Divarasib plus cetuximab in KRAS G12C-positive colorectal cancer: a phase 1b trial

KRAS G12C mutation is prevalent in ~4% of colorectal cancer (CRC) and is associated with poor prognosis. Divarasib, a KRAS G12C inhibitor, has shown modest activity as a single agent in KRAS G12C-positive CRC at 400 mg. Epidermal growth factor receptor has been recognized as a major upstream activator of RAS-MAPK signaling, a proposed key mechanism of resistance to KRAS G12C inhibition in CRC. Here, we report on divarasib plus cetuximab (epidermal growth factor receptor inhibitor) in patients with KRAS G12C-positive CRC (n = 29) from arm C of an ongoing phase 1b trial. The primary objective was to evaluate safety. Secondary objectives included preliminary antitumor activity. The safety profile of this combination was consistent with those of single-agent divarasib and cetuximab. Treatment-related adverse events led to divarasib dose reductions in four patients (13.8%); there were no treatment withdrawals. The objective response rate was 62.5% (95% confidence interval: 40.6%, 81.2%) in KRAS G12C inhibitor-naive patients (n = 24). The median duration of response was 6.9 months. The median progression-free survival was 8.1 months (95% confidence interval: 5.5, 12.3). As an exploratory objective, we observed a decline in KRAS G12C variant allele frequency associated with response and identified acquired genomic alterations at disease progression that may be associated with resistance. The manageable safety profile and encouraging antitumor activity of divarasib plus cetuximab support the further investigation of this combination in KRAS G12C-positive CRC.ClinicalTrials.gov identifier: NCT04449874.

Single-Agent Divarasib (GDC-6036) in Solid Tumors with a KRAS G12C Mutation

BACKGROUND

Divarasib (GDC-6036) is a covalent KRAS G12C inhibitor that was designed to have high potency and selectivity.

METHODS

In a phase 1 study, we evaluated divarasib administered orally once daily (at doses ranging from 50 to 400 mg) in patients who had advanced or metastatic solid tumors that harbor a KRAS G12C mutation. The primary objective was an assessment of safety; pharmacokinetics, investigator-evaluated antitumor activity, and biomarkers of response and resistance were also assessed.

RESULTS

A total of 137 patients (60 with non-small-cell lung cancer [NSCLC], 55 with colorectal cancer, and 22 with other solid tumors) received divarasib. No dose-limiting toxic effects or treatment-related deaths were reported. Treatment-related adverse events occurred in 127 patients (93%); grade 3 events occurred in 15 patients (11%) and a grade 4 event in 1 patient (1%). Treatment-related adverse events resulted in a dose reduction in 19 patients (14%) and discontinuation of treatment in 4 patients (3%). Among patients with NSCLC, a confirmed response was observed in 53.4% of patients (95% confidence interval [CI], 39.9 to 66.7), and the median progression-free survival was 13.1 months (95% CI, 8.8 to could not be estimated). Among patients with colorectal cancer, a confirmed response was observed in 29.1% of patients (95% CI, 17.6 to 42.9), and the median progression-free survival was 5.6 months (95% CI, 4.1 to 8.2). Responses were also observed in patients with other solid tumors. Serial assessment of circulating tumor DNA showed declines in KRAS G12C variant allele frequency associated with response and identified genomic alterations that may confer resistance to divarasib.

CONCLUSIONS

Treatment with divarasib resulted in durable clinical responses across KRAS G12C-positive tumors, with mostly low-grade adverse events. (Funded by Genentech; ClinicalTrials.gov number, NCT04449874.).

Comprehensive pan-cancer genomic landscape of KRAS altered cancers and real-world outcomes in solid tumors

Recent clinical development of KRAS inhibitors has heightened interest in the genomic landscape of KRAS-altered cancers. We performed a pan-cancer analysis of KRAS-altered samples from 426,706 adult patients with solid or hematologic malignancies using comprehensive genomic profiling; additional analyses included 62,369 liquid biopsy and 7241 pediatric samples. 23% of adult pan-cancer samples had KRAS alterations; 88% were mutations, most commonly G12D/G12V/G12C/G13D/G12R, and prevalence was similar in liquid biopsies. Co-alteration landscapes were largely similar across KRAS mutations but distinct from KRAS wild-type, though differences were observed in some tumor types for tumor mutational burden, PD-L1 expression, microsatellite instability, and other mutational signatures. Prognosis of KRAS-mutant versus other genomic cohorts of lung, pancreatic, and colorectal cancer were assessed using a real-world clinicogenomic database. As specific KRAS inhibitors and combination therapeutic strategies are being developed, genomic profiling to understand co-alterations and other biomarkers that may modulate response to targeted or immunotherapies will be imperative.

Abstract P5-17-05: A phase I/Ib study of inavolisib (GDC-0077) in combination with fulvestrant in patients (pts) with PIK3CA-mutated hormone receptor-positive/HER2-negative (HR+/HER2-) metastatic breast cancer

Background Dysregulating mutations in PIK3CA, which encodes the catalytic PI3K p110α subunit, are common in breast cancer and other solid tumors. There are limited data available on the role of PI3Kα inhibition in the post-cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) setting. Inavolisib is a PI3Kα-selective inhibitor and degrader of mutated PI3Kα that has demonstrated encouraging preliminary antitumor activity in patients with PIK3CA-mutated HR+ breast cancer as a single agent, and in combination with antiestrogen therapy. An open-label, phase I/Ib dose-escalation study of inavolisib alone and in combination with endocrine and targeted therapies is ongoing (NCT03006172; GO39374). Data for inavolisib in combination with fulvestrant in female pts with PIK3CA-mutated, HR+/HER2- breast cancer (Arm D) are presented. Methods Safety (NCI-CTCAE v4), pharmacokinetics (PK), and preliminary antitumor activity (assessed every 2 cycles via RECIST v1.1; clinical benefit rate [CBR]: stable disease for ≥24 weeks, partial response [PR], or complete response; progression-free survival [PFS]) of 9 mg inavolisib administered orally once daily in combination with 500 mg intramuscular fulvestrant on Day 1 (and Day 15 of Cycle 1) of 28-day cycles were assessed until intolerable toxicity or disease progression. Early dynamics of PIK3CA-mutation allele frequency were assessed from circulating tumor (ct)DNA samples. Results At clinical cutoff (April 5, 2021), 55 pts were enrolled in Arm D and enrollment was ongoing. Thirty-seven pts (67%) had received ≥2 prior lines of therapy for metastatic breast cancer, 19 (35%) had received chemotherapy in the metastatic setting, 26 (47%) had received prior fulvestrant, and 53 (96%) had received a prior CDK4/6i. Median inavolisib treatment duration was 5.3 months (range 0.2-31.9); cumulative dose intensity was 98%. Thirty-two pts (58%) had dose modifications (interruptions, reductions, and/or discontinuations) due to adverse events (AEs). The most common treatment-related AEs (≥15% of pts) were hyperglycemia (31 pts, 56%), diarrhea (21 pts, 38%), stomatitis (grouped term; 19 pts, 35%), nausea (17 pts, 31%), and dysgeusia (nine pts, 16%). Grade ≥3 treatment-related AEs in ≥2 pts were hyperglycemia (13 pts, 24%) and alanine aminotransferase increased (two pts, 4%). No grade 3 rash was observed. Thirty-eight pts (70%) discontinued treatment: 36, due to radiographic or clinical disease progression; one, due to physician’s decision; and one, due to death (unrelated serious AE of hypertrophic cardiomyopathy). No treatment-related AE resulted in treatment discontinuation. Overall, 12/49 pts with measurable disease achieved a PR (25%; three of the responding pts had received prior fulvestrant; 11, prior CDK4/6i). Nine pts (18%) had a confirmed PR. CBR was 49% (27/55 pts). Preliminary median PFS was 7.1 months (0-29). Analysis of ctDNA from most pts demonstrated decreased PIK3CA-mutation allele frequency during treatment. The PK of inavolisib in combination with fulvestrant was similar to single-agent inavolisib PK. Conclusion Inavolisib in combination with fulvestrant demonstrated a manageable safety profile, encouraging preliminary antitumor activity, similar PK to inavolisib alone, and pharmacodynamic modulation (i.e., decreased PIK3CA-mutation allele frequency in ctDNA), including in patients who previously progressed on a CDK4/6i. Inavolisib continues to be developed in breast cancer and other solid tumors.

Citation Format: Dejan Juric, Phillippe L Bedard, Andrés Cervantes, Valentina Gambardella, Mafalda Oliveira, Cristina Saura, Kevin M Kalinsky, Erika Hamilton, Antoine Italiano, Ian E Krop, Peter Schmid, Nicholas C Turner, Andrea Varga, Stephanie Royer-Joo, Katherine E Hutchinson, Jennifer L Schutzman, Komal L Jhaveri. A phase I/Ib study of inavolisib (GDC-0077) in combination with fulvestrant in patients (pts) with PIK3CA-mutated hormone receptor-positive/HER2-negative (HR+/HER2-) metastatic breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-17-05.

Abstract PS11-11: Targeted safety events from a phase I/Ib study evaluating GDC-0077 alone and in combination with endocrine therapy (ET) ± palbociclib (palbo) in patients (pts) with PIK3CA-mutant (mut), hormone receptor-positive/HER2-negative metastatic breast cancer (HR+/HER2- mBC)

Background

Activating mutations in PIK3CA, encoding the p110α subunit of phosphatidylinositol 3-kinase (PI3K) occur in ~40% of HR+/HER2- BCs. GDC-0077, a PI3Kα-selective inhibitor and mutant PI3Kα degrader, is being developed as an anticancer agent. A phase I/Ib study of GDC-0077 alone and combined with other therapies is ongoing in pts with locally advanced or metastatic PIK3CAmut, HR+/HER2- mBC (NCT03006172). Targeted safety events are presented here.

Methods

Safety was assessed via NCI-CTCAE v4 for GDC-0077 administered alone (Arm A), with letrozole and palbo (Arm B), with letrozole (Arm C), with fulvestrant (Arm D), or with fulvestrant and palbo (Arm E, plus metformin in Arm F for pts with body mass index ≥ 30 and/or HbA1c ≥ 5.7%), in 28-day cycles until intolerable toxicity or disease progression. GDC-0077 was administered orally daily at 3, 6, 9, or 12 mg; letrozole, at 2.5 mg orally daily; palbo, at 125 mg orally 21/28 days; and fulvestrant, at 500 mg intramuscularly every 4 weeks. Targeted adverse events (AEs) included hyperglycemia, diarrhea, stomatitis (includes stomatitis, mucosal inflammation, mouth ulceration, glossitis, lip ulceration, palatal ulcer, and tongue ulceration), rash (includes rash, maculopapular rash, dermatitis acneiform, erythema, and erythematous rash), neutropenia (includes neutropenia and neutrophil count decreased), thrombocytopenia, and pneumonitis.

Results

As of clinical data cutoff (03/20/2020), 157 pts were enrolled and treated (Arm A: 20; Arm B: 33; Arm C: 37; Arm D: 39; Arm E: 13; Arm F: 15). Median cumulative dose intensity was 97.2% for GDC-0077, 90.6% for palbo, 99.9% for letrozole, and 100% for fulvestrant.

Pneumonitis was reported in 2 pts, both in palbo-containing arms (grade 1 in Arm B; grade 2 in Arm F). Hyperglycemia required antihyperglycemic treatment in 69 pts (44%), and the most frequent agents used were metformin (39%; except Arm F where this was required as part of study treatment), empagliflozin (16%), and sitagliptin (15%). Fifteen pts (10%) required GDC-0077 dose reductions due to hyperglycemia. Stomatitis treatment was administered in 51 pts (32%), with dexamethasone mouthwash used most frequently (22%). Neutropenia and thrombocytopenia were managed with palbo dose reduction in 13 pts (21%) and 1 pt (2%), respectively. Overall, treatment-related AEs led to GDC-0077 discontinuation in 2 pts (1%) (grade 3 hyperglycemia in Arm B; grade 2 panniculitis in Arm F).

Conclusion

Targeted safety events with GDC-0077 alone and in combination ET ± palbo were manageable and required minimal GDC-0077 dose modifications or discontinuations. No unexpected safety events were reported in combination with palbo. A phase III study of GDC-0077 in combination with palbo and fulvestrant is enrolling currently (NCT04191499).

Pts, n (%)Treatment-related AEsTreatment-related grade ≥ 3 AEsAll arms;All arms;N = 157N = 157Hyperglycemia98 (62)36 (23)Stomatitis (grouped terms)69 (44)2 (1)Diarrhea68 (43)0Rash (grouped terms)19 (12)1 (1)Palbo arms (B/E/F);Palbo arms (B/E/F);N = 61N = 61Neutropenia45 (74)36 (59)Stomatitis (grouped terms)41 (66)2 (3)Thrombocytopenia19 (31)4 (7)

Citation Format: Mafalda Olivera, Komal Jhaveri, Dejan Juric, Philippe L Bedard, Andrés Cervantes, Valentina Gambardella, Erika Hamilton, Antoine Italiano, Kevin Kalinsky, Ian E Krop, Peter Schmid, Nicolas Turner, Andrea Varga, Guiyuan Lei, Stephanie Royer-Joo, Piia Thomas, Jennifer L Schutzman, Cristina Saura. Targeted safety events from a phase I/Ib study evaluating GDC-0077 alone and in combination with endocrine therapy (ET) ± palbociclib (palbo) in patients (pts) with PIK3CA-mutant (mut), hormone receptor-positive/HER2-negative metastatic breast cancer (HR+/HER2- mBC) [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS11-11.

Abstract PD1-02: A phase I/Ib study evaluating GDC-0077 + palbociclib (palbo) + fulvestrant in patients (pts) with PIK3CA-mutant (mut), hormone receptor-positive/HER2-negative metastatic breast cancer (HR+/HER2- mBC)

Background

GDC-0077 is a PI3Kα-selective inhibitor and mutant PI3Kα degrader that demonstrates antitumor activity in PIK3CAmut BC xenograft models. A phase I/Ib study of GDC-0077 alone and combined with endocrine therapy ± the CDK4/6 inhibitor (i) palbo is ongoing (NCT03006172). Data from GDC-0077 + palbo + fulvestrant in pts with PIK3CAmut, HR+/HER2- mBC are presented herein.

Methods

Safety (NCI-CTCAE v4), pharmacokinetics (PK), and preliminary antitumor activity (clinical benefit rate [CBR]: RECIST v1.1 stable disease for ≥ 24 weeks, partial response [PR], or complete response) of 9 mg oral once daily GDC-0077 + 125 mg palbo 21/28 days + 500 mg intramuscular fulvestrant on day 1 (and day 15 of cycle 1) of 28-day cycles were assessed in Arms E and F, until intolerable toxicity or disease progression. In Arm F, pts were obese and/or pre-diabetic (body mass index ≥ 30 kg/m2 and/or HbA1c ≥ 5.7%) and also received metformin up to 2000 mg daily starting at 500 mg in cycle 1 day 1, prior to initiating GDC-0077 at cycle 1 day 15 instead of day 1 as in Arm E. Additional key eligibility criteria included Eastern Cooperative Oncology Group performance status (ECOG PS) 0-1, no prior PI3Ki therapy, no prior CDK4/6i, and ≤ 1 prior chemotherapy for Arm E (no restrictions on prior CDK4/6i or chemotherapy for Arm F). PIK3CAmut allele frequency was assessed in circulating tumor (ct) DNA from serial plasma collections.

Results

At clinical cutoff (03/20/2020), 28 pts were enrolled (13 in Arm E and 15 in Arm F). Median age was 55 years in Arm E and 65 years in Arm F. ECOG PS was 0 in 8 pts (62%) in Arm E and in 7 pts (47%) in Arm F. Three (23%) and 12 (80%) pts in Arm E and F, respectively, had received ≥ 2 prior lines of therapy for mBC. One pt (8%) in Arm E and 10 pts (67%) in Arm F received prior fulvestrant. Nine pts (60%) received prior CDK4/6i (all Arm F). Median GDC-0077 treatment duration was 7.8 months (range 0.1-13.9) in Arm E and 6.5 months (1.2-11.2) in Arm F. GDC-0077 cumulative dose intensity was 98% in Arm E and 88% in Arm F. Thirteen pts (46%) discontinued treatment: 11, due to radiographic disease progression (3 in Arm E, 8 in Arm F); 1, due to an adverse event (AE; treatment-related grade 2 panniculitis in Arm F); and 1 pt withdrew (Arm F). The most common treatment-related AEs (≥ 4 pts) were stomatitis (grouped term; 92%), neutropenia (85%), diarrhea and hyperglycemia (62% each), fatigue (38%), alopecia, nausea, and thrombocytopenia (31% each) in Arm E; and hyperglycemia (67%), diarrhea and neutropenia (53% each), nausea (47%), stomatitis (grouped term; 47%), anemia, decreased appetite, and blurred vision (27% each) in Arm F. Grade ≥ 3 treatment-related AEs (≥ 2 pts) were neutropenia (62%) and hyperglycemia (23%) in Arm E; and hyperglycemia and neutropenia (47% each), and anemia (13%) in Arm F. AEs led to GDC-0077 dose reduction in 2 pts (15%) in Arm E and 4 pts (27%) in Arm F. The PK of GDC-0077 in combination with palbo + fulvestrant was similar to single agent GDC-0077. Overall, 7/25 pts (28%) with measurable disease had a PR (5/10 [50%] pts in Arm E; 2/15 [13%] pts in Arm F, both received prior fulvestrant), of whom 6 pts (24%; 4 in Arm E; 2 in Arm F) had a confirmed PR. CBR was 61% (17/28 pts: 8 in Arm E; 9 in Arm F). PIK3CAmut allele frequency by ctDNA analysis decreased during treatment in most pts.

Conclusion

This study demonstrated a manageable safety profile when combining GDC-0077 at its single agent recommended phase II dose of 9 mg with palbo + fulvestrant at standard doses, similar PK to GDC-0077 alone, preliminary anti-tumor activity, and modulation of PIK3CAmut allele frequency in ctDNA. In obese and/or pre-diabetic patients enrolled to Arm F, hyperglycemia was frequent despite initiating metformin prior to GDC-0077. A phase III study of GDC-0077 + palbo + fulvestrant is enrolling currently (NCT04191499).

Citation Format: Philippe L Bedard, Komal Jhaveri, Andrés Cervantes, Valentina Gambardella, Erika Hamilton, Antoine Italiano, Kevin Kalinsky, Ian E Krop, Mafalda Oliveira, Cristina Saura, Peter Schmid, Nicolas Turner, Andrea Varga, Katherine E Hutchinson, Guiyuan Lei, Stephanie Royer-Joo, Piia Thomas, Jennifer L Schutzman, Dejan Juric. A phase I/Ib study evaluating GDC-0077 + palbociclib (palbo) + fulvestrant in patients (pts) with PIK3CA-mutant (mut), hormone receptor-positive/HER2-negative metastatic breast cancer (HR+/HER2- mBC) [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PD1-02.

Abstract PS5-12: Preliminary correlative analysis of clinical outcomes with PIK3CA mutation (mut) status from a phase I/Ib study of GDC-0077 in patients (pts) with hormone receptor-positive/HER2-negative metastatic breast cancer (HR+/HER2- mBC)

Background

Mutations in p110α, encoded by PIK3CA, are present in ~40% of HR+/HER2- BCs. GDC-0077, a PI3Kα-selective inhibitor and mutant PI3Kα degrader, elicits antitumor activity in PIK3CAmut preclinical models as a single agent and when combined with endocrine therapy (ET). New evidence suggests BCs harboring multiple PIK3CAmut exhibit increased signaling through the PI3K/AKT pathway and are more sensitive to PI3Kα inhibitors compared with BCs with a single PIK3CAmut. We report a preliminary analysis of PIK3CAmut status with clinical outcomes from an ongoing study of GDC-0077 alone or with ET (letrozole/fulvestrant) ± palbociclib (palbo) in pts with PIK3CAmut HR+/HER2- mBC (NCT03006172).

Methods

Detectable PIK3CAmut from local tumor tissue/blood-based assay or tumor tissue by cobas PIK3CA assay were required to enroll. Plasma-derived circulating tumor (ct) DNA was collected at baseline (BL), cycle 1 day 15 (C1D15), and C2D1 (in the cohort where GDC-0077 starts at C1D15) to detect PIK3CAmut. Paired tumor samples were analyzed for Ki67 and pAKT/pS6 expression by immunohistochemistry. Single vs multiple PIK3CAmut was correlated with the percentage of pharmacodynamic (PD) inhibition of Ki67/pAKT/pS6 expression; with the PIK3CAmut allele frequency ratio between BL and C1D15 or C2D1 (MAFr15); with best overall response (BOR, RECIST v1.1); and with time on treatment (TOT) in days. Statistical analyses: Kruskal-Wallis and Mann-Whitney-Wilcoxon for group and pairwise comparisons, respectively, and two-sample proportion testing for categorical comparisons.

Results

Data cutoff was 03/20/2020. PIK3CAmut were detected in 87/103 (84.5%) pts with BL ctDNA available for sequencing. Multiple PIK3CAmut were detected in 21/87 (24.1%) BL ctDNA samples: 9 from pts treated with single-agent GDC-0077; 8 from pts treated with GDC-0077 + letrozole/fulvestrant; and 4 from pts treated with GDC-0077 + letrozole/fulvestrant + palbo. The median number of lines of prior therapy for metastatic disease was not different between pts with multiple (3.0 lines) vs single (2.5 lines) PIK3CAmut detected at BL (p = 0.205). Median percentage inhibition of Ki67/pAKT/pS6 expression was greater in pts with multiple (-65.8, -70.3, -66.8%, respectively) vs single (-42.1, -34.1, -29.5%) PIK3CAmut detected at BL (p = 0.095, 0.002, 0.056). Median MAFr15 was lower in pts with multiple (MAFr15 0.01) vs single PIK3CAmut (MAFr15 0.15) detected at BL (p = 0.004). Of 73 pts with both BL ctDNA-detected PIK3CAmut and BOR data, 16/16 (100%) with multiple PIK3CAmut experienced BOR of partial response (PR) or stable disease (SD) while 42/57 (73.7%) with single PIK3CAmut experienced BOR of PR or SD (p = 0.051). No pts with multiple PIK3CAmut detected experienced a BOR of progressive disease. Median TOT was greater in pts with multiple PIK3CAmut (196 days) vs single PIK3CAmut (140.5 days) detected at BL, but this was not significant (p = 0.1804).

Conclusions

The fraction of pts in which multiple PIK3CAmut were identified from BL ctDNA in this HR+/HER2- mBC dataset (24.1%) was slightly higher than reported elsewhere. This may be due to the method of detection (blood vs tissue) and/or the definition of multiple PIK3CAmut used. Pts in which multiple PIK3CAmut were detected by ctDNA exhibited greater depth of PD biomarker inhibition in tumors and experienced PR/SD more often compared with pts in which only one PIK3CAmut was detected. However, no significant associations were observed with the number of prior lines of therapy for metastatic disease or TOT. The dataset is currently too small to assess the impact of different treatment regimens in this study but will be re-evaluated as the data mature.

Citation Format: Komal Jhaveri, Dejan Juric, Andrea Varga, Nicolas Turner, Peter Schmid, Cristina Saura, Mafalda Oliveira, Ian E Krop, Kevin Kalinsky, Antoine Italiano, Erika Hamilton, Valentina Gambardella, Andrés Cervantes, Philippe L Bedard, Bonnie P Liu, Jessica W Chen, Junko Aimi, Stephanie Royer-Joo, Jennifer L Schutzman, Katherine E Hutchinson. Preliminary correlative analysis of clinical outcomes with PIK3CA mutation (mut) status from a phase I/Ib study of GDC-0077 in patients (pts) with hormone receptor-positive/HER2-negative metastatic breast cancer (HR+/HER2- mBC) [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS5-12.

Abstract CT109: A phase I/Ib study evaluating GDC-0077 plus fulvestrant in patients with PIK3CA-mutant, hormone receptor-positive/HER2-negative breast cancer

Background: PIK3CA encodes the PI3K p110α subunit, and dysregulating mutations are widely seen in breast cancer (BC) and other solid tumors. GDC-0077 (G) is a potent p110α-selective inhibitor that degrades mutant p110α and demonstrates antitumor activity in PIK3CA-mutant BC xenograft models, either as a single agent, or combined with anti-estrogen therapy. From an ongoing, open-label, phase I/Ib dose-escalation study of G alone and combined with endocrine + targeted therapies (NCT03006172), we present data of G + fulvestrant (F) in postmenopausal patients (pts) with PIK3CA-mutant, hormone receptor-positive/HER2-negative BC, including a food-effect assessment on the pharmacokinetics (PK) of G. Methods: Safety (NCI-CTCAE v4), PK, and preliminary antitumor activity (clinical benefit rate [CBR]: RECIST v1.1 stable disease for ≥24 weeks, partial response [PR], or complete response) of 9 mg oral once-daily G + 500 mg intramuscular F on Day 1 (and Day 15 of Cycle 1) of 28-day cycles were assessed until intolerable toxicity/disease progression. The effect of a standard high-fat meal on the PK of G was evaluated after a single dose and at steady state. Relevant signaling and pharmacodynamic (PD) biomarkers were assessed using circulating tumor (ct) DNA samples. Results: At clinical cutoff (Jul 19, 2019), 20 pts were enrolled in the food-effect portion of the G + F arm. Fifteen (75%) had received ≥2 prior lines of therapy for metastatic BC. Median G treatment duration was 5.9 months (range 1.7-17.8); cumulative dose intensity, 98%. Adverse events (AEs) led to dose reduction in 3 pts (15%). The most common treatment-related (TR) AEs (≥4 pts, 20%) were hyperglycemia (11, 55%), diarrhea (10, 50%), stomatitis (grouped term; 9, 45%), nausea (8, 40%), decreased appetite (7, 35%), dysgeusia, fatigue, and muscle spasms (4 each, 20%). Grade ≥3 TRAEs were hyperglycemia, nausea, lymphopenia, hyperamylasemia, and hyperlipasemia (1 each, 5%). The PK of G in combination with F was similar to single-agent PK. Comparable G exposures (Cmax and AUC0-24) were observed following administration in fasted or fed states. Seventeen pts (85%) discontinued treatment, all due to radiographic/clinical disease progression. Overall, 5/14 pts with measurable disease had a PR (36%; 2 received prior F; 4, prior CDK4/6i), of whom 2 pts (14%) had a confirmed PR. CBR was 60% (12/20 pts). Most pts showed decreased ctDNA PIK3CA-mutant allele frequency during treatment. Conclusion: G + F demonstrated a manageable safety profile, similar PK to G alone, preliminary antitumor activity, and PD modulation of PIK3CA-mutant allele frequency in ctDNA. The presence of food did not significantly impact the rate or extent of G absorption following single or multiple doses. Additional pts are being enrolled in the G + F arm to further inform the safety and efficacy of this combination.

Citation Format: Kevin Kalinsky, Dejan Juric, Philippe L. Bedard, Mafalda Oliveira, Andres Cervantes, Erika Hamilton, Ian E. Krop, Nick Turner, Peter Schmid, Andrea Varga, Antoine Italiano, Zachary Veitch, Cristina Saura, Valentina Gambardella, Sravanthi Cheeti, Naoki Kotani, Guiyuan Lei, Katherine E. Hutchinson, Stephanie Royer-Joo, Anjali Vaze, Jennifer L. Schutzman, Komal Jhaveri. A phase I/Ib study evaluating GDC-0077 plus fulvestrant in patients with PIK3CA-mutant, hormone receptor-positive/HER2-negative breast cancer [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 CT109.

Phase I study of the checkpoint kinase 1 inhibitor GDC-0575 in combination with gemcitabine in patients with refractory solid tumors

BACKGROUND

Checkpoint kinase 1 (Chk1) inhibition following chemotherapy-elicited DNA damage overrides cell cycle arrest and induces mitotic catastrophe and cell death. GDC-0575 is a highly-selective oral small-molecule Chk1 inhibitor that results in tumor shrinkage and growth delay in xenograft models. We evaluated the safety, tolerability, and pharmacokinetic properties of GDC-0575 alone and in combination with gemcitabine. Antitumor activity and Chk1 pathway modulation were assessed.

PATIENTS AND METHODS

In this phase I open-label study, in the dose escalation stage, patients were enrolled in a GDC-0575 monotherapy Arm (1) or GDC-0575 combination with gemcitabine Arm (2) to determine the maximum tolerated dose. Patients in arm 2 received either i.v. gemcitabine 1000 mg/m2 (arm 2a) or 500 mg/m2 (arm 2b), followed by GDC-0575 (45 or 80 mg, respectively, as RP2D). Stage II enrolled disease-specific cohorts.

RESULTS

Of 102 patients treated, 70% were female, the median age was 59 years (range 27-85), and 47% were Eastern Cooperative Oncology Group PS 0. The most common tumor type was breast (37%). The most frequent adverse events (all grades) related to GDC-0575 and/or gemcitabine were neutropenia (68%), anemia (48%), nausea (43%), fatigue (42%), and thrombocytopenia (35%). Maximum concentrations of GDC-0575 were achieved within 2 hours of dosing, and half-life was ∼23 hours. No pharmacokinetic drug-drug interaction was observed between GDC-0575 and gemcitabine. Among patients treated with GDC-0575 and gemcitabine, there were four confirmed partial responses, three occurring in patients with tumors harboring TP53 mutation. Pharmacodynamic data were consistent with GDC-0575 inhibition of gemcitabine-induced expression of pCDK1/2.

CONCLUSION

GDC-0575 can be safely administered as a monotherapy and in combination with gemcitabine; however, overall tolerability with gemcitabine was modest. Hematological toxicities were frequent but manageable. Preliminary antitumor activity was observed but limited to a small number of patients with a variety of refractory solid tumors treated with GDC-0575 and gemcitabine.

CLINICAL TRIAL NUMBER

NCT01564251.

Racial and Ethnic Composition of Cancer Clinical Drug Trials: How Diverse Are We?

Many approved drugs demonstrate different pharmacokinetics, pharmacodynamics, and/or safety across racial and ethnic groups. The primary objective of the current study was to summarize the racial and ethnic makeup of cancer clinical drug trials using cancer drugs approved by the U.S. Food and Drug Administration (FDA) between January 1, 2010, and July 31, 2016. In clinical studies used for FDA approvals, 82.3% of participants identified as white, 10.2% as Asian, 2.3% as black, and 4.7% as Hispanic. Black participants made up 7.7% of U.S. and Canadian cancer clinical drug trials and 2.6% of global cancer clinical drug trials while Asian participants made up 13.5% of global cancer clinical drug trials but only 1.8% of U.S. and Canadian cancer clinical drug trials. The current study indicates that although cancer clinical drug trials have become more inclusive of Asian participants, other racial and ethnic minority groups remain under-represented. This may result in an inadequate understanding of drug safety and efficacy in many racial and ethnic populations.

A phase IB dose-escalation study of the safety and pharmacokinetics of pictilisib in combination with either paclitaxel and carboplatin (with or without bevacizumab) or pemetrexed and cisplatin (with or without bevacizumab) in patients with advanced non-small cell lung cancer

AIM

The phosphatidylinositol 3-kinase (PI3K) pathway is a potential therapeutic target in non-small cell lung cancer (NSCLC). This study aimed to evaluate the pan-PI3K inhibitor pictilisib in combination with first-line treatment regimens that were the standard of care at the time of study, in patients with NSCLC.

PATIENTS AND METHODS

A 3 + 3 dose-escalation study was performed using a starting daily dose of 60 mg pictilisib on days 1-14 of a 21-day cycle. Depending on bevacizumab eligibility and NSCLC histology, patients also received either paclitaxel + carboplatin or pemetrexed + cisplatin, ± bevacizumab every 3 weeks. The primary objectives of the study were to assess safety and tolerability and to identify dose-limiting toxicities (DLTs), the maximum tolerated dose (MTD) and a recommended phase II dose (RP2D), for each combination.

RESULTS

All 66 treated patients experienced at least one adverse event (AE). Grade ≥III AEs, serious AEs and deaths occurred in 57 (86.4%), 56 (84.8%) and 9 (13.6%) patients, respectively. Three patients reported DLTs across the four arms of the study. The MTD was not reached in any arm and the RP2D of pictilisib was determined to be 330 mg (capsules) or 340 mg (tablets) on a '14 days on, 7 days off' schedule. The best confirmed response was partial response in 29 (43.9%) patients and stable disease in 20 (30.9%) patients.

CONCLUSION

Combining pictilisib with various standard-of-care first-line treatment regimens is feasible from a safety perspective in patients with NSCLC, and encouraging preliminary anti-tumour activity was observed.

A Phase I Dose-Escalation Study of the Safety and Pharmacokinetics of Pictilisib in Combination with Erlotinib in Patients with Advanced Solid Tumors

BACKGROUND

Epidermal growth factor receptor (EGFR) and phosphatidylinositol 3-kinase (PI3K) are involved in the proliferation and survival of many cancer types. Enhanced antitumor activity may be achieved through combined inhibition of these pathways. We report results for pictilisib (GDC-0941, a class I pan-PI3K inhibitor) plus erlotinib (an EGFR tyrosine kinase inhibitor) in patients with advanced solid tumors.

MATERIALS AND METHODS

A 3 + 3 dose-escalation study was carried out at a starting daily dose of 60 mg pictilisib on days 1-21 of a 28-day cycle and 150 mg erlotinib from day 2 of cycle 1. The primary objectives of the study were to assess safety and tolerability, identify dose-limiting toxicities (DLTs), estimate the maximum tolerated dose, and identify the recommended phase II dose (RP2D). Evaluation of a dose-expansion cohort at the RP2D was performed.

RESULTS

Fifty-seven patients were treated in the study. All patients experienced at least one adverse event (AE). Grade ≥3 AEs, serious AEs, and deaths were reported in 38 (66.7%), 19 (33.3%), and 4 (7.0%) patients, respectively. DLTs occurred in nine patients across eight cohorts and the RP2D was determined to be 340 mg pictilisib on a "5 days on, 2 days off" schedule plus 100 mg erlotinib. Two patients (3.5%) experienced partial response and 19 (33.3%) had stable disease.

CONCLUSION

Combining pictilisib with erlotinib in patients with advanced solid tumors is feasible; however, antitumor activity is limited. Additional studies may identify patients likely to benefit from combined inhibition of EGFR and PI3K pathways.

IMPLICATIONS FOR PRACTICE

Combining drugs targeting different signaling pathways in cancer growth and survival could overcome drug resistance and improve antitumor activity. In this first-in-human study for the combination, addition of the PI3K inhibitor pictilisib to the EGFR tyrosine kinase inhibitor erlotinib resulted in toxicity that led to dose and schedule modifications to identify a tolerable recommended phase II dose of 340 mg pictilisib on a "5 days on, 2 days off" schedule plus 100 mg erlotinib daily. The limited antitumor activity observed, however, suggests that additional studies are needed to identify patients most likely to benefit from combined EGFR and PI3K inhibition.

Phase I Study of GDC-0425, a Checkpoint Kinase 1 Inhibitor, in Combination with Gemcitabine in Patients with Refractory Solid Tumors

Purpose: Chk1 inhibition potentiates DNA-damaging chemotherapy by overriding cell-cycle arrest and genome repair. This phase I study evaluated the Chk1 inhibitor GDC-0425 given in combination with gemcitabine to patients with advanced solid tumors.Experimental Design: Patients received GDC-0425 alone for a 1-week lead-in followed by 21-day cycles of gemcitabine plus GDC-0425. Gemcitabine was initially administered at 750 mg/m² (Arm A), then increased to 1,000 mg/m² (Arm B), on days 1 and 8 in a 3 + 3 + 3 dose escalation to establish maximum tolerated dose (MTD). GDC-0425 was initially administered daily for three consecutive days; however, dosing was abbreviated to a single day on the basis of pharmacokinetics and tolerability. TP53 mutations were evaluated in archival tumor tissue. On-treatment tumor biopsies underwent pharmacodynamic biomarker analyses.Results: Forty patients were treated with GDC-0425. The MTD of GDC-0425 was 60 mg when administered approximately 24 hours after gemcitabine 1,000 mg/m² Dose-limiting toxicities included thrombocytopenia (n = 5), neutropenia (n = 4), dyspnea, nausea, pyrexia, syncope, and increased alanine aminotransferase (n = 1 each). Common related adverse events were nausea (48%); anemia, neutropenia, vomiting (45% each); fatigue (43%); pyrexia (40%); and thrombocytopenia (35%). The GDC-0425 half-life was approximately 15 hours. There were two confirmed partial responses in patients with triple-negative breast cancer (TP53-mutated) and melanoma (n = 1 each) and one unconfirmed partial response in a patient with cancer of unknown primary origin.Conclusions: Chk1 inhibition with GDC-0425 in combination with gemcitabine was tolerated with manageable bone marrow suppression. The observed preliminary clinical activity warrants further investigation of this chemopotentiation strategy. Clin Cancer Res; 23(10); 2423-32. ©2016 AACR.

The Caenorhabditis elegans EGL-15 signaling pathway implicates a DOS-like multisubstrate adaptor protein in fibroblast growth factor signal transduction

EGL-15 is a fibroblast growth factor receptor in the nematode Caenorhabditis elegans. Components that mediate EGL-15 signaling have been identified via mutations that confer a Clear (Clr) phenotype, indicative of hyperactivity of this pathway, or a suppressor-of-Clr (Soc) phenotype, indicative of reduced pathway activity. We have isolated a gain-of-function allele of let-60 ras that confers a Clr phenotype and implicated both let-60 ras and components of a mitogen-activated protein kinase cascade in EGL-15 signaling by their Soc phenotype. Epistasis analysis indicates that the gene soc-1 functions in EGL-15 signaling by acting either upstream of or independently of LET-60 RAS. soc-1 encodes a multisubstrate adaptor protein with an amino-terminal pleckstrin homology domain that is structurally similar to the DOS protein in Drosophila and mammalian GAB1. DOS is known to act with the cytoplasmic tyrosine phosphatase Corkscrew (CSW) in signaling pathways in Drosophila. Similarly, the C. elegans CSW ortholog PTP-2 was found to be involved in EGL-15 signaling. Structure-function analysis of SOC-1 and phenotypic analysis of single and double mutants are consistent with a model in which SOC-1 and PTP-2 act together in a pathway downstream of EGL-15 and the Src homology domain 2 (SH2)/SH3-adaptor protein SEM-5/GRB2 contributes to SOC-1-independent activities of EGL-15.

Fibroblast growth factor signaling in Caenorhabditis elegans

Growth factor receptor tyrosine kinases (RTKs), such as the fibroblast growth factor receptor (FGFR), play a major role in how cells communicate with their environment. FGFR signaling is crucial for normal development, and its misregulation in humans has been linked to developmental abnormalities and cancer. The precise molecular mechanisms by which FGFRs transduce extracellular signals to effect specific biologic responses is an area of intense research. Genetic analyses in model organisms have played a central role in our evolving understanding of these signal transduction cascades. Genetic studies in the nematode C. elegans have contributed to our knowledge of FGFR signaling by identifying genes involved in FGFR signal transduction and linking their gene products together into signaling modules. This review will describe FGFR-mediated signal transduction in C. elegans and focus on how these studies have contributed to our understanding of how FGFRs orchestrate the assembly of intracellular signaling pathways.

soc-2 encodes a leucine-rich repeat protein implicated in fibroblast growth factor receptor signaling

Activation of fibroblast growth factor (FGF) receptors elicits diverse cellular responses including growth, mitogenesis, migration, and differentiation. The intracellular signaling pathways that mediate these important processes are not well understood. In Caenorhabditis elegans, suppressors of clr-1 identify genes, termed soc genes, that potentially mediate or activate signaling through the EGL-15 FGF receptor. We demonstrate that three soc genes, soc-1, soc-2, and sem-5, suppress the activity of an activated form of the EGL-15 FGF receptor, consistent with the soc genes functioning downstream of EGL-15. We show that soc-2 encodes a protein composed almost entirely of leucine-rich repeats, a domain implicated in protein-protein interactions. We identified a putative human homolog, SHOC-2, which is 54% identical to SOC-2. We find that shoc-2 maps to 10q25, shoc-2 mRNA is expressed in all tissues assayed, and SHOC-2 protein is cytoplasmically localized. Within the leucine-rich repeats of both SOC-2 and SHOC-2 are two YXNX motifs that are potential tyrosine-phosphorylated docking sites for the SEM-5/GRB2 Src homology 2 domain. However, phosphorylation of these residues is not required for SOC-2 function in vivo, and SHOC-2 is not observed to be tyrosine phosphorylated in response to FGF stimulation. We conclude that this genetic system has allowed for the identification of a conserved gene implicated in mediating FGF receptor signaling in C. elegans.

Diverse transposable elements are mobilized in hybrid dysgenesis in Drosophila virilis

We describe a system of hybrid dysgenesis in Drosophila virilis in which at least four unrelated transposable elements are all mobilized following a dysgenic cross. The data are largely consistent with the superposition of at least three different systems of hybrid dysgenesis, each repressing a different transposable element, which break down following the hybrid cross, possibly because they share a common pathway in the host. The data are also consistent with a mechanism in which mobilization of a single element triggers that of others, perhaps through chromosome breakage. The mobilization of multiple, unrelated elements in hybrid dysgenesis is reminiscent of McClintock's evidence [McClintock, B. (1955) Brookhaven Symp. Biol. 8, 58-74] for simultaneous mobilization of different transposable elements in maize.