The impact of young adult colorectal cancer: incidence and trends in Colorado

Aim: Far less is known about colorectal cancer (CRC) incidence in individuals under the age of 50. This study examined CRC incidence in order to better understand the changing CRC population. Methods: This study analyzed 39,525 CRC cases from the Colorado Central Cancer Registry from 1992 through 2013. Age-adjusted incidence, observed and relative 5-year survival, and estimated annual percentage change was analyzed. Results: Age-adjusted rates averaging 1.7% per year were observed in the under-50 population, while falling on average 4.3% per year (p < 0.05) in the over-50 population. Average-adjusted incidence rose in males under 50 by 2.7% per year (p < 0.05). Conclusion: The absolute incidence of CRC continues to fall in Colorado, however incidence is rising in individuals under 50, particularly males.

Evaluation of the efficacy of dasatinib, a Src/Abl inhibitor, in colorectal cancer cell lines and explant mouse model

Background

Dysregulation of the Src pathway has been shown to be important at various stages of cancer. Dasatinib is a potent Src/Abl inhibitor and has demonstrated to have anti-proliferative and anti-invasive activity in many preclinical models. The objective of this study was to determine the anti-tumor activity of dasatinib using in vitro and in vivo preclinical colorectal (CRC) models.

Methods

CRC cell lines and patient-derived tumor explant (PDX) models were used to investigate the efficacy of dasatinib. We treated 50 CRC cell lines with dasatinib for 72 hours and proliferation was assayed by a sulforhodamine B (SRB) assay; an IC₅₀ ≤ 0.08 μmol/L was considered sensitive. We treated 17 patient-derived CRC explants with dasatinib (50 mg/kg/day, administered once-daily) for 28 days to determine in vivo efficacy. Tumor growth inhibition (TGI) ≥ 50% was considered sensitive.

Results

We found that 8 out of 50 CRC cell lines reached an IC₅₀ ≤ 0.08 μmol/L with dasatinib treatment. In addition, of 17 CRC explants grown in the xenograft mouse model, 2 showed sensitivity to dasatinib. The anti-tumor effects observed in this study were a result of G1 cell cycle arrest as the dasatinib sensitive CRC cell lines exhibited G1 inhibition. Moreover, those CRC cell lines that were responsive (0.08 μmol/L) to treatment demonstrated a significant baseline increase in Src and FAK gene expression.

Conclusion

Dasatinib demonstrated significant anti-proliferative activity in a subset of CRC cell lines in vitro, especially in those with increased Src expression at baseline, but only showed modest efficacy in CRC explants. Dasatinib is currently being studied in combination with chemotherapy in patients with advanced CRC, as its use as a single agent appears limited.

Colon Cancer, Version 1.2017, NCCN Clinical Practice Guidelines in Oncology

This portion of the NCCN Guidelines for Colon Cancer focuses on the use of systemic therapy in metastatic disease. Considerations for treatment selection among 32 different monotherapies and combination regimens in up to 7 lines of therapy have included treatment history, extent of disease, goals of treatment, the efficacy and toxicity profiles of the regimens, KRAS/NRAS mutational status, and patient comorbidities and preferences. Location of the primary tumor, the BRAF mutation status, and tumor microsatellite stability should also be considered in treatment decisions.

Phase I/II Trial of Labetuzumab Govitecan (Anti-CEACAM5/SN-38 Antibody-Drug Conjugate) in Patients With Refractory or Relapsing Metastatic Colorectal Cancer

Purpose The objectives were to evaluate dosing schedules of labetuzumab govitecan, an antibody-drug conjugate targeting carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5) for tumor delivery of 7-ethyl-10-hydroxycamptothecin (SN-38), in an expanded phase II trial of patients with relapsed or refractory metastatic colorectal cancer. Patients and Methods Eligible patients with at least one prior irinotecan-containing therapy received labetuzumab govitecan once weekly at 8 and 10 mg/kg, or two times per week at 4 and 6 mg/km on weeks 1 and 2 of 3-week repeated cycles. End points were safety, response, pharmacokinetics, and immunogenicity. Results Eighty-six patients who had undergone a median of five prior therapies (range, one to 13) were each enrolled into one of the four cohorts. On the basis of Response Evaluation Criteria in Solid Tumors 1.1, 38% of these patients had a tumor as well as plasma carcinoembryonic antigen reduction from baseline after labetuzumab govitecan treatment; one patient achieved a partial response with a sustained response spanning > 2 years, whereas 42 patients had stable disease as the best overall response. Median progression-free survival and overall survival were 3.6 and 6.9 months, respectively. The major toxicities (grade ≥ 3) among all cohorts were neutropenia (16%), leukopenia (11%), anemia (9%), and diarrhea (7%). The antibody-drug conjugate's mean half-life was 16.5 hours for the four cohorts. Anti-drug/anti-antibody antibodies were not detected. The two once-weekly dose schedules, showing comparable toxicity and efficacy, were chosen for further study. Conclusion Monotherapy with labetuzumab govitecan demonstrated a manageable safety profile and therapeutic activity in heavily pretreated patients with metastatic colorectal cancer, all with prior irinotecan therapy. Further studies of labetuzumab govitecan treatment alone or in combination with other therapies in earlier settings are indicated.

Therapy of Small Cell Lung Cancer (SCLC) with a Topoisomerase-I-inhibiting Antibody-Drug Conjugate (ADC) Targeting Trop-2, Sacituzumab Govitecan

Purpose: We evaluated a Trop-2-targeting antibody conjugated with SN-38 in metastatic small cell lung cancer (mSCLC) patients.Experimental Design: Sacituzumab govitecan was studied in patients with pretreated (median, 2; range, 1-7) mSCLC who received either 8 or 10 mg/kg i.v. on days 1 and 8 of 21-day cycles. The primary endpoints were safety and objective response rate (ORR); duration of response, progression-free survival (PFS), and overall survival (OS) were secondary endpoints.Results: Sixty percent of patients showed tumor shrinkage from baseline CTs. On an intention-to-treat basis (N = 50), the ORR was 14% (17% for the 10-mg/kg group); the median response duration, 5.7 months; the clinical benefit rate (CBR ≥4 months), 34%; median PFS, 3.7 months; and median OS, 7.5 months. There was a suggested improvement in PR, CBR, and PFS with sacituzumab govitecan in second-line patients who were sensitive to first-line therapy, but no difference between first-line chemosensitive versus chemoresistant patients in the overall population. There was a statistically significant higher OS in those patients who received prior topotecan versus no topotecan therapy in a small subgroup. Grade ≥3 adverse events included neutropenia (34%), fatigue (13%), diarrhea (9%), and anemia (6%). Trop-2 tumor staining was not required for patient selection. No antibodies to the drug conjugate or its components were detected on serial blood collections.Conclusions: Sacituzumab govitecan appears to have a safe and effective therapeutic profile in heavily pretreated mSCLC patients, including those who are chemosensitive or chemoresistant to first-line chemotherapy. Additional studies as a monotherapy or combination therapy are warranted. Clin Cancer Res; 23(19); 5711-9. ©2017 AACR.

Abstract 3734: Pharmacokinetics of sacituzumab govitecan (IMMU-132), an antibody-drug conjugate (ADC) targeting Trop-2, in patients with diverse advanced solid tumors

BACKGROUND: Sacituzumab govitecan (IMMU-132), an ADC targeting Trop-2, an antigen present in many solid tumors, uses SN-38, a topoisomerase I inhibitor that has nanomolar potency derived from irinotecan (IRI), and a pH sensitive linker that releases SN-38 gradually (in vitro, 50% released per 1 day in serum). Clinical studies in patients (pts) with diverse solid tumors have shown manageable toxicity (dose-limiting neutropenia, diarrhea but lower incidence than IRI) and encouraging efficacy.

METHODS: Conjugate and IgG were monitored in pts given 8 (N = 24) or 10 mg/kg (N = 29) by ELISA. SN-38 and glucuronidated SN-38 (SN-38G) were measured by reversed-phase HPLC. SN-38 and SN-38G levels are expressed as the amount of drug dissociated from the conjugate (i.e., Free SN-38) and the amount bound to the IgG (Total SN-38). UGT1A1 status was determined in baseline blood sample from 146 pts.

RESULTS: IMMU-132 cleared with a half-life of 11.7-18.9 h, depending on the assay, while the IgG half-life was 4-5 days, which agrees with in vitro drug-release data. Levels of Free SN-38 at 30 min or 1 d after injection were &lt;2% and ~ 5% of Total SN-38, respectively, indicating most SN-38 in serum is bound to the conjugate. Free SN-38 clears with a half-life of ~20 h, which is consistent with SN-38 clearance in IRI therapy. No correlation was found between Free SN-38 in serum at 30 min and the incidence of severe neutropenia. Total and Free levels of SN-38G were similar, supporting in vitro results indicating that SN-38 is not glucuronidated while bound to the IgG. Free SN-38G levels were lower than Free SN-38 (SN-38G/SN-38 AUC ratio = 0.52), explaining the lower incidence of severe diarrhea. PK parameters for 8 and 10 mg/kg group were similar; no major differences in toxicity. UGT1A1 status showed 43% and 44% with *1*1 and *1*28 haplotype, respectively, and 13% with *28*28 haplotype, which is associated with higher risk of severe neutropenia and diarrhea for IRI therapy. With IMMU-132, 58% of the *28*28 pts had severe neutropenia compared to ~40% of the *1*1 and *1*28 pts, and 16% of the *28*28 pts had grade 3 diarrhea compared to 5-8% of the *1*1 and *1*28. In 3 of 4 cancer indications, objective response rate and clinical benefit ratio favored the 10 mg/kg group.

CONCLUSION: IMMU-132 cleared as predicted from in vitro serum stability data, with no difference between the 8 and 10 mg/kg groups. Current data show neutropenia did not correlate with Free SN-38 levels in serum at 30 min, and low SN-38G levels support the lower incidence of severe diarrhea. While pts with the *28*28 haplotype had a somewhat higher incidence of severe neutropenia or diarrhea than *1*1 and *1*28 pts, the overall incidence of each is small, suggesting toxicity management rather than screening is appropriate. With no major difference in safety and PK, but improved responses with 10 mg/kg, 10 mg/kg is selected for future clinical studies.

Citation Format: Robert M. Sharkey, Allyson J. Ocean, Alexander N. Starodub, Aditya Bardia, Michael Guarino, Wells A. Messersmith, Jordan D. Berlin, Vincent J. Picozzi, Rebecca Moroose, William A. Wegener, Pius Maliakal, Serengulam V. Govindan, David M. Goldenberg. Pharmacokinetics of sacituzumab govitecan (IMMU-132), an antibody-drug conjugate (ADC) targeting Trop-2, in patients with diverse advanced solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3734. doi:10.1158/1538-7445.AM2017-3734

Therapy of Advanced Non-Small-Cell Lung Cancer With an SN-38-Anti-Trop-2 Drug Conjugate, Sacituzumab Govitecan

Purpose Trop-2, expressed in most solid cancers, may be a target for antibody-drug conjugates (ADCs) in non-small-cell lung cancer (NSCLC). We studied sacituzumab govitecan (IMMU-132), a Trop-2 ADC, for the targeting of SN-38. Patients and Methods We evaluated IMMU-132 in a single-arm multicenter trial in patients with pretreated metastatic NSCLC who received either 8 or 10 mg/kg on days 1 and 8 of 21-day cycles. The primary end points were safety and objective response rate (ORR). Progression-free survival and overall survival were secondary end points. Results Fifty-four patients were treated. In the response-assessable study population (n = 47), which had a median of three prior therapies (range, two to seven), the ORR was 19%; median response duration, 6.0 months (95% CI, 4.8 to 8.3 months); and clinical benefit rate (complete response + partial response + stable disease ≥ 4 months), 43%. ORR in the intention-to-treat (ITT) population was 17% (nine of 54). Responses occurred with a median onset of 3.8 months, including patients who had relapsed or progressed after immune checkpoint inhibitor therapy. Median ITT progression-free survival was 5.2 months (95% CI, 3.2 to 7.1 months) and median ITT overall survival, 9.5 months (95% CI, 5.9 to 16.7 months). Grade 3 or higher adverse events included neutropenia (28%), diarrhea (7%), nausea (7%), fatigue (6%), and febrile neutropenia (4%). One patient developed a transient immune response, despite patients receiving a median of 10 doses. More than 90% of 26 assessable archival tumor specimens were highly positive (2+, 3+) for Trop-2 by immunohistochemistry, which suggests that Trop-2 is not a predictive biomarker for response. Conclusion IMMU-132 was well-tolerated and induced durable responses in heavily pretreated patients with metastatic NSCLC. This ADC should be studied further in this disease and in other patients with Trop-2-expressing tumors.

A phase IB study of the combination of selumetinib (AZD6244, ARRY-142886) and cyclosporin A (CsA) in patients with advanced solid tumors with an expansion cohort in metastatic colorectal cancer (mCRC)

2587

Background: MEK inhibition is of interest in cancer drug development. However, better strategies are needed to overcome acquired resistance to MEK inhibitors. Preclinical studies have shown Wnt pathway overexpression in KRAS mutant cell lines resistant to the MEK inhibitor, selumetinib. The combination of selumetinib and cyclosporin A (CsA), a non-canonical Wnt pathway modulator, demonstrated antitumor activity in patient-derived xenograft (PDX) models. We conducted an NCI CTEP-approved Phase I/IB trial (NCI # 9571/COMIRB # 13-2628/NCT02188264) of selumetinib and CsA combination. Biomarkers of response are being co-developed. Methods: Patients with advanced solid tumors were treated with the combination of selumetinib and CsA in dose escalation followed by an expansion cohort in patients with irinotecan and oxaliplatin-refractory mCRC (n = 20). The expansion cohort utilized a selumetinib “run-in” to evaluate efficacy in RAS-WT and RAS-MT mCRC to identify those patients most likely to respond to the combination. Results: As of January 2017, 18 patients were enrolled in the dose escalation phase and 20 patients were enrolled in the dose expansion phase. The most common adverse events and grade 3/4 toxicities were rash, hypertension, and edema. Three DLTs - Grade 3 hypertension, rash and increased creatinine were reported. The maximum tolerated dose was identified as selumetinib 75 mg BID and CsA 2 mg/kg BID on a 28-day cycle. The selumetinib “run-in” did not favor a specific RAS type. Two partial responses were noted. Sixteen patients had stable disease, and 6 patients had progression of disease as their best response to therapy. Conclusions: Selumetinib in combination with cyclosporin A appears to be well tolerated with evidence of activity in mCRC. Tumor response data are currently being updated. FZD will be evaluated as a potential biomarker of response. Clinical trial information: NCT02188264.

Efficacy and Safety of Anti-Trop-2 Antibody Drug Conjugate Sacituzumab Govitecan (IMMU-132) in Heavily Pretreated Patients With Metastatic Triple-Negative Breast Cancer

Purpose Trop-2, expressed in most triple-negative breast cancers (TNBCs), may be a potential target for antibody-drug conjugates. Sacituzumab govitecan, an antibody-drug conjugate, targets Trop-2 for the selective delivery of SN-38, the active metabolite of irinotecan. Patients and Methods We evaluated sacituzumab govitecan in a single-arm, multicenter trial in patients with relapsed/refractory metastatic TNBC who received a 10 mg/kg starting dose on days 1 and 8 of 21-day repeated cycles. The primary end points were safety and objective response rate; secondary end points were progression-free survival and overall survival. Results In 69 patients who received a median of five prior therapies (range, one to 12) since diagnosis, the confirmed objective response rate was 30% (partial response, n = 19; complete response, n = 2), the median response duration was 8.9 (95% CI, 6.1 to 11.3) months, and the clinical benefit rate (complete response + partial response + stable disease ≥ 6 months) was 46%. These responses occurred early, with a median onset of 1.9 months. Median progression-free survival was 6.0 (95% CI, 5.0 to 7.3) months, and median overall survival was 16.6 (95% CI, 11.1 to 20.6) months. Grade ≥ 3 adverse events included neutropenia (39%), leukopenia (16%), anemia (14%), and diarrhea (13%); the incidence of febrile neutropenia was 7%. The majority of archival tumor specimens (88%) were moderately to strongly positive for Trop-2 by immunohistochemistry. No neutralizing antibodies to the ADC or antibody were detected, despite repeated cycles developed. Conclusion Sacituzumab govitecan was well tolerated and induced early and durable responses in heavily pretreated patients with metastatic TNBC. As a therapeutic target and predictive biomarker, Trop-2 warrants further research.

Abstract P4-22-15: Sacituzumab govitecan (IMMU-132), an anti-Trop-2-SN-38 antibody-drug conjugate (ADC) for the treatment of relapsed/refractory, metastatic triple-negative breast cancer (mTNBC): Updated results

Background. mTNBC has an aggressive course with limited effective therapy options and a median progression-free survival (PFS) of 2-4 months (mos) with standard therapy. Sacituzumab govitecan (IMMU-132) is an ADC targeting Trop-2, an antigen present in many epithelial cancers, including TNBC, and delivering SN-38, a topoisomerase I inhibitor as its therapeutic moiety. IMMU-132 was awarded Breakthrough Therapy designation by FDA based on its previously reported activity in relapsed/refractory mTNBC patients. Here we present updated results from the mTNBC cohort of an ongoing phase I/II study (ClinicalTrials.gov, NCT01631552).

Methods. mTNBC patients (pts) received IMMU-132 10 mg/kg on days 1 and 8 every 21 days. Trop-2 expression was not required for enrollment, but available tumor specimens underwent immunohistological (IHC) testing. Efficacy was assessed locally by RECIST 1.1; ORR, PFS and overall survival (OS) were determined for all pts. Pharmacokinetic parameters were estimated in select pts with adequate blood sampling. Immunogenicity to IMMU-132 was examined in all pts.

Results. We previously reported preliminary efficacy results in 51 mTNBC patients. Here we present data on 69 patients with data cutoff June 5, 2016. Median age was 56 years (31-81) and a median of 5 prior therapies (range 1-12), with 66 evaluable for response; ORR was 29% (19/66) 2 confirmed complete (CR) and 17 confirmed partial responses (PR). The median intention-to-treat PFS is 5.6 mos (95% CI, 3.6-7.1 mos) and median OS is 14.3 mos (95% CI, 10.5-18.8 mos). PRs included 2 pts whose tumors did not respond to anti-PD-L1 therapy. The duration of response in the 19 confirmed responders (8 continuing therapy) is 11.5 mos (95% CI = 7.6 to 12.7). The clinical benefit rate (CR+PR+SD&gt;6 mos) for the 66 assessable patients is currently 45.5%. The majority (88%) of archival tumor specimens were moderately (2+) to strongly (3+) positive by IHC for Trop-2, precluding using Trop-2 expression as a selection criterion. Among current adverse events, grade &gt;3 drug-related toxicities included neutropenia (35%), leukopenia (16%), anemia (13%), vomiting (9%), diarrhea (10%), and febrile neutropenia (4%). Clearance kinetics in 8 pts showed IMMU-132 and IgG had a terminal half-life of 15.3 ± 2.7 h and 86.5 ± 40.5 h, respectively, with area under the curve for free SN-38 (unbound) only 3% of the total amount of SN-38 (e.g., IgG bound). Thus, most SN-38 remains bound to the conjugate, and is released at a rate predicted from in vitro serum stability studies. No pt developed anti-IMMU-132 antibodies.

Conclusion The Trop-2-targeting ADC, IMMU-132, delivering cytotoxic doses of SN-38, shows high objective and durable tumor responses with manageable toxicity in heavily-pretreated pts with mTNBC in this updated cohort, supporting further development in this population with an unmet medical need.

Citation Format: Bardia A, Diamond JR, Mayer IA, Isakoff SJ, Abramson V, Starodub AN, O'Shaughnessy J, Kalinsky K, Moroose R, Shah N, Juric D, Shapiro GI, Guarino M, Ocean AJ, Messersmith WA, Berlin JD, Wegener WA, Sharkey RM, Goldenberg DM, Vahdat LT. Sacituzumab govitecan (IMMU-132), an anti-Trop-2-SN-38 antibody-drug conjugate (ADC) for the treatment of relapsed/refractory, metastatic triple-negative breast cancer (mTNBC): Updated results [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P4-22-15.

A phase IB study of the combination of selumetinib (AZD6244; ARRY-142886) and cyclosporin A (CsA) in patients with advanced solid tumors with an expansion cohort in metastatic colorectal cancer (mCRC)

609

Background: Targeting MEK is of interest in the development of novel agents for treatment of many malignancies. However, better strategies are needed to overcome acquired resistance to MEK inhibitors. Preclinical studies have shown Wnt pathway overexpression in KRAS mutant cell lines resistant to the MEK inhibitor, Selumetinib. The combination of selumetinib and cyclosporin A (CsA), a non-canonical WnT pathway modulator, demonstrated antitumor activity in patient-derived xenograft (PDX) models. We are conducting an NCI CTEP-approved Phase I/IB trial (NCI # 9571/COMIRB # 13-2628) of selumetinib and CsA combination. Biomarkers of response to therapy are being co-developed. We hypothesize that this combination will be safe and potentially effective in patients with mCRC and that upregulation of FZD2 may predict for sensitivity. Methods: Phase I trial with initial dose escalation investigating the combination of selumetinib and CsA in patients with advanced solid tumors (n = 18) followed by an expansion cohort in patients with irinotecan and oxaliplatin-refractory mCRC (n = 20). The expansion cohort utilizes a selumetinib “run-in” to evaluate efficacy in RAS-WT and RAS-MT mCRC to identify those patients most likely to respond to the combination. Results: 18 patients were enrolled in the dose escalation phase and 10 patients have been enrolled in the dose expansion phase as of September 2016. Grade 1 or 2 nausea and rash were reported as the most common AEs. Most commonly reported Grade 3 or 4 toxicities were hypertension, elevated liver enzymes and rash. Three DLTs were reported with Grade 3 hypertension noted at dose level 1 and 2 and grade 3 rash reported at dose level 2. The maximum tolerated dose was defined as Selumetinib 75 mg BID and CsA 2 mg/kg BID on a 28-day cycle. Two partial responses and sixteen stable disease responses have been observed. Six patients have exhibited progressive disease. Conclusions: Selumetinib in combination with cyclosporin A appears to be well-tolerated with evidence of activity in solid tumors. Expansion cohort will complete enrollment this month. Clinical trial information: NCT02188264.

Development and Maintenance of a Preclinical Patient Derived Tumor Xenograft Model for the Investigation of Novel Anti-Cancer Therapies

Patient derived tumor xenograft (PDTX) models provide a necessary platform in facilitating anti-cancer drug development prior to human trials. Human tumor pieces are injected subcutaneously into athymic nude mice (immunocompromised, T cell deficient) to create a bank of tumors and subsequently are passaged into different generations of mice in order to maintain these tumors from patients. Importantly, cellular heterogeneity of the original tumor is closely emulated in this model, which provides a more clinically relevant model for evaluation of drug efficacy studies (single agent and combination), biomarker analysis, resistant pathways and cancer stem cell biology. Some limitations of the PDTX model include the replacement of the human stroma with mouse stroma after the first generation in mice, inability to investigate treatment effects on metastasis due to the subcutaneous injections of the tumors, and the lack of evaluation of immunotherapies due to the use of immunocompromised mice. However, even with these limitations, the PDTX model provides a powerful preclinical platform in the drug discovery process.

Regulation of Head and Neck Squamous Cancer Stem Cells by PI3K and SOX2

Background

We have an incomplete understanding of the differences between cancer stem cells (CSCs) in human papillomavirus-positive (HPV-positive) and -negative (HPV-negative) head and neck squamous cell cancer (HNSCC). The PI3K pathway has the most frequent activating genetic events in HNSCC (especially HPV-positive driven), but the differential signaling between CSCs and non-CSCs is also unknown.

Methods

We addressed these unresolved questions using CSCs identified from 10 HNSCC patient-derived xenografts (PDXs). Sored populations were serially passaged in nude mice to evaluate tumorigenicity and tumor recapitulation. The transcription profile of HNSCC CSCs was characterized by mRNA sequencing, and the susceptibility of CSCs to therapy was investigated using an in vivo model. SOX2 transcriptional activity was used to follow the asymmetric division of PDX-derived CSCs. All statistical tests were two-sided.

Results

CSCs were enriched by high aldehyde dehydrogenase (ALDH) activity and CD44 expression and were similar between HPV-positive and HPV-negative cases (percent tumor formation injecting ≤ 1x10(3) cells: ALDH(+)CD44(high) = 65.8%, ALDH(-)CD44(high) = 33.1%, ALDH(+)CD44(high) = 20.0%; and injecting 1x10(5) cells: ALDH(-)CD44(low) = 4.4%). CSCs were resistant to conventional therapy and had PI3K/mTOR pathway overexpression (GSEA pathway enrichment, P < .001), and PI3K inhibition in vivo decreased their tumorigenicity (40.0%-100.0% across cases). PI3K/mTOR directly regulated SOX2 protein levels, and SOX2 in turn activated ALDH1A1 (P < .001 013C and 067C) expression and ALDH activity (ALDH(+) [%] empty-control vs SOX2, 0.4% ± 0.4% vs 14.5% ± 9.8%, P = .03 for 013C and 1.7% ± 1.3% vs 3.6% ± 3.4%, P = .04 for 067C) in 013C and 067 cells. SOX2 enhanced sphere and tumor growth (spheres/well, 013C P < .001 and 067C P = .04) and therapy resistance. SOX2 expression prompted mesenchymal-to-epithelial transition (MET) by inducing CDH1 (013C P = .002, 067C P = .01), followed by asymmetric division and proliferation, which contributed to tumor formation.

Conclusions

The molecular link between PI3K activation and CSC properties found in this study provides insights into therapeutic strategies for HNSCC. Constitutive expression of SOX2 in HNSCC cells generates a CSC-like population that enables CSC studies.

Antitumor activity of a potent MEK inhibitor, TAK-733, against colorectal cancer cell lines and patient derived xenografts

BACKGROUND

CRC is a significant cause of cancer mortality, and new therapies are needed for patients with advanced disease. TAK-733 is a highly potent and selective investigational novel MEK allosteric site inhibitor.

MATERIALS AND METHODS

In a preclinical study of TAK-733, a panel of CRC cell lines were exposed to varying concentrations of the agent for 72 hours followed by a sulforhodamine B assay. Twenty patient-derived colorectal cancer xenografts were then treated with TAK-733 in vivo. Tumor growth inhibition index (TGII) was assessed to evaluate the sensitivity of the CRC explants to TAK-733 while linear regression was utilized to investigate the predictive effects of genotype on the TGII of explants.

RESULTS

Fifty-four CRC cell lines were exposed to TAK-733, while 42 cell lines were deemed sensitive across a broad range of mutations. Eighty-two percent of the cell lines within the sensitive subset were BRAF or KRAS/NRAS mutant, whereas 80% of the cell lines within the sensitive subset were PIK3CA WT. Twenty patient-derived human tumor CRC explants were then treated with TAK-733. In total, 15 primary human tumor explants were found to be sensitive to TAK-733 (TGII ≤ 20%), including 9 primary human tumor explants that exhibited tumor regression (TGII > 100%). Explants with a BRAF/KRAS/NRAS mutant and PIK3CA wild-type genotype demonstrated increased sensitivity to TAK-733 with a median TGII of -6%. MEK-response gene signatures also correlated with responsiveness to TAK-733 in KRAS-mutant CRC.

CONCLUSIONS

The MEK inhibitor TAK-733 demonstrated robust antitumor activity against CRC cell lines and patient-derived tumor explants. While the preclinical activity observed in this study was considerable, single-agent efficacy in the clinic has been limited in CRC, supporting the use of these models in an iterative manner to elucidate resistance mechanisms that can guide rational combination strategies.

Abstract CT064: Treatment for metastatic platinum-resistant urothelial cancer (PRUC) with an anti-Trop-2-SN-38 antibody-drug conjugate (ADC), sacituzumab govitecan (IMMU-132): phase I/II clinical experience

Background. Patients (pts) with PRUC have an aggressive disease with limited therapeutic options. Sacituzumab govitecan (IMMU-132) is an ADC comprised of SN-38, the active metabolite of the topoisomerase inhibitor, irinotecan, conjugated to an anti-Trop-2 humanized mAb. In vitro and in vivo preclinical data show that this is a unique ADC, with a high drug:antibody ratio of 7.6. It is capable of delivering up to 136-fold more SN-38 than its parent drug, irinotecan, in a human cancer xenograft. The ADC and mAb are immunotherapeutic in vitro (ADCC). Expression of Trop-2 is elevated in most epithelial cancers (&gt;80%), including UC. The efficacy and safety of this new ADC is examined in PRUC pts.

Methods. A Phase I/II clinical trial (ClinicalTrials.gov, NCT01631552) is enrolling PRUC pts. IMMU-132 is administered on days 1 and 8 of 21-day treatment cycles. Treatment is continued based on tolerance or until progression, with safety and response assessments (RECIST 1.1) made every week and every 8 weeks, respectively.

Results. Fifteen PRUC pts were enrolled by 11/10/15 and 14 are evaluable [median age 68 yrs, 93% M, 71% with ECOG 1, 71% with visceral metastases], with a median of 2 (range, 1-5) prior chemotherapies. IMMU-132 doses given were 8 mg/kg (N = 3), 10 mg/kg (N = 10), or 12 mg/kg (N = 1).

Six patients have confirmed partial response, providing an objective tumor response rate of 46% in 13 patients assessable by RECIST 1.1. The clinical benefit ratio (PR+SD &gt; 4 months) is 57%. The current median progression-free survival (PFS) is 8.1 months with 50% maturity (# events divided by # patients), and median overall survival (OS) is 10.8 months, with 79% patients still alive.

Among collected adverse events so far among 15 UC pts enrolled before 8/31/15, grade 3+ drug-related toxicities above 5% incidence (single events) are neutropenia (9%), diarrhea (9%) and staphylococcal bacteremia (9%). No patient developed antibodies (by ELISA) to the antibody or drug.

Conclusion. Compared to historical response rates of &lt; 20% in this clinical setting, PFS of 2-4 mos, and OS of 4-9 mos for pts with PRUC, the early efficacy seen in this study to date combined with the toxicity profile encourage further study of IMMU-132 at the 10 mg/kg dosing level.

Citation Format: Scott T. Tagawa, Bishoy Faltas, Elaine Lam, Wells A. Messersmith, Philip Saylor, Aditya Bardia, Julio J. Hajdenberg, Alicia K. Morgans, Jordan D. Berlin, Emerson Lim, Kevin Kalinsky, Pius Maliakal, Robert M. Sharkey, Francois Wilhelm, David M. Goldenberg, Allyson J. Ocean. Treatment for metastatic platinum-resistant urothelial cancer (PRUC) with an anti-Trop-2-SN-38 antibody-drug conjugate (ADC), sacituzumab govitecan (IMMU-132): phase I/II clinical experience. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr CT064.

Therapy of relapsed/refractory metastatic triple-negative breast cancer (mTNBC) with an anti-Trop-2-SN-38 antibody-drug conjugate (ADC), sacituzumab govitecan (IMMU-132): Phase II results

LBA509

Notice of Retraction: “Therapy of relapsed/refractory metastatic triple-negative breast cancer (mTNBC) with an anti-Trop-2-SN-38 antibody-drug conjugate (ADC), sacituzumab govitecan (IMMU-132): Phase II results.” ASCO's Confidentiality Policy requires that abstracts be considered confidential and embargoed from the time of submission until the findings have been publicly released in conjunction with the ASCO Annual Meeting. Abstract LBA509, published in the 2016 ASCO Annual Meeting Proceedings Part II, violated this policy and was retracted from publication and presentation at the 2016 ASCO Annual Meeting.