#ColorectalCancer #Immunotherapy #ICI #XL888
#CombinationTherapy
Colorectal cancer (CRC) is one of the
leading
causes of cancer-related death worldwide, especially in advanced stages where
treatment options become limited. The advent of
immunotherapy, particularly
immune checkpoint inhibitors (ICIs), has transformed the treatment landscape of
several solid tumors. In CRC, these treatments have shown
remarkable efficacy
in patients with microsatellite instability (MSI) or
mismatch repair deficiency
(dMMR), leading to prolonged and sometimes durable responses.
However, these
hypermutated forms represent
only about
5% of metastatic colorectal cancers (pMMR), leaving the
vast
majority of patients without real benefit from ICIs. In this context, it
becomes essential to
develop combination strategies capable of
recruiting or
activating immune cells in these patients.
This study explores the
safety,
feasibility,
and
immunologic impact of an innovative combination.
Pembrolizumab, an
anti-PD-1 antibody, is paired with
XL888, an inhibitor known to regulate the
stability of several proteins involved in tumor growth and immune response.
This combination could
reduce resistance mechanisms, remodel the
tumor
microenvironment, and
enhance ICI response in patients with advanced CRC who
are refractory to standard treatments.
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Activating immunity, overcoming resistance?
The study included two patient groups.
Fourteen
patients with advanced gastrointestinal cancers were enrolled in a
dose-escalation phase to evaluate the tolerability of
XL888 at doses of 45, 60,
and 90 mg in combination with
pembrolizumab. The 90 mg dose was selected as the
recommended dose for the next phase.
A
subsequent expansion cohort of
16 patients
with advanced pMMR colorectal cancer received
pembrolizumab (200 mg) plus XL888
(90 mg). Treatment continued until disease progression or the emergence of
adverse events.
Evaluation criteria included
clinical
tolerability and
in-depth immune analyses. Researchers assessed
plasma
cytokines and
circulating immune cells to evaluate systemic immune response. In
parallel,
liver metastasis biopsies were examined using
CyTOF and
mIHC to
assess the combination’s effect on the
tumor microenvironment.
Clinically, results were
modest.
No objective
responses were observed, and
25% of patients experienced
disease stabilization.
However,
treatment was well tolerated, with only
12.5% experiencing
grade 3 or
4 adverse events, confirming the combination’s feasibility.
Immunologic analyses revealed
significant
immune system changes. In
liver metastases, a decrease in
CD68+ macrophages and
IL-6+ cells suggested a
reduction in local inflammation. In the blood,
B and T
lymphocytes decreased while several
inflammatory cytokines increased,
indicating
systemic immune activation.
Despite these encouraging biological signals,
the
liver tumor microenvironment remained
poorly infiltrated by lymphocytes,
limiting the effectiveness of PD-1 blockade. These results demonstrate
real
immune modulation but insufficient on its own to trigger a significant
antitumor clinical response in this context.
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An immune awakening… but no response?
pMMR colorectal cancer remains
largely
unresponsive to immunotherapy, particularly in the presence of
liver
metastases, where the
tumor microenvironment is notably poor in infiltrating T
lymphocytes (TILs). This lack of local immune response is a major barrier to
ICI efficacy, despite their proven effectiveness in other tumor types.
The primary challenge is to
remodel this
immunosuppressive environment to
promote T-cell infiltration and activation,
thus
restoring sensitivity to ICIs in pMMR tumors.
This study investigates the
potential of the
XL888-pembrolizumab combination to
reactivate immune responses in pMMR
colorectal cancer by targeting
resistance mechanisms related to the stability
of tumor and immune proteins.
While observed
clinical efficacy was limited,
immunological signals confirmed real modulation of the immune system, both
within tumors and systemically. This biological response indicates an active
pharmacological effect, though
insufficient to induce tumor regression in this
setting.
Despite its limitations, this study provides
valuable data on the feasibility and biological effects of this combination. It
lays the groundwork for strategies aimed at
extending the benefits of
immunotherapy to previously non-responsive patients.
Future trials could target patients with
lung
metastases, which typically have more immune cell infiltration, or incorporate
additional
immune-stimulating agents to further enhance T-cell activation.
Earlier integration into the treatment sequence, particularly in
synergy with
chemotherapy or radiotherapy, may also boost the effectiveness of this
approach.
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