Drugging the Undruggable

Drugging the Undruggable

Long thought to be untreatable, KRAS is one of the most difficult to treat oncogenic drivers responsible for approximately 25% of all tumors, including 68% of pancreatic tumors and 20% of all non–small cell lung cancers (NSCLC).

We now have a treatment – sotorasib – for patients with locally advanced or metastatic NSCLC that is driven by a KRAS mutation (G12C). And, now, there is a second treatment – adagrasib – under study, which, according to a presentation recently made at the annual meeting of the American Society of Clinical Oncology, looks promising.

Ras is a membrane-bound regulatory protein (G protein) belonging to the family of guanosine triphosphatases (GTPases). Ras functions as a guanosine diphosphate/triphosphate binary switch by cycling between the active GTP-bound and the inactive GDP-bound states in response to extracellular stimuli. The KRAS (G12C) mutation affects the active form of KRAS and results in abnormally high concentrations of GTP-bound KRAS leading to hyperactivation of downstream oncogenic pathways and uncontrolled cell growth, specifically of ERK and MEK signaling pathways.

At the ASCO annual meeting in June, Spira and colleagues reported the results of cohort A of the KRYSTAL-1 study evaluating adagrasib as second-line therapy patients with advanced solid tumors harboring a KRAS (G12C) mutation. Like sotorasib, adagrasib is a KRAS (G12C) inhibitor that irreversibly and selectively binds KRAS (G12C), locking it in its inactive state. In this study, patients had to have failed first-line chemotherapy and immunotherapy with 43% of lung cancer patients responding. The 12-month overall survival (OS) was 51%, median overall survival was 12.6 and median progression-free survival (PFS) was 6.5 months. Twenty-five patients with KRAS (G12C)–mutant NSCLC and active, untreated central nervous system metastases received adagrasib in a phase 1b cohort. The intracranial overall response rate was 31.6% and median intracranial PFS was 4.2 months. Systemic ORR was 35.0% (7/20), the disease control rate was 80.0% (16/20) and median duration of response was 9.6 months. Based on these data, a phase 3 trial evaluating adagrasib monotherapy versus docetaxel in previously treated patients with KRAS (G12C) mutant NSCLC is ongoing.

The Food and Drug Administration approval of sotorasib in 2021 was, in part, based on the results of a single-arm, phase 2, second-line study of patients who had previously received platinum-based chemotherapy and/or immunotherapy. An ORR rate of 37.1% was reported with a median PFS of 6.8 months and median OS of 12.5 months leading to the FDA approval. Responses were observed across the range of baseline PD-L1 expression levels: 48% of PD-L1 negative, 39% with PD-L1 between 1%-49%, and 22% of patients with a PD-L1 of greater than 50% having a response.

The major toxicities observed in these studies were gastrointestinal (diarrhea, nausea, vomiting) and hepatic (elevated liver enzymes). About 97% of patients on adagrasib experienced any treatment-related adverse events, and 43% experienced a grade 3 or 4 treatment-related adverse event leading to dose reduction in 52% of patients, a dose interruption in 61% of patients, and a 7% discontinuation rate. About 70% of patients treated with sotorasib had a treatment-related adverse event of any grade, and 21% reported grade 3 or 4 treatment-related adverse events.

A subgroup in the KRYSTAL-1 trial reported an intracranial ORR of 32% in patients with active, untreated CNS metastases. Median overall survival has not yet reached concordance between systemic and intracranial disease control was 88%. In addition, preliminary data from two patients with untreated CNS metastases from a phase 1b cohort found cerebrospinal fluid concentrations of adagrasib with a mean ratio of unbound brain-to-plasma concentration of 0.47, which is comparable or exceeds values for known CNS-penetrant tyrosine kinase inhibitors.

Unfortunately, KRAS (G12C) is not the only KRAS mutation out there. There are a myriad of others, such as G12V and G12D. Hopefully, we will be seeing more drugs aimed at this set of important mutations. Another question, of course, is when and if these drugs will move to the first-line setting.

Schiller is a medical oncologist and founding member of Oncologists United for Climate and Health. She is a former board member of the International Association for the Study of Lung Cancer and a current board member of the Lung Cancer Research Foundation.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.

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