelizumab, an anti-PD-1 monoclonal antibody, in patients with advanced solid tumors: A phase I/II trial in progress

TPS3146

Background: While immune surveillance plays a critical role in preventing tumor proliferation and metastasis, tumors develop resistance mechanisms to suppress and/or escape the immune system. T-cell immunoglobulin and mucin-domain containing-3 (TIM-3) and programmed cell death protein-1 (PD-1) function as immune checkpoint receptors on tumor-infiltrating lymphocytes. Overlap in expression and function suggests TIM-3 and PD-1 cooperate to maximize effector T-cell exhaustion, leading to a decreased antitumor immune response. Although blockade of TIM-3 alone is unlikely to result in an efficacious antitumor immune response, combined TIM-3/PD-1 blockade may enhance the antitumor properties of anti-PD-1 therapies alone. BGB-A425 is an investigational IgG1-variant monoclonal antibody against TIM-3. Tislelizumab, an anti-PD-1 antibody, was engineered to minimize binding to FcɣR on macrophages in order to abrogate antibody-dependent phagocytosis, a mechanism of T-cell clearance and potential resistance to anti-PD-1 therapy. This phase 1/2 study will assess the safety/tolerability, pharmacokinetic (PK) profile, and antitumor activity of BGB-A425 in combination with tislelizumab in patients with advanced solid tumors. Methods: This is an open-label phase 1/2 study (NCT03744468) of BGB-A425 in combination with tislelizumab in patients with histologically/cytologically confirmed advanced, metastatic, unresectable solid tumors. Phase 1 will determine the recommended phase 2 dose (RP2D) for combination treatment; phase 2 will assess the antitumor effects of the combination in select tumor types. In phase 1, up to 42 patients will be enrolled into sequential cohorts of increasing doses of intravenous (IV) BGB-A425 in combination with tislelizumab 200 mg IV, based on a 3+3 study design. During Cycle 1, patients will receive BGB-A425 alone on Day 1 followed by tislelizumab alone on Day 8. If no dose-limiting toxicities are observed, patients will receive both BGB-A425 and tislelizumab sequentially on Day 29 and every 21 days thereafter. Once the RP2D is determined, the combination therapy will be evaluated in up to 120 patients with select tumor types in phase 2. Safety/tolerability profile and RP2D determination (phase 1) and objective response rate per RECIST v1.1 (phase 2) are primary objectives; secondary objectives include antitumor activity, PK profile, and immunogenicity of combination therapy. Clinical trial information: NCT03744468 .

Wee1 Inhibition Enhances the Anti-Tumor Effects of Capecitabine in Preclinical Models of Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is an aggressive subtype defined by lack of hormone receptor expression and non-amplified HER2. Adavosertib (AZD1775) is a potent, small-molecule, ATP-competitive inhibitor of the Wee1 kinase that potentiates the activity of many DNA-damaging chemotherapeutics and is currently in clinical development for multiple indications. The purpose of this study was to investigate the combination of AZD1775 and capecitabine/5FU in preclinical TNBC models. TNBC cell lines were treated with AZD1775 and 5FU and cellular proliferation was assessed in real-time using IncuCyte^® Live Cell Analysis. Apoptosis was assessed via the Caspase-Glo 3/7 assay system. Western blotting was used to assess changes in expression of downstream effectors. TNBC patient-derived xenograft (PDX) models were treated with AZD1775, capecitabine, or the combination and assessed for tumor growth inhibition. From the initial PDX screen, two of the four TNBC PDX models demonstrated a better response in the combination treatment than either of the single agents. As confirmation, two PDX models were expanded for statistical comparison. Both PDX models demonstrated a significant growth inhibition in the combination versus either of the single agents. (TNBC012, p < 0.05 combo vs. adavosertib or capecitabine, TNBC013, p < 0.01 combo vs. adavosertib or capecitabine.) An enhanced anti-proliferative effect was observed in the adavosertib/5FU combination treatment as measured by live cell analysis. An increase in apoptosis was observed in two of the four cell lines in the combination when compared to single-agent treatment. Treatment with adavosertib as a single agent resulted in a decrease in p-CDC2 in a dose-dependent manner that was also observed in the combination treatment. An increase in γH2AX in two of the four cell lines tested was also observed. No significant changes were observed in Bcl-xL following treatment in any of the cell lines. The combination of adavosertib and capecitabine/5FU demonstrated enhanced combination effects both in vitro and in vivo in preclinical models of TNBC. These results support the clinical investigation of this combination in patients with TNBC, including those with brain metastasis given the CNS penetration of both agents.

Abstract P1-19-25: Wee1 inhibition enhances the anti-tumor effects of capecitabine in preclinical models of triple negative breast cancer

Background: Triple-negative breast cancer (TNBC) is an aggressive subtype defined by lack of hormone receptor expression and non-amplified HER2. TNBC accounts for approximately 15% of breast cancer cases, however, is associated with an increased risk of cancer recurrence, brain metastasis, and death due to metastatic breast cancer. Mutations in p53 are common in TNBC, occurring in approximately 85% of tumors. While a number of promising targeted therapies are on the horizon in TNBC including immunotherapy, there remains an unmet need for active targeted therapies where chemotherapy remains the standard treatment for metastatic disease and results in a median survival of 12-18 months. Adavosertib (AZD1775) is a potent, small molecule, ATP-competitive inhibitor of the Wee1 kinase that potentiates the activity of many DNA-damaging chemotherapeutics and is currently in clinical development for multiple indications. AZD1775 potentiates the activity of DNA-damaging and antimetabolite chemotherapeutics in preclinical models without TP53-deficiency, possibly due to baseline replicative stress or compromised DNA repair proficiency. A previous unbiased screen of CTEP compounds in TNBC PDX models demonstrated that the combination of adavosertib and capecitabine/5FU had greater anti-proliferative effects than either of the single agents. The purpose of this study was to further investigate the combination of adavosertib and capecitabine/5FU in preclinical TNBC models. Methods: HCC1937, CAL51, MDA-MB-231 and MDA-MB-468 cells were plated in 96-well plates and exposed to increasing concentrations of adavosertib, 5FU, or the combination. Cellular proliferation was assessed in real-time using IncuCyte® Live Cell Analysis. Apoptosis was assessed via the Caspase-Glo 3/7 assay system. Western blotting was used to assess changes in expression of CDC2, phospho-CDC2, H2AX, and Bcl-xL. TNBC PDX models CU_TNBC_012 and CU_TNBC_013 were treated with vehicle, adavosertib, capecitabine, or the combination and assessed for tumor growth inhibition. Results: From the initial PDX screen, two of the four TNBC PDX models demonstrated a better response in the combination treatment than either of the single agents. As confirmation, two PDX models were expanded for statistical comparison. Both PDX models demonstrated a significant growth inhibition in the combination versus either of the single agents. (TNBC012, p&lt;0.05 combo vs adavosertib or capecitabine, TNBC013, p&lt;0.01 combo vs adavosertib or capecitabine ). An enhanced antiproliferative effect was observed in the adavosertib/5FU combination treatment as measured by live cell analysis. An increase in apoptosis was observed in two of the four cell lines in the combination when compared to single agent treatment. Treatment with single agent adavosertib resulted in an increase in p-cdc2 in a dose dependent manner that was also observed in the combination treatment. Similar results were observed with γH2AX in two of the four cell lines tested. No significant changes were observed in Bcl-xL following treatment in any of the cell lines. Conclusions: The combination of adavosertib and capecitabine/5-FU demonstrated enhanced combination effects both in vitro and in vivo in preclinical models of TNBC. These results support the clinical investigation of this combination in patients with TNBC, including those with brain metastasis given the CNS penetration of both agents.

Citation Format: Todd M Pitts, Dennis M Simmons, Kyrie Dailey, Stacey M Bagby, Sarah J Hartman, Betelehem W Yacob, Brian Gittleman, John J Tentler, Diana Cittely, D. Ryan Ormond, Wells A Messersmith, S Gail Eckhardt, Jennifer R Diamond. Wee1 inhibition enhances the anti-tumor effects of capecitabine in preclinical models of triple negative breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P1-19-25.

The role of neoadjuvant chemotherapy in elderly patients with borderline or locally advanced pancreatic cancer: Is it safe and feasible?

685

Background: For borderline resectable (BRPC) or locally advanced pancreatic cancer (LAPC), neoadjuvant (NAT) FOLFIRINOX or gemcitabine plus nab-paclitaxel (GnP) are standard treatment options and these regimens have shown a survival advantage over single-agent gemcitabine. However, the role of these modern therapeutic regimens in elderly patients is debatable. In this analysis, we evaluated the outcomes of neoadjuvant treatment (NAT) with combination chemotherapy in elderly patients. Methods: 230 consecutive patients who underwent neoadjuvant treatment for BRPC/LAPC discussed and planned for NAT at the University of Colorado Cancer Center from January 2011 to March 2019 were reviewed. 214 patients who received FOLFIRINOX (n = 143) or GnP (n = 71) were eligible for analysis. We divided all patients into three groups ( < 70, 70-74, ≥75 years) and compared the short-term and long-term outcomes. Results: Of 214 patients, patients < 70 (n = 147) received FOLFIRINOX more frequently than the other groups (p < 0.001): FOLFIRINOX: 115 cases, GnP: 32 cases, 70-74 years (n = 33): FOLFIRINOX: 15 cases, GnP: 18 cases, and ≥75 years (n = 34): FOLFIRINOX: 13 cases, GnP: 21 cases. Resection rates were not statistically different between three groups ( < 70: 62%, 70-74: 70%, ≥75 years: 56%, p = 0.504). There was a slight trend towards worse survival in the two older groups (Median Survival Time [MST]: < 70: 23.2 mo., 70-74: 19.5 mo., ≥75 years: 17.6 mo., p = 0.075) The FOLFIRINOX group was superior to GnP group in all three groups (MST: < 70: 25.6 vs 18.2 mo., p = 0.017; 70-74: 33.2 vs 16.1mo., p = 0.029; ≥75 years: not reached vs 16.1 mo., p = 0.135). There were no toxic deaths or 30 day mortality after pancreatectomy in the study population. Conclusions: Neoadjuvant combination chemotherapy regimens were safe and feasible for elderly patients. Neoadjuvant therapy with FOLFIRINOX was associated with a survival advantage vs GnP and is an good option for fit and elderly patients ≥75 years.

An assessment of dose intensity of the TNT approach on outcomes in locally advanced rectal cancer

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Background: Patients with clinical stage II or III locally advanced rectal cancer may be treated with the total neoadjuvant therapy (TNT) approach; chemotherapy with 4 mths of FOLFOX followed by chemoradiation (chemo/XRT) with capecitabine for 5 wks administered before surgery. We hypothesized that full dose intensity is not necessary for treatment benefit. Methods: A retrospective chart review was conducted on patients with newly diagnosed rectal cancer recommended to receive TNT by the multidisciplinary (multiD) colorectal cancer tumor board at the University of Colorado Cancer Center (UCCC). The primary objective was to evaluate dose intensity of TNT and its impact on response assessed by biopsy and/or imaging (MRI). Results: Between January 31, 2016 and January 31, 2019, 80 patients were recommended the TNT approach for cancer management by the multiD team. Of those, 48 completed their neoadjuvant treatment at UCCC and were included in the analysis. The average age was 55 years (range 23-80) and 61% were male. Thirty-one patients had an ECOG of 0 and 17 had an ECOG of 1. Overall responses were 44% complete response (CR, n = 21), 15% near complete response (nCR, n = 7), 35% partial response (PR, n = 17), and 6% no response (NR, n = 3). See Table for responses seen by dose intensity for chemotherapy. Two patients did not receive their full planned XRT course, and 9 patients had their capecitabine doses held/decreased during chemoradiation. Conclusions: This single center retrospective analysis of patients receiving the TNT approach for rectal cancer provides data supporting that achieving full dose intensity is not necessary to achieve treatment benefit.

[Table: see text]

A phase II study investigating cabozantinib in patients with refractory metastatic colorectal cancer (AGICC 17CRC01)

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Background: Therapeutic resistance to antiangiogenics in metastatic colorectal cancer (mCRC) inevitably develops via multiple mechanisms including upregulation of the MET kinase pathway. Cabozantinib, an oral multityrosine kinase inhibitor targeting MET, AXL, and VEGFR, demonstrated significant anti-tumor activity in CRC xenograft and cell line models. Methods: A single-arm, two-stage phase II study was conducted at 7 AGICC centers nationwide. 44 patients (pts) with mCRC who had progressed on or were intolerant of standard of care agents were treated with cabozantinib 60 mg daily in q3 wk cycles. The primary endpoint was 12-wk PFS rate. Based on the control arm of phase III CORRECT study, the Kaplan-Meier 12-wk PFS rate estimate was 13% and served as the null hypothesis. This study was powered at 0.906 to detect the alternative hypothesis of 12-wk PFS rate of 33% with a type I error rate of 0.044. Secondary endpoints were safety, RR, OS, and retrospective analysis of PFS and RR based on RAS, BRAF, and PIK3CA mutation status. Results: 44 pts were enrolled and 34 pts were response-evaluable as having undergone at least the first 6-wk restaging scan. 10 pts discontinued treatment prior to the first 6-wk scan due to clinical disease progression. Median number of cycles was 4 and median follow-up was 2.5 months. As of data-cutoff 8/23/2019, 55 Grade 3/4 AEs were reported with the most common being hypertension, fatigue, diarrhea, pain, HFS, nausea, vomiting, and proteinuria. 32 SAEs occurred in 18 pts. 5 Grade 5 AEs were reported: disease progression (3), disseminated intravascular coagulopathy, and bowel perforation. 15 pts (34%) achieved ≥ 12-wk PFS and 8 patients remain on treatment. Best response was 1 PR and 31 SD with a DCR at 6 wks of 72.7%. Of the pts who achieved ≥ 12-wk PFS, 12 had left-sided primary tumors, 5 had a RAS mutation, 1 had a PIK3CA mutation, and all pts were BRAF WT and MSI stable. Conclusions: Cabozantinib was deemed safe and demonstrates encouraging efficacy in a heavily pretreated mCRC pt population. These results support further investigation of cabozantinib in mCRC. Clinical trial information: NCT03542877.

Development of an Adrenocortical Cancer Humanized Mouse Model to Characterize Anti-PD1 Effects on Tumor Microenvironment

CONTEXT

Although the development of immune checkpoint inhibitors has transformed treatment strategies of several human malignancies, research models to study immunotherapy in adrenocortical carcinoma (ACC) are lacking.

OBJECTIVE

To explore the effect of anti-PD1 immunotherapy on the alteration of the immune milieu in ACC in a newly generated preclinical model and correlate with the response of the matched patient.

DESIGN, SETTING, AND INTERVENTION

To characterize the CU-ACC2-M2B patient-derived xenograft in a humanized mouse model, evaluate the effect of a PD-1 inhibitor therapy, and compare it with the CU-ACC2 patient with metastatic disease.

RESULTS

Characterization of the CU-ACC2-humanized cord blood-BALB/c-Rag2nullIl2rγnullSirpaNOD model confirmed ACC origin and match with the original human tumor. Treatment of the mice with pembrolizumab demonstrated significant tumor growth inhibition (60%) compared with controls, which correlated with increased tumor infiltrating lymphocyte activity, with an increase of human CD8+ T cells (P < 0.05), HLA-DR+ T cells (P < 0.05) as well as Granzyme B+ CD8+ T cells (<0.001). In parallel, treatment of the CU-ACC2 patient, who had progressive disease, demonstrated a partial response with 79% to 100% reduction in the size of target lesions, and no new sites of metastasis. Pretreatment analysis of the patient's metastatic liver lesion demonstrated abundant intratumoral CD8+ T cells by immunohistochemistry.

CONCLUSIONS

Our study reports the first humanized ACC patient-derived xenograft mouse model, which may be useful to define mechanisms and biomarkers of response and resistance to immune-based therapies, to ultimately provide more personalized care for patients with ACC.

Abstract B107: Metabolic reprogramming enhances the efficacy of mTOR inhibition in colorectal cancer

Background: PI3K/mTOR pathway is mutated in 10-20% of colorectal cancer (CRC) specimens and has been associated with poor survival. Phosphatidic acid (PA) is a central lipid membrane metabolite and lipid second messenger which has been shown to target mTOR. It is thought that PA lipid signaling to mTOR in part promotes mTOR mediated cancer cell growth, proliferation and survival. Diacylglycerol kinases (DGKs) are one of several mechanisms of PA generation. In this study, we found diacylglycerol kinases to be synthetically lethal in mTOR inhibitor resistant CRC. We evaluated the anti-proliferative, pharmacodynamic and metabolic effects of dual inhibition with mTOR (TAK-228) and DGK (ritanserin and R59022) inhibitors. Methods: A synthetic lethal screen was performed with two TAK-228 resistant colorectal cancer cell lines (HCT116 and SW620). Subsequent experiments were performed with one TAK-228 sensitive (DLD1) and one resistant (HCT116) CRC cell lines. Efficacy of TAK-228/ritanserin and TAK-228/R59022 combination therapy was evaluated with CellTiter-Glo cell viability and clonogenic colony formation assays. Global metabolomics profiling of DLD1 and HCT116 cells upon treatment with TAK-228, R59022, and in combination was performed using ultra high pressure liquid chromatography coupled to mass spectrometry. Pharmacologic DGK inhibition was phenocopied using lentiviral shRNA knockdown of DGKα. Immunoblotting was performed to evaluate mechanism of action of TAK-228 combination therapy. Results: TAK-228 combined with ritanserin and R59022 demonstrated decreased cell viability and colony formation as compared to either single agent. Immunoblotting confirmed TAK-228 abrogates PI3K/mTOR pathway activity. DGK inhibition alone resulted in a compensatory activation of mTOR signaling. DGK inhibition disrupted the phosphatidic acid pathway in DLD1 and HCT116 as evidenced by a decrease in PA synthesis and elevation of glycerol 3-phosphate levels, respectively: altering energy metabolism. Specifically, in HCT116, glucose utilization, glutaminolysis, and Krebs cycle anaplerosis were elevated; while one carbon metabolism was decreased. Lentiviral shRNA transduction resulted in DGKα knockdown as evaluated by RT-PCR and immunoblot. Phenocopy combination therapy with TAK-228 and DGKα knockdown resulted in an increased sensitivity to mTOR inhibition compared to mock transduced control. Conclusions: Pharmacologic and shRNA knockdown inhibition of DGK in combination with mTOR inhibition resulted in decreased cancer cell viability and decreased colony formation. Pharmacologic inhibition of mTOR and DGK, alone or in combination, alter metabolic wiring in crucial pathways such as energy metabolism, nucleotide biosynthesis, and the generation of lipid precursors. Impaired phosphatidic acid production may sensitize cells to mTOR inhibition. These results suggest a therapeutic anti-cancer advantage of simultaneously targeting lipid signaling/metabolism via diacylglycerol kinases and mTOR.

Citation Format: Peter J Klauck, Hayley J Hawkins, Madison Weber, Stacey M Bagby, Christopher H Lieu, Sarah J Hartman, Betelehem W Yacob, Kelly D Sullivan, Monica Brown, Julie A Reisz, Angelo D’Alessandro, Wells A Messersmith, S Gail Eckhardt, Todd M Pitts. Metabolic reprogramming enhances the efficacy of mTOR inhibition in colorectal cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr B107. doi:10.1158/1535-7163.TARG-19-B107

Drug Design Targeting T-Cell Factor-Driven Epithelial-Mesenchymal Transition as a Therapeutic Strategy for Colorectal Cancer

Metastasis is the cause of 90% of mortality in cancer patients. For metastatic colorectal cancer (mCRC), the standard-of-care drug therapies only palliate the symptoms but are ineffective, evidenced by a low survival rate of ∼11%. T-cell factor (TCF) transcription is a major driving force in CRC, and we have characterized it to be a master regulator of epithelial-mesenchymal transition (EMT). EMT transforms relatively benign epithelial tumor cells into quasi-mesenchymal or mesenchymal cells that possess cancer stem cell properties, promoting multidrug resistance and metastasis. We have identified topoisomerase IIα (TOP2A) as a DNA-binding factor required for TCF-transcription. Herein, we describe the design, synthesis, biological evaluation, and in vitro and in vivo pharmacokinetic analysis of TOP2A ATP-competitive inhibitors that prevent TCF-transcription and modulate or reverse EMT in mCRC. Unlike TOP2A poisons, ATP-competitive inhibitors do not damage DNA, potentially limiting adverse effects. This work demonstrates a new therapeutic strategy targeting TOP2A for the treatment of mCRC and potentially other types of cancers.

Rectal Cancer, Version 2.2018, NCCN Clinical Practice Guidelines in Oncology

The NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines) for Rectal Cancer address diagnosis, staging, surgical management, perioperative treatment, management of recurrent and metastatic disease, disease surveillance, and survivorship in patients with rectal cancer. This portion of the guidelines focuses on the management of localized disease, which involves careful patient selection for curative-intent treatment options that sequence multimodality therapy usually comprised of chemotherapy, radiation, and surgical resection.

Anal Carcinoma, Version 2.2018, NCCN Clinical Practice Guidelines in Oncology

The NCCN Guidelines for Anal Carcinoma provide recommendations for the management of patients with squamous cell carcinoma of the anal canal or perianal region. Primary treatment of anal cancer usually includes chemoradiation, although certain lesions can be treated with margin-negative local excision alone. Disease surveillance is recommended for all patients with anal carcinoma because additional curative-intent treatment is possible. A multidisciplinary approach including physicians from gastroenterology, medical oncology, surgical oncology, radiation oncology, and radiology is essential for optimal patient care.

NCCN Guidelines Insights: Colon Cancer, Version 2.2018

The NCCN Guidelines for Colon Cancer provide recommendations regarding diagnosis, pathologic staging, surgical management, perioperative treatment, surveillance, management of recurrent and metastatic disease, and survivorship. These NCCN Guidelines Insights summarize the NCCN Colon Cancer Panel discussions for the 2018 update of the guidelines regarding risk stratification and adjuvant treatment for patients with stage III colon cancer, and treatment of BRAF V600E mutation-positive metastatic colorectal cancer with regimens containing vemurafenib.

Abstract 3855: Preclinical investigation of novel ALDH1A1 inhibitors in pancreatic cancer

Introduction: Pancreatic adenocarcinoma remains a devastating disease, with a predicted 5-year survival at the time of diagnosis of less than 10%, and likely the number 2 cause of U.S. cancer deaths in the next decade. The lack of effective therapies and resistance to cytotoxic agents contribute to the poor outcomes in this patient population. Aldehyde dehydrogenases (ALDHs) are a family of enzymes that play important biological and metabolic roles in the human body. ALDH activity has been identified in many human malignancies as a marker of tumor initiating cells. In pancreatic cancer, ALDH1A1 has been shown to be upregulated in cancer stem cells (CSCs) and has been attributed to tumorigenesis and chemotherapeutic resistance.

Methods: Six novel ALDH1A1 inhibitor drugs from the National Center for Advancing Translational Sciences (NCATS) were screened on human pancreatic cancer cell lines using the Cell Titer-Glo Assay. Proliferation assays were also performed with the three best performing inhibitors on a total of eight human pancreatic cancer cell lines. The best performing ALDH1A1 inhibitor drug were chosen and tested in combination with gemcitabine and paclitaxel on patient-derived tumor organoids (PDTOs). The combination effects were assessed over a 7-day period using the IncuCyte ZOOM live cell imager and CellTiter-Glo 3D Assay.

Results: We assessed the anti-proliferative effects of 6 novel ALDH1A1 inhibitors on 4 pancreatic cancer cell lines. Two out of 4 pancreatic cell lines showed moderate treatment effects to 3 ALDH1A1 inhibitors. Further evaluation of one of the ALDH1A1 inhibitor on 8 additional pancreatic cancer cell lines revealed similar results. While several pancreatic cell lines showed some moderate activity at higher levels of drug exposure, most of the pancreatic cancer cell lines treated were more resistant. We next investigated the treatment effects of ALDH1A1 inhibitor in combination with gemcitabine or paclitaxel on PDTO 269 and 272. A combination effect with the ALDH1A1 inhibitor and paclitaxel was observed after 72 hours of drug exposure in both PDTO 269 and 272. In contrast, treatment with the ALDH1A1 inhibitor with gemcitabine did not further decrease growth when compared to single agent ALDH1A1 and gemcitabine.

Conclusions: Although single agent activity of novel ALDH1A1 inhibitors is limited at significantly reducing cellular proliferation, inhibition of ALDH1A1 in combination with paclitaxel appears to have potent anti-tumor activity in PDTOs. These findings support further investigation of this combinational therapy for the treatment of pancreatic cancer. Additional studies are currently underway to evaluate this combinational activity in more preclinical pancreatic cancer models and to elucidate the underlying mechanisms whereby the inhibition of ALDH1A1 enhances the anti-tumor potential of paclitaxel.

Citation Format: Betelehem W. Yacob, John J. Arcaroli, Maraake Taddese, Todd M. Pitts, Stacey M. Bagby, Sarah J. Hartman, S.Lindsey Davis, Christopher H. Lieu, Alexis D. Leal, Wells A. Messersmith. Preclinical investigation of novel ALDH1A1 inhibitors in pancreatic cancer [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 3855.

Abstract 4720: Ataxia telangiectasia mutated (ATM) kinase inhibitor AZD0156 in combination with 5-fluorouracil and irinotecan in preclinical models of colorectal cancer

Background: AZD0156 is an oral inhibitor of ATM, a serine threonine kinase that plays a key role in DNA damage response associated with DNA double strand breaks. Topoisomerase-I inhibitors like irinotecan induce single-strand DNA breaks, which are converted to double-strand breaks during DNA replication. Thus the combination of AZD0156 and irinotecan is a rational combination for clinical use. Irinotecan is used clinically to treat a variety of malignancies, including colorectal cancer (CRC), usually in combination with 5-fluorouracil (5FU) as FOLFIRI. An ongoing phase 1 clinical trial is evaluating AZD0156 in combination with single-agent irinotecan and FOLFIRI in patients with refractory cancers (NCT02588105). The purpose of this study is to evaluate AZD0156 in combination with irinotecan and 5FU in preclinical models of CRC to help inform clinical use.

Methods: Anti-proliferative effects of single-agent AZD0156 and combination therapy with SN38 (active metabolite of irinotecan) and 5FU were evaluated in CRC cell lines using the Cell-Titer Glo assay. Immunoblotting and cell cycle analysis were performed to determine the mechanism of enhanced combination effects. Four CRC patient derived xenograft (PDX) models were treated with AZD0156, irinotecan, and 5FU alone and in combination for assessment of tumor growth inhibition (TGI).

Results: An enhanced antiproliferative effect was observed with the combination treatment over either single agent. A more significant synergistic effect was demonstrated with the combination of AZD0156 and SN38 as compared with the combination of AZD0156 and 5FU. Cell cycle data demonstrated enhanced cell cycle arrest with combination therapy as compared to single agents. Immunoblotting results suggest a decrease in phosphorylated gamma-H2AX in cell lines treated with combination therapies. Increased TGI was observed in CRC PDX models treated with the combination of AZD0156 and irinotecan as compared to single-agent therapy in 3 of 4 models. There was not a significant change in TGI with the addition of 5FU for triplet therapy in the majority of models.

Conclusions: The combination of AZD0156 with irinotecan is synergistic in in vitro models and is associated with increased TGI in CRC PDX in vivo models. The addition of 5FU to AZD0156 and irinotecan did not result in increased TGI as compared to doublet therapy in CRC PDX models, though did not decrease the AZD0156/irinotecan combination effect. An ongoing clinical trial is evaluating this combination in patients with cancers refractory to standard treatments (NCT02588105).

Citation Format: S. Lindsey Davis, Marina I. Schlaepfer, Stacey M. Bagby, Sarah J. Hartman, Betelehem W. Yacob, Tonia Tse, Dennis M. Simmons, Jennifer R. Diamond, Christopher H. Lieu, Alexis D. Leal, Elaine B. Cadogan, Gareth D. Hughes, Stephen T. Durant, Wells A. Messersmith, Todd M. Pitts. Ataxia telangiectasia mutated (ATM) kinase inhibitor AZD0156 in combination with 5-fluorouracil and irinotecan in preclinical models of colorectal cancer [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 4720.

Abstract 1315: Combination of Wee1 inhibition with targeted and standard chemotherapy in preclinical models of pancreatic ductal adenocarcinoma

Introduction: Pancreatic ductal adenocarcinoma (PDA) is the fourth leading cause of cancer death and has a 5-year survival rate of less than 7%. The poor prognosis associated with PDA is related in part to a lack of screening tests to promote early detection and ineffective systemic targeted therapies. Adavosertib (AZD1775, MK1775) is a selective Wee1 inhibitor with promising preclinical activity in PDA and synergy with cytotoxic chemotherapy in other cancer types. Wee1 is a tyrosine kinase that activates in the G2M cell cycle checkpoint in response to DNA damage. Inhibition of Wee1 with adavosertib prevents the phosphorylation of CDC2, thus allowing unrepaired DNA to enter mitosis and ultimately succumb to mitotic catastrophe. The purpose of this study was to investigate adavosertib in combination with standard chemotherapy and other targeted agents in preclinical models of PDA.

Methods: Athymic nude mice were implanted with PDA PDX models on the right and left flanks. When the average tumor volume reached 100-300 mm3, mice were randomized into one of the following treatments: vehicle, adavosertib, irinotecan, navitoclax, capecitabine, adavosertib + irinotecan, or adavosertib + navitoclax, adavosertib + capecitabine. Tumor volume was calculated using the following equation: volume = (length × width) × 0.52. Four pancreatic cancer cell lines were plated in 96-well plates and Cell Titer-Glo proliferation assays were performed to determine the most effective combination doses of irinotecan, 5FU, or navitoclax with adavosertib in vitro. Combination effects were analyzed using CalcuSyn software. The most effective doses within each cell line were selected and used for Caspase 3/7 apoptosis assays and cell cycle analyses by flow cytometry. Western blots were performed to evaluate changes in downstream effectors.

Results: In vivo, the combination of adavosertib with either irinotecan or navitoclax resulted in decreased tumor growth compared to the respective single agents. The combination of adavosertib with irinotecan, 5FU, or navitoclax in vitro resulted in greater antiproliferative effects in all cell lines, and the several combinations were synergistic in all cell lines as determined by CI values less than 1. Navitoclax increased apoptosis in several cell lines both as a single agent and was enhanced in combination with adavosertib. Irinotecan proved to be more cell cycle dependent and significantly altered the cell cycle in all cell lines. Irinotecan increased phospho-CDC2 and decreased PHH3, while adavosertib increased gamma-H2AX as a single agent and in combination.

Conclusions: The combination of adavosertib with either irinotecan, 5FU, or navitoclax in vivo decreased tumor growth and had enhanced antiproliferative effects in vitro. These data support future studies with adavosertib in combination with standard therapies or navitoclax to treat PDA.

Citation Format: Sarah J. Hartman, Stacey M. Bagby, Betelehem W. Yacob, Dennis M. Simmons, Tonia E. Tse, Christopher H. Lieu, S. Lindsey Davis, Alexis D. Leal, Jennifer R. Diamond, Wells A. Messersmith, Todd M. Pitts. Combination of Wee1 inhibition with targeted and standard chemotherapy in preclinical models of pancreatic ductal adenocarcinoma [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 1315.

Comprehensive Genomic Landscapes in Early and Later Onset Colorectal Cancer

PURPOSE

The incidence rates of colorectal cancers are increasing in young adults. The objective of this study was to investigate genomic differences between tumor samples collected from younger and older patients with colorectal cancer.

EXPERIMENTAL DESIGN

DNA was extracted from 18,218 clinical specimens, followed by hybridization capture of 3,769 exons from 403 cancer-related genes and 47 introns of 19 genes commonly rearranged in cancer. Genomic alterations (GA) were determined, and association with patient age and microsatellite stable/microsatellite instability high (MSS/MSI-H) status established.

RESULTS

Overall genomic alteration rates in the younger (<40) and older (≥50) cohorts were similar in the majority of the genes analyzed. Gene alteration rates in the microsatellite stable (MSS) younger and older cohorts were largely similar, with several notable differences. In particular, TP53 (FDR < 0.01) and CTNNB1 (FDR = 0.01) alterations were more common in younger patients with colorectal cancer, and APC (FDR < 0.01), KRAS (FDR < 0.01), BRAF (FDR < 0.01), and FAM123B (FDR < 0.01) were more commonly altered in older patients with colorectal cancer. In the MSI-H cohort, the majority of genes showed similar rate of alterations in all age groups, but with significant differences seen in APC (FDR < 0.01), BRAF (FDR < 0.01), and KRAS (FDR < 0.01).

CONCLUSIONS

Tumors from younger and older patients with colorectal cancer demonstrated similar overall rates of genomic alteration. However, differences were noted in several genes relevant to biology and response to therapy. Further study will need to be conducted to determine whether the differences in gene alteration rates can be leveraged to provide personalized therapies for young patients with early-onset sporadic colorectal cancer.

A phase I study of ALX148, a CD47 blocker, in combination with established anticancer antibodies in patients with advanced malignancy

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Background: CD47 is a myeloid checkpoint upregulated by tumor cells to evade the host’s immune response. ALX148 (A) is a fusion protein comprised of a high affinity CD47 blocker linked to an inactive human immunoglobulin Fc region. ALX148 is well tolerated in combination with pembrolizumab (P) or trastuzumab (T) with no maximum tolerated dose (MTD) identified (ASCO 2018 #3068, SITC 2018 #P335). Safety and antitumor activity of ALX148 (10 mg/kg QW) in combination with T or P are reported in patients (pts) including those with anti-HER2 or checkpoint inhibitor (CPI) relapsed/refractory diseases. Methods: Patients with malignancy including non-small cell lung cancer (NSCLC: CPI resistant/refractory or PD-L1 tumor proportion score <50%) and head and neck squamous cell carcinoma (HNSCC: progressed on platinum therapy) received A+P. Patients with HER2 malignancy including gastric/gastroesophageal junction (GEJ) cancer (progressed on T + fluoropyrimidine-based therapy) received A+T. Safety, response, pharmacokinetic (PK), and pharmacodynamic (PD) markers were assessed. Preliminary data from fully enrolled cohorts are reported as of 20 Jan 2019 (safety)/28 Jan 2019 (efficacy). Results: Seventy-nine pts received A+P (All, n=50; NSCLC, n=23; HNSCC, n=20) or A+T (All, n=29; Gastric/GEJ, n=23) as of data cutoff. Forty-seven pts reported mostly low grade treatment related adverse events. The most common were fatigue (11%), AST increase (9%), ALT increase (8%), anemia (8%), and platelets decreased (6%). In select tumor histologies, anticancer activity was observed in initial response-evaluable pts [NSCLC (n=23) 1PR, 8SD; HNSCC (n=17) 3PR, 4SD; and Gastric/GEJ (n=21) 4PR, 6SD]. Preliminary results indicate favorable ALX148 PK and CD47 target occupancy profiles, and positive effects on tumor infiltrating immune cells. Results will be updated at presentation. Conclusions: ALX148 demonstrates excellent tolerability with favorable PK/PD characteristics to date. Objective responses were observed in patients with late line NSCLC, HNSCC, and Gastric/GEJ, including disease relapsed/refractory to prior CPI and HER2-targeted therapies. Clinical trial information: NCT03013218.

High incidence of advanced stage cancer and prolonged rectal bleeding history before diagnosis in young-onset patients with colorectal cancer

3576

Background: In contrast to the older population, the incidence of colorectal cancer (CRC) in younger patients (aged < 50 years) has been increasing in the last three decades. Younger patients tend to present with more advanced disease, thought to be in part related to lack of routine screening colonoscopies. The goal of this study was to examine characteristics of young-onset CRC and potentially identify factors that may aid in earlier diagnosis and treatment. Methods: We collected data for patients available through the University of Colorado Cancer Center Cancer Registry. Inclusion criteria included: 1) Diagnosis of colon or rectal cancer between the years 2012-2018 and 2) age at diagnosis of less than 50 years. Pertinent data including baseline characteristics, clinical presentation, family history, pathology, molecular testing, staging, and treatment were collected. Results: 211 patients with young-onset CRC were available for review. Mean age at diagnosis was 42.4 years and 55.5% were males. A total of 42.1% had rectal cancer and a majority of the colon cancer diagnoses had left-sided tumors (66%). Regarding clinical presentation, 52.2% presented with rectal bleeding prior to diagnosis. Of those who presented with rectal bleeding, the average time from the onset of bleeding to diagnosis was 271.17 days. 42.9% of young-onset CRC were stage IV at the time of initial diagnosis. Evaluation of the pathology specimens showed that 89.6% were adenocarcinomas and 63.5% were grade 2 or higher. At diagnosis, the mean BMI was 26.6 and the mean CEA was 135.5. A total of 72.5% of young-onset patients had a positive family history of any cancer. KRAS or NRAS mutations were present in 49.6% of patients, BRAF V600E mutations were present in 3.8%, and 10.8% were MSI-H. Conclusions: Prolonged rectal bleeding history prior to diagnosis was noted in a significant proportion of young-onset patients with colorectal cancer. Patients and primary care physicians should be made aware of this finding in order to facilitate timely referral for colonoscopy which may lead to earlier diagnosis, less advanced disease at diagnosis, and improved outcomes.

Pancreatic Tumor Microenvironment Modulation by EphB4-ephrinB2 Inhibition and Radiation Combination

PURPOSE

A driving factor in pancreatic ductal adenocarcinoma (PDAC) treatment resistance is the tumor microenvironment, which is highly immunosuppressive. One potent immunologic adjuvant is radiotherapy. Radiation, however, has also been shown to induce immunosuppressive factors, which can contribute to tumor progression and formation of fibrotic tumor stroma. To capitalize on the immunogenic effects of radiation and obtain a durable tumor response, radiation must be rationally combined with targeted therapies to mitigate the influx of immunosuppressive cells and fibrosis. One such target is ephrinB2, which is overexpressed in PDAC and correlates negatively with prognosis.Experimental Design: On the basis of previous studies of ephrinB2 ligand-EphB4 receptor signaling, we hypothesized that inhibition of ephrinB2-EphB4 combined with radiation can regulate the microenvironment response postradiation, leading to increased tumor control in PDAC. This hypothesis was explored using both cell lines and in vivo human and mouse tumor models.

RESULTS

Our data show this treatment regimen significantly reduces regulatory T-cell, macrophage, and neutrophil infiltration and stromal fibrosis, enhances effector T-cell activation, and decreases tumor growth. Furthermore, our data show that depletion of regulatory T cells in combination with radiation reduces tumor growth and fibrosis.

CONCLUSIONS

These are the first findings to suggest that in PDAC, ephrinB2-EphB4 interaction has a profibrotic, protumorigenic role, presenting a novel and promising therapeutic target.

Biomarkers to predict immune-related adverse events with checkpoint inhibitors

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Background: Immune-related adverse events (IRAE) occur commonly with immune checkpoint inhibitor therapy for the treatment of cancer, although the specific event and severity can vary widely. Little is known regarding factors that may predict which patients will develop an IRAE. The goal of this study is to identify blood biomarkers predictive of IRAE associated with immune checkpoint inhibitor therapy. Methods: Blood samples collected from patients with melanoma prior to receiving therapy with immune checkpoint inhibitors were obtained from the University of Colorado Skin Cancer Biorepository. Testing for a panel of autoantibodies and cytokines (ANA, CCP 3.1, IL-1 beta, IL-2, IL-6, IL-10, IL-12, IP-10, MCP-1, TNF alpha, IFN alpha 2, IFN gamma) in serum samples from patients who had at least one documented IRAE was performed by Exsera BioLabs. Descriptive statistics were used to evaluate biomarker levels in relation to type, grade, and number of adverse events. Results: Pre-treatment samples from 45 patients were evaluated. Median age was 55; 26 were male and 19 were female. The most common IRAEs were colitis (n = 22), thyroid dysfunction (n = 21), and dermatitis (n = 20). Most IRAEs were grade 2 in severity, and the majority of patients (n = 36) experienced more than 1 IRAE. TNF alpha was elevated in 60% of patient samples, while IFN alpha 2 was elevated in 44%. Borderline ANA was detected in 27% of samples and ANA was positive in 11%. No samples had elevation of IL-2. Between 9% and 18% of samples had elevation of the other immune markers tested (IFN gamma, IL-1 beta, IL-6, IL-10, IL-12, and CCP 3.1). Elevation of TNF alpha and IFN alpha 2 were associated with higher grades of IRAEs. No associations between immune markers and the number or type of adverse events in an individual patient were noted. Results from 15 patients who did not have a documented IRAE on immune checkpoint inhibitor therapy are currently pending to confirm these findings are unique to patients developing IRAE. Conclusions: This preliminary data suggests that baseline elevations of TNF alpha and IFN alpha 2 may predict development of IRAEs with immune checkpoint inhibitor therapy. Results from samples from patients who did not develop an IRAE on therapy will be reported at the meeting.

Characterization of immune responses to anti-PD-1 mono and combination immunotherapy in hematopoietic humanized mice implanted with tumor xenografts

Background

The success of agents that reverse T-cell inhibitory signals, such as anti-PD-1/PD-L1 therapies, has reinvigorated cancer immunotherapy research. However, since only a minority of patients respond to single-agent therapies, methods to test the potential anti-tumor activity of rational combination therapies are still needed. Conventional murine xenograft models have been hampered by their immune-compromised status; thus, we developed a hematopoietic humanized mouse model, hu-CB-BRGS, and used it to study anti-tumor human immune responses to triple-negative breast cancer (TNBC) cell line and patient-derived colorectal cancer (CRC) xenografts (PDX).

Methods

BALB/c-Rag2^nullIl2rγ^nullSIRPα^NOD (BRGS) pups were humanized through transplantation of cord blood (CB)-derived CD34+ cells. Mice were evaluated for human chimerism in the blood and assigned into experimental untreated or nivolumab groups based on chimerism. TNBC cell lines or tumor tissue from established CRC PDX models were implanted into both flanks of humanized mice and treatments ensued once tumors reached a volume of ~150mm³. Tumors were measured twice weekly. At end of study, immune organs and tumors were collected for immunological assessment.

Results

Humanized PDX models were successfully established with a high frequency of tumor engraftment. Humanized mice treated with anti-PD-1 exhibited increased anti-tumor human T-cell responses coupled with decreased Treg and myeloid populations that correlated with tumor growth inhibition. Combination therapies with anti-PD-1 treatment in TNBC-bearing mice reduced tumor growth in multi-drug cohorts. Finally, as observed in human colorectal patients, anti-PD-1 therapy had a strong response to a microsatellite-high CRC PDX that correlated with a higher number of human CD8+ IFNγ+ T cells in the tumor.

Conclusion

Hu-CB-BRGS mice represent an in vivo model to study immune checkpoint blockade to human tumors. The human immune system in the mice is inherently suppressed, similar to a tumor microenvironment, and thus allows growth of human tumors. However, the suppression can be released by anti-PD-1 therapies and inhibit tumor growth of some tumors. The model offers ample access to lymph and tumor cells for in-depth immunological analysis. The tumor growth inhibition correlates with increased CD8 IFNγ+ tumor infiltrating T cells. These hu-CB-BRGS mice provide a relevant preclinical animal model to facilitate prioritization of hypothesis-driven combination immunotherapies.

Electronic supplementary material

The online version of this article (10.1186/s40425-019-0518-z) contains supplementary material, which is available to authorized users.