Biomedical Engineering Reference
In-Depth Information
Efficacy studies were also conducted to fully compare
ALT-801 treatment with that of Proleukin-based thrice-daily
high-dose IL-2 administration. A375 tumor-bearing nude
mice treated with 0.5 mg/kg ALT-801 or PBS daily for four
injections followed by a 10-day rest period and then four
more daily injections or with 0.4mg/kg IL-2 every 8 h for
5 days followed by a 9-day rest period and then every 8 h for
five more daily injections. In this study, each single dose of
IL-2 had 3.2 times the activity as the ALT-801 dose and the
cumulative dose of IL-2 was 12-fold higher than that of
ALT-801. As shown in Figure 31.3F, both ALT-801 and IL-2
treatment inhibited tumor growth to a similar degree fol-
lowing two dosing cycles. However, the IL-2 regimen also
exhibited more toxicity based on clinical observations
(hypoactivity, mottled skin, and hunched postures) and
decreased body weight than was observed in ALT-801-
treated mice (J. Wen, unpublished data). The potency of
ALT-801 observed at a dose as low as 0.15 mg/kg dose in the
A375 tumor model (Figure 31.3B) [17]. Given that ALT-801
was as effective as a 12-fold higher cumulative dose of IL-2
in reducing tumor burden without the overt signs of toxicity,
this study provides additional support that ALT-801 could
offer safer and more effective treatment for cancer than
current high-dose IL-2 therapies.
The acute single-dose and multidose toxicity of ALT-
801wasalsoextensivelyevaluationinHLA-A
0201/K
b
transgenic mice. This strain was selected since the pres-
ence of HLA-A
0201 domain, for which the 264scTCR is
restricted, may influence the pharmacokinetics and/or tox-
icity of this protein and should give a more relevant view of
the parameters than other nonhuman animal models. At an
single dose of up to 7.5mg/kg, equivalent to over 50 times
the single dose of recombinant human IL-2 approved for
treatment of cancer patients, exhibited no drug related
mortalities and no or minimal differences were observed
between ALT-801 and PBS-treated groups in terms of
gross pathology, hematology (including lymphocyte
counts), and serum chemistry. The primary difference
observed in the histopathology was a moderate increase in
immune inflammation in the liver in the ALT-801 group
compared with control animals. These results are expected
based on lymphocyte infiltration previously observed in
immune organs of recombinant IL-2-treated mice [41].
Various toxicology studies employing multidose ALT-
801 treatment regimens in HLA-A
0201 transgenic mice
also demonstrated that two cycles of four daily consecutive
i.v. injections at up to 0.5 mg/kg of ALT-801 did not result in
obvious toxicological effects. Additionally, no adverse clin-
ical signs were observed at doses up to 1.85 mg/kg given
nine times over a 2-week period, though dose- and schedule-
dependent changes, including increases in normalized
lymph node, lung, pancreas, and spleen weights, decreases
in serum alkaline phosphatase and increases in serum
AST/ALT levels, and changes in hematology and tissue
histopathology, were observed in some ALT-801 treated
mice compared to the control group. These ALT-801-
induced changes return to control levels by 2 weeks after
treatment. Overall, the changes observed following repeated
ALT-801 administration in HLA-A2.1/K
b
-transgenic mice
appeared to be consistent with the reported biological
activity of IL-2 in other mouse models [41] and no addition
toxicity effects due to the scTCR domain were evident.
A GLP study was also conducted to determine the
reactivity of ALT-801 to normal human tissues by immu-
nohistochemical techniques. In a panel of 35 normal
human tissue specimens from at least three unrelated
donors, tissue-cross reactivity of ALT-801 was noted pri-
marily in the bone marrow, T-cell regions of the spleen,
tonsil, and lymph nodes. It has been well characterized that
expression of human IL-2 receptor subunits gives rise to
various mid- to high-affinity receptor forms on the surface
of T and B cells, NK cells, and monocytes [42]. As ALT-
801 functionally binds to the IL-2 receptor, the observed
tissue cross-reactivity of immune organs was expected.
There was no tissue cross-reactivity of ALT-801 with other
tissues or cell types. These findings are consistent with the
results of biodistribution studies reported for other IL-2
fusion proteins including the nontargeted albumin/IL-2
fusion [43]. Expression of HLA-A
0201 was also assessed
on the panel of human tissues but no correlation between
ALT-801 reactivity of these tissues and the HLA-A
0201
status of the tissues or donors was observed. Thus, p53-
specific scTCR domain of ALT-801 does not appear to
exhibit detectable reactivity to normal human tissues,
consistent with previous studies of this TCR [15].
31.4.2 Antitumor Mechanism-of-Action Studies
of ALT-801
Initial analysis of residual tumors from ALT-801-treated
mice provided evidence that the antitumor activity of ALT-
801 is likely mediated by the innate immune system via
NK cell activation and tumor infiltration [17]. The effect of
ALT-801 on immune cells was further investigated in A375
tumor-bearing nude mice over time during the course of
treatment [23]. Daily administration of either ALT-801 or
the control MART1scTCR/IL-2 fusion for 3 or more days
resulted in an increase in IL-2 receptor (IL-2R) expression
on immune cells, consistent with the known biological
activities of IL-2. These results suggest that ALT-801
treatment can augment subsequent immune responsiveness
(via IL-2R-positive cells) to the fusion protein. In addition,
repeated administration of ALT-801 (1.6mg/kg i.v. daily)
in A375 tumor-bearing mice resulted in massive treatment-
dependent infiltration of CD45R
รพ
cells into the tumors
(Figure 31.4A ). This effect was not observed following
treatment with MART1scTCR/IL-2 or PBS, verifying the
target specificity of this effect (Figure 31.4B). The tumor
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