As more is understood about the biology of PDAC tumors, targeting common KRAS variants in these tumors following exhaustion of all curative intent surgery, chemotherapy, and radiation ushers in a novel postadjuvant setting for investigators.
Despite the high prevalence of KRAS mutations in pancreatic cancers, a limited number of cases harbor an actionable point mutation.1 Unlike other tumors where variants in KRAS, such as G12C, are more prominent,2 explorations into the more common subtypes in pancreatic cancer have begun to provide more guidance for therapeutic development as significant differences in survival outcomes come to light.1,3,4
The most common KRAS mutations in patients with pancreatic ductal adenocarcinoma (PDAC) are found in the G12 codon. Occurring in up to 44% of patients, G12D is the most common mutational substitution, with G12V (34%) and G12R (20%) having the second and third highest incidence.5 Unfortunately, although G12C has been shown to improve outcomes when targeted with KRAS G12C inhibitors, such as adagrasib (Krazati) and sotorasib (Lumakras), this target is only actionable in up to 3% of patients with PDAC.2,5,6
A recent undertaking by investigators sought to characterize prognostic and molecular differences among variants G12D and G12R. Findings were presented at the 2023 American Society for Clinical Oncology (ASCO) Annual Meeting.3
In the updated 2023 analysis, the investigators leveraged data from a genomic database to analyze immune marker prevalence and variant expression in KRAS, as well as assess survival outcomes from claims data among those with KRAS-mutant PDAC.3
The identified mutations in the subset were G12R (n = 621), G12V (n = 1294), G12C (n = 74), and G12D (n = 1766).3 These groups had similar median ages of 68, 67, 66, and 67 years, respectively. Immune checkpoint marker prevalence findings showed that 23.5% of those with G12Cmutant disease were PD-L1 positive via the VENTANA PD-L1 (SP142) immunohistochemistry (IHC) assay. Among those with G12D-, G12V-, and G12R-mutant disease, the rates of IHC PD-L1 positivity were 19.0%, 14.2%, and 13.0%, respectively.3
Tumor mutational burden was also assessed with low rates of positivity noted across the groups at 2.7%, 1.0%, 1.4%, and 1.1%, for the G12C, G12D, G12V, and G12R groups, respectively.3 Mismatch repair deficient and microsatellite instability–high disease was noted in 1.4%, 0.9%, 1.0%, and 0.6% of patients in these subgroups, respectively.3
A comparison of overall survival (OS) outcomes were reported for G12R (n = 890) vs G12D (n = 2604), as well as for G12V (n = 1836) vs G12D. For G12R vs G12D, the median OS was 396 days (95% CI, 361-425) vs 311 days (95% CI, 294-329), for a median difference of 85 days (HR, 0.809; 95% CI, 0.743-0.880; P < .00001). For patients with G12V-mutant disease, the median OS was 362 days (HR, 0.911; 95% CI, 0.854-0.972; P = .005), with a median difference of 51 days compared with patients with G12Dmutant disease.3
Study authors noted that “metformin appeared to impact survival in the KRAS G12R subgroup.”
The tumor microenvironment also revealed that B cell, M2 macrophages, and CD8+ T-cell infiltration trended higher in patients with G12R-mutant disease vs G12D (P < .05). The false discovery rate adjusted P value (q) was used to compared CD4+ T-cell infiltration and showed a trend toward higher rates in the G12Rmutant group vs G12D-mutant group (q < .05).3
Another approach to leveraging KRAS variants is through vaccination. Specifically, an investigational KRAS-targeted vaccine, ELI-002, has been designed to engage lymph node–specific activity and encourage the lasting potency of these agents.4
At the 2023 ASCO meeting, preliminary results from the AMPLIFY-201 trial (NCT04853017) were presented for the 2-peptide formulation of the vaccine product. Specifically, the agent is a 3-component lymph node–targeting amphiphile cancer vaccine comprising KRAS G12D- and G12R-modified peptide antigens and a toll-like receptor 9 (TLR9) agnostic DNA adjuvant.4,7 The amphiphile ligands were previously assessed as a modification method in solid tumor chimeric antigen receptor (CAR) T-cell therapy for solid tumors.8 The modified cells targeted lymph nodes and primed CAR T cells in the lymph node microenvironment, resulting in expansion in murine models.8
“Conventional vaccine components [eg, peptide antigens and molecular adjuvants] are rapidly absorbed into blood capillaries after administration, leading to poor delivery to lymph nodes, where protective immune responses are orchestrated,” Eileen M. O’Reilly, MD, and coinvestigators wrote in findings from the study. “Amph-modification promotes albumin binding to reprogram vaccines for enhanced lymph node delivery, resulting in coordinated transport of antigen and adjuvant to immune cells. Improved uptake by antigen-presenting cells results in enhanced antigen presentation and co-stimulation to cognate T cells. Restricted delivery to lymph nodes prevents systemic exposure to avoid toxic effects of potent adjuvants.” O’Reilly is the Winthrop Rockefeller Endowed Chair of Medical Oncology, codirector of medical initiatives at the David M. Rubenstein Center for Pancreatic Cancer Research, and section head of hepatopancreaticobiliary and neuroendocrine cancers at Memorial Sloan Kettering Cancer Center in New York, New York. She is also the 2023 Giants of Cancer Care® award winner in the gastrointestinal cancer category.
Prior to enrollment in the AMPLIFY-201 study, patients needed to have received locoregional therapy, including surgery plus neoadjuvant/ adjuvant chemotherapy. During the screening period, 92 patients were assessed for mutant KRAS variants of either G12R or G12D, imaging for no evidence of disease, and analysis for minimal residual disease status confirmed by either circulating tumor DNA (ctDNA) positivity or positive serum biomarker. The most common reason for noninclusion was ctDNA, CA19-9 level, or carcinoembryonic antigen (CEA) negativity (n = 40).4
Twenty-five patients—20 with PDAC and 5 with colorectal cancer (CRC)—were enrolled across 5 cohorts. All patients received a fixed dose of the KRAS G12D/G12R-modified peptide (AmphPeptides 2P) at 1.4 mg. Ascending doses of the TLR9 agnostic DNA adjuvant (Amph-CPG-7909) were administered as follows: 0.1 mg (cohort 1; n = 3), 0.5 mg (cohort 2; n = 6), 2.5 mg (cohort 3; n = 5), 5.0 mg (cohort 4; n = 5), and 10.0 mg (cohort 5; n = 6).4 Of note, no patients with CRC were enrolled in cohorts 3 or 5.
Overall, the median age was 61 years (range, 37-77), and 60% of participants were women. The median BMI was 23.4 kg/m2 (range, 16.0-38.0). Most patients were White (84.0%) and had an ECOG performance status of 0 (72.0%). At screening, most patients had stage III/IV disease (68.0%). All patients had prior systemic therapy and surgery, with 28% of patients also having received radiation therapy.4
The prime immunization period was week 0 through 7, with dosing occurring on weeks 0, 1, 2, 3, 5, and 7. No doses were administered on weeks 8 through 17. The booster immunization period occurred on weeks 17 through 25, with doses administered on weeks 20, 21, 22, and 23. The follow-up period concluded at week 105. Serum biomarkers were assessed at baseline, week 17, week 25, and week 105, with ctDNA assessments conducted at baseline, between weeks 2 and 3, between weeks 5 and 6, week 17, week 20, weeks 24 and 25, and at the end of the follow-up period.
The primary end points of the study are safety, tolerability, and recommended phase 2 dose. Secondary end points include tumor biomarker reduction and clearance assessing the ctDNA and/or CA19-9 or CEA expression. Finally, investigators identified immunogenicity and relapse-free survival (RFS), using RECIST 1.1 criteria as exploratory end points. At data cutoff, follow-up was ongoing for biomarker response, duration of response, RFS, and OS.4
Early discontinuation was reported as follows: cohort 1 (n = 2), cohort 2 (n = 4), cohort 3 (n = 3), cohort 4 (n = 2), cohort 5 (n = 2). In cohort 4, one patient remained on treatment, at a median follow-up of 17.3 weeks; and 4 patients in cohort 5 remained on treatment, with a median follow-up of 13.0 weeks. The remainder of the patients completed treatment. No patients experienced dose-limiting toxicities, grade 3 or higher, serious treatment-related adverse events (AEs), or cytokine release syndrome events. Additionally, investigators reported that injection-site reactions reported for 3 patients were grades 1 and 2. Further, an increase in AEs was not observed with dose escalation of Amph-CpG-7909.
The best overall biomarker response from baseline was 77% (n = 17 of 22), and clearance of ctDNA was reported in 32% of patients (n = 7 of 22). Of note, mutant KRAS-specific T-cell responses were observed with an average 56-fold increase (range, 2-423). In pancreatic tumors, T-cell infiltration was 10- to 29-fold higher than previously reported in pancreatic literature, according to investigators.4 CD4 and CD8 T-cell responses were observed, with 50% of patients demonstrating mixed responses, 13% having only CD8 responses, and 38% having only CD4 responses. Finally, investigators reported that patients generated broad responses targeting multiple mutant KRAS antigens beyond G12D and G12R, with 10% of patients having 1 antigen response, 25% of patients have a response of 2 to 4 antigens, 30% having a response of 5 to 6 antigens, and 35% having a response of 7 antigens.4
In an analysis of a pancreatic tumor receiving the 2.5-mg dose of Amph-CpG-7909, investigators identified that ctDNA increased prior to radiographic relapse, and that PD-L1 expression of 10% was noted in this sample, possibly suggesting that this may be a mechanism of resistance for ELI-002.4
AMPLIFY-7P, a phase 1/2 study (NCT05726864) evaluating a 7-peptide formulation of ELI-002, has been initiated to evaluate the construct against 7 of the most common KRAS mutations. The expansive targets may have implications for several solid tumors, and next steps include pursuing the efficacy of the vaccination for patients with cancers such as non–small cell lung cancer, CRC, PDAC, or those with mutations in KRAS G12D, G12R, G12V, G12A, G12C, G12S, G13D, G12D, or NRAS G12R, G12V, G12C, or G12S.9
Both studies presented at the 2023 ASCO meeting shine additional light on the untapped potential of the previously deemed untargetable KRAS mutation.1 As more is understood about the biology of PDAC tumors, targeting common KRAS variants in these tumors following exhaustion of all curative intent surgery, chemotherapy, and radiation ushers in a novel postadjuvant setting for investigators.4
With advances in developing point mutation–specific treatments, such as adagrasib and sotorasib, for the treatment of patients with KRAS G12C–mutant lung cancer, its early days to judge how effective efforts to unpack the variety of variants that are actionable for patients with pancreatic cancer.10,11