Pharmaceutical Intermediates for KRAS
Sotorasib (AMG 510) target undruggable target KRAS, X-crystal structure of AMG510 in complex with KRASG12C was reported, also the synthesis of AMG and MRTX849 was summarized, Ebuy Chemical Co as a pharmaceutical intermediates supplier could provide kinds of building blocks.
Kirsten rat sarcoma viral oncogene homolog (KRAS) is a proto-oncogene of the RAS-MAPK pathway. KRAS mutations are present in a variety of malignancies including lung, colorectal, and pancreatic cancer.
KRAS mutations are found in 20%–30% of non-small cell lung cancer (NSCLC). KRASG12C is the most prevalent KRAS mutation, and has been identified in approximately 15 % of NSCLC.
Recently, sotorasib (AMG 510), a KRAS G12C inhibitor, was approved for the therapy for KRAS mutation patients, it was really a major breakthrough for those patients harboring KRAS G12C mutations, G12C only accounts for a fraction of those with KRAS mutations and eventual resistance to G12C inhibitors are unavoidable.
The KRAS protein is a GTPase that transmits intracellular signals upon binding to GTP. Under physiologic conditions, this system is maintained by guanine nucleotide exchange factors, favoring the GDP-bound inactive form. However, KRAS mutations promote the maintenance of the GTP-bound active form. These mutations potentiate downstream effects such as cell proliferation, differentiation, and survival.
Most KRAS mutations are missense mutations of the 12th codon, glycine. These mutations result in changes from glycine to another amino acid in the KRAS protein. 90% of pancreatic cancers exhibit KRAS G12D and KRAS G12V mutations that are currently considered “difficult to target”, due to the protein being chemically intractable. KRAS G12D is also the most common mutation in colorectal cancer, with a strong correlation to poor prognosis. KRAS G12C is another significant mutation found in 13% of lung cancers and 3% of colorectal cancer. This mutation, identified as an oncogenic driver of tumorigenesis, has been considered druggable, as the presence of the substituted cysteine provides a target for drug binding.
The biochemical and biophysical properties of common KRAS mutations (G12A, G12C, G12D, G12R, G12V, G13D, Q61L, and Q61H), have been characterized by Hunter et al. Different KRAS mutations were classified based on the level of intrinsic GTPase activity and RAF affinity. RAF is a family of kinases activated by RAS that participate in the mitogen-activated protein kinase (MAPK) cascade.
In the below Fig.1 summarizes the RAS pathway and demonstrates (potential) opportunities to target the cascade. The properties of each KRAS mutation were then combined to generate a prediction model of the activation of the RAF kinase pathway compared to other growth signaling pathways such as PI3K. For example, the G12D mutation which has a low affinity for RAF and a high level of intrinsic GTPase activity would be predicted to show the lowest rate of RAF activation compared to G12A- and G61-L tumors.
Fig.1 KRAS and KRAS pathway targeted preclinical and clinical agents
Why KRAS targeting had been difficult? RAS signaling is complex and regulated through a balance between activation factors (guanine nucleotide exchange factors (GEFs) such as SOS, RASGRP) and inactivation factors (GTPase-activating proteins(GAPs)-neurofibromin, p120GAP) resulting in alternative active form(GTP-bound) and inactive form(GDP-bound) . RAS activation facilitates downstream activation of RAF-MAPK pathway (cell cycle proliferation and gene expression), PI3K pathway (anti-apoptosis) and RALGDs pathway (cell proliferation). Prior to activation, KRAS undergoes a multistep posttranslational modification including farnesylation, geranylgeranylation, and palmitoylation. Even though KRAS is one of the most common driver mutations in non-small cell lung cancer (NSCLC), direct targeting of KRAS protein was challenging due to its small size, relatively smooth and shallow surface, lack of drug binding pockets except for GDP/GTP binding, picomolar affinity for guanosine triphosphate (GTP) leading to indirect targeting of upstream or downstream pathway.
Several attempts to target upstream pathways by targeting farnesyl transferase or geranylgeranyl transferase which helps in membrane localization of KRAS proteins were unsuccessful in solid tumors. The efficacy of farnesyl transferase inhibitor (FTI) -R115777 (tipifarnib) was evaluated in various solid tumors including breast cancer, NSCLC, small cell lung cancer which showed no significant antitumor activity or objective response rates.
Lonafarnib (SCH 66336) is another FTI that showed no objective responses in colorectal cancer and does not improve PFS or OS in ovarian cancer in combination with chemotherapy. In a phase 2 clinical trial, lonafarnib and paclitaxel showed clinical activity in metastatic NSCLC leading to a phase 3 trial of lonafarnib in combination with paclitaxel and carboplatin which was terminated. Downstream pathway of MAPK and PI3K pathway were also targeted in KRAS mutated solid tumors either as monotherapy or in combination of AKT inhibitor and MEK inhibitor showed no PFS benefit or no clinical activity on tumor response were reported. However, overlapping toxicities were noted with the combination of AKT and MEK inhibitors which limits dose escalation needed for clinical activity. (Nagasaka et al., 2021)
Sotorasib (AMG510) is a highly selective and irreversible KRASG12C inhibitor (Fig. 1) that binds at allosteric pocket (the switch II pocket S-IIP) leading to trapping of KRAS in inactive GDP bound state. In phase 1, a multicenter open-label trial involving heavily pretreated patients (n = 129) of at least 3 (60.5%) prior lines of cancer-specific treatments were enrolled with a median follow-up of 11.7 months. No dose-limiting toxic effects were observed. The most common adverse events were diarrhea (in 38 patients [29.5%]), fatigue (in 30 [23.3%]), and nausea (in 27 [20.9%]). Grade 3 treatment-related adverse events were reported in 11.6% of patients which include, an increase in aspartate aminotransferase (AST) / alanine aminotransferase (ALT)/alkaline phosphatase (alk phos), anemia, hepatitis, diarrhea, hyponatremia. Efficacy analysis showed objective response rates of 32.2% of the patients across all dose levels and 35.3% at the target dose of 960 mg in NSCLC with a median duration of response of 10.9 months, the median time to response of 1.4 months and median progression-free survival of 6.3 months.
The reported X-crystal structure of AMG510 in complex with KRASG12C was shown in the Fig.2. (Lanman et al., 2020)
Fig.2 X-crystal structure of AMG510 in complex with KRASG12C
MG510 synthesis route was reported (kinds of intermediates could be supplied by Ebuy Chemical), (Lanman et al., 2020)
MRTX849 synthesis route was reported (WO2017201161, (“Synthesis of MRTX849,” 2020)), kinds of intermediates could be supplied by Ebuy Chemical Co.
Ebuy Chemical Co as a pharmaceutical intermediates Supplier could provide this scaffold from gram to kilogram with high quality.